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8/21/97 4:00 PM
a
FEATURES Precision Performance in Standard SO-8 Pinout Low Offset Voltage: 50 V max Low Offset Voltage Drift: 0.6 V/ C max Very Low Bias Current: +25 C (100 pA max) -55 C to +125 C (450 pA max) Very High Open-Loop Gain (2000 V/mV min) Low Supply Current (Per Amplifier): 625 A max Operates From 62 V to 620 V Supplies High Common-Mode Rejection: 120 dB min Pin Compatible to LT1013, AD706, AD708, OP221, LM158, and MC1458/1558 with Improved Performance APPLICATIONS Strain Gauge and Bridge Amplifiers High Stability Thermocouple Amplifiers Instrumentation Amplifiers Photo-Current Monitors High-Gain Linearity Amplifiers Long-Term Integrators/Filters Sample-and-Hold Amplifiers Peak Detectors Logarithmic Amplifiers Battery-Powered Systems GENERAL DESCRIPTION
Dual Low Bias Current Precision Operational Amplifier OP297
PIN CONNECTIONS Plastic Epoxy-DIP (P Suffix) 8-Pin Cerdip (Z Suffix) 8-Pin Narrow Body SOIC (S Suffix)
OUT A 1 +IN A 3 V- 4
-
8
A - B
V+ OUT B -IN B +IN B
+
-IN A 2
7 6 5
Errors due to common-mode signals are eliminated by the OP297's common-mode rejection of over 120 dB. The OP297's power supply rejection of over 120 dB minimizes offset voltage changes experienced in battery powered systems. Supply current of the OP297 is under 625 A per amplifier and it can operate with supply voltages as low as 2 V. The OP297 utilizes a super-beta input stage with bias current cancellation to maintain picoamp bias currents at all temperatures. This is in contrast to FET input op amps whose bias currents start in the picoamp range at 25C, but double for every 10C rise in temperature, to reach the nanoamp range above 85C. Input bias current of the OP 297 is under 100 pA at 25C and is under 450 pA over the military temperature range. Combining precision, low power and low bias current, the OP297 is ideal for a number of applications including instrumentation amplifiers, log amplifiers, photodiode preamplifiers and long-term integrators. For a single device, see the OP97; for a quad, see the OP497.
400 1200 UNITS TA = +25C VS = 15V VCM = 0V
+
The OP297 is the first dual op amp to pack precision performance into the space-saving, industry standard 8-pin SO package. Its combination of precision with low power and extremely low input bias current makes the dual OP297 useful in a wide variety of applications. Precision performance of the OP297 includes very low offset, under 50 V, and low drift, below 0.6 V/C. Open-loop gain exceeds 2000 V/mV insuring high linearity in every application.
60 I B- 40 VS = 15V VCM = 0V
INPUT CURRENT (pA)
20 0 20 IOS
NUMBER OF UNITS
IB+
300
200
100
-40 -60 -75 -50 -25 0 25 50 75 TEMPERATURE (C)
0 -100 -80 -60 -40 -20 0 20 40 60 80 100 INPUT OFFSET VOLTAGE (V)
100 125
Figure 1. Low Bias Current Over Temperature
Figure 2. Very Low Offset
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Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 World Wide Web Site: http://www.analog.com Fax: 617/326-8703 (c) Analog Devices, Inc., 1997
