Ultrafast SiGe
Voltage Comparators
ADCMP580/ADCMP581/ADCMP582
FEATURES
FUNCTIONAL BLOCK DIAGRAM
VCCI
VTP TERMINATION
VP NONINVERTING
INPUT
VN INVERTING
INPUT
VCCO
ADCMP580/
ADCMP581/
ADCMP582
Q OUTPUT
CML/ECL/
PECL
Q OUTPUT
VEE
VTN TERMINATION
LE INPUT
HYS
LE INPUT
VEE
APPLICATIONS
04672-001
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
Figure 1.
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 the Analog Devices, Inc. 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 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_VQ.
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.
Rev. A
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 ©2005–2007 Analog Devices, Inc. All rights reserved.
ADCMP580/ADCMP581/ADCMP582
TABLE OF CONTENTS
Features .............................................................................................. 1
Typical Application Circuits ......................................................... 10
Applications....................................................................................... 1
Application Information................................................................ 11
Functional Block Diagram .............................................................. 1
Power/Ground Layout and Bypassing..................................... 11
General Description ......................................................................... 1
ADCMP58x Family of Output Stages ..................................... 11
Revision History ............................................................................... 2
Using/Disabling the Latch Feature........................................... 11
Specifications..................................................................................... 3
Optimizing High Speed Performance ..................................... 12
Timing Information ......................................................................... 5
Comparator Propagation Delay Dispersion............................... 12
Absolute Maximum Ratings............................................................ 6
Comparator Hysteresis .............................................................. 13
Thermal Considerations.............................................................. 6
Minimum Input Slew Rate Requirement ................................ 13
ESD Caution.................................................................................. 6
Outline Dimensions ....................................................................... 14
Pin Configurations and Function Descriptions ........................... 7
Ordering Guide .......................................................................... 14
Typical Performance Characteristics ............................................. 8
REVISION HISTORY
8/07—Rev. 0 to Rev. A
Changes to Figure 1.......................................................................... 1
Changes to Table 4............................................................................ 7
Changes to Figure 9.......................................................................... 8
Changes to Figure 21, Figure 22, and Figure 23 ......................... 10
Changes to Using/Disabling the Latch Feature .......................... 11
Changes to Comparator Hysteresis Section and Figure 29....... 13
Changes to Ordering Guide .......................................................... 14
7/05—Revision 0: Initial Version
Rev. A | 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 Temperature Coefficient
Input Bias Current
