(8.1.7)--Chapter 8模拟电子技术基础.ppt

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1、Chapter 8 FET AmplifiersChapter 8 FET AmplifiersChapter 8 FET AmplifiersFET Small-Signal Model JEFT Fixed-Bias ConfigurationJEFT SourceFollower ConfigurationJEFT Common-Gate ConfigurationDepletion-Type MOSFETsOutlineChapter 8 FET Amplifiers8.1 FET Small-Signal Model(a)neglecting the the channel-leng

2、th modulation effect(b)including the effect of channel-length modulation,modeled by output resistance ro=|VA|/ID.Chapter 8 FET AmplifiersThe Small-Signal Models(a)The T model of the MOSFET augmented with the drain-to-source resistance ro.(b)An alternative representation of the T model.Chapter 8 FET

3、AmplifiersModeling the Body EffectSmall-signal equivalent-circuit model of a MOSFET in which the source is not connected to the body.Chapter 8 FET AmplifiersSingle-Stage MOS AmplifierCharacteristic parametersBasic structure Three configurationsCommon-source configurationCommon-drain configurationCom

4、mon-gate configurationChapter 8 FET AmplifiersCharacteristic Parameters of AmplifierThis is the two-port network of amplifier.Voltage signal source.Output signal is obtained from the load resistor.Chapter 8 FET AmplifiersDefinitionsInput resistance with no loadInput resistanceOpen-circuit voltage ga

5、inVoltage gainChapter 8 FET AmplifiersDefinitions(contd)Short-circuit current gainCurrent gainShort-circuit transconductance gainChapter 8 FET AmplifiersDefinitions(contd)Open-circuit overall voltage gainOverall voltage gainChapter 8 FET AmplifiersDefinitions(contd)Output resistance of amplifier pro

6、perOutput resistanceChapter 8 FET AmplifiersDefinitions(contd)Voltage amplifierChapter 8 FET AmplifiersDefinitions(contd)Voltage amplifierChapter 8 FET AmplifiersDefinitions(contd)Transconductance amplifierChapter 8 FET AmplifiersRelationshipsVoltage divided coefficientChapter 8 FET Amplifiers8.2 JE

7、FT Fixed-Bias Configuration Basic structure of the circuit used to realize single-stage discrete-circuit MOS amplifier configurations.Chapter 8 FET AmplifiersThe Common-Source AmplifierCommon-source amplifier based on the circuit of basic structure.Biasing with constant-current source.CC1 And CC2 ar

8、e coupling capacitors.CS is the bypass capacitor.Chapter 8 FET AmplifiersEquivalent Circuit of the CS AmplifierChapter 8 FET AmplifiersEquivalent Circuit of the CS AmplifierSmall-signal analysis performed directly on the amplifier circuit with the MOSFET model implicitly utilized.Chapter 8 FET Ampli

9、fiersCharacteristics of CS AmplifierInput resistanceVoltage gainOverall voltage gainOutput resistanceChapter 8 FET AmplifiersSummary of CS AmplifierVery high input resistanceModerately high voltage gainRelatively high output resistanceChapter 8 FET AmplifiersSmall-signal Equivalent CircuitChapter 8

10、FET AmplifiersSmall-signal Equivalent Circuit with ro NeglectedChapter 8 FET AmplifiersCharacteristics of CS Amplifier with a Source ResistanceInput resistanceVoltage gainOverall voltage gainOutput resistanceChapter 8 FET AmplifiersSummary of CS Amplifier with a Source ResistanceIncluding RS results

11、 in a gain reduction by the factor(1+gmRS)RS takes the effect of negative feedback.Chapter 8 FET Amplifiers8.3 JEFT Self-Bias Configuration Chapter 8 FET AmplifiersEquivalent Circuit of the AmplifierChapter 8 FET AmplifiersCharacteristics of CS AmplifierInput resistanceVoltage gainOverall voltage ga

12、inOutput resistanceChapter 8 FET Amplifiers8.4 JEFT SourceFollower Configuration Biasing with current sourceInput signal is applied to gate,output signal is taken at the source.Chapter 8 FET AmplifiersThe Common Source-Follower AmplifierSmall-signal equivalent-circuit modelT model makes analysis sim

13、plerDrain is signal groundedChapter 8 FET AmplifiersSmall-Signal Analysis Performed Directly on the CircuitChapter 8 FET AmplifiersCircuit for Determining the Output Resistance of CD AmplifierChapter 8 FET AmplifiersCharacteristics of CD AmplifierInput resistanceVoltage gainOverall voltage gainOutpu

14、t resistanceChapter 8 FET AmplifiersSummary of CD or Source-Follow AmplifierVery high input resistanceVoltage gain is less than but close to unityRelatively low output resistanceVoltage buffer amplifierPower amplifierChapter 8 FET AmplifiersSummary and ComparisonsThe CS amplifier is the best suited

15、for obtaining the bulk of gain required in an amplifier.Including resistance RS in the source lead of CS amplifier provides a number of improvements in its performance.The low input resistance of CG amplifier makes it useful only in specific application.It has excellent high-frequency response.Can b

16、e used as a current buffer.Source follower finds application as a voltage buffer and as the output stage in a multistage amplifier.Chapter 8 FET Amplifiers 8.5 JEFT Common-Gate Configuration Biasing with constant current source IInput signal vsig is applied to the sourceOutput is taken at the drainG

17、ate is signal groundedCC1 and CC2 are coupling capacitorsChapter 8 FET AmplifiersThe Common-Gate AmplifierA small-signal equivalent circuit of the amplifier in fig.(a).T model is used in preference to the modelNeglecting roChapter 8 FET AmplifiersThe Common-Gate Amplifier Fed with a Current-Signal I

18、nputChapter 8 FET AmplifiersCharacteristics of CG AmplifierInput resistanceVoltage gainOverall voltage gainOutput resistanceChapter 8 FET AmplifiersSummary of CG AmplifierNoninverting amplifierLow input resistanceHas nearly identical voltage gain of CS amplifier,but the overall voltage gain is smaller by the factor(1+gmRsig）Relatively high output resistanceCurrent followerSuperior high-frequency performance