8/21/97 4:00 PM
OP297-SPECIFICATIONS
ELECTRICAL CHARACTERISTICS (@ V =
S
15 V, TA = +25 C, unless otherwise noted.)
OP297A/E Min Typ Max 25 0.1 20 20 0.5 20 17 20 30 50 OP297F Min Typ 50 0.1 35 35 0.5 20 17 20 30 500 1500 13 114 114 13 13 2 0.05 3200 14 135 125 14 13.7 525 625 20 0.15 500 150 3 1200 13 114 114 13 13 2 0.05 Max 100 OP297G Min Typ Max 80 0.1 50 50 0.5 20 17 20 30 500 3200 14 135 125 14 13.7 525 625 20 0.15 500 150 3 200 Units V V/mo pA pA V p-p nV/Hz nV/Hz fAHz M G V/mV V dB dB V V A V V/s kHz dB pF
Parameter Input Offset Voltage Long-Term Input Voltage Stability Input Offset Current Input Bias Current Input Noise Voltage Input Noise Voltage Density Input Noise Current Density Input Resistance Differential Mode Input Resistance Common-Mode Large-Signal Voltage Gain Input Voltage Range Common-Mode Rejection Power Supply Rejection Output Voltage Swing Supply Current Per Amplifier Supply Voltage Slew Rate Gain Bandwidth Product Channel Separation Input Capacitance
Symbol Conditions VOS
IOS IB en p-p en en in RIN RINCM AVO IVR CMR PSR VO VO ISY VS SR GBWP CS CIN
VCM = 0 V VCM = 0 V 0.1 Hz to 10 Hz fO = 10 Hz fO = 1000 Hz fO = 10 Hz
100 100
150 150
200 200
VO = 10 V RL = 2 k (Note 1) VCM = 13 V VS = 2 V to 20 V RL = 10 k RL = 2 k No Load Operating Range AV = +1 VO = 20 V p-p fO = 10 Hz
500 2000 13 120 120 13 13 2 0.05 4000 14 140 130 14 13.7 525 625 20 0.15 500 150 3
NOTES 1 Guaranteed by CMR test. Specifications subject to change without notice.
ELECTRICAL CHARACTERISTICS (@ V =
S
15 V, -55 C TA +125 C for OP297A, unless otherwise noted.)
Conditions Min OP297A Typ Max Units
Parameter
Symbol
Input Offset Voltage Average Input Offset Voltage Drift Input Offset Current Input Bias Current Large-Signal Voltage Gain Input Voltage Range Common-Mode Rejection Power Supply Rejection Output Voltage Swing Supply Current Per Amplifier Supply Voltage
NOTES 1 Guaranteed by CMR test. Specifications subject to change without notice.
VOS TCVOS IOS IB AVO IVR CMR PSR VO ISY VS
VCM = 0 V VCM = 0 V VO = 10 V, RL = 2 k (Note 1) VCM = 13 VS = 2.5 V to 20 V RL = 10 k No Load Operating Range
1200 13 114 114 13 2.5
45 0.2 60 60 2700 13.5 130 125 13.4 575
100 0.6 450 450
750 20
V V/C pA pA V/mV V dB dB V A V
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OP297 ELECTRICAL CHARACTERISTICS (@ V =
S
15 V, -40 C TA +85 C for OP297E/F/G, unless otherwise noted.)
Min OP297E Typ Max 35 0.2 50 50 1200 13 114 114 13 2.5 3200 13.5 130 0.15 13.4 550 750 20 100 0.6 450 450 OP297F Min Typ Max 80 0.5 80 80 1000 2500 13 13.5 108 130 108 13 2.5 0.15 13.4 550 750 20 300 2.0 750 750 700 13 108 108 13 2.5 OP297G Min Typ Max 110 0.6 80 80 2500 13.5 130 0.3 13.4 550 750 20 400 2.0 750 750 Units V V/C pA pA V/mV V dB dB V A V
Parameter Input Offset Voltage Average Input Offset Voltage Drift Input Offset Current Input Bias Current Large-Signal Voltage Gain Input Voltage Range Common-Mode Rejection Power Supply Rejection
Symbol VOS TCVOS IOS IB AVO IVR CMR PSR
Conditions
Output Voltage Swing VO Supply Current Per Amplifier ISY Supply Voltage VS
NOTES 1 Guaranteed by CMR test. Specifications subject to change without notice.
