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110 MSPS/140 MSPS Analog Interface for Flat Panel Displays AD9985
FEATURES
Automated clamping level adjustment 140 MSPS maximum conversion rate 300 MHz analog bandwidth 0.5 V to 1.0 V analog input range 500 ps p-p PLL clock jitter at 110 MSPS 3.3 V power supply Full sync processing Sync detect for hot plugging Midscale clamping Power-down mode Low power: 500 mW typical 4:2:2 output format mode
FUNCTIONAL BLOCK DIAGRAM
AUTO CLAMP LEVEL ADJUST 8
RAIN
CLAMP
A/D
ROUTA
AUTO CLAMP LEVEL ADJUST 8
GAIN
CLAMP
A/D
GOUTA
AUTO CLAMP LEVEL ADJUST 8
BAIN HSYNC COAST
CLAMP
A/D
BOUTA MIDSCV
APPLICATIONS
RGB graphics processing LCD monitors and projectors Plasma display panels Scan converters Microdisplays Digital TV
CLAMP FILT SOGIN
SYNC PROCESSING AND CLOCK GENERATION
DTACK HSOUT VSOUT SOGOUT REF REF BYPASS
04799-0-001
SCL SDA A0 SERIAL REGISTER AND POWER MANAGEMENT
AD9985
Figure 1.
GENERAL DESCRIPTION
The AD9985 is a complete 8-bit, 140 MSPS, monolithic analog interface optimized for capturing RGB graphics signals from personal computers and workstations. Its 140 MSPS encode rate capability and full power analog bandwidth of 300 MHz support resolutions up to SXGA (1280 x 1024 at 75 Hz). The AD9985 includes a 140 MHz triple ADC with internal 1.25 V reference, a PLL, and programmable gain, offset, and clamp control. The user provides only a 3.3 V power supply, analog input, and Hsync and COAST signals. Three-state CMOS outputs may be powered from 2.5 V to 3.3 V. The AD9985's on-chip PLL generates a pixel clock from the Hsync input. Pixel clock output frequencies range from 12 MHz to 140 MHz. PLL clock jitter is 500 ps p-p typical at 140 MSPS. When the COAST signal is presented, the PLL maintains its output frequency in the absence of Hsync. A sampling phase adjustment is provided. Data, Hsync, and clock output phase relationships are maintained. The AD9985 also offers full sync processing for composite sync and sync-on-green applications. A clamp signal is generated internally or may be provided by the user through the CLAMP input pin. This interface is fully programmable via a 2-wire serial interface. Fabricated in an advanced CMOS process, the AD9985 is provided in a space-saving 80-lead LQFP surface-mount plastic package and is specified over the -40C to +85C temperature range.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. www.analog.com Tel: 781.329.4700 Fax: 781.326.8703 (c) 2004 Analog Devices, Inc. All rights reserved.
AD9985 TABLE OF CONTENTS
Revision History ........................................................................... 2 Specifications..................................................................................... 3 Explanation of Test Levels........................................................... 6 Absolute Maximum Ratings............................................................ 7 ESD Caution.................................................................................. 7 Pin Configuration and Function Descriptions............................. 8 Design Guide................................................................................... 11 General Description................................................................... 11 Digital Inputs .............................................................................. 11 Input Signal Handling................................................................ 11 Hsync, Vsync Inputs................................................................... 11 Serial Control Port ..................................................................... 11 Output Signal Handling............................................................. 11 Clamping ..................................................................................... 11 RGB Clamping........................................................................ 11 YUV Clamping ....................................................................... 12 Gain and Offset Control............................................................ 12 Auto Offset .............................................................................. 12 Sync-on-Green............................................................................ 13 Clock Generation ....................................................................... 13 Power Management.................................................................... 14 Timing.......................................................................................... 15 Hsync Timing ............................................................................. 15 Coast Timing............................................................................... 15 2-Wire Serial Register Map ....................................................... 16 2-Wire Serial Control Register Detail Chip Identification... 19 PLL Divider Control .................................................................. 19 Clock Generator Control .......................................................... 19 Clamp Timing............................................................................. 20 Hsync Pulsewidth....................................................................... 20 Input Gain ................................................................................... 20 Input Offset ................................................................................. 20 Mode Control 1 .......................................................................... 21 2-Wire Serial Control Port........................................................ 26 Data Transfer via Serial Interface............................................. 26 Sync Slicer.................................................................................... 28 Sync Separator ............................................................................ 28 PCB Layout Recommendations ............................................... 29 Analog Interface Inputs ............................................................. 29 Power Supply Bypassing ............................................................ 29 PLL ............................................................................................... 30 Outputs (Both Data and Clocks).............................................. 30 Digital Inputs .............................................................................. 30 Voltage Reference ....................................................................... 30 Outline Dimensions ....................................................................... 31 Ordering GuIde .......................................................................... 31
REVISION HISTORY
5/04--Revision 0: Initial Version
Rev. 0 | Page 2 of 32
AD9985 SPECIFICATIONS
Analog Interface: VD = 3.3 V, VDD = 3.3 V, ADC clock = maximum conversion rate, unless otherwise noted. Table 1.
AD9985KSTZ-110 Parameter RESOLUTION DC ACCURACY Differential Nonlinearity Integral Nonlinearity No Missing Codes ANALOG INPUT Input Voltage Range Minimum Maximum Gain Tempco Input Bias Current Input Offset Voltage Input Full-Scale Matching Offset Adjustment Range REFERENCE OUTPUT Output Voltage Temperature Coefficient SWITCHING PERFORMANCE Maximum Conversion Rate Minimum Conversion Rate Data to Clock Skew tBUFF tSTAH tDHO tDAL tDAH tDSU tSTASU tSTOTSU HSYNC Input Frequency Maximum PLL Clock Rate Minimum PLL Clock Rate PLL Jitter Sampling Phase Tempco DIGITAL INPUTS Input Voltage, High (VIH) Input Voltage, Low (VIL) Input Current, High (VIH) Input Current, Low (VIL) Input Capacitance Temp Test Level Min Typ 8 0.5 Max Min AD9985KSTZ-140 Typ 8 0.5 Max Unit Bits LSB LSB LSB LSB
25C Full 25C Full Full
I VI I VI VI
+1.25/-1.0 +1.35/-1.0 0.5 1.85 2.0 Guaranteed
+1.35/-1.0 1.45/-1.0 0.5 2.0 2.3 Guaranteed
Full Full 25C 25C Full Full Full Full Full Full Full Full Full Full Full Full Full Full Full Full Full Full Full Full 25C Full Full Full Full Full Full 25C
VI VI V IV IV V VI VI V V VI IV IV VI VI VI VI VI VI VI VI IV VI IV IV IV IV VI VI V V V
0.5 1.0 100 1 1 7 1.5 49 1.25 50 110 -0.5 4.7 4.0 300 4.7 4.0 250 4.7 4.0 15 110 400 15 2.5 0.8 -1.0 +1.0 3 3 2.5 10 +2.0 140 -0.5 4.7 4.0 300 4.7 4.0 250 4.7 4.0 15 140 400 400 15 8.0 52 7 1.5 49 1.25 50 1.0 100
0.5
1 1 8.0 52
46
46
V p-p V p-p ppm/C A A mV % FS % FS V ppm/C MSPS MSPS ns s s ns s s ns s s kHz MHz MHz ps p-p ps p-p ps/C V V A A pF
10 +2.0
110 12 7001 10001
110 12 7001 7001
0.8 -1.0 +1.0
Rev. 0 | Page 3 of 32
AD9985
AD9985KSTZ-110 Parameter DIGITAL OUTPUTS Output Voltage, High (VOH) Output Voltage, Low (VOL) Duty Cycle DATACK Output Coding POWER SUPPLY VD Supply Voltage VDD Supply Voltage PVD Supply Voltage ID Supply Current (VD) IDD Supply Current (VDD)2 IPVD Supply Current (PVD) Total Power Dissipation Power-Down Supply Current Power-Down Dissipation DYNAMIC PERFORMANCE Analog Bandwidth, Full Power Transient Response Overvoltage Recovery Time Signal-to-Noise Ratio (SNR) (Without Harmonics) fIN = 40.7 MHz Crosstalk THERMAL CHARACTERISTICS JC Junction-to-Case Thermal Resistance JA Junction-to-Ambient Thermal Resistance Temp Full Full Full Test Level VI VI IV Min VD -0.1 45 50 Binary 3.3 3.3 3.3 132 19 8 525 5 16.5 300 2 1.5 44 43 55 0.1 55 Typ Max Min VD -0.1 45 50 Binary 3.3 3.3 3.3 180 26 11 650 5 16.5 300 2 1.5 43 42 55 0.1 55 AD9985KSTZ-140 Typ Max Unit V V %
Full Full Full 25C 25C 25C Full Full Full 25C 25C 25C 25C Full Full
IV IV IV V V V VI VI VI V V V V V V
3.15 2.2 3.15
3.45 3.45 3.45
3.15 2.2 3.15
3.45 3.45 3.45
760 15 50
900 15 50
V V V mA mA mA mW mA mW MHz ns ns dB dB dBc
V V
16 35
16 35
C/W C/W
1 2
VCO range = 10, charge pump current = 110, PLL divider = 1693. DATACK load = 15 pF, data load = 5 pF.
Rev. 0 | Page 4 of 32
AD9985
Table 2.
