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Six LVPECL Outputs, SiGe Clock Fanout Buffer ADCLK946
FEATURES
4.8 GHz operating frequency 75 fs rms broadband random jitter On-chip input terminations 3.3 V power supply
FUNCTIONAL BLOCK DIAGRAM
ADCLK946
VREF VT CLK CLK REFERENCE LVPECL Q0 Q0 Q1 Q1 Q2 Q2 Q3 Q3 Q4 Q4 Q5 Q5
08053-001
APPLICATIONS
Low jitter clock distribution Clock and data signal restoration Level translation Wireless communications Wired communications Medical and industrial imaging ATE and high performance instrumentation
GENERAL DESCRIPTION
The ADCLK946 is an ultrafast clock fanout buffer fabricated on the Analog Devices, Inc., proprietary XFCB3 silicon germanium (SiGe) bipolar process. This device is designed for high speed applications requiring low jitter. The device has a differential input equipped with center-tapped, differential, 100 on-chip termination resistors. The input accepts dc-coupled LVPECL, CML, 3.3 V CMOS (single ended), and ac-coupled 1.8 V CMOS, LVDS, and LVPECL inputs. A VREF pin is available for biasing ac-coupled inputs. The ADCLK946 features six full-swing emitter-coupled logic (ECL) output drivers. For LVPECL (positive ECL) operation, bias VCC to the positive supply and VEE to ground. For ECL operation, bias VCC to ground and VEE to the negative supply. The ECL output stages are designed to directly drive 800 mV each side into 50 terminated to VCC - 2 V for a total differential output swing of 1.6 V. The ADCLK946 is available in a 24-lead LFCSP and is specified for operation over the standard industrial temperature range of -40C to +85C.
Figure 1.
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. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 (c)2009 Analog Devices, Inc. All rights reserved.
ADCLK946 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications ....................................................................................... 1 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Electrical Characteristics ............................................................. 3 Absolute Maximum Ratings............................................................ 5 Determining Junction Temperature .......................................... 5 ESD Caution .................................................................................. 5 Thermal Performance ...................................................................5 Pin Configuration and Function Descriptions..............................6 Typical Performance Characteristics ..............................................7 Functional Description .....................................................................9 Clock Inputs ...................................................................................9 Clock Outputs ................................................................................9 PCB Layout Considerations ...................................................... 10 Input Termination Options ....................................................... 11 Outline Dimensions ....................................................................... 12 Ordering Guide .......................................................................... 12
REVISION HISTORY
4/09--Revision 0: Initial Version
Rev. 0 | Page 2 of 12
ADCLK946 SPECIFICATIONS
ELECTRICAL CHARACTERISTICS
Typical (typ) values are given for VCC - VEE = 3.3 V and TA = 25C, unless otherwise noted. Minimum (min) and maximum (max) values are given over the full VCC - VEE = 3.3 V 10% and TA = -40C to +85C variation, unless otherwise noted. Table 1. Clock Inputs and Outputs
Parameter DC INPUT CHARACTERISTICS Input Voltage High Level Input Voltage Low Level Input Differential Range Input Capacitance Input Resistance Single-Ended Mode Differential Mode Common Mode Input Bias Current Hysteresis DC OUTPUT CHARACTERISTICS Output Voltage High Level Output Voltage Low Level Output Voltage Differential Reference Voltage Output Voltage Output Resistance Symbol VIH VIL VID CIN Min VEE + 1.6 VEE 0.4 0.4 50 100 50 20 10 VOH VOL VOD VREF VCC - 1.26 VCC - 1.99 610 (VCC + 1)/2 235 VCC - 0.76 VCC - 1.54 960 Typ Max VCC VCC - 0.2 3.4 Unit V V V p-p pF k A mV V V mV V Test Conditions/Comments
1.7 V between input pins
Open VT
50 to (VCC - 2.0 V) 50 to (VCC - 2.0 V) 50 to (VCC - 2.0 V) -500 A to +500 A
Table 2. Timing Characteristics
Parameter AC PERFORMANCE Maximum Output Frequency Output Rise/Fall Time Propagation Delay Temperature Coefficient Output-to-Output Skew Part-to-Part Skew 1 Additive Time Jitter Integrated Random Jitter Broadband Random Jitter 2 Crosstalk-Induced Jitter 3 CLOCK OUTPUT PHASE NOISE Absolute Phase Noise fIN = 1 GHz Symbol Min 4.5 tR, tF tPD 40 150 Typ 4.8 75 185 50 9 90 220 28 45 Max Unit GHz ps ps fs/C ps ps fs rms fs rms fs rms Test Conditions/Comments See Figure 4 for differential output voltage vs. frequency, >0.8 V differential output swing 20% to 80% measured differentially VICM = 2 V, VID = 1.6 V p-p
VID = 1.6 V p-p BW = 12 kHz - 20 MHz, CLK = 1 GHz VID = 1.6 V p-p, 8 V/ns, VICM = 2 V
28 75 90
-119 -134 -145 -150 -150
dBc/Hz dBc/Hz dBc/Hz dBc/Hz dBc/Hz
Input slew rate > 1 V/ns (see Figure 11 for more details) @ 100 Hz offset @ 1 kHz offset @ 10 kHz offset @ 100 kHz offset >1 MHz offset
1 2
The output skew is the difference between any two similar delay paths while operating at the same voltage and temperature. Measured at the rising edge of the clock signal; calculated using the SNR of the ADC method. 3 The amount of added jitter measured at the output while two related, asynchronous, differential frequencies are applied to the inputs.