VCM = 0 V VCM = 0 V VO = 10 V, RL = 2 k (Note 1) VCM = 13 VS = 2.5 V to 20 V RL = 10 k No Load Operating Range
Wafer Test Limits (@ V =
S
15 V, TA = +25 C, unless otherwise noted.)
Symbol VOS IOS IB AVO IVR CMR PSR VO ISY Conditions VCM = 0 V VCM = 0 V VO = 10 V, RL = 2 k (Note 1) VCM = 13 V VS = 2 V to l 8 V RL = 2 k No Load Limit 200 200 200 1200 13 114 114 13 625 Units V max pA max pA max V/mV min V min dB min dB min V min A max
Parameter Input Offset Voltage Input Offset Current Input Bias Current Large-Signal Voltage Gain Input Voltage Range Common-Mode Rejection Power Supply Output Voltage Swing Supply Current Per Amplifier
NOTES 1. Guaranteed by CMR test. Electrical tests are performed at wafer probe to the limits shown. Due to variations in assembly methods and normal yield loss, yield after packaging is not guaranteed for standard product dice. Consult factory to negotiate specifications based on dice lot qualifications through sample lot assembly and testing.
DICE CHARACTERISTICS
Dimension shown in inches and (mm). Contact factory for latest dimensions
OUTPUT A
+VS
0.118 (3.00) -INPUT A OUTPUT B +INPUT A
-INPUT B -VS 0.074 (1.88) +INPUT B
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OP297
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 V Input Voltage2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 V Differential Input Voltage2 . . . . . . . . . . . . . . . . . . . . . . . . 40 V Output Short-Circuit Duration . . . . . . . . . . . . . . . . Indefinite Storage Temperature Range Z Package . . . . . . . . . . . . . . . . . . . . . . . . . -65C to +175C P, S Package . . . . . . . . . . . . . . . . . . . . . . . -65C to +150C Operating Temperature Range OP297A (Z) . . . . . . . . . . . . . . . . . . . . . . . -55C to +125C OP297E, F (Z) . . . . . . . . . . . . . . . . . . . . . . -40C to +85C OP297F, G (P, S) . . . . . . . . . . . . . . . . . . . -40C to +85C Junction Temperature Z Package . . . . . . . . . . . . . . . . . . . . . . . . . -65C to +175C P, S Package . . . . . . . . . . . . . . . . . . . . . . . -65C to +150C Lead Temperature Range (Soldering, 60 sec) . . . . . . . +300C
ABSOLUTE MAXIMUM RATINGS 1 Package Type 8-Pin Cerdip (Z) 8-Pin Plastic DIP (P) 8-Pin SO (S)
3 JA JC
Units C/W C/W C/W
134 96 150
12 37 41
NOTES 1 Absolute maximum ratings apply to both DICE and packaged parts, unless otherwise noted. 2 For supply voltages less than 20 V, the absolute maximum input voltage is equal to the supply voltage. 3 JA is specified for worst case mounting conditions, i.e., JA is specified for device in socket for cerdip and P-DIP, packages; JA is specified for device soldered to printed circuit board for SO package.
ORDERING GUIDE1
Model OP297AZ OP297EZ OP297EP OP297FP OP297FS OP297FS-REEL OP297FS-REEL7 OP297GP OP297GS OP297GS-REEL OP297GS-REEL72
Temperature Range -55C to +125C -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-Pin Cerdip 8-Pin Cerdip 8-Pin Plastic DIP 8-Pin Plastic DIP 8-Pin SO 8-Pin SO 8-Pin SO 8-Pin Plastic DIP 8-Pin SO 8-Pin SO 8-Pin SO
Package Option1 Q-8 Q-8 N-8 N-8 SO-8 SO-8 SO-8 N-8 SO-8 SO-8 SO-8
NOTES 1 Burn-in is available on extended industrial temperature range parts in cerdip, and plastic DIP packages. For outline information see Package Information section. 2 For availability and burn-in information on SO packages, contact your local sales office.
-
1/2 OP-297 V1 20Vp-p @ 10Hz 2k
+
50k 50
-
1/2 OP-297 V2
+
CHANNEL SEPARATION = 20 log
)
V1 V2/10000
)
WARNING!
ESD SENSITIVE DEVICE
Figure 3. Channel Separation Test Circuit
CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the OP297 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.
