The Operational Amplifier

The Operational Amplifier (Op-Amp)

Electronic Devices, 9th edition Thomas L. Floyd

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Chapter Goals • Develop understanding of linear amplification concepts such as: – – – – – – –

Voltage gain, current gain, and power gain Gain conversion to decibel representation Input and output resistances Biasing for linear amplification Distortion in amplifiers Two-port representations of amplifiers Understand behavior and characteristics of ideal differential and op amps. – Demonstrate circuit analysis techniques for ideal op amps. – Characterize inverting, non-inverting amplifiers.

Electronic Devices, 9th edition Thomas L. Floyd

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Amplification Introduction

A complex periodic signal can be represented as the sum of many individual sine waves. We consider only one component with amplitude Vs = 1 mV and frequency ωs with 0 phase (signal is used as reference): Amplifier output is sinusoidal with same frequency but different amplitude Vo and phase θ: Electronic Devices, 9th edition Thomas L. Floyd

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Amplification Introduction (cont.) Amplifier output power is: Here, we desire PO = 100 W with RL = 8 Ω and Vs = 1 mV Output power also requires output current which is:

Input current is given by Output phase is zero because circuit is purely resistive.

Electronic Devices, 9th edition Thomas L. Floyd

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Amplification Voltage Gain & Current Gain • Voltage Gain: Magnitude and phase of voltage gain are given by and For our example, • Current Gain: Magnitude of current gain is given by

Electronic Devices, 9th edition Thomas L. Floyd

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Amplification Power Gain • Power Gain:

For our example,

Electronic Devices, 9th edition Thomas L. Floyd

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Amplification Expressing Gain in Decibels (dB) The logarithmic decibel or dB scale compresses the huge numeric range of gains encountered in real systems.

Electronic Devices, 9th edition Thomas L. Floyd

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Amplification Expressing Gain in dB - Example For our example:

Electronic Devices, 9th edition Thomas L. Floyd

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Mismatched Source and Load Resistances    

In introductory circuit theory, the maximum power transfer theorem is usually discussed. Maximum power transfer occurs when the source and load resistances are matched (equal in value). In most amplifier applications, however, the opposite situation is desired. A completely mismatched condition is used at both the input and output ports of the amplifier.

Electronic Devices, 9th edition Thomas L. Floyd

© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved.

Mismatched Source and Load Resistances For the voltage amplifier shown If Rin >> Rs and Rout> RS or infinite Rid, and Ro