# Electronic_Circuits

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```					                        Electronic Circuits (EI 234)
EC UNIT 1
1) What is an amplifier?
A circuit that increases the amplitude of the given input signal in an amplier.

2) What is biasing ?
The process of giving proper supply voltages and resistances for obtaining the Q
point is called biasing.

3) What are the factors to be considered for selecting the operating point?
While selecting the operating point the following factors are to be considered
 Dc and AC loads at the output of the stages
 The maximum transistor rating.
 The available power supply.
 The peak signal execution to be handled by the amplifier.
 The tolerance distortion.

4) FET is a unipolar device – justify
FET operation depends only on the flow of majority carriers holes for P-channel
FETs and electrons for N-channel FET. Therefore they are called as uinpolar devices.

5) What are the advantages of Fixed bias?
Small number of components required
If the supply voltage is large compared to VBE of the transistor than the
base current becomes largely independent of the voltage VBE.

6) What are the disadvantages of Fixed bias?
Since  is a large quantity, this is a very poor bias stable circuit.
This is not used for biasing the base.
7) Define the h – parameter

8) What is ‘Darlington connection’?
Connection of two transistors whose over all current gain is the product of
individual current gain.
It has very high input impedance and produces very large output currents.
It is used with voltage regulations and power amplifier.

9) What is thermal runaway?
During abnormal conditions of the transistor as the temperature increases the
output of collector current and collector leakage current also increases which lead to
further increases in temperature. This high temperature leads to the breakdown of the
transistor circuit called as Thermal Runaway.

10) Define the parameters of FET.
 drain resistance (rd) – it is the reciprocal of the slope of the drain
characteristic in saturation region.
 Transconductance (gm) – it is the change in drain current for the given change
in gate to source voltage.
 Amplification factor () – it is defined as the product of rd and gm

11) What are the advantages of FET input stage?
Has a high input impedance.
There is no minority carrier, as a result it can switch off faster.
Long life.
Ruggedness
Low noise.
High power gain.
Better thermal stability.

12) List the biasing circuit of FET.
 gate bias
 self bias
 voltage divider bias
 source bias
 current source bias.

13) What do you understand by dc operating point?
When a transistor is biased certain current and voltage conditions are established
for the transistor. These conditions are known as dc operating point.
It must be stable for the proper operating of the transistor.
It shifts with changes in transistor parameters such as , Ico, and VBE.

Adv - * harmonic are absent
 efficiency improved.
 Less distortion
 More output.

Dis adv- * need bulky and expensive transformer.
 occurance of cross over distortion.

15) What is power amplifier?
The stage which develops and feeds sufficient power to the load handling the
large signals is called.

16) Explain the types of power amplifier?
   class A amplifier
   class B amplifier
   class C amplifier
   class AB amplifier

It is a multistage amplifier having two or more single stage common emitter
connections.
Out put of first stage is given to the input of the next stage.

18) What is bias stablisation?
The resistive biasing circuits uses negative feedback to stabilize the operating
point. This negative feed back reduces the gain of the amplifier. The compensation
technique are used to stabilize the operating point.

19) what is stability factor?
It is defined as the ratio of a small change in the collector current to the
corresponding small change in the collector base leakage current, keeping  and VBE
constant.

20) What is the advantages of self bias?
 Ic cab be reduced.
 Provide stable position of operating point.
 One dc supply is necessary.

21) what are the distortions of the amplifier?
 amplitude or harmonic distortion
 frequency distortion
 phase distortion

22) what are the applications of FET.
 used in chopper amplifier.
 used in flip flop
 used in constant current source
 used in attenuator.

23) what is the significance of common emitter amplifier?
 voltage gain and current gain high
 power gain high
 most versatile
 better power transfer.
EC UNIT 11

24) Define CMRR.
The ability of the differential amplifier ,and it is the ratio of the difference mode
gain Ad to the Common mode gain Ac.
25) What is tuned amplifier?
Tuned circuit select and amplifies a particular frequency or a narrow band of
frequencies. Higher the Q of the tank circuit narrow the bandwidth . it is used extensively

26) How the tuned circuits are classified?
Tuned amplifiers

Small signal                large signal

Single tuned       double tuned          staggered tuned

Capacitor coupled        inductance coupled

27) Mention the important characteristics of operational amplifier
 input bias current
 input offset current
 input offset voltage

28) what are the important characteristics of ideal amplifier?
 good stability
 high gain.

29) List the application of operational amplifier
 it is used as a voltage regulator
 used to detect the required signal from the unwanted signal.

