上海交通大学：《模拟电子技术》课程教学资源（PPT课件）chapter 8 Feedback

Chapter 8 FeedbackIntroduction8.1 The general feedback structure8.2Someproperties of negative feedback8.3 The four basic feedback topologies8.4 The series-shunt feedback amplifier8.5 The series-series feedback amplifier8.6 The shunt-shunt and shunt-series feedbackamplifier8.10 Stability study using bode plot8.11 Freguency compensationMicroelectronicCircuits

Microelectronic Circuits Chapter 8 Feedback Introduction 8.1 The general feedback structure 8.2 Some properties of negative feedback 8.3 The four basic feedback topologies 8.4 The series-shunt feedback amplifier 8.5 The series-series feedback amplifier 8.6 The shunt-shunt and shunt-series feedback amplifier 8.10 Stability study using bode plot 8.11 Frequency compensation

IntroductionIt's impossible to think of electronic circuits withoutsomeformsoffeedbackNegativefeedbackDesensitize the gainReducenonlineardistortionReduce theeffectof noiseControl the input and output impedance> Extend the bandwidth of the amplifierThebasicidea ofnegativefeedbackisto tradeoffbetweengainandotherdesirableproperties.Positive feedback will causetheamplifieroscillationMicroelectronic Circuits

Microelectronic Circuits Introduction ⚫ It’s impossible to think of electronic circuits without some forms of feedback. ⚫ Negative feedback ➢ Desensitize the gain ➢ Reduce nonlinear distortion ➢ Reduce the effect of noise ➢ Control the input and output impedance ➢ Extend the bandwidth of the amplifier ⚫ The basic idea of negative feedback is to trade off between gain and other desirable properties. ⚫ Positive feedback will cause the amplifier oscillation

Three Parts: Partl: The basic concept and someProperties of negative feedbackPartll: The four basic feedback and analysis Partlll: The loop gain, stability problemand frequency compensationMicroelectronicCircuits

Microelectronic Circuits Three Parts: ⚫ PartI: The basic concept and some Properties of negative feedback ⚫ PartII: The four basic feedback and analysis ⚫ PartIII: The loop gain, stability problem and frequency compensation

PartIJudgment and PropertiesThe basic conceptoffeedbackexamplesMicroelectronic Circuits

Microelectronic Circuits PartI The basic concept Judgment and Properties of feedback examples

Partl: The basic concept and someProperties of negative feedback8.1TheGeneralFeedbackStructureXSourceLoadThis is a signal-flow diagram, and the quantities x represent either voltage orcurrentsignalsIn electronic circuits, part of or all output signal is fed back toinput, and affects the input signal value, which is called feedback.Microelectronic Circuits

Microelectronic Circuits PartI: The basic concept and some Properties of negative feedback This is a signal-flow diagram, and the quantities x represent either voltage or current signals. In electronic circuits, part of or all output signal is fed back to input, and affects the input signal value, which is called feedback. 8.1 The General Feedback Structure

The feedback judgment foramplifier circuits0+Vcc+Vcc0+VccIcoRb2+RblBTUBQO++IBQuouoUEQu,uiRbEO000(b)(c)(a)Microelectronic Circuits

Microelectronic Circuits The feedback judgment for amplifier circuits

Negativefeedbackandpositivefeedback:Accordingtotheeffectingoffeedback1)positive feedback increases the signal that appearsat the input of the basic amplifier2) negative feedback reduces the signal that appearsat the input of the basic amplifierX, =x,-XfDCfeedbackandACfeedback:1) Feedback quantity only contains DC quantity, is called DCfeedback2) Feedback quantity only contains AC quantity, is called ACfeedbackUsually AC feedback and DC feedback are concomitantMicroelectronicCircuits

Microelectronic Circuits Negative feedback and positive feedback： According to the effecting of feedback 1) positive feedback increases the signal that appears at the input of the basic amplifier 2) negative feedback reduces the signal that appears at the input of the basic amplifier DC feedback and AC feedback： 1) Feedback quantity only contains DC quantity，is called DC feedback 2) Feedback quantity only contains AC quantity，is called AC feedback Usually AC feedback and DC feedback are concomitant i s f x = x − x

The feedbackjudgment :R2O05OururAAAOO0uououoR(b)(a)(c)(a) No feedback(b) Feedback exists(c) No feedbackMicroelectronic Circuits

Microelectronic Circuits The feedback judgment ： (a) No feedback (b) Feedback exists (c) No feedback

The judgment of feedback parityInstantaneous polaritymethod:1)Regulate thepolarityof input signal relative toground at sometime.2) Decide all points'parity step by step, at last getthe parity of output signal.3) According to the parity of output signal decides theparity of amount of feedback.4) Ifamount of feedback increases the signal thatappears at the input of the basic amplifier, the circuitinducts the positive feedback. Otherwise,itinductsthenegativefeedbackMicroelectronicCircuits

Microelectronic Circuits Instantaneous polarity method： The judgment of feedback parity 1) Regulate the polarity of input signal relative to ground at sometime. 2) Decide all points’ parity step by step, at last get the parity of output signal. 3) According to the parity of output signal decides the parity of amount of feedback. 4) If amount of feedback increases the signal that appears at the input of the basic amplifier, the circuit inducts the positive feedback. Otherwise, it inducts the negative feedback

RUN+upOOu+u.iFUDuDAAOiinuouo+0urUNR,ACuUNp0i④R2R2UFupS④(b)(a)(c)To integrated operational amplifiers, theinputquantity can be Up or in (ip)MicroelectronicCircuits

Microelectronic Circuits To integrated operational amplifiers，the input quantity can be UD or iN（iP）