Feedback ELZ 303 - Elektronik II

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Feedback

ELZ 303 - Elektronik II

Dr. Mehmet Siraç Özerdem

Elektrik Elektronik Müh. Bölümü

Dicle Universitesi

Microelectronic Circuits – Fourth Edition

Adel S. Sedra, Kenneth C. Smith, 1998 Oxford University Press

Copyright 2004 by Oxford University Press, Inc.

Feedback

Microelectronic Circuits - Fifth Edition Sedra/Smith

General structure of the feedback amplifier. This is a

signal-flow diagram, and the quantities x represent either

voltage or current signals.

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Copyright 2004 by Oxford University Press, Inc.Microelectronic Circuits - Fifth Edition Sedra/Smith

Feedback

A : Open loop gain (AOL)

Af : Closed loop gain

: Feedback factor

1+ A : Amount of feedback


Example : Non inverting op-amp

(ideal Op-amp => Ri → and Ro=0)

a) =?

b) A=104 and Af = 10, R2/R1=?

c) Amount of feedback in dB = ?

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Feedback

Illustrating the application of negative feedback to

improve the signal-to-noise ratio in amplifiers.


Illustrating the application of negative feedback to reduce

the nonlinear distortion in amplifiers.

Curve (a) shows the amplifier transfer characteristic

without feedback.

Curve (b) shows the characteristic with negative

feedback ( 0.01) applied.

Feedback

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current-mixing voltage-sampling

(shunt–shunt) topology

The four basic feedback topologies

voltage-mixing voltage-sampling

(series–shunt) topology

current-mixing current-sampling

(shunt–series) topology

voltage-mixing current-sampling

(series–series) topology

Feedback :


Example

A transistor amplifier with shunt–series feedback.

(Biasing not shown.)

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An example of the series–series feedback topology.

(Biasing not shown.)

Example


Example

(a) The inverting op-amp configuration redrawn as

(b) an example of shunt–shunt feedback

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1. The series–shunt feedback amplifier

ideal structure equivalent circuit.


1. The series–shunt feedback amplifier

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1. The series–shunt feedback amplifier (The practical situation)

Derivation of the A circuit and circuit for the series–shunt feedback amplifier.

Block diagram of a practical series–shunt feedback

amplifier


Two-Port

Network

h parameters

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The circuit with the feedback network represented by

its h parameters



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Copyright 2004 by Oxford University Press, Inc.Microelectronic Circuits - Fifth Edition Sedra/Smith1

. T

he

seri

es–

shu

nt

feed

ba

ck a

mp

lifi

er

(Summary)


Example

μ= 104

Rid=100k

ro=1k

RL=2k

R1=1k

R2=1M

Rs=10k

A=?

= ?

Af = (Vo/Vs) = ?

Rin = ?

Rout = ?

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Example (continued)


2. The series–series feedback amplifier

ideal structure

equivalent circuit

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2. The series–series feedback amplifier


2. The series–series feedback amplifier (The practical situation)


Block diagram of a practical series–series feedback

amplifier

12


Two-Port

Network

z parameters



The circuit with the feedback network represented by

its z parameters

13




. T

he

seri

es–

seri

es f

eed

ba

ck a

mp

lifi

er

(Summary)

14


Example

IC1=0.6mA

IC2=1mA

IC3=4mA

hfe=100

ro →

A=?

= ?

Af = (Io/Vs) = ?

Vo/Vs = ?

Rin = Rif = ?

Rof = ?


Example (continued)

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Example (continued)

Calculation of

Calculation of Rout


3. The shunt–shunt feedback amplifier

ideal structure

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3. The shunt–shunt feedback amplifier


3. The shunt–shunt feedback amplifier (The practical situation)


Block diagram of a practical shunt–shunt feedback

amplifier

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Two-Port

Network

y parameters


. T

he

shu

nt–

shu

nt

feed

ba

ck a

mp

lifi

er

(Summary)

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Example

= 100

VBE = 0.7 V

Vo/Vs = ?

Rin = ?

Rout = ?


Example (continued)

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Example (continued)


4. The shunt–series feedback amplifier

ideal structure

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4. The shunt–series feedback amplifier


4. The shunt–series feedback amplifier (The practical situation)


Block diagram of a practical shunt–series feedback

amplifier

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Two-Port

Network

g parameters


. T

he

shu

nt-

seri

es f

eed

ba

ck a

mp

lifi

er

(Summary)

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Example

= 100

VA = 75 V

Iout/Iin = ?

Rin = ?

Rout = ?


Example (continued)

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Example (continued)

Calculation of

Calculation of Rout

Feedback ELZ 303 - Elektronik II

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