ECE 342 Electronic Circuits Lecture 28 Feedback Topologiesemlab.illinois.edu/ece342/notes/Lec_28.pdfElectronic Circuits Lecture 28 Feedback Topologies Jose E. Schutt-Aine Electrical

ECE 342 – Jose Schutt‐Aine 1

ECE 342Electronic Circuits

Lecture 28Feedback Topologies

Jose E. Schutt-AineElectrical & Computer Engineering

University of Illinoisjesa@Illinois.edu

ECE 342 – Jose Schutt‐Aine 2

Series-Shunt Feedback

Voltage mixing-voltage sampling feedback

ECE 342 – Jose Schutt‐Aine 3

Shunt- Series Feedback

Current mixing-current sampling feedback

ECE 342 – Jose Schutt‐Aine 4

Series-Series Feedback

Voltage mixing-current sampling feedback

ECE 342 – Jose Schutt‐Aine 5

Shunt-Shunt Feedback

Current mixing-voltage sampling feedback

ECE 342 – Jose Schutt‐Aine 6

Transfer Function Representation

Use a two-terminal representation of system for input and output

ECE 342 – Jose Schutt‐Aine 7

Y-parameter Representation

1 11 1 12 2

2 21 1 22 2

I y V y VI y V y V

ECE 342 – Jose Schutt‐Aine 8

Y Parameter Calculations

2 2

1 211 21

1 10 0V V

I Iy yV V

To make V2= 0, place a short at port 2

ECE 342 – Jose Schutt‐Aine 9

Z Parameters

1 11 1 12 2

2 21 1 22 2

V z I z IV z I z I

ECE 342 – Jose Schutt‐Aine 10

Z-parameter Calculations

2 2

1 211 21

1 10 0I I

V Vz zI I

To make I2= 0, place an open at port 2

ECE 342 – Jose Schutt‐Aine 11

H Parameters

1 11 1 12 2

2 21 1 22 2

V h I h VI h I h V

ECE 342 – Jose Schutt‐Aine 12

H Parameter Calculations

To make V2= 0, place a short at port 2

2 2

1 211 21

1 10 0V V

V Ih hI I

ECE 342 – Jose Schutt‐Aine 13

G Parameters

1 11 1 12 2

2 21 1 22 2

I g V g IV g V g I

ECE 342 – Jose Schutt‐Aine 14

G-Parameter Calculations

2 2

1 211 21

1 10 0I I

I Vg gV V

To make I2= 0, place an open at port 2

ECE 342 – Jose Schutt‐Aine 15

Series-Shunt Feedback - Ideal

1o

fs

V AAV A

Negative feedback decreases the gain

o

i

VAV

ECE 342 – Jose Schutt‐Aine 16

Series-Shunt Feedback – Equivalent Circuit

1if iR R A

Negative feedback increases the input resistance and decreases the output resistance by a factor equal to the feedback

/ 1of oR R A

ECE 342 – Jose Schutt‐Aine 17

Series-Shunt Feedback - Actual

ECE 342 – Jose Schutt‐Aine 18

Series-Shunt Feedback : h-Parameters

Account for all 4 h parameters

ECE 342 – Jose Schutt‐Aine 19

Series-Shunt Feedback : h-Parameters

12 12basic feedbackamplifier network

h h 21 21feedback basicnetwork amplifier

h h

ECE 342 – Jose Schutt‐Aine 20

Series-Series Feedback - Ideal

1o

fs

I AAV A

Negative feedback decreases the gain

o

i

IAV

ECE 342 – Jose Schutt‐Aine 21

Series-Series Feedback – Equivalent Circuit

1if iR R A 1of oR R A

Negative feedback increases the input resistance and increases the output resistance by a factor equal to the feedback

ECE 342 – Jose Schutt‐Aine 22

Series-Series Feedback - Actual

ECE 342 – Jose Schutt‐Aine 23

Series-Series Feedback: Z Parameters

Account for all 4 z parameters

ECE 342 – Jose Schutt‐Aine 24

12 12basic feedbackamplifier network

z z21 21feedback basic

network amplifierz z

Series-Series Feedback: Z Parameters

ECE 342 – Jose Schutt‐Aine 25

Shunt-Shunt Feedback - Ideal

o

i

VAI

ECE 342 – Jose Schutt‐Aine 26

Shunt-Shunt Feedback

/ 1if iR R A / 1of oR R A

Negative feedback decreases the input resistance and decreases the output resistance by a factor equal to the feedback

12 12basic feedbackamplifier network

y y 21 21feedback basicnetwork amplifier

y y

1o

fs

V AAI A

Negative feedback decreases the gain

ECE 342 – Jose Schutt‐Aine 27

Shunt-Series Feedback - Ideal

o

i

IAI

ECE 342 – Jose Schutt‐Aine 28

Shunt-Series Feedback

/ 1if iR R A 1of oR R A

Negative feedback decreases the input resistance and increases the output resistance by a factor equal to the feedback

1o

fs

I AAI A

Negative feedback decreases the gain

12 12basic feedbackamplifier network

g g 21 21feedback basicnetwork amplifier

g g

ECE 342 – Jose Schutt‐Aine 29

Rules for Series-Shunt Feedback

1 11 1 12 2

2 21 1 22 2

V h I h VI h I h V

2 2

1 211 21

1 10 0V V

V Ih hI I

1 1

1 212 22

2 20 0

I I

V Ih hV V

ECE 342 – Jose Schutt‐Aine 30

Rules for Series-Series Feedback

1 11 1 12 2

2 21 1 22 2

V z I z IV z I z I

2 2

1 211 21

1 10 0I I

V Vz zI I

1 1

1 212 22

2 20 0

I I

V Vz zI I

ECE 342 – Jose Schutt‐Aine 31

Rules for Shunt-Shunt Feedback

2 2

1 211 21

1 10 0V V

I Iy yV V

1 11 1 12 2

2 21 1 22 2

I y V y VI y V y V

1 1

1 212 22

2 20 0

V V

I Iy yV V

ECE 342 – Jose Schutt‐Aine 32

Rules for Shunt-Series Feedback

1 11 1 12 2

2 21 1 22 2

I g V g IV g V g I

2 2

1 211 21

1 10 0I I

I Vg gV V

1 1

1 212 22

2 20 0

V V

I Vg gI I