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Ultrafast, 4 ns Single-Supply Comparators AD8611/AD8612
FEATURES
4 ns propagation delay at 5 V Single-supply operation: 3 V to 5 V 100 MHz input Latch function
PIN CONFIGURATIONS
V+ 1 IN+ 2 IN- 3
8
QA QA
06010-001
06010-003
AD8611
7
6 GND TOP VIEW V- 4 (Not to Scale) 5 LATCH
APPLICATIONS
High speed timing Clock recovery and clock distribution Line receivers Digital communications Phase detectors High speed sampling Read channel detection PCMCIA cards Zero-crossing detector High speed analog-to-digital converter (ADC) Upgrade for LT1394 and LT1016 designs
Figure 1. 8-Lead Narrow Body SOIC (R-8)
V+ 1 IN+ 2 IN- 3 V- 4
8
QA QA LATCH
06010-002
AD8611
TOP VIEW (Not to Scale)
7 6 5
GND
Figure 2. 8-Lead MSOP (RM-8)
QA QA GND LEA V- INA- INA+
1 2 3 4 5 6 7 14 QB 13 QB
AD8612
TOP VIEW (Not to Scale)
12 GND 11 LEB 10 V+ 9 8
INB- INB+
Figure 3. 14-Lead TSSOP (RU-14)
GENERAL DESCRIPTION
The AD8611/AD8612 are single and dual 4 ns comparators with latch function and complementary output. The latch is not functional if VCC is less than 4.3 V. Fast 4 ns propagation delay makes the AD8611/AD8612 good choices for timing circuits and line receivers. Propagation delays for rising and falling signals are closely matched and tracked over temperature. This matched delay makes the AD8611/AD8612 good choices for clock recovery because the duty cycle of the output matches the duty cycle of the input. The AD8611 has the same pinout as the LT1016 and LT1394, with lower supply current and a wider common-mode input range, which includes the negative supply rail. The AD8611/AD8612 are specified over the industrial temperature range (-40C to +85C). The AD8611 is available in both 8-lead MSOP and narrow 8-lead SOIC surface-mount packages. The AD8612 is available in a 14-lead TSSOP surface-mount package.
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 (c)2006 Analog Devices, Inc. All rights reserved.
AD8611/AD8612 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications....................................................................................... 1 Pin Configurations ........................................................................... 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 5 Thermal Resistance ...................................................................... 5 ESD Caution.................................................................................. 5 Pin Configurations and Function Descriptions ........................... 6 Typical Performance Characteristics ............................................. 7 Applications..................................................................................... 10 Optimizing High Speed Performance ..................................... 10 Upgrading the LT1394 and LT1016......................................... 10 Maximum Input Frequency and Overdrive............................ 10 Output Loading Considerations............................................... 11 Using the Latch to Maintain a Constant Output.................... 11 Input Stage and Bias Currents .................................................. 11 Using Hysteresis ......................................................................... 11 Clock Timing Recovery............................................................. 12 A 5 V, High Speed Window Comparator................................ 12 Outline Dimensions ....................................................................... 16 Ordering Guide .......................................................................... 17
REVISION HISTORY
8/06--Rev. 0 to Rev. A Updated Format..................................................................Universal Added No Latch if VCC < 4.3 V .........................................Universal Changes to Pin Names .......................................................Universal Added Pin Configurations and Function Descriptions Page ..... 6 Changes to Table 8.......................................................................... 12 Changes to Figure 26...................................................................... 12 Changes to Ordering Guide .......................................................... 17 4/00--Revision 0: Initial Version
Rev. A | Page 2 of 20
AD8611/AD8612 SPECIFICATIONS
V+ = 5.0 V, V- = VGND = 0 V, TA = 25C, unless otherwise noted. Table 1.