AD9985BSTZ-110 Parameter RESOLUTION DC ACCURACY Differential Nonlinearity Integral Nonlinearity ANALOG INPUT Input Voltage Range Minimum Maximum Gain Tempco Input Bias Current Input Offset Voltage Input Full-Scale Matching Offset Adjustment Range REFERENCE OUTPUT Output Voltage Temperature Coefficient SWITCHING PERFORMANCE Maximum Conversion Rate Minimum Conversion Rate Data to Clock Skew tBUFF tSTAH tDHO tDAL tDAH tDSU tSTASU tSTAH HSYNC Input Frequency Maximum PLL Clock Rate Minimum PLL Clock Rate PLL Jitter Sampling Phase Tempco DIGITAL INPUTS Input Voltage, High (VIH) Input Voltage, Low (VIL) Input Current, High (IIH) Input Current, Low (IIL) Input Capacitance DIGITAL OUTPUTS Output Voltage, High (VOH) Output Voltage, Low (VOL) Duty Cycle, DATACK Output Coding Temp Test Level Min Typ 8 0.5 0.5 Max Unit Bits LSB LSB LSB LSB
25C Full 25C Full
I VI I VI
+1.25/-1.0 +1.5/-1.0 1.85 3.2
Full Full 25C 25C Full Full Full Full Full Full Full Full Full Full Full Full Full Full Full Full Full Full Full Full 25C Full Full Full Full Full Full 25C Full Full Full
VI VI V IV IV VI VI VI VI V VI IV IV VI VI VI VI VI VI VI VI IV VI IV IV IV IV VI VI V V V VI VI IV
0.5 1.0 100 1 2 7 1.5 49 1.25 100 110 -0.5 4.7 4.0 300 4.7 4.0 250 4.7 15 110 400 15 2.5 0.8 -1.0 1.0 3 VD -0.1 45 50 Binary 0.1 55 10 +2.0 8.0 52
46
V p-p V p-p ppm/C A A mV % FS % FS V ppm/C MSPS MSPS ns s s ns s s ns s s kHz MHz MHz ps p-p ps p-p ps/C V V A A pF V V %
110 12 7001 10001
Rev. 0 | Page 5 of 32
AD9985
AD9985BSTZ-110 Parameter POWER SUPPLY VD Supply Voltage VDD Supply Voltage PVD Supply Voltage ID Supply Current (VD) IDD Supply Current (VDD) 2 IPVD Supply Current (PVD) Total Power Dissipation Power-Down Supply Current Power-Down Dissipation DYNAMIC PERFORMANCE Analog Bandwidth, Full Power Transient Response Overvoltage Recovery Time Signal-to-Noise Ratio (SNR) (Without Harmonics) fIN = 40.7 MHz Crosstalk THERMAL CHARACTERISTICS JC Junction-to-Case Thermal Resistance JA Junction-to-Ambient Thermal Resistance
1 2
Temp Full Full Full 25C 25C 25C Full Full Full 25C 25C 25C 25C Full Full
Test Level IV IV IV V V V VI VI VI V V V V V V
Min 3.15 2.2 3.15
Typ 3.3 3.3 3.3 132 19 8 525 5 16.5 300 2 1.5 44 43 55
Max 3.45 3.45 3.45
Unit V V V mA mA mA mW mA mW MHz ns ns dB dB dBc
760 15 50
V V
16 35
C/W C/W
VCO range = 10, charge pump current = 110, PLL divider = 1693. DATACK load = 15 pF, data load = 5 pF.
.
EXPLANATION OF TEST LEVELS
Test Level I. II. III. IV. V. 100% production tested. 100% production tested at 25C and sample tested at specified temperatures. Sample tested only. Parameter is guaranteed by design and characterization testing. Parameter is a typical value only.
VI. 100% production tested at 25C; guaranteed by design and characterization testing.
Rev. 0 | Page 6 of 32
AD9985 ABSOLUTE MAXIMUM RATINGS
Table 3.
Parameter VD VDD Analog Inputs VREF IN Digital Inputs Digital Output Current Operating Temperature Storage Temperature Maximum Junction Temperature Maximum Case Temperature Rating 3.6 V 3.6 V VD to 0.0 V VD to 0.0 V 5 V to 0.0 V 20 mA -40C to +85C -65C to +150C 150C 150C
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions outside of those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum ratings for extended periods may affect device reliability.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
Rev. 0 | Page 7 of 32
AD9985 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
SOGOUT DATACK RED <0> RED <1> RED <2> RED <3> RED <4> RED <5> RED <6> RED <7> HSOUT VSOUT GND GND GND VDD GND VDD VDD VD
80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61
GND GREEN <7> GREEN <6> GREEN <5> GREEN <4> GREEN <3> GREEN <2> GREEN <1> GREEN <0>
1 2 3 4 5 6 7 8 9
PIN 1 INDICATOR
60 59 58 57 56 55 54 53 52
GND VD REF BYPASS SDA SCL A0 RAIN GND VD VD GND SOGIN GAIN GND VD VD GND BAIN VD GND
GND 10 VDD 11 BLUE <7> 12 BLUE <6> 13 BLUE <5> 14 BLUE <4> 15 BLUE <3> 16 BLUE <2> 17 BLUE <1> 18 BLUE <0> 19 GND 20
AD9985
TOP VIEW (Not to Scale)
51 50 49 48 47 46 45 44 43 42 41
21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
VSYNC
FILT
MIDSCV
COAST
GND
GND
GND
GND
GND
HSYNC
GND
CLAMP
GND
PVD
PVD
PVD
PVD
VDD
VDD
VD
Figure 2. Pin Configuration
Table 4. Complete Pinout List
Pin Type Inputs Mnemonic RAIN GAIN BAIN HSYNC VSYNC SOGIN CLAMP COAST Red [7:0] Green [7:0] Blue [7:0] DATACK HSOUT VSOUT SOGOUT REF BYPASS MIDSCV FILT VD VDD PVD GND SDA SCL A0 Function Analog Input for Converter R Analog Input for Converter G Analog Input for Converter B Horizontal SYNC Input Vertical SYNC Input Input for Sync-on-Green Clamp Input (External CLAMP Signal) PLL COAST Signal Input Outputs of Converter Red, Bit 7 is the MSB Outputs of Converter Green, Bit 7 is the BSB Outputs of Converter Blue, Bit 7 is the BSB Data Output Clock HSYNC Output (Phase-Aligned with DATACK) VSYNC Output (Phase-Aligned with DATACK) Sync-on-Green Slicer Output Internal Reference Bypass Internal Midscale Voltage Bypass Connection for External Filter Components for Internal PLL Analog Power Supply Output Power Supply PLL Power Supply Ground Serial Port Data I/O Serial Port Data Clock (100 kHz Maximum Serial Port Address Input 1
Rev. 0 | Page 8 of 32
Outputs
References
Value 0.0 V to 1.0V 0.0 V to 1.0V 0.0 V to 1.0V 3.3 V CMOS 3.3 V CMOS 0.0 V to 1.0 V 3.3 V CMOS 3.3 V CMOS 3.3 V CMOS 3.3 V CMOS 3.3 V CMOS 3.3 V CMOS 3.3 V CMOS 3.3 V CMOS 3.3 V CMOS 1.25 V
Pin No. 54 48 43 30 31 49 38 29 70-77 2-9 12-19 67 66 64 65 58 37 33 39, 42, 45, 46, 51, 52, 59, 62 11, 22, 23, 69, 78, 79 26, 27, 34, 35 1, 10, 20, 21, 24, 25, 28, 32, 36, 40, 41, 44, 47, 50, 53, 60, 61, 63, 68, 80 57 56 55
Power Supply
3.3 V 3.3 V 3.3 V 0V 3.3 V CMOS 3.3 V CMOS 3.3 V CMOS
Control
04799-0-002
AD9985
Table 5. Pin Function Descriptions
Pin Name OUTPUTS HSOUT Function Horizontal Sync Output A reconstructed and phase-aligned version of the Hsync input. Both the polarity and duration of this output can be programmed via serial bus registers. By maintaining alignment with DATACK and Data, data timing with respect to horizontal sync can always be determined. Vertical Sync Output A reconstructed and phase-aligned version of the video Vsync. The polarity of this output can be controlled via a serial bus bit. The placement and duration in all modes is set by the graphics transmitter. Sync-On-Green Slicer Output
VSOUT
SOGOUT
This pin outputs either the signal from the Sync-on-Green slicer comparator or an unprocessed but delayed version of the Hsync input. See the Sync Processing Block Diagram (Figure 14) to view how this pin is connected. (Note: Besides slicing off SOG, the output from this pin gets no other additional processing on the AD9985. Vsync separation is performed via the sync separator.) SERIAL PORT (2-Wire) SDA Serial Port Data I/O SCL Serial Port Data Clock A0 Serial Port Address Input 1 For a full description of the 2-wire serial register and how it works, refer to the 2-wire serial control port section. DATA OUTPUTS RED Data Output, Red Channel GREEN Data Output, Green Channel BLUE Data Output, Blue Channel The main data outputs. Bit 7 is the MSB. The delay from pixel sampling time to output is fixed. When the sampling time is changed by adjusting the PHASE register, the output timing is shifted as well. The DATACK and HSOUT outputs are also moved, so the timing relationship among the signals is maintained. For exact timing information, refer to Figure 9, Figure 10, and Figure 11. DATA CLOCK OUTPUT DATACK Data Output Clock The main clock output signal used to strobe the output data and HSOUT into external logic. It is produced by the internal clock generator and is synchronous with the internal pixel sampling clock. When the sampling time is changed by adjusting the PHASE register, the output timing is shifted as well. The Data, DATACK, and HSOUT outputs are all moved, so the timing relationship among the signals is maintained. INPUTS RAIN Analog Input for Red Channel GAIN Analog Input for Green Channel BAIN Analog Input for Blue Channel High impedance inputs that accept the Red, Green, and Blue channel graphics signals, respectively. (The three channels are identical, and can be used for any colors, but colors are assigned for convenient reference.) They accommodate input signals ranging from 0.5 V to 1.0 V full scale. Signals should be ac-coupled to these pins to support clamp operation. HSYNC Horizontal Sync Input This input receives a logic signal that establishes the horizontal timing reference and provides the frequency reference for pixel clock generation. The logic sense of this pin is controlled by serial Register 0EH Bit 6 (Hsync Polarity). Only the leading edge of Hsync is active; the trailing edge is ignored. When Hsync Polarity = 0, the falling edge of Hsync is used. When Hsync Polarity = 1, the rising edge is active. The input includes a Schmitt trigger for noise immunity, with a nominal input threshold of 1.5 V. VSYNC Vertical Sync Input The input for vertical sync.
Rev. 0 | Page 9 of 32
AD9985
Pin Name SOGIN Function Sync-on-Green Input This input is provided to assist with processing signals with embedded sync, typically on the Green channel. The pin is connected to a high speed comparator with an internally generated threshold. The threshold level can be programmed in 10 mV steps to any voltage between 10 mV and 330 mV above the negative peak of the input signal. The default voltage threshold is 150 mV. When connected to an ac-coupled graphics signal with embedded sync, it will produce a noninverting digital output on SOGOUT. (This is usually a composite sync signal, containing both vertical and horizontal sync information that must be separated before passing the horizontal sync signal to Hsync.) When not used, this input should be left unconnected. For more details on this function and how it should be configured, refer to the Sync-on-Green section. External Clamp Input This logic input may be used to define the time during which the input signal is clamped to ground. It should be exercised when the reference dc level is known to be present on the analog input channels, typically during the back porch of the graphics signal. The CLAMP pin is enabled by setting control bit Clamp Function to 1 (Register 0FH, Bit 7, default is 0). When disabled, this pin is ignored and the clamp timing is determined internally by counting a delay and duration from the trailing edge of the Hsync input. The logic sense of this pin is controlled by Clamp Polarity Register 0FH, Bit 6. When not used, this pin must be grounded and Clamp Function programmed to 0. Clock Generator Coast Input (Optional) This input may be used to cause the pixel clock generator to stop synchronizing with Hsync and continue producing a clock at its current frequency and phase. This is useful when processing signals from sources that fail to produce horizontal sync pulses during the vertical interval. The COAST signal is generally not required for PC-generated signals. The logic sense of this pin is controlled by Coast Polarity (Register 0FH, Bit 3). When not used, this pin may be grounded and Coast Polarity programmed to 1, or tied HIGH (to VD through a 10 k resistor) and Coast Polarity programmed to 0. Coast Polarity defaults to 1 at power-up. Internal Reference BYPASS
CLAMP
COAST
REF BYPASS
Bypass for the internal 1.25 V band gap reference. It should be connected to ground through a 0.1 F capacitor. The absolute accuracy of this reference is 4%, and the temperature coefficient is 50 ppm, which is adequate for most AD9985 applications. If higher accuracy is required, an external reference may be employed instead. MIDSCV Midscale Voltage Reference BYPASS Bypass for the internal midscale voltage reference. It should be connected to ground through a 0.1 F capacitor. The exact voltage varies with the gain setting of the Blue channel. FILT External Filter Connection For proper operation, the pixel clock generator PLL requires an external filter. Connect the filter shown in Figure 8 to this pin. For optimal performance, minimize noise and parasitics on this node. POWER SUPPLY VD Main Power Supply These pins supply power to the main elements of the circuit. They should be filtered and as quiet as possible. VDD Digital Output Power Supply A large number of output pins (up to 25) switching at high speed (up to 110 MHz) generates a lot of power supply transients (noise). These supply pins are identified separately from the VD pins so special care can be taken to minimize output noise transferred into the sensitive analog circuitry. If the AD9985 is interfacing with lower voltage logic, VDD may be connected to a lower supply voltage (as low as 2.5 V) for compatibility. PVD Clock Generator Power Supply The most sensitive portion of the AD9985 is the clock generation circuitry. These pins provide power to the clock PLL and help the user design for optimal performance. The designer should provide quiet, noise-free power to these pins. GND Ground The ground return for all circuitry on-chip. It is recommended that the AD9985 be assembled on a single solid ground plane, with careful attention given to ground current paths.
Rev. 0 | Page 10 of 32
AD9985 DESIGN GUIDE
GENERAL DESCRIPTION
The AD9985 is a fully integrated solution for capturing analog RGB signals and digitizing them for display on flat-panel monitors or projectors. The circuit is ideal for providing a computer interface for HDTV monitors or as the front end to high performance video scan converters. Implemented in a high performance CMOS process, the interface can capture signals with pixel rates up to 110 MHz. The AD9985 includes all necessary input buffering, signal dc restoration (clamping), offset and gain (brightness and contrast) adjustment, pixel clock generation, sampling phase control, and output data formatting. All controls are programmable via a 2-wire serial interface. Full integration of these sensitive analog functions makes system design straightforward and less sensitive to the physical and electrical environment. With a typical power dissipation of only 500 mW and an operating temperature range of 0C to 70C, the device requires no special environmental considerations. slightly and providing a high quality signal over a wider range of conditions. Using a Fair-Rite #2508051217Z0 High Speed Signal Chip Bead inductor in the circuit of Figure 3 gives good results in most applications.
RGB INPUT 75 47nF RAIN GAIN BAIN
Figure 3. Analog Input Interface Circuit
HSYNC, VSYNC INPUTS
The interface also takes a horizontal sync signal, which is used to generate the pixel clock and clamp timing. This can be either a sync signal directly from the graphics source, or a preprocessed TTL or CMOS level signal. The Hsync input includes a Schmitt trigger buffer for immunity to noise and signals with long rise times. In typical PC-based graphic systems, the sync signals are simply TTL-level drivers feeding unshielded wires in the monitor cable. As such, no termination is required.
DIGITAL INPUTS
All digital inputs on the AD9985 operate to 3.3 V CMOS levels. However, all digital inputs are 5 V tolerant. Applying 5 V to them will not cause any damage.
SERIAL CONTROL PORT
The serial control port is designed for 3.3 V logic. If there are 5 V drivers on the bus, these pins should be protected with 150 series resistors placed between the pull-up resistors and the input pins.
INPUT SIGNAL HANDLING
The AD9985 has three high impedance analog input pins for the Red, Green, and Blue channels. They will accommodate signals ranging from 0.5 V to 1.0 V p-p. Signals are typically brought onto the interface board via a DVI-I connector, a 15-pin D connector, or via BNC connectors. The AD9985 should be located as close as practical to the input connector. Signals should be routed via matched-impedance traces (normally 75 ) to the IC input pins. At that point the signal should be resistively terminated (75 to the signal ground return) and capacitively coupled to the AD9985 inputs through 47 nF capacitors. These capacitors form part of the dc restoration circuit. In an ideal world of perfectly matched impedances, the best performance can be obtained with the widest possible signal bandwidth. The ultrawide bandwidth inputs of the AD9985 (300 MHz) can track the input signal continuously as it moves from one pixel level to the next, and digitize the pixel during a long, flat pixel time. In many systems, however, there are mismatches, reflections, and noise, which can result in excessive ringing and distortion of the input waveform. This makes it more difficult to establish a sampling phase that provides good image quality. It has been shown that a small inductor in series with the input is effective in rolling off the input bandwidth
OUTPUT SIGNAL HANDLING
The digital outputs are designed and specified to operate from a 3.3 V power supply (VDD). They can also work with a VDD as low as 2.5 V for compatibility with other 2.5 V logic.
CLAMPING
RGB Clamping
To properly digitize the incoming signal, the dc offset of the input must be adjusted to fit the range of the on-board A/D converters. Most graphics systems produce RGB signals with black at ground and white at approximately 0.75 V. However, if sync signals are embedded in the graphics, the sync tip is often at ground and black is at 300 mV. Then white is at approximately 1.0 V. Some common RGB line amplifier boxes use emitterfollower buffers to split signals and increase drive capability. This introduces a 700 mV dc offset to the signal, which must be removed for proper capture by the AD9985. The key to clamping is to identify a portion (time) of the signal when the graphic system is known to be producing black. An offset is then introduced which results in the A/D converters producing a black output (code 00h) when the known black
Rev. 0 | Page 11 of 32
04799-0-003
AD9985
input is present. The offset then remains in place when other signal levels are processed, and the entire signal is shifted to eliminate offset errors. In most PC graphics systems, black is transmitted between active video lines. With CRT displays, when the electron beam has completed writing a horizontal line on the screen (at the right side), the beam is deflected quickly to the left side of the screen (called horizontal retrace), and a black signal is provided to prevent the beam from disturbing the image. In systems with embedded sync, a blacker-than-black signal (Hsync) is produced briefly to signal the CRT that it is time to begin a retrace. For obvious reasons, it is important to avoid clamping on the tip of Hsync. Fortunately, there is virtually always a period following Hsync, called the back porch, where a good black reference is provided. This is the time when clamping should be done. The clamp timing can be established by simply exercising the CLAMP pin at the appropriate time (with External Clamp = 1). The polarity of this signal is set by the clamp polarity bit. A simpler method of clamp timing employs the AD9985 internal clamp timing generator. The clamp placement register is programmed with the number of pixel times that should pass after the trailing edge of HSYNC before clamping starts. A second register (clamp duration) sets the duration of the clamp. These are both 8-bit values, providing considerable flexibility in clamp generation. The clamp timing is referenced to the trailing edge of Hsync because, though Hsync duration can vary widely, the back porch (black reference) always follows Hsync. A good starting point for establishing clamping is to set the clamp placement to 09H (providing 9 pixel periods for the graphics signal to stabilize after sync) and set the clamp duration to 14H (giving the clamp 20 pixel periods to reestablish the black reference). Clamping is accomplished by placing an appropriate charge on the external input coupling capacitor. The value of this capacitor affects the performance of the clamp. If it is too small, there will be a significant amplitude change during a horizontal line time (between clamping intervals). If the capacitor is too large, then it will take excessively long for the clamp to recover from a large change in incoming signal offset. The recommended value (47 nF) results in recovering from a step error of 100 mV to within 1/2 LSB in 10 lines with a clamp duration of 20 pixel periods on a 60 Hz SXGA signal. Clamping to midscale rather than to ground can be accomplished by setting the clamp select bits in the serial bus register. Each of the three converters has its own selection bit so that they can be clamped to either midscale or ground independently. These bits are located in Register 10H and are Bits 0-2. The midscale reference voltage that each A/D converter clamps to is provided on the MIDSCV pin (Pin 37). This pin should be bypassed to ground with a 0.1 F capacitor, even if midscale clamping is not required.
OFFSET = 7FH OFFSET = 3FH 1.0 INPUT RANGE (V) OFFSET = 00H
0.5 OFFSET = 7FH
0
OFFSET = 3FH
00H GAIN
FFH
Figure 4. Gain and Offset Control
GAIN AND OFFSET CONTROL
The AD9985 can accommodate input signals with inputs ranging from 0.5 V to 1.0 V full scale. The full-scale range is set in three 8-bit registers (Red Gain, Green Gain, and Blue Gain). Note that increasing the gain setting results in an image with less contrast. The offset control shifts the entire input range, resulting in a change in image brightness. Three 7-bit registers (Red Offset, Green Offset, Blue Offset) provide independent settings for each channel. The offset controls provide a 63 LSB adjustment range. This range is connected with the full-scale range, so if the input range is doubled (from 0.5 V to 1.0 V) then the offset step size is also doubled (from 2 mV per step to 4 mV per step). Figure 4 illustrates the interaction of gain and offset controls. The magnitude of an LSB in offset adjustment is proportional to the full-scale range, so changing the full-scale range also changes the offset. The change is minimal if the offset setting is near midscale. When changing the offset, the full-scale range is not affected, but the full-scale level is shifted by the same amount as the zero-scale level.
YUV Clamping
YUV graphic signals are slightly different from RGB signals in that the dc reference level (black level in RGB signals) can be at the midpoint of the graphics signal rather than at the bottom. For these signals, it can be necessary to clamp to the midscale range of the A/D converter range (80H) rather than at the bottom of the A/D converter range (00H).
Auto Offset
In addition to the manual offset adjustment mode (via Registers 0Bh to 0Dh), the AD9985 also includes circuitry to automatically calibrate the offset for each channel. By monitoring the output of each ADC during the back porch of the input signals, the AD9985 can self-adjust to eliminate any
Rev. 0 | Page 12 of 32
04799-0-004
OFFSET = 00H
AD9985
offset errors in its own ADC channels as well as any offset errors present on the incoming graphics or video signals. To activate the auto-offset mode, set Register 1Dh, Bit 7 to 1. Next, the target code registers (19h through 1Bh) must be programmed. The values programmed into the target code registers should be the output code desired from the AD9985 during the back porch reference time. For example, for RGB signals, all three registers would normally be programmed to code 1, while for YPbPr signals the green (Y) channel would normally be programmed to code 1 and the blue and red channels (Pb and Pr) would normally be set to 128. Any target code value between 1 and 254 can be set, although the AD9985's offset range may not be able to reach every value. Intended target code values range from (but are not limited to) 1 to 40 when ground clamping and 90 to 170 when midscale clamping. The ability to program a target code for each channel gives users a large degree of freedom and flexibility. While in most cases all channels will be set to either 1 or 128, the flexibility to select other values allows for the possibility of inserting intentional skews between channels. It also allows for the ADC range to be skewed so that voltages outside of the normal range can be digitized. (For example, setting the target code to 40 would allow the sync tip, which is normally below black level, to be digitized and evaluated.) Lastly, when in auto offset mode, the manual offset registers (0Bh to 0Dh) have new functionality. The values in these registers are digitally added to the value of the ADC output. The purpose of doing this is to match a benefit that is present with manual offset adjustment. Adjusting these registers is an easy way to make brightness adjustments. Although some signal range is lost with this method, it has proven to be a very popular function. In order to be able to increase and decrease brightness, the values in these registers in this mode are signed twos complement. The digital adder is used only when in auto offset mode. Although it cannot be disabled, setting the offset registers to all 0's will effectively disable it by always adding 0.