Input Bias Current Temperature Coefficient
Input Offset Current
Input Resistance
Input Resistance, Differential Mode
Input Resistance, Common Mode
Active Gain
Common-Mode Rejection Ratio
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
Condition
VP, VN
VOS
ΔVOS/dT
IP, IN
ΔIB/dT
Min
−2.0
−2.0
−10.0
VCM = −2.0 V to +3.0 V
RHYS = ∞
±4
10
15
50
+2
47 to 53
50
500
48
60
1
Each pin, VTT at ac ground
VOD = 200 mV
VOD = 200 mV
47 to 53
175
100
Open termination
Open termination
Open termination
AV
CMRR
ZIN
tPLOH, tPLOL
tPL
−0.8
0.2
tS
tH
VOD = 200 mV
VOD = 200 mV
−1.8
0.2
tS
tH
VOD = 200 mV
VOD = 200 mV
VCCO − 1.8
0.2
tS
tH
ZOUT
VOH
VOL
VOH
VOH
VOH
VOL
VOL
VOL
Typ
VOD = 200 mV
VOD = 200 mV
0.4
95
−90
0.4
70
−65
0.4
30
−25
Max
Unit
+3.0
+2.0
+10.0
V
V
mV
μV/°C
μA
nA/°C
μA
Ω
kΩ
kΩ
dB
dB
mV
30.0
±5.0
Ω
ps
ps
0
0.5
V
V
ps
ps
+0.8
0.5
V
V
ps
ps
VCCO − 0.8
0.5
V
V
ps
ps
50 Ω to GND
50 Ω to GND
50 Ω to GND
−0.10
−0.50
340
50
0
−0.40
395
+0.03
−0.35
450
Ω
V
V
mV
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
−0.99
−1.06
−1.11
−1.43
−1.50
−1.55
340
−0.87
−0.94
−0.99
−1.26
−1.33
−1.38
395
−0.75
−0.82
−0.87
−1.13
−1.20
−1.25
450
V
V
V
V
V
V
mV
Rev. A | 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 Temperature Coefficient
Propagation Delay Skew—Rising
Transition to Falling Transition
Overdrive Dispersion
VOH
VOH
VOH
VOL
VOL
VOL
tPD
ΔtPD/dT
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
Min
Typ
Max
Unit
VCCO − 0.99
VCCO − 1.06
VCCO − 1.11
VCCO − 1.43
VCCO − 1.50
VCCO − 1.55
340
VCCO − 0.87
VCCO − 0.94
VCCO − 0.99
VCCO − 1.26
VCCO − 1.33
VCCO − 1.35
395
VCCO − 0.75
VCCO − 0.82
VCCO − 0.87
VCCO − 1.13
VCCO − 1.20
VCCO − 1.25
450
V
V
V
V
V
V
mV
VOD = 500 mV
VOD = 500 mV, 5 V/ns
Slew Rate Dispersion
Pulse Width Dispersion
Duty Cycle Dispersion 5% to 95%
Common-Mode Dispersion
Equivalent Input Bandwidth 1
BWEQ
Toggle Rate
Deterministic Jitter
DJ
Deterministic Jitter
DJ
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
RJ
PWMIN
PWMIN
tR, tF
50 mV < VOD < 1.0 V
10 mV < VOD < 200 mV
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
VCCI
VEE
180
0.25
10
ps
ps/°C
ps
10
15
15
15
10
5
8
ps
ps
ps
ps
ps
ps/V
GHz
12.5
15
Gbps
ps
25
ps
0.2
100
80
37
ps
ps
ps
ps
+4.5
−5.5
+5.0
−5.0
+5.5
−4.5
V
V
IVCCI
IVEE
PD
VCCI = 5.0 V, 50 Ω to GND
VEE = −5.0 V, 50 Ω to GND
50 Ω to GND
−50
6
−40
230
8
−34
260
mA
mA
mW
IVCCI
IVEE
PD
VCCI = 5.0 V, 50 Ω to −2 V
VEE = −5.0 V, 50 Ω to −2 V
50 Ω to −2 V
−35
6
−25
155
8
−19
200
mA
mA
mW
VCCO
IVCCI
IVCCO
IVEE
PD
PSRVCCI
PSRVEE
PSRVCCO
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)
+3.3
6
44
−25
310
−75
−60
−75
+5.0
8
55
−19
350
V
mA
mA
mA
mW
dB
dB
dB
+2.5
−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. A | 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 Figure 2.
LATCH ENABLE
50%
LATCH ENABLE
tS
tPL
tH
DIFFERENTIAL
INPUT VOLTAGE
VN
VN ± VOS
VOD
tPDL
tPLOH
Q OUTPUT
50%
tF
tPDH
tPLOL
tR
04672-028
50%
Q OUTPUT
Figure 2. Comparator Timing Diagram
Table 2. Timing Descriptions
Symbol
tPDH
Timing
Input-to-Output High Delay
tPDL
Input-to-Output Low Delay
tPLOH
Latch Enable-to-Output High Delay
tPLOL
Latch Enable-to-Output Low Delay
tH
Minimum Hold Time
tPL
tS
Minimum Latch Enable Pulse Width
Minimum Setup Time
tR
Output Rise Time
tF
Output Fall Time
VN
VOD
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. A | Page 5 of 16
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 Range, 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
−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
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.
