ANALOG DEVICES Dual Low Bias Current Precision Operational Amplifier OP-297 FEATURES e Precision Performance in Standard SO-8 Pinout Low Offset Voltage ..............::sscscesssrsssssesereseesnees 50..V Max Low Offset Voltage Drift ...................cscecs0 0.6.V/C Max Very Low Bias Current +25C 100pA Max 55C 0 $1 25C nc eecccceseenesnonsestecsncsoesesensesnars 450pA Max Very High Open-Loop Gain 2000V/mV Min Low Supply Current (Per Amplifier) ............... 625A Max Operates From +2V to +20V Supplies High Common-Mode Rejection .............00.0+ 120dB Min Pin Compatible to LT1013, AD706, AD708, OP-221, LM158, and MC1458/1558 with Improved Performance APPLICATIONS Strain Guage and Bridge Amplifiers High Stability Thermocouple Amplifiers Instrumentation Amplifiers Photo-Current Monitors High-Gain Linearity Amplifiers Long-Term Integrators/Filters Sample-and-Hold Amplifiers Peak Detectors Logarithmic Amplifiers Battery-Powered Systems GENERAL DESCRIPTION The OP-297 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 OP-297 useful in a wide variety of applications. LOW BIAS CURRENT OVER TEMPERATURE 60 N tT B- Vg = 15V 40 \ N Vem=0V_| N = IN {p+ a 20 5 N zy NX NN 5 20 ~~ los ~~ $ \ ~ 40 Ps -60 -75 -50 -25 0 25 S50 75 100 125 TEMPERATURE (C) REV. B 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. Precision performance of the OP-297 includes very low offset, under SOV, and low drift, below 0.64V/C. Open-loop gain ex- ceeds 2000V/mV insuring high linearity in every application. Errors due to common-mode signals are eliminated by the OP-297s common-mode rejection of over 120dB. The OP-297's power supply rejection of over 120dB minimizes offset voltage changes experienced in battery powered systems. Supply current of the OP-297 is under 625A per amplifier and it can operate with supply voltages as low as +2V. Continued PIN CONNECTIONS PLASTIC MINI-DIP (P-Suffix) 8-PIN CERDIP (Z-Suffix) 8-PIN SO (S-Suffix) Lec (RC-Suffix) VERY LOW OFFSET 400 777 TTT 1200 UNITS Taz +25C Vg = 15V Vom = 0V 8 200 NUMBER OF UNITS = Q So 0 "Fe eR Lp rp be 100 -80 -60-40-20 0 20 40 60 80 100 INPUT OFFSET VOLTAGE (y1V) One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703 Twx: 710/394-6577 Telex: 924491 Cable: ANALOG NORWOODMASSOP-297 GENERAL DESCRIPTION Continued The OP-297 utilizes a super-beta input stage with bias current cancellation to maintain picoamp bias currents at alltemperatures. This is in contrast to FET input op amps whose bias currents start in the picoamp range at 25C, but double for every 10C rise in temperature, to reach the nanoamp range above 85C. Input bias current of the OP-297 is under 100pA at 25C and is under 450pA over the military temperature range. Combining precision, low power and low bias current, the OP- 297 is ideal for a number of applications including instrumenta- tion amplifiers, log amplifiers, photo-diode preamplifiers and long- term integrators. For a single device, see the OP-97; for a quad, see the OP-497. ORDERING INFORMATIONt PACKAGE Ta =+25C OPERATING Vos MAX CERDIP PLASTIC Lec TEMPERATURE (uV) 8-PIN 8-PIN 20-CONTACT RANGE 50 OP297AZ/883" OP297ARC/883* MIL 50 OP297AZ MIL 50 OP297EZ MiL 400 OP297FZ OP297FP XIND 200 OP297GP XIND 200 op297astt _ XIND For devices processed in total compliance to MIL-STD-883, add /883 after part number. Consult