Slide điện tử tương tự chapter 6 feedback

CHAPTER 6: FEEDBACKDR.. PHẠM NGUYỄN THANH LOAN 1 cuu duong than cong...  Introduction  Classification  Voltage series feedback Kiểu điện áp nối tiếp  Voltage shunt feedback Kiểu điện

CHAPTER 6: FEEDBACK

DR PHẠM NGUYỄN THANH LOAN

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 Introduction

 Classification

 Voltage series feedback (Kiểu điện áp nối tiếp)

 Voltage shunt feedback (Kiểu điện áp song song)

 Current series feedback(Kiểu dòng điện nối tiếp)

 Current shunt feedback (Kiểu dòng điện song song)

 Chapter 18 (ref.1)

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 Feedback: a part of output is used to feed the input

 2 kinds of feedback:

negative and positive

 Applications:

 Positive feedback  oscillator

 Negative feedback

amflifier

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Negative feedback?

 Advantage of negative feedback

 Stable gain

 Increase input impedance and decrease output impedance

 Increase bandwidth

 Increase linear region

 Reduce noise

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 Base on the input connection to determine series or shunt (nối tiếp/song song) and output signal to

derermine voltage/current (điện áp/dòng điện)

 voltage series feedback (Kiểu điện áp nối tiếp)

 voltage shunt feedback (Kiểu điện áp song song)

 current series feedback (Kiểu dòng điện nối tiếp)

 current shunt feedback (Kiểu dòng điện song song)

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 Base on the input connection to determine series or shunt and output signal to deterrmine voltage/current

 Kiểu điện áp nối tiếp (voltage series feedback)

 Input: voltage; output: voltage

 Kiểu điện áp song song (voltage shunt feedback)

 Input: current; Output: voltage

 Kiểu dòng điện nối tiếp (current series feedback))

 Input: voltage; Output: current

 Kiểu dòng điện song song (current shunt feedback)

 Input:current; Output: current

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Voltage series feedback (1/3)

 A=Vo/Vi (withoutVf)

 β=Vf/Vo

 Af = Vo/Vs (overall gain)

 Zi = Vi/Ii;

Zif=Vs/Ii=Zi(1+βA)

 Zof=Zo/(1+βA)

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Voltage series feedback(2/3)

 Vi =Vs - Vf

 Af = Vo/Vs = A/(1+βA)

 Zi = Vi/Ii; Zif=Vs/Ii  Zif = Zi(1+βA)

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Voltage series feedback (3/3)

 A = - gm(RD//Ro//(R1+R2)

= - gm.RL

 β=Vf/Vo=- R2/(R1+R2)

 Af=A/(1+βA)

 Zif=Zi(1+βA)

 Zof=Zo/(1+βA)

m g R

R L R R

L

R m g f

A

) 2 1

/(

2 1

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Voltage shunt feedback (1/2)

 A=Vo/Ii

 β=If/Vo

 Af=Vo/Is=A/(1+βA)

 Zif=Zi/(1+βA)

 Zof=Zo/(1+βA)

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Voltage shunt feedback (2/2)

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Current series feedback (1/2)

 A=Io/Vi

 β=Vf/Io

 Af=Io/Vs=A/(1+βA)

 Zif=Zi(1+βA)

 Zof=Zo(1+βA)

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Current series feedback (2/2)

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Current shunt feedback (1/2)

 A=Io/Ii

 β=If/Io

 Af=Io/Is=A/(1+βA)

 Zif=Zi/(1+βA)

 Zof=Zo(1+βA)

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Current shunt feedback(2/2)

A=Io/Ii β=If/Ie2=RE/(re+RE+Rf)

Af=Io/Is=A/(1+βA)

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Impedances with feedback

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Impact on Bandwidth

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 Chapter 18: 1, 2, 3, 4, 5

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