THERMAL CONSIDERATIONS
The ADCMP580/ADCMP581/ADCMP582 16-lead LFCSP
option has a θJA (junction-to-ambient thermal resistance) of
70°C/W in still air.
ESD CAUTION
−25 mA
−40 mA
−40 mA
−40°C to +125°C
125°C
−65°C to +150°C
Rev. A | Page 6 of 16
ADCMP580/ADCMP581/ADCMP582
Figure 3. ADCMP580 Pin Configuration
Figure 4. ADCMP581 Pin Configuration
14 HYS
13 VEE
TOP VIEW
(Not to Scale)
VCCI 5
VTN 4
9 GND
ADCMP582
12 VCCO
11 Q
10 Q
9 VCCO
04672-005
VN 3
VTT 8
10 Q
LE 7
VP 2
15 GND
16 VCCI
11 Q
PIN 1
INDICATOR
LE 6
VTP 1
04672-004
14 HYS
13 VEE
15 GND
TOP VIEW
(Not to Scale)
12 GND
VTT 8
VTN 4
9 GND
ADCMP581
LE 7
VN 3
10 Q
VCCI 5
14 HYS
16 VCCI
VP 2
11 Q
PIN 1
INDICATOR
LE 6
VTP 1
12 GND
04672-003
VTT 8
LE 7
TOP VIEW
(Not to Scale)
VCCI 5
VTN 4
ADCMP580
LE 6
VN 3
13 VEE
PIN 1
INDICATOR
VTP 1
VP 2
15 GND
16 VCCI
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
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
7
LE
8
VTT
9, 12
GND/VCCO
10
Q
11
Q
13
14
VEE
HYS
15
Heat Sink
Paddle
GND
N/C
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. Exposed metal
at package corners is connected to the heat sink paddle.
Rev. A | Page 7 of 16
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
60
HYSTERESIS (mV)
BIAS CURRENT (µA)
VIN COMMON-MODE BIAS SWEEP
8
6
4
50
40
30
20
2
–2
0
2
4
COMMON-MODE (V)
0
04672-006
0
–4
10
1
100
Figure 6. Bias Current vs. Common-Mode Voltage
10k
Figure 9. Hysteresis vs. RHYS Control Resistor
–0.8
2.5
VOH vs. TEMPERATURE
OUTPUT (NECL)
–0.9
2.4
VOH vs. TEMPERATURE
OUTPUT (PECL)
–1.0
OUTPUT (V)
2.3
–1.1
–1.2
2.1
VOL vs. TEMPERATURE
OUTPUT (NECL)
–1.3
2.2
2.0
–1.4
VOL vs. TEMPERATURE
OUTPUT (PECL)
–5
45
95
145
TEMPERATURE (°C)
1.9
–55
04672-007
–1.5
–55
–5
45
95
145
TEMPERATURE (°C)
Figure 7. ADCMP581 Output Voltage vs. Temperature
04672-010
OUTPUT (V)
1k
RHYS CONTROL RESISTOR (Ω)
04672-009
10
Figure 10. ADCMP582 Output Voltage vs. Temperature
80
8
70
7
60
6
50
5
OFFSET (mV)
40
30
4
3
+25°C COMMON-MODE OFFSET SWEEP
2
10
1
0
0
100
200
300
400
–IHYST (µA)
500
600
Figure 8. Hysteresis vs. −IHYST
–55°C COMMON-MODE OFFSET SWEEP
0
–2
0
2
COMMON-MODE (V)
Figure 11. A Typical VOS vs. Common-Mode Voltage
Rev. A | Page 8 of 16
4
04672-011
20
04672-008
HYSTERESIS (mV)
+125°C COMMON-MODE OFFSET SWEEP
45
4
43
3
41
2
39
1
37
tR/tF (ps)
5
0
–1
35
33
31
LOT2 CHAR1 RISE
LOT2 CHAR1 FALL
LOT3 CHAR1 RISE
LOT3 CHAR1 FALL
–3
–4
–5
–2
–1
29
QRISE
QRISE
QFALL
QFALL
27
0
1
2
3
VCM (V)
25
–55
–35
–15
5
25
45
65
85
105
125
TEMPERATURE (°C)
Figure 12. ADCMP580 Propagation Delay Error vs. Common-Mode Voltage
Figure 15. ADCMP581 tR/tF vs. Temperature
500mV
M1
M1
M1
500mV
Figure 16. ADCMP582 Eye Diagram at 2.5 Gbps
Figure 13. ADCMP580 Eye Diagram at 7.5 Gbps
18
16
12
10
8
6
OD DISPERSION FALL
2
0
OD DISPERSION RISE
