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rev. e 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. 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 companies. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781/329-4700 www.analog.com fax: 781/326-8703 ? 2003 analog devices, inc. all rights reserved. op297 dual low bias current precision operational amplifier features low offset voltage: 50 v max low offset voltage drift: 0.6 v/ c max very low bias current: 100 pa max very high open-loop gain: 2000 v/mv min low supply current (per amplifier): 625 a max operates from 2 v to 20 v supplies high common-mode rejection: 120 db min pin compatible to lt1013, ad706, ad708, op221, lm158, and mc1458/1558 with improved perfor mance applications strain gage 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 8 7 6 5 1 2 3 4 outa ?na +ina v+ outb ?nb +inb v b a general description the op297 is the first dual op amp to pack precision performance into the space-saving, industry-standard, 8-lead soic 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. temperature ( c) input current (pa) 60 ?0 ?5 ?0 125 ?5 0 25 50 75 100 40 20 0 ?0 ?0 i b i b + i os v s = 15v v cm = 0v figure 1. low bias current over temperature 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, ensuring high linearity in every application. errors due to common-mode signals are eliminated by the op297? common-mode rejection of over 120 db, whic h mini- mizes offset voltage changes experienced in battery- powered systems. supply current of the op297 is under 625 a per amplifier, and the part can operate with supply voltages as low as 2 v. 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. 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. input offset voltage ( v) number of units 400 0 ?00 ?0 60 ?0 ?0 ?0 0 20 40 300 200 100 80 100 t a = 25 c v s = 15v v cm = 0v 1200 units figure 2. very low offset
rev. e ? op297?pecifications op297e op297f op297g parameter symbol conditions min typ max min typ max min typ max unit input offset voltage v os 25 50 50 100 80 200 v long-term input voltage stability 0.1 0.1 0.1 v/mo input offset current i os v cm = 0 v 20 100 35 150 50 200 pa input bias current i b v cm = 0 v 20 100 35 150 50 200 pa input noise voltage e n p-p 0.1 hz to 10 hz 0.5 0.5 0.5 v p-p input noise voltage density e n f o = 10 hz 20 20 20 nv/ hz f o = 1000 hz 17 17 17 nv/ hz input noise current density i n f o = 10 hz 20 20 20 fa/ hz input resistance differential mode r in 30 30 30 m ? input resistance common-mode r incm 500 500 500 g ? large-signal v o = 10 v voltage gain a vo r l = 2 k ? 2000 4000 1500 3200 1200 3200 v/mv input voltage range * v cm 13 14 13 14 13 14 v common-mode rejection cmrr v cm = 13 v 120 140 114 135 114 135 db power supply rejection psrr v s = 2 v to 20 v 120 130 114 125 114 125 db output voltage swing v o r l = 10 k ? 13 14 13 14 13 14 v r l = 2 k ? 13 13.7 13 13.7 13 13.7 v supply current per amplifier i sy no load 525 625 525 625 525 625 a supply voltage v s operating range 2 20 2 20 2 20 v slew rate sr 0.05 0.15 0.05 0.15 0.05 0.15 v/ s gain bandwidth product gbwp a v = +1 500 500 500 khz channel separation cs v o = 20 v p-p 150 150 150 db f o = 10 hz input capacitance c in 333pf * guaranteed by cmr test. specifications subject to change without notice. electrical characteristics op297e op297f op297g parameter symbol conditions min typ max min typ max min typ max unit input offset voltage v os 35 100 80 300 110 400 v average input offset voltage drift tcv os 0.2 0.6 0.5 2.0 0.6 2.0 v/ c input offset current i os v cm = 0 v 50 450 80 750 80 750 pa input bias current i b v cm = 0 v 50 450 80 750 80 750 pa large-signal voltage gain a vo v o = 10 v, r l = 2 k ? 1200 3200 1000 2500 800 2500 v/mv input voltage range * v cm 13 13.5 13 13.5 13 13.5 v common-mode rejection cmrr v cm = 13 114 130 108 130 108 130 db power supply rejection psrr v s = 2.5 v to 20 v 114 0.15 108 0.15 108 0.3 db output voltage swing v o r l = 10 k ? 13 13.4 13 13.4 13 13.4 v supply current per amplifier i sy no load 550 750 550 750 550 750 a supply voltage v s operating range 2.5 20 2.5 20 2.5 20 v * guaranteed by cmr test. specifications subject to change without notice. (@ v s = 15 v, t a = 25 c, unless otherwise noted.) electrical characteristics (@ v s = 15 v, ?0 c t a +85 c for op297e/f/g, unless otherwise noted.)
rev. e op297 e3e 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. absolute maximum ratings 1 supply voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 v input voltage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 v differential input voltage 2 . . . . . . . . . . . . . . . . . . . . . . . . 40 v output short-circuit duration . . . . . . . . . . . . . . . . . indefinite storage temperature range z package . . . . . . . . . . . . . . . . . . . . . . . . . e65 c to +175 c p, s packages . . . . . . . . . . . . . . . . . . . . . . e65 c to +150 c operating temperature range op297e (z) . . . . . . . . . . . . . . . . . . . . . . . . e40 c to +85 c op297f, op297g (p, s) . . . . . . . . . . . . . . e40 c to +85 c junction temperature z package . . . . . . . . . . . . . . . . . . . . . . . . . e65 c to +175 c p, s packages . . . . . . . . . . . . . . . . . . . . . . e65 c to +150 c lead temperature range (soldering, 60 sec) . . . . . . . . 300 c package types ja 3 jc unit 8-lead cerdip (z) 134 12 c/w 8-lead pdip (p) 96 37 c/w 8-lead soic (s) 150 41 c/w notes 1 stresses above those listed under absolute maximum ratings may cause perma- nent damage to the device. this is a stress rating only; and 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. 2 for supply voltages less than 20 v, the absolute maximum input voltage is equal to the supply voltage. 3 ) ) 1/2 op297 2k 1/2 op297 50 v 2 figure 3. channel separation test circuit ordering guide model temperature range package description package options op297ez e40 c to +85 c 8-lead cerdip q-8 op297fp e40 c to +85 c 8-lead pdip n-8 OP297FS e40 c to +85 c 8-lead soic r-8 OP297FS-reel e40 c to +85 c 8-lead soic r-8 OP297FS-reel7 e40 c to +85 c 8-lead soic r-8 op297gp e40 c to +85 c 8-lead pdip n-8 op297gs e40 c to +85 c 8-lead soic r-8 op297gs-reel e40 c to +85 c 8-lead soic r-8 op297gs-reel7 e40 c to +85 c 8-lead soic r-8
rev. e e4e op297 input offset voltage (pa) number of units 0 e100 e80 60 e60 e40 e20 0 20 40 200 100 80 100 1200 units t a = 25 c v s = 15v v cm = 0v 300 400 tpc 1. typical distribution of input offset voltage temperature ( c) input current (pa) 60 e60 e75 e50 125 e25 0 25 50 75 100 40 20 0 e20 e40 i b e i b + i os v s = 15v v cm = 0v tpc 4. input bias, offset current vs. temperature source resistance ( ) effective offset voltage ( v) 10000 10 10 10m 100 1m 100k 10k 1k 100 1000 v s = 15v v cm = 0v balanced or unbalanced t a = +25 c e55 c t a +125 c tpc 7. effective offset voltage vs. source resistance input bias current (pa) number of units 0 e100 e80 60 e60 e40 e20 0 20 40 250 200 150 100 50 80 100 1200 units t a = 25 c v s = 15v v cm = 0v tpc 2. typical distribution of input bias current input current (pa) 60 e40 e15 e20 40 20 0 v s = 15v v cm = 0v common-mode voltage (v) e10 e5 0 5 10 15 i b e i b + i os tpc 5. input bias, offset current vs. common-mode voltage source resistance ( ) effective offset voltage drift ( v/ c) 100 0.1 10 10m 1m 100k 10k 1k 100 v s = 15v v cm = 0v balanced or unbalanced 100m 1 tpc 8. effective tcv os vs. source resistance 0 e100 1200 units t a = 25 c v s = 15v v cm = 0v number of units 400 300 200 100 input offset voltage (p a ) e80 60 e60 e40 e20 0 20 40 80 100 tpc 3. typical distribution of input offset current time after power applied ( minutes ) deviation from final value ( v) 0 01 2345 1 3 2 t a = 25 c v s = 15v v cm = 0v tpc 6. input offset voltage warm-up drift time from output short (minutes) short-circuit current (ma) 35 e35 04 12 3 20 5 25 30 15 10 0 e30 e25 e20 e15 e10 e5 v s = 15v output shorted to ground t a = e55 c t a = +25 c t a = +125 c t a = +125 c t a = +25 c t a = e55 c tpc 9. short circuit current vs. time, temperature etypical performance characteristics
rev. e op297 e5e supply voltage ( v ) total supply current ( a) 1300 800 0 20 5 10 15 1200 1100 1000 900 t a = e55 c t a = +25 c t a = +125 c no load tpc 10. total supply current vs. supply voltage frequency ( hz ) 1000 1 1 1000 10 10 100 voltage noise density (nv/ hz) hz) ) ) hz ) ) ) hz) hz hz hz hz ) ) h hz hz ) ) ) ) hz) ) h hz
