BrookeECE51_10_Operational_Amplifier_2

# BrookeECE51_10_Operational_Amplifier_2 - Chapter12...

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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 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 Chapter Goals 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 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 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 2245 + = +- = Chap 11-5 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 . 200 196 200 FGE 196 200 4 10 1 4 10 1 =- = = + = + = β A A v A Chap 11-6 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. x i x v = out R Chap 11-7 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 + + + = = ∴ = + = β β + + = ∴ 2 1 1 R R A o R out R β Since, R o /(1+A β )<<(R 1 +R 2 ), β 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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BrookeECE51_10_Operational_Amplifier_2 - Chapter12...

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