factory for 883 data sheet. T Burn-inis available on extended industrial temperature range parts in CerDIP, and plastic DIP packages. For ordering information, see PMIs Data Book, Section 2. TT For availability and burn-in information on SO packages, contact your local sales office. ABSOLUTE MAXIMUM RATINGS (Note 1) Supply VOHtage! oo. ee eeescecessessssscseeseceesesessssessuvsssssseses +20V Input Voltage (Note 2)... eee ccceseesessesssssesssseessesesersssenss +20V Differential Input Voltage (Note 2) .........ccccccesseseseeesssee 40V Output Short-Circuit Duration ...........ccsceceeeceeseeeeees Indefinite Storage Temperature Range _ 2, RC-Package -65C to +175C P, S-Package ........cccccccssssecsescsscssesseseceeeeseseens 65C to 150C Operating Temperature Range OP-297A (Z, RC) oo. eeeccesecsesssescesessessesesenees 55C to +125C OP-297E, F (Z) oo. ceeeceeeeeeeeeesceeeceneesenerseeeees 40C to +85C OP-297F, G (P, S) voc ececeeeesseeceecnseressssaeeaes 40C to +85C Junction Temperature Z, RO-Package ........eeeeseeesescsseessercseeseseecees 65C to+175C P, S-Package .........seescessevecesesssseeecessussssesses -65C to +150C Lead Temperature Range (Soldering, 60 sec) ...........0. 300C PACKAGE TYPE ja (Note 3) Gc UNITS 8-Pin CerDIP (Z) 134 12 C/W 8-Pin Plastic DIP (P) 96 37 C 20-Contact LCC (RC) 88 33 C/W 8-Pin SO (S) 150 41 C/W NOTES: 1. Absolute maximum ratings apply to both DICE and packaged parts, unless otherwise noted. 2. For supply voltages less than +20V, the absolute maximum input voltage is equal to the supply voltage. 3. @j,a is specified for worst case mounting conditions, i.e., Ga is specified for device in socket for CerDIP, P-DIP, and LCC packages; @j, is specified for device soldered to printed circuit board for SO package. ELECTRICAL CHARACTERISTICS at Vs =+15V, T, = +25C, unless otherwise noted. OP-297A/E OP-297F OP-297G PARAMETER SYMBOL CONDITIONS MIN TYP MAX MIN TYP MAX MIN TYP MAX UNITS Input Offset - 25 50 - 50 100 - 80 200 Vv Voltage Vos X Long-Term Input - . - - 0.1 - - A ~ Vi Voltage Stability o4 or. byimo Input Offset = - 20 100 - 35 150 - 200 A Current los Vom = OV 50 P Input Bias Vom =0V - 20 +100 - 35 +150 ~ 50 +200 A Current la cM p Input Noise e 0.1Hz to 10Hz - 0s - - Os - - Os - V Voltage APP , . , , BPP Input Noise fo = 10Hz - 20 - - 20 - - 20 - VW H, Voltage Density fo = 1000Hz - 17 - - 17 - - 17 -~ ayvne InputNoise in fo = 10Hz - 20 - - 20 - - 20 - IAWHz Current Density Input Resistance Rin _ 30 _ _ 30 _ _ 30 _ Ma Differential Mode Input Resistance - 500 - - 500 - - 500 - GQ Common-Mode Rincm L Signal Vo=+10V arge-signal Avo Ri = 2k 2000 4000 - 1500 3200 - 1200 += 3200 - Vim Voltage Gain -2- REV. BOP-297 ELECTRICAL CHARACTERISTICS at Vs = +15V, Ta = +25C, unless otherwise noted. Continued OP-297A/E OP-297F OP-297G PARAMETER SYMBOL CONDITIONS MIN TYP MAX MIN TYP MAX MIN TYP MAX UNITS ! nput Voltage iVR (Note 1) 3000414 - #300414 ~ +30 +14 - V Range Common-Mode CMR Vom =13V 120 140 - 114135 - 114185 - dB Rejection Pi ower Supply PSR Vg = 42V to 420V 120 130 - 14125 - 114125 - 4B Rejection Output Voltage y R= 10kQ 413 +14 - 413 414 ~ 413 +14 - y Swing Ry = 2kQ +13 413.7 - H3 413.7 - 413 (413.7 - Supply Current Per Amplifier Isy No Load ~ 525 625 - 525 625 - 525 625 pA Supply Voltage Vs Operating Range +2 - +20 +2 - +20 +2 - +20 Vv