8/21/97 4:00 PM a Dual Low Bias Current Precision Operational Amplifier OP297 GENERAL DESCRIPTION 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 µV, and low drift, below 0.6 µV/°C. Open-loop gain exceeds 2000 V/mV insuring high linearity in every application. Plastic Epoxy-DIP (P Suffix) 8-Pin Cerdip (Z Suffix) 8-Pin Narrow Body SOIC (S Suffix) OUT A 1 8 V+ 7 OUT B +IN A 3 6 –IN B V– 4 5 +IN B 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 25°C, but double for every 10°C rise in temperature, to reach the nanoamp range above 85°C. Input bias current of the OP 297 is under 100 pA at 25°C 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 I B– 40 VS = ±15V VCM = 0V IB+ 1200 UNITS NUMBER OF UNITS INPUT CURRENT (pA) B 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 µA per amplifier and it can operate with supply voltages as low as ± 2 V. 60 20 0 20 A – + –IN A 2 – 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 PIN CONNECTIONS + FEATURES Precision Performance in Standard SO-8 Pinout Low Offset Voltage: 50 V max Low Offset Voltage Drift: 0.6 V/ⴗC max Very Low Bias Current: ␣ ␣ +25ⴗC (100 pA max) ␣ ␣ –55ⴗC to +125ⴗC (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 IOS 300 TA = +25°C VS = ±15V VCM = 0V 200 100 –40 –60 –75 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 Figure 1. Low Bias Current Over Temperature 0 –100 –80 –60 –40 –20 0 20 40 60 80 100 INPUT OFFSET VOLTAGE (µV) Figure 2. Very Low Offset REV. D 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 © Analog Devices, Inc., 1997 8/21/97 4:00 PM OP297–SPECIFICATIONS ELECTRICAL CHARACTERISTICS (@ V = ⴞ15 V, T = +25ⴗC, unless otherwise noted.) S Parameter Symbol Conditions 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 VOS IOS IB en p-p en en in A ␣ ␣ ␣ ␣ OP297A/E Min Typ Max 25 RIN RINCM Supply Current Per Amplifier Supply Voltage Slew Rate Gain Bandwidth Product Channel Separation AVO IVR CMR PSR VO VO ISY VS SR GBWP CS Input Capacitance CIN VO = ± 10 V RL = 2 kΩ (Note 1) VCM = ± 13 V VS = ± 2 V to ± 20 V RL = 10 kΩ RL = 2 kΩ No Load Operating Range AV = +1 VO = 20 V p–p fO = 10 Hz 50 0.1 20 20 0.5 20 17 20 VCM = 0 V VCM = 0 V 0.1 Hz to 10 Hz fO = 10 Hz fO = 1000 Hz fO = 10 Hz 2000 ± 13 120 120 ± 13 ± 13 ±2 0.05 ␣ ␣ ␣ ␣ OP297F Min Typ 50 ␣ ␣ ␣ ␣ ␣ OP297G Min Typ Max 100 0.1 35 35 0.5 20 17 20 100 ± 100 Max 80 0.1 50 50 0.5 20 17 20 150 ± 150 200 200 ± 200 Units µV µV/mo pA pA µV p-p nV/√Hz nV/√Hz fA√Hz 30 30 30 MΩ 500 500 500 GΩ 3200 ± 14 135 125 ± 14 ± 13.7 525 625 ± 20 0.15 500 150 V/mV V dB dB V V µA V V/µs kHz dB 3 pF 4000 ± 14 140 130 ± 14 ± 13.7 525 625 ± 20 0.15 500 150 1500 ± 13 114 114 ± 13 ± 13 ±2 0.05 3 3200 ± 14 135 125 ± 14 ± 13.7 525 625 ± 20 0.15 500 150 1200 ± 13 114 114 ± 13 ± 13 ±2 0.05 3 NOTES 1 Guaranteed by CMR test. Specifications subject to change without notice. ELECTRICAL CHARACTERISTICS (@ V = ⴞ15 V, –55ⴗC ≤ T ≤ +125ⴗC for OP297A, unless otherwise noted.) S 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 VOS TCVOS IOS IB AVO IVR CMR PSR VO ISY VS A Conditions VCM = 0 V VCM = 0 V VO = ± 10 V, RL = 2 kΩ (Note 1) VCM = ± 13 VS = ± 2.5 V to ± 20 V RL = 10 kΩ No Load Operating Range ␣␣␣␣␣ Min 1200 ± 13 114 114 ± 13 ± 2.5 OP297A Typ 45 0.2 60 60 2700 ± 13.5 130 125 ± 13.4 575 Max Units 100 0.6 450 ± 450 µV µV/°C pA pA V/mV V dB dB V µA V 750 ± 20 NOTES 1 Guaranteed by CMR test. Specifications subject to change without notice. –2– REV. D 8/21/97 4:00 PM OP297 ELECTRICAL CHARACTERISTICS (@ V = ⴞ15 V, –40ⴗC ≤ T ≤ +85ⴗC for OP297E/F/G, unless otherwise noted.) S Parameter Symbol Input Offset Voltage Average Input Offset Voltage Drift Input Offset Current Input Bias Current Large-Signal Voltage Gain VOS Input Voltage Range Common-Mode Rejection Power Supply Rejection IVR CMR PSR TCVOS IOS IB AVO Output Voltage Swing VO Supply Current Per Amplifier ISY Supply Voltage VS A ␣ ␣ ␣ ␣ OP297E Min Typ Max Conditions VCM = 0 V VCM = 0 V VO = ±10 V, RL = 2 kΩ (Note 1) VCM = ± 13 VS = ± 2.5 V to ±20 V RL = 10 kΩ No Load Operating Range ␣ ␣ ␣ ␣ OP297F Min Typ Max ␣ ␣ ␣ ␣ ␣ OP297G Min Typ Max Units 35 100 80 300 110 400 µV 0.2 50 50 0.6 450 ± 450 0.5 80 80 2.0 750 ± 750 0.6 80 80 2.0 750 ± 750 µV/°C pA pA 1200 ± 13 114 3200 ± 13.5 130 1000 2500 ± 13 ± 13.5 108 130 700 ± 13 108 2500 ± 13.5 130 V/mV V dB 114 ± 13 0.15 ± 13.4 550 750 ± 20 108 ± 13 108 ± 13 0.3 ± 13.4 550 750 ± 20 dB V µA V ± 2.5 ± 2.5 0.15 ± 13.4 550 750 ± 20 ± 2.5 NOTES 1 Guaranteed by CMR test. Specifications subject to change without notice. Wafer Test Limits (@ V = ⴞ15 V, T = +25ⴗC, unless otherwise noted.) S A Parameter Symbol Conditions Limit Units Input Offset Voltage Input Offset Current VOS IOS VCM = 0 V 200 200 µV max pA max Input Bias Current Large-Signal Voltage Gain Input Voltage Range Common-Mode Rejection Power Supply Output Voltage Swing Supply Current Per Amplifier IB AVO IVR CMR PSR VO ISY VCM = 0 V VO = ± 10 V, RL = 2 kΩ (Note 1) VCM = ± 13 V VS = ± 2 V to ± l 8 V RL = 2 kΩ No Load ± 200 1200 ± 13 114 114 ± 13 625 pA max V/mV min V min dB min dB min V min µA max 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 +VS OUTPUT A 0.118 (3.00) –INPUT A OUTPUT B +INPUT A –INPUT B –VS +INPUT B 0.074 (1.88) REV. D –3– 8/21/97 4:00 PM OP297 ABSOLUTE MAXIMUM RATINGS 1 Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 20 V Input Voltage2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 20 V Differential Input Voltage2 . . . . . . . . . . . . . . . . . . . . . . . . 