ADCMP581

Ultrafast SiGe Voltage Comparators ADCMP580/ADCMP581/ADCMP582 FEATURES 180 ps propagation delay 25 ps overdrive and slew rate dispersion 8 GHz equivalent input rise time bandwidth 100 ps minimum pulse width 37 ps typical output rise/fall 10 ps deterministic jitter (DJ) 200 fs random jitter (RJ) −2 V to +3 V input range with +5 V/−5 V supplies On-chip terminations at both input pins Resistor-programmable hysteresis Differential latch control Power supply rejection > 70 dB FUNCTIONAL BLOCK DIAGRAM VTP TERMINATION VP NONINVERTING INPUT VN INVERTING INPUT VTN TERMINATION ADCMP580/ ADCMP581/ ADCMP582 Q OUTPUT CML/ECL/ PECL Q OUTPUT LE INPUT HYS LE INPUT Figure 1. APPLICATIONS Automatic test equipment (ATE) High speed instrumentation Pulse spectroscopy Medical imaging and diagnostics High speed line receivers Threshold detection Peak and zero-crossing detectors High speed trigger circuitry Clock and data signal restoration GENERAL DESCRIPTION The ADCMP580/ADCMP581/ADCMP582 are ultrafast voltage comparators fabricated on Analog Devices’ proprietary XFCB3 Silicon Germanium (SiGe) bipolar process. The ADCMP580 features CML output drivers; the ADCMP581 features reduced swing ECL (negative ECL) output drivers; and the ADCMP582 features reduced swing PECL (positive ECL) output drivers. All three comparators offer 180 ps propagation delay and 100 ps minimum pulse width for 10 Gbps operation with 200 fs random jitter (RJ). Overdrive and slew rate dispersion are typically less than 15 ps. The ±5 V power supplies enable a wide −2 V to +3 V input range with logic levels referenced to the CML/NECL/PECL outputs. The inputs have 50 Ω on-chip termination resistors with the optional capability to be left open (on an individual pin basis) for applications requiring high impedance input. The CML output stage is designed to directly drive 400 mV into 50 Ω transmission lines terminated to ground. The NECL output stages are designed to directly drive 400 mV into 50 Ω terminated to −2 V. The PECL output stages are designed to directly drive 400 mV into 50 Ω terminated to VCCO − 2 V. High speed latch and programmable hysteresis are also provided. The differential latch input controls are also 50 Ω terminated to an independent VTT pin to interface to either CML or ECL or to PECL logic. The ADCMP580/ADCMP581/ADCMP582 are available in a 16-lead LFCSP package. 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 © 2005 Analog Devices, Inc. All rights reserved. 04672-001 ADCMP580/ADCMP581/ADCMP582 TABLE OF CONTENTS Specifications..................................................................................... 3 Timing Information ......................................................................... 5 Absolute Maximum Ratings............................................................ 6 Thermal Considerations.............................................................. 6 ESD Caution.................................................................................. 6 Pin Configurations and Function Descriptions ........................... 7 Typical Performance Characteristics ............................................. 8 Typical Application Circuits.......................................................... 10 Application Information................................................................ 11 Power/Ground Layout and Bypassing..................................... 11 ADCMP58x Family of Output Stages ..................................... 11 Using/Disabling the Latch Feature........................................... 