Slew Rate SR 0.05 0.15 - 0.05 0.15 - 0.05 0.15 - Viws Gain Bandwith GBWP Ay=41 - 500 - - 500 - -~ 500 - kHz Product Channel | cs Vo=20Vp - 150 - - 150 - - 150 - 3B Separation fo = 10Hz Input Cc - ~ - 3 - - - F Capacitance IN 3 8 P NOTE: 1. Guaranteed by CMR test. ELECTRICAL CHARACTERISTICS at Vs = 15V, ~55C < Ta < +125C for OP-297A, unless otherwise noted. OP-297A PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Input Offset Voltage Vos - 45 100 pv Average Input Offset Voltage Drift TCVos - 0.2 0.6 pvc input Offset Current los Vom = 0V - 60 450 pA Input Bias Current Ip Vom =0V - 60 450 pA Large-Signal = = - Vs Voltage Gain Avo Vo =+10V, RL = 2kQ 1200 2700 mv Input Voltage Range IVR (Note 1) 413 $13.5 - Vv Common-Mode Rejection CMR Vom = 113 114 130 - dB Power Supply PSR Vg = 42.5V to #20V 414 125 - dB Rejection Output Voltage Swing Vo Ri = 10kQ 13 +13.4 - Vv Supply Current id ~ 575 750 Per Amplifier Isy No Loa pA Supply Voltage Vs Operating Range +2.5 - +20 Vv NOTE: 1. Guaranteed by CMR test. REV. BOP-297 ELECTRICAL CHARACTERISTICS at Vs = +15V, -40C < Tas +85C for OP-297E/F/G, unless otherwise noted. OP-297E OP-297F OP-297G PARAMETER SYMBOL CONDITIONS MIN TYP MAX MIN TYP MAX MIN TYP MAX UNITS Input Offset Voltage Vos - 35 100 - 80 300 ~ 110 400 pv Average Input . - . A _ A - . . f Offset Voltage Drift TCVos 0.2 0.6 0.5 2.0 0.6 2.0 pvec Input Offset Current los Vom = 0V ~ 50 450 - 80 750 - 80 750 pA Input Bias i Vom =0V 50 4450 80 +750 80 +750 A Current 8 om = ~ ~ ~ P Large-Signal A Vo =#10V, Ry, = 2k 1200 3200 1000 2500 800 2500 vimv Voltage Gain vo o* mms ~ ~ Input Volt nput vouage iVR (Note 1) #13 413.5 - #13 413.5 - H3 413.5 - Vv Range Common-Mode CMR Vom =+13V 144130 - 108 130 - 108 =-130 - dB Rejection Power Supply ve PSR Vg = +42.5V to +20V 114 0.15 - 108 0.15 - 108 0.3 - dB Rejection Output Voltage Vo RL = 10ka #13 413.4 - #13 413.4 - #13 413.4 - V Swing Supply Current Per Amplifier Isy No Load - 550 750 - 550 750 - 550 750 pA Supply Voltage Vs Operating Range 42.5 - +20 42.5 - +20 +2.5 - +20 Vv NOTE: 1. Guaranteed by CMR test. CHANNEL SEPARATION TEST CIRCUIT V1 20Vp-p @ 10Hz eS 2kQ 50kQ, WA 50Q >O Vo = V4 CHANNEL SEPARATION = 20 log ( oA ~4 REV. BOP-297 DICE CHARACTERISTICS OUTA -INA +INA V~ +IN B -INB OUTB V+ ONAN WON es Fe e For additional DICE information, refer to PMIs Data Book, Section 2. DIE SIZE 0.071 x 0.114 inch, 8,094 sq. mils (1.80 x 2.90 mm, 5.22 sq. mm) WAFER TEST LIMITS at Vs = +15V, Ta = +25C, unless otherwise noted. OP-297GBC PARAMETER SYMBOL CONDITIONS LIMIT UNITS Input Offset Voltage Vos 200 pV MAX Input Offset Current los Vom =0V 200 pA MAX Input Bias Current fg Vom =0V +200 pA MAX Large-Signal : Vo =+10V, RL = 2k Voltage Gain Avo oO L Q 4200 VimV MIN Input Voltage Range IVR (Note 1) 413 V MIN Common-Mode Rejection CMR Vom=+13V 114 dB MIN Power Supply PSR Vg =42V to +18V 11400 dB MIN Rejection . RL =10kQ +13 Output Voltage Swing Vo R, = 2k 3 V MIN Supply Current Per Amplifier Isy No Load 625 pA 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. REV. B 5.OP-297 TYPICAL PERFORMANCE CHARACTERISTICS NUMBER OF UNITS TYPICAL DISTRIBUTION OF INPUT OFFSET VOLTAGE 400-7 TT 1200 UNITS Ta= 425C Vs = 15V 300 Vom = OV 200 B 100 0 z Lbs Shr. -100 -80 -60 -40-20 0 20 40 60 80 100 INPUT OFFSET VOLTAGE (pV) INPUT BIAS, OFFSET CURRENT vs TEMPERATURE 