40 V Output Short-Circuit Duration . . . . . . . . . . . . . . . . Indefinite Storage Temperature Range Z Package . . . . . . . . . . . . . . . . . . . . . . . . . –65°C to +175°C P, S Package . . . . . . . . . . . . . . . . . . . . . . . –65°C to +150°C Operating Temperature Range OP297A (Z) . . . . . . . . . . . . . . . . . . . . . . . –55°C to +125°C OP297E, F (Z) . . . . . . . . . . . . . . . . . . . . . . –40°C to +85°C OP297F, G (P, S) . . . . . . . . . . . . . . . . . . . –40°C to +85°C Junction Temperature Z Package . . . . . . . . . . . . . . . . . . . . . . . . . –65°C to +175°C P, S Package . . . . . . . . . . . . . . . . . . . . . . . –65°C to +150°C Lead Temperature Range (Soldering, 60 sec) . . . . . . . +300°C Package Type JA3 JC Units 8-Pin Cerdip (Z) 8-Pin Plastic DIP (P) 8-Pin SO (S) 134 96 150 12 37 41 °C/W °C/W °C/W 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 θJA is specified for worst case mounting conditions, i.e., θJA is specified for device in socket for cerdip and P-DIP, packages; θJA is specified for device soldered to printed circuit board for SO package. ORDERING GUIDE1 Model Temperature Range Package Description Package Option1 OP297AZ OP297EZ OP297EP OP297FP OP297FS OP297FS-REEL OP297FS-REEL7 OP297GP OP297GS OP297GS-REEL OP297GS-REEL72 –55°C to +125°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C 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 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 + 2kΩ 50kΩ 50Ω – 1/2 OP-297 V2 + CHANNEL SEPARATION = 20 log ) ) V1 V2/10000 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. –4– WARNING! ESD SENSITIVE DEVICE REV. D 8/21/97 4:00 PM Typical Performance Characteristics– OP297 400 250 100 Figure 4. Typical Distribution of Input Offset Voltage 150 100 0 –100 –80 –60 –40 –20 0 20 40 200 100 0 –100 –80 –60 –40 –20 0 20 40 60 80 100 INPUT OFFSET CURRENT (pA) 60 80 100 Figure 5. Typical Distribution of Input Bias Current Figure 6. Typical Distribution of Input Offset Current ±3 IB+ 20 0 IOS 20 40 INPUT CURRENT (pA) 40 VS = ±15V VCM = 0V TA = +25°C VS = ±15V DEVIATION FROM FINAL VALUE (µV) 60 IB– IB– IB+ 20 0 IOS –20 –40 –40 –60 100 125 10000 BALANCED OR UNBALANCED VS = ±15V VCM = 0V 1000 100 –55°C ≤ TA ≤ 125°C TA = +25°C 10 100 1k 10k 100k 1M SOURCE RESISTANCE (Ω) 10M Figure 10. Effective Offset Voltage vs. Source Resistance REV. D ±2 ±1 –10 –5 0 5 10 15 COMMON-MODE VOLTAGE (VOLTS) Figure 8. Input Bias, Offset Current vs. Common-Mode Voltage BALANCED OR UNBALANCED VS = ±15V VCM = 0V 10 1 100 1k 10k 100k 1M 10M SOURCE RESISTANCE (Ω) 100M Figure 11. Effective TCVOS vs. Source Resistance –5– 0 1 2 3 4 5 TIME AFTER POWER APPLIED (MINUTES) Figure 9. Input Offset Voltage WarmUp Drift 100 0.1 TA = +25°C VS = ±15V VCM = 0V 0 –15 