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Typical Performance Characteristics- OP297
400 1200 UNITS TA = +25C VS = 15V VCM = 0V
NUMBER OF UNITS
250 1200 UNITS 200 TA = +25C VS = 15V VCM = 0V
NUMBER OF UNITS
300 400 1200 UNITS TA = +25C VS = 15V VCM = 0V
NUMBER OF UNITS
300
150
200
200
100
100
50
100
0 -100 -80 -60 -40 -20 0 20 40 60 80 100 INPUT OFFSET VOLTAGE (V)
0 -100 -80 -60 -40 -20
0
20 40
60 80 100
INPUT BIAS CURRENT (pA)
0 -100 -80 -60 -40 -20 0 20 40 60 80 100 INPUT OFFSET CURRENT (pA)
Figure 4. Typical Distribution of Input Offset Voltage
Figure 5. Typical Distribution of Input Bias Current
Figure 6. Typical Distribution of Input Offset Current
60 IB- 40 VS = 15V VCM = 0V INPUT CURRENT (pA)
60 40 20 0 IOS -20 -40 -60
100 125
3 TA = +25C VS = 15V
DEVIATION FROM FINAL VALUE (V)
IB- IB+
TA = +25C VS = 15V VCM = 0V 2
INPUT CURRENT (pA)
IB+ 20 0 20 IOS
1
-40 -60 -75 -50 -25 0 25 50 75 TEMPERATURE (C)
0 -15 -10 -5 0 5 10 15 COMMON-MODE VOLTAGE (VOLTS)
0
1 2 3 4 5 TIME AFTER POWER APPLIED (MINUTES)
Figure 7. Input Bias, Offset Current vs. Temperature
Figure 8. Input Bias, Offset Current vs. Common-Mode Voltage
Figure 9. Input Offset Voltage WarmUp Drift
EFFECTIVE OFFSET VOLTAGE DRIFT (V/C)
10000
EFFECTIVE OFFSET VOLTAGE (V)
100
SHORT-CIRCUIT CURRENT (mA)
BALANCED OR UNBALANCED VS = 15V VCM = 0V 1000
BALANCED OR UNBALANCED VS = 15V VCM = 0V 10
100 -55C TA 125C
1
TA = +25C 10 10 100 1k 10k 100k 1M SOURCE RESISTANCE () 10M
0.1
100
1k 10k 100k 1M 10M SOURCE RESISTANCE ()
100M
35 30 25 20 15 10 5 0 -5 -10 -15 -20 -25 -30 -35
TA = -55C TA = +25C TA = +125C VS = 15V OUTPUT SHORTED TO GROUND TA = +125C TA = +25C TA = -55C 0 1 2 3 4 TIME FROM OUTPUT SHORT (MINUTES)
Figure 10. Effective Offset Voltage vs. Source Resistance
Figure 11. Effective TCVOS vs. Source Resistance
Figure 12. Short Circuit Current vs. Time, Temperature
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OP297-Typical Performance Characteristics
1300 COMMON-MODE REJECTION (dB) NO LOAD 160 140 120 100 80 60 40 20 0 1 10 100 1k 10k FREQUENCY (Hz) 100k 1M POWER SUPPLY REJECTION (dB) TA = +25C VS = 15V 140 120 100 80 60 +PSR 40 20 -PSR
TA = +25C VS = 15V VS = 10Vp-p
TOTAL SUPPLY CURRENT (A)
1200
TA = +125C
1100 TA = +25C 1000 TA = -55C 900
800 0
5 10 15 SUPPLY VOLTAGE (VOLTS)
20
0.1
1
10
100
1k
10k
100k 1M
FREQUENCY (Hz)
Figure 13. Total Supply Current vs. Supply Voltage
Figure 14. Noise Density vs. Frequency
Figure 15. Open Loop Gain Linearity
100 TA = +25C VS = 2V TO 15V
Hz)
1000
Hz)
10 TA = +25C VS = 2V TO 20V
10000
TA = -55C TA = +25C
Hz)
CURRENT NOISE DENSITY (fA/
VOLTAGE NOISE DENSITY (nV/
TOTAL NOISE DENSITY (V/
0
CURRENT NOISE VOLTAGE NOISE
100
1 10Hz
OPEN-LOOP GAIN (V/mV)
TA = +125C
1000
1kHz 0.1
100
10
1kHz 10Hz
100 1
VS = 15V VO = 10V
10
1
10
100
1000
1
0.01
102
FREQUENCY (Hz)
103 104 105 106 SOURCE RESISTANCE ()
107
2
3
5
10
20
LOAD RESISTANCE (k)
Figure 16. Common-Mode Rejection vs. Frequency
Figure 17. Total Noise Density vs. Source Resistance
Figure 18. Maximum Output Swing vs. Load Resistance
DIFFERENTIAL INPUT VOLTAGE (10V/DIV)
35
35 TA = +25C VS = 15V AVCL = +1 1%THD fo = 1kHz 30
OUTPUT SWING (Vp-p)
OUTPUT SWING (Vp-p)
RL = 10k VS = 15V VCM = 0V
30
TA = +125C
25 20 15 10 5 0
25 20 15 10 5 0
TA = +25C VS = 15V AVCL = +1 1%THD RL = 10k
TA = +25C
TA = -55C
-15
10 -10 -5 0 5 OUTPUT VOLTAGE (VOLTS)
15
10
100
1k
10k
100
1k