11 Optimizing High Speed Performance ..................................... 12 Comparator Propagation Delay Dispersion ........................... 12 Comparator Hysteresis .............................................................. 13 Minimum Input Slew Rate Requirement ................................ 13 Outline Dimensions ....................................................................... 14 Ordering Guide .......................................................................... 14 REVISION HISTORY 7/05—Revision 0: Initial Version Rev. 0 | Page 2 of 16 ADCMP580/ADCMP581/ADCMP582 SPECIFICATIONS VCCI = +5.0 V; VEE = −5.0 V; VCCO = +3.3 V; TA = 25°C, unless otherwise noted. Table 1. Parameter DC INPUT CHARACTERISTICS Input Voltage Range Input Differential Range Input Offset Voltage Offset Voltage Tempco Input Bias Current Input Bias Current Tempco Input Offset Current Input Resistance Input Resistance, Differential Mode Input Resistance, Common Mode Active Gain Common-Mode Rejection Hysteresis LATCH ENABLE CHARACTERISTICS Latch Enable Input Impedance Latch to Output Delay Latch Minimum Pulse Width ADCMP580 (CML) Latch Enable Input Range Latch Enable Input Differential Latch Setup Time Latch Hold Time ADCMP581 (NECL) Latch Enable Input Range Latch Enable Input Differential Latch Setup Time Latch Hold Time ADCMP582 (PECL) Latch Enable Input Range Latch Enable Input Differential Latch Setup Time Latch Hold Time DC OUTPUT CHARACTERISTICS ADCMP580 (CML) Output Impedance Output Voltage High Level Output Voltage Low Level Output Voltage Differential ADCMP581 (NECL) Output Voltage High Level Output Voltage High Level Output Voltage High Level Output Voltage Low Level Output Voltage Low Level Output Voltage Low Level Output Voltage Differential Symbol VP, VN VOS ΔVOS/dT IP, IN ΔIB/dT Condition Min −2.0 −2.0 −10.0 Open termination Typ Max +3.0 +2.0 +10.0 30.0 ±5.0 Unit V V mV μV/°C μA nA/°C μA Ω kΩ kΩ dB dB mV Ω ps ps 0 0.5 V V ps ps V V ps ps V V ps ps Open termination Open termination AV CMRR VCM = −2.0 V to +3.0 V RHYS = ∞ Each pin, VTT at ac ground VOD = 200 mV VOD = 200 mV −0.8 0.2 ±4 10 15 50 2 47 to 53 50 500 48 60 1 47 to 53 175 100 ZIN tPLOH, tPLOL tPL tS tH VOD = 200 mV VOD = 200 mV −1.8 0.2 0.4 95 −90 tS tH VOD = 200 mV VOD = 200 mV VCCO − 1.8 0.2 0.4 70 −65 +0.8 0.5 tS tH VOD = 200 mV VOD = 200 mV 0.4 30 −25 VCCO − 0.8 0.5 ZOUT VOH VOL 50 Ω to GND 50 Ω to GND 50 Ω to GND 50 Ω to −2 V, TA = 125°C 50 Ω to −2 V, TA = 25°C 50 Ω to −2 V, TA = −55°C 50 Ω to −2 V, TA = 125°C 50 Ω to −2 V, TA = 25°C 50 Ω to −2 V, TA = −55°C 50 Ω to −2.0 V −0.10 −0.50 340 −0.99 −1.06 −1.11 −1.43 −1.50 −1.55 340 50 0 −0.40 395 −0.87 −0.94 −0.99 −1.26 −1.33 −1.38 395 0.03 −0.35 450 −0.75 −0.82 −0.87 −1.13 −1.20 −1.25 450 Ω V V mV V V V V V V mV VOH VOH VOH VOL VOL VOL Rev. 0 | Page 3 of 16 ADCMP580/ADCMP581/ADCMP582 Parameter ADCMP582 (PECL) Output Voltage High Level Output Voltage High Level Output Voltage High Level Output Voltage Low Level Output Voltage Low Level Output Voltage Low Level Output Voltage Differential AC PERFORMANCE Propagation Delay Propagation Delay Tempco Prop Delay Skew—Rising Transition to Falling Transition Overdrive Dispersion Slew Rate Dispersion Pulse Width Dispersion Duty Cycle Dispersion 5% to 95% Common-Mode Dispersion Equivalent Input Bandwidth 1 Toggle Rate Deterministic Jitter Deterministic Jitter RMS Random Jitter Minimum Pulse Width Minimum Pulse Width Rise/Fall Time POWER SUPPLY Positive Supply Voltage Negative Supply Voltage ADCMP580 (CML) Positive Supply Current Negative Supply Current Power Dissipation ADCMP581 (NECL) Positive Supply Current Negative