OP297FSZ

Dual Low Bias Current Precision Operational Amplifier OP297 FEATURES 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 60 PIN CONFIGURATION OUTA 1 –INA 2 +INA 3 V– 4 A B 8 7 6 5 V+ OUTB 00300-001 –INB +INB Figure 1. VS = ±15V VCM = 0V 40 INPUT CURRENT (pA) 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 20 IB– 0 IB+ –20 IOS –40 –50 –25 GENERAL DESCRIPTION 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. 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, ensuring high linearity in every application. 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. 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. Rev. F 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. 400 0 25 50 TEMPERATURE (°C) 75 100 125 Figure 2. Low Bias Current over Temperature 1200 UNITS TA = 25°C VS = ±15V VCM = 0V 300 NUMBER OF UNITS 200 100 –60 –40 –20 0 20 40 60 80 100 INPUT OFFSET VOLTAGE (µV) 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. 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 ©2006 Analog Devices, Inc. All rights reserved. 00300-003 0 –100 –80 00300-002 –60 –75 OP297 TABLE OF CONTENTS Features .............................................................................................. 1 Applications....................................................................................... 1 General Description ......................................................................... 1 Pin Configuration............................................................................. 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Electrical Characteristics............................................................. 3 Absolute Maximum Ratings............................................................ 4 Thermal Resistance ...................................................................... 4 ESD Caution.................................................................................. 4 Typical Performance Characteristics ............................................. 5 Applications Information ................................................................ 9 AC Performance ............................................................................9 Guarding and Shielding................................................................9 Open-Loop Gain Linearity ....................................................... 10 Applications..................................................................................... 11 Precision Absolute Value Amplifier......................................... 11 Precision Current Pump............................................................ 11 Precision Positive Peak Detector.............................................. 11 Simple Bridge Conditioning Amplifier ................................... 11 Nonlinear Circuits...................................................................... 12 Outline Dimensions ....................................................................... 13 Ordering Guide .......................................................................... 