SHORT-CIRCUIT CURRENT (mA) Figure 7. Input Bias, Offset Current vs. Temperature EFFECTIVE OFFSET VOLTAGE DRIFT (µV/°C) –60 –75 –50 –25 0 25 50 75 TEMPERATURE (°C) TA = +25°C VS = ±15V VCM = 0V 300 INPUT BIAS CURRENT (pA) 60 INPUT CURRENT (pA) 1200 UNITS 50 0 –100 –80 –60 –40 –20 0 20 40 60 80 100 INPUT OFFSET VOLTAGE (µV) EFFECTIVE OFFSET VOLTAGE (µV) TA = +25°C VS = ±15V VCM = 0V 200 200 10 400 1200 UNITS NUMBER OF UNITS NUMBER OF UNITS 300 TA = +25°C VS = ±15V VCM = 0V NUMBER OF UNITS 1200 UNITS 35 30 25 20 15 10 5 0 –5 –10 –15 –20 –25 –30 –35 TA = –55°C TA = +25°C TA = +125°C VS = ±15V OUTPUT SHORTED TO GROUND TA = +125°C TA = +25°C TA = –55°C 0 1 2 3 4 TIME FROM OUTPUT SHORT (MINUTES) Figure 12. Short Circuit Current vs. Time, Temperature 8/21/97 4:00 PM OP297–Typical Performance Characteristics 1300 TA = +25°C 1000 TA = –55°C 900 0 ±5 ±10 ±15 SUPPLY VOLTAGE (VOLTS) 100 10 1 10 100 1 1000 40 20 DIFFERENTIAL INPUT VOLTAGE (10µV/DIV) 80 +PSR 40 100 1k 10k FREQUENCY (Hz) 10Hz 1kHz 0.1 15 Figure 19. Power Supply Rejection vs. Frequency 100k 1M TA = +125°C 1000 VS = ±15V VO = ±10V 1kHz 100 102 103 104 105 106 SOURCE RESISTANCE (Ω) 1 107 3 2 5 10 20 LOAD RESISTANCE (kΩ) Figure 17. Total Noise Density vs. Source Resistance Figure 18. Maximum Output Swing vs. Load Resistance 35 TA = +25°C VS = ±15V AVCL = +1 1%THD fo = 1kHz 25 TA = +25°C VS = ±15V AVCL = +1 1%THD RL = 10kΩ 30 20 15 10 0 10 –10 –5 0 5 OUTPUT VOLTAGE (VOLTS) 10k TA = –55°C 5 –15 1k TA = +25°C OUTPUT SWING (Vp-p) TA = –55°C 100 Figure 15. Open Loop Gain Linearity 10Hz OUTPUT SWING (Vp-p) TA = +25°C 10 FREQUENCY (Hz) 1 0.01 1 10000 30 TA = +125°C 0.1 100k 1M 35 RL = 10kΩ VS = ±15V VCM = 0V –PSR 60 TA = +25°C VS = ±2V TO ±20V FREQUENCY (Hz) Figure 16. Common-Mode Rejection vs. Frequency 100 20 10 Hz) Hz) VOLTAGE NOISE 60 10 CURRENT NOISE DENSITY (fA/ Hz) VOLTAGE NOISE DENSITY (nV/ 100 CURRENT NOISE 80 Figure 14. Noise Density vs. Frequency 1000 0 100 1 Figure 13. Total Supply Current vs. Supply Voltage TA = +25°C VS = ±2V TO ±15V 120 TA = +25°C VS = ±15V ∆VS = 10Vp-p 120 0 ±20 100 140 OPEN-LOOP GAIN (V/mV) 800 TA = +25°C VS = ±15V POWER SUPPLY REJECTION (dB) COMMON-MODE REJECTION (dB) 1100 TOTAL NOISE DENSITY (µV/ TOTAL SUPPLY CURRENT (µA) TA = +125°C 1200 10 140 160 NO LOAD 25 20 15 10 5 10 100 1k 10k LOAD RESISTANCE (Ω) Figure 20. Open Loop Gain vs. Load Resistance –6– 0 100 1k 10k 100k FREQUENCY (Hz) Figure 21. Maximum Output Swing vs. Frequency REV. D 8/21/97 4:00 PM OP297 100 40 TA = –55°C 90 20 135 0 180 –20 225 50 TA = +25°C VS = ±15V –EDGE OUTPUT IMPEDANCE (Ω) 60 PHASE TA = +25°C VS = ±15V AVCL = +1 VOUT = 100mVp-p 60 OVERSHOOT (%) GAIN PHASE SHIFT (DEG) OPEN-LOOP GAIN (dB) 80 1000 70 VS = ±15V CL = 30pF RL = 1MΩ +EDGE 40 30 20 100 10 1 0.1 0.01 10 TA = +125°C –40 100 1k 10k 100 1M FREQUENCY (Hz) 0 10M 10 1000 100 LOAD CAPACITANCE (pF) 0.001 10000 100 1k 10k 100k FREQUENCY (Hz) 1M Figure 24. Open Loop Output Impedance vs Frequency Figure 23. Small Signal Overshoot vs. Capacitance Load Figure 22. Open Loop Gain, Phase vs. Frequency 10 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. 