47nF RAIN 47nF BAIN 47nF 1nF SOG
04799-0-005
GAIN
Figure 5. Typical Clamp Configuration
CLOCK GENERATION
A phase-locked loop (PLL) is employed to generate the pixel clock. In this PLL, the Hsync input provides a reference frequency. A voltage controlled oscillator (VCO) generates a much higher pixel clock frequency. This pixel clock is divided by the PLL divide value (Registers 01H and 02H) and phase compared with the Hsync input. Any error is used to shift the VCO frequency and maintain lock between the two signals. The stability of this clock is a very important element in providing the clearest and most stable image. During each pixel time, there is a period during which the signal is slewing from the old pixel amplitude and settling at its new value. Then there is a time when the input voltage is stable, before the signal must slew to a new value (Figure 6). The ratio of the slewing time to the stable time is a function of the bandwidth of the graphics DAC and the bandwidth of the transmission system (cable and termination). It is also a function of the overall pixel rate. Clearly, if the dynamic characteristics of the system remain fixed, the slewing and settling time is likewise fixed. This time must be subtracted from the total pixel period, leaving the stable period. At higher pixel frequencies, the total cycle time is shorter, and the stable pixel time becomes shorter as well.
PIXEL CLOCK INVALID SAMPLE TIMES
SYNC-ON-GREEN
The Sync-on-Green input operates in two steps. First, it sets a baseline clamp level off of the incoming video signal with a negative peak detector. Second, it sets the sync trigger level to a programmable level (typically 150 mV) above the negative peak. The Sync-on-Green input must be ac-coupled to the Green analog input through its own capacitor, as shown in Figure 5. The value of the capacitor must be 1 nF 20%. If Sync-onGreen is not used, this connection is not required. Note that the Sync-on-Green signal is always negative polarity.
04799-0-006
Figure 6. Pixel Sampling Times
Any jitter in the clock reduces the precision with which the sampling time can be determined, and must also be subtracted from the stable pixel time. Considerable care has been taken in the design of the AD9985's clock generation circuit to minimize jitter. As indicated in Figure 7, the clock jitter of the AD9985 is less than 5% of the total pixel time in all operating modes, making the reduction in the valid sampling time due to jitter negligible.
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AD9985
14
3.
12
PIXEL CLOCK JITTER (p-p) (%)
The 3-Bit Charge Pump Current Register. This register allows the current that drives the low-pass loop filter to be varied. The possible current values are listed in Table 7.
Ip1 0 0 1 1 0 0 1 1 Ip0 0 1 0 1 0 1 0 1 Current (A) 50 100 150 250 350 500 750 1500
10
Table 7. Charge Pump Current/Control Bits
Ip2 0 0 0 0 1 1 1 1
8 6
4
2 0
04799-0-007
0
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 FREQUENCY (MHz)
Figure 7. Pixel Clock Jitter vs. Frequency
4.
The PLL characteristics are determined by the loop filter design, by the PLL charge pump current, and by the VCO range setting. The loop filter design is illustrated in Figure 8. Recommended settings of VCO range and charge pump current for VESA standard display modes are listed in Table 9.
CP 0.0082F RZ 2.7k CZ 0.082F PVD
The 5-Bit Phase Adjust Register. The phase of the generated sampling clock may be shifted to locate an optimum sampling point within a clock cycle. The phase adjust register provides 32 phase-shift steps of 11.25 each. The Hsync signal with an identical phase shift is available through the HSOUT pin. The COAST pin is used to allow the PLL to continue to run at the same frequency, in the absence of the incoming Hsync signal or during disturbances in Hsync (such as equalization pulses). This may be used during the vertical sync period, or any other time that the Hsync signal is unavailable. The polarity of the COAST signal may be set through the coast polarity register. Also, the polarity of the Hsync signal may be set through the Hsync polarity register. If not using automatic polarity detection, the Hsync and COAST polarity bits should be set to match the respective polarities of the input signals.
FILT
Figure 8. PLL Loop Filter Detail
Four programmable registers are provided to optimize the performance of the PLL: 1. The 12-Bit Divisor Register. The input Hsync frequencies range from 15 kHz to 110 kHz. The PLL multiplies the frequency of the Hsync signal, producing pixel clock frequencies in the range of 12 MHz to 110 MHz. The Divisor register controls the exact multiplication factor. This register may be set to any value between 221 and 4095. (The divide ratio that is actually used is the programmed divide ratio plus one.) The 2-Bit VCO Range Register. To improve the noise performance of the AD9985, the VCO operating frequency range is divided into three overlapping regions. The VCO range register sets this operating range. Table 6 lists the frequency ranges for the lowest and highest regions.
Pixel Clock Range (MHz) AD9985KSTZ AD9985BSTZ 12-32 12-30 32-64 30-60 64-110 60-110 110-140
04799-0-008
POWER MANAGEMENT
The AD9985 uses the activity detect circuits, the active interface bits in the serial bus, the active interface override bits, and the power-down bit to determine the correct power state. There are three power states--full-power, seek mode, and power-down. Table 8 summarizes how the AD9985 determines what power mode to be in and which circuitry is powered on/off in each of these modes. The power-down command has priority over the automatic circuitry. Table 8. Power-Down Mode Descriptions
Mode FullPower Seek Mode PowerDown
1 2
2.
Inputs Power-Down1 1 1
Sync Detect2 1 0
Powered On or Comments Everything Serial Bus, Sync Activity Detect, SOG, Band Gap Reference Serial Bus, Sync Activity Detect, SOG, Band Gap Reference
Table 6. VCO Frequency Ranges
PV1 0 0 1 1 PV0 0 1 0 1
0
X
Power-down is controlled via Bit 1 in serial bus Register 0FH. Sync detect is determined by OR'ing Bits 7, 4, and 1 in serial bus Register 14H.
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AD9985
Table 9. Recommended VCO Range and Charge Pump Current Settings for Standard Display Formats
AD9985KSTZ Standard Modes VGA Refresh Rate (Hz) 60 72 75 85 56 60 72 75 85 60 70 75 80 85 60 75 60 60 60 60 Horizontal Frequency (kHz) 31.5 37.7 37.5 43.3 35.1 37.9 48.1 46.9 53.7 48.4 56.5 60.0 64.0 68.3 64.0 80.0 15.75 31.47 45.0 33.75 Pixel Rate (MHz) 25.175 31.500 31.500 36.000 36.000 40.000 50.000 49.500 56.250 65.000 75.000 78.750 85.500 94.500 108.000 135.000 13.51 27.00 74.25 74.25 PLL Div 799 835 841 831 1025 1055 1039 1055 1047 1343 1327 1313 1335 1383 1687 1687 857 857 1649 2199 AD9985BSTZ
Resolution 640 x 480
SVGA
800 x 600
XGA
1024 x 768
SXGA TV Modes 480i 480p 720p 1080i
1280 x 1024
VCORNGE 00 00 00 01 01 01 01 01 01 10 10 10 10 10 10 11 00 00 10 10
Current 110 110 110 100 100 100 101 101 101 101 100 100 101 101 110 110 011 110 100 100
VCORNGE 00 01 01 01 01 01 01 01 01 10 10 10 10 10 10
Current 011 010 010 010 010 011 100 100 101 011 011 011 100 100 101
720 x 480 720 x 483 1280 x 720 1920 x 1080
00 00 10 10
011 011 011 011
TIMING
The following timing diagrams show the operation of the AD9985. The output data clock signal is created so that its rising edge always occurs between data transitions and can be used to latch the output data externally. There is a pipeline in the AD9985, which must be flushed before valid data becomes available. This means that four data sets are presented before valid data is available.
tPER tCYCLE
DATACK
The Hsync input is used as a reference to generate the pixel sampling clock. The sampling phase can be adjusted, with respect to Hsync, through a full 360 in 32 steps via the phase adjust register (to optimize the pixel sampling time). Display systems use Hsync to align memory and display write cycles, so it is important to have a stable timing relationship between Hsync output (HSOUT) and data clock (DATACK). Three things happen to Horizontal Sync in the AD9985. First, the polarity of Hsync input is determined and will thus have a known output polarity. The known output polarity can be programmed either active high or active low (Register 0EH, Bit 5). Second, HSOUT is aligned with DATACK and data outputs. Third, the duration of HSOUT (in pixel clocks) is set via Register 07H. HSOUT is the sync signal that should be used to drive the rest of the display system.
tSKEW
DATA HSOUT
04799-0-009
COAST TIMING
In most computer systems, the Hsync signal is provided continuously on a dedicated wire. In these systems, the COAST input and function are unnecessary and should not be used, and the pin should be permanently connected to the inactive state. In some systems, however, Hsync is disturbed during the Vertical Sync period (Vsync). In some cases, Hsync pulses
Figure 9. Output Timing
HSYNC TIMING
Horizontal Sync (Hsync) is processed in the AD9985 to eliminate ambiguity in the timing of the leading edge with respect to the phase-delayed pixel clock and data.
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AD9985
disappear. In other systems, such as those that employ Composite Sync (Csync) signals or embedded Sync-on-Green (SOG), Hsync includes equalization pulses or other distortions during Vsync. To avoid upsetting the clock generator during Vsync, it is important to ignore these distortions. If the pixel clock PLL sees extraneous pulses, it will attempt to lock to this new frequency, and will have changed frequency by the end of
RGBIN HSYNC P0 P1 P2 P3 P4 P5 P6 P7
the Vsync period. It will then take a few lines of correct Hsync timing to recover at the beginning of a new frame, resulting in a "tearing" of the image at the top of the display. The COAST input is provided to eliminate this problem. It is an asynchronous input that disables the PLL input and allows the clock to free-run at its then-current frequency. The PLL can free-run for several lines without significant frequency drift.
PxCK HS 5-PIPE DELAY ADCCK
DATACK DOUTA HSOUT D0 D1 D2 D3 D4 D5 D6 D7
04799-0-010
.