14 REVISION HISTORY 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 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 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 Rev. F | Page 2 of 16 OP297 SPECIFICATIONS ELECTRICAL CHARACTERISTICS @ VS = ±15 V, TA = 25°C, unless otherwise noted. Table 1. OP297E 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 1 Common-Mode Rejection Power Supply Rejection Output Voltage Swing Supply Current per Amplifier Supply Voltage Slew Rate Gain Bandwidth Product Channel Separation Input Capacitance 1 OP297F Max 50 Min Typ 50 0.1 35 35 0.5 20 17 20 30 500 1500 ±13 114 114 ±13 ±13 625 ±20 ±2 0.05 3200 ±14 135 125 ±14 ±13.7 525 0.15 500 150 3 1200 ±13 114 114 ±13 ±13 625 ±20 ±2 0.05 Max 100 Min OP297G Typ 80 0.1 50 50 0.5 20 17 20 30 500 3200 ±14 135 125 ±14 ±13.7 525 0.15 500 150 3 Max 200 Unit μV μV/mo pA pA μV p-p nV/√Hz nV/√Hz fA/√Hz MΩ GΩ V/mV V dB dB V V μA V V/μs kHz dB pF Symbol VOS Conditions Min Typ 25 0.1 20 20 0.5 20 17 20 30 500 IOS IB en p-p en in RIN RINCM AVO VCM CMRR PSRR 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 kΩ 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 2000 ±13 120 120 ±13 ±13 ±2 0.05 4000 ±14 140 130 ±14 ±13.7 525 0.15 500 150 3 625 ±20 Guaranteed by CMR test. @ VS = ±5 V, –40°C ≤ TA ≤ +85°C for OP297E/OP297F/OP297G, unless otherwise noted. Table 2. OP297E Parameter Input Offset Voltage Average Input Offset Voltage Drift Input Offset Current Input Bias Current Large Signal Voltage Gain Input Voltage Range 1 Common-Mode Rejection Power Supply Rejection Output Voltage Swing Supply Current per Amplifier Supply Voltage 1 OP297F Max 100 0.6 450 ±450 1000 ±13 108 108 ±13 750 ±20 ±2.5 Min Typ 80 0.5 80 80 2500 ±13.5 130 0.15 ±13.4 550 750 ±20 Max 300 2.0 750 ±750 800 ±13 108 108 ±13 ±2.5 Min OP297G Typ 110 0.6 80 80 2500 ±13.5 130 0.3 ±13.4 550 750 ±20 Max 400 2.0 750 ±750 Unit μV μV/°C pA pA V/mV V dB dB V μA V Symbol VOS TCVOS IOS IB AVO VCM CMRR PSRR VO ISY VS Conditions Min Typ 35 0.2 50 50 VCM = 0 V VCM = 0 V VO = ±10 V RL = 2 kΩ VCM = ±13 VS = ±2.5 V to ±20 V RL = 10 kΩ No Load Operating Range 1200 ±13 114 114 ±13 ± 2.5 3200 ±13.5 130 0.15 ±13.4 550 Guaranteed by CMR test. Rev. F | Page 3 of 16 OP297 ABSOLUTE MAXIMUM RATINGS Table 3. Parameter Supply Voltage Input Voltage1 Differential Input Voltage1 Output Short-Circuit Duration Storage Temperature Range Z Package P, S Packages Operating Temperature Range OP297E (Z) OP297F, OP297G (P, S) Junction Temperature Z Package P, S Packages Lead Temperature (Soldering, 60 sec) 1 Rating ±20 V ±20 V 40 V Indefinite −65°C to +175°C −65°C to +150°C −40°C to +85°C −40°C to +85°C −65°C to +175°C −65°C to +150°C 300°C 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 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. Table 4. Thermal Resistance Package Type 8-Lead CERDIP (Z-Suffix) 8-Lead PDIP (P-Suffix) 8-Lead SOIC (S-Suffix) θJA 134 96 150 θJC 12 37 41 Unit °C/W °C/W °C/W For supply voltages less than ±20 V, the absolute maximum input voltage is equal to the supply voltage. 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. 