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）