Rev. 0 | Page 3 of 12
ADCLK946
Table 3. Power
Parameter POWER SUPPLY Supply Voltage Requirement Power Supply Current Negative Supply Current Positive Supply Current Power Supply Rejection 1 Output Swing Supply Rejection 2
1 2
Symbol VCC - VEE IVEE IVCC PSRVCC PSRVCC
Min 2.97
Typ
Max 3.63
Unit V mA mA ps/V dB
Test Conditions/Comments 3.3 V + 10% Static VCC - VEE = 3.3 V 10% VCC - VEE = 3.3 V 10% VCC - VEE = 3.3 V 10% VCC - VEE = 3.3 V 10%
90 245 <3 28
115 275
Change in tPD per change in VCC. Change in output swing per change in VCC.
Rev. 0 | Page 4 of 12
ADCLK946 ABSOLUTE MAXIMUM RATINGS
Table 4.
Parameter Supply Voltage VCC - VEE Input Voltage CLK, CLK CLK, CLK to VT Pin (CML, LVPECL Termination) CLK to CLK Input Termination, VT to CLK, CLK Maximum Voltage on Output Pins Maximum Output Current Voltage Reference (VREF) Operating Temperature Range Ambient Junction Storage Temperature Range Rating 6.0 V VEE - 0.5 V to VCC + 0.5 V 40 mA 1.8 V 2 V VCC + 0.5 V 35 mA VCC to VEE -40C to +85C 150C -65C to +150C
DETERMINING JUNCTION TEMPERATURE
To determine the junction temperature on the application printed circuit board (PCB), use the following equation: TJ = TCASE + (JT x PD) where: TJ is the junction temperature (C). TCASE is the case temperature (C) measured by the customer at the top center of the package. JT is as indicated in Table 5. PD is the power dissipation. Values of JA are provided for package comparison and PCB design considerations. JA can be used for a first-order approximation of TJ by the equation TJ = TA + (JA x PD) where TA is the ambient temperature (C). Values of JB are provided in Table 5 for package comparison and PCB design considerations.
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 above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ESD CAUTION
THERMAL PERFORMANCE
Table 5.
Parameter Junction-to-Ambient Thermal Resistance Still Air 0.0 m/sec Airflow Moving Air 1.0 m/sec Airflow 2.5 m/sec Airflow Junction-to-Board Thermal Resistance Moving Air 1.0 m/sec Airflow Junction-to-Case Thermal Resistance (Die-to-Heat Sink) Moving Air Junction-to-Top-of-Package Characterization Parameter Still Air 0 m/sec Airflow
1
Symbol
Description
Value1
Unit
JA JMA JMA
Per JEDEC JESD51-2 Per JEDEC JESD51-6 Per JEDEC JESD51-6
54.3 47.5 42.6
C/W C/W C/W
JB JC
Per JEDEC JESD51-8 (moving air) Per MIL-Std. 883, Method 1012.1
33.0 2.0
C/W C/W
JT
Per JEDEC JESD51-2
0.9
C/W
Results are from simulations. The PCB is a JEDEC multilayer type. Thermal performance for actual applications requires careful inspection of the conditions in the application to determine if they are similar to those assumed in these calculations.