1/2 OP297 + 50kΩ 50Ω – V1 20V p-p @ 10Hz 2kΩ 1/2 OP297 + – V2 CHANNEL SEPARATION = 20 log V1 V2/10000 Figure 4. Channel Separation Test Circuit Rev. F | Page 4 of 16 00300-004 OP297 TYPICAL PERFORMANCE CHARACTERISTICS 400 60 1200 UNITS TA = 25°C VS = ±15V VCM = 0V INPUT CURRENT (pA) VS = ±15V VCM = 0V 40 300 NUMBER OF UNITS 20 IB– 0 IB+ –20 IOS –40 200 100 –80 –60 –40 –20 0 20 40 INPUT OFFSET VOLTAGE (pA) 60 80 100 00300-005 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 125 Figure 5. Typical Distribution of Input Offset Voltage 250 1200 UNITS Figure 8. Input Bias, Offset Current vs. Temperature 60 VS = ±15V VCM = 0V 40 INPUT CURRENT (pA) 200 TA = 25°C VS = ±15V VCM = 0V NUMBER OF UNITS IB– 20 IB+ 150 100 0 IOS 50 –20 00300-006 –80 –60 –40 –20 0 20 40 INPUT OFFSET VOLTAGE (pA) 60 80 100 –10 –5 0 5 COMMON-MODE VOLTAGE (V) 10 15 Figure 6. Typical Distribution of Input Bias Current 400 1200 UNITS TA = 25°C VS = ±15V VCM = 0V Figure 9. Input Bias, Offset Current vs. Common-Mode Voltage ±3 DEVIATION FROM FINAL VALUE (µV) TA = 25°C VS = ±15V VCM = 0V 300 NUMBER OF UNITS ±2 200 ±1 100 00300-007 –80 –60 –40 –20 0 20 40 INPUT OFFSET VOLTAGE (pA) 60 80 100 0 1 2 3 4 TIME AFTER POWER APPLIED (Minutes) 5 Figure 7. Typical Distribution of Input Offset Current Figure 10. Input Offset Voltage Warm-Up Drift Rev. F | Page 5 of 16 00300-010 0 –100 0 00300-009 0 –100 –40 –15 00300-008 0 –100 –60 –75 OP297 10000 BALANCED OR UNBALANCED VS = ±15V VCM = 0V 1300 NO LOAD EFFECTIVE OFFSET VOLTAGE (µV) TOTAL SUPPLY CURRENT (µA) 1200 TA = +125°C 1000 1100 TA = +25°C 1000 100 –55°C ≤ TA ≤ +125°C TA = –55°C 900 00300-011 10 100 1k 10k 100k 1M 10M 0 ±5 SOURCE RESISTANCE (Ω) ±10 SUPPLY VOLTAGE (V) ±15 ±20 Figure 11. Effective Offset Voltage vs. Source Resistance 100 EFFECTIVE OFFSET VOLTAGE DRIFT (µV/°C) Figure 14. Total Supply Current vs. Supply Voltage 160 TA = 25°C VS = ±15V 10 COMMON-MODE REJECTION (dB) BALANCED OR UNBALANCED VS = ±15V VCM = 0V 140 120 100 1 80 60 1k 10k 100k 1M 10M 100M 00300-012 1 10 SOURCE RESISTANCE (Ω) 100 1k 10k FREQUENCY (Hz) 100k 1M Figure 12. Effective TCVOS vs. Source Resistance 35 30 25 TA = –55°C TA = +25°C TA = +125°C VS = ±15V OUTPUT SHORTED TO GROUND Figure 15. Common-Mode Rejection Frequency 160 TA = 25°C VS = ±15V ΔVS = 10V p-p 20 15 10 5 0 –5 –10 –15 –20 –25 –30 –35 0 POWER SUPPLY REJECTION (dB) SHORT-CIRCUIT CURRENT (mA) 140 120 100 TA = +125°C TA = +25°C TA = –55°C 00300-013 80 60 1 2 3 TIME FROM OUTPUT SHORT (Minutes) 4 1 10 100 1k FREQUENCY (Hz) 10k 100k 1M Figure 13. Short-Circuit Current vs. Time, Temperature Figure 16. Power Supply Rejection vs. Frequency Rev. F | Page 6 of 16 00300-016 40 0.1 00300-015 0.1 100 40 00300-014 10 TA = +25°C 800 OP297 1000 TA = 25°C VS = ±2V TO ±15V 1000 DIFFERENTIAL INPUT VOLTAGE (10µV/DIV) VOLTAGE NOISE DENSITY (nV/√Hz) CURRENT NOISE DENSITY (fA/√Hz) RL = 10kΩ VS = ±15V VCM = 0V TA = +125°C 100 CURRENT NOISE 100 TA = +25°C 0 10 VOLTAGE NOISE 10 TA = –55°C 00300-017 1 10 100 FREQUENCY (Hz) –15 –10 –5 0 5 10 15 OUTPUT VOLTAGE (V) Figure 17. Voltage Noise Density and Current Noise Density vs. Frequency 10 TA = 25°C VS = ±2V TO ±20V Figure 20. Differential Input Voltage vs. Output Voltage 35 30 OUTPUT SWING (V p-p) TOTAL NOISE DENSITY (nV/√Hz) 1 10Hz 25 20 15 10 5 TA = 25°C VS = ±15V AVCL = +1 1% THD fO = 1kHz 1kHz 0.1 1kHz 10Hz 00300-018 103 104 105 SOURCE RESISTANCE (Ω) 106 107 100 1k LOAD RESISTANCE (Ω) 10k Figure 18. Total Noise Density vs. Source Resistance 10000 TA = –55°C TA = +25°C Figure 21. Output Swing vs. Load Resistance 35 TA = 25°C VS = ±15V AVCL = +1 1% THD fO = 1kHz RL = 10kΩ VS = ±15V VO = ±10V 30 OUTPUT SWING (V p-p) OPEN-LOOP GAIN (V/mV) 25 20 15 10 5 TA = +125°C 1000 100 1 00300-019 2 5 6 7 8 9 10 3 4 LOAD RESISTANCE (kΩ) 20 1k 10k FREQUENCY (Hz) 100k Figure 