Dual Low Bias Current Precision Operational Amplifier OP297 PIN CONFIGURATION Low offset voltage: 50 μV maximum Low offset voltage drift: 0.6 μV/°C maximum Very low bias current: 100 pA maximum Very high open-loop gain: 2000 V/mV minimum Low supply current (per amplifier): 625 μA maximum Operates from ±2 V to ±20 V supplies High common-mode rejection: 120 dB minimum –INB V– 4 5 +INB VS = ±15V VCM = 0V INPUT CURRENT (pA) 40 20 I B– 0 I B+ –20 IOS –60 –75 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 125 00300-002 –40 Figure 2. Low Bias Current over Temperature 400 1200 UNITS TA = 25°C VS = ±15V VCM = 0V NUMBER OF UNITS 300 200 100 0 –100 –80 –60 –40 –20 0 20 40 INPUT OFFSET VOLTAGE (µV) 60 80 100 00300-003 The OP297 uses 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 OP297 is under 100 pA at 25°C and is under 450 pA over the military temperature range per amplifier. This part can operate with supply voltages as low as ±2 V. 6 B 60 The OP297 is the first dual op amp to pack precision performance into the space saving, industry-standard 8-lead SOIC package. The combination of precision with low power and extremely low input bias current makes the dual OP297 useful in a wide variety of applications. Errors due to common-mode signals are eliminated by the common-mode rejection of over 120 dB, which minimizes offset voltage changes experienced in battery-powered systems. The supply current of the OP297 is under 625 μA. OUTB +INA 3 A Figure 1. GENERAL DESCRIPTION Precision performance of the OP297 includes very low offset (less than 50 μV) and low drift (less than 0.6 μV/°C). Openloop gain exceeds 2000 V/mV, ensuring high linearity in every application. V+ 7 –INA 2 APPLICATIONS Strain gage and bridge amplifiers High stability thermocouple amplifiers Instrumentation amplifiers Photocurrent monitors High gain linearity amplifiers Long-term integrators/filters Sample-and-hold amplifiers Peak detectors Logarithmic amplifiers Battery-powered systems 8 OUTA 1 00300-001 FEATURES Figure 3. Very Low Offset 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 device, see the OP497. Rev. G 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 ©2008 Analog Devices, Inc. All rights reserved. OP297 TABLE OF CONTENTS Features .............................................................................................. 1 AC Performance ............................................................................9 Applications ....................................................................................... 1 Guarding and Shielding ................................................................9 General Description ......................................................................... 1 Open-Loop Gain Linearity ....................................................... 10 Pin Configuration ............................................................................. 1 Application Circuits ....................................................................... 11 Revision History ............................................................................... 2 Precision Absolute Value Amplifier ......................................... 11 Specifications..................................................................................... 3 Precision Current Pump ............................................................ 11 Electrical Characteristics ............................................................. 3 Precision Positive Peak Detector .............................................. 11 Absolute Maximum Ratings............................................................ 4 Simple Bridge Conditioning Amplifier ................................... 11 Thermal Resistance ...................................................................... 4 Nonlinear Circuits ...................................................................... 12 ESD Caution .................................................................................. 4 Outline Dimensions ....................................................................... 13 Typical Performance Characteristics ............................................. 5 Ordering Guide .......................................................................... 14 Applications Information ................................................................ 9 REVISION HISTORY 4/08—Rev. F to Rev. G Changes to Table 2 Conditions ....................................................... 3 Changes to Table 2 Power Supply Rejection Parameter .............. 3 Changes to Figure 5, Figure 6, Figure 7 ......................................... 5 Changes to Figure 16 ........................................................................ 6 Updated Outline Dimensions ....................................................... 13 Changes to Ordering Guide .......................................................... 14 2/06—Rev. E to Rev. F Updated Format .................................................................. Universal Changes to Features.......................................................................... 1 Deleted OP297 Spice Macro Model Section ................................. 9 Updated Outline Dimensions ....................................................... 13 Changes to Ordering Guide .......................................................... 14 10/02—Rev. C to Rev. D Edits to Figure 16 ...............................................................................6 10/02—Rev. B to Rev. C Edits to Specifications .......................................................................2 Deleted Wafer Test Limits ................................................................3 Deleted Dice Characteristics ............................................................3 Deleted Absolute Maximum Ratings ..............................................4 Edits to Ordering Guide ...................................................................4 Updated Outline Dimensions ....................................................... 12 7/03—Rev. D to Rev. E Changes to TPCs 13 and 16 ............................................................ 4 Edits to Figures 12 and 14 ............................................................... 8 Changes to Nonlinear Circuits Section ......................................... 8 Rev. G | Page 2 of 16 OP297 SPECIFICATIONS ELECTRICAL CHARACTERISTICS @ VS = ±15 V, TA = 25°C, unless otherwise noted. Table 1. Parameter Input Offset Voltage Long-Term Input Voltage Stability Input Offset Current Input Bias Current Input Noise Voltage Input Noise Voltage Density Symbol VOS Conditions IOS IB en p-p en Input Noise Current Density Input Resistance Differential Mode Common-Mode Large Signal Voltage Gain in VCM = 0 V VCM = 0 V 0.1 Hz to 10 Hz fOUT = 10 Hz fOUT = 1000 Hz fOUT = 10 Hz RIN RINCM AVO Input Voltage Range 1 Common-Mode Rejection Power Supply Rejection VCM CMRR PSRR Output Voltage Swing VOUT Supply Current per Amplifier Supply Voltage Slew Rate Gain Bandwidth Product Channel Separation ISY VS SR GBWP CS Input Capacitance CIN 1 VOUT = ±10 V, RL = 2 kΩ VCM = ±13 V VS = ±2 V to ±20 V RL = 10 kΩ RL = 2 kΩ No load Operating range Min OP297E Typ Max 25 50 0.1 20 +20 0.5 20 17 20 2000 30 500 4000 ±13 120 120 ±13 ±13 ±2 0.05 AV = +1 VOUT = 20 V p-p, fOUT = 10 Hz Min 100 ±100 OP297F Typ Max 50 100 0.1 35 +35 0.5 20 17 20 1500 30 500 3200 ±14 140 130 ±13 114 114 ±14 ±13.7 525 ±13 ±13 625 ±20 0.15 500 150 ±2 0.05 3 Min 150 ±150 OP297G Typ Max 80 200 0.1 50 +50 0.5 20 17 20 Unit μV μV/month 200 ±200 pA pA μV p-p nV/√Hz nV/√Hz fA/√Hz 1200 30 500 3200 MΩ GΩ V/mV ±14 135 125 ±13 114 114 ±14 135 125 V dB dB ±14 ±13.7 525 ±13 ±13 ±14 ±13.7 525 0.15 500 150 V V μA V V/μs kHz dB 3 pF 625 ±20 0.15 500 150 ±2 0.05 3 625 ±20 Guaranteed by CMR test. @ VS = ±15 V, −40°C ≤ TA ≤ +85°C, unless otherwise noted. Table 2. Parameter Input Offset Voltage Average Input Offset Voltage Drift Input Offset Current Input Bias Current Large Signal Voltage Gain Symbol VOS TCVOS IOS IB AVO Input Voltage Range 1 Common-Mode Rejection Power Supply Rejection VCM CMRR PSRR Output Voltage Swing Supply Current per Amplifier Supply Voltage VOUT ISY VS 1 Conditions VCM = 0 V VCM = 0 V VOUT = ±10 V, RL = 2 kΩ VCM = ±13 VS = ±2.5 V to ±20 V RL = 10 kΩ No load Operating range OP297E Typ 35 0.2 50 +50 1200 3200 Min ±13 114 114 ±13.5 130 ±13 ±13.4 550 ±2.5 Guaranteed by CMR test. Rev. G | Page 3 of 16 Max 100 0.6 450 ±450 750 ±20 OP297F Typ 80 0.5 80 +80 1000 2500 Min ±13 108 108 ±13.5 130 ±13 ±13.4 550 ±2.5 Max 300 2.0 750 ±750 Min 800 750 ±20 OP297G Typ 110 0.6 80 +80 2500 ±13 108 108 ±13.5 130 ±13 ±13.4 550 ±2.5 Max 400 2.0 750 ±750 Unit μV μV/°C pA pA V/mV V dB dB 750 ±20 V μA V OP297 ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE Table 3. Parameter Supply Voltage Input Voltage1 Differential Input Voltage1 Output Short-Circuit Duration Storage Temperature Range Z-Suffix P-Suffix, S-Suffix Operating Temperature Range OP297E (Z-Suffix) OP297F, OP297G (P-Suffix, S-Suffix) Junction Temperature Z-Suffix P-Suffix, S-Suffix Lead Temperature (Soldering, 60 sec) 1 Rating ±20 V ±20 V 40 V Indefinite θJA is specified for worst-case mounting conditions, that is, θJA is specified for device in socket for CERDIP and PDIP packages; θJA is specified for device soldered to printed circuit board for the SOIC package. −65°C to +175°C −65°C to +150°C Package Type 8-Lead CERDIP (Z-Suffix) 8-Lead PDIP (P-Suffix) 8-Lead SOIC (S-Suffix) Table 4. Thermal Resistance −40°C to +85°C −40°C to +85°C ESD CAUTION −65°C to +175°C −65°C to +150°C 300°C For supply voltages less than ±20 V, the absolute maximum input voltage is equal to the supply voltage. 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. – 1/2 OP297 + V1 20V p-p @ 10Hz 2kΩ 50kΩ 50Ω – 1/2 OP297 V2 CHANNEL SEPARATION = 20 log V1 V2/10000 Figure 4. Channel Separation Test Circuit Rev. G | Page 4 of 16 00300-004 + θJA 134 96 150 θJC 12 37 41 Unit °C/W °C/W °C/W OP297 TYPICAL PERFORMANCE CHARACTERISTICS 400 60 VS = ±15V VCM = 0V TA = 25°C VS = ±15V VCM = 0V 1200 UNITS 40 INPUT CURRENT (pA) NUMBER OF UNITS 300 200 20 IB– 0 IB+ –20 IOS 100 –80 –60 –40 –20 0 20 40 INPUT OFFSET VOLTAGE (µV) 60 80 100 –60 –75 00300-005 0 –100 Figure 5. Typical Distribution of Input Offset Voltage 0 25 50 TEMPERATURE (°C) 75 100 125 60 TA = 25°C VS = ±15V VCM = 0V 1200 UNITS VS = ±15V VCM = 0V 40 INPUT CURRENT (pA) 200 150 100 50 IB– 20 IB+ 0 IOS –80 –60 –40 –20 0 20 40 INPUT BIAS CURRENT (pA) 60 80 100 –40 –15 00300-006 0 –100 Figure 6. Typical Distribution of Input Bias Current ±3 DEVIATION FROM FINAL VALUE (µV) TA = 25°C VS = ±15V VCM = 0V 300 200 100 –80 –60 –40 –20 0 20 40 INPUT OFFSET CURRENT (pA) 60 80 100 10 15 Figure 7. Typical Distribution of Input Offset Current TA = 25°C VS = ±15V VCM = 0V ±2 ±1 0 00300-007 0 –100 –5 0 5 COMMON-MODE VOLTAGE (V) Figure 9. Input Bias, Offset Current vs. Common-Mode Voltage 400 1200 UNITS –10 00300-009 –20 0 1 2 3 4 TIME AFTER POWER APPLIED (Minutes) Figure 10. Input Offset Voltage Warm-Up Drift Rev. G | Page 5 of 16 5 00300-010 NUMBER OF UNITS –25 Figure 8. Input Bias, Offset Current vs. Temperature 250 NUMBER OF UNITS –50 00300-008 –40 OP297 10k 1300 NO LOAD TOTAL SUPPLY CURRENT (µA) 1k 100 –55°C ≤ TA ≤ +125°C TA = +125°C 1100 TA = +25°C 1000 TA = –55°C 900 100 1k 10k 100k 1M 10M 800 SOURCE RESISTANCE (Ω) 0 COMMON-MODE REJECTION (dB) 10 1 10k 100k 1M 10M 100M SOURCE RESISTANCE (Ω) 140 120 100 80 60 40 1 10 100 1k 10k FREQUENCY (Hz) 100k 1M Figure 15. Common-Mode Rejection vs. Frequency 160 35 30 TA = –55°C POWER SUPPLY REJECTION (dB) 25 TA = +25°C 20 15 TA = +125°C 10 VS = ±15V OUTPUT SHORTED TO GROUND 5 0 –5 –10 –15 TA = +125°C –20 TA = +25°C –25 TA = 25°C VS = ±15V ΔVS = 10V p-p 140 120 100 80 60 40 TA = –55°C –30 0 1 2 3 TIME FROM OUTPUT SHORT (Minutes) 4 20 0.1 00300-013 SHORT-CIRCUIT CURRENT (mA) ±20 TA = 25°C VS = ±15V Figure 12. Effective TCVOS vs. Source Resistance –35 ±15 160 BALANCED OR UNBALANCED VS = ±15V VCM = 0V 00300-012 EFFECTIVE OFFSET VOLTAGE DRIFT (µV/°C) 100 1k ±10 SUPPLY VOLTAGE (V) Figure 14. Total Supply Current vs. Supply Voltage Figure 11. Effective Offset Voltage vs. Source Resistance 0.1 100 ±5 00300-015 10 00300-014 TA = +25°C 00300-011 10 1200 1 10 100 1k FREQUENCY (Hz) 10k 100k Figure 16. Power Supply Rejection vs. Frequency Figure 13. Short-Circuit Current vs. Time, Temperature Rev. G | Page 6 of 16 1M 00300-016 EFFECTIVE OFFSET VOLTAGE (µV) BALANCED OR UNBALANCED VS = ±15V VCM = 0V OP297 1k VOLTAGE NOISE 1 10 1 10 1 1k 100 FREQUENCY (Hz) TA = +125°C TA = +25°C 0 TA = –55°C –15 35 30 OUTPUT SWING (V p-p) 0.1 1kHz 1k 15 25 TA = 25°C VS = ±15V AVCL = +1 1% THD fOUT = 1kHz 20 15 10 10k 100k SOURCE RESISTANCE (Ω) 1M 10M 0 10 100 1k LOAD RESISTANCE (Ω) 35 TA = –55°C TA = +25°C VS = ±15V VOUT = ±10V TA = 25°C VS = ±15V AVCL = +1 1% THD fOUT = 1kHz RL = 10kΩ 30 OUTPUT SWING (V p-p) 10k 10k Figure 21. Output Swing vs. Load Resistance Figure 18. Total Noise Density vs. Source Resistance TA = +125°C 1k 25 20 15 10 5 100 1 2 3 4 5 6 7 8 9 10 LOAD RESISTANCE (kΩ) 20 0 100 00300-019 OPEN-LOOP GAIN (V/mV) 10 5 10Hz 00300-018 0.01 100 5 1k 10k FREQUENCY (Hz) Figure 22. Maximum Output Swing vs. Frequency Figure 19. Open-Loop Gain vs. Load Resistance Rev. G | Page 7 of 16 100k 00300-022 TOTAL NOISE DENSITY (nV/√Hz) TA = 25°C VS = ±2V TO ±20V 1kHz 0 Figure 20. Differential Input Voltage vs. Output Voltage 10 10Hz –5 OUTPUT VOLTAGE (V) Figure 17. Voltage Noise Density and Current Noise Density vs. Frequency 1 –10 00300-021 10 RL = 10kΩ VS = ±15V VCM = 0V 00300-020 CURRENT NOISE CURRENT NOISE DENSITY (fA/√Hz) 100 100 DIFFERENTIAL INPUT VOLTAGE (10µV/DIV) TA = 25°C VS = ±2V TO ±15V 00300-017 VOLTAGE NOISE DENSITY (nV/√Hz) 1k OP297 1k 100 VS = ±15V CL = 30pF RL = 1MΩ 60 PHASE 40 TA = 25°C VS = ±15V 100 90 TA = –55°C 20 135 0 180 10 1 0.1 0.01 225 –20 OUTPUT IMPEDANCE (Ω) OPEN-LOOP GAIN (dB) GAIN PHASE SHIFT (Degrees) 80 1k 10k 100k FREQUENCY (Hz) 1M 270 10M Figure 23. Open-Loop Gain, Phase vs. Frequency TA = 25°C VS = ±15V AVCL = +1 VOUT = 100mV p-p –EDGE 40 +EDGE 30 20 10 0 10 100 1k LOAD CAPACITANCE (pF) 10k 00300-024 OVERSHOOT (%) 50 100 1k 10k FREQUENCY (Hz) 100k Figure 25. Open-Loop Output Impedance vs. Frequency 70 60 0.001 10 Figure 24. Small Signal Overshoot vs. Load Capacitance Rev. G | Page 8 of 16 1M 00300-025 –40 100 00300-023 TA = +125°C OP297 APPLICATIONS INFORMATION Extremely low bias current over a wide 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 unnecessary 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 can vary over the full range of the supply voltages used. AC PERFORMANCE The ac characteristics of the OP297 are highly stable over its full operating temperature range. Unity gain small signal response is shown in Figure 26. Extremely tolerant of capacitive loading on the output, the OP297 displays excellent response with 1000 pF loads (see Figure 27). 100 90 20mV 5µs Figure 28. Large Signal Transient Response (AVCL = +1) GUARDING AND SHIELDING To maintain the extremely high input impedances of the OP297, care is taken in circuit board layout and manufacturing. Board surfaces must be kept scrupulously clean and free of moisture. Conformal coating is recommended to provide a humidity barrier. Even a clean PCB can have 100 pA of leakage currents between adjacent traces, therefore guard rings should be used around the inputs. Guard traces operate at a voltage close to that on the inputs, as shown in Figure 29, to minimize leakage currents. 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 placed on both sides of the circuit board. NONINVERTING AMPLIFIER UNITY-GAIN FOLLOWER 10 10 – – + + 1/2 OP297 5µs 00300-026 0% 20mV 00300-028 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 1 V of either rail. The output typically swings to within 1 V of the rails when using a 10 kΩ load. 10 0% 1/2 OP297 Figure 26. Small Signal Transient Response (CL = 100 pF, AVCL = +1) MINI-DIP BOTTOM VIEW INVERTING AMPLIFIER 8 100 1 A 90 – 1/2 OP297 B 00300-029 + Figure 29. Guard Ring Layout and Considerations 10 20mV 5µs 00300-027 0% Figure 27. Small Signal Transient Response (CL = 1000 pF, AVCL = +1) Rev. G | Page 9 of 16 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 30 illustrates the typical open-loop gain linearity of the OP297 over the military temperature range. RL = 10kΩ VS = ±15V VCM = 0V TA = +125°C TA = +25°C 0 TA = –55°C –15 –10 –5 0 5 10 OUTPUT VOLTAGE (V) Figure 30. Open-Loop Linearity of the OP297 Rev. G | Page 10 of 16 15 00300-030 OPEN-LOOP GAIN LINEARITY DIFFERENTIAL INPUT VOLTAGE (10µV/DIV) OP297 OP297 APPLICATION CIRCUITS PRECISION ABSOLUTE VALUE AMPLIFIER PRECISION POSITIVE PEAK DETECTOR The circuit in Figure 31 is a precision absolute value amplifier with an input impedance of 30 MΩ. The high gain and low TCVOS of the OP297 ensure 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. In Figure 33, 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. 1kΩ +15V 1N4148 C2 0.1µF 2 R3 1kΩ R1 1kΩ 8 1/2 OP297 + 4 1 5 6 D2 1N4148 C3 0.1µF 1/2 OP297 1kΩ + 1kΩ 7 + SIMPLE BRIDGE CONDITIONING AMPLIFIER Figure 34 shows a simple bridge conditioning amplifier using the OP297. The transfer function is ΔR ⎞ RF VOUT = VREF ⎛⎜ ⎟ ⎝ R + ΔR ⎠ R 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. 15V RF VREF 4 R5 100kΩ 1 R + ΔR IOUT 10mA MAX 3 – 1/2 OP297 1 VOUT + +15V 8 7 1/2 OP297 5 IOUT = VIN R5 = VIN 100Ω = 10mA/V 6 5 6 – –15V – 8 1/2 OP297 + 7 VOUT = VREF RF ΔR R + ΔR R 4 Figure 34. Simple Bridge Condition Amplifier Using the OP297 00300-032 R4 10kΩ 0.1µF REF43 + 3 VOUT 2N930 2 1/2 OP297 + 7 Figure 33. Precision Positive Peak Detector R2 2kΩ R3 10kΩ – – 1/2 OP297 –15V Maximum output current of the precision current pump shown in Figure 32 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. R1 through R4 should be matched resistors. 2 5 0V < VOUT < 10V PRECISION CURRENT PUMP R2 10kΩ + RESET Figure 31. Precision Absolute Value Amplifier VIN 6 1 CH – –15V R1 10kΩ – 1/2 OP297 Figure 32. Precision Current Pump Rev. G | Page 11 of 16 00300-034 3 VIN – D1 1N4148 00300-031 2 C1 30pF VIN 1kΩ 3 0.1µF 00300-033 +15V OP297 R2 33kΩ NONLINEAR CIRCUITS Due to its low input bias currents, the OP297 is an ideal log amplifier in nonlinear circuits such as the square and square root circuits shown in Figure 35 and Figure 36. Using the squaring circuit of Figure 35 as an example, the analysis begins by writing a voltage loop equation across Transistor Q1, Transistor Q2, Transistor Q3, and Transistor Q4. ⎛I ⎞ ⎟ + VT2 ln⎜ IN ⎜I ⎟ ⎝ S2 ⎠ ⎛I ⎞ ⎟ = VT3 ln⎜ OUT ⎜ I ⎟ ⎝ S3 ⎠ ⎛I ⎞ ⎟ + VT4 ln⎜ REF ⎜ I ⎟ ⎝ S4 ⎠ 6 IOUT ⎞ ⎟ ⎟ ⎠ Q1 VIN 2lnIIN = lnIOUT + lnIREF = ln(IOUT × IREF) (I IN )2 ⎛ R2 VOUT = ⎜⎜ ⎝ I REF ⎞⎛ VIN ⎞ 2 ⎟⎜ ⎟⎝ R1 ⎟⎠ ⎠ (VIN )(I REF ) Q3 10 9 R3 50kΩ 4 R4 50kΩ –15V 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%. R1 R2 33kΩ 6 IOUT + Q3 10 8 4 V– VOUT + MAT04E 8 C1 100pF V+ 1/2 OP297 7 7 Q2 6 5 – 5 – 1/2 OP297 1 IREF 9 14 13 Q4 12 R3 50kΩ R4 50kΩ –15V 00300-035 1 2 Q1 3 3 + 1 8 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; R2 can be varied to keep the output voltage within the usable range. C2 100pF VIN 8 1/2 OP297 7 14 Q4 12 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 can be used to set IREF. A similar analysis made for the square root circuit of Figure 36 leads to its transfer function 2 – 13 V– Op Amp A2 forms a current-to-voltage converter, which gives VOUT = R2 × IOUT. Substituting (VIN/R1) for IIN and the previous equation