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FEATURES Dual IF Inputs, 70 MHz-250 MHz Diversity or Two Independent IF Signals Separate Attenuation Paths Oversample RF Channels 20 MSPS on a Single Carrier 10 MSPS/Channel in Diversity Mode Total Signal Range 90+ dB 30 dB from Automatic Gain-Ranging (AGC) 60 dB from A/D Converter Range >100 dB After Processing Gain Digital Outputs 11-Bit ADC Word 3-Bit RSSI Word 2 Clock, A/B Indicator Single 5 V Power Supply Output DVCC 3.3 V or 5 V 775 mW Power Dissipation APPLICATIONS Communications Receivers PCS/Cellular Base Stations GSM, CDMA, TDMA Wireless Local Loop, Fixed Access
Dual Channel, Gain-Ranging ADC with RSSI AD6600
two input channels, each with 1 GHz input amplifiers and 30 dB of automatic gain-ranging circuitry. Both channels are sampled with a 450 MHz track-and-hold followed by an 11-bit, 20 MSPS analog-to-digital converter. Digital RSSI outputs, an A/B channel indicator, a 2x Clock output, references, and control circuitry are all on-chip. Digital output signals are two's complement, CMOS-compatible and interface directly to 3.3 V or 5 V digital processing chips. The primary use for the dual analog input structure is sampling both antennas in a two-antenna diversity receiver. However, Channels A and B may also be used to sample two independent IF signals. Diversity, or dual-channel mode, is limited to 10 MSPS per channel. In single-channel mode, the full clock rate of 20 MSPS may be applied to a single carrier. The AD6600 may be used as a stand-alone sampling chip, or it may be combined with the AD6620 Digital Receive Signal Processor. The AD6620 provides 10 dB-25 dB of additional processing gain before passing data to a fixed- or floating-point DSP. Driving the AD6600 is simplified by using the AD6630 differential IF amplifier. The AD6630 is easily matched to inexpensive SAW filters from 70 MHz to 250 MHz. Designed specifically for cellular/PCS receivers, the AD6600 supports GSM, IS-136, CDMA and Wireless LANs, as well as proprietary air interfaces used in WLL/fixed-access systems. Units are available in plastic, surface-mount packages (44-lead LQFP) and specified over the industrial temperature range (-40C to +85C).
PRODUCT DESCRIPTION
The AD6600 mixed-signal receiver chip directly samples signals at analog input frequencies up to 250 MHz. The device includes
FUNCTIONAL BLOCK DIAGRAM
NOISE FILTER
FLT 0dB, -12dB, -24dB AIN ATTEN AIN GAIN DETECT PEAK SET RSSI 3 RSSI GAIN BIN ATTEN BIN 0dB, -12dB, -24dB 630
FLT RESONANT PORT
AB_OUT
ANALOG MUX
+12, +18dB GAIN
ENCODE A/D CONVERTER TWO'S COMPLEMENT 11 3 RSSI ENCODE RSSI [2:0] D10-D0
SELECT GAIN
AD6600
TIMING
CLK2
A_SEL
B_SEL
AVCC
GND
ENC
ENC
DVCC
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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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 (c) Analog Devices, Inc., 2000
AD6600-SPECIFICATIONS
DC SPECIFICATIONS (AVCC = 5 V, DVCC = 3.3 V; T
Parameter ANALOG INPUTS (AIN, AIN/BIN, BIN) Differential Analog Input Voltage Range1 Differential Analog Input Resistance2 Differential Analog Input Capacitance PEAK DETECTOR (Internal), RSSI Resolution RSSI Gain Step RSSI Hysteresis3 RESONANT PORT (FLT, FLT) Differential Port Resistance Differential Port Capacitance A/D CONVERTER Resolution ENCODE INPUTS (ENC, ENC) Differential Input Voltage (AC-Coupled)4 Differential Input Resistance Differential Input Capacitance A/B MODE INPUTS (A_SEL, B_SEL)5 Input High Voltage Range Input Low Voltage Range POWER SUPPLY Supply Voltages AVCC DVCC Supply Current IAVCC (AVCC = 5.0 V) IDVCC (DVCC = 3.3 V) POWER CONSUMPTION6 Temp Full Full 25C
MIN
= -40 C, TMAX = +85 C unless otherwise noted.)
Test Level V IV V Min AD6600AST Typ 2.0 200 1.5 3 6 6 630 1.75 11 0.4 11 2.5 4.75 0.0 5.25 0.5 Max Unit V p-p pF Bits dB dB pF Bits V p-p k pF V V
160
240
Full Full Full Full Full Full 25C 25C Full Full
V V V V IV IV V V IV IV
Full Full Full Full Full
II IV II II II
4.75 3.0
5.0 3.3 145 15 775
5.25 5.25 182 20 976
V V mA mA mW
NOTES 1 Analog Input Range is a function of input frequency. See ac specifications for 70 MHz-250 MHz inputs. 2 Analog Input Impedance is a function of input frequency. See ac specifications for 70 MHz-450 MHz inputs. 3 Six dB of digital hysteresis is used to eliminate level uncertainty at the RSSI threshold points due to noise and amplitude variations. 4 Encode inputs should be ac-coupled and driven differentially. See Encoding the AD6600 for details. 5 A_SEL and B_SEL should be tied directly to ground or AVCC. 6 Maximum power consumption is computed as maximum current at nominal supplies. Specifications subject to change without notice.
DIGITAL SPECIFICATIONS (AVCC = 5 V, DVCC = 3.3 V; T
Parameter Temp
1
MIN
= -40 C, TMAX = +85 C unless otherwise noted.)
Min AD6600AST Typ CMOS DVCC - 0.2 0.2 DVCC - 0.35 0.35 Two's Complement DVCC - 0.2 0.2 DVCC - 0.3 0.35 Max Unit
Test Level
LOGIC OUTPUTS (D10-D0, AB_OUT, RSSI2-0) Logic Compatibility Logic "1" Voltage (DVCC = 3.3 V) Full Logic "0" Voltage (DVCC = 3.3 V) Full Logic "1" Voltage (DVCC = 5.0 V) Full Logic "0" Voltage (DVCC = 5.0 V) Full Output Coding (D10-D0) CLK2x OUTPUT1, 2 Logic "1" Voltage (DVCC = 3.3 V) Logic "0" Voltage (DVCC = 3.3 V) Logic "1" Voltage (DVCC = 5.0 V) Logic "0" Voltage (DVCC = 5.0 V) Full Full Full Full
II II IV IV
2.8 4.0
0.5 0.5
V V V V
II II IV IV
2.8 4.0
0.5 0.5
V V V V
NOTES 1 Digital output load is one LCX gate. 2 CLK2x output voltage levels, high and low, tested at switching rate of 10 MHz. Specifications subject to change without notice.
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AD6600 TIMING REQUIREMENTS AND SWITCHING SPECIFICATIONS
Parameter A/D CONVERTER Conversion Rate Maximum Conversion Rate Minimum Conversion Rate Aperture Uncertainty ENCODE INPUTS (ENC, ENC)2 Period Pulsewidth High3 Pulsewidth Low4 2x CLOCK OUTPUT (CLK2x)5 Output Frequency Output Period6 CLK2x Pulsewidth Low6 Output Risetime7 Output Falltime7 OUTPUT RISE/FALL TIMES8 Output Risetime (D10:D0, RSSI2:0) Output Falltime (D10:D0, RSSI2:0) Output Risetime (AB_OUT) Output Falltime (AB_OUT) Name fENC tj tENC tENCH tENCL Full Full 25C Full Full Full II IV V II IV IV 20 6 0.3 50 20 20 2x fENC tENCL tENCH tENCH/2 3 2.6 8 8.4 6 6.2 Temp Test Level
1
AD6600AST Typ 1/(tENC)
(AVCC = 5 V, DVCC = 3.3 V; ENC and ENC = 20 MSPS; TMIN = -40 C, TMAX = +85 C unless otherwise noted.)
Min Max Unit MSPS MSPS MSPS ps rms ns ns ns MSPS ns ns ns ns ns ns ns ns ns
tCLK2x_1 tCLK2x_2 tCLK2xL
Full Full Full Full Full Full Full Full Full
V V V V V V V V V
NOTES 1 See AD6600 Timing Diagrams. 2 All switching specifications tested by driving ENC and ENC differentially. 3 Several timing specifications are a function of Encode high time, t ENCH; these specifications are shown in the data tables and timing diagrams. Encode duty cycle should be kept as close to 50% as possible. 4 Encode pulse low directly affects the amount of settling time available at FLT resonant port. See External Analog (Resonant) Filter section for details. 5 The 2x Clock is generated internally, therefore some specifications are functions of encode period and duty cycle. All timing measurements to or from CLK2 x are referenced to 2.0 V crossing. 6 This specification IS a function of Encode period and duty cycle; reference timing diagrams Figure 8. 7 Output rise time is measured from 20% point to 80% point of total CLK2 x voltage swing; output fall time is measured from 80% point to 20% point of total CLK2 x voltage swing. 8 Output rise time is measured from 20% point to 80% point of total data voltage swing; output fall time is measured from 80% point to 20% point of total data voltage swing. All outputs specified with 10 pF load. Specifications subject to change without notice.
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AD6600-SPECIFICATIONS
TIMING REQUIREMENTS AND SWITCHING SPECIFICATIONS1, 2
(AVCC = 5 V, DVCC = 3.3 V; ENC and ENC = 20 MSPS, Duty Cycle = 50%; TMIN = -40 C, TMAX = +85 C unless otherwise noted.)
Parameter ENCODE/CLK2x Encode Rising to CLK2x Falling3 Encode Rising to CLK2x Rising4 @ Encode = 13 MSPS, 50% Duty Cycle @ Encode = 20 MSPS, 50% Duty Cycle CLK2x/DATA (D10:0, RSSI2:0)5 CLK2x to DATA Rising Low Delay3 CLK2x to DATA Hold Time3 CLK2x to DATA Falling Low3, 6 CLK2x to DATA Setup Time4 @ Encode = 13 MSPS, 50% Duty Cycle @ Encode = 20 MSPS, 50% Duty Cycle6 CLK2x/AB_OUT5 CLK2x to AB_OUT Rising Low Delay3 CLK2x to AB_OUT Hold Time3 CLK2x to AB_OUT Falling Low Delay3, 6 CLK2x to AB_OUT Setup Time4 @ Encode = 13 MSPS, 50% Duty Cycle @ Encode = 20 MSPS, 50% Duty Cycle6 ENCODE/DATA (D10:0, RSSI2:0) ENCODE to DATA Rising Low Delay4 ENCODE to DATA Hold Time4 @ Encode = 13 MSPS, 50% Duty Cycle @ Encode = 20 MSPS, 50% Duty Cycle ENCODE to DATA Falling Low Delay4 ENCODE to DATA Delay (Setup)4 @ Encode = 13 MSPS, 50% Duty Cycle @ Encode = 20 MSPS, 50% Duty Cycle6 ENCODE/AB_OUT ENCODE to AB_OUT Rising Low Delay4 ENCODE to AB_OUT Delay (Hold)4 @ Encode = 13 MSPS, 50% Duty Cycle @ Encode = 20 MSPS, 50% Duty Cycle ENCODE to AB_OUT Falling Low Delay4 ENCODE to AB_OUT Delay (Setup)4 @ Encode = 13 MSPS, 50% Duty Cycle @ Encode = 20 MSPS, 50% Duty Cycle6 Name tCF tCR Temp Full Full Full Full Full Full 25C Full Full Full 25C Full Full Full 25C Full Full Full 25C Full Full Full Full Full Full Full Full 25C Full Full Full Full Full Full Full Full 25C Full Test Level IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV Min 6.5 25.7 19.0 3.0 3.0 10.0 11.0 16.5 5.0 3.0 7.0 7.0 12.0 10.7 12.5 2.0 -1.0 AD6600AST Typ 8.0 tCF + (tENCH)/2 27.2 20.5 6.5 6.5 15.0 15.5 tENCH - t2x_DFL 23.0 10.0 9.5 11.0 11.0 18.0 19.0 tENCH - t2x_AFL 19.5 7.0 6.0 tCR + t2x_DRL tEN_DRL 33.7 27.0 tCR + t2x_DFL tENC - tEN_DFL 34.2 14.5 14.0 tCR + t2x_ARL tEN_ARL 38.2 31.5 tCR + t2x_AFL tENC - tEN_AFL 30.7 11.5 10.5 Max 9.5 28.7 22.0 Unit ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns
t2x_DRL tH_D2x t2x_DFL tS_D2x
20.0 22.0
t2x_ARL tH_A2x t2x_AFL tS_A2x
23.0 26.0
tEN_DRL tH_DEN tEN_DFL tS_DEN
28.7 22.0
26.2 8.0 6.0
tEN_ARL tH_AEN tEN_AFL tS_AEN
32.7 26.0
22.2 5.0 2.0
NOTES 1 See AD6600 Timing Diagrams. 2 All switching specifications tested by driving ENC and ENC differentially. 3 This specification IS NOT a function of Encode period and duty cycle. 4 This specification IS a function of Encode period and duty cycle. 5 CLK2x referenced to 2.0 V crossing; digital output levels referenced to 0.8 V and 2.0 V crossings; all outputs with 10 pF load. 6 For these particular specifications, the 25C specification is valid from 25C to 85C. The Full temperature specification includes cold temperature extreme and covers the entire range, -40C to +85C. Specifications subject to change without notice.
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AD6600 AC SPECIFICATIONS
Parameter ANALOG INPUTS Analog Input 3 dB Bandwidth2 Differential Analog Input Voltage Range 70 MHz 150 MHz 200 MHz 250 MHz Differential Analog Input Impedance3 70 MHz 150 MHz 200 MHz 250 MHz 300 MHz 350 MHz 400 MHz 450 MHz Full-Scale Input Power 70 MHz 150 MHz 200 MHz 250 MHz Full-Scale Gain Tolerance4 70 MHz-250 MHz 200 MHz5 Gain Error AIN = 200 MHz @ -76 dBFS Gain Matching (Input A:B) 70 MHz-250 MHz 200 MHz Range-to-Range Gain Tolerance 70 MHz-250 MHz Range-to-Range Phase Tolerance 70 MHz 250 MHz Channel Isolation6 70 MHz-250 MHz Noise7 Minimum Attenuation Level Maximum Attenuation Level Attenuator 3OIP8 Signal-to-Noise Ratio (SNR)9, 10, 11 AIN = 70 MHz @ -1 dBFS @ -6 dBFS @ -10 dBFS @ -12 dBFS to -42 dBFS @ -54 dBFS AIN = 150 MHz @ -1 dBFS @ -6 dBFS @ -10 dBFS @ -12 dBFS to -42 dBFS @ -54 dBFS
1
(AVCC = 5 V, DVCC = 3.3 V; ENC and ENC = 20 MSPS, Duty Cycle = 50%; TMIN = -40 C, TMAX = +85 C unless otherwise noted.)
