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Unformatted text preview: Chapter12 Operational Amplifier Applications Microelectronic Circuit Design Richard C. Jaeger Travis N. Blalock Chap 12  1 Continue study of methods to determine transfer functions of circuits containing op amps. Study nonideal 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 Chapter Goals Nonideal Operational Amplifier Various error terms arise in practical operational amplifiers due to nonideal behavior. Some of the nonideal characteristics include: Finite openloop gain that causes gain error Nonzero output resistance Finite input resistance Finite CMRR Commonmode input resistance DC error sources Output voltage and current limits Chap 113 Finite Openloop Gain 2 1 1 o v o v 2 1 1 1 v R R R R R R + = = + = is called feedback factor. 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 is called loop gain. For A >>1, 1 2 1 1 R R ideal A + = = 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 . Chap 114 Gain Error Gain Error is given by GE= (ideal gain)(actual gain) For noninverting amplifier, Gain error is also expressed as a fractional or percentage error. ) 1 ( 1 1 1 A A A GE + = + = A A A A FGE 1 1 1 1 1 1 2245 + = + = Chap 115 Gain Error: Example Problem : Find ideal and actual gain and gain error is percent Given data : Closedloop gain of 200 (46 dB), openloop 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 arent designed to compensate for finite openloop gain of amplifier. Analysis : 200 1 = 02 . 200 196 200 FGE 196 200 4 10 1 4 10 1 = = = + = + = A A v A Chap 116 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 noninverting amplifiers. x i x v = out R Chap 117 Nonzero Output Resistance (contd.) 2 i o i x i + = Analysis: o R A id v x v o i = 2 1 x v 2 i R R + = Also, v id = v 1 and 2 1 1 1 x v x i 1 x v x v 2 1 1 1 v R R o R A out R R R R + + + = = = + = + + = 2 1 1 R R A o R out R Since, R o /(1+A )<<(R 1 +R 2 ), A o R out R + 2245 1 If A is infinite, R out =0 Thus, shunt feedback at output reduces R out....
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 Fall '08
 MartinBrooke
 Amplifier, Operational Amplifier

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