电路与电子技术：Chapter-9 Amplifiers Specifications and External Characteristics

1、Chapter 9Amplifiers: Specifications andExternal Characteristics Chapter 9Amplifiers: Specifications andExternal Characteristics1.Use various amplifier models to calculate amplifier performance for given sources and loads.2. Compute amplifier efficiency.3. Understand the importance of input and outpu

2、t impedances of amplifiers.4. Determine the best type of ideal amplifier for various applications.5. Understand linear and nonlinear distortion in amplifiers.6. Specify the pulse-response parameters of amplifiers.7. Work with differential amplifiers and specify common-mode rejection requirements.8.

3、Understand the various sources of dc offsets and design balancing circuits.BASIC AMPLIFIER CONCEPTSIdeally, an amplifier produces an output signal with identical waveshape as the input signal, but with a larger amplitude. tvAtvivoInverting versus Noninverting AmplifiersInverting amplifiers have nega

4、tive voltage gain, and the output waveform is an inverted version of the input waveform. Noninverting amplifiers have positive voltage gain.Voltage-Amplifier ModelCurrent GainioiiiA LiviiLoioiRRARvRviiAPower GainioPPG LiviviiooioRRAAAIVIVPPG2CASCADED AMPLIFIERS21vvvAAA Simplified Models for Cascaded

5、 Amplifier StagesFirst, determine the voltage gain of the first stage accounting for loading by the second stage. The overall voltage gain is the product of the gains of the separate stages.The input impedance is that of the first stage, and the output impedance is that of the last stage.POWER SUPPL

6、IES AND EFFICIENCYBBBAAAsIVIVPCurrent-Amplifier ModelAisc is the current gain of the amplifier with the output short circuited.Transconductance-Amplifier ModeliomviGscscConnect a short circuit across the output terminals and analyze the circuit to determine Gmsc.Transresistance-Amplifier ModeliomivR

7、ococOpen circuit the output terminals and analyze the circuit to determine Rmoc.IMPORTANCE OF AMPLIFIER IMPEDANCES IN VARIOUS APPLICATIONSSome applications call for amplifiers with high input (or output) impedance while others call for low input (or output) impedance.Other applications call for ampl

8、ifiers that have specific input and/or output impedances.The proper classification of a given amplifier depends on the ranges of source and load impedances with which the amplifier is used. FREQUENCY RESPONSEiovAVVDetermining Complex Gain 302000cos1 . 0ttvi 152000cos10ttvo45100301 . 01510iovAVVLINEA

9、R WAVEFORM DISTORTIONIf the gain of an amplifier has a different magnitude for the various frequency componentsof the input signal, a form of distortion known as amplitude distortion occurs.Phase DistortionIf the phase shift of an amplifier is not proportional to frequency, phase distortion occurs.R

10、equirements for Distortionless AmplificationTo avoid linear waveform distortion, an amplifier should have constant gain magnitude and a phaseresponse that is linear versus frequency for the range of frequencies contained in the input signal.PULSE RESPONSERise TimeBtr35. 0Tilt%100 tiltpercentagePPFor

11、 small amounts of tilt,TfL200 tiltpercentageTRANSFER CHARACTERISTIC AND NONLINEAR DISTORTIONThe transfer characteristic is a plot of instantaneous output amplitude versus instantaneous input amplitude.Curvature of the transfer characteristic results innonlinear distortion.Harmonic DistortionFor a si

12、newave input, nonlinear distortion produces output components having frequencies that are integer multiples of the input frequency. tVtvaaicos tVtVtVVtvaaao3cos2coscos3210122VVD 133VVD 144VVD Total Harmonic Distortion (THD) Total harmonic distortion is a specification that indicates the degree of no

13、nlinear distortion produced by an amplifier.25242322DDDDDDIFFERENTIAL AMPLIFIERSA differential amplifier has two input terminals: aninverting input and a noninverting input.Ideally, a differential amplifier produces an output that is proportional to the difference between two input signals.21iiidvvviddovAv Common-mode Signal21cm21iiivvvCommon-Mode Rejection RatiocmcmiiddovAvAvcmlog 20CMRRAAdOFFSET VOLTAGE, BIAS CURRENT, AND OFFSET CURRENTReal differential amplifiers suffer from imperfections