Rev. 0 | Page 5 of 12
ADCLK946
VCC Q0 Q0 Q1 Q1 VEE
PIN 1 INDICATOR
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
VEE CLK CLK VREF VT VEE 1 2 3 4 5 6
24 23 22 21 20 19
18 17 16 15 14 13
ADCLK946
TOP VIEW (Not to Scale)
VCC Q2 Q2 Q3 Q3 VCC
VEE Q5 Q5 Q4 Q4 VEE
7 8 9 10 11 12
NOTES: 1. EXPOSED PADDLE MUST BE CONNECTED TO VEE.
Figure 2. Pin Configuration
Table 6. Pin Function Descriptions
Pin No. 1, 6, 7, 12, 19 2 3 4 5 8, 9 10, 11 13, 18, 24 14, 15 16, 17 20, 21 22, 23 Mnemonic VEE CLK CLK VREF VT Q5, Q5 Q4, Q4 VCC Q3, Q3 Q2, Q2 Q1, Q1 Q0, Q0 EPAD Description Negative Supply Pin. Differential Input (Positive). Differential Input (Negative). Reference Voltage. This pin provides the reference voltage for biasing ac-coupled CLK and CLK inputs. Center Tap. This pin provides the center tap of a 100 input resistor for CLK and CLK inputs. Differential LVPECL Outputs. Differential LVPECL Outputs. Positive Supply Pin. Differential LVPECL Outputs. Differential LVPECL Outputs. Differential LVPECL Outputs. Differential LVPECL Outputs. EPAD must be soldered to VEE.
Rev. 0 | Page 6 of 12
08053-002
ADCLK946 TYPICAL PERFORMANCE CHARACTERISTICS
VCC = 3.3 V, VEE = 0.0 V, VICM = VREF, TA = 25C, clock outputs terminated at 50 to VCC - 2 V, unless otherwise noted.
C3
C4
C3
C4
C4 100mV/DIV 500ps/DIV
08053-003
100mV/DIV
100ps/DIV
Figure 3. LVPECL Output Waveform @ 200 MHz
1.8 1.7
DIFFERENTIAL OUTPUT VOLTAGE (V)
Figure 6. LVPECL Output Waveform @ 1000 MHz
189 188
PROPAGATION DELAY (ps)
1.6 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5
08053-004
187 186 185 184 183 182 -40
0
1000
2000
3000
4000
5000
-20
0
20
40
60
80
FREQUENCY (MHz)
TEMPERATURE (C)
Figure 4. Differential Output Swing vs. Frequency
Figure 7. Propagation Delay vs. Temperature
205 200
PROPAGATION DELAY (ps)
205
PROPAGATION DELAY (ps)
195 190 185 180 175 170 165
08053-005
195
+85C 185 +25C 175
-40C
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
1.1
1.3
1.5
1.7
1.9
2.1
2.3
2.5
2.7
2.9
3.1
DIFFERENTIAL INPUT VOLTAGE SWING (V)
DC COMMON-MODE VOLTAGE (V)
Figure 5. Propagation Delay vs. Differential Input Voltage
Figure 8. Propagation Delay vs. Common-Mode Voltage vs. Temperature, Input Slew Rate > 25 V/ns
Rev. 0 | Page 7 of 12
08053-008
160
165 0.9
08053-007
0.4
08053-006
C3
ADCLK946
1.56
DIFFERENTIAL OUTPUT VOLTAGE SWING (V)
-90 -100 -40C
PHASE NOISE (dBc/Hz)
1.54 1.52 1.50 1.48 1.46 1.44 1.42 2.75
-110 -120 -130 -140 -150 -160 -170 10 ADCLK946
+25C
+85C
CLOCK SOURCE 100 1k 10k 100k 1M 10M 100M
08053-011
2.85
2.95
3.05
3.15
3.25
3.35
3.45
3.55
3.65
3.75
POWER SUPPLY (V)
08053-009
FREQUENCY OFFSET (Hz)
Figure 9. Differential Output Swing vs. Power Supply Voltage vs. Temperature, VID = 1.6 V p-p
300 IVCC
Figure 11. Absolute Phase Noise Measured @1 GHz with Agilent E5052
300
250
250 RANDOM JITTER (fS rms)
CURRENT (mA)
200 +85C +25C -40C
200
150
150
100 IVEE 50
100
50
08053-010
2.97
3.30 POWER SUPPLY (V)
3.63
0
5
10
15
20
25
INPUT SLEW RATE (V/ns)
Figure 10. Power Supply Current vs. Power Supply Voltage vs. Temperature, All Outputs Loaded (50 to VCC - 2 V)
Figure 12. RMS Jitter vs. Input Slew Rate, VID Method
Rev. 0 | Page 8 of 12
08053-012
0
0
ADCLK946 FUNCTIONAL DESCRIPTION
CLOCK INPUTS