Parameter INPUT CHARACTERISTICS Offset Voltage Offset Voltage Drift Input Bias Current Input Offset Current Input Common-Mode Voltage Range Common-Mode Rejection Ratio Large Signal Voltage Gain Input Capacitance LATCH ENABLE INPUT Logic 1 Voltage Threshold Logic 0 Voltage Threshold Logic 1 Current Logic 0 Current Latch Enable Pulse Width Setup Time Hold Time DIGITAL OUTPUTS Logic 1 Voltage Logic 1 Voltage Logic 0 Voltage DYNAMIC PERFORMANCE Input Frequency Propagation Delay Propagation Delay Differential Propagation Delay (Rising Propagation Delay vs. Falling Propagation Delay) Rise Time Fall Time POWER SUPPLY Power Supply Rejection Ratio V+ Supply Current 2 Ground Supply Current2 V- Supply Current2 Symbol VOS -40C TA +85C VOS/T IB IB IOS VCM CMRR AVO CIN VIH VIL IIH IIL tPW(E) tS tH VOH VOH VOL fMAX tP tP tP VCM = 0 V -40C TA +85C VCM = 0 V 0 V VCM 3.0 V RL = 10 k -6 -7 0.0 55 4 -4 -4.5 4 3.0 85 3000 3.0 1.65 1.60 -0.3 -2.7 3 0.5 0.5 3.0 2.4 3.35 3.4 0.25 100 4.0 5 5 0.5 2.5 1.1 55 73 5.7 3.5 2.2 -40C TA +85C
1 2
Conditions
Min
Typ 1
Max 7 8
Unit mV mV V/C A A A V dB V/V pF V V A A ns ns ns V V V MHz ns ns ns ns ns ns dB mA mA mA mA mA
VCC > 4.3 V VCC > 4.3 V VCC > 4.3 V, VLH = 3.0 V VCC > 4.3 V, VLL = 0.3 V VCC > 4.3 V VCC > 4.3 V VCC > 4.3 V IOH = 50 A, VIN > 250 mV IOH = 3.2 mA, VIN > 250 mV IOL = 3.2 mA, VIN > 250 mV 400 mV p-p sine wave 200 mV step with 100 mV overdrive 1 -40C TA +85C 100 mV step with 5 mV overdrive 100 mV step with 100 mV overdrive1 20% to 80% 80% to 20%
2.0 -1.0 -5
0.8
0.4
5.5
2.0
PSRR I+ IGND I-
4.5 V V+ 5.5 V -40C TA +85C VO = 0 V, RL = -40C TA +85C
10 10 7 7 4 5
Guaranteed by design. Per comparator.
Rev. A | Page 3 of 20
AD8611/AD8612
V+ = 3.0 V, V- = VGND = 0 V, TA = 25C, unless otherwise noted. Table 2.
Parameter INPUT CHARACTERISTICS Offset Voltage Input Bias Current Input Common-Mode Voltage Range Common-Mode Rejection Ratio OUTPUT CHARACTERISTICS Output High Voltage Output Low Voltage LATCH ENABLE INPUT POWER SUPPLY Power Supply Rejection Ratio Supply Currents V+ Supply Current 2 Ground Supply Current2 V- Supply Current2 DYNAMIC PERFORMANCE Propagation Delay
1 2
Symbol VOS IB IB VCM CMRR VOH VOL
Conditions
Min
Typ 1 -4.0 -4.5
Max 7
Unit mV A A V dB V V
VCM = 0 V -40C TA +85C 0 V VCM 1.0 V IOH = -3.2 mA, VIN > 250 mV IOL = +3.2 mA, VIN > 250 mV Not functional if VCC < 4.3 V 2.7 V V+ 6 V VO = 0 V, RL = -40C TA +85C -40C TA +85C
-6 -7 0 55 1.2 1
1.0
0.3
PSRR I+ IGND I-
46 4.5 2.5 2 6.5 10 3.5 5.5 3.5 4.8 6.5
dB mA mA mA mA mA mA ns
-40C TA +85C tP 100 mV step with 20 mV overdrive 3 4.5
Output high voltage without pull-up resistor. It may be useful to have a pull-up resistor to V+ for 3 V operation. Per comparator. 3 Guaranteed by design.
Rev. A | Page 4 of 20
AD8611/AD8612 ABSOLUTE MAXIMUM RATINGS
Table 3.
Parameter Total Analog Supply Voltage Digital Supply Voltage Input Voltage1 Differential Input Voltage Output Short-Circuit Duration to GND Storage Temperature Range R, RU, RM Packages Operating Temperature Range Junction Temperature Range R, RU, RM Packages Lead Temperature Range (Soldering, 10 sec)
1
Rating 7.0 V 7.0 V 4 V 5 V Indefinite -65C to +150C -40C to +85C -65C to +150C 300C
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 RESISTANCE
Table 4.
