BrookeECE51_09_Operational_Amplifiers

BrookeECE51_09_Operational_Amplifiers - Chapter 11...

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Chapter 11 Operational Amplifiers Microelectronic Circuit Design Richard C. Jaeger Travis N. Blalock Chap 11-1
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Chapter Goals Understand behavior and characteristics of ideal differential and op amps. Demonstrate circuit analysis techniques for ideal op amps. Characterize inverting, non-inverting, summing and instrumentation amplifiers, voltage follower and integrator. Learns factors involved in circuit design using op amps. Provide and introduction to active filters Explore applications of op amps in nonlinear circuits, such as precision rectifiers. Provide examples of multivibrator circuits employing positive feedback. Demonstrate use of ac analysis capability of SPICE. Chap 11-2
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Differential Amplifier Model: Basic Represented by: A = open-circuit voltage gain v id = ( v + -v - ) = differential input signal voltage R id = amplifier input resistance R o = amplifier output resistance Signal developed at amplifier output is in phase with the voltage applied at + input (non-inverting) terminal and 180 ° out of phase with that applied at - input (inverting) terminal. Chap 11-3
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Differential Amplifier Model: With Source and Load R L = load resistance R S = Thevenin equivalent resistance of signal source v s = Thevenin equivalent voltage of signal source L R o R L R A + = id v * o v •Op amp circuits are mostly dc-coupled amplifiers. Signals v o and v s may have a dc component representing a dc shift of the input away from Q-point. Op-amp amplifies both dc and ac components. L R o R L R S R id R id R v A + + = = s v o v S R id R id R + = s v id v and Chap 11-4
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Differential Amplifier Model: With Source and Load (Example) Problem : Calculate voltage gain Given Data : A =100, R id =100k , R o = 100 , R S =10k , R L =1000 Analysis : Ideal amplifier’s output depends only on input voltage difference and not on source and load resistances.This can be achieved by using fully mismatched resistance condition ( R id >> R S or infinite R id and R o << R L or zero R o ). or A = open-loop gain (maximum voltage gain available from the device) dB 3 . 38 6 . 82 0 100 100 1000 k 100 k 10 k 100 100 s v o v = = + + = + + = = L R o R L R S R id R id R v A id v o v A = A v A = = id v o v Chap 11-5
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Ideal Operational Amplifier Ideal op amp is a special case of ideal differential amplifier with infinite gain, infinite R id and zero R o . and If A is infinite, v id is zero for any finite output voltage. Infinite input resistance R id forces input currents i + and i - to be zero. Ideal op amp has following assumptions: Infinite common-mode rejection, power supply rejection, open-loop bandwidth, output voltage range, output current capability and slew rate Zero output resistance, input-bias currents and offset current, input-offset voltage.
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