The ADCLK946 accepts a differential clock input and distributes it to all six LVPECL outputs. The maximum specified frequency is the point at which the output voltage swing is 50% of the standard LVPECL swing (see Figure 4). The device has a differential input equipped with center-tapped, differential, 100 on-chip termination resistors. The input accepts dc-coupled LVPECL, CML, 3.3 V CMOS (single ended), and ac-coupled 1.8 V CMOS, LVDS, and LVPECL inputs. A VREF pin is available for biasing ac-coupled inputs (see Figure 1). Maintain the differential input voltage swing from approximately 400 mV p-p to no more than 3.4 V p-p. See Figure 14 through Figure 17 for various clock input termination schemes. Output jitter performance is degraded by an input slew rate below 1 V/ns, as shown in Figure 12. The ADCLK946 is specifically designed to minimize added random jitter over a wide input slew rate range. Whenever possible, clamp excessively large input signals with fast Schottky diodes because attenuators reduce the slew rate. Input signal runs of more than a few centimeters should be over low loss dielectrics or cables with good high frequency characteristics. Thevenin-equivalent termination uses a resistor network to provide 50 termination to a dc voltage that is below VOL of the LVPECL driver. In this case, VS_DRV on the ADCLK946 should equal VCC of the receiving buffer. Although the resistor combination shown in Figure 15 results in a dc bias point of VS_DRV - 2 V, the actual common-mode voltage is VS_DRV - 1.3 V because there is additional current flowing from the ADCLK946 LVPECL driver through the pull-down resistor. LVPECL Y-termination is an elegant termination scheme that uses the fewest components and offers both odd- and even-mode impedance matching. Even-mode impedance matching is an important consideration for closely coupled transmission lines at high frequencies. Its main drawback is that it offers limited flexibility for varying the drive strength of the emitter-follower LVPECL driver. This can be an important consideration when driving long trace lengths but is usually not an issue.
VS_DRV
ADCLK946
Z0 = 50 VCC - 2V Z0 = 50
VS = VS_DRV
50
08053-014
50
LVPECL
CLOCK OUTPUTS
The specified performance necessitates using proper transmission line terminations. The LVPECL outputs of the ADCLK946 are designed to directly drive 800 mV into a 50 cable or into microstrip/stripline transmission lines terminated with 50 referenced to VCC - 2 V, as shown in Figure 14. The LVPECL output stage is shown in Figure 13. The outputs are designed for best transmission line matching. If high speed signals must be routed more than a centimeter, either the microstrip or the stripline technique is required to ensure proper transition times and to prevent excessive output ringing and pulse-width-dependent, propagation delay dispersion.
VCC
VS_DRV
Figure 14. DC-Coupled, 3.3 V LVPECL
VS_DRV
ADCLK946
50 SINGLE-ENDED (NOT COUPLED) 50 127 127
VCC
LVPECL
Figure 15. DC-Coupled, 3.3 V LVPECL Far-End Thevenin Termination
VS_DRV
ADCLK946
Z0 = 50 50 Z0 = 50
VS = VS_DRV
50
08053-016
50
LVPECL
Figure 16. DC-Coupled, 3.3 V LVPECL Y-Termination
Q Q
100 DIFFERENTIAL 100 (COUPLED) 0.1nF TRANSMISSION LINE
08053-013
VS_DRV
ADCLK946
0.1nF
VCC
LVPECL
Figure 13. Simplified Schematic Diagram of the LVPECL Output Stage
Figure 17. AC-Coupled, LVPECL with Parallel Transmission Line
Figure 14 through Figure 17 depict various LVPECL output termination schemes. When dc-coupled, VCC of the receiving buffer should match the VS_DRV.