Supply Current Power Dissipation ADCMP582 (PECL) Logic Supply Voltage Input Supply Current Output Supply Current Negative Supply Current Power Dissipation Power Supply Rejection (VCCI) Power Supply Rejection (VEE) Power Supply Rejection (VCCO) 1 Symbol VOH VOH VOH VOL VOL VOL Condition Vcco = 3.3 V 50 Ω to VCCO − 2 V, TA = 125°C 50 Ω to VCCO − 2 V, TA = 25°C 50 Ω to VCCO − 2 V, TA = −55°C 50 Ω to VCCO − 2 V, TA = 125°C 50 Ω to VCCO − 2 V, TA = 25°C 50 Ω to VCCO − 2 V, TA = −55°C 50 Ω to VCCO − 2.0 V VOD = 500 mV VOD = 500 mV, 5 V/ns 50 mV < VOD < 1.0 V 10 mV < VOD < 200m V 2 V/ns to 10 V/ns 100 ps to 5 ns 1.0 V/ns, 15 MHz, VCM = 0.0 V VOD = 0.2 V, −2 V < VCM < 3 V 0.0 V to 400 mV input tR = tF = 25 ps, 20/80 >50% output swing VOD = 500 mV, 5 V/ns PRBS31 − 1 NRZ, 5 Gbps VOD = 200 mV, 5 V/ns PRBS31 − 1 NRZ, 10 Gbps VOD = 200 mV, 5 V/ns, 1.25 GHz ΔtPD < 5 ps ΔtPD < 10 ps 20/80 Min VCCO − 0.99 VCCO − 1.06 VCCO − 1.11 VCCO − 1.43 VCCO − 1.50 VCCO − 1.55 340 Typ VCCO − 0.87 VCCO − 0.94 VCCO − 0.99 VCCO − 1.26 VCCO − 1.33 VCCO − 1.35 395 180 0.25 10 10 15 15 15 10 5 8 12.5 15 25 0.2 100 80 37 Max VCCO − 0.75 VCCO − 0.82 VCCO − 0.87 VCCO − 1.13 VCCO − 1.20 VCCO − 1.25 450 Unit V V V V V V mV ps ps/°C ps ps ps ps ps ps ps/V GHz Gbps ps ps ps ps ps ps tPD ΔtPD/dT BWEQ DJ DJ RJ PWMIN PWMIN tR, tF VCCI VEE IVCCI IVEE PD IVCCI IVEE PD VCCO IVCCI IVCCO IVEE PD PSRVCCI PSRVEE PSRVCCO +4.5 −5.5 VCCI = +5.0 V, 50 Ω to GND VEE = −5.0 V, 50 Ω to GND 50 Ω to GND VCCI = +5.0 V, 50 Ω to −2 V VEE = −5.0 V, 50 Ω to −2 V 50 Ω to −2 V +5.0 −5.0 +5.5 −4.5 8 −34 260 8 −19 200 +5.0 8 55 −19 350 V V mA mA mW mA mA mW V mA mA mA mW dB dB dB −50 6 −40 230 6 −25 155 +3.3 6 44 −25 310 −75 −60 −75 −35 +2.5 VCCI = +5.0 V, 50 Ω to VCCO − 2 V VCCO = +5.0 V, 50 Ω to VCCO − 2 V VEE = −5.0 V, 50 Ω to VCCO − 2 V 50 Ω to VCCO − 2 V VCCI = 5.0 V + 5% VEE = −5.0 V + 5% VCCO = 3.3 V + 5% (ADCMP582) −35 Equivalent input bandwidth assumes a simple first-order input response and is calculated with the following formula: BWEQ = 0.22/(trCOMP2 – trIN2), where trIN is the 20/80 transition time of a quasi-Gaussian input edge applied to the comparator input and trCOMP is the effective transition time digitized by the comparator. Rev. 0 | Page 4 of 16 ADCMP580/ADCMP581/ADCMP582 TIMING INFORMATION Figure 2 shows the ADCMP580/ADCMP581/ADCMP582 compare and latch timing relationships. Table 2 provides the definitions of the terms shown in the figure. LATCH ENABLE 50% LATCH ENABLE tS tH tPL DIFFERENTIAL INPUT VOLTAGE VN VOD VN ± VOS tPDL Q OUTPUT tPLOH 50% tPDH tF 50% Q OUTPUT tR Figure 2. Comparator Timing Diagram Table 2. Timing Descriptions Symbol tPDH tPDL tPLOH tPLOL tH tPL tS tR tF VN VOD Timing Input to Output High Delay Input to Output Low Delay Latch Enable to Output High Delay Latch Enable to Output Low Delay Minimum Hold Time Minimum Latch Enable Pulse Width Minimum Setup Time Output Rise Time Output Fall Time Normal Input Voltage Voltage Overdrive Description Propagation delay measured from the time the input signal crosses the reference (± the input offset voltage) to the 50% point of an output low-to-high transition. Propagation delay measured from the time the input signal crosses the reference (± the input offset voltage) to the 50% point of an output high-to-low transition. Propagation delay measured from the 50% point of the latch enable signal low-to-high transition to the 50% point of an output low-to-high transition. Propagation delay measured from the 50% point of the latch enable signal low-to-high transition to the 50% point of an output high-to-low transition. Minimum