Chapter12 - Chapter12 Operational Amplifier Applications...

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Jaeger/Blalock 7/1/07 Microelectronic Circuit Design, 3E McGraw-Hill Chapter12 Operational Amplifier Applications Microelectronic Circuit Design Richard C. Jaeger Travis N. Blalock Chap 12 - 1
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Jaeger/Blalock 7/1/07 Microelectronic Circuit Design, 3E McGraw-Hill Chapter Goals Continue study of methods to determine transfer functions of circuits containing op amps. Study non-ideal op amp behavior. Demonstrate circuit analysis techniques for ideal and non- ideal op amps. Learns factors involved in circuit design using op amps. Understand frequency response limitations of op amp circuits. Model amplifier limitations due to limited bandwidth and slew rate of the op amp. Perform SPICE simulation of nonideal op amp circuits. Chap 12 - 2
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Jaeger/Blalock 7/1/07 Microelectronic Circuit Design, 3E McGraw-Hill Non-ideal Operational Amplifier Various error terms arise in practical operational amplifiers due to non- ideal behavior. Some of the non-ideal characteristics include: Finite open-loop gain that causes gain error Nonzero output resistance Finite input resistance Finite CMRR Common-mode input resistance DC error sources Output voltage and current limits Chap 11-3
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Jaeger/Blalock 7/1/07 Microelectronic Circuit Design, 3E McGraw-Hill Finite Open-loop Gain 2 1 1 o v o v 2 1 1 1 v R R R R R R + = = + = β β is called feedback factor. β β A A v A A A A + = = = = = 1 s v o v ) o v s v ( ) 1 v s v ( id v o v A β is called loop gain. For A β >>1, 1 2 1 1 R R ideal A + = = β β β β β A A A + = + = = = 1 s v s v 1 s v o v s v 1 v s v id v No longer zero , v id is small for large A β . Chap 11-4
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Jaeger/Blalock 7/1/07 Microelectronic Circuit Design, 3E McGraw-Hill Gain Error Gain Error is given by GE= (ideal gain)-(actual gain) For non-inverting amplifier, Gain error is also expressed as a fractional or percentage error. ) 1 ( 1 1 1 β β β β A A A GE + = + = β β β β β A A A A FGE 1 1 1 1 1 1 + = + = Chap 11-5
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Jaeger/Blalock 7/1/07 Microelectronic Circuit Design, 3E McGraw-Hill Gain Error: Example Problem : Find ideal and actual gain and gain error is percent Given data : Closed-loop gain of 200 (46 dB), open-loop gain of op amp is 10,000 (80 dB). Approach :Amplifier is designed to give ideal gain and deviations from ideal case are determined. Hence, . R 1 and R 2 aren’t designed to compensate for finite open-loop gain of amplifier. Analysis : 200 1 = β 02 . 0 200 196 200 FGE 196 200 4 10 1 4 10 1 = = = + = + = β A A v A Chap 11-6
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Jaeger/Blalock 7/1/07 Microelectronic Circuit Design, 3E McGraw-Hill Nonzero Output Resistance Output terminal is driven by test source v x and current i x is calculated to determine output resistance (all independent sources are turned off).The equivalent circuit is same For both inverting and non-inverting amplifiers.
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