100 90 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. 10 0% 20mV 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 kΩ load. 5µs Figure 26. Small-Signal Transient Response (CLOAD = 1000 pF, AVCL = +1) AC PERFORMANCE 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 5µs 100 90 Figure 27. Large-Signal Transient Response (AVCL = +1) GUARDING AND SHIELDING 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 10 0% 20mV 5µs Figure 25. Small-Signal Transient Response (CLOAD = 100 pF, AVCL = +1) REV. D –7– 8/21/97 4:00 PM OP297 UNITY-GAIN FOLLOWER NONINVERTING AMPLIFIER – – 1/2 OP-297 1/2 OP-297 + + INVERTING AMPLIFIER MINI-DIP BOTTOM VIEW 8 1 – 1/2 OP-297 A + B Figure 28. Guard Ring Layout and Connections APPLICATIONS 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. PRECISION ABSOLUTE VALUE AMPLIFIER The circuit of Figure 30 is a precision absolute value amplifier with an input impedance of 30 MΩ. 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 C2 OPEN-LOOP GAIN LINEARITY 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. 0.1µF 2 DIFFERENTIAL INPUT VOLTAGE (10µV/DIV) VIN RL = 10kΩ VS = ±15V VCM = 0V 3 – 1/2 OP-297 + C1 30pF 8 4 R1 R3 1kΩ 1kΩ D1 1N4148 6 D2 1 C3 5 – 1/2 OP-297 + 7 0V < VOUT < 10V 1N4148 R2 2kΩ 0.1µF TA = +125°C –15V TA = +25°C Figure 30. Precision Absolute Value Amplifier TA = –55°C –15 10 –10 –5 0 5 OUTPUT VOLTAGE (VOLTS) PRECISION CURRENT PUMP 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 MΩ with linearity better than 16 bits. 15 Figure 29. Open-Loop Linearity of the OP297 –8– REV. D 8/21/97 4:00 PM OP297 PRECISION POSITIVE PEAK DETECTOR SIMPLE BRIDGE CONDITIONING AMPLIFIER In Figure 32, the CH must be of polystyrene, Teflon®*, 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. Figure 33 shows a simple bridge conditioning amplifier using the OP297. The transfer function is: ∆R RF V OUT =V REF R + ∆R R R3 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. 10kΩ R1 – 10kΩ R2 VIN + 10kΩ 2 3 – 1/2 OP-297 R5 1 IOUT ±10mA 100Ω + 1kΩ +15V +15V 1N4148 8 R4 + 1/2 OP-297 7 10kΩ – 5 VIN 1kΩ 2 – 3 + 1/2 OP-297 0.1µF 1 6 2N930 1kΩ 6 8 1/2 OP-297 5 + 4 – 7 0.1µF CH 4 –15V RESET V V IOUT = IN = IN = 10mA/V R5 100Ω 1kΩ –15V Figure 32. Precision Positive Peak Detector Figure 31. Precision Current Pump +5V 2 6 VREF 2.5V RF REF-43 R R 4 2 R + ∆R R 3 – 1/2 OP-297 1 VOUT + +5V 6 5 VOUT = VREF – 8 1/2 OP-297 + ( ∆R R + ∆R ( 7 4 –5V Figure 33. A Simple Bridge Conditioning Amplifier Using the OP297 *Teflon is a registered trademark of the Dupont Company REV. D –9– RF R VOUT 8/21/97 4:00 PM OP297 Exponentiating both sides of the equation leads to: NONLINEAR CIRCUITS 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. 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 IO = Op amp A2 forms a current-to-voltage converter which gives VOUT = R2 × 10. Substituting (VIN/R1) for IIN and the above equation for IO yields: R2 V IN V OUT = I REF R1 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 × IREF) (I IN )2 I REF 2 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 33kΩ 6 IO – 1/2 OP-297 A2 5 7 VOUT + 1 2 Q1 3 6 7 Q2 5 MAT-04E C1 100pF 8 Q3 V+ IREF 9 R1 33kΩ IIN 2 – 8 1/2 OP-297 3 A1 + 4 13 12 10 VIN 14 Q4 R3 1 50kΩ R4 50kΩ –15V V– Figure 34. Squaring Amplifier –10– REV. D 8/21/97 4:00 PM OP297 R2 33kΩ C2 100pF 6 IO IIN 2 5 – 1/2 OP-297 7 VOUT + MAT-04E Q1 1 IREF 3 C1 13 100pF V+ 6 R1 VIN 2 33kΩ 3 – 5 8 1/2 OP-297 + 7 Q2 8 Q3 9 10 R5 R3 2kΩ 50kΩ 1 14 Q4 12 R4 50kΩ 4 –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%. REV. D 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 25°C. –11– 8/21/97 4:00 PM OP297 R3 + 99 R4 – V2 13 C2 C4 D3 5 6 R8 12 15 RIN2 8 Q1 Q2 R7 G1 + 2 –IN 16 C3 R9 – E1 R1 RIN1 +IN –+ 7 11 R5 4 R6 98 – EREF D4 14 9 EOS + R2 10 – V3 I1 50 G2 R10 C5 C7 R11 R13 – E2 + 17 C6 + 1 D2 D1 3 + IOS CIN R12 – E3 22 R14 G3 R15 C8 98 99 D7 R16 ISY D8 D5 G6 R18 V4 26 +– 22 25 23 D6 L1 V5 27 –+ 28 29 R19 R17 D9 G4 G5 D 10 G7 50 Figure 36. OP297 Macro-Model –12– REV. D 8/21/97 4:00 PM 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 • REV. D • 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 –13– 8/21/97 4:00 PM 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 0.060 (1.52) 0.015 (0.38) PIN 1 0.210 (5.33) MAX 0.325 (8.25) 0.300 (7.62) 0.195 (4.95) 0.115 (2.93) 0.130 (3.30) MIN 0.160 (4.06) 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) SEATING PLANE 8-Lead Cerdip (Q-8) 0.005 (0.13) MIN 0.055 (1.4) MAX 8 5 0.310 (7.87) 0.220 (5.59) 1 4 PIN 1 0.405 (10.29) MAX 0.200 (5.08) MAX 0.320 (8.13) 0.290 (7.37) 0.060 (1.52) 0.015 (0.38) 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 0.150 (3.81) MIN SEATING PLANE 0.015 (0.38) 0.008 (0.20) 15° 0° 8-Lead Narrow Body (SOIC) (SO-8) 0.1968 (5.00) 0.1890 (4.80) 0.1574 (4.00) 0.1497 (3.80) PIN 1 0.0098 (0.25) 0.0040 (0.10) SEATING PLANE 8 5 1 4 0.2440 (6.20) 0.2284 (5.80) 0.0688 (1.75) 0.0532 (1.35) 0.0500 0.0192 (0.49) (1.27) 0.0138 (0.35) BSC 0.0196 (0.50) x 45° 0.0099 (0.25) 0.0098 (0.25) 0.0075 (0.19) –14– 8° 0° 0.0500 (1.27) 0.0160 (0.41) REV. D –15– 8/21/97 4:00 PM PRINTED IN U.S.A. 000000000 OP297 –16– REV. D