Precision Gain=10 DIFFERENTIAL AMPLIFIER

Size: px

Start display at page:

Download "Precision Gain=10 DIFFERENTIAL AMPLIFIER"

Derek Booker
5 years ago
Views:

1 INA Precision Gain= DIFFERENTIAL AMPLIFIER FEATURES ACCURATE GAIN: ±.% max HIGH COMMON-MODE REJECTION: 8dB min NONLINEARITY:.% max EASY TO USE PLASTIC 8-PIN DIP, SO-8 SOIC PACKAGES APPLICATIONS G = DIFFERENTIAL AMPLIFIER G = + AMPLIFIER G = AMPLIFIER G = + AMPLIFIER INSTRUMENTATION AMPLIFIER DESCRIPTION The INA is a monolithic Gain = differential amplifier consisting of a precision op amp and on-chip metal film resistors. The resistors are laser trimmed for accurate gain and high common-mode rejection. Excellent TCR tracking of the resistors maintains gain accuracy and common-mode rejection over temperature. In R kω R kω 7 Sense Output The differential amplifier is the foundation of many commonly used circuits. The INA provides this precision circuit function without using an expensive resistor network. The INA is available in 8-pin plastic DIP and SO-8 surface-mount packages. +In R kω kω 4 Reference International Airport Industrial Park Mailing Address: PO Box 4 Tucson, AZ 874 Street Address: 7 S. Tucson Blvd. Tucson, AZ 87 Tel: () 74- Twx: 9-9- Cable: BBRCORP Telex: -49 FAX: () 889- Immediate Product Info: (8) Burr-Brown Corporation PDS-79D Printed in U.S.A. July, 99

2 SPECIFICATIONS ELECTRICAL At + C, V S = ±V, unless otherwise specified. INAKP, U PARAMETER CONDITIONS MIN TYP MAX UNITS GAIN Initial () V/V Error.. % vs Temperature 4 ppm/ C Nonlinearity ().. % OUTPUT Related Voltage I O = +ma, ma V Rated Current = V +, ma Impedance. Ω Current Limit To Common +4/ ma Capacitive Load Stable Operation pf INPUT Impedance Differential kω Common-Mode kω Voltage Range Differential ± V Common-Mode ± V Common-Mode Rejection () T A = T MIN to T MAX 8 db OFFSET VOLTAGE RTI (4) Initial µv vs Temperature. µv/ C vs Supply ±V S = V to 8V µv/v vs Time µv/mo NOISE VOLTAGE RTI () f B =.Hz to Hz µvp-p f O = khz nv/ Hz DYNAMIC RESPONSE Small Signal db MHz Full Power BW = Vp-p khz Slew Rate V/µs Settling Time:.% = V Step µs.% = V Step µs.% V CM = V Step, V DIFF = V µs POWER SUPPLY Rated V Voltage Range Derated Performance ± ±8 V Quiescent Current = V ±. ± ma TEMPERATURE RANGE Specification +7 C Operation 4 +8 C Storage + C NOTES: () Connected as difference amplifier (see Figure ). () Nonlinearity is the maximum peak deviation from the best-fit straight line as a percent of full-scale peakto-peak output. () With zero source impedance (see Maintaining CMR section). (4) Includes effects of amplifiers s input bias and offset currents. () Includes effect of amplifier s input current noise and thermal noise contribution of resistor network. PIN CONFIGURATION Top View Ref In +In () 8 kω kω 7 kω kω 4 INA DIP/SOIC NC Output Sense ELECTROSTATIC DISCHARGE SENSITIVITY This integral circuit can be damaged by ESD. Burr-Brown recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet published specifications. NOTE: () Pin indentifier for SO-8 package. Model number identification may be abbreviated on SO-8 package due to limited available space. INA

3 DICE INFORMATION 7B 8 7A PAD FUNCTION Reference In +In 4 Sense Output 7A, 7B (Connect Both) 8 (Op Amp +In) 9 (Op Amp In) Substrate Bias: Electrically connected to supply. 9 MECHANICAL INFORMATION 4 MILS (.") MILLIMETERS Die Size 8 x ±. x. ±. Die Thickness ±. ±.8 Min. Pad Size 4 x 4. x. INA DIE TOPOGRAPHY Backing: Gold ABSOLUTE MAXIMUM RATINGS Power Supply Voltage... ±8V Input Voltage Range... ±V S Operating Temperature Range: P, U... 4 C to +8 C Storage Temperature Range... 4 C to +8 C Lead Temperature (soldering, s): P... + C Wave Soldering (s, max) U... + C Output Short Circuit to Common... Continuous ORDERING INFORMATION MODEL PACKAGE TEMPERATURE RANGE INAKP 8-Pin Plastic DIP C to +7 C INAU SO-8 Surface Mount C to +7 C PACKAGING INFORMATION PACKAGE DRAWING MODEL PACKAGE NUMBER () INAKP 8-Pin Plastic DIP INAU SO-8 Surface Mount 8 NOTE: () For detailed drawing and dimension table, please see end of data sheet, or Appendix D of Burr-Brown IC Data Book. The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems. INA

TYPICAL PERFORMANCE CURVES T A = + C, V S = ±V, unless otherwise noted.