60 T Ne Vg = 15V 40 WK Vem = OV _| N\ N a p+ S 20 K a \ & oO \ NN 5 20 los ~~ g pene! ~ ~40 ve -60 ~75 -50 -25 0 25 50 75 100 125 TEMPERATURE (C) EFFECTIVE OFFSET VOLTAGE vs SOURCE RESISTANCE 10000 EFFECTIVE OFFSET VOLTAGE (uV) 1000 BALANCED OR UNBALANCED Vs = t15V Vom = OV 100 58C STaS1 Tas 425C 10 100 ik 10k 100k 1M SOURCE RESISTANCE (Q) 10 10M NUMBER OF UNITS INPUT CURRENT (pA) EFFECTIVE OFFSET VOLTAGE DRIFT (uV/C) TYPICAL DISTRIBUTION OF INPUT BIAS CURRENT 280-7] TTI 1200 UNITS Ta = +25C _ Vs = 15V 200 - Vom=0V 7 150 100 50 0 -}'-]" 100 -80 -60 -40-20 0 20 40 60 80 100 INPUT BIAS CURRENT (pA) INPUT-BIAS, OFFSET CURRENT vs COMMON-MODE VOLTAGE 1 Ta = +25C | Vs = 415V 60 40 'e Ip+ ra Leo los Pa L- "| 20 a a 40 15 +10 - 0 5 10 COMMON-MODE VOLTAGE (VOLTS) 15 EFFECTIVE TCVos vs SOURCE RESISTANCE 100 BALANCED OR UNBALANCED Vs = t15V Vom = OV Oo = 0.1 100 =1k 10k 100k 1M 10M 100M SOURCE RESISTANCE (Q) DEVIATION FROM FINAL VALUE (V) NUMBER OF UNITS SHORT-CIRCUIT CURRENT (mA) TYPICAL DISTRIBUTION OF INPUT OFFSET CURRENT 400 7-7 J TI 1200 UNITS fs Ta = 425C Vg = 415V 300 = Vom = OV 200 400 0 ae 8) ae. -100 -80 -60 40-20 0 20 40 60 80 100 INPUT OFFSET CURRENT (pA) INPUT OFFSET VOLTAGE WARM-UP DRIFT +3 T Ta = 425C | Vg =+15V Vom = OV +2 +1 0 0 1 2 3 4 5 TIME AFTER POWER APPLIED (MINUTES) SHORT-CIRCUIT CURRENT vs TIME, TEMPERATURE 35 30 Ta = -55C 25 20 Ta = +25C 15 = 40 Ta = +125C 5 FV. =415V 0 } OUTPUT SHORTED - TO GROUND -10 ~15 A= +125C 20 = +25C 25 -30 Ta = -55C -35 0 1 2 3 4 TIME FROM OUTPUT SHORT (MINUTES) REV. BOP-297 TYPICAL PERFORMANCE CHARACTERISTICS Continued TOTAL SUPPLY CURRENT vs SUPPLY VOLTAGE 1300 1 NO LOAD < 1200 Ta = +125C , Ww & 1100 a > /- Ta = 425C 2 4000 2 an z Ta = -55C 900 P an 800 0 +5 10 +15 +20 SUPPLY VOLTAGE (VOLTS) NOISE DENSITY vs FREQUENCY 1000 1000 > Ta = +25C = Vg = 22V TO 415V z > & 100 CURRENT *00 z Ww a w VOLTAGE a NOISE 2 10 10 5 5 g 1 1000 1 10 FREQUENCY (Hz) 100 OPEN-LOOP GAIN LINEARITY Ry = 10k Vg =+15V Vom=0V Ta=+125C Ta = +25C Ta=-55C DIFFERENTIAL INPUT VOLTAGE (10pV/DIV) -10 -5 0 5 10 15 OUTPUT VOLTAGE (VOLTS) 4 a REV. B Hz) CURRENT NOISE DENSITY (fA/ COMMON-MODE REJECTION (dB) COMMON-MODE REJECTION vs FREQUENCY 160 Ta = +25C Vs = t15V 140 120 100 80 60 40 20 1 10 100 ik 10k 100k 41M FREQUENCY (Hz) TOTAL NOISE DENSITY vs SOURCE RESISTANCE 10 _ Ta= +25C le Vg = 2V TO 420V 4 > 1 a a a a 5 04 z a < 4kHz 10Hz 0.01 102 103 104 = 105-108 SOURCE RESISTANCE (2) MAXIMUM OUTPUT SWING vs LOAD RESISTANCE Ta = +25C Vs = 15V = Avet=+1 a 1%THD = fo = tkHz z s wn @ 5 3 10k 0 10 100 1k LOAD RESISTANCE () 107 OPEN-LOOP GAIN (V/mV) POWER SUPPLY REJECTION (dB) 140 120 8 2 o 2 o > Q no oO 0.1 1 10000 1000 OUTPUT SWING (Vp.p) 100 POWER SUPPLY REJECTION vs FREQUENCY q I Ta = 425C Vg =+15V AVg = 10Vp.5 A 77 WSN 10 100 1k 10k 100k 1M FREQUENCY (Hz) OPEN-LOOP GAIN vs LOAD RESISTANCE Ta=55C Ta = +25C Ta = 4125C Vg =+15V Vo =110V 1 2 3 5 10 20 LOAD RESISTANCE (kQ) MAXIMUM OUTPUT SWING vs FREQUENCY Ta = +25C Vg =t15V Avo. = +1 1% THD Ry = 10k 10k FREQUENCY (Hz) 100 4k 100kOP-297 TYPICAL PERFORMANCE CHARACTERISTICS Continued OPEN-LOOP GAIN, SMALL-SIGNAL OVERSHOOT OPEN-LOOP OUTPUT PHASE vs FREQUENCY vs CAPACITANCE LOAD IMPEDANCE vs FREQUENCY 100 TMT TTT 1000 T Vg = +15V Ta = +25C EDGE Ta = +25C 80 +4 C, = 30pF Vg = +15V | Vg =+15V GAIN Ri = Ma AvcL=+1 e 