0
50
100
150
OVERDRIVE (mV)
200
250
04672-014
DISPERSION (ps)
14
4
20ps/DIV
Figure 14. Dispersion vs. Overdrive
Rev. A | Page 9 of 16
04672-016
04672-013
M1
04672-015
–2
04672-012
PROPAGATION DELAY ERROR (ps)
ADCMP580/ADCMP581/ADCMP582
ADCMP580/ADCMP581/ADCMP582
TYPICAL APPLICATION CIRCUITS
GND
VTP
50Ω
50Ω
VP
VIN
VN
VP
VN
Q
ADCMP580
ADCMP580
CML
Q
VTN
50Ω
VEE
04672-017
LATCH
INPUTS
50Ω
04672-021
1kΩ
Figure 21. Disabling the Latch Feature on the ADCMP580
Figure 17. Zero-Crossing Detector with CML Outputs
VTP
VN
Q
VP
ADCMP581
VN
Q
VTN
50Ω
50Ω
750Ω
VP
ADCMP580
VN
HYS
50Ω
VEE
VCCO
Figure 19. Adding Hysteresis Using the HYS Control
VIN
VTH
–
50Ω
Q
ADCMP580
04672-020
Q
LATCH
INPUTS
50Ω
VTT
VEE
RSPECL
50Ω
50Ω
VTT = VCCO – 2V
Figure 23. Disabling the Latch Feature on the ADCMP582
GND
50Ω
50Ω
ADCMP582
750Ω
04672-019
50Ω
RSECL
Figure 22. Disabling the Latch Feature on the ADCMP581
Figure 18. LVDS to a 50 Ω Back-Terminated (RS) ECL Receiver
+
VTT = –2V
04672-018
VTT
LATCH
INPUTS
0Ω TO 5kΩ
ADCMP581
04672-022
VN
04672-023
VP
VP
Figure 20. Comparator with −2 to +3 V Input Range
Rev. A | Page 10 of 16
ADCMP580/ADCMP581/ADCMP582
APPLICATION INFORMATION
GND
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.
50Ω
Q
Q
16mA
VEE
04672-024
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.
50Ω
Figure 24. Simplified Schematic Diagram of the ADCMP580 CML Output Stage
GND/VCCO
Q
ADCMP58x FAMILY OF OUTPUT STAGES
VEE
04672-025
Q
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 for the ADCMP580 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
can also be used. If these high speed signals must be routed
more than a centimeter, 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.
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, the latch function can be disabled
by connecting the LE pin to VEE with an external pull-down
resistor and by leaving the LE pin to ground. To prevent excessive
power dissipation, the resistor should be 1 kΩ for the ADCMP580.
When using the ADCMP581 comparators, the latch can be
disabled by connecting the LE pin to VEE with an external 750 Ω
resistor and leaving the LE pin connected to −2 V. 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. A | Page 11 of 16
ADCMP580/ADCMP581/ADCMP582
OPTIMIZING HIGH SPEED PERFORMANCE
COMPARATOR PROPAGATION DELAY DISPERSION
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.
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 that 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.
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.
Propagation delay dispersion is a specification that becomes
important in critical timing applications, such as data communications, 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