RESPONSE (R LOAD =, C LOAD = pf) TOTAL HARMONIC DISTORTION AND NOISE vs FREQUENCY A = db, Vrms, kω

4 TYPICAL PERFORMANCE CURVES T A = + C, V S = ±V, unless otherwise noted. STEP RESPONSE SMALL SIGNAL RESPONSE (No Load) Output Voltage (mv) µs/div µs/div SMALL SIGNAL RESPONSE (R LOAD =, C LOAD = pf) TOTAL HARMONIC DISTORTION AND NOISE vs FREQUENCY A = db, Vrms, kω load Output Voltage (mv) THD + N (%).. Noninverting Inverting µs/div khz low-pass filtered. k k k Frequency (Hz) UT (V) MAXIMUM UT vs I OUT (Negative Swing) V S = ±8V V S = ±V V S = ±V UT (V) MAXIMUM UT vs I OUT (Positive Swing) V S = ±8V V S = ±V V S = ±V. V S = ±V 4 8 I OUT (ma). V S = ±V 8 4 I OUT (ma) INA 4

5 TYPICAL PERFORMANCE CURVES (CONT) T A = + C, V S = ±V, unless otherwise noted. CMR vs FREQUENCY 4 POWER SUPPLY REJECTION vs FREQUENCY CMR (db) 9 8 PSRR (db) 8 7 k k k Frequency (Hz) APPLICATIONS INFORMATION Figure shows the basic connections required for operation of the INA. Power supply bypass capacitors should be connected close to the device pins as shown. 4 7 INA R R kω kω V V µf R kω kω FIGURE. Basic Power Supply and Signal Connections. The differential input signal is connected to pins and as shown. The source impedance connected to the inputs must be equal to assure good common-mode rejection. A Ω mismatch in source impedance will degrade the commonmode rejection of a typical device to approximately 8dB. If the source has a known source impedance mismatch, an additional resistor in series with one input can be used to preserve good common-mode rejection. The output is referred to the output reference terminal (pin ) which is normally grounded. A voltage applied to the Ref terminal will be summed with the output signal. The source impedance of a signal applied to the Ref terminal should be less than Ω to maintain good common-mode rejection. µf + UT = (V V ) 4 k k k Frequency (Hz) Figure shows a voltage applied to pin to trim the offset voltage of the INA. The known Ω source impedance of the trim circuit is compensated by the Ω resistor in series with pin to maintain good CMR. R R V V Ω FIGURE. Offset Adjustment. Compensates for some impedance at pin. See text. R = V V Offset Adjustment Range = ±mv INA Referring to Figure, the CMR depends upon the match of the internal /R ratio to the R /R ratio. A CMR of db requires resistor matching of.%. To maintain high CMR over temperature, the resistor TCR tracking must be better than ppm/ C. These accuracies are difficult and expensive to reliably achieve with discrete components. Ω 499kΩ +V V kω INA

6 V INA Ω kω kω Ω Gain Adjust E In A R INA V Ω kω kω To eliminate adjustment interactions, first adjust gain with V grounded. Ω FIGURE. Difference Amplifier with Gain and CMR Adjust. kω kω V kω INA kω FIGURE 4. Precision G = Inverting Amplifier. Gain Error =.% maximum Nonlinearity =.% maximum Gain Drift =.ppm/ C = V E CMR Adjust E +In R A R E = ( + R /R ) (E E ) To make a high performance high gain instrumentation amplifier, the INA can be combined with state-of-the-art op amps. For low source impedance applications, OPA7s will give the best noise, offset, and temperature drift. At source impedances above about kω, the bias current noise of the OPA7 reacting with input impedance degrades noise. For these applications, use an OPA or a dual OPA FET input op amp for lower noise. For an electrometer grade IA, use the OPA8 see table below. Using the INA for the difference amplifier also extends the input commonmode range of the instrumentation amplifier to ±V. A conventional IA with a unity-gain difference amplifier has an input common-mode range limited to ±V for an output swing of ±V. This is because a unity-gain difference amp needs ±V at the input for V at the output, allowing only V additional for common-mode. R R GAIN CMRR NOISE AT khz A, A (Ω) (kω) (V/V) (db) I b (pa) (nv/ Hz) OPA7A OPAB OPA8LM FIGURE. Precision Instrumentation Amplifier. INA R R kω kω E Output INA R R kω kω V V kω R kω V V = V + V V IN kω = V IN FIGURE 7. Precision Summing Amplifier. ±V Safe Input R kω INA This circuit follows an / divider with a gain of for an overall gain of unity. With an / divider, the input signal can exceed V without damage. FIGURE. Voltage Follower with Input Protection. V IN = V IN Gain Error =.% maximum FIGURE 8. Precision G = Buffer. INA

High Speed FET-Input INSTRUMENTATION AMPLIFIER

High Speed FET-Input INSTRUMENTATION AMPLIFIER FEATURES FET INPUT: I B = 2pA max HIGH SPEED: T S = 4µs (G =,.%) LOW OFFSET VOLTAGE: µv max LOW OFFSET VOLTAGE DRIFT: µv/ C max HIGH COMMON-MODE REJECTION: