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Analog Circuits

For

EC / EE / IN

By

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Syllabus

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Syllabus for Analog Circuits

Small Signal Equivalent Circuits of Diodes, BJTs, MOSFETs and Analog CMOS. Simple Diode Circuits,

Clipping, Clamping, Rectifier. BIASING and Bias Stability of Transistor and FET Amplifiers.

Amplifiers, Single-and Multi-Stage, Differential and Operational, Feedback, and Power. Frequency

Response of Amplifiers. Simple Op-Amp Circuits. Filters. Sinusoidal Oscillators, Criterion for

Oscillation, Single-Transistor and Op-Amp Configurations. Function Generators and Wave-Shaping

Circuits, 555 Timers. Power Supplies.

Analysis of GATE Papers

Year ECE EE IN

2015 8.00 6.00 13.00

2014 8.50 5.60 13.00

2013 15.00 8.00 18.00

2012 6.00 5.00 5.00

2011 10.00 5.00 15.00

2010 9.00 4.00 9.00

2009 12.00 8.00 11.00

2008 8.67 13.00 11.00

2007 16.00 9.00 28.00

2006 10.67 8.00 18.00

Over All Percentage 10.38% 7.16% 14.1%


Contents

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CCoonntteennttss

Chapters Page No.

#1. Diode Circuits-Anaylsis & Application 1 – 31

Wave Shaping Circuit 1

Linear Wave Shaping Circuits 1 – 9

Non Linear Wave Shaping Circuits 9 – 13

Rectifiers and Power Supplies 14 – 17

Zener Voltage Regulator 18

Solved Examples 18 – 20

Assignment 1 21 – 25


Answer Keys & Explanations 28 – 31

#2. AC & DC Biasing-BJTs & FET 32 – 67

Introduction 32 – 33

Operating Point 33 – 38

BIAS Stabilization 38 – 46

Compensation Techniques 46 – 55




#3. Small Signal Modeling Of BJT & FET 68 – 106

Introduction 68

BJT Transistor Modeling 68 – 74

The Hybrid Equivalent Model 74 – 78

Characteristics of Amplifiers 78 – 84

FET Small Signal Model 84 – 86





#4. BJT & JFET Frequency Response 107 – 132

Introduction 107 – 109

Low Frequency Response –BJT Amplifier 109 – 112

Low frequency Response –FET Amplifier 113 – 117


Contents

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High Frequency Response –BJT Applfier 117 – 119

High Frequency Response -FET Amplifier 119 – 123




#5. Feedback & Oscillator Circuits 133 – 163

Classification of Amplifier 133 – 135

Feedback Amplifiers 135 – 136

Feedback Connection Types 136 – 139

Various Types of Oscillators 139 – 143

Tuned Oscillator Circuit 143 – 149





#6. Operational Amplifiers & Its Applications 164 – 226

Differential Amplifiers 164 – 165

Analysis of Differential Amplifier 165 – 166

Common Mode Rejection Ratio (CMRR) 166 – 174

Practical Op-Amp Circuits 174 – 190

Astable Multivibrator (Square Wave Generator) 190 – 193

Zero-Crossing Detector 193 – 203

The 555 Timer 203 – 208





#7. Power Amplifiers 227 – 250 Introduction 227 – 229

Series –Fed Class Amplifer 229

DC Bias Operation 230

AC Operation 230 – 233

Transformer Coupled Amplifier 233 – 234

Push Pull Amplifier 234 – 235

Transformer Coupled Push Pull Circuit 235 – 236


Contents

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Complementary –Symmetry Circuit 236 – 239

Total Hormonic Distrtion 239 – 240




Module Test 248 – 263

Test Questions 248 – 257


Reference Books 264


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“Live as if you were to die tomorrow.

Learn as if you were to live forever.”

…. M. K. Gandhi

Diode Circuits - Analysis

and Application

Learning Objectives After reading this chapter, you will know

1. Wave Shaping Circuit

2. Clippers and Champers

3. Rectifiers and Power Supplies

4. Efficiency, Regulation, Ripple Frequency, Form Factor, Ripple Factor

Wave Shaping Circuits Wave shaping circuits are of two types

(A) Linear wave shaping circuits

(B) Non linear wave shaping circuits

Linear Wave Shaping Circuits The process by which the wave form of non-sinusoidal signal is altered by passing it through the

linear network is called the linear wave shaping.

High Pass Circuit

High Pass Circuit

This circuit is called the high pass filter because it passes the high frequency components and

attenuates the low frequency components.

For low frequency, the reactance of the capacitance is large.