for IOUT yields R1 33kΩ 2 + MAT04E 1 Q2 5 VOUT Figure 36. Square Root Amplifier I REF VOUT = R2 R1 33kΩ 3 Exponentiating both sides of the equation leads to I OUT = 6 V+ 7 IREF 3 C1 100pF All the transistors of the MAT04 are precisely matched and at the same temperature, so the IS and VT terms cancel, where 5 – 1/2 OP297 Figure 35. Squaring Amplifier Rev. G | Page 12 of 16 00300-036 ⎛I VT1 ln⎜⎜ IN ⎝ I S1 C2 100pF OP297 OUTLINE DIMENSIONS 0.400 (10.16) 0.365 (9.27) 0.355 (9.02) 8 5 1 0.280 (7.11) 0.250 (6.35) 0.240 (6.10) 4 0.100 (2.54) BSC 0.325 (8.26) 0.310 (7.87) 0.300 (7.62) 0.060 (1.52) MAX 0.210 (5.33) MAX 0.015 (0.38) MIN 0.150 (3.81) 0.130 (3.30) 0.115 (2.92) SEATING PLANE 0.022 (0.56) 0.018 (0.46) 0.014 (0.36) 0.195 (4.95) 0.130 (3.30) 0.115 (2.92) 0.015 (0.38) GAUGE PLANE 0.430 (10.92) MAX 0.005 (0.13) MIN 0.014 (0.36) 0.010 (0.25) 0.008 (0.20) COMPLIANT TO JEDEC STANDARDS MS-001 CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN. CORNER LEADS MAY BE CONFIGURED AS WHOLE OR HALF LEADS. Figure 37. 8-Lead Plastic Dual In-Line Package [PDIP] P-Suffix (N-8) Dimensions shown in inches and (millimeters) 0.005 (0.13) MIN 8 0.055 (1.40) MAX 5 0.310 (7.87) 0.220 (5.59) 1 4 0.100 (2.54) BSC 0.320 (8.13) 0.290 (7.37) 0.405 (10.29) MAX 0.060 (1.52) 0.015 (0.38) 0.200 (5.08) MAX 0.150 (3.81) MIN 0.200 (5.08) 0.125 (3.18) 0.023 (0.58) 0.014 (0.36) 0.070 (1.78) 0.030 (0.76) SEATING PLANE 15° 0° 0.015 (0.38) 0.008 (0.20) CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN. Figure 38. 8-Lead Ceramic Dual In-Line Package [CERDIP] Z-Suffix (Q-8) Dimensions shown in inches and (millimeters) Rev. G | Page 13 of 16 070606-A 0.070 (1.78) 0.060 (1.52) 0.045 (1.14) OP297 5.00 (0.1968) 4.80 (0.1890) 8 1 5 4 1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) COPLANARITY 0.10 SEATING PLANE 6.20 (0.2441) 5.80 (0.2284) 1.75 (0.0688) 1.35 (0.0532) 0.51 (0.0201) 0.31 (0.0122) 0.50 (0.0196) 0.25 (0.0099) 45° 8° 0° 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157) COMPLIANT TO JEDEC STANDARDS MS-012-A A 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. 012407-A 4.00 (0.1574) 3.80 (0.1497) Figure 39. 8-Lead Standard Small Outline Package [SOIC_N] Narrow Body S-Suffix (R-8) Dimensions shown in millimeters and (inches) ORDERING GUIDE Model OP297EZ OP297FP OP297FPZ 1 OP297FS OP297FS-REEL OP297FS-REEL7 OP297FSZ1 OP297FSZ-REEL1 OP297FSZ-REEL71 OP297GP OP297GPZ1 OP297GS OP297GS-REEL OP297GS-REEL7 OP297GSZ1 OP297GSZ-REEL1 OP297GSZ-REEL71 1 Temperature Range −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 −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 Package Description 8-Lead CERDIP 8-Lead PDIP 8-Lead PDIP 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead PDIP 8-Lead PDIP 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N Z = RoHS Compliant Part. Rev. G | Page 14 of 16 Package Options Q-8 (Z-Suffix) N-8 (P-Suffix) N-8 (P-Suffix) R-8 (S-Suffix) R-8 (S-Suffix) R-8 (S-Suffix) R-8 (S-Suffix) R-8 (S-Suffix) R-8 (S-Suffix) N-8 (P-Suffix) N-8 (P-Suffix) R-8 (S-Suffix) R-8 (S-Suffix) R-8 (S-Suffix) R-8 (S-Suffix) R-8 (S-Suffix) R-8 (S-Suffix) OP297 NOTES Rev. G | Page 15 of 16 OP297 NOTES ©2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D00300-0-4/08(G) Rev. G | Page 16 of 16