time after the negative transition of the latch enable signal that the input signal must remain unchanged to be acquired and held at the outputs. Minimum time that the latch enable signal must be high to acquire an input signal change. Minimum time before the negative transition of the latch enable signal that an input signal change must be present to be acquired and held at the outputs. Amount of time required to transition from a low to a high output as measured at the 20% and 80% points. Amount of time required to transition from a high to a low output as measured at the 20% and 80% points. Difference between the input voltages VP and VN for output true. Difference between the input voltages VP and VN for output false. Rev. 0 | Page 5 of 16 04672-028 tPLOL ADCMP580/ADCMP581/ADCMP582 ABSOLUTE MAXIMUM RATINGS Table 3. Parameter SUPPLY VOLTAGES Positive Supply Voltage (VCCI to GND) Negative Supply Voltage (VEE to GND) Logic Supply Voltage (VCCO to GND) INPUT VOLTAGES Input Voltage Differential Input Voltage Input Voltage, Latch Enable HYSTERESIS CONTROL PIN Applied Voltage (HYS to VEE) Maximum Input/Output Current OUTPUT CURRENT ADCMP580 (CML) ADCMP581 (NECL) ADCMP582 (PECL) TEMPERATURE Operating Temperature, Ambient Operating Temperature, Junction Storage Temperature Range Rating −0.5 V to +6.0 V –6.0 V to +0.5 V −0.5 V to +6.0 V Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. THERMAL CONSIDERATIONS −3.0 V to +4.0 V −2 V to +2 V −2.5 V to +5.5 V −5.5 V to +0.5 V 1 mA −25 mA −40 mA −40 mA −40°C to +125°C 125°C −65°C to +150°C The ADCMP580/ADCMP581/ADCMP582 LFCSP 16-lead package option has a θJA (junction-to-ambient thermal resistance) of 70°C/W in still air. 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 6 of 16 ADCMP580/ADCMP581/ADCMP582 PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS 15 GND 15 GND 16 VCCI 15 GND 16 VCCI 16 VCCI 14 HYS 14 HYS 13 VEE 13 VEE 14 HYS 13 VEE VTP 1 VP 2 VN 3 VTN 4 PIN 1 INDICATOR 12 GND 11 Q 10 Q 9 GND VTP 1 VP 2 VN 3 VTN 4 PIN 1 INDICATOR 12 GND 11 Q 10 Q 9 GND VTP 1 VP 2 VN 3 VTN 4 PIN 1 INDICATOR 12 VCCO 11 Q 10 Q 9 VCCO ADCMP580 TOP VIEW (Not to Scale) ADCMP581 TOP VIEW (Not to Scale) ADCMP582 TOP VIEW (Not to Scale) VTT 8 VTT 8 VCCI 5 VCCI 5 VCCI 5 04672-002 04672-003 VTT 8 LE 7 LE 7 LE 7 LE 6 LE 6 LE 6 Figure 3. ADCMP580 Pin Configuration Figure 4. ADCMP581 Pin Configuration Figure 5. ADCMP582 Pin Configuration Table 4. Pin Function Descriptions Pin No. 1 2 3 4 5, 16 6 Mnemonic VTP VP VN VTN VCCI LE Description Termination Resistor Return Pin for VP Input. Noninverting Analog Input. Inverting Analog Input. Termination Resistor Return Pin for VN Input. Positive Supply Voltage. Latch Enable Input Pin, Inverting Side. In compare mode (LE = low), the output tracks changes at the input of the comparator. In latch mode (LE = high), the output reflects the input state just prior to the comparator being placed into latch mode. LE must be driven in complement with LE. Latch Enable Input Pin, Noninverting Side. In compare mode (LE = high), the output tracks changes at the input of the comparator. In latch mode (LE = low), the output reflects the input state just prior to the comparator being placed into latch mode. LE must be driven in complement with LE. Termination Return Pin for the LE/LE Input Pins. For the ADCMP580 (CML output stage), this pin should be connected to the GND ground. For the ADCMP581 (ECL output stage), this pin should be connected to the –2 V termination potential. For the ADCMP582 (PECL output stage), this pin should be connected to the VCCO – 2 V termination potential. Digital