(a) Sinusoidal Input: Vo

Vi=

R

R + 1/jωC=

1

1 − j1

ωRC

R

C

+ +

− −

Vi Vo

CH

AP

TE

R

1


Diode Circuits - Analysis and Application


Vo

Vi =

1

1 − j (f1f

)

Where, f1 =1

2πRC

|Vo

Vi| =

1

√1 + (f1

f⁄ )

2, ∠

Vo

Vi= −tan−1(−f1/f) = tan−1(f1/f)

Gain-Frequency Plot of High Pass Circuit

(b) Step Input:

Vi (t) = Vc(t) + Vo(t), …………………………………….... (1)

Vi(t) = 1/C ∫ i dt + Vo(t) = iR, ……………………….. (2)

So Vi(t) =1/RC ∫ Vo(t) dt + Vo(t) = V u(t)……….. (3)

For step input Vi(t) = {V for t ≥ 0

0 other wise

It is a single time constant circuit and a first order equation is obtained.

The general solution of any single time constant circuit can be written as,

Vo(t) = Vf + (Vi − Vf)e−t/τ, ……………………………... (4)

Here, Vf = 0; Vi = V, Vo (t) = Ve−t

τ

Where τ = 1/RC

For the circuit in high pass circuit fig, Vf = 0 and Vi = Vsubstituting in E.q., (4), we have

Output Voltage of High Pass Circuit When Input is a Step Voltage

Vo(t)

0 t

V

Vi(t)

V

t

𝐒𝐭𝐞𝐩 𝐈𝐧𝐩𝐮𝐭

|Vo/Vi|

f1 f

1

0.707




(c) Pulse Input:

Vi(t) = V[u(t) − u(t − tp)]

1. Vo = Ve−t/τ, Vp = Ve−tp/τ

2. Vo = V2e−(t−tp)/τ, V2 = Vp − V

Pulse Input Signal

τ large ⇒ Slow response and

τ small ⇒ Fast response

Output of High Pass Filter, When Input is a Pulse

For a low time constant the peak – to – peak amplitudes will be double. The process of

converting pulses into spikes by means of a low time constant is called peaking. In high pass RC

circuit, the average level of the output is always zero. The area above the zero axis should be

equal to the area below the zero axis, A1 = A2.

V

Vo

Vo(t) Vi

tp

t

−V

(c)

(a)

Ve−t/RC

t

V

Vp = Ve−tp/RC

(Vp − V)et(t−tp)/RC

(b)

t V

Vo

Vi Vo(t)

Vp

tp

t

Vi(t)

tp O

V




(d) Square Wave Input:

(a) Square Wave Input

A square wave is a waveform as shown in fig (a) which is periodic with time period T such that it

maintains a level V′ for time T1 and V′′for time T2 where T = T1 + T2.

Figure (b) (c) (d) and (e) show output wave forms of the high pass RC circuit under

steady-state conditions for the cases (i) RC>>T (ii) RC>T (iii) RC=T and (iv) RC<<T

Case (i): For arbitrarily large time constant value, the output is same as that of input but with zero

dc level.

(b) Output When RC is Very Large

Case (ii): When RC>T, the output is in the form of a tilt.

(c) Output When RC>T

V1e−t/RC

V2e−(t−T1)/RC

V1

T1 T2

V2

V1′

V1

V1′

V2′

V V

0 t

Vo

V 0

T1 T2

t Zero Voltage

T

A2

A1

Vi, Vo

T1 T2 T

Vi V′

V′′

t

Vdc

V

ϕV




Case (iii): When RC is comparable to T, the output rises and falls exponentially.

(d) Output When RC is Comparable to T

Case (iv): When RC<<T, the output consists of alternative positive and negative spikes.

(e) Output When RC <<T

More generally the response to a square wave must have the appearance shown below:

The four levels V1, V1′, V2, V2

′ can be determined from (refer below figure)

V1′ = V1e−T1/τ, V1

′ − V2 = V

V2′ = V2e−T2/τ, V1

− V2′ = V

For symmetrical square wave

T1 = T2 = T/2

V1 = −V2, V1′ = −V2 and the response is shown below in Fig. (b)

Percentage tilt ‘P’ is defined by

P = V1 − V1

′

V/2× 100 ≈

T

2τ× 100 %

= πf1

f× 100 %

Where f1 = 1

2πτ and f =

1

T

T2

T1

V

T

V

Vo

Vi

V1e−t/RC

Vi

Vo

V2e−(t−T1)/RC

V2

T1 T2

T

V1


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