10k
100k
LOAD RESISTANCE ()
FREQUENCY (Hz)
Figure 19. Power Supply Rejection vs. Frequency
Figure 20. Open Loop Gain vs. Load Resistance
Figure 21. Maximum Output Swing vs. Frequency
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OP297
100 80 VS = 15V CL = 30pF RL = 1M
70 60
OVERSHOOT (%) TA = +25C VS = 15V AVCL = +1 VOUT = 100mVp-p -EDGE
OUTPUT IMPEDANCE ()
1000 100 10 1 0.1 0.01 0.001 TA = +25C VS = 15V
GAIN
OPEN-LOOP GAIN (dB)
60 40 20 0 TA = -55C 90 135 180 225 TA = +125C
50 40 30 20 10 0
-20 -40
PHASE SHIFT (DEG)
PHASE
+EDGE
100
1k
10k 100 1M FREQUENCY (Hz)
10M
10
1000 100 LOAD CAPACITANCE (pF)
10000
10
100
1k 10k 100k FREQUENCY (Hz)
1M
Figure 22. Open Loop Gain, Phase vs. Frequency
Figure 23. Small Signal Overshoot vs. Capacitance Load
Figure 24. Open Loop Output Impedance vs Frequency
APPLICATIONS INFORMATION
Extremely low bias current over the full military temperature range makes the OP297 attractive for use in sample-and-hold amplifiers, peak detectors, and log amplifiers that must operate over a wide temperature range. Balancing input resistances is not necessary with the OP297 Offset voltage and TCVOS are degraded only minimally by high source resistance, even when unbalanced. The input pins of the OP297 are protected against large differential voltage by back-to-back diodes and current-limiting resistors. Common-mode voltages at the inputs are not restricted, and may vary over the full range of the supply voltages used. The OP297 requires very little operating headroom about the supply rails, and is specified for operation with supplies as low as +2 V. Typically, the common-mode range extends to within one volt of either rail. The output typically swings to within one volt of the rails when using a 10 k load.
AC PERFORMANCE
100 90
10 0%
20mV
5s
Figure 26. Small-Signal Transient Response (CLOAD = 1000 pF, AVCL = +1)
100 90
The OP297'S AC characteristics are highly stable over its full operating temperature range. Unity-gain small-signal response is shown in Figure 25. Extremely tolerant of capacitive loading on the output, the OP297 displays excellent response even with 1000 pF loads (Figure 26).
10 0%
20mV
100 90
5s
Figure 27. Large-Signal Transient Response (AVCL = +1)
GUARDING AND SHIELDING
10 0%
20mV
5s
To maintain the extremely high input impedances of the OP297, care must be taken in circuit board layout and manufacturing. Board surfaces must be kept scrupulously clean and free of moisture. Conformal coating is recommended to provide
Figure 25. Small-Signal Transient Response (CLOAD = 100 pF, AVCL = +1)
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OP297
UNITY-GAIN FOLLOWER NONINVERTING AMPLIFIER
-
1/2 OP-297
-
1/2 OP-297
+
+
INVERTING AMPLIFIER MINI-DIP BOTTOM VIEW 8 1 A B
-
1/2 OP-297
+
Figure 28. Guard Ring Layout and Connections
a humidity barrier. Even a clean PC board can have 100 pA of leakage currents between adjacent traces, so guard rings should be used around the inputs. Guard traces are operated at a voltage close to that on the inputs, as shown in Figure 28, so that leakage currents become minimal. In noninverting applications, the guard ring should be connected to the common-mode voltage at the inverting input. In inverting applications, both inputs remain at ground, so the guard trace should be grounded. Guard traces should be on both sides of the circuit board.