Temp Full Full Full Full Full 25C 25C 25C 25C 25C 25C 25C 25C Full Full Full Full Full 25C Test Level V V V V V V V V V V V V V V V V V V I Min AD6600AST Typ 450 2.45 2.57 2.62 2.86 197-j24 188-j48 175-j57 161-j67 151-j73 140-j80 141-j75 173-j107 5.8 6.3 6.7 7.7 0.5 0.1 Max Unit MHz V p-p V p-p V p-p V p-p dBm dBm dBm dBm dB dB
-1.0
+1.0
25C Full Full Full Full Full Full Full Full Full
I V II V V V IV V V V
-1.5 0.1 0.05 0.1 0.2 0.5 45 50 34 869 +33
+1.5
dB dB dB dB Degree Degree dB V rms V rms dBm
-0.5
+0.5
25C 25C 25C 25C 25C 25C 25C 25C 25C 25C
IV V IV IV IV IV V IV IV IV
55 45 41 31 55 45 41 31
59 54.5 49 48 6 34 58 54 49 48 6 34
dB dB dB dB dB dB dB dB dB dB
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AD6600-SPECIFICATIONS
AC SPECIFICATIONS (continued)
Parameter ANALOG INPUTS (Continued) Signal-to-Noise Ratio (Continued) AIN = 200 MHz @ -1 dBFS @ -6 dBFS @ -10 dBFS @ -12 dBFS to -42 dBFS @ -54 dBFS AIN = 250 MHz @ -1 dBFS @ -6 dBFS @ -10 dBFS @ -12 dBFS to -42 dBFS @ -54 dBFS SECOND HARMONIC AIN = 70 MHz @ -1 dBFS @ -6 dBFS @ -12 dBFS to -42 dBFS AIN = 150 MHz @ -1 dBFS @ -6 dBFS @ -12 dBFS to -42 dBFS AIN = 200 MHz9, 10, 11 @ -1 dBFS @ -6 dBFS @ -10 dBFS @ -12 dBFS to -42 dBFS @ -54 dBFS AIN = 250 MHz @ -1 dBFS @ -6 dBFS @ -12 dBFS to -42 dBFS THIRD HARMONIC AIN = 70 MHz @ -1 dBFS @ -6 dBFS @ -12 dBFS to -42 dBFS AIN = 150 MHz @ -1 dBFS @ -6 dBFS @ -12 dBFS to -42 dBFS AIN = 200 MHz9, 10, 11 @ -1 dBFS @ -6 dBFS @ -10 dBFS @ -12 dBFS to -42 dBFS @ -54 dBFS AIN = 250 MHz @ -1 dBFS @ -6 dBFS @ -12 dBFS to -42 dBFS AIN = 70 MHz-250 MHz @ -75 dBFS Temp Test Level Min AD6600AST Typ Max Unit
25C 25C 25C 25C 25C 25C 25C 25C 25C 25C
I V I I I IV V IV IV IV
55 45 40.5 31 52 43 40 30
57.5 53.5 49 48 6 34 56 53.5 49 48 6 34
dB dB dB dB dB dB dB dB dB dB
Full Full Full Full Full Full 25C Full 25C Full Full Full Full Full
V V V V V V I V I V V V V V 50 48
69 68 68 6 60 59 67 6 60 56 55 65 6 50 54 62 65 6
dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc
Full Full Full Full Full Full 25C Full 25C Full Full Full Full Full Full
V V V V V V I V I V V V V V IV 28 50 55
77 76 67 6 65 70 66 6 55 58 66 65 6 62 50 56 65 6 35
dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc
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AD6600 AC SPECIFICATIONS (continued)
Parameter WORST OTHER SPUR (4th or Higher) AIN = 70 MHz @ -1 dBFS @ -6 dBFS @ -12 dBFS to -42 dBFS AIN = 150 MHz @ -1 dBFS @ -6 dBFS @ -12 dBFS to -42 dBFS AIN = 200 MHz @ -1 dBFS @ -6 dBFS @ -10 dBFS @ -12 dBFS to -42 dBFS AIN = 250 MHz @ -1 dBFS @ -6 dBFS @ -12 dBFS to -42 dBFS Temp Test Level Min AD6600AST Typ Max Unit
Full Full Full Full Full Full 25C Full 25C Full Full Full Full
V V V V V V I V I V V V V 60 55
74.5 71 68 6 67 65 67 6 67 66 66 65 6 66.5 65 65 6
dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc dBc
NOTES 1 AIN, AIN/BIN, BIN: The AD6600 analog inputs are unconditionally stable and guarantee proper operation over the 70 MHz-250 MHz specified operating range. Circuit board layout is critical on this device, and proper PCB layout must be employed to achieve specified results. 2 Analog Input 3 dB Bandwidth is determined by internal track-and-hold. The front-end attenuators have a bandwidth of 1 GHz. 3 Measured real and imaginary values using Network Analyzer. 4 Full-scale gain tolerance is the typical variation in gain at a given IF input frequency. The nominal value for full-scale input power is a function of frequency as shown in previous specification. 5 Full-scale gain tolerance measured at 200 MHz analog input referenced to 6.7 dBm nominal full-scale input power. For the gain measurement test, the input signal level is set to -6 dBFS. Tuning port bandwidth is set to 50 MHz. 6 Main channel set to full-scale input power. Diversity channel swept from -20 dBFS to -90 dBFS. 7 Measurement includes thermal and quantization noise at 70 MHz analog input. Tuning port bandwidth is set to 50 MHz. 8 Test tones at 160.05 MHz and 170.05 MHz. 9 Measurements at -1 dFBS, -6 dBFS, and -10 dBFS are in highest attenuation mode, RSSI = 101. 10 Each gain-range is checked at ~3 dB from RSSI trip point (not in hysteresis); nominally -16 dBFS (RSSI = 100), -22 dBFS (RSSI = 011), -28 dBFS (RSSI = 010), -35 dBFS (RSSI = 001). 11 Measurement at -54 dBFS is in the lowest attenuation mode, RSSI = 000. Specifications subject to change without notice.
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AD6600
ABSOLUTE MAXIMUM RATINGS 1
Parameter ELECTRICAL AVCC Voltage DVCC Voltage Analog Input Voltage2 Analog Input Current2 Digital Input Voltage3 Output Current4 Resonant Port Voltage5 ENVIRONMENTAL Operating Temperature Range (Ambient) Maximum Junction Temperature Lead Temperature (Soldering, 10 sec) Storage Temperature Range (Ambient)
6
Min Max 0 0 0 0 0 7 7 AVCC 25 AVCC 4 AVCC
Unit V V V mA V mA V
EXPLANATION OF TEST LEVELS Test Level
I.
100% Production Tested.
II. 100% Production Tested at 25C and guaranteed by design and characterization at temperature extremes. IV. Parameter is guaranteed by design and characterization testing. V. Parameter is a typical value only.
ORDERING GUIDE
-40 +85 150 300 -65 +150
C C C C
Model AD6600AST
Temperature Package Range Description -40C to +85C (Ambient)
Package Option
NOTES 1 Absolute maximum ratings are limiting values to be applied individually, and beyond which the serviceability of the circuit may be impaired. Functional operability is not necessarily implied. Exposure to absolute maximum rating conditions for an extended period of time may affect device reliability. 2 Pins AIN, AIN, BIN, BIN. 3 Pins ENC, ENC, A_SEL, B_SEL. 4 Pins D10:0, RSSI2:0, AB_OUT, CLK2x. 5 Pins FLT, FLT. 6 Typical thermal impedance (44-lead LQFP); JC = 16C/W, JA = 55C/W.
AD6600ST/PCB
44-Terminal LQFP ST-44 (Low-Profile Quad Plastic Flatpack) Evaluation Board with AD6600AST
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 the AD6600 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.
WARNING!
ESD SENSITIVE DEVICE
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AD6600
PIN FUNCTION DESCRIPTIONS
Pin Number 1, 33 2, 5, 13, 19, 21, 24, 30, 32 3 4, 14, 15, 18, 20, 25, 31 6-8 9, 10 11 12 16, 17 22 23 26 27 28 29 34 35-43 44
Name DVCC GND C1 AVCC RSSI[2:0] B_SEL, A_SEL AIN AIN FLT, FLT BIN BIN ENC ENC CLK2x AB_OUT D0 D1-D9 D10
Function Digital VCC for Digital Outputs. Can be 3.3 V. Ground. Internal Bias Point. Bypass by 0.01 F to GND. 5 V Power Supply. RSSI Digital Output Bits. Mode Select Pins for Analog Input Channel A and B Sampling. True Analog Input Channel A. Complementary Analog Input Channel A. Resonant Filter Pins for External LC Noise Filter. Complementary Analog Input Channel B. True Analog Input Channel B. Complementary Encode Input. True Encode Input. 2x Clock Output Used for Clocking Digital Filter Chips. Digital Output Flag Indicating Whether Output Is Input A (High) or B (Low). Digital Data Output Bit (Least Significant Bit)* . Digital Data Output Bits* . Digital Data Output Bit (Most Significant Bit)* .
*Digital Outputs (D10:D0) in Two's Complement Format.
PIN CONFIGURATION
D10 (MSB)
44 43 42 41 40 39 38 37 36 35 34 DVCC 1 GND 2 C1 3 AVCC 4 GND 5 RSSI2 6 RSSI1 7 RSSI0 8 B_SEL 9 A_SEL 10 AIN 11 12 13 14 15 16 17 18 19 20 21 22
FLT AVCC AVCC AVCC AVCC GND GND GND FLT BIN AIN
PIN 1 IDENTIFIER
D9
D0 (LSB)
D8
D6
D7
D5
D4
D3
D2
D1
33 DVCC 32 GND 31 AVCC 30 GND
AD6600
TOP VIEW (Not to Scale)
29 AB_OUT 28 CLK2 27 ENC 26 ENC 25 AVCC 24 GND 23 BIN
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AD6600
DEFINITIONS OF SPECIFICATIONS Analog Bandwidth Full-Scale Gain Tolerance
Unit-to-unit variation in full-scale input power.
Full-Scale Input Power
The analog input frequency at which the spectral power of the fundamental frequency (as determined by the FFT analysis) is reduced by 3 dB. The bandwidth is determined by the internal track-and-hold when the filter node is resonated.
Aperture Delay
Expressed in dBm. Computed using the following equation: V 2FULL SCALE rms Z INPUT = 10 log 0.001
The delay between the 50% point of the rising edge of the ENCODE command and the instant at which the analog inputis sampled.
Aperture Uncertainty (Jitter)
PowerFULL SCALE
The sample-to-sample variation in aperture delay.
Attenuator 3OIP
Gain Matching (Input A:B)
Variation in full-scale power between A and B inputs.
Harmonic Distortion, 2nd
The third order intercept point of the front end of the AD6600. It is the point at which the third order products would theoretically intercept the input signal level if the input level could increase without bounds. This is measured using the ADC within the AD6600 while the input is stimulated with dual tones in the minimum attenuation (i.e., maximum gain) range.
Channel Isolation
The ratio of the rms signal amplitude to the rms value of the second harmonic component, reported in dBc.
Harmonic Distortion, 3rd
The ratio of the rms signal amplitude to the rms value of the third harmonic component, reported in dBc.
Integral Nonlinearity
The amount of signal leakage from one channel to the next when one channel is driven with a full-scale input, and the other channel is swept from -20 dBFS to -90 dBFS with a frequency offset. The leakage is measured on the side with the smaller signal.
Differential Analog Input Resistance, Differential Analog Input Capacitance and Differential Analog Input Impedance
The deviation of the transfer function from a reference line measured in fractions of 1 LSB using a "best straight line" determined by a least square curve fit.
Minimum Conversion Rate
The encode rate at which the SNR of the lowest analog signal frequency drops by no more than 3 dB below the guaranteed limit.
Maximum Conversion Rate
The real and complex impedances measured at each analog input port. The resistance is measured statically and the capacitance and differential input impedances are measured with a network analyzer.
Differential Analog Input Voltage Range
The encode rate at which parametric testing is performed.
Noise (For Any Range Within the ADC)
FS dBm -SNR dBc -Signal dBFS 10
The peak-to-peak differential voltage that must be applied to the converter to generate a full-scale response. Peak differential voltage is computed by observing the voltage on a single pin and subtracting the voltage from the other pin, which is 180 degrees out of phase. Peak-to-peak differential is computed by rotating the inputs phase 180 degrees and taking the peak measurement again. The difference is then computed between both peak measurements.
Differential Nonlinearity
VNOISE = Z x 0.001 x 10
where: Z FS SNR Signal
is the input impedance, is the full-scale of the device for the frequency in question, is the value for the particular input level, is the signal level within the ADC reported in dB below full scale. This value includes both thermal and quantization noise.
The deviation of any code width from an ideal 1 LSB step.
Differential Resonant Port Resistance
Range-Range Gain Tolerance
The resistance shunted across the resonant port (nominally 630 ). Used to determine the filter bandwidth and gain of that stage.
Encode Pulsewidth/Duty Cycle
The gain error in the RSSI attenuator ladder from one range to the next.
Range-Range Phase Tolerance
The phase error in the RSSI attenuator ladder from one range to the next.
Differential Resonant Port Capacitance
Pulsewidth high is the minimum amount of time that the ENCODE pulse should be left in logic "1" state to achieve rated performance; pulsewidth low is the minimum time ENCODE pulse should be left in low state. See timing implications of changing tENCH in text. At a given clock rate, these specifications define an acceptable Encode duty cycle.
The capacitance between the two resonant pins. Used to determine filter bandwidth and resonant frequency.
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AD6600
RSSI Gain Step AD6600 TRANSFER FUNCTION
The input amplitude span between taps of the RSSI (received signal strength) attenuator ladder. Ideally each stage should span 6 dB of input power.
RSSI Hysteresis
60 54 48 42
SNR - dB
The amount of movement in the RSSI switch points, depending on the direction of approach. Hysteresis prevents unnecessary RSSI toggling when input signal power is near a threshold.
Signal-to-Noise Ratio (Without Harmonics)
36 30 24 18 12 6 0 -100 -90 -80 -70 -60 -50 -40 -30 AIN LEVEL - dBFS -20 -10 0
The ratio of the rms signal amplitude (set at 1 dB below full scale) to the rms value of the sum of all other spectral components, excluding the first five harmonics and dc.
Worst Other Spur
The ratio of the rms signal amplitude to the rms value of the worst spurious component (excluding the second and third harmonic) reported in dBc.
Figure 1. SNR vs. Input Power
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AD6600
EQUIVALENT CIRCUITS
AVCC FLT 315 GND
4 /8 100 GND AVCC 100 AIN BUF VREF BUF GAIN GAIN STAGE
EXTERNAL LC FILTER
AVCC
AVCC
ATTENUATOR STAGE
EQUIVALENT INPUT R SHOWN ONLY
FLT GND 315
AVCC
AIN
FROM GAIN STAGE
TO T/H
GND
GND
Figure 2. Analog Input Stage (Channel A Shown; Channel B Is Equivalent)
Figure 5. Resonant (LC Noise Filter) Port
AVCC
AVCC ISEL_A ISEL_B
AVCC
AVCC
AVCC R1 17k 1/2
R1 17k 1/2
AVCC
A_SEL BIAS GND GND
B_SEL
ENCODE R2 8k 1/2 TIMING CIRCUITS R2 8k 1/2
ENCODE
GND
Figure 3. A_SEL, B_SEL Input Mode Pins
Figure 6. Encode Inputs
DVCC
DVCC
CURRENT MIRROR
CURRENT MIRROR
DVCC VREF VREF D10-D0 RSSI [2:0]
DVCC
500
CLK2 AB_OUT
CURRENT MIRROR
CURRENT MIRROR
Figure 4. Digital Outputs
Figure 7. CLK2 , AB_OUT Outputs
-12-
REV. 0
AD6600
AD6600 TIMING DIAGRAMS
tENCH
ENCODE
tENCL
tENC
tCF1
CLK2 CLK2 2
tCR1 tCLK2
L
tCF2
CLK2 1
tCR2 tCLK2
tCLK2
L
2
tCLK2 tCLK2
H1
1
tCLK2
H2
CLK2 2
CLK2 1
CLK2 2
t2 t2
D [10:0] RSSI [2:0]
1_DRL
1_DFL
t2
AB_OUT
t2
1_ARL
1_AFL
Figure 8. Encode to CLK2
Delays and CLK2
Propagation Delays
tENCH
ENCODE
tENCL
tENC
tCF1
CLK2 CLK2 2
tCR1 tCLK2
L
tCF2
CLK2 1
tCR2 tCLK2
tCLK2
L
2
tCLK2 tCLK2
H1
1
tCLK2
CLK2 2
H2
CLK2 1
CLK2 2
tH_D2
D [10:0] RSSI [2:0]
tS_D2
tH_D2
tS_D2
tH_A2
tS_A2
tH_A2
tS_A2
AB_OUT
Figure 9. CLK2
Setup-and-Hold Time Characteristics
tENCH
ENCODE ENCODE
tENCL
ENCODE
tENC
ENCODE
2
tCF1
