ANALOG ELECTRONICS CIRCUIT

UNIT 1 Single And Multistage Amplifiers

CLASSIFICATION OF AMPLIFIERS

ON THE BASIS OF

INPUT

OUTPUT

Freq Response

Mode of Operation

Coupling Method

CLASSIFICATION OF AMPLIFIERS
ON THE BASIS OF INPUT Small signal Large signal

CLASSIFICATION OF AMPLIFIERS
ON THE BASIS OF OUTPUT VOLTAGE AMP POWER AMP

CLASSIFICATION OF AMPLIFIERS
ON THE BASIS OF FREQ RANGE DC FREQ (0 Hz10 Hz) AUDIO FREQ (20Hz- 20 Khz ) RADIO FREQ (FEW Hz Hundred Khz)

CLASSIFICATION OF AMPLIFIERS
ON THE BASIS OF COUPLING METHOD RC COUPLED TRANSFORMER COUPLED DIRECT COUPLED

R C COUPLED AMP

TRANSFORMER COUPLED

DIRECT COUPLED

CLASSIFICATION OF AMPLIFIERS
ON THE BASIS MODE OF OPERATION CLASS A CLASS B CLASS AB CLASS C

CLASS A AMPLIFIER

CLASS B

CLASS AB

CLASS C

DISTORTION IN AMPLIFIER
WHEN OUTPUT IS NOT REPLICA OF INPUT THEN AMP IS SAID TO HAVE DISTORTION IT OCCURS DUE TO NONLINEARITY IN CHARACTERISTICS OF TRANSISTOR ALSO DUE TO ASSOCIATED CIRCUIT

DISTORTION IN AMPLIFIER

3 TYPES

AMPLITUDE OR NON LINEAR

FREQ

PHASE

AMP DISTORTION
OCCOUR WHEN TRANSISTOR OPERATES IN NONLINEAR PART OF ITS TRANSFER CHAR. ALSO KNOWN AS HARMONIC DISTORTION MORE PROMINENT FOR LARGE SIGNAL LEVELS

AMP DISTORTION
OUTPUT CONTAIS NEW FREQ S OTHER THAN FUNDAMENTAL FREQ.

AMP DISTORTION

FREQ. DISTORTION
ARBITRARY SIGNAL HAVE DIFFERENT FREQ. COMPONENT WHICH ARE AMPLIFIED UNEQUALLY , SO GENRATES FREQ DIST. IF AMPLIFICATION OF DIFFERENT FREQ COMPONENTS IS DIFFERENT THEN OUTPUT IS NOT EXACT REPLICA OF INPUT

FREQ DISTORTION

PHASE OR DELAY DISTORTION

IF DELAY IS INTRODUCED IN THE CIRCUIT IS DIFFERENT FOR VARIOUS FREQS NOT IMPORTANT IN AUDIO AMP IMPORTANT IN TV SETS

PHASE DISTORTION

FREQUENCY RESPONSE OF AN AMPLIFIER

FREQUENCY RESPONSE OF AN AMPLIFIER

FREQUENCY RESPONSE OF AN AMPLIFIER

VOLTAGE GAIN VS FREQ.

FREQUENCY RESPONSE OF AN AMPLIFIER

FREQUENCY RESPONSE OF AN AMPLIFIER

FREQUENCY RESPONSE OF AN AMPLIFIER

FREQUENCY RESPONSE OF AN AMPLIFIER

FREQUENCY RESPONSE OF AN AMPLIFIER

3DB CONCEPT

Step Response of an Amplifier

Freq response is used to check fidelity. another tech. is by applying step input to an amplifier & check for the fidelity of an amp. Advantages of applying step input are (1) Easily commercially available (2) Small distortions are perceptible clearly

Step Response of an Amplifier

Output of freq response of amp. & step response is almost same. Edge distortion of step voltage is related to high freq response

Step Response of an Amplifier

Distortion of flat portion is related to closely related with low freq response .

Rise Time

Rise time
Output voltage vo=V(1-e-t/RC)

Rise time
Applying KVL to circuit: vo=R.I + 1 C I dt taking laplace on both sides V(s)= R I(s)+ 1 s C I (s) = {RC s + 1 } Cs * I(s) I(s)= V C (1+ R C s ) Output equ. Vo= 1 c I dt

Rise time
Taking laplace on both sides vo = 1 c s *I(s) vo(s) = 1 c s [V c / 1 + RCs] vo(s) = V s(1+ RCs) =V RC (s+1 RC) s = V *(1 s - 1 s+1 RC) taking inverse laplace vo=V(1-e-t/RC)

Rise time
Rise time is difference between two time intervals ie. t1 :- time required to reach one tenth of it final value output = 0.1RC t2:- time required to reach nine tenth of it final value output = 2.3RC Rise time tr=t2-t1=2.2RC

Passband of cascaded stage

Considering n stage non interacting stages having 3dB upper freq. of fH, fH, fH.. Let fH(n)is complete upper 3dB freq cascade amplifier If all stages are considerded to be identical ie. fH= fH= fH= fH 1/1+(fH(n) / fH1 )2.. 1/1+(fH(n) / fHn )2 =1/ 2

Passband of cascaded stage

fH(n) can be calculated from [ 1/1+(fH(n) / fH)2]n= 1/ 2 or fH(n) / fH = 21/n -1 Similarly for lower 3 dB for n non interacting stages fL(n) / fL = 1/21/n -1

Passband of cascaded stage

For example: for n=2 given fH =10 Khz Upper 3 db freq fH(n) / fH = 21/n -1 fH(n) / fH = .64 or 6.4 Khz

for n =3 given fH =10 Khz Upper 3 db freq fH(n) / fH = 21/n -1 fH(n) / fH = 0.51 or 5.1 Khz

Passband of cascaded stage

For example: for n=2 for n =3 given fL =10 hz given fL =10 hz Lower 3 db freq Lower 3 db freq fL(n) / fL = 1/21/n -1 fL(n) / fL = 10/.64 fL(n) / fL = 10/.51 or 15.62 hz or 19.6 hz

RC COUPLED AMP.