APPLICATIONS
PRECISION ABSOLUTE VALUE AMPLIFIER
The circuit of Figure 30 is a precision absolute value amplifier with an input impedance of 30 M. The high gain and low TCVOS of the OP297 insure accurate operation with microvolt input signals. In this circuit, the input always appears as a common-mode signal to the op amps. The CMR of the OP297 exceeds 120 dB, yielding an error of less than 2 ppm.
+15V
OPEN-LOOP GAIN LINEARITY
C2 0.1F R1 1k C1 30pF 1 C3 0.1F -15V
TA = +25C
The OP297 has both an extremely high gain of 2000 V/mV minimum and constant gain linearity. This enhances the precision of the OP297 and provides for very high accuracy in high closed loop gain applications. Figure 29 illustrates the typical open-loop gain linearity of the OP297 over the military temperature range.
DIFFERENTIAL INPUT VOLTAGE (10V/DIV)
R3 1k 6
2
- +
8
D1 1N4148 D2
- +
VIN
RL = 10k VS = 15V VCM = 0V
3
1/2 OP-297 4
5 1N4148
1/2 OP-297
7 0V < VOUT < 10V
R2 2k
TA = +125C
Figure 30. Precision Absolute Value Amplifier
PRECISION CURRENT PUMP
TA = -55C
-15
10 -10 -5 0 5 OUTPUT VOLTAGE (VOLTS)
15
Maximum output current of the precision current pump shown in Figure 31 is 10 mA. Voltage compliance is 10 V with 15 V supplies. Output impedance of the current transmitter exceeds 3 M with linearity better than 16 bits.
Figure 29. Open-Loop Linearity of the OP297
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OP297
PRECISION POSITIVE PEAK DETECTOR SIMPLE BRIDGE CONDITIONING AMPLIFIER
In Figure 32, the CH must be of polystyrene, Teflon(R)*, or polyethylene to minimize dielectric absorption and leakage. The droop rate is determined by the size of CH and the bias current of the OP297.
R3 10k R1 - VIN + 10k 10k R2 2
Figure 33 shows a simple bridge conditioning amplifier using the OP297. The transfer function is:
R RF V OUT =V REF R + R R
-
1/2 OP-297 1 +15V
R5 100
The REF43 provides an accurate and stable reference voltage for the bridge. To maintain the highest circuit accuracy, RF should be 0.1% or better with a low temperature coefficient.
IOUT 10mA
1k
3
+
1N4148
+15V 0.1F 6 1k
8 R4 10k 7
1/2 OP-297 4
+
5
VIN 1k
2
- +
3
1/2 OP-297
1
2N930
-
6
CH
8 1/2 OP-297 5 + 4
-
7 0.1F
VOUT
-15V RESET 1k
V V IOUT = IN = IN = 10mA/V R5 100
-15V
Figure 31. Precision Current Pump
Figure 32. Precision Positive Peak Detector
+5V 2 6 REF-43 R 4 R 2 2.5V VREF
RF
-
1/2 OP-297 1 VOUT
R
R + R
3
+
+5V 6 VOUT = VREF
- +
8 7
(
R R + R
(
RF R
5
1/2 OP-297 4 -5V
Figure 33. A Simple Bridge Conditioning Amplifier Using the OP297
*Teflon is a registered trademark of the Dupont Company
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OP297
NONLINEAR CIRCUITS
Exponentiating both sides of the equation leads to:
IO = (I IN )2 I REF
Due to its low input bias currents, the OP297 is an ideal log amplifier in nonlinear circuits such as the square and squareroot circuits shown in Figures 34 and 35. Using the squaring circuit of Figure 34 as an example, the analysis begins by writing a voltage loop equation across transistors Q1, Q2, Q3 and Q4.
