SECTION 1 SINGLE-SUPPLY AMPLIFIERS - Analog Devices

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with the differential inputs to prevent unwanted noise from reaching the inputs.Here, capacitors, C X1 , C X2 , and C X3 , connected across the inputs of theinstrumentation amplifier, form common-mode (C X1 and C X2 ) and differentialmode(C X3 ) low-pass filters with the two resistors, R X . Time constants R X -C X1 andR X -C X2 should be well-matched (1% or better), because imbalances in theseimpedances can generate a differential error voltage which will be amplified.On the other hand, an additional benefit of using a differentially-connectedcapacitor is that it can reduce common-mode capacitive imbalance. This differentialconnection helps to preserve high-frequency AC common-mode rejection. Sinceseries resistors are required to form the low-pass filter, errors due to poor layout(CMR imbalance), component tolerance of R X (input bias current-induced offsetvoltage) and resistor thermal noise must be considered in the design process. Inapplications where the sensor is an RTD or a resistive strain gauge, R X can beomitted, provided the sensor is close to the amplifier.EXTERNAL COMMON-MODE AND DIFFERENTIAL-MODEINPUT FILTERS PREVENT RFI RECTIFICATION ININSTRUMENTATION AMPLIFIER CIRCUITSFigure 1.1830
REFERENCES1. Systems Application Guide, Chapter 1, pg. 21-55, Analog Devices,Incorporated, Norwood, MA, 1993.2. Linear Design Seminar, Section 1, pp. 19-22, Analog Devices,Incorporated, Norwood, MA, 1995.3. Lew Counts, Product Line Director, Advanced Linear Products,Analog Devices, Incorporated, personal communication, 1995.4. Walt Jung, and James Wong, Op amp selection minimizes impact ofsingle-supply design, EDN, May 27, 1993, pp. 119-124.5. E. Jacobsen, and J. Baum, Home-brewed circuits tailor sensor outputsto specialized needs, EDN, January 5, 1995, pp. 75-82.6. Walt Jung, Corporate Staff Applications Engineer, Analog Devices,Incorporated, personal communication, January 27, 1995.7. Walt Jung, Analog-Signal-Processing Concepts Get More Efficient,Electronic Design Analog Applications Issue, June 24, 1993,pp. 12-27.8. C.Kitchin and L.Counts , Instrumentation Amplifier ApplicationGuide, Analog Devices, Incorporated, Norwood, MA, 1991.31
Page 1 and 2: SECTION 1SINGLE-SUPPLY AMPLIFIERSRa
Page 3 and 4: typically have open-loop gains betw
Page 5 and 6: from the many applications where co
Page 7 and 8: RAIL-TO-RAIL INPUT STAGE TOPOLOGYFi
Page 9 and 10: OP AMP OUTPUT STAGES USINGCOMPLEMEN
Page 11 and 12: These considerations, as well as th
Page 13 and 14: Since the input signal, V IN+ ,as w
Page 15 and 16: Circuit Ga in = V OH(MIN) - V OL(MA
Page 17 and 18: PERFORMANCE SUMMARY OF AD822 IN-AMP
Page 19 and 20: the current through the gain settin
Page 21 and 22: I OA3 =−(V IN +) ⎛ R13 + R5 RG
Page 23 and 24: In this circuit, R1 and R2 form a v
Page 25 and 26: the PNP input transistors are force
Page 27 and 28: Of course, the amplified bridge out
Page 29: the circuit has an adjustment range

SECTION 1 SINGLE-SUPPLY AMPLIFIERS - Analog Devices

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