Outline

Review

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Summary

Single time Constant (STC) Networks

Voltage Amplifiers

Frequency Response of Amplifiers

Outline

1

Single time Constant (STC) Networks

Frequency Response of Amplifiers

Review

1/21/2015

Amplifier Saturation

Circuit Models for Amplifiers

NonLinear Transfer Characterstics(T.F) and Biasing

Review

2

Circuit Models for Amplifiers

NonLinear Transfer Characterstics(T.F) and

Different Types of Amplifiers

Voltage Amplifier

Current Amplifier

TransConductance Amplifier

TransResistance Amplifier

Different Types of Amplifiers

Amplifier

Amplifier

Voltage Amplifier

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Voltage Amplifier

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Input resistance RiOutput resitance R0Open circuit voltage gain AVo

Voltage Amplifier (Input section)

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Voltage Amplifier (Input section)

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Inorder not to lose a significant portion of the input signal in coupling the signal source to the amplifier input ,the amplifier must be designed to have input resistance Rgreater than Rs

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Voltage Amplifier (Input section)

Inorder not to lose a significant portion of the input signal in coupling the signal source to the amplifier input ,the amplifier must be

input resistance Ri must

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Voltage Amplifier (Input section)

Voltage Amplifier (Input section)

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Voltage Amplifier (Input section)

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Voltage Amplifier (Input section)

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Ri >> Rs

Voltage Amplifier (Input section)

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Voltage Amplifier (Output section)

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Voltage Amplifier (Output section)

Voltage Amplifier (Output section)

Using voltage divider rule

Voltage Gain is given by

Voltage Amplifier (Output section)

Using voltage divider rule

Voltage Gain is given by

Inorder not to lose gain in couplingto a load, the output resistancethan the load resistance RL

Ro

Overall voltage Gain vousing

o /vs can be found by

Frequency Response of Amplifiers

A linear amplifier fed at its input with a sinewave signal Vi and frequency

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Frequency Response of Amplifiers

A linear amplifier fed at its input with a sine-and frequency

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Frequency Response of Amplifiers

Whenever a sine-wave signal is applied to a linear circuit ,the resulting output is sinusiodal with the same frequency as the input

The output sinusoid will have different amplitude and will be shifted in phase relative to the input

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Frequency Response of Amplifiers

wave signal is applied to a linear circuit ,the resulting output is sinusiodal with the same frequency as the input

The output sinusoid will have different amplitude and will be shifted in phase relative

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Two plots w.r.t frequency on X

Magnitude plot Phase plot

This plots together called as

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Frequency Response of Amplifiers

Two plots w.r.t frequency on X-axis

This plots together called as Bode plots

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Frequency Response of Amplifiers

Magnitude plot

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Magnitude plot

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Phase Plot

Phase plot

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Phase Plot

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Amplifier Bandwidth

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Amplifier Bandwidth

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STC Networks

An STC network is onecan be reduced to, one

(capacitance or inductance) and one resistance

An STC network formed by of an and a resistance R has a time constant

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STC Networks

one that is composed of ,orone reactive component

(capacitance or inductance) and one resistance

An STC network formed by of an capacitance Chas a time constant =CR

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STC Networks

An STC network formed by of an capacitance C and a resistance R has a time constant

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STC Networks

An STC network formed by of an capacitance C and a resistance R has a time constant =CR

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STC Networks

An STC network formed by of an and a resistance R has a time constant

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STC Networks

An STC network formed by of an inductance Lhas a time constant =L/R

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STC Networks

Most STC networks can be classified into two categories

Low Pass Filter High Pass Filter

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STC Networks

Most STC networks can be classified into two

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lowpasslowpass

bandpassbandpass

STC Networks

highpasshighpass

bandstopbandstop

STC Networks Filters (ideal)

lowpasslowpass

bandpassbandpass

STC Networks Filters (

bandstopbandstop

highpasshighpass

Filters (RealisticRealistic)

STC Networks

This passes low frequency sine wave inputs with little or no attenuation at w= 0

Attenuates the high frequency input sinusoids This is a Low pass Filter1/21/2015

STC Networks

This passes low frequency sine wave inputs with little or no attenuation at w= 0

Attenuates the high frequency input sinusoids

a Low pass Filter25

STC Networks

This attenuates low frequency sine wave inputs with little or no attenuation at w= 0

Passes the high frequency input sinusoids This is a High pass Filter

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STC Networks

This attenuates low frequency sine wave inputs with little or no attenuation at w= 0

Passes the high frequency input sinusoids

a High pass Filter

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Consider the circuit below.

R

CVI

+

_

1( )

1( ) 1OV jw jwC

V jw jwRCRi jwC

Low pass filter circuit

Low Pass FilterConsider the circuit below.

C VO

+

_

1( ) 1V jw jwRC

Low pass filter circuit

Low Pass Filter

1( )

1( ) 1OV jw jwC

V jw jwRCRi jwC

Low Pass Passive Filter

jSubstituting

1( ) 1V jw jwRC

Low Pass Passive Filter

= s

Low Pass Passive Filter

Substituting

0 = Corner Frequency

Low Pass Passive Filter

0 = 1 / RC

= Corner Frequency

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Design Low pass Filtercutoff frequency 150Hz

Filter for sub woofer withHz

Consider the circuit below.

C

RVi+

_

( )1( ) 1

OV jw jwRCRV jw jwRCRi jwC

High Pass Filter

High Pass Passive Filter

Consider the circuit below.

VO

+

_

1( ) 1V jw jwRCRV jw jwRC

jwC

High Pass Filter

High Pass Passive Filter

( )1( ) 1

OV jw jwRCRV jw jwRCRi jwC

High Pass Passive Filter

jSubstituting

( ) 1V jw jwRCV jw jwRC

High Pass Passive Filter

= s

High Pass Passive Filter

Substituting

0 = Corner Frequency

High Pass Passive Filter

0 = 1 / RC

= Corner Frequency

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Active Filter

Active Element

BJTAmplifier

MOS Amplifier 34

Active Filter

Active Element

MOS Amplifier

OPAMP Amplifier

Frequency response of STC networks

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Frequency response of STC networks

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Frequency response of STC networks

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Frequency response of STC networks

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ExampleExample

Original signal

Low-pass filtered

High-pass filtered

Band-pass filtered

Band-stop filtered