CLK2 CLK2 2
tCR1 tCLK2
L
tCF2
CLK2 1
tCR2 tCLK2
tCLK2
L
tCLK2 tCLK2
H1
1
tCLK2
H2
CLK2 2
CLK2 1
CLK2 2
tEN_DFL tEN_DRL
D [10:0] RSSI [2:0]
tEN_AFL
tEN_ARL
AB_OUT
Figure 10. Encode to CLK2
Delays and Encode Propagation Delays
REV. 0
-13-
AD6600
tENCH
ENCODE ENCODE
tENCL
ENCODE
tENC
ENCODE
2
tCF1
CLK2 CLK2 2
tCR1 tCLK2
L
tCF2
CLK2 1
tCR2 tCLK2
tCLK2
L
tCLK2 tCLK2
H1
1
tCLK2
H2
CLK2 2
CLK2 1
CLK2 2
tH_DEN
D [10:0] RSSI [2:0]
tS_DEN
tH_DEN
tS_DEN
tH_AEN
AB_OUT
tS_AEN
tH_AEN
tS_AEN
Figure 11. Encode Setup-and-Hold Time Characteristics
3
2.6
CLK2
8 D [10:0] RSSI [2:0] 6 AB_OUT
8.4
6.2
Figure 12. Typical Output Rise and Fall Times
20
30
50
ENCODE
40% 18 8 8 18 30 20
CLK2
Figure 13. Encode = 20 MSPS, Duty Cycle = 40%
30
20
50
ENCODE 23 8 CLK2
60% 23 8 20 30
Figure 14. Encode = 20 MSPS, Duty Cycle = 60%
-14-
REV. 0
AD6600
NOISE FILTER FLT 0dB, -12dB, -24dB FLT RESONANT PORT
630
AIN
ATTEN
AIN
AB_OUT GAIN
DETECT PEAK SET RSSI
ANALOG MUX
+12, +18dB GAIN
ENCODE
A/D CONVERTER TWO'S COMPLEMENT
3 RSSI
GAIN
D10-D0
11 3
RSSI
RSSI [2:0]
SELECT GAIN ENCODE
BIN BIN
ATTEN
0dB, -12dB, -24dB
AD6600
TIMING
CLK2
A_SEL
B_SEL
AVCC
GND
ENC
ENC
DVCC
Figure 15. Functional Block Diagram
THEORY OF OPERATION
0 101 100 011 010 001 000 -12 -18 -24 -30 -36 -42 -48 -54 -60 -66 -72 -78 -84 -90
The AD6600, dual-channel, gain-ranging ADC integrates analog IF circuitry with high speed data conversion. Each analog input stage is a 1 GHz, 0 dB to -24 dB, phase-compensated step attenuator; the step size in each attenuator is 12 dB. Both input stages drive an analog multiplex function followed by a 12 dB/ 18 dB gain amplifier. A simple LC noise filter at the output of the gain amplifier is required to resonate at the desired IF. This resonant filter port precedes a wide input bandwidth (450 MHz) track-and-hold followed by an 11-bit analog-to-digital converter (ADC). A high speed synchronous peak detector monitors signal strength at both input channels. The peak detector drives RSSI circuitry that automatically adjusts attenuation and gain on a clock-by-clock basis. The three RSSI indicator bits and the eleven ADC bits are available at the output providing an exponent and mantissa data format. Together these integrated components form an IF sampling, high dynamic range ADC system. It is helpful to view this device as a stand-alone ADC using automatic gain control. The gain control referred to in this data sheet as "gain-ranging" works to maintain a constant SNR over as wide a range as possible.
000
-90 0 4 8
-96 12 16 20 24 28 32 36 40 44 48 52 56 60 SNR - dB 12dB SNR WINDOW
Figure 16. SNR for Gain-Ranging ADC
AD6600 SUBCIRCUITS Input Step Attenuator and Gain Stage
As stated previously, the AD6600 has a floating-point output: eleven mantissa bits and three exponent bits. As shown in Figure 16, at the lowest input levels SNR increases 1 dB for a 1 dB increase in input power. In this range, the AD6600 is set for maximum gain. However, when the input signal level reaches the gain-ranging section (approximately -42 dBFS), the SNR is contained between about 50 dB and 56 dB or between 44 dB and 56 dB including the effects of hysteresis. Although Figure 16 does not indicate so, there are slight differences between the SNR from one gain range to the next as the gain amp switches between 12 dB and 18 dB. Once the final RSSI range has been exceeded (approximately -12 dBFS), SNR again increases 1 dB per 1 dB input power increase until converter full scale is reached. Again, this performance is very much like the effects of a typical analog AGC loop.
REV. 0
The AD6600 has two identical input attenuators, Channel A and Channel B. These dual inputs are typically used as diversity channels but may also process two independent IF signals. For maximum oversampling the device is used in single channel mode; in this case only one input channel is required. The attenuator steps are 0 dB, -12 dB and -24 dB. The attenuator settings are based on the decisions of the RSSI stage (see Peak Detector/ RSSI section). The outputs of the attenuators connect to an analog multiplexer that selects either Channel A or B for subsequent processing (see Input Mode). The selected signal drives a dual-gain amplifier set to either 12 dB or 18 dB; the selected gain is also determined by the RSSI stage. Therefore, based on all possible combinations of attenuation and gain, the input signal receives -12 dB to +18 dB of voltage gain in 6 dB steps (Table I). Overall gain-matching is typically within 0.1 dB. With a bandwidth of 1 GHz, the phase delay through the front-end ranges from 0.2 degrees to 0.5 degrees, depending on input frequency. Additionally, the input impedance does not change with attenuator settings so there is no AM-to-PM distortion. -15-
AIN - dBFS
101 100 011 010 001
AD6600
Table I. Attenuator and Gain Settings ADC Encoder
Attenuator 0 dB 0 dB -12 dB -12 dB -24 dB -24 dB
Gain Amp +18 dB +12 dB +18 dB +12 dB +18 dB +12 dB
Total +18 dB +12 dB +6 dB 0 dB -6 dB -12 dB
RSSI Word 000 001 010 011 100 101
After the calibration period is complete (one clock cycle), the appropriate gain and attenuator settings are determined and set. Once settled, the internal track-and-hold freezes the input signal so that the ADC encoder may digitize the signal. During digitization, the peak detector/RSSI circuitry is already looking at the next sample. When the AD6600 is in dual channel mode, the process is interleaved: while Channel B is monitored for signal strength, Channel A is digitized. This allows the RSSI to update on a clock-by-clock basis.
ENCODE DIGITIZE OLD DATA T-AND-H HOLD T-AND-H TRACK ADC DIGITIZE T-AND-H HOLD
High-Speed Peak Detector and RSSI Circuitry
The peak detector along with the attenuator and dual gain amplifier form the control loop within the AD6600. The peak detector is designed to follow the analog input one clock cycle before the conversion is actually made. Therefore, while the converter section of the AD6600 is converting sample "n," the peak detector is already looking at sample "n+1." While looking at the "n+1" sample (the calibration period), the peak detector examines the envelope of the input signal. The more of an envelope that is tracked, the more accurate the gain setting. At the very least, the peak detector must be presented either a positive or negative sinusoidal peak, which represents about one-half of a sine wave cycle. Since the peak detector works for a complete cycle prior to conversion, the absolute minimum IF frequency that can be determined is twice the sample rate per channel. Therefore, at 15 MSPS, the minimum IF frequency that can be sampled would be 30 MHz. Note that the more cycles of the input that are monitored by the peak detector, the more accurate the gain setting will be. Therefore, the actual minimum IF frequency recommended is higher than this. The minimum specified frequency is 70 MHz. Since the RSSI control loop is performed on a sample-by-sample basis, the AD6600 very accurately follows the signals into and out of a deep fade.
Hysteresis
IF INPUT
INTERNAL 2 CLOCK RSSI CAL.