Ground Pin/Positive Logic Power Supply Terminal. For the ADCMP580/ADCMP581, this pin should be connected to the GND pin. For the ADCMP582, this pin should be connected to the positive logic power VCCO supply. Inverting Output. Q is logic low if the analog voltage at the noninverting input, VP, is greater than the analog voltage at the inverting input, VN, provided that the comparator is in compare mode. See the LE/LE descriptions (Pin 6 to Pin 7) for more information. Noninverting Output. Q is logic high if the analog voltage at the noninverting input, VP, is greater than the analog voltage at the inverting input, VN, provided that the comparator is in compare mode. See the LE/LE descriptions (Pin 6 to Pin 7) for more information. Negative Power Supply. Hysteresis Control. Leave this pin disconnected for zero hysteresis. Connect this pin to the VEE supply with a suitably sized resistor to add the desired amount of hysteresis. Refer to Figure 9 for proper sizing of the HYS hysteresis control resistor. Analog Ground. The metallic back surface of the package is not electrically connected to any part of the circuit. It can be left floating for optimal electrical isolation between the package handle and the substrate of the die. It can also be soldered to the application board if improved thermal and/or mechanical stability is desired. 7 LE 8 VTT 9, 12 GND/VCCO 10 Q 11 Q 13 14 VEE HYS 15 Heat Sink Paddle GND N/C Rev. 0 | Page 7 of 16 04672-004 ADCMP580/ADCMP581/ADCMP582 TYPICAL PERFORMANCE CHARACTERISTICS VCCI = +5.0 V, VEE = −5.0 V, VCCO = +3.3 V, TA = 25°C, unless otherwise noted. 12 80 70 10 VIN COMMON-MODE BIAS SWEEP 60 HYSTERESIS (mV) BIAS CURRENT (μA) 8 50 40 30 20 6 4 2 04672-005 04672-009 10 0 0 10 100 RESISTOR (Ω) 1k 0 –4 –2 0 COMMON MODE (V) 2 4 10k Figure 6. Bias Current vs. Common-Mode Voltage Figure 9. Hysteresis vs. RHYS Control Resistor –0.8 VOH VS TEMP OUTPUT (NECL) –0.9 2.5 2.4 VOH VS TEMP OUTPUT (PECL) 2.3 OUTPUT (V) –1.0 OUTPUT (V) –1.1 2.2 –1.2 VOL VS TEMP OUTPUT (NECL) –1.3 2.1 04672-007 VOL VS TEMP OUTPUT (PECL) 1.9 –55 –1.5 –55 –5 45 TEMP (°C) 95 145 –5 45 TEMP (°C) 95 145 Figure 7. ADCMP581 Output Voltage vs. Temperature Figure 10. ADCMP582 Output Voltage vs. Temperature 80 70 60 HYSTERESIS (mV) OFFSET (mV) 8 125°C COMMON-MODE OFFSET SWEEP 7 6 5 4 3 25°C COMMON-MODE OFFSET SWEEP 2 –55°C COMMON-MODE OFFSET SWEEP 04672-008 04672-011 50 40 30 20 10 0 0 100 200 300 –IHYST (μA) 400 500 1 0 –2 600 0 2 4 COMMON-MODE (V) Figure 8. Hysteresis vs. −IHYST Rev. 0 | Page 8 of 16 Figure 11. A Typical VOS vs. Common- Mode Voltage 04672-010 –1.4 2.0 ADCMP580/ADCMP581/ADCMP582 5 4 3 2 45 43 41 39 TPD ERROR (ps) TR/TF (ps) LOT2 CHAR1 RISE LOT2 CHAR1 FALL LOT3 CHAR1 RISE LOT3 CHAR1 FALL –1 0 VCM (V) 1 2 3 1 0 –1 –2 –3 –4 –5 –2 37 35 33 31 29 QBARRISE QRISE QBARFALL QFALL –35 –15 5 25 45 65 85 105 04672-031 27 25 –55 125 TEMPERATURE (°C) Figure 12. ADCMP580 Prop Delay vs. Common-Mode Voltage Figure 15. ADCMP581 TR/TF vs. Temperature 500mV M1 M1 M1 M1 04672-029 500mV 20ps/DIV Figure 13. ADCMP580 Eye Diagram at 7.5 Gbps Figure 16. ADCMP582 Eye Diagram at 2.5 Gbps 18 16 14 DISPERSION (PS) 12 10 8 6 4 2 OD DISPERSION RISE 0 0 50 100 150 200 OVERDRIVE (mV) OD DISPERSION FALL 04672-032 250 Figure 14. Dispersion vs. Overdrive Rev. 0 | Page 9 of 16 04672-030 04672-033 ADCMP580/ADCMP581/ADCMP582 TYPICAL APPLICATION CIRCUITS GND VTP VIN VP VN VTN 50Ω 50Ω Q VP VN ADCMP580 CML ADCMP580 Q 1.5kΩ 50Ω 50Ω 04672-025 LATCH INPUTS Figure 17. Zero-Crossing Detector with CML Outputs 04672-020 VEE Figure 21. Disabling the Latch Feature on the ADCMP580 