100 S a 60 Lu _ Vout = 100MV_.5 are J z z Oo 10 = PHASE N | a 2 f G 40 pe lA=-55C 90 GB a / 5 N \ a & a 1 Sg 20 135 & i K a = 0.1 ac 0 MN NT 180 E o @ a 20 925 xz 0.01 Ta = +125C _40 WW | LL 0.001 100. tk 40k 100k iM 10M 10 100 1000 10000 10 100 1k 10k {100k 1M FREQUENCY (Hz) LOAD CAPACITANCE (pF) FREQUENCY (Hz) SIMPLIFIED SCHEMATIC (One Amplifier is Shown) e OV+ o @ Vout cn 2.5kQ kK w | 2.5kQ. e +IN O-~A\Ae# RR Loi. ~B~ REV. BOP-297 APPLICATIONS INFORMATION Extremely low bias current over the full military temperature range makes the OP-297 attractive for use in sample-and-hold amplifi- - ers, peak detectors, and log amplifiers that must operate over a wide temperature range. Balancing input resistances is not nec- essary with the OP-297. Offset voltage and TC Vos are degraded only minimally by high source resistance, even when unbalanced. The input pins of the OP-297 are protected against large differ- ential voltage by back-to-back diodes and current-limiting resis- tors. Common-mode voltages at the inputs are not restricted, and may vary over the full range of the supply voltages used. The OP-297 requires very little operating headroom about the supply rails, andis specified for operation with supplies as low as +2V. 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 10kQ load. AC PERFORMANCE The OP-297'S AC characteristics are highly stable over its full operating temperature range. Unity-gain small-signal response is shown in Figure 1. Extremely tolerant of capacitive loading on the output, the OP-297 displays excellent response even with 1000pF loads (Figure 2). FIGURE 1: Smail-Signal Transient Response (Croan = 100pF, Ayc. = +1) REV. B _9- FIGURE 2: Smaill-Signal Transient Response (CLoap = 1000pF, Avcz = +1) FIGURE 3: Large-Signal Transient Response (Ayc. = +1) GUARDING AND SHIELDING To maintain the extremely high input impedances of the OP-297, 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 a humidity barrier. Even aclean PC board can have 100pA of leak- age 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 4, so that leakage currents become minimal. innoninverting applications, the guard ring should be connected to the common-mode voitage at the in- verting 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.OP-297 UNITY-GAIN FOLLOWER WY | | 1/2 \ OP-297 O eV a ro INVERTING AMPLIFIER { 1/2 | OP-297 -O NONINVERTING AMPLIFIER co w~ 1/2 | | OP-297 MINI-DIP BOTTOM VIEW FIGURE 4: Guard Ring Layout and Connections OPEN-LOOP GAIN LINEARITY The OP-297 has both an extremely high gain of 2000V/mV mini- mum and constant gain linearity. This enhances the precision of the OP-297 and provides for very high accuracy in high closed- loop gain applications. Figure 5 illustrates the typical open-loop gain linearity of the OP-297 over the military temperature range. Ta = +125C Ta = +25C Ta=-55C DIFFERENTIAL INPUT VOLTAGE (10pV/DIV) ~15 -10 -5 0 5 10 15 OUTPUT VOLTAGE (VOLTS) FIGURE 5: Open-Loop Linearity of the OP-297 -10- APPLICATIONS PRECISION ABSOLUTE VALUE AMPLIFIER The circuit of Figure 6 is a precision absolute value amplifier with an input impedance of 30MQ. The high gain and low TCVos of the OP-297 insure accurate operation with microvolt input sig- nals. In this circuit, the input always appears as acommon-mode signal to the op amps. The CMR of the