RSSI CALIBRATION
RSSI SET
AMPLIFIER CONTROL
NOISE FILTER DISCHARGE
NOISE FILTER SETTLING
T/H INPUT
4/8 AMP CLAMPED NOISE FILTER SETTLING
Figure 17. Internal Timing
Figure 17 shows the internal timing of the chip. The encode applied to the device initiates several actions. The first and most important is that the track-and-hold is placed in hold, thus sampling the analog input at that instant. The second action is that the peak detector of the RSSI circuitry is initialized. During this period, the analog input envelope is monitored to determine signal power. The AD6600 is in calibration mode for about onequarter of the encode period. While the AD6600 is in calibration, the external noise filter is discharged and the amplifier driving the filter disabled. Since this filter is shared between the two input channels in dual channel mode, this greatly reduces the feedthrough between the channels that would otherwise exist. One-quarter of an encode period after the calibration is complete, the amplifier is re-enabled and allowed to settle to its new signal conditions for sampling by the wideband T/H on the next encode signal. The final action is that the signal on the resonant port is sampled by the track-and-hold. This happens on the next rising edge of the encode.
Input Mode Select
The AD6600 employs hysteresis to prevent the gain-ranging from unnecessarily changing when the signal envelope is near an RSSI threshold. The hysteresis is digital and will account for exactly 6 dB of shift, depending on whether the signal is increasing or decreasing. This effect is shown in the dashed lines of the overall transfer function, Figure 16.
External LC Noise Filter, Resonant Port
The output of the attenuator/gain stage drives the wide bandwidth track-and-hold (T/H), followed by the ADC encoder. Because the attenuator/gain stage has a very wide bandwidth (~1 GHz), an LC filter or "resonant port" is provided to limit the amount of wideband noise delivered to the ADC. The simple LC filter does not provide signal selectivity and should typically be 35 MHz to 50 MHz wide. However, because the ADC's track-and-hold itself has a wide bandwidth (~450 MHz), this noise-limiting filter is critical to meeting overall sensitivity. Specific details on selecting components for the resonant port are provided later in the text (Understanding the External Analog Filter).
The AD6600 has two operating modes: single channel and dual channel. In single channel mode, the ADC always samples Channel A or always samples Channel B. In dual channel mode, the ADC converter is sampling Channel A and Channel B on alternating Encode cycles. Two control pins are provided to select the desired mode of operation. A_SEL and B_SEL arbitrate the selection of how these input channels are connected to the output. Table II shows the truth table for selection of the input.
-16-
REV. 0
AD6600
Table II. Selecting AD6600 Operating Mode Table V. 16-Bit, Fixed-Point Data Format
Mode Dual: A/B Single: A Single: B Not Valid
A_SEL 1 1 0 0
B_SEL 1 0 1 0
Output vs. Encode Clock n n+1 n+2 n+3 A A B - B A B - A A B - B A B -
RSSI 101 100 011 010 001 000
11-Bit Word DATA DATA DATA DATA DATA DATA
16-Bit Data Format DATAx 32 DATAx 16 DATAx 8 DATAx 4 DATAx 2 DATAx 1
Corresponds to a Shift Right of 5 4 3 2 1 0
A_SEL and B_SEL are not logic inputs and should be tied directly to ground or analog VCC (5 V analog). In dual channel mode, the AB_OUT signal indicates which input is currently available on the digital output. When the AB_OUT is 1, the digital output is the digitized version of Channel A. Likewise, when AB_OUT is 0, the Channel B is available on the digital output (Table III).
Table III. AB_OUT for Dual Channel Operation
When mated with the AD6620, Digital Receive Processor Chip, the AD6600 floating point data (mantissa + exponent) is automatically converted to 16-bit two's complement format by the AD6620.
APPLYING THE AD6600 Encoding the AD6600
A_SEL and B_SEL = 1 D[10:0], RSSI[2:0] AB_OUT
Data Output Stage
Output Data vs. Encode Clock n n+1 n+2 n+3 A 1 B 0 A 1 B 0
The output stage provides data in the form of mantissa, D[10:0], and exponent, RSSI[2:0], where D[10:0] represents the output of the 11-bit ADC coded as two's complement, and RSSI[2:0] represents the gain-range setting coded in offset binary. Table IV shows the nominal gain-ranges for a nominal 2 V p-p differential full-scale input. Keep in mind that the actual full-scale input voltage and power will vary with input frequency.
Table IV. Interpreting the RSSI Bits
The AD6600 encode signal must be a high quality, extremely low phase noise source to prevent degradation of performance. Digitizing high frequency signals (IF range 70 MHz-250 MHz) places a premium on encode clock phase noise. SNR performance can easily degrade by 3 dB-4 dB with 70 MHz input signals when using a high-jitter clock source. At higher IFs (up to 250 MHz), and with high-jitter clock sources, the higher slew rates of the input signals reduce performance even further. See AN-501, Aperture Uncertainty and ADC System Performance for complete details. For optimum performance, the AD6600 must be clocked differentially. The encode signal is usually ac-coupled into the ENC and ENC pins via a transformer or capacitors. These pins are biased internally and require no additional bias. Figure 18 shows one preferred method for clocking the AD6600. The sine source (low jitter) is converted from single-ended to differential using an RF transformer. The back-to-back Schottky diodes across the transformer secondary limit clock excursions into the AD6600 to approximately 0.8 V p-p differential. This helps prevent the larger voltage swings of the clock from feeding through to other portions of the AD6600, and limits the noise presented to the encode inputs. A crystal clock oscillator can also be used to drive the RF transformer if an appropriate limiting resistor (typically 100 ) is placed in the series with the primary.
T1-1T SINE SOURCE 100 ENCODE
Differential Analog Input Voltage (V p-p) 0.5 < VIN 0.25 < VIN < 0.5 0.125 < VIN < 0.25 0.0625 < VIN < 0.125 0.03125 < VIN < 0.0625 VIN < 0.03125
RSSI [2:0] Decimal Binary Equiv. 101 100 011 010 001 000 5 4 3 2 1 0
Attenuation or Gain (dB) -12 -6 0 +6 +12 +18
The digital processing chip which follows the AD6600 can combine the 11 bits of two's complement data with the 3 RSSI bits to form a 16-bit equivalent output word. Table V explains how the RSSI data can be interpreted when using a PLD or ASIC. Basically, the circuit performs right shifts of the data depending on the RSSI word. This can also be performed in software using the following pseudo code fragment: r0 = dm (rssi); r2 = 5; r0 = r2-r0; r1 = dm (adc); (11 bits, MSB justified into DSP word) rshift r1, r0; (arithmetic shift to extend the sign bit) The result of the shifted data is a 16-bit fixed-point word that can be used as any normal 16-bit word.
AD6600
ENCODE 5082-2810 DIODES
Figure 18. Transformer-Coupled Sine Source
REV. 0
-17-
AD6600
If a low jitter ECL/PECL clock is available, another option is to ac-couple a differential ECL/PECL signal to the encode input pins as shown in Figure 19.
VT 0.1 F ENCODE ECL/ PECL 0.1 F
When general purpose gain blocks are used, matching can easily be achieved using a transformer. Most gain blocks are available with 50 input and output ports. Thus matching to the 200 impedance of the AD6600 requires only a 1:4 (impedance ratio) transformer as shown in Figure 21.
FROM MIXER OUTPUT
AD6600
ENCODE
50 GAIN BLOCK
AD6600
ADC
Figure 21. Transformer-Coupled Gain Block
VT
Figure 19. AC-Coupled ECL/PECL Encode
Driving the Analog Inputs
As with most new high-speed, high dynamic range analog-to-digital converters, the analog input to the AD6600 is differential. Differential inputs allow much improvement in performance on-chip as IF signals are processed through attenuation and gain stages. Most of the improvement is a result of differential analog stages having high rejection of even-order harmonics. There are also benefits at the PCB level. First, differential inputs have high common-mode rejection to stray signals such as ground and power noise. They also provide good rejection to common-mode signals such as local oscillator feedthrough. Driving a differential analog input introduces some new challenges. Most RF/IF amplifiers are single-ended and may not obviously interface to the AD6600. However, using simple techniques, a clean interface is possible. The recommended method to drive the analog input port is shown in Figure 20. The AD6600 input is actually designed to match easily to a SAW filter such as SAWTEK 855297. This allows the SAW filter to be used in a differential mode, which often improves the operations of a SAW filter. Using network analyzer data for both the SAW filter output and the AD6600 input ports (see data tables for AD6600 S11 data), a conjugate match can be used for maximum power transfer. Often an adequate match can be achieved simply by using a shunt inductor to make the port look real (Figure 20). For more details on how to exactly match networks, see RF Circuit Design by Chris Bowick, ISBN: 0-672-21868-2.