Package Type 8-Lead SOIC (R) 8-Lead MSOP (RM) 14-Lead TSSOP (RU)
1
The analog input voltage is equal to 4 V or the analog supply voltage, whichever is less.
JA1 158 240 240
JC 43 43 43
Unit C/W C/W C/W
JA is specified for the worst-case conditions, that is, a device in socket for P-DIP and a device soldered in circuit board for SOIC and TSSOP.
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. A | Page 5 of 20
AD8611/AD8612 PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
QA QA GND
1 2 3 4 5 6 7 14 QB 13 QB
AD8612
TOP VIEW (Not to Scale)
12 GND 11 LEB 10 V+ 9 8
V+ 1 IN+ 2 IN- 3
8
QA QA
06010-001
LEA
V+ 1 IN+ 2 IN- 3 V- 4
8
QA QA
06010-002
AD8611
7
AD8611
TOP VIEW (Not to Scale)
V- INA- INA+
7 6 5
LATCH
INB+
Figure 4. 8-Lead Narrow Body SOIC Pin Configuration
Figure 5. 8-Lead MSOP Pin Configuration
Figure 6. 14-Lead TSSOP Pin Configuration
Table 5. Pin Function Descriptions
Pin No. SOIC and TSSOP MSOP 1 10 2 3 4 5 5 6 3, 12 7 1 8 2 14 13 4 11 7 6 8 9
Mnemonic V+ IN+ IN- V- LATCH GND QA QA QB QB LEA LEB INA+ INA- INB+ INB-
Description Positive Supply Terminal. Noninverting Analog Input of the Differential Input Stage. Inverting Analog Input of the Differential Input Stage. Negative Supply Terminal. Latch Enable Input. Negative Logic Supply One of Two Complementary Output for Channel A. One of Two Complementary Output for Channel A. One of Two Complementary Output for Channel B. One of Two Complementary Output for Channel B. Channel A Latch Enable. Channel B Latch Enable. Noninverting Analog Input of the Differential Input Stage for Channel A. Inverting Analog Input of the Differential Input Stage for Channel A. Noninverting Analog Input of the Differential Input Stage for Channel B. Inverting Analog Input of the Differential Input Stage for Channel B.
Rev. A | Page 6 of 20
06010-003
6 GND TOP VIEW V- 4 (Not to Scale) 5 LATCH
GND
INB-
AD8611/AD8612 TYPICAL PERFORMANCE CHARACTERISTICS
8 7 V+ = 5V OVERDRIVE > 10mV
18 14
V+ = 5V TA = 25C OVERDRIVE = 5mV
PD-
PROPAGATION DELAY (ns)
6 5
PD-
PROPAGATION DELAY (ns)
12
PD+
4
PD+
8
3 2 1
06010-004
6
2
0 -50
-25
0
25 50 TEMPERATURE (C)
75
100
0
0.5
1.5 1.0 SOURCE RESISTANCE (k)
2.0
2.5
Figure 7. Propagation Delay vs. Temperature
Figure 10. Propagation Delay vs. Source Resistance
18 16
PD-
V+ = 5V TA = 25C
8 7
PD+
TA = 25C STEP = 100mV OVERDRIVE > 10mV
PROPAGATION DELAY (ns)
PROPAGATION DELAY (ns)
14 12 10
PD+
6 5
PD-
4 3 2 1
8 6 4 2
06010-005
0
5
10 15 OVERDRIVE (mV)
20
25
2
3
4 SUPPLY VOLTAGE (V)
5
6
Figure 8. Propagation Delay vs. Overdrive
Figure 11. Propagation Delay vs. Supply Voltage
V+ = 5V TA = 25C 7 OVERDRIVE > 10mV
PROPAGATION DELAY (ns)
8
35 30
PROPAGATION DELAY (ns)
PD-
TA = 25C STEP = 100mV OVERDRIVE = 50mV
6 5 4 3 2 1
06010-006
25
PD+
PD+
20 15 10 5
PD-
0
20
40 CAPACITANCE (pF)
60
80
2
3 4 5 COMMON-MODE VOLTAGE (V)
6
Figure 9. Propagation Delay vs. Load Capacitance
Figure 12. Propagation Delay vs. Common-Mode Voltage
Rev. A | Page 7 of 20
06010-009
0
0
06010-008
0
0
06010-007
0
AD8611/AD8612
1.2 VS = 3V
0.40 +25C 0.35 +85C -40C
1.0
0.30
0.8
LOAD CURRENT (V)
VOS (mV)
VS = 5V 0.6
0.25 0.20 0.15 0.10
-40C
+85C +25C
0.4
0.2
0.05
06010-010
06010-013 06010-015
0 -60
-40
-20
0
20
40
60
80
100
0
0
2
TEMPERATURE (C)
4 6 8 SINK CURRENT (mA)
10
12
Figure 13. Offset Voltage vs. Temperature
Figure 16. Output Low Voltage vs. Load Current (Sinking) Over Temperature
40 35 30 25
ISY+ (mA)
V+ = 5V TA = 25C
OUTPUT HIGH VOLTAGE (V)
4.0 3.8 3.6 +85C 3.4 +25C 3.2 3.0 2.8 2.6
06010-011
20 15 10 5 0
-40C
1
10 INPUT FREQUENCY (MHz)
100
2
4 6 8 LOAD CURRENT (mA)
10
12
Figure 14. Supply Current vs. Input Frequency
Figure 17. Output High Voltage vs. Load Current (Sourcing) Over Temperature
2.0 V+ = 5V 1.8 1.6 1.4
TIMING (ns)
8 7 6 VS = 5V 5
ISY (mA)
1.2 1.0 0.8 0.6 0.4 0.2 0 -50 -25 0 HOLD TIME SETUP TIME
4 3 2 1 VS = 3V
25 50 TEMPERATURE (C)
75
100
06010-012
0 -60
-40
-20
0 20 40 TEMPERATURE (C)
60
80
100
Figure 15. Latch Setup and Hold Time vs. Temperature
Figure 18. Supply Current vs. Temperature
Rev. A | Page 8 of 20
06010-014
2.4 0
AD8611/AD8612
0 -0.5 -1.0 -1.5
IGND (mA)
VIN V+ = 5V TA = 25C
-2.0 -2.5 -3.0 -3.5 -4.0
VOLTAGE
VS = 3V
0V
VOUT
VS = 5V
-VIN TRACE @ 10mV/DIV VOUT TRACE @ 1V/DIV
50
50 0 TEMPERATURE (C)
100
06010-016
-4.5
TIME (2ns/DIV)
Figure 19. IGND vs. Temperature
Figure 22. Falling Edge Response
0
V+ = 5V TA = 25C
VOUT
-0.5
-1.0
ISY (mA)
-1.5
VS = 3V
VOLTAGE
0V VIN
-2.0
VS = 5V
-2.5
-VIN TRACE @ 10mV/DIV VOUT TRACE @ 1V/DIV
-40
-20
0
20
40
60
80
100
06010-017
-3.0 -60
TEMPERATURE (C)
TIME (4ns/DIV)
Figure 20. ISY- vs. Temperature
Figure 23. Response to a 50 MHz, 100 mV Input Sine Wave
V+ = 5V TA = 25C
VOUT
VOLTAGE
0V
VIN
-VIN TRACE @ 10mV/DIV VOUT TRACE @ 1V/DIV TIME (2ns/DIV)
06010-018
Figure 21. Rising Edge Response
Rev. A | Page 9 of 20
06010-020
06010-019
AD8611/AD8612 APPLICATIONS
OPTIMIZING HIGH SPEED PERFORMANCE
As with any high speed comparator or amplifier, proper design and layout of the AD8611/AD8612 should be used to ensure optimal performance. Excess stray capacitance or improper grounding can limit the maximum performance of high speed circuitry. Minimizing resistance from the source to the comparator's input is necessary to minimize the propagation delay of the circuit. Source resistance in combination with the equivalent input capacitance of the AD8611/AD8612 creates an R-C filter that could cause a lagged voltage rise at the input to the comparator. The input capacitance of the AD8611/AD8612 in combination with stray capacitance from an input pin to ground results in several picofarads of equivalent capacitance. Using a surface-mount package and a minimum of input trace length, this capacitance is typically around 3 pF to 5 pF. A combination of 3 k source resistance and 3 pF of input capacitance yields a time constant of 9 ns, which is slower than the 4 ns propagation delay of the AD8611/AD8612. Source impedances should be less than 1 k for best performance. Another important consideration is the proper use of powersupply-bypass capacitors around the comparator. A 1 F bypass capacitor should be placed within 0.5 inches of the device between each power supply pin and ground. Another 10 nF ceramic capacitor should be placed as close as possible to the device in parallel with the 1 F bypass capacitor. The 1 F capacitor reduces any potential voltage ripples from the power supply, and the 10 nF capacitor acts as a charge reservoir for the comparator during high frequency switching. A continuous ground plane on the PC board is also recommended to maximize circuit performance. A ground plane can be created by using a continuous conductive plane over the surface of the circuit board, only allowing breaks in the plane for necessary traces and vias. The ground plane provides a low inductive current return path for the power supply, thus eliminating any potential differences at various ground points throughout the circuit board caused from ground bounce. A proper ground plane can also minimize the effects of stray capacitance on the circuit board. two voltages at the inputs to the comparator. The LT1016 has an input voltage range from 1.25 V above the negative supply to 1.5 V below the positive supply. The AD8611 input voltage range extends down to the negative supply voltage to within 2 V of V+. If the input common-mode voltage is exceeded, input signals should be shifted or attenuated to bring them into range, keeping in mind the note about source resistance in the Optimizing High Speed Performance section. For example, an AD8611 powered from a 5 V single supply has its noninverting input connected to a 1 V peak-to-peak, high frequency signal centered around 2.3 V and its inverting input connected to a fixed 2.5 V reference voltage. The worst-case input common-mode voltage to the AD8611 is 2.65 V. This is well below the 3.0 V input common-mode voltage range to the comparator. Note that signals much greater than 3.0 V result in increased input currents and may cause the comparator to operate more slowly. The input bias current to the AD8611 is 7 A maximum over temperature (-40C to +85C). This is identical to the maximum input bias current for the LT1394, and half of the maximum IB for the LT1016. Input bias currents to the AD8611 and LT1394 flow out from the comparator's inputs, as opposed to the LT1016 whose input bias current flows into its inputs. Using low value resistors around the comparator and low impedance sources will minimize any potential voltage shifts due to bias currents. The AD8611 is able to swing within 200 mV of ground and within 1.5 V of positive supply voltage. This is slightly more output voltage swing than the LT1016. The AD8611 also uses less current than the LT1016--5 mA as compared to 25 mA of typical supply current. The AD8611 has a typical propagation delay of 4 ns, compared with the LT1394 and LT1016, whose propagation delays are typically 7 ns and 10 ns, respectively.
MAXIMUM INPUT FREQUENCY AND OVERDRIVE
The AD8611 can accurately compare input signals up to 100 MHz with less than 10 mV of overdrive. The level of overdrive required increases with ambient temperature, with up to 50 mV of overdrive recommended for a 100 MHz input signal and an ambient temperature of +85C. It is not recommend to use an input signal with a fundamental frequency above 100 MHz because the AD8611 could draw up to 20 mA of supply current and the outputs may not settle to a definite state. The device returns to its specified performance once the fundamental input frequency returns to below 100 MHz.
UPGRADING THE LT1394 AND LT1016
The AD8611 single comparator is pin-for-pin compatible with the LT1394 and LT1016 and offers an improvement in propagation delay over both comparators. These devices can easily be replaced with the higher performance AD8611; however, there are differences, so it is useful to ensure that the system still operates properly. The five major differences between the AD8611 and the LT1016 include input voltage range, input bias currents, propagation delay, output voltage swing, and power consumption. Input common-mode voltage is found by taking the average of the
Rev. A | Page 10 of 20
AD8611/AD8612
OUTPUT LOADING CONSIDERATIONS
The AD8611 can deliver up to 10 mA of output current without increasing its propagation delay. The outputs of the device should not be connected to more than 40 TTL input logic gates or drive less than 400 of load resistance. The AD8611 output has a typical output swing between ground and 1 V below the positive supply voltage. Decreasing the output load resistance to ground lowers the maximum output voltage due to the increase in output current. Table 6 shows the typical output high voltage vs. load resistance to ground. Table 6. Maximum Output Voltage vs. Resistive Load
Output Load to Ground 300 500 1 k 10 k >20 k V+ - VOUT, HI (typ) 1.5 V 1.3 V 1.2 V 1.1 V 1.0 V
after the latch voltage goes high for the output to remain latched to its voltage. The latch input is TTL and CMOS compatible, so a logic high is a minimum of 2.0 V and a logic low is a maximum of 0.8 V. The latch circuitry in the AD8611/AD8612 has no built-in hysteresis. At or below approximately 4.1 V, the latch pin becomes unresponsive and should normally be tied low for low VCC operation.
INPUT STAGE AND BIAS CURRENTS
The AD8611 and AD8612 each use a bipolar PNP differential input stage. This enables the input common-mode voltage range to extend from within 2.0 V of the positive supply voltage to 200 mV below the negative supply voltage. Therefore, using a single 5 V supply, the input common-mode voltage range is -200 mV to +3.0 V. Input common-mode voltage is the average of the voltages at the two inputs. For proper operation, the input common-mode voltage should be kept within the commonmode voltage range. The input bias current for the AD8611/AD8612 is 4 A, which is the amount of current that flows from each input of the comparator. This bias current goes to zero on an input that is high and doubles on an input that is low, which is a characteristic common to any bipolar comparator. Care should be taken in choosing resistances to be connected around the comparator because large resistors could significantly decrease the voltage due to the input bias current. The input capacitance for the AD8611/AD8612 is typically 3 pF. This is measured by inserting a 5 k source resistance in series with the input and measuring the change in propagation delay.
Connecting a 500 to 2 k pull-up resistor to V+ on the output helps increase the output voltage so that it is closer to the positive rail; in this configuration, however, the output voltage will not reach its maximum until 20 ns to 50 ns after the output voltage switches. This is due to the R-C time constant between the pull-up resistor and the output and load capacitances. The output pull-up resistor cannot improve propagation delay. The AD8611 is stable with all values of capacitive load; however, loading an output with greater than 30 pF increases the propagation delay of that channel. Capacitive loads greater than 500 pF also create some ringing on the output wave. Table 7 shows propagation delay vs. several values of load capacitance. The loading on one output of the AD8611 does not affect the propagation delay of the other output. Table 7. Propagation Delay vs. Capacitive Load
CL (pF) <10 33 100 390 680 tPD Rising (ns) 3.5 5 8 14.5 26 tPD Falling (ns) 3.5 5 7 10 15
USING HYSTERESIS
Hysteresis can easily be added to a comparator through the addition of positive feedback. Adding hysteresis to a comparator offers an advantage in noisy environments where it is undesirable for the output to toggle between states when the input signal is close to the switching threshold. Figure 24 shows a simple method for configuring the AD8611 or AD8612 with hysteresis.
SIGNAL COMPARATOR
USING THE LATCH TO MAINTAIN A CONSTANT OUTPUT
With the VCC supply at a nominal 5 V, the latch input to the AD8611/AD8612 can be used to retain data at the output of the comparator. When the latch voltage goes high, the output voltage remains in its previous state, independent of changes in the input voltage. The setup time for the AD8611/AD8612 is 0.5 ns and the hold time is 0.5 ns. Setup time is defined as the minimum amount of time the input voltage must remain in a valid state before the latch is activated for the latch to function properly. Hold time is defined as the amount of time the input must remain constant
VREF
R1
R2
06010-021
CF
Figure 24. Configuring the AD8611/AD8612 with Hysteresis
In Figure 24, the input signal is connected directly to the inverting input of the comparator. The output is fed back to the noninverting input through R1 and R2. The ratio of R1 to R1 + R2 establishes the width of the hysteresis window, with VREF setting the center of the window, or the average switching voltage. The QA or QB output switches low when the input
Rev. A | Page 11 of 20
AD8611/AD8612
voltage is greater than VHI, and does not switch high again until the input voltage is less than VLO, as given in Equation 1:
V HI = (V + - 1.5 V REF ) VLO = VREF x R2 R1 + R2 R1 + V REF R1 + R2
A 5 V, HIGH SPEED WINDOW COMPARATOR
A window comparator circuit is used to detect when a signal is between two fixed voltages. The AD8612 can be used to create a high speed window comparator, as shown in Figure 26. In this example, the reference window voltages are set as:
VHI = R2 R1 + R2 VLO = R4 R3 + R 4
(1)
where V+ is the positive supply voltage. The capacitor CF is optional and can be added to introduce a pole into the feedback network. This has the effect of increasing the amount of hysteresis at high frequencies, which is useful when comparing relatively slow signals in high frequency noise environments. At frequencies greater than fP, the hysteresis window approaches VHI = V+ - 1.5 V and VLO = 0 V. For frequencies less than fP, the threshold voltages remain as in Equation 1.