Rev. 0 | Page 9 of 12
08053-017
VEE
200
200
08053-015
83
83
ADCLK946
PCB LAYOUT CONSIDERATIONS
The ADCLK946 buffer is designed for very high speed applications. Consequently, high speed design techniques must be used to achieve the specified performance. It is critically important to use low impedance supply planes for both the negative supply (VEE) and the positive supply (VCC) planes as part of a multilayer board. Providing the lowest inductance return path for switching currents ensures the best possible performance in the target application. The following references to the ground plane assume that the VEE power plane is grounded for LVPECL operation. Note that, for ECL operation, the VCC power plane becomes the ground plane. It is also important to adequately bypass the input and output supplies. Place a 1 F electrolytic bypass capacitor within several inches of each VCC power supply pin to the ground plane. In addition, place multiple high quality 0.001 F bypass capacitors as close as possible to each of the VCC supply pins, and connect the capacitors to the ground plane with redundant vias. Carefully select high frequency bypass capacitors for minimum inductance and ESR. To improve the effectiveness of the bypass at high frequencies, minimize parasitic layout inductance. Also, avoid discontinuities along input and output transmission lines that can affect jitter performance. In a 50 environment, input and output matching have a significant impact on performance. The buffer provides internal 50 termination resistors for both CLK and CLK inputs. Normally, the return side is connected to the reference pin that is provided. Carefully bypass the termination potential using ceramic capacitors to prevent undesired aberrations on the input signal due to parasitic inductance in the termination return path. If the inputs are dc-coupled to a source, take care to ensure that the pins are within the rated input differential and common-mode ranges. If the return is floated, the device exhibits a 100 crosstermination, but the source must then control the commonmode voltage and supply the input bias currents. There are ESD/clamp diodes between the input pins to prevent the application from developing excessive offsets to the input transistors. ESD diodes are not optimized for best ac performance. When a clamp is required, it is recommended that appropriate external diodes be used.
Exposed Metal Paddle
The exposed metal paddle on the ADCLK946 package is both an electrical connection and a thermal enhancement. For the device to function properly, the paddle must be properly attached to the VEE pin. When properly mounted, the ADCLK946 also dissipates heat through its exposed paddle. The PCB acts as a heat sink for the ADCLK946. The PCB attachment must provide a good thermal path to a larger heat dissipation area. This requires a grid of vias from the top layer down to the VEE power plane (see Figure 18). The ADCLK946 evaluation board (ADCLK946/PCBZ) provides an example of how to attach the part to the PCB.
VIAS TO VEE POWER PLANE
Figure 18. PCB Land for Attaching Exposed Paddle
Rev. 0 | Page 10 of 12
08053-018
ADCLK946
INPUT TERMINATION OPTIONS
VCC VT 50 CLK CLK
VREF
VT
VREF
50
50 CLK CLK
50
08053-019
CONNECT VT TO VCC.
CONNECT VT TO VREF .
Figure 19. Interfacing to CML Inputs
Figure 21. AC-Coupling Differential Signals Inputs, Such as LVDS
VREF VT
VREF VT VCC - 2V 50 CLK CLK 50
50 CLK CLK
50
08053-020
CONNECT VT TO VCC - 2V.
Figure 20. Interfacing to PECL Inputs
Figure 22. Interfacing to AC-Coupled Single-Ended Inputs
Rev. 0 | Page 11 of 12
08053-022
CONNECT VT, VREF , AND CLK. PLACE A BYPASS CAPACITOR FROM VT TO GROUND. ALTERNATIVELY, VT, VREF , AND CLK CAN BE CONNECTED, GIVING A CLEANER LAYOUT AND A 180 PHASE SHIFT.
08053-021
ADCLK946 OUTLINE DIMENSIONS
4.00 BSC SQ 0.60 MAX 0.60 MAX 0.50 BSC 0.50 0.40 0.30 1.00 0.85 0.80 12 MAX 0.80 MAX 0.65 TYP
19 18 EXPOSED PAD 24 1
PIN 1 INDICATOR *2.45 2.30 SQ 2.15
6
PIN 1 INDICATOR
TOP VIEW
3.75 BSC SQ
(BO OMVIEW) TT
13 12
7
0.23 MIN 2.50 REF
0.05 MAX 0.02 NOM 0.20 REF COPLANARITY 0.08
SEATING PLANE
0.30 0.23 0.18
FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET.
080808-A
*COMPLIANT TO JEDEC STANDARDS MO-220-VGGD-2 EXCEPT FOR EXPOSED PAD DIMENSION
Figure 23. 24-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 4 mm x 4 mm Body, Very Thin Quad CP-24-2 Dimensions shown in millimeters
ORDERING GUIDE
Model ADCLK946BCPZ1 ADCLK946BCPZ-REEL71 ADCLK946/PCBZ1
1
Temperature Range -40C to +85C -40C to +85C
Package Description 24-Lead LFCSP_VQ 24-Lead LFCSP_VQ Evaluation Board
Package Option CP-24-2 CP-24-2
Z = RoHS Compliant Part.
(c)2009 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D08053-0-4/09(0)
Rev. 0 | Page 12 of 12

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