VTP VP VN VTN VP VN Q ADCMP581 Q 50Ω VTT LATCH INPUTS 50Ω VP VN ADCMP581 50Ω 450Ω RSECL 50Ω 04672-023 04672-021 VTT VEE Figure 18. LVDS to a 50 Ω Back-Terminated (RS) ECL Receiver Figure 22. Disabling the Latch Feature on the ADCMP581 ADCMP580 HYS VP VN ADCMP582 RSPECL 04672-026 0Ω TO 5kΩ 50Ω 50Ω 1kΩ 50Ω 50Ω 04672-027 VEE VTT Figure 19. Adding Hysteresis Using the HYS Control Figure 23. Disabling the Latch Feature on the ADCMP582 GND 50Ω VIN VTH + 50Ω Q Q ADCMP580 – Figure 20. Comparator with −2 to +3 V Input Range 04672-022 LATCH INPUTS Rev. 0 | Page 10 of 16 ADCMP580/ADCMP581/ADCMP582 APPLICATION INFORMATION POWER/GROUND LAYOUT AND BYPASSING The ADCMP58x family of comparators 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, particularly for the negative supply (VEE), the output supply plane (VCCO), and the ground plane (GND). Individual supply planes are recommended as part of a multilayer board. Providing the lowest inductance return path for the switching currents ensures the best possible performance in the target application. It is also important to adequately bypass the input and output supplies. A 1 μF electrolytic bypass capacitor should be placed within several inches of each power supply pin to ground. In addition, multiple high quality 0.1 μF bypass capacitors should be placed as close as possible to each of the VEE, VCCI, and VCCO supply pins and should be connected to the GND plane with redundant vias. High frequency bypass capacitors should be carefully selected for minimum inductance and ESR. Parasitic layout inductance should be strictly avoided to maximize the effectiveness of the bypass at high frequencies. GND 50Ω 50Ω Q Q 16mA 04672-014 VEE Figure 24. Simplified Schematic Diagram of the ADCMP580 CML Output Stage GND / Vcco ADCMP58x FAMILY OF OUTPUT STAGES Specified propagation delay dispersion performance is achieved by using proper transmission line terminations. The outputs of the ADCMP580 family comparators are designed to directly drive 400 mV into 50 Ω cable or microstrip/stripline transmission lines terminated with 50 Ω referenced to the proper return. The CML output stage is shown in the simplified schematic diagram in Figure 24. Each output is back-terminated with 50 Ω for best transmission line matching. The outputs of the ADCMP581/ADCMP582 are illustrated in Figure 25; they should be terminated to −2 V for ECL outputs of ADCMP581 and VCCO − 2 V for PECL outputs of ADCMP582. As an alternative, Thevenin equivalent termination networks may also be used. If these high speed signals must be routed more than a centimeter, then either microstrip or stripline techniques are required to ensure proper transition times and to prevent excessive output ringing and pulse width-dependent propagation delay dispersion. Q Q VEE Figure 25. Simplified Schematic Diagram of the ADCMP581/ADCMP582 ECL/PECL Output Stage USING/DISABLING THE LATCH FEATURE The latch inputs (LE/LE) are active low for latch mode and are internally terminated with 50 Ω resistors to the VTT pin. When using the ADCMP580, VTT should be connected to ground. When using the ADCMP581, VTT should be connected to −2 V. When using the ADCMP582, VTT should be connected externally to VCCO − 2 V, preferably with its own low inductance plane. When using the ADCMP580/ADCMP582, the latch function can be disabled by connecting the LE pin to VEE with an external pull-down resistor and leaving the LE pin disconnected. To prevent excessive power dissipation, the resistor should be 1.5 kΩ for the ADCMP580 and 1 kΩ for the ADCMP582. When using the ADCMP581 comparators, the