The output of the A1 comparator goes high when the input signal exceeds VHI, and the output of A2 goes high only when VIN drops below VLO. When the input voltage is between VHI and VLO, both comparator outputs are low, turning off both Q1 and Q2, thus driving VOUT to a high state. If the input signal goes outside of the reference voltage window, VOUT goes low. To ensure a minimum of switching delay, the use of high speed transistors is recommended for Q1 and Q2. Using the AD8612 with 2N3960 transistors provides a total propagation delay from VIN to VOUT of less than 10 ns. Table 8. Window Comparator Output States
VOUT 200 mV +5 V 200 mV
5V R1 5V VHI 6 7 10 A1 3 4 1 1k 500 1k VOUT Q1 Q2
CLOCK TIMING RECOVERY
Comparators are often used in digital systems to recover clock timing signals. High speed square waves transmitted over any distance, even tens of centimeters, can become distorted due to stray capacitance and inductance. Poor layout or improper termination can also cause reflections on the transmission line, further distorting the signal waveform. A high speed comparator can be used to recover the distorted waveform while maintaining a minimum of delay. Figure 25 shows VOUT vs. VIN as the AD8611 is used to recover a 65 MHz, 100 mV peak-to-peak distorted clock signal into a 4 V peak-to-peak square wave. The lower trace is the input to the AD8611, and the upper trace is the QA or QB output from the comparator. The AD8611 is powered from a 5 V single supply.
Input Voltage VIN < VLO VLO < VIN < VHI VIN > VHI
5V
R2
AD8612
VIN
5V 9
VOUT 2V/DIV
AD8612
A2 5 11 14 12 1k 500
R3
VLO
8
R4
20mV/DIV VIN
Figure 26. A High Speed Window Comparator
TIME (10ns/DIV)
Figure 25. Using the AD8611 to Recover a Noisy Clock Signal
06010-022
Rev. A | Page 12 of 20
06010-023
NOTES 1. Q1, Q2 = 2N3960. 2. PINS 2 AND 13 ARE NO CONNECTS.
AD8611/AD8612
SPICE Model * AD8611 SPICE Macro-Model Typical Values * 1/2000, Ver. 1.0 * TAM/ADSC * * Node assignments * * * * * * * * * .SUBCKT AD8611 * * INPUT STAGE * * Q1 Q2 IBIAS RC1 RC2 CL1 CIN VCM1 D1 EOS * * Reference Voltages * EREF RREF * 98 98 0 0 POLY(2) 100E3 (99,0) (50,0) 0 0.5 0.5 4 6 99 4 6 4 1 99 5 3 3 2 5 50 50 6 2 7 7 1 5 5 800E-6 1E3 1E3 3E-13 3E-12 DC DX POLY(1) (31,98) 1E-3 1 1.9 PIX PIX non-inverting input | | | | | | | | 1 inverting input | | | | | | | 2 positive supply | | | | | | 99 negative supply | | | | | 50 Latch | | | | 80 DGND | | | 51 Q | | 45 QNOT | 65
Rev. A | Page 13 of 20
AD8611/AD8612
* CMRR = 66dB, ZERO AT 1 kHz * ECM1 RCM1 RCM2 CCM1 * * Latch Section * 30 30 31 30 98 31 98 31 POLY(2) 10E3 5 15.9E-9 (1,98) (2,98) 0 0.5 0.5
RX E1 S1 R2 C3 E2 R3 *
80 10 10 11 12 13 12
51 98 11 12 98 98 13
100E3 (4,6) (80,51) 1 5 (12,98) 500 4E-12 1 1 SLATCH1
* Power Supply Section * GSY1 GSY2 RSY * * Gain Stage Av = 250 fp=100 MHz * G2 R1 C1 E3 E4 V1 V2 D2 D3 * * Q Output *
Rev. A | Page 14 of 20
99 52 52
52 50 51
POLY(1) POLY(1) 10
(99,50) (99,50)
4E-3 3
-2 7E-3
6E-4 -.6E-3
98 20 20 97 52 97 22 20 22