VARIABLE DURATION
Figure 10. 4:4:4 Mode (For RGB and YUV)
RGBIN HSYNC
P0
P1
P2
P3
P4
P5
P6
P7
PxCK HS 5-PIPE DELAY ADCCK
DATACK GOUTA ROUTA Y0 U0 Y1 V1 Y2 U2 Y3 V3 Y4 U4 Y5 V5 Y6 U6 Y7 V7
04799-0-011
HSOUT
VARIABLE DURATION
Figure 11. 4:2:2 Mode (For YUV Only)
2-WIRE SERIAL REGISTER MAP
The AD9985 is initialized and controlled by a set of registers, that determine the operating modes. An external controller is employed to write and read the control registers through the two-line serial interface port. Table 10. Control Register Map
Hex Address 00H 01H* Write and Read or Read Only RO R/W Default Value 01101001
Bits 7:0 7:0
Register Name Chip Revision PLL Div MSB
02H*
R/W
7:4
1101****
PLL Div LSB
Function An 8-bit register that represents the silicon revision level. This register is for Bits [11:4] of the PLL divider. Greater values mean the PLL operates at a faster rate. This register should be loaded first whenever a change is needed. This will give the PLL more time to lock. Bits [7:4] of this word are written to the LSBs [3:0] of the PLL divider word.
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AD9985
Hex Address 03H Write and Read or Read Only R/W Bits 7:3 Default Value 01****** **001*** 04H 05H 06H 07H 08H 09H 0AH 0BH 0CH 0DH 0EH R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W 7:3 7:0 7:0 7:0 7:0 7:0 7:0 7:1 7:1 7:1 7:0 10000*** 10000000 10000000 00100000 10000000 10000000 10000000 1000000* 1000000* 1000000* 0******* *1****** **0***** ***0**** Phase Adjust Clamp Placement Clamp Duration Hsync Output Pulsewidth Red Gain Green Gain Blue Gain Red Offset Green Offset Blue Offset Sync Control Register Name Function Bits [7:6] VCO Range. Selects VCO frequency range. (See PLL description.) Bits [5:3] Charge Pump Current. Varies the current that drives the low-pass filter. (See PLL description.) ADC Clock Phase Adjustment. Larger values mean more delay. (1 LSB = T/32) Places the clamp signal an integer number of clock periods after the trailing edge of the Hsync signal. Number of clock periods that the clamp signal is actively clamping. Sets the number of pixel clocks that HSOUT will remain active. Controls ADC input range (contrast) of each respective channel. Greater values give less contrast. Controls dc offset (brightness) of each respective channel. Greater values decrease brightness. Bit 7 - Hsync Polarity Override. (Logic 0 = Polarity determined by chip, Logic 1 = Polarity set by Bit 6 in Register 0EH.) Bit 6 - Hsync Input Polarity. Indicates polarity of incoming Hsync signal to the PLL. (Logic 0 = Active Low, Logic 1 = Active High.) Bit 5 - Hsync Output Polarity. (Logic 0 = Logic High Sync, Logic 1 = Logic Low Sync.) Bit 4 - Active Hsync Override. If set to Logic 1, the user can select the Hsync to be used via Bit 3. If set to Logic 0, the active interface is selected via Bit 6 in Register 14H. Bit 3 - Active Hsync Select. Logic 0 selects Hsync as the active sync. Logic 1 selects Sync-on-Green as the active sync. Note that the indicated Hsync will be used only if Bit 4 is set to Logic 1 or if both syncs are active. (Bits 1, 7 = Logic 1 in Register 14H.) Bit 2 - Vsync Output Invert. (Logic 1 = No Invert, Logic 0 = Invert.) Bit 1 - Active Vsync Override. If set to Logic 1, the user can select the Vsync to be used via Bit 0. If set to Logic 0, the active interface is selected via Bit 3 in Register 14H. Bit 0 - Active Vsync Select. Logic 0 selects raw Vsync as the output Vsync. Logic 1 selects sync separated Vsync as the output Vsync. Note that the indicated Vsync will be used only if Bit 1 is set to Logic 1. Bit 7 - Clamp Function. Chooses between Hsync for Clamp signal or another external signal to be used for clamping. (Logic 0 = Hsync, Logic 1 = Clamp.) Bit 6 - Clamp Polarity. Valid only with external Clamp signal. (Logic 0 = Active High, Logic 1 Selects Active Low.) Bit 5 - Coast Select. Logic 0 selects the coast input pins to be used for the PLL coast. Logic 1 selects Vsync to be used for the PLL coast. Bit 4 - Coast Polarity Override. (Logic 0 = Polarity determined by chip, Logic 1 = Polarity set by Bit 3 in Register 0FH.) Bit 3 - Coast Polarity. Selects polarity of external Coast signal. (Logic 0 = Active Low, Logic 1 = Active High.) Bit 2 - Seek Mode Override. (Logic 1 = Allow Low Power Mode, Logic 0 = Disallow Low Power Mode.) Bit 1 - PWRDN. Full Chip Power-Down, Active Low. (Logic 0 = Full Chip Power-Down, Logic 1 = Normal.) Sync-on-Green Threshold. Sets the voltage level of the Sync-on-Green slicer's comparator.
****0***
*****0** ******0*
*******0
0FH
R/W
7:1
0*******
*1****** **0***** ***0**** ****1*** *****1** ******1* 10H R/W 7:3 10111*** Sync-on-Green Threshold
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AD9985
Hex Address Write and Read or Read Only Bits Default Value *****0** ******0* *******0 11H R/W 7:0 00100000 Sync Separator Threshold Register Name Function Bit 2 - Red Clamp Select. Logic 0 selects clamp to ground. Logic 1 selects clamp to midscale (voltage at Pin 37). Bit 1 - Green Clamp Select. Logic 0 selects clamp to ground. Logic 1 selects clamp to midscale (voltage at Pin 37). Bit 0 - Blue Clamp Select. Logic 0 selects clamp to ground. Logic 1 selects clamp to midscale (voltage at Pin 37). Sync Separator Threshold. Sets how many internal 5 MHz clock periods the sync separator will count to before toggling high or low. This should be set to some number greater than the maximum Hsync or equalization pulsewidth. Pre-Coast. Sets the number of Hsync periods that Coast becomes active prior to Vsync. Post-Coast. Sets the number of Hsync periods that Coast stays active following Vsync. Bit 7 - Hsync detect. It is set to Logic 1 if Hsync is present on the analog interface; otherwise it is set to Logic 0. Bit 6 - AHS: Active Hsync. This bit indicates which analog Hsync is being used. (Logic 0 = Hsync Input Pin, Logic 1 = Hsync from Sync-onGreen.) Bit 5 - Input Hsync Polarity Detect. (Logic 0 = Active Low, Logic 1 = Active High.) Bit 4 - Vsync Detect. It is set to Logic 1 if Vsync is present on the analog interface; otherwise it is set to Logic 0. Bit 3 - AVS: Active Vsync. This bit indicates which analog Vsync is being used. (Logic 0 = Vsync Input Pin, Logic 1 = Vsync from Sync Separator.) Bit 2 - Output Vsync Polarity Detect. (Logic 0 = Active Low, Logic 1 = Active High.) Bit 1 - Sync-on-Green Detect. It is set to Logic 1 if sync is present on the Green video input; otherwise it is set to 0. Bit 0 - Input Coast Polarity Detect. (Logic 0 = Active Low, Logic 1 = Active High.) Bits [7:2] Reserved for future use. Must be written to 111111 for proper operation. Bit 1 - 4:2:2 Output Formatting Mode (Logic 0 = 4:2:2 mode, Logic 1= 4:4:4 mode) Bit 0 - Must be set to 0 for proper operation. Reserved for future use. Reserved for future use. Reserved for future use. Target Code for Auto Offset Operation. Target Code for Auto Offset Operation. Target Code for Auto Offset Operation. Must be written to 11h for proper operation. Enables the auto offset circuitry. Holds the offset output of the auto offset at the current value. Must be written to 9 for proper operation. Changes the update rate of the auto offset. Must be set to default value.
12H 13H 14H
R/W R/W RO
7:0 7:0 7:0
00000000 00000000
Pre-Coast Post-Coast Sync Detect
15H
R/W
7:2 1 0 7:0 7:0 7:0 7:0 7:0 7:0 7:0 7 6 5:2 1:0 7:0
111111** ******1* *******1
Reserved Output Formats Reserved Test Register Test Register Test Register Red Target Code Green Target Code Blue Target Code Reserved Auto Offset Enable Hold Auto Offset Reserved Update Mode Test Register
16H 17H 18H 19H 1AH 1BH 1CH 1DH
R/W RO RO R/W R/W R/W R/W R/W
00000100 00000100 00000100 00010001 0******* *0****** **1001** ******10 0000****
1EH
R/W
*The AD9985 updates the PLL divide ratio only when the LSBs are written to (Register 02H).
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AD9985
2-WIRE SERIAL CONTROL REGISTER DETAIL CHIP IDENTIFICATION
00 7-0 Chip Revision An 8-bit register that represents the silicon revision.
CLOCK GENERATOR CONTROL
03 7-6 VCO Range Select Two bits that establish the operating range of the clock generator. VCORNGE must be set to correspond with the desired operating frequency (incoming pixel rate). The PLL gives the best jitter performance at high frequencies. For this reason, to output low pixel rates and still get good jitter performance, the PLL actually operates at a higher frequency but then divides down the clock rate afterwards. Table 11 shows the pixel rates for each VCO range setting. The PLL output divisor is automatically selected with the VCO range setting. Table 11. VCO Ranges
PV1 0 0 1 1 PV0 0 1 0 1 Pixel Clock Range (MHz) AD9985KSTZ AD9985BSTZ 12-32 12-30 32-64 30-60 64-110 60-110 110-140
PLL DIVIDER CONTROL
01 7-0 PLL Divide Ratio MSBs The 8 most significant bits of the 12-bit PLL divide ratio PLLDIV. The operational divide ratio is PLLDIV + 1. The PLL derives a master clock from an incoming Hsync signal. The master clock frequency is then divided by an integer value, such that the output is phase-locked to Hsync. This PLLDIV value determines the number of pixel times (pixels plus horizontal blanking overhead) per line. This is typically 20% to 30% more than the number of active pixels in the display. The 12-bit value of the PLL divider supports divide ratios from 2 to 4095. The higher the value loaded in this register, the higher the resulting clock frequency with respect to a fixed Hsync frequency. VESA has established some standard timing specifications that assist in determining the value for PLLDIV as a function of horizontal and vertical display resolution and frame rate (Table 9). However, many computer systems do not conform precisely to the recommendations, and these numbers should be used only as a guide. The display system manufacturer should provide automatic or manual means for optimizing PLLDIV. An incorrectly set PLLDIV will usually produce one or more vertical noise bars on the display. The greater the error, the greater the number of bars produced. The power-up default value of PLLDIV is 1693 (PLLDIVM = 69H, PLLDIVL = DxH). The AD9985 updates the full divide ratio only when the LSBs are changed. Writing to the MSB by itself will not trigger an update. 02 7-4 PLL Divide Ratio LSBs The 4 least significant bits of the 12-bit PLL divide ratio PLLDIV. The operational divide ratio is PLLDIV + 1. The power-up default value of PLLDIV is 1693 (PLLDIVM = 69H, PLLDIVL = DxH). The AD9985 updates the full divide ratio only when this register is written to.
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The power-up default value is 01. 03 5-3 CURRENT Charge Pump Current Three bits that establish the current driving the loop filter in the clock generator.
Current (A) 50 100 150 250 350 500 750 1500
Table 12. Charge Pump Currents
CURRENT 000 001 010 011 100 101 110 111
CURRENT must be set to correspond with the desired operating frequency (incoming pixel rate). The power-up default value is current = 001. 04 7-3 Clock Phase Adjust A 5-bit value that adjusts the sampling phase in 32 steps across one pixel time. Each step represents an 11.25 shift in sampling phase. The power-up default value is 16.
AD9985
CLAMP TIMING
05 7-0 Clamp Placement An 8-bit register that sets the position of the internally generated clamp. When Clamp Function (Register 0FH, Bit 7) = 0, a clamp signal is generated internally, at a position established by the clamp placement and for a duration set by the clamp duration. Clamping is started (Clamp Placement) pixel periods after the trailing edge of Hsync. The clamp placement may be programmed to any value between 1 and 255. The clamp should be placed during a time that the input signal presents a stable black-level reference, usually the back porch period between Hsync and the image. When Clamp Function = 1, this register is ignored. 06 7-0 Clamp Duration An 8-bit register that sets the duration of the internally generated clamp. For the best results, the clamp duration should be set to include the majority of the black reference signal time that follows the Hsync signal trailing edge. Insufficient clamping time can produce brightness changes at the top of the screen, and a slow recovery from large changes in the average picture level (APL), or brightness. When Clamp Function = 1, this register is ignored. 09 7-0 Green Channel Gain Adjust An 8-bit word that sets the gain of the Green channel. See REDGAIN (08). 7-0 Blue Channel Gain Adjust An 8-bit word that sets the gain of the Blue channel. See REDGAIN (08).
0A
INPUT OFFSET
0B 7-1 Red Channel Offset Adjust This and the following two offset registers have two modes of operation. One mode is when the auto offset function is turned off (manual mode) and the other is when auto offset is turned on. When in manual offset adjustment mode (auto offset turned off) this register behaves exactly like the AD9883A. It is a 7-bit offset binary word that sets the dc offset of the Red channel. One LSB of offset adjustment equals approximately one LSB change in the ADC offset. Therefore, the absolute magnitude of the offset adjustment scales as the gain of the channel is changed. A nominal setting of 63 results in the channel nominally clamping the back porch (during the clamping interval) to Code 00. An offset setting of 127 results in the channel clamping to Code 64 of the ADC. An offset setting of 0 clamps to Code -63 (off the bottom of the range). Increasing the value of Red Offset decreases the brightness of the channel. When in auto offset mode, the value in this register is digitally added to the red channel ADC output. The purpose of doing this is to match a benefit that is present with manual offset adjustment. Adjusting these registers is an easy way to make brightness adjustments. Although some signal range is lost with this method, it has proven to be a very popular function. In order to be able to increase and decrease brightness, the values in these registers in this mode are signed twos complement (as opposed to manual mode where the values in this register are binary). The digital adder is used only when in auto offset mode. Although it cannot be disabled, setting this register to all 0's will effectively disable it by always adding 0. 0C 7-1 Green Channel Offset Adjust This register works exactly like the Red Channel Offset Adjust register (0Bh), except it is for the Green Channel. 7-1 Blue Channel Offset Adjust This register works exactly like the Red Channel Offset Adjust register (0Bh), except it is for the Blue Channel.
HSYNC PULSEWIDTH
07 7-0 Hsync Output Pulsewidth An 8-bit register that sets the duration of the Hsync output pulse. The leading edge of the Hsync output is triggered by the internally generated, phase-adjusted PLL feedback clock. The AD9985 then counts a number of pixel clocks equal to the value in this register. This triggers the trailing edge of the Hsync output, which is also phase adjusted.
INPUT GAIN
08 7-0 Red Channel Gain Adjust An 8-bit word that sets the gain of the Red channel. The AD9985 can accommodate input signals with a full-scale range of between 0.5 V and 1.0 V p-p. Setting REDGAIN to 255 corresponds to a 1.0 V input range. A REDGAIN of 0 establishes a 0.5 V input range. Note that increasing REDGAIN results in the picture having less contrast (the input signal uses fewer of the available converter codes). See Figure 4.
0D
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AD9985
MODE CONTROL 1
0E 7 Hsync Input Polarity Override This register is used to override the internal circuitry that determines the polarity of the Hsync signal going into the PLL.
Function Hsync Polarity Determined by Chip Hsync Polarity Determined by User
Table 16. Active Hsync Override Settings
Override 0 1 Result Autodetermines the Active Interface Override, Bit 3 Determines the Active Interface
The default for this register is 0. 0E 3 Active Hsync Select This bit is used under two conditions. It is used to select the active Hsync when the override bit is set (Bit 4). Alternately, it is used to determine the active Hsync when not overriding but both Hsyncs are detected.
Result HSYNC Input Sync-on-Green Input
Table 13. Hsync Input Polarity Override Settings
Override Bit 0 1
The default for Hsync polarity override is 0 (polarity determined by chip). 0E 6 HSPOL Hsync Input Polarity A bit that must be set to indicate the polarity of the Hsync signal that is applied to the PLL Hsync input.
Function Active Low Active High Select 0 1
Table 17. Active HSYNC Select Settings
Table 14. Hsync Input Polarity Settings
HSPOL 0 1
The default for this register is 0. 0E 2 Vsync Output Invert This bit inverts the polarity of the Vsync output. Table 18 shows the effect of this option.
Vsync Output Invert No Invert
Active Low means the leading edge of the Hsync pulse is negative going. All timing is based on the leading edge of Hsync, which is the falling edge. The rising edge has no effect. Active high is inverted from the traditional Hsync, with a positive-going pulse. This means that timing will be based on the leading edge of Hsync, which is now the rising edge. The device will operate if this bit is set incorrectly, but the internally generated clamp position, as established by Clamp Placement (Register 05H), will not be placed as expected, which may generate clamping errors. The power-up default value is HSPOL = 1. 0E 5 Hsync Output Polarity This bit determines the polarity of the Hsync output and the SOG output. Table 15 shows the effect of this option. SYNC indicates the logic state of the sync pulse.
SYNC Logic 1 (Positive Polarity) Logic 0 (Negative Polarity)
Table 18. Vsync Output Invert Settings
Setting 0 1
The default setting for this register is 0. 0E 1 Active Vsync Override This bit is used to override the automatic Vsync selection. To override, set this bit to Logic 1. When overriding, the active interface is set via Bit 0 in this register.
Result Autodetermines the Active Vsync Override, Bit 0 Determines the Active Vsync
Table 19. Active Vsync Override Settings
Override 0 1
The default for this register is 0. 0E 0 Active Vsync Select This bit is used to select the active Vsync when the override bit is set (Bit 1).
Result Vsync Input Sync Separator Output
Table 15. Hsync Output Polarity Settings
Setting 0 1
Table 20. Active Vsync Select Settings
Select 0 1
The default setting for this register is 0. 0E 4 Active Hsync Override This bit is used to override the automatic Hsync selection, To override, set this bit to Logic 1. When overriding, the active Hsync is set via Bit 3 in this register.
Rev. 0 | Page 21 of 32
The default for this register is 0.
AD9985
0F 7 Clamp Input Signal Source This bit determines the source of clamp timing.
Function Internally Generated Clamp Signal Externally Provided Clamp Signal
The default for coast polarity override is 0. 0F 3 Coast Input Polarity This bit indicates the polarity of the Coast signal that is applied to the PLL COAST input.
Function Active Low Active High
Table 21. Clamp Input Signal Source Settings
Clamp Function 0 1
Table 25. Coast Input Polarity Settings
Coast Polarity 0 1
A 0 enables the clamp timing circuitry controlled by clamp placement and clamp duration. The clamp position and duration is counted from the leading edge of Hsync. A 1 enables the external CLAMP input pin. The three channels are clamped when the CLAMP signal is active. The polarity of CLAMP is determined by the Clamp Polarity bit (Register 0FH, Bit 6). The power-up default value is Clamp Function = 0. 0F 6 Clamp Input Signal Polarity This bit determines the polarity of the externally provided CLAMP signal.
Function Active Low Active High
Active Low means that the clock generator will ignore Hsync inputs when Coast is low, and continue operating at the same nominal frequency until Coast goes high. Active High means that the clock generator will ignore Hsync inputs when Coast is high, and continue operating at the same nominal frequency until Coast goes low. This function needs to be used along with the Coast Polarity Override bit (Bit 4). The power-up default value is 1. 0F 2 Seek Mode Override This bit is used to either allow or disallow the low power mode. The low power mode (Seek Mode) occurs when there are no signals on any of the Sync inputs.
Result Allow Seek Mode Disallow Seek Mode
Table 22. Clamp Input Signal Polarity Settings
Clamp Function 1 0
Logic 1 means that the circuit will clamp when CLAMP is low, and it will pass the signal to the ADC when CLAMP is high. Logic 0 means that the circuit will clamp when CLAMP is high, and it will pass the signal to the ADC when CLAMP is low. The power-up default value is Clamp Polarity = 1. 0F 5 Coast Select This bit is used to select the active Coast source. The choices are the Coast Input pin or Vsync. If Vsync is selected, the additional decision of using the Vsync input pin or the output from the sync separator needs to be made (Register 0E, Bits 1, 0).
Result Coast Input Pin Vsync (See above Text)
Table 26. Seek Mode Override Settings
Select 1 0
The default for this register is 1. 0F 1 PWRDN This bit is used to put the chip in full power-down. See the Power Management section for details of which blocks are powered down.
Result Power-Down Normal Operation
Table 27. Power-Down Settings
Select 0 1
Table 23. Power-Down Settings
Select 0 1
10
0F
4 Coast Input Polarity Override This register is used to override the internal circuitry that determines the polarity of the Coast signal going into the PLL.
Result Determined by Chip Determined by User
Rev. 0 | Page 22 of 32
7-3 Sync-on-Green Slicer Threshold This register allows the comparator threshold of the Sync-on-Green slicer to be adjusted. This register adjusts it in steps of 10 mV, with the minimum setting equaling 10 mV (11111) and the maximum setting equaling 330 mV (00000). The default setting is 23, which corresponds to a threshold value of 100 mV; for a threshold of 150 mV, the setting should be 18.
Table 24. Coast Input Polarity Override Settings
Override Bit 0 1
AD9985
10 2 Red Clamp Select This bit determines whether the Red channel is clamped to ground or to midscale. For RGB video, all three channels are referenced to ground. For YCbCr (or YUV), the Y channel is referenced to ground, but the CbCr channels are referenced to midscale. Clamping to midscale actually clamps to Pin 37.
Function Clamp to Ground Clamp to Midscale (Pin 37)
13
7-0 Post-Coast This register allows the coast signal to be applied following the Vsync signal. This is necessary in cases where post-equalization pulses are present. The step size for this control is one Hsync period. The default is 0.
Table 28. Red Clamp Select Settings
Clamp 0 1
14
7 Hsync Detect This bit is used to indicate when activity is detected on the Hsync input pin (Pin 30). If Hsync is held high or low, activity will not be detected.
Function No Activity Detected Activity Detected
The default setting for this register is 0. 10 1 Green Clamp Select This bit determines whether the Green channel is clamped to ground or to midscale.
Function Clamp to Ground Clamp to Midscale (Pin 37)
Table 31. Hsync Detection Results
Detect 0 1
Table 29. Green Clamp Select Settings
Clamp 0 1
The Sync Processing Block Diagram (Figure 14) shows where this function is implemented. 14 6 AHS - Active Hsync This bit indicates which Hsync input source is being used by the PLL (Hsync input or Sync-on-Green). Bits 7 and 1 in this register determine which source is used. If both Hsync and SOG are detected, the user can determine which has priority via Bit 3 in Register 0EH. The user can override this function via Bit 4 in Register 0EH. If the override bit is set to Logic 1, this bit will be forced to whatever the state of Bit 3 in Register 0EH is set to.
Bit 1 (SOG Detect) 0 1 0 1 X Bit 4, Reg 0EH (Override) 0 0 0 0 1
The default setting for this register is 0. 10 0 Blue Clamp Select This bit determines whether the Blue channel is clamped to ground or to midscale.
Function Clamp to Ground Clamp to Midscale (Pin 37)
Table 30. Blue Clamp Select Settings
Clamp 0 1
Table 32. Active Hsync Results
Bit 7 (Hsync Detect) 0 0 1 1 X
The default for this register is 0. 11 7-0 Sync Separator Threshold This register is used to set the responsiveness of the sync separator. It sets how many internal 5 MHz clock periods the sync separator must count to before toggling high or low. It works like a low-pass filter to ignore Hsync pulses in order to extract the Vsync signal. This register should be set to some number greater than the maximum Hsync pulsewidth. Note that the sync separator threshold uses an internal dedicated clock with a frequency of approximately 5 MHz. The default for this register is 32. 12 7-0 Pre-Coast This register allows the coast signal to be applied prior to the Vsync signal. This is necessary in cases where pre-equalization pulses are present. The step size for this control is one Hsync period. The default is 0.
AHS Bit 3 in 0EH 1 0 Bit 3 in 0EH Bit 3 in 0EH
AHS = 0 means use the Hsync pin input for Hsync. AHS = 1 means use the SOG pin input for Hsync. The override bit is in Register 0EH, Bit 4. 14 5 Detected Hsync Input Polarity Status This bit reports the status of the Hsync input polarity detection circuit. It can be used to determine the polarity of the Hsync input. The detection circuit's location is shown in the Sync Processing Block Diagram (Figure 14).
Rev. 0 | Page 23 of 32
AD9985
Table 33. Detected Hsync Input Polarity Status
Hsync Polarity Status 0 1 Result Negative Positive
Table 37. Sync-on-Green Detection Results
Detect 0 1 Function No Activity Detected Activity Detected
14
4
Vsync Detect
This bit is used to indicate when activity is detected on the Vsync input pin (Pin 31). If Vsync is held steady high or low, activity will not be detected. Table 34. Vsync Detection Results
Detect 0 1 Function No Activity Detected Activity Detected
The Sync Processing Block Diagram (Figure 14) shows where this function is implemented. 14 0 Detected Coast Polarity Status This bit reports the status of the Coast input polarity detection circuit. It can be used to determine the polarity of the Coast input. The detection circuit's location is shown in the Sync Processing Block Diagram (Figure 14).
Result Coast Polarity Negative Coast Polarity Positive
The Sync Processing Block Diagram (Figure 14) shows where this function is implemented. 14 3 AVS - Active Vsync This bit indicates which Vsync source is being used: the Vsync input or output from the sync separator. Bit 4 in this register determines which is active. If both Vsync and SOG are detected, the user can determine which has priority via Bit 0 in Register 0EH. The user can override this function via Bit 1 in Register 0EH. If the override bit is set to Logic 1, this bit will be forced to whatever the state of Bit 0 in Register 0EH is set to.
Bit 1, Reg 0EH (Override) 0 0 1
Table 38. Detected Coast Input Polarity Status
Polarity Status 0 1
This indicates that Bit 1 of Register 5 is the 4:2:2 output mode select bit. 15 1 4:2:2 Output Mode Select This bit configures the output data in 4:2:2 mode. This mode can be used to reduce the number of data lines used from 24 down to 16 for applications using YUV, YCbCr, or YPbPr graphics signals. A timing diagram for this mode is shown in Figure 11. Recommended input and output configurations are shown in Table 39. Table 39. 4:2:2 Output Mode Select
Select 0 1 Output Mode 4:2:2 4:4:4
Table 35. Active Vsync Results
Bit 4, Reg 14H (Vsync Detect) 1 0 X AVS 0 1 Bit 0 in 0EH
AVS = 0 means Vsync input. AVS = 1 means Sync separator.
Table 40. 4:2:2 Input/Output Configuration The override bit is in Register 0EH, Bit 1. 14 2 Detected Vsync Output Polarity Status This bit reports the status of the Vsync output polarity detection circuit. It can be used to determine the polarity of the Vsync output. The detection circuit's location is shown in the Sync Processing Block Diagram (Figure 14).
Result Active Low Active High Channel Red Green Blue Input Connection V Y U Output Format U/V Y High Impedance
Table 36. Detected Vsync Output Polarity Status
Vsync Polarity Status 0 1
19
7:0
Red Target Code
This specifies the targeted value of the final offset for the Red channel when auto offset is employed (Register 0x1D Bit 7 = 1). Default is 4. 1A 7:0 Green Target Code
14
1 Sync-on-Green Detect This bit is used to indicate when sync activity is detected on the Sync-on-Green input pin (Pin 49).
This specifies the targeted value of the final offset for the Green channel when auto offset is employed (Register 0x1D Bit 7 = 1). Default is 4.
Rev. 0 | Page 24 of 32
AD9985
1B 7:0 Blue Target Code This specifies the targeted value of the final offset for the Blue channel when auto offset is employed (Register 0x1D Bit 7 = 1). Default is 4. 1D 7 Auto Offset Enable
Enables the auto offset circuitry. Default is 0. 1D 6 Hold Auto Offset
Holds the offset output of the auto offset at the current value. Default is 0. 1D 1:0 Update Mode
Changes the update rate of the auto offset. Default is `10'. Table 41. Auto Offset Update Rate
Update Mode 00 01 10 Auto-Offset Update Timing Every Clamp cycle. Every 16 Clamp cycles. Every 64 Clamp cycles.
Rev. 0 | Page 25 of 32
AD9985
2-WIRE SERIAL CONTROL PORT
A 2-wire serial control interface (I2C) is provided. Up to two AD9985 devices may be connected to the 2-wire serial interface, with each device having a unique address. The 2-wire serial interface comprises a clock (SCL) and a bidirectional data (SDA) pin. The analog flat panel interface acts as a slave for receiving and transmitting data over the serial interface. When the serial interface is not active, the logic levels on SCL and SDA are pulled high by external pull-up resistors. Data received or transmitted on the SDA line must be stable for the duration of the positive-going SCL pulse. Data on SDA must change only when SCL is low. If SDA changes state while SCL is high, the serial interface interprets that action as a start or stop sequence. There are five components to serial bus operation: * * * * * Start Signal Slave Address Byte Base Register Address Byte Data Byte to Read or Write Stop Signal If the AD9985 does not acknowledge the master device during a write sequence, the SDA remains high so the master can generate a stop signal. If the master device does not acknowledge the AD9985 during a read sequence, the AD9985 interprets this as "end of data." The SDA remains high so the master can generate a stop signal. Writing data to specific control registers of the AD9985 requires that the 8-bit address of the control register of interest be written after the slave address has been established. This control register address is the base address for subsequent write operations. The base address autoincrements by one for each byte of data written after the data byte intended for the base address. data transfer, read from (1) or write to (0) the slave device. If the transmitted slave address matches the address of the device (set by the state of the SA1-0 input pins in Table 42), the AD9985 acknowledges by bringing SDA low on the ninth SCL pulse. If the addresses do not match, the AD9985 does not acknowledge. Table 42. Serial Port Addresses
Bit 7 A6 (MSB) 1 1 Bit 6 A5 0 0 Bit 5 A4 0 0 Bit 4 A3 1 1 Bit 3 A2 1 1 Bit 2 A1 0 0 Bit 1 A0 0 1
DATA TRANSFER VIA SERIAL INTERFACE
For each byte of data read or written, the MSB is the first bit of the sequence.