rev. e e6e op297 frequency ( hz ) open-loop gain (db) e40 100 1k 10m 10k 100 1m v s = 15v c l = 30pf r l = 1m t a = e55 c t a = +125 c gain phase phase shift (deg) e20 0 20 40 60 100 80 tpc 19. open loop gain, phase vs. frequency load capacitance (p f ) overshoot (%) 0 0 100 eedge 10 20 30 40 50 60 70 1000 10000 +edge t a = 25 c v s = 15v a vcl = +1 v out = 100mv p-p tpc 20. small-signal over- shoot vs. load capacitance frequency ( hz ) output impedance ( ) 1000 0.001 10 100 1k 100 10 0.01 0.1 1 10k 100k 1m t a = 25 c v s = 15v tpc 21. open loop output impedance vs frequency applications information extremely low bias current over a wide temperature range m akes 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 tcv os are degraded only minimally by high source resistance, even when unbalanced. the input pins of the op297 are protected against large differ- ential voltage by back-to-back diodes and current-limiting resistors. common-mode voltages at the inputs are not re stricted 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 1 v of either rail. the output typically swings to within 1 v of the rails when using a 10 k load. ac performance the op297?s ac characteristics are highly stable over its full operating temperature range. unity gain small-signal response is shown in figure 4. extremely tolerant of capacitive loading on the output, the op297 displays excellent response with 1000 pf loads (figure 5). 10 0% 100 90 5 s 20mv figure 4. small-signal transient response (c load = 100 pf, a vcl = 1) 10 0% 100 90 5 s 20mv figure 5. small-signal transient response (c load = 1000 pf, a vcl = 1) 10 0% 100 90 5 s 20mv figure 6. large-signal transient response (a vcl = 1)
rev. e op297 e7e unity-gain follower inverting amplifier noninverting amplifier mini-dip bottom view 1 8 b a 1/2 op297 1/2 op297 1/2 op297 figure 7. guard ring layout and connections 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 mois- ture. c onformal 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 are operated at a voltage close to that on the inputs, as shown in figure 7, 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. 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 8 illustrates the typical open-loop gain linearity of the op297 over the military temperature range. t a = +25 c output voltage ( v ) differential input voltage (10 v/div) 0 e15 r l = 10k v s = 15v v cm = 0v t a = +125 c t a = e55 c e10 e5 0 5 15 10 figure 8. open-loop linearity of the op297 applications precision absolute value amplifier the circuit of figure 9 is a precision absolute value amplifier with an input impedance of 30 m . the high gain and low tcv os 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. 1/2 op297 1/2 op297 +15v c2 0.1 f r1 1k c1 30pf d1 1n4148 d2 1n4148 r2 2k 0v v out
rev. e e8e op297 precision positive peak detector in figure 11, the c h must be of polystyrene, teflon , or poly- ethylene to minimize dielectric absorption and leakage. the droop rate is determined by the size of c h and the bias current of the op297. 2n930 1/2 op297 +15v 0.1 f 1k 1n4148 reset v in 5 6 7 1 28 3 0.1 f 1/2 op297 1k 1k c h e15v v out 1k figure 11. precision positive peak detector simple bridge conditioning amplifier figure 12 shows a simple bridge conditioning amplifier using the op297. the transfer function is vv r rr r r out ref f = + the ref43 provides an accurate and stable reference voltage for the bridge. to maintain the highest circuit accuracy, r f should be 0.1% or better with a low temperature coefficient. 