RC COUPLED AMP.
Coupling cap.(Cb1 & Cb2) act as blocking cap to keep dc component out . Resistors R1 R2 & Re provide desired bias By pass cap Ce prevent loss of amp. Due to feed back. Value of Bypass cap Ce is chosen large so as to act as short circuit across Re

Low frequency response of RC coupled stage

Effect of bypass cap is considered in next section For present we assume that these cap are arbitrarily large & act as short circuit We are showing intermediate stage

Low frequency response of RC coupled stage

Low frequency response of RC coupled stage

Replacing amp by its norton equvalant Rb=R1| | R2 Ry=Rc Ri= input resistance of next stage Low freq equ model is obtained by neglegting all shut cap (bypass cap ) & junction cap.

Low frequency response of RC coupled stage

Low frequency response of RC coupled stage

Let Ro= Ro | | Ry Ri =Ri | |Rb Replacing Norton equ by Thevenin equ. We get a high pass circuit

Effect of bypass Cap on low freq response

Effect of emitter bypass cap on low freq response

Effect of emitter bypass cap on low freq response

Effect of emitter bypass cap on low freq response

High freq model of transistor

High freq model of transistor

High freq model of transistor

High freq model of transistor

High freq model of transistor

Multistage CE amp.

Multistage CE amp.

Multistage CE amp.

Unit -3 Oscillators
Sinusoidal oscillator Barkhausen criteria General form of oscillator R-C phase shift oscillator Wein bridge oscillator Crystal oscillator

Oscillator
It is a device that generates repetitive wave form of fixed amp & freq without any external input signal Oscillator converts dc energy into ac energy at very high freq. This device covers the frequency range from a few Hz to many GHz It does not create energy, but merely acts as an energy converter

Difference between oscillator & amplifier

Amp takes energy from dc power source & converts it into ac source at desired freq Different parameters (freq , magnitude ) of ac power generated at output are controlled by the ac signal voltage applied at input of amplifier. Generally we speak of an oscillator as generating a sinusoidal signal, But it does not create energy, merely acts as an energy converter Function of an oscillator is reverse of that of a rectifier and, therefore, sometimes called inverter.

Difference between oscillator & amplifier

Amplifier

Oscillator

Difference between alternator & oscillator

Alternator is a mechanical device that have rotating parts, converts mechanical energy into ac energy and that cannot produce ac energy of high frequency not exceeding 1000 Hz An oscillator is a non-rotating electronic device that converts dc energy into ac energy of frequency ranging from a few Hz to many GHz.

Advantages over alternators

i) Portable and cheap in cost. (ii) An oscillator is a non-rotating device. Consequently, there is no wear and tear and hence longer life. (iii) Frequency of oscillation may be conveniently varied. (iv) Voltage or currents of any frequency (20 Hz to 100 MHz) adjustable over a wide range can be generated. (v) Frequency once set remains constant for a considerable period of time. (vi) Operation of an oscillator is silent, as there is no moving part in it. (vii) High operation efficiencydue to absence of moving part, there is no wastage of energy owing to friction.

Classification

Output waveform

Frequency range

Components, or circuit configuration

Output waveform :If the output waveform is sinusoidal, it is called harmonic oscillator otherwise it is called relaxation oscillator, which include square, triangular and saw tooth waveforms.

Freq range
Type of oscillator Audio Freq oscillator(AF) Radio freq (RF) High freq (HF) Very high freq VHF Microwave oscillator Freq range 20 Hz 20 KHz 20 KHz 30 MHz 1.5 - 30 MHz 30-300 MHz Beyond 3 GHz

Circuit components used & basic principle involved

Feedback oscillator Negative resistance oscillator:- an osc. in which negative resistance is produced by amplifying device or by other means so as to neutralize positive resistance of osc circuit is called negative resistance oscillator

Negative resistance oscillator

I/V char of gunn diode

Harmonic oscillator vs relaxation oscillator

Energy always flow in one direction i.e.from active to passive components Freq of oscillation is determined by feedback path Energy is exchanged between active & passive oscillator Freq of oscillation is determined by time constants ie charging & discharging time constants.

Operation of oscillator

Feedback circuit Vo=A Vin

Operation of oscillator

Vf = A Vin

Operation of oscillator

Oscillation die out when A less than one Oscillation build up when A is greater than one

Operation of oscillator

Oscillation constant when A equals one

Condition of sustained oscillation

The loop gain of circuit must be equal to unity Phase shift must be around zero These two conditions for sustained oscillation are called barkhausen

criteria

Essentials of a transistor oscillator

1) 2) 3) 3 element of oscillator Oscillatory circuit Amplifier Feedback network

Oscillatory circuit

Oscillatory circuit
The capacitor stores energy in its electric field.Whenever there is voltage across its plates The inductor stores energy in its magnetic field whenever current flows through it.

OSCILLATORY CIRCUIT
Oscillators employ both active and passive components. The active components provide energy conversion mechanism. Typical active devices are transistor, FET etc. Capacitors used in oscillators circuits should be of high quality. Because of low losses and excellent stability, silver mica or ceramic capacitors are generally preferred. FREQ OF OSCILLATION f=1/2 LC hz