19. Open-Loop Gain vs. Load Resistance Figure 22. Maximum Output Swing vs. Frequency Rev. F | Page 7 of 16 00300-022 0 100 00300-021 0.01 102 0 10 00300-020 1 1 1000 OP297 100 80 GAIN OPEN-LOOP GAIN (dB) 1000 VS = ±15V CL = 30pF RL = 1MΩ OUTPUT IMPEDANCE (Ω) PHASE SHIFT (Deg) 100 TA = 25°C VS = ±15V 60 40 20 0 PHASE TA = –55°C 10 1 0.1 –20 TA = +125°C 00300-023 0.01 1k 10k 100k FREQUENCY (Hz) 1M 10M 100 1k 10k FREQUENCY (Hz) 100k 1M Figure 23. Open-Loop Gain, Phase vs. Frequency 70 60 50 OVERSHOOT (%) Figure 25. Open-Loop Output Impedance vs. Frequency TA = 25°C VS = ±15V AVCL = +1 VOUT = 100mV p-p –EDGE 40 +EDGE 30 20 10 0 0 100 1000 LOAD CAPACITANCE (pF) 10000 Figure 24. Small Signal Overshoot vs. Load Capacitance 00300-024 Rev. F | Page 8 of 16 00300-025 –40 100 0.001 10 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. 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. 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. 100 90 10 0% 00300-028 20mV 5µs Figure 28. Large Signal Transient Response (AVCL = 1) UNITY-GAIN FOLLOWER NONINVERTING AMPLIFIER 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). – 1/2 OP297 – 1/2 OP297 + + INVERTING AMPLIFIER 8 MINI-DIP BOTTOM VIEW 1 100 90 A – 1/2 OP297 B + 00300-029 10 10 Figure 29. Guard Ring Layout and Considerations 0% GUARDING AND SHIELDING 00300-026 20mV 5µs Figure 26. Small Signal Transient Response (CLOAD = 100 pF, AVCL = 1) 100 90 10 0% 00300-027 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 PC board can have 100 pA of leakage currents between adjacent traces, so 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. 20mV 5µs Figure 27. Small Signal Transient Response (CLOAD = 1000 pF, AVCL = 1) Rev. F | Page 9 of 16 OP297 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. DIFFERENTIAL INPUT VOLTAGE (10µV/DIV) OPEN-LOOP GAIN LINEARITY RL = 10kΩ VS = ±15V VCM = 0V TA = +125°C TA = +25°C 0 TA = –55°C –15 –10 –5 0 5 10 15 OUTPUT VOLTAGE (V) Figure 30. Open-Loop Linearity of the OP297 Rev. F | Page 10 of 16 00300-030 OP297 APPLICATIONS PRECISION ABSOLUTE VALUE AMPLIFIER 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. +15V PRECISION POSITIVE PEAK DETECTOR 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 0.1µF C2 0.1µF R1 1kΩ R3 1kΩ VIN 2 1kΩ 3 1/2 OP297 + – 1 1kΩ CH 6 5 1/2 OP297 + – 7 VOUT 0.1µF 00300-033 2 – 8 C1 30pF 1 D1 1N4148 5 – VIN 3 1/2 OP297 4 6 1/2 OP297 RESET 7 1kΩ 2N930 –15V + 0V < VOUT < 10V + C3 0.1µF D2 1N4148 R2 2kΩ 00300-031 Figure 33. Precision Positive Peak Detector SIMPLE BRIDGE CONDITIONING AMPLIFIER Figure 34 shows a simple bridge conditioning amplifier using the OP297. The transfer function is –15V Figure 31. Precision Absolute Value Amplifier PRECISION CURRENT PUMP 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. R3 10kΩ R1 10kΩ VIN R2 10kΩ ΔR ⎞ R F 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 VREF 2 3 RF 1/2 OP297 + – 1 +15V 8 R6 10kΩ REF43 IOUT 10mA 2 4 R + ΔR 3 1/2 OP297 + – 1 VOUT 7 1/2 OP297 – IOUT = VIN R5 = VIN 100Ω = 10mA/V –15V 00300-032 4 Figure 32. Precision Current Pump Figure 34. A Simple Bridge Condition Amplifier Using the OP297 Rev. F | Page 11 of 16 00300-034 + R4 10kΩ 5 6 6 5 1/2 OP297 + – 8 7 VOUT = VREF RF ΔR R + ΔR R OP297 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. R2 33kΩ C2 100pF 6 IO 5 1/2 OP297 + MAT04E 13 – 7 VOUT IREF ⎛I VT 