15v 3 2 1 1/2 op297 v out v out = v ref r + r r r r f 5 6 7 1/2 op297 v ref 4 8 ref43 r + r r f 4 figure 12. a simple bridge conditioning amplifier using the 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 figures 13 and 14. using the squaring circuit of figure 13 as an example, the analysis begins by writ ing a voltage loop equation across transistors q1, q2, q3, and q4. vln i i vln i i vln i i vln i i t in s t in s t o s t ref s 1 1 2 2 3 3 4 4 + = + all the transistors of the mat04 are precisely matched and at the same temperature, so the i s and v t terms cancel, giving 2 ln i ln i ln i ln i in o ref o =+ = () i ref exponentiating both sides of the equation leads to i i i o in ref = () 2 op amp a2 forms a current-to-voltage converter, which gives v out = r2 i o . substituting (v in /r1) for i in and the above equation for i o yields v r i v r out ref in = 2 1 2 a similar analysis made for the square-root circuit of figure 14 leads to its transfer function vr vi r out in ref = ()( ) 2 1 1/2 op297 7 6 5 v out r2 33k c2 100pf i o 1/2 op297 e15v 1 2 3 v+ ve i ref r3 50k q3 r1 33k v in q1 q2 q4 13 14 12 r4 50k 8 9 10 4 8 6 5 7 2 3 1 c1 100pf mat04e figure 13. squaring amplifier 1/2 op297 7 6 5 v out r2 33k c2 100pf i o 1/2 op297 e15v 1 2 3 v+ ve i ref r3 50k r1 33k v in q1 r4 50k 7 9 10 4 8 3 1 c1 100pf mat04e 8 q3 5 6 q4 13 12 14 q2 figure 14. square-root amplifier
rev. e op297 e9e c in i os 3 d1 ein d2 q1 r1 r2 r5 q2 r6 10 11 g1 c3 r7 i1 d4 d3 r4 r3 c2 14 13 v3 e1 r8 c4 r9 e ref v2 50 98 12 6 5 99 8 r in2 2 +in r in1 e os 1 79 4 15 16 50 r16 r17 23 i sys g4 g5 28 29 22 d6 d5 26 27 d7 d8 g6 r18 r19 d9 d10 g7 v4 v5 l1 25 99 98 9 r10 c5 g1 r11 r13 c6 c7 r12 e2 r14 e3 r15 c8 g3 figure 15. macro model in these circuits, i ref is a function of the negative power supply. to maintain accuracy, the negative supply should be well regu- lated. for applications where very high accuracy is required, a voltage reference may be used to set i ref . an important consider- ation 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 i ref , 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 14 and 15 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 v os , i os , i b , a vo , cmr, v o , and i sy . 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.
rev. e e10e op297 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 5810qx q2 6911qx r5 10 4 96 r6 11 4 96 d1 89dx d2 98dx * 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 C
rev. e op297 e11e outline dimensions 8-lead plastic dual in-line package [pdip] p-suffix (n-8) dimensions shown in inches and (millimeters) seating plane 0.180 (4.57) max 0.150 (3.81) 0.130 (3.30) 0.110 (2.79) 0.060 (1.52) 0.050 (1.27) 0.045 (1.14) 8 1 4 5 0.295 (7.49) 0.285 (7.24) 0.275 (6.98) 0.100 (2.54) bsc 0.375 (9.53) 0.365 (9.27) 0.355 (9.02) 0.150 (3.81) 0.135 (3.43) 0.120 (3.05) 0.015 (0.38) 0.010 (0.25) 0.008 (0.20) 0.325 (8.26) 0.310 (7.87) 0.300 (7.62) 0.022 (0.56) 0.018 (0.46) 0.014 (0.36) 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 compliant to jedec standards mo-095aa 0.015 (0.38) min 8-lead standard small outline package (soic) narrow body s-suffix (r-8) dimensions shown in millimeters and (inches) 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157) 0.50 (0.0196) 0.25 (0.0099) 45 8 0 1.75 (0.0688) 1.35 (0.0532) seating plane 0.25 (0.0098) 0.10 (0.0040) 85 4 1 5.00 (0.1968) 4.80 (0.1890) 4.00 (0.1574) 3.80 (0.1497) 1.27 (0.0500) bsc 6.20 (0.2440) 5.80 (0.2284) 0.51 (0.0201) 0.31 (0.0122) coplanarity 0.10 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 compliant to jedec standards ms-012aa 8-lead ceramic dual in-line package [cerdip] z-suffix (q-8) dimensions shown in inches and (millimeters) 1 4 85 0.310 (7.87) 0.220 (5.59) pin 1 0.005 (0.13) min 0.055 (1.40) max 0.100 (2.54) bsc 15 0 0.320 (8.13) 0.290 (7.37) 0.015 (0.38) 0.008 (0.20) seating plane 0.200 (5.08) max 0.405 (10.29) 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) 0.060 (1.52) 0.015 (0.38) controlling dimensions are in inches; millimeters dimensions (in parentheses) are rounded-off inch equivalents for reference only and are not appropriate for use in design
rev. e c00300e0e7/03(e) e12e op297 revision history location page 7/03

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