OP-297 exceeds 120aB, yielding an error of less than 2ppm. Dy 1N4148 Do bo OV < Vout < 10V FIGURE 6: Precision Absolute Value Amplifier REV. BOP-297 PRECISION CURRENT PUMP Maximum output current of the precision current pump shown in Figure 7 is +10mA. Voltage compliance is +10V with t15V sup- plies. Output impedance of the current transmitter exceeds 3MQ with linearity better than 16 bits. PRECISION POSITIVE PEAK DETECTOR In Figure 8, the Cy must be of polystyrene, Teflon, or poly- ethylene to minimize dielectric absorption and leakage. The droop rate is determined by the size of Cy and the bias current of the OP-297. lout PO 10mA FIGURE 7: Precision Current Pump SIMPLE BRIDGE CONDITIONING AMPLIFIER Figure 9 shows a simple bridge conditioning amplifier using the OP-297. The transfer function is: AR Re R+AR/ R The REF-43 provides an accurate and stable reference voltage for the bridge. To maintain the highest circuit accuracy, Rr should be 0.1% or better with a low temperature coefficient. Vout = Veer +5V I: 6 25V VREF REF-43 Re WA | - 1 = O Vout 3 Vv Vv AR Re OUT = YREF R+AR! A FIGURE 9: A simple bridge conditioning amplifier using the OP-297, 1kQ 15V FIGURE 8: Precision Positive Peak Detector "Teflon is a registered trademark of the Dupont Company REV. B -11-OP-297 NONLINEAR CIRCUITS Due to its low input bias currents, the OP-297 is an ideal log amplifier in nonlinear circuits such as the square and square-root circuits shown in Figures 10 and 11. Using the squaring circuit of Figure 10 as an example, the analysis begins by writing a voltage loop equation across transistors Qy, Qo, Q3 and Q4. lo [Ree = Vq3 In (2) + V4 In All the transistors of the MAT-04 are precisely matched and at the same temperature, so the Ig and V+; terms cancel, giving: | | | + Vro In (7 | V in| TH Ns iso 2 In ty = In Io + In IRee = In (Io x IREF) Exponentiating both sides of the equation leads to: = {lin IREF Op amp Az forms a current-to-voltage converter which gives Vout = Re x Io. Substituting (Vin/R1) for lin and the above equation for lo yields: Vour=( 22} OUT \Irer) \ Ry A similar analysis made for the square-root circuit of Figure 11 leads to its transfer function: (Vin)(Rer) Vout = Ro R 1 Ry Vin O-VWA4 33kQ. FIGURE 10: Squaring Amplifier -12- REV. BOP-297 Re Na A A 33kQ. Co 100pF 6 q 74 oVour vy lo 5 Ry Vin 33kQ FIGURE 11: Square-Root Amplifier In these circuits, IRE 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 Iperf. An important con- sideration 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 Iperf, or R; and Re 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 100mV to 10V. For a similar input voltage range, the accuracy of the squaring circuit is better than 0.5%. LICENSE STATEMENT AND LIMITED WARRANTY OP-297 SPICE MACRO-MODEL Figures 12 and 13 show the node and netlist fora SPICE macro- model of the OP-297. The model is a simplified version of the actual device and simulates important DC parameters such as Vos, los, Ip, 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 OP-297. The poles and zeros in the model were determined from the actual open and closed-loop gain and phase response of the OP-297. In this way, the model presents an accurate AC representation of the actual device. The model assumes an ambient temperature of 25C. The OP-297 macro-model is protected under United States copyright laws and California trade secret laws. Precision Monolithics, Inc. hereby grants users of this macro-model, hereto referred to as the licensee, a nonexclusive, nontransferable license to use the OP-297 macro-model as long as the licensee abides by the terms of this agreement. Before using the OP-297 macro-model, the licensee should read this license. If the licensee does not accept these terms, this Data Sheet should be returned to PMI within 30 days. The licensee agrees to treat this macro-model just like a book, except that the licensee may not loan, rent, lease, or license this macro-model, in whole, in part, or in modified form, to anyone outside the licensee's company. The licensee may modify the OP-297 macro-model to suit his specific applications, and the licensee may make copies of this macro-model for use within his company only. This macro-model is provided solely and exclusively for use by PMI customers to assist them in the assessment of the OP-297 for possible applications. The OP-297 macro-model is provided "as is. PMI makes no warranty, either express or implied, including but not limited to any implied warranties or merchantability and fitness for a particular purpose using this macro-model. In no event will PMI be liable for special, collateral, incidental, or consequential damages in connection with or arising out of the use of this macro-model. Although every effort has been made to ensure accuracy of the information contained in this data sheet, PMI assumes no responsibility for inadvertent errors. PMI reserves the right to make changes to the product and the macro-model without prior notice. REV. B -13-OP-297 339 e e o Rg Rg Vo 13 C4 5 6 12 Re 15 16 < Gy R7 Cz E Rog 98 : ~ ~ D, ERer 14 = V3 50 - Cg C7 17 Ri Ria 22 WW oO > > Ge ZRi9 = C5 Eg 2Ri2 E Es Ria (PjGasPis == Cg 98 99 o* . . . < Rig D7 Ds Ge F Rig > _ Isy Ds V4 26 (-}-_# 22 b 23 25 Ly De Vv. eSTYYY No 27 s < 28 294 < = Riz = Rig Dg Ga Gs D, 0 G7 50 o o ? FIGURE 12: OP-297 Macro-Model -14 REV. BOP-297 : OP-297 SPICE MACRO-MODEL @ pmi 1990 * NODE ASSIGNMENTS * NONINVERTING INPUT INVERTING INPUT OUTPUT POSITIVE SUPPLY NEGATIVE SUPPLY | : SUBCKT OP-297 1 2 30 99 50 * INPUT STAGE & POLE AT 6 MHZ +e * eH RIN1 1 7 2500 RIN2 2 8 2500 Ri 8 8 5E11 R2 7 8 5E11 R383 5 99 612 R4 6 99 612 CIN 7 8 3E-12 c2 5 6 21.67E-12 H 4 50 0.1E-3 loS 7 8 20E-12 EOS 9 7 POLY(1) 19 23 25E-6 1 Qi 5 8 10 OX Q2 6 9 11 OX R5 10 4 96 R611 4 96 Di 8 9 DX D2 9 8 DX EREF 98 0 230 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 D312 :13 DX D4 14 12 DX *NEGATIVE ZERO AT ~1.8 MHZ R8 15 16 1E6 C4 15 16 -88.4E-15 RQ 16 98 1 Ei 15 98 12 23 1E6 *POLE AT 1.8 MHZ Ri0 17 98 1E6 C5.) 17:98 88.4E-15 G2 98 17 16 23 1E-6 *COMMON-MODE GAIN NETWORK WITH ZERO AT 50 HZ R11 18 19 1E6 C6 618 #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 1E-6 *OUTPUT STAGE R16 23 99 160K R17 23 50 160K ISY 99 50 331E-6 Rig 25 99 200 R19 25 50 200 Li 25 30 1E-7 G4 28 +50 22 25 5E-3 G5 29 50 25 22 5E-3 G6 25-93 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 D 27 22 DX D7 99 28 DX D8 99 29 DX D9 50 28 DY D190 50 29 DY *MODELS USED MODEL QX NPN (BF=2.5E6) MODEL DX __D (IS=1-15) MODEL DY __D (IS=1E-15 BV=50) *ENDS OP-297 FIGURE 13: OP-297 SPICE Net-List REV. B -15-L6/LL-G-9ZSL9 V'S'N NI GALNIYd -16-