latch can be disabled by connecting the LE pin to GND with an external 450 Ω resistor and leaving the LE pin disconnected. The idea is to create an approximate 0.5 V offset using the internal resistor as half of the voltage divider. The VTT pin should be connected as recommended. Rev. 0 | Page 11 of 16 04672-015 ADCMP580/ADCMP581/ADCMP582 OPTIMIZING HIGH SPEED PERFORMANCE As with any high speed comparator, proper design and layout techniques are essential to obtaining the specified performance. Stray capacitance, inductance, inductive power, and ground impedances or other layout issues can severely limit performance and can cause oscillation. Discontinuities along input and output transmission lines can also severely limit the specified pulse width dispersion performance. For applications in a 50 Ω environment, input and output matching have a significant impact on data-dependent (or deterministic) jitter (DJ) and pulse width dispersion performance. The ADCMP58x family of comparators provides internal 50 Ω termination resistors for both VP and VN inputs. The return side for each termination is pinned out separately with the VTP and VTN pins, respectively. If a 50 Ω termination is desired at one or both of the VP/VN inputs, the VTP and VTN pins can be connected (or disconnected) to (from) the desired termination potential as appropriate. The termination potential should be carefully bypassed using ceramic capacitors as discussed previously to prevent undesired aberrations on the input signal due to parasitic inductance in the termination return path. If a 50 Ω termination is not desired, either one or both of the VTP/VTN termination pins can be left disconnected. In this case, the open pins should be left floating with no external pull downs or bypassing capacitors. For applications that require high speed operation but do not have on-chip 50 Ω termination resistors, some reflections should be expected, because the comparator inputs can no longer provide matched impedance to the input trace leading up to the device. It then becomes important to back-match the drive source impedance to the input transmission path leading to the input to minimize multiple reflections. For applications in which the comparator is less than 1 cm from the driving signal source, the source impedance should be minimized. High source impedance in combination with parasitic input capacitance of the comparator could cause undesirable degradation in bandwidth at the input, thus degrading the overall response. It is therefore recommended that the drive source impedance should be no more than 50 Ω for best high speed performance. COMPARATOR PROPAGATION DELAY DISPERSION The ADCMP58x family of comparators has been specifically designed to reduce propagation delay dispersion over a wide input overdrive range of 5 mV to 500 mV. Propagation delay dispersion is a change in propagation delays, which results from a change in the degree of overdrive or slew rate (how far or fast the input signal exceeds the switching threshold). The overall result is a higher degree of timing accuracy. Propagation delay dispersion is a specification that becomes important in critical timing applications, such as data communication, automatic test and measurement, instrumentation, and event-driven applications, such as pulse spectroscopy, nuclear instrumentation, and medical imaging. Dispersion is defined as the variation in the overall propagation delay as the input overdrive conditions are changed (see Figure 26 and Figure 27). For the ADCMP58x family of comparators, dispersion is typically