1ln⎜ IN ⎜I ⎝ S1 ⎞ ⎛I ⎟ + VT 2 ln⎜ IN ⎟ ⎜I ⎠ ⎝ S2 ⎞ ⎛I ⎟ = VT 3ln⎜ O ⎟ ⎜I ⎠ ⎝ S3 ⎞ ⎛I ⎟ + VT 4 ln⎜ REF ⎟ ⎜I ⎠ ⎝ S4 ⎞ ⎟ ⎟ ⎠ R1 33kΩ Q1 1 3 7 Q2 5 8 C1 100pF V+ 6 14 Q4 12 All the transistors of the MAT04 are precisely matched and at the same temperature, so the IS and VT terms cancel, where 2 ln IIN = ln IO + ln IREF = ln (IO × IREF) Exponentiating both sides of the equation leads to Q3 10 9 VIN 2 3 1/2 OP297 + 4 V– – 8 1 R3 50kΩ R4 50kΩ –15V 00300-036 IO (I )2 = IN I REF Figure 36. Square Root Amplifier Op Amp A2 forms a current-to-voltage converter, which gives VOUT = R2 × IO. Substituting (VIN/R1) for IIN and the above equation for IO yields 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. 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. 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%. ⎛ R2 VOUT = ⎜ ⎜I ⎝ REF ⎞⎛ VIN ⎞ 2 ⎟⎜ ⎟⎝ R1 ⎟ ⎠ ⎠ A similar analysis made for the square root circuit of Figure 36 leads to its transfer function VOUT = R2 (VIN )(I REF ) R1 C2 100pF R2 33kΩ 6 2 1 Q1 3 IO 6 7 Q2 5 8 Q3 10 1 5 1/2 OP297 + – 7 VOUT MAT04E VIN R1 33kΩ C1 100pF V+ 2 3 9 IREF 14 13 Q4 12 1/2 OP297 + 4 V– – 8 R3 50kΩ R4 50kΩ –15V Figure 35. Squaring Amplifier Rev. F | Page 12 of 16 00300-035 OP297 OUTLINE DIMENSIONS 0.400 (10.16) 0.365 (9.27) 0.355 (9.02) 8 1 5 4 0.280 (7.11) 0.250 (6.35) 0.240 (6.10) 0.005 (0.13) MIN 0.055 (1.40) MAX 5 PIN 1 0.100 (2.54) BSC 0.210 (5.33) MAX 0.150 (3.81) 0.130 (3.30) 0.115 (2.92) 0.022 (0.56) 0.018 (0.46) 0.014 (0.36) 0.070 (1.78) 0.060 (1.52) 0.045 (1.14) 0.060 (1.52) MAX 0.015 (0.38) MIN 0.325 (8.26) 0.310 (7.87) 0.300 (7.62) 0.195 (4.95) 0.130 (3.30) 0.115 (2.92) 8 0.310 (7.87) 0.220 (5.59) 1 4 0.015 (0.38) GAUGE PLANE SEATING PLANE 0.430 (10.92) MAX 0.100 (2.54) BSC 0.014 (0.36) 0.010 (0.25) 0.008 (0.20) 0.405 (10.29) MAX 0.200 (5.08) MAX 0.200 (5.08) 0.125 (3.18) 0.023 (0.58) 0.014 (0.36) 0.070 (1.78) 0.030 (0.76) 0.060 (1.52) 0.015 (0.38) 0.150 (3.81) MIN SEATING PLANE 15° 0° 0.320 (8.13) 0.290 (7.37) 0.005 (0.13) MIN 0.015 (0.38) 0.008 (0.20) COMPLIANT TO JEDEC STANDARDS MS-001-BA 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. 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 37. 8-Lead Plastic Dual In-Line Package [PDIP] P-Suffix (N-8) Dimensions shown in inches and (millimeters) 5.00 (0.1968) 4.80 (0.1890) 8 5 Figure 38. 8-Lead Ceramic Dual In-Line Package [CERDIP] Z-Suffix (Q-8) Dimensions shown in inches and (millimeters) 4.00 (0.1574) 3.80 (0.1497) 1 6.20 (0.2440) 4 5.80 (0.2284) 1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) 1.75 (0.0688) 1.35 (0.0532) 0.50 (0.0196) × 45° 0.25 (0.0099) 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) 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 39. 8-Lead Standard Small Outline Package (SOIC) Narrow Body S-Suffix (R-8) Dimensions shown in millimeters and (inches) Rev. F | Page 13 of 16 OP297 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 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 8-Lead PDIP 8-Lead PDIP 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC 8-Lead SOIC Package Options Q-8 N-8 N-8 R-8 R-8 R-8 R-8 R-8 R-8 N-8 N-8 R-8 R-8 R-8 R-8 R-8 R-8 Z = PB-free part. Rev. F | Page 14 of 16 OP297 NOTES Rev. F | Page 15 of 16 OP297 NOTES ©2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. C00300-0-2/06(F) Rev. F | Page 16 of 16