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Operational Amplifiers

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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Operational Amplifiers

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  1. Operational Amplifiers A brief introduction BAE 5413

  2. 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.) BAE 5413

  3. 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 BAE 5413

  4. 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 BAE 5413

  5. 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: BAE 5413

  6. Non-Inverting Amplifier BAE 5413

  7. Non-Inverting Amplifier • Input and output impedances can be calculated as approximately: BAE 5413

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