Operational Amplifiers

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Operational Amplifiers - PowerPoint PPT Presentation

Operational Amplifiers. A brief introduction. Op-Amp Introduction. Need exists for a circuit element that can perform: Add, subtract, multiply, divide, differentiate, integrate Evolved from Analog Computers Op-Amp properties

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Presentation Transcript

Operational Amplifiers

A brief introduction

BAE 5413

Op-Amp Introduction
• Need exists for a circuit element that can perform:
• Add, subtract, multiply, divide, differentiate, integrate
• Evolved from Analog Computers
• Op-Amp properties
• Single building block which can be assembled into above functions by adding passive components (R,L,C)
• Inexpensive (used in high volume)
• Compact
• Op-Amp analysis
• Use assumptions of “Ideal Op-Amp” to allow low frequency performance to be approximated
• Typically have near ideal characteristics but frequency response of an integrator (G(s) = 1/ts). (Otherwise, the high bandwidth would be impossibly difficult to manage.)

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Ideal Op-Amp Assumptions
• Differential function
• Vout = A•DV
• Infinite
• Intrinsic gain: A = 
• Input impedance: Zin = 
• Bandwidth: Vout  f(w)
• Zero
• Input offset voltage: Vio= 0 for Vout+ Vio= A•DV
• Input impedance: Zout = 0

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Inverting Amplifier
• Consider the circuit configuration to the right
• Assuming intrinsic gain of the op-amp is very large for the frequency of interest:
• Voutis finite and typically within +15 to -15 V implying DV is very small
• Assuming ib is very small given the intrinsic input impedance is very large, Vb must be very small

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Inverting Amplifier
• Amplifier performance is a function of external components only for ideal assumptions
• Input and output impedances of the amplifier can be calculated as approximately:

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Non-Inverting Amplifier
• Input and output impedances can be calculated as approximately:

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