FROM MIXER OUTPUT
In the rare case that better matching is required, a conjugate match between the amplifier selected and the transformercoupled analog input can be achieved by placing the matching network between the amplifier and the transformer (Figure 22). For more details on matching, see the reference mentioned previously for more details.
FROM MIXER OUTPUT MATCHING NETWORK 50 GAIN BLOCK
AD6600
ADC
Figure 22. Gain Block and Matching Network
Understanding the External Analog Filter
Two primary trade-offs must be made when designing the external resonant filter. The obvious one is the bandwidth of the filter. The second, not so obvious, trade-off is settling time of the filter nodes. Resonant Filter Bandwidth determines the amount of noise that is limited at the center frequency chosen. If the resonant filter is too wide, little noise improvement is seen. If the resonant filter is too narrow, amplitude variation can be seen due to the tolerance of filter components. If the narrow filter is off center due to these tolerances (or drift), the 4x/8x signal will fall on the transition band of the filter. An optimum starting point for this filter is approximately 50 MHz. Resonant Filter Settling limits the amount of capacitance of this filter. The output of the 4x/8x amplifier is clamped when the ADC is processing its input (encode high time). This prevents the amp output from feeding through to the ADC (T/H) and corrupting the ADC results. But, upon the falling edge of encode, the amp must now come out of clamp and present an accurate signal to the ADC T/H. The RC of the external filter determines the settling of the amp. If the amp output does not settle, the ADC sees an attenuated signal. So obviously, a narrow bandwidth is desired to improve noise performance; but if the filter is too narrow, the amp will not settle and the ADC will see an attenuated signal. Figure 23 shows a simplified model of the 4x/8x amplifier. A key point to note is that the resistor values in the collector legs are 315 nominal with a tolerance of 20%. The filter performance is determined by these values in conjunction with the internal parasitic capacitance, board parasitics and the external filter components.
SAW #1
AD6630
SAW #2
AD6600
ADC
Figure 20. Cascaded SAW Filters with AD6630
Where gain is required, the AD6630 differential, low noise, IF gain block is recommended. This amplifier provides 24 dB of gain and provides limiting to prevent damage to the SAW filter and AD6600. The AD6630 is designed to reside between two SAW filters. This low noise device is ideally suited to many applications of the AD6600. For more information on the AD6630, reference the AD6630 data sheet.
-18-
REV. 0
AD6600
AVCC RESONANT FILTER PORT FLT FLT FROM GAIN STAGE CLAMP 315 315
So for settling purposes, with 13 MSPS encode and 50% duty cycle, the maximum allowable capacitance for proper settling is CTOTAL = 13.6 pF. As stated above, this CTOTAL includes the external capacitors, the board parasitics, and the AD6600 parasitics. The parasitics of the AD6600 (lead, internal bond pad and internal connections) at FLT and FLT are 1.75 pF 0.35 pF (differential). If the resistors are at maximum value (315 + 20%), the maximum allowable capacitance is CTOTAL = 11.3 pF. If the duty cycle is less than 50%, the maximum allowable capacitance is further decreased to allow for settling.
Power Supplies
ENCODE GND
Figure 23. 4 x/8 x Amplifier Clamp Circuitry
Figure 24 shows why settling is important for this circuit. If the 4x/8x amp does not settle (come out of clamp), the amplitude presented to the ADC will be decreased. This results in decreased gain when the filter capacitance is too high.
ENCODE HOLD TRACK HOLD
Care should be taken when selecting a power source. Linear supplies are strongly recommended. Switching supplies tend to have radiated components that may be "received" by the AD6600. Each of the power supply pins should be decoupled as closely to the package as possible using 0.1 F chip capacitors. The AD6600 has separate digital and analog power supply pins. The analog supplies are denoted AVCC and the digital supply pins are denoted DVCC. Although analog and digital supplies may be tied together, best performance is achieved when the supplies are separate. This is because the fast digital output swings can couple switching current back into the analog supplies. Note that AVCC must be held within 5% of 5 Volts; however, the DVCC supply may be varied according to output digital logic family. The AD6600 is specified for DVCC = 3.3 V as this is a common supply for digital ASICS.
Output Loading
RESONANT FILTER
CLAMPED
SETTLING
Figure 24. 4 x/8 x Amplifier Settling
This explains why the total capacitance allowed for the external filter varies depending on the clock rate (actually encode clock high time). If the encode is 13 MSPS and the duty cycle is 50%, the allowable settling time is 38.5 ns (1/2 of the encode time). Our assumption is that the amp should be allowed to settle to 1/4 LSB in this time period. This has been proven with both simulation and empirical analysis. If the settling is assumed to be an RC circuit, then: T = RC; t = time; n = number of bits
VO = A 1 - e t /T A- A/2 1-
n
(
) = A (1 - e )
t /T
Care must be taken when designing the data receivers for the AD6600. Note from the equivalent circuits shown earlier (see Equivalent Circuits) that D[10:0] and RSSI[2:0] contain a 500 output series resistor. To minimize capacitive loading, there should only be one gate on each output pin. Extra capacitive loading will increase output timing and invalidate timing specifications. CLK2x and AB_OUT do not contain the output series resistors. Testing for digital output timing is performed with 10 pF loads.
Layout Information
1 = 1 - e t /T 2n
1 = e t /T 2n 1 t = l n n 2 T T= l n 2n
()
t
The schematic of the evaluation board (Figure 25) represents a typical implementation of the AD6600. A multilayer board is recommended to achieve best results. It is highly recommended that high quality, ceramic chip capacitors be used to decouple each supply pin to ground directly at the device. The pinout of the AD6600 facilitates ease of use in the implementation of high frequency, high resolution design practices. All of the digital outputs are segregated to two sides of the chip, with the inputs on the opposite side for isolation purposes. Care should be taken when routing the digital output traces. To prevent coupling through the digital outputs into the analog portion of the AD6600, minimal capacitive loading should be placed on these outputs. It is recommended that a fanout of only one be used for all AD6600 digital outputs. The layout of the analog inputs and the external resonant filter are critical. No digital traces must be routed near, under, or above these portions of the circuit. The transformers used for coupling into the analog inputs must be located as close as possible to the analog inputs of the AD6600. The external resonant filter components must be physically close to the filterinput pins, yet separated from the analog inputs. -19-
CTOTAL =
(TENCODE x 0.5) = 38.5 ns = 13.6 pF R x l n (8192) 315 x l n (8192)
In this case, CTOTAL includes all parasitics and external capacitance. R is nominally 315 . The 8192 is (4 x 2048), which is 1/4 LSB of the converter (11 bits, 2048).
REV. 0
AD6600
The layout of the Encode circuit is equally critical. Any noise received on this circuitry will result in corruption in the digitization process and lower overall performance. The Encode clock must be isolated from the digital outputs and the analog inputs.
Evaluation Board
The evaluation board for the AD6600 is straightforward, containing all required circuitry for evaluating the device. The only external connections required are power supplies, clock and the analog inputs. The evaluation board includes the option for an on-board, clock oscillator for encode. Power to the analog supply pins of the AD6600 is connected via the power terminal block (TB1). Power for the digital interface is supplied via Pin 1 of J201, or the VDD e-hole located adjacent to J201. The VDD supply can vary between 3.3 V to 5.0 V and sets the level for the output digital data (J201). The J201 connector mates directly with the AD6620 (Receive Signal Processor) evaluation board, Part # AD6620S/PCB, allowing complete evaluation of system performance. The two analog inputs are connected via SMA connectors AIN and BIN, which are transformer-coupled to the AD6600 inputs. The transformers have a turns-ratio of 1:4 to match the input resistance of the AD6600 (200 ) to 50 at the SMA connectors.
The Encode signal may be generated using an on-board crystal oscillator, U100. If an on-board crystal is used, R104 must be removed from the board to prevent loading of the oscillator's output. The on-board oscillator may be replaced by an external encode source via the SMA connector labeled ENCODE. If an external source is used, it must be a high quality and very low phase noise source. The high IF range of the AD6600 (70 MHz -250 MHz) demands that the Encode clock be sufficiently pure to maintain performance. The AD6600 output data is latched using 74LCX574 (U201, U202) latches. The clock for these latches is determined by jumper selection on header J1. The clock can be a delayed version of the encode clock (CLKA, CLKB), or the CLK2x generated by the AD6600. A clock is also distributed with the output data (J201) that is labeled CLKX (Pin 11, J201). The CLKx is selected with jumpers on header J1 and can be CLKA, CLKB, or CLK2x. The resonant LC filter components (SEL2, C2 and C3) are omitted. The user must install proper values based on the IF chosen. See Understanding the External Analog Filter section of the data sheet for guidelines on selecting these components.
Table VI. AD6600ST/PCB Bill of Material
Item 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Quantity 3 14 2 1 4 2 1 1 1 2 2 1 1 2 3 1 2 1
Reference AIN, BIN, ENCODE C1, C102-108, C114, C117-118, C120-121, C299 C100-101 C111 C112-C113, C115-116 CR1-2 DUT J1 J201 R1-2 R100-R101 R103 R104 R298-R299 T1-T2, T4 TB1 U201-U202 U204
Description SMA Connector Ceramic Chip Capacitor 1206, 0.1 F Tantalum Chip Capacitor, 10 F Ceramic Chip Capacitor 0805, 0.1 F Ceramic Chip Capacitor 0508, 0.1 F 1N2810 Schottky Diode AD6600AST 20-Pin Double Row Male Header 50-Pin Double Row Male Header, Right Angle Omitted Surface Mount Resistor 1206, 10 k Surface Mount Resistor 1206, 100 Surface Mount Resistor 1206, 50 Surface Mount Resistor 1206, 2 k Surface Mount Transformer Mini-Circuits T4-1T PCTB2 Terminal Block 74LCX574 Octal Latch 74LVQ00 Two Input NAND Gate
-20-
REV. 0
D5
D6
D4
D3
D9
D8
D7
D2
D1
(MSB) D10
C111 0.1 F 1 DVCC 2 GND 3 C1 4 AVCC 5 GND 6 RSSI2 7 RSSI1 8 RSSI0 9 B_SEL AVCC 25 GND 24 BIN 23 AVCC AVCC FLT FLT GND AVCC AIN GND GND AVCC BIN GND 10 A_SEL 11 AIN VCC ENC 26 ENC 27 CLK_2 AB_OUT 29 GND 30 GND AVCC 31 VCC GND 32 GND DVCC 33 VDD
VDD
C112 0.01 F
GND
D0 (LSB)
VCC
VCC
VCC
GND
GND
VCC
GND
REV. 0
R1 A B CLK CLKX CLKA CLK_2X CLKB CLKB GND GND CLKA VDD CR1 1N2810 C113 0.01 F CR2 1N2810 R2 C1 0.1 F 2 1 H20DM J1 20 1 19 2 18 3 17 4 16 5 15 6 14 7 13 8 12 9 11 10 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 RSSI0 RSSI1 RSSI2 U201 74LCX574 A/B D0 D1 D2 D3 D4 D5 D6 9 8 7 6 5 4 3 2 8D 7D 6D 5D 4D 3D 2D 1D CK 11 2 CLK U202 74LCX574 8Q 7Q 6Q 5Q 4Q 3Q 2Q 1Q OE 1 12 13 14 15 16 17 18 19 A/B BIT0 BIT1 BIT2 BIT3 BIT4 BIT5 BIT6 44 43 42 41 40 39 38 37 36 35 34 A/B BIT10 BIT9 BIT8 BIT7 BIT6 BIT5 BIT4 BIT3 CLK CLKX BIT2 BIT1 BIT0 GND GND GND GND GND GND GND RSSIB2 RSSIB1 RSSIB0 GND 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 H50DM J201 50 49 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND A/B GND REMOVE 21 AND 30 CLK
CLKREF
VCC
T4 TI-4T 4 3
R103 100
6
14 U100 VCC 8 OUT VEE
7 K1115
C114 0.1 F
1:4
SMA ENCODE
R104 50
Figure 25. AD6600ST/PCB Schematic Diagram
AD6600AST
CLK2X 28 D7 D8 D9 D10 RSSI2 RSSI1 RSSI0 GND T2 T1-4T 3 4 SMA BIN 2 6 1:4 C3 SEL CLKREF R299 2k + VCC C100 C102 C104 C106 C108 C120 C121 GND GND 9 10 C299 0.1 F 1 C116 0.01 F VDD R298 2 U204 74LVQ00 1 2 3 9 8 7 6 5 4 3 2 12 13 14 15 16 17 18 19 20 21 22 8D 7D 6D 5D 4D 3D 2D 1D CK 11 SEL2 C2 SEL VCC VDD C118 U204 74LVQ00 8 TB1 PCTB2 1 2
-21-
VCC
GND
A R100 10k VCC
B R101 10k VCC
B
A
T1 TI-4T 4 3
SMA AIN
2
8Q 7Q 6Q 5Q 4Q 3Q 2Q 1Q OE 1
12 13 14 15 16 17 18 19
BIT7 BIT8 BIT9 BIT10 RSSIB2 RSSIB1 RSSIB0
6
1
1:4
C115 0.01 F
U204 74LVQ00 4 5 6 CLKA U204 74LVQ00 GND GND 12 13 11
AD6600
+
C101
C103
C105
C107
C117
AD6600
Figure 26. AD6600ST/PCB Top Side Silk Screen
Figure 27. AD6600ST/PCB Top Side Copper
Figure 29. AD6600ST/PCB Power Supply Layer (Negative)
Figure 28. AD6600ST/PCB Bottom Side Copper
Figure 30. AD6600ST/PCB Ground Layer (Negative)
-22-
REV. 0
AD6600
Connecting the AD6600 with the AD6620
The AD6600 interfaces directly to the AD6620 Digital Receive Signal Processor as shown in Figure 31. No additional external components are required. Note that the layout requirements discussed previously do apply and deviations can result in degraded performance. The digital outputs of the AD6600 must connect directly to the AD6620 inputs with no additional fanout. Additional loading on the outputs will compromise timing performance.
(MSB) D10 D9 D8 D7 D6 D5 D4 D3 AD6600 D2 D1 (LSB) D0 IN15 IN14 IN13 IN12 IN11 IN10 IN9 IN8 IN7 IN6 IN5 IN4 IN3 IN2 IN1 IN0 EXP2 EXP1 EXP0 A/B CLK
Figure 32 shows the timing details between the AD6600 and the AD6620. On Clock 1, D[10:0], RSSI[2:0], and AB_OUT are captured by the AD6620. Since AB_OUT has changed state from the previous clock, the D[10:0] and RSSI[2:0] are processed by the AD6620. This clock allows adequate setup and hold time for AB_OUT, D[10:0], and RSSI[2:0] to be captured by the AD6620. On Clock2, D[10:0], RSSI[2:0], and AB_OUT are captured by the AD6620. Since AB_OUT has not changed from the previous clock, the D[10:0] and RSSI[2:0] are ignored by the AD6620. This clock is concerned only with the AB_OUT setupand-hold time.
AD6620
ENC
ENC
RSSI2 RSSI1 RSSI0 AB_OUT CLK2
Figure 31. AD6600/AD6620 Connections
38.5 CLK2
38.5
CLOCK1 3.0 D [10:0] RSSI [2:0] 16.5
CLOCK2 3.0 16.5
12.5 7.0 AB_OUT
Figure 32. AD6600 to AD6620 Timing at 13 MSPS
REV. 0
-23-
AD6600
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
0.063 (1.60) MAX 0.030 (0.75) 0.018 (0.45)
34 33
0.472 (12.00) SQ
23 22
SEATING PLANE TOP VIEW
(PINS DOWN)
0.394 (10.0) SQ
44 1 11
12
0.006 (0.15) 0.002 (0.05) 0.057 (1.45) 0.053 (1.35)
0.031 (0.80) BSC
0.018 (0.45) 0.012 (0.30)
-24-
REV. 0
PRINTED IN U.S.A.
C00966-2.5-7/00 (rev. 0)
44-Terminal LQFP (Low-Profile Quad Plastic Flatpack) (ST-44)

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