20 98 98 0 0 21 52 21 20
(12,98) 1000 10E-13 (99,0) (51,0) DC DC DX DX
0.25
1 1 0.8 0.8
AD8611/AD8612
Q3 Q4 RB1 RB2 CB1 CB2 RO1 D4 RO2 EO1 EO2 * * Q NOT Output * Q5 Q6 RB3 RB4 CB3 CB4 RO3 D5 RO4 EO3 EO4 * * MODELS * .MODEL PIX PNP(BF=100,IS=1E-16) .MODEL NOX NPN(BF=100,VAF=130,IS=1E-14) .MODEL DX D(IS=1E-14) .MODEL SLATCH1 VSWITCH(ROFF=1E6,RON=500, +VOFF=2.1,VON=1.4) .ENDS AD8611 99 67 63 60 99 62 66 64 67 63 97 61 62 61 62 61 51 64 65 65 51 60 66 51 2000 2000 0 1E-12 1 DX 500 (20,51) (20,51) 1 1 5E-12 NOX NOX 99 47 43 40 99 42 46 44 47 97 40 41 42 41 42 41 51 44 45 45 43 51 46 51 2000 2000 0.5E-12 1E-12 1 DX 500 (20,51) (20,51) 1 1 NOX NOX
Rev. A | Page 15 of 20
AD8611/AD8612 OUTLINE DIMENSIONS
3.20 3.00 2.80
5.00 (0.1968) 4.80 (0.1890)
5
3.20 3.00 2.80 PIN 1
8
1
5.15 4.90 4.65
4
4.00 (0.1574) 3.80 (0.1497) 1
8
5 4
6.20 (0.2440) 5.80 (0.2284)
0.65 BSC 0.95 0.85 0.75 0.15 0.00 0.38 0.22 SEATING PLANE 1.10 MAX 8 0 0.80 0.60 0.40
0.25 (0.0098) 0.10 (0.0040)
1.27 (0.0500) BSC
1.75 (0.0688) 1.35 (0.0532)
0.50 (0.0196) x 45 0.25 (0.0099)
0.23 0.08
0.51 (0.0201) COPLANARITY SEATING 0.31 (0.0122) 0.10 PLANE
8 0.25 (0.0098) 0 1.27 (0.0500) 0.40 (0.0157) 0.17 (0.0067)
COPLANARITY 0.10
COMPLIANT TO JEDEC STANDARDS MO-187-AA
COMPLIANT TO JEDEC STANDARDS MS-012-AA CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
Figure 27. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters
5.10 5.00 4.90
Figure 28. 8-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-8) Dimensions shown in millimeters and (inches)
14
8
4.50 4.40 4.30
1 7
6.40 BSC
PIN 1 1.05 1.00 0.80 0.65 BSC 1.20 MAX 0.15 0.05 0.30 0.19
0.20 0.09
SEATING COPLANARITY PLANE 0.10
8 0
0.75 0.60 0.45
COMPLIANT TO JEDEC STANDARDS MO-153-AB-1
Figure 29. 14-Lead Thin Shrink Small Outline Package [TSSOP] (RU-14) Dimensions shown in millimeters
Rev. A | Page 16 of 20
AD8611/AD8612
ORDERING GUIDE
Model AD8611ARM-REEL AD8611ARM-R2 AD8611ARMZ-REEL 1 AD8611ARMZ-R21 AD8611AR AD8611AR-REEL AD8611AR-REEL7 AD8611ARZ1 AD8611ARZ-REEL1 AD8611ARZ-REEL71 AD8612ARU AD8612ARU-REEL AD8612ARUZ1 AD8612ARUZ-REEL1
1
Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C
Package Description 8-Lead Mini Small Outline Package [MSOP] 8-Lead Mini Small Outline Package [MSOP] 8-Lead Mini Small Outline Package [MSOP] 8-Lead Mini Small Outline Package [MSOP] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 14-Lead Thin Shrink Small Outline Package [TSSOP] 14-Lead Thin Shrink Small Outline Package [TSSOP] 14-Lead Thin Shrink Small Outline Package [TSSOP] 14-Lead Thin Shrink Small Outline Package [TSSOP]
Package Option RM-8 RM-8 RM-8 RM-8 R-8 R-8 R-8 R-8 R-8 R-8 RU-14 RU-14 RU-14 RU-14
Branding G1A G1A G1A G1A
Z = Pb-free part.
Rev. A | Page 17 of 20
AD8611/AD8612 NOTES
Rev. A | Page 18 of 20
AD8611/AD8612 NOTES
Rev. A | Page 19 of 20
AD8611/AD8612 NOTES
(c)2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. C06010-0-8/06(A)
Rev. A | Page 20 of 20

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