Op amp A2 forms a current-to-voltage converter which gives VOUT = R2 x 10. Substituting (VIN/R1) for IIN and the above equation for IO yields:
R2 V IN V OUT = I REF R1
2
I I I I V T1 ln IN +V T2 ln IN =V T 3 ln O +V T 4 ln REF I S1 I S2 I S3 I S4
All the transistors of the MAT04 are precisely matched and at the same temperature, so the IS and VT terms cancel, giving: 2 ln IIN = ln IO + ln IREF = ln (IO x IREF)
A similar analysis made for the square-root circuit of Figure 35 leads to its transfer function:
V OUT = R2
(V IN )(I REF ) R1
C2 100pF R2 33k 6 IO 1 2 Q1 3 6 7 Q2 5
-
5
+
1/2 OP-297 A2
7
VOUT
MAT-04E
C1 100pF 8 Q3 10 R1 VIN 33k IIN 8 1/2 OP-297 3 A1 +4 2 9 IREF 14 Q4 12 13
V+
-
1
R3 50k R4 50k -15V
V-
Figure 34. Squaring Amplifier
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OP297
R2 33k C2 100pF 6
-
1/2 OP-297 7 VOUT
IO
5
+
MAT-04E
IIN C1
2
Q1 1 3
IREF
13 100pF V+ 6 R1 VIN 33k 3 2 7 Q2 5 1 R5 2k 8 Q3 10 R3 50k 9
14 Q4 12
- +
8
1/2 OP-297 4
R4 50k -15V
V-
Figure 35. Square-Root Amplifier
In these circuits, IREF is a function of the negative power supply. To maintain accuracy, the negative supply should be well regulated. For applications where very high accuracy is required, a voltage reference may be used to set IREF. An important consideration for the squaring circuit is that a sufficiently large input voltage can force the output beyond the operating range of the output op amp. Resistor R4 can be changed to scale IREF, or R1, and R2 can be varied to keep the output voltage within the usable range. Unadjusted accuracy of the square-root circuit is better than 0.1% over an input voltage range of 100 mV to 10 V. For a similar input voltage range, the accuracy of the squaring circuit is better than 0.5%.
OP297 SPICE MACRO-MODEL
Figures 36 and 37 show the node end net list for a SPICE macro model of the OP297. The model is a simplified version of the actual device and simulates important dc parameters such as VOS, IOS, IB, AVO, CMR, VO and ISY. AC parameters such as slew rate, gain and phase response and CMR change with frequency are also simulated by the model. The model uses typical parameters for the OP297. The poles and zeros in the model were determined from the actual open and closed-loop gain and phase response of the OP297. In this way, the model presents an accurate ac representation of the actual device. The model assumes an ambient temperature of 25C.
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OP297
99 R3 R4
+
- V2
13 C4 R8 15 16
C2 5 6 12
D3
2 -IN
RIN2
G1
R7
C3
+
8 R1
Q1
Q2
- E1
R9
CIN 1 +IN 7 RIN1
IOS
3 R2
D1
D2
10 R5 4
11 D4 14 I1
-+
EOS
9
50
C6
C7
17
R11
R13
22
+
+
G2 98
R10
C5
- E2
R12
- E3
R14
G3
R15
+
- V3
C8
99
R16 ISY D5 26 22 23 D6 27
D7
D8 V4
G6
R18
+-
25 V5 L1
-+
28 R17 D9 50 G4 G5 D 10 G7 29 R19
Figure 36. OP297 Macro-Model
+
R6
98
- EREF
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OP297
Table I. SPICE Net-List
OP297 SPICE MACRO-MODEL * * NODE ASSIGNMENTS *NONINVERTING INPUT INVERTING INPUT OUTPUT POSITIVE SUPPLY NEGATIVE SUPPLY * SUBCKT OP297 1 2 30 99 50 * INPUT STAGE & POLE AT 6 MHz * RIN1 1 7 2500 RIN2 2 8 2500 R1 8 3 5E11 R2 7 3 5E11 R3 5 99 612 R4 6 99 612 CIN 7 8 3E-12 C2 5 6 21.67E-12 I1 4 50 0.1E-3 IOS 7 8 20E-12 EOS 9 7 POLY(1) 19 23 25E-6 1 Q1 5 8 10 QX Q2 6 9 11 QX R5 10 4 96 R6 11 4 96 D1 8 9 DX D2 9 8 DX * EREF 98 0 23 0 1 * GAIN STAGE & DOMINANT POLE AT 0.13 HZ * R7 12 98 2.45E9 C3 12 98 500E-12 G1 98 12 5 6 1.634E-3 V2 99 13 1.5 V3 14 50 1.5 D3 12 13 DX D4 14 12 DX * * NEGATIVE ZERO AT -1 8 MHz * R8 15 16 1E6 C4 15 16 -88.4E-15 R9 16 98 1 E1 15 98 12 23 1E6 *
* POLE AT 1.8 MHz * R10 17 98 1E6 C5 17 98 88 4E-15 G2 98 17 16 23 1 E-6 * * COMMON-MODE GAIN NETWORK WITH ZERO AT 50 HZ * R11 18 19 1E6 C6 18 19 3.183E-9 R12 19 98 1 E2 18 98 3 23 100E-3 * * POLE AT 6 MHz * R15 22 98 1E6 C8 22 98 26.53E-15 G3 98 22 17 23 1 E-6 * * OUTPUT STAGE * R16 23 99 160K R17 23 50 160K ISY 99 50 331 E-6 R18 25 99 200 R19 25 50 200 L1 25 30 1 E-7 G4 28 50 22 25 5E-3 G5 29 50 25 22 5E-3 G6 25 99 99 22 5E-3 G7 50 25 22 50 5E-3 V4 26 25 1.8 V5 25 27 1.3 D5 22 26 DX D6 27 22 DX D7 99 28 DX D8 99 29 DX D9 50 28 DY D10 50 29 DY * * MODELS USED * * MODEL QX NPN BF=2.5E6) * MODEL DX D IS = 1 E-15) * MODEL DY D IS = 1 E-15 BV = 50) * ENDS OP297
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OP297
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead Plastic DIP (N-8)
0.430 (10.92) 0.348 (8.84)
8 5
0.280 (7.11) 0.240 (6.10)
1 4
PIN 1 0.210 (5.33) MAX 0.160 (4.06) 0.115 (2.93)
0.060 (1.52) 0.015 (0.38) 0.130 (3.30) MIN SEATING PLANE
0.325 (8.25) 0.300 (7.62) 0.195 (4.95) 0.115 (2.93)
0.022 (0.558) 0.100 0.070 (1.77) 0.014 (0.356) (2.54) 0.045 (1.15) BSC
0.015 (0.381) 0.008 (0.204)
8-Lead Cerdip (Q-8)
0.005 (0.13) MIN
8
0.055 (1.4) MAX
5
0.310 (7.87) 0.220 (5.59)
1 4
PIN 1 0.405 (10.29) MAX 0.200 (5.08) MAX 0.060 (1.52) 0.015 (0.38) 0.150 (3.81) MIN SEATING PLANE
0.320 (8.13) 0.290 (7.37)
0.200 (5.08) 0.125 (3.18) 0.023 (0.58) 0.100 0.070 (1.78) 0.014 (0.36) (2.54) 0.030 (0.76) BSC
15 0
0.015 (0.38) 0.008 (0.20)
8-Lead Narrow Body (SOIC) (SO-8)
0.1968 (5.00) 0.1890 (4.80)
8 1 5 4
0.1574 (4.00) 0.1497 (3.80)
0.2440 (6.20) 0.2284 (5.80)
PIN 1 0.0098 (0.25) 0.0040 (0.10)
0.0688 (1.75) 0.0532 (1.35)
0.0196 (0.50) x 45 0.0099 (0.25)
SEATING PLANE
0.0500 0.0192 (0.49) (1.27) 0.0138 (0.35) BSC
0.0098 (0.25) 0.0075 (0.19)
8 0
0.0500 (1.27) 0.0160 (0.41)
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OP297
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PRINTED IN U.S.A.
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