When the serial interface is inactive (SCL and SDA are high), communications are initiated by sending a start signal. The start signal is a high-to-low transition on SDA while SCL is high. This signal alerts all slaved devices that a data transfer sequence is coming. The first eight bits of data transferred after a start signal comprise a 7-bit slave address (the first seven bits) and a single R/W bit (the eighth bit). The R/W bit indicates the direction of
SDA
tBUFF tSTAH
SCL
tDHO tDAL
tDSU
tSTASU
tSTOSU
tDAH
Figure 12. Serial Port Read/Write Timing
Rev. 0 | Page 26 of 32
04799-0-012
AD9985
Data is read from the control registers of the AD9985 in a similar manner. Reading requires two data transfer operations: The base address must be written with the R/W bit of the slave address byte low to set up a sequential read operation. Reading (the R/W bit of the slave address byte high) begins at the previously established base address. The address of the read register autoincrements after each byte is transferred. To terminate a read/write sequence to the AD9985, a stop signal must be sent. A stop signal comprises a low-to-high transition of SDA while SCL is high. A repeated start signal occurs when the master device driving the serial interface generates a start signal without first generating a stop signal to terminate the current communication. This is used to change the mode of communication (read, write) between the slave and master without releasing the serial interface lines. Serial Interface Read/Write Examples Write to one control register * * Start Signal Slave Address Byte (R/W Bit = Low) * * * * * * * * * * * * * * * * * * * * * *
SDA
Data Byte to Base Address Data Byte to (Base Address + 1) Data Byte to (Base Address + 2) Data Byte to (Base Address + 3) Stop Signal
Read from one control register Start Signal Slave Address Byte (R/W Bit = Low) Base Address Byte Start Signal Slave Address Byte (R/W Bit = High) Data Byte from Base Address Stop Signal
Read from four consecutive control registers Start Signal Slave Address Byte (R/W Bit = Low) Base Address Byte Start Signal Slave Address Byte (R/W Bit = High) Data Byte from Base Address Data Byte from (Base Address + 1) Data Byte from (Base Address + 2) Data Byte from (Base Address + 3) Stop Signal
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 ACK
04799-0-014
* Base Address Byte * Data Byte to Base Address * Stop Signal Write to four consecutive control registers * Start Signal * Slave Address Byte (R/W Bit = Low) * Base Address Byte
SCL
Figure 13. Serial Interface--Typical Byte Transfer
Rev. 0 | Page 27 of 32
AD9985
SYNC STRIPPER NEGATIVE PEAK CLAMP SOG MUX 1 HSYNC IN SOG OUT PLL ACTIVITY DETECT POLARITY DETECT COMP SYNC ACTIVITY DETECT SYNC SEPARATOR INTEGRATOR 1/S VSYNC
HSYNC MUX 2 COAST COAST MUX 3 POLARITY DETECT CLOCK GENERATOR
HSYNC OUT PIXEL CLOCK
HSYNC OUT
AD9985
VSYNC IN
VSYNC OUT ACTIVITY DETECT POLARITY DETECT MUX 4
04799-0-0015
Figure 14. Sync Processing Block Diagram
Table 43. Control of the Sync Block Muxes via the Serial Register
Mux No. 1 and 2 3 4 Serial Bus Control Bit 0EH: Bit 3 0FH: Bit 5 0EH: Bit 0 Control Bit State 0 1 0 1 0 1 Result Pass Hsync Pass Sync-on-Green Pass Coast Pass Vsync Pass Vsync Pass Sync Separator Signal
SYNC SLICER
The purpose of the sync slicer is to extract the sync signal from the Green graphics channel. A sync signal is not present on all graphics systems, only those with Sync-on-Green. The sync signal is extracted from the Green channel in a two-step process. First, the SOG input is clamped to its negative peak (typically 0.3 V below the black level). Next, the signal goes to a comparator with a variable trigger level, nominally 0.15 V above the clamped level. The "sliced" sync is typically a composite sync signal containing both Hsync and Vsync. up when Hsync pulses are present. But since Hsync pulses are relatively short in width, the counter only reaches a value of N before the pulse ends. It then starts counting down, eventually reaching 0 before the next Hsync pulse arrives. The specific value of N will vary for different video modes, but will always be less than 255. For example, with a 1 s width Hsync, the counter will only reach 5 (1 s/200 ns = 5). When Vsync is present on the composite sync, the counter will also count up. However, since the Vsync signal is much longer, it will count to a higher number M. For most video modes, M will be at least 255. So, Vsync can be detected on the composite sync signal by detecting when the counter counts to higher than N. The specific count that triggers detection (T) can be programmed through the serial register (11H). Once Vsync has been detected, there is a similar process to detect when it goes inactive. At detection, the counter first resets to 0, then starts counting up when Vsync goes away. Similar to the previous case, it will detect the absence of Vsync when the counter reaches the threshold count (T). In this way, it will reject noise and/or serration pulses. Once Vsync is detected to be absent, the counter resets to 0 and begins the cycle again.
SYNC SEPARATOR
A sync separator extracts the Vsync signal from a composite sync signal. It does this through a low-pass filter-like or integrator-like operation. It works on the idea that the Vsync signal stays active for a much longer time than the Hsync signal, so it rejects any signal shorter than a threshold value, which is somewhere between an Hsync pulsewidth and a Vsync pulsewidth. The sync separator on the AD9985 is simply an 8-bit digital counter with a 5 MHz clock. It works independently of the polarity of the composite sync signal. (Polarities are determined elsewhere on the chip.) The basic idea is that the counter counts
Rev. 0 | Page 28 of 32
AD9985
PCB LAYOUT RECOMMENDATIONS
The AD9985 is a high precision, high speed analog device. As such, to get the maximum performance from the part, it is important to have a well laid out board. The following is a guide for designing a board using the AD9985. power plane to the capacitor to the power pin. Do not make the power connection between the capacitor and the power pin. Placing a via underneath the capacitor pads, down to the power plane, is generally the best approach. It is particularly important to maintain low noise and good stability of PVD (the clock generator supply). Abrupt changes in PVD can result in similarly abrupt changes in sampling clock phase and frequency. This can be avoided by careful attention to regulation, filtering, and bypassing. It is highly desirable to provide separate regulated supplies for each of the analog circuitry groups (VD and PVD). Some graphic controllers use substantially different levels of power when active (during active picture time) and when idle (during horizontal and vertical sync periods). This can result in a measurable change in the voltage supplied to the analog supply regulator, which can in turn produce changes in the regulated analog supply voltage. This can be mitigated by regulating the analog supply, or at least PVD, from a different, cleaner power source (for example, from a 12 V supply). It is also recommended to use a single ground plane for the entire board. Experience has repeatedly shown that the noise performance is the same or better with a single ground plane. Using multiple ground planes can be detrimental because each separate ground plane is smaller, and long ground loops can result. In some cases, using separate ground planes is unavoidable. For those cases, it is recommended to at least place a single ground plane under the AD9985. The location of the split should be at the receiver of the digital outputs. For this case it is even more important to place components wisely because the current loops will be much longer (current takes the path of least resistance). An example of a current loop is shown in Figure 15.
N PLA ND OU R G
ANALOG INTERFACE INPUTS
Using the following layout techniques on the graphics inputs is extremely important. Minimize the trace length running into the graphics inputs. This is accomplished by placing the AD9985 as close as possible to the graphics VGA connector. Long input trace lengths are undesirable because they pick up more noise from the board and other external sources. Place the 75 termination resistors (see Figure 3) as close to the AD9985 chip as possible. Any additional trace length between the termination resistors and the input of the AD9985 increases the magnitude of reflections, which will corrupt the graphics signal. Use 75 matched impedance traces. Trace impedances other than 75 will also increase the chance of reflections. The AD9985 has very high input bandwidth (500 MHz). While this is desirable for acquiring a high resolution PC graphics signal with fast edges, it means that it will also capture any high frequency noise present. Therefore, it is important to reduce the amount of noise that gets coupled to the inputs. Avoid running any digital traces near the analog inputs. Due to the high bandwidth of the AD9985, low-pass filtering the analog inputs can sometimes help to reduce noise. (For many applications, filtering is unnecessary.) Experiments have shown that placing a series ferrite bead prior to the 75 termination resistor is helpful in filtering out excess noise. Specifically, the part used was the #2508051217Z0 from FairRite, but each application may work best with a different bead value. Alternately, placing a 100 to 120 resistor between the 75 termination resistor and the input coupling capacitor can also be beneficial.
E
POWER PLANE
AD988 3A
DI GI T
TPUT T OU RA AL
It is recommended to bypass each power supply pin with a 0.1 F capacitor. The exception is when two or more supply pins are adjacent to each other. For these groupings of powers/ grounds, it is necessary to have only one bypass capacitor. The fundamental idea is to have a bypass capacitor within about 0.5 cm of each power pin. Also, avoid placing the capacitor on the opposite side of the PC board from the AD9985, as that interposes resistive vias in the path. The bypass capacitors should be physically located between the power plane and the power pin. Current should flow from the
Rev. 0 | Page 29 of 32
TA L
GR
O UN
D PL A
NE
DIGITAL DATA R
ECEIV
ER
Figure 15. Current Loop
04799-0-016
DI
GI
CE
POWER SUPPLY BYPASSING
ANALO G
AD9985
PLL
Place the PLL loop filter components as close to the FILT pin as possible. Do not place any digital or other high frequency traces near these components. Use the values suggested in the data sheet with 10% tolerances or less. to add vias or extra length to the output trace in order to get the resistors closer). If possible, limit the capacitance that each of the digital outputs drives to less than 10 pF. This can easily be accomplished by keeping traces short and by connecting the outputs to only one device. Loading the outputs with excessive capacitance will increase the current transients inside of the AD9985, creating more digital noise on its power supplies.
OUTPUTS (BOTH DATA AND CLOCKS)
Try to minimize the trace length that the digital outputs have to drive. Longer traces have higher capacitance, which requires more current, which causes more internal digital noise. Shorter traces reduce the possibility of reflections. Adding a series resistor of value 22 to 100 can suppress reflections, reduce EMI, and reduce the current spikes inside of the AD9985. However, if 50 traces are used on the PCB, the data outputs should not need resistors. A 22 resistor on the DATACK output should provide good impedance matching that will reduce reflections. If series resistors are used, place them as close to the AD9985 pins as possible (although try not
DIGITAL INPUTS
The digital inputs on the AD9985 were designed to work with 3.3 V signals, but are tolerant of 5.0 V signals. Therefore, no extra components need to be added if using 5.0 V logic. Any noise that gets onto the Hsync input trace will add jitter to the system. Therefore, minimize the trace length and do not run any digital or other high frequency traces near it.
VOLTAGE REFERENCE
Bypass with a 0.1 F capacitor. Place as close to the AD9985 pin as possible. Make the ground connection as short as possible.
Rev. 0 | Page 30 of 32
AD9985 OUTLINE DIMENSIONS
0.75 0.60 0.45 SEATING PLANE 1.60 MAX
80 1 PIN 1
16.00 BSC SQ
61 60
TOP VIEW (PINS DOWN)
14.00 BSC SQ
1.45 1.40 1.35
10 6 2
0.15 0.05
SEATING PLANE
0.20 0.09 7 3.5 0 0.10 MAX COPLANARITY
VIEW A
20 21 40 41
0.65 BSC
VIEW A
ROTATED 90 CCW
COMPLIANT TO JEDEC STANDARDS MS-026-BEC
0.38 0.32 0.22
Figure 16. 80-Lead Low Profile Quad Flat Package (LQFP) (ST-80-2) Dimensions shown in millimeters
ORDERING GUIDE
Model AD9985KSTZ-1101 AD9985KSTZ-1401 AD9985BSTZ-1101 AD9985/PCB Temperature Range 0C to 70C 0C to 70C -40C to +85C 25C Package Description LQFP LQFP LQFP Evaluation Board Package ST-80 ST-80 ST-80
1
Z = Pb-free part.
Rev. 0 | Page 31 of 32
AD9985 NOTES
Purchase of licensed I2C components of Analog Devices or one of its sublicensed Associated Companies conveys a license for the purchaser under the Philips I2C Patent Rights to use these components in an I2C system, provided that the system conforms to the I2C Standard Specification as defined by Philips.
(c) 2004 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D04799-0-5/04(0)
Rev. 0 | Page 32 of 32

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