30) What are the advantages of differential amplifier?
 it offers high input resistance
 it exhibits stability
 high immunity to noise and interference signal
 doesn’t requires any capacitors

31) applications of differential amplifier?
 used in operational amplifier
   used in electronic instruments
   used in RF and IF amplifier.
   Used in Mixer
   Used in limiters and modulators and detectors

32) Draw the block diagram of copper stabilized dc amplifier.

chopped             amplified               consatnt
Dc i/p   CHOPPER        dc      AC           dc       PEAK          dc
AMPLIFIER             DETECTOR

33) what is meant by common mode of an differential amplifier?
Same input voltage Vin is applied to both ends. This voltage is called a common
mode signal. If the differential amplifier is perfectly symmetrical there is no a.c output
voltage. Since equal voltage Vin drive both inputs simultaneously there is almost no
current through the wire between the emitter.

34) what are the various modes of the differential amplifier?
 differential input with differential output
 differential input with sinle output
 single input with differential output
 single input with sinle output

35) compare the various differential mode voltage gain.

INPUT                   OUTPUT                 A                      V OUT
Differential            differential           Rc / re                A ( V1-V2)
Differential            sinle                  Rc / 2re               A ( V1-V2)
Sinle                   differential           Rc / re                A V1 or –AV2
Sinle                   sinle                  Rc / 2re               A V1 or –AV2

36) What are the properties of an ideal amplifier?
 it should have an infinite input impedance Zi = 
 it should have a zero output impedance Z0= 0
 it should have an infinite open loop gain Avol = -
 band width is infinite = 

37) what is input offset current of an op- amp?
It is the difference between the two input bias current .
Ios = Ib1 – Ib2
38) what is input offset voltage of an op- amp?
It is the difference between the two input voltage .
Vos = V1 – V2

39) what is input bias current of an op- amp?
It the ratio of the input current applied to the differential amplifier.
Ib = ( Ib1 + Ib2 ) / 2

40) what is slew rate of the differential amplifier?
If the differential input is applied to an op- amp and this input changes suddenly
from zero voltage level to some constant voltage , the output voltage changes rapidly but
not instantaneously at a rate is called slew rate.

EC UNIT 3
41) what are the important feedback configuration?
 voltage series feedback
 voltage shunt feedback
 current series feedback
 current shunt feedback

42) state the Barkhausen criteria.
The essential condition for maintaining oscillators are
 magnitude of loop gain must be zero.
 The total phase shift around the closed loop is zero or 360 degree.

43) What are the adventages of negative feed back amplifier?
 frequency distortion and phase distortion is less
 nonlinear distortion is less
 band width is high
 noises also reduced

44) what are the various types of oscillator?
According to the types of waveform
 sinusoidal oscillator
 relaxation oscillator
According to the fundamental mechanism involved
 negative resistance oscillator
 feed back oscillator
According to the frequency
 audio frequency oscillator
 ultra high frequency oscillator
   micro wave frequency oscillator
According to the type of circuit
   LC tuned oscillator
   RC tuned oscillator

45) Mention the types of feedback amplifier.
 positive feedback
 negative feedback

46) what is positive feedback?
If the feed back voltage or current is applied in phase with the input signal so as to
increase the input signal , it is called positive feedback.
Af = A / ( 1-AB)
Where A= amplifier gain
B=feedback ratio.

47) what is negative feedback?
If the feed back voltage or current is applied out of phase with the input signal so
as to reduce the input signal , it is called negative feedback.
Af = A / ( 1+AB)
Where A= amplifier gain
B=feedback ratio.

48) what are the advantages of negative feedback?
 high fidelity
 high gain
 decreased distortion
 reduced noise
 increased bandwidth

49) what is the principle of an oscillator?
Oscillator can be considered to be an amplifier that provides its own input signal
derived from its output. A number of different waveform can be obtained from different
kind of oscillator.

50) what is the difference between oscillator and amplifier?
An amplifier the frequency , waveform and magnitude of the output voltage are
governed by the input signal and in an oscillator the frequency the waveform and
magnitude of the output voltage depend only upon the device used for the amplifier and
associated circuit.

51) what is hartley oscillator?
hartley oscillator circuit is the simple available oscillator circuit. The amplified
energy in the output circuit is feedback to the input circuit by mutual inductive coupling.
Frequency of oscillation = 1/ 2 sqrt ( Leq *C)
52) what is colpitts oscillator?
colpitts oscillator differ from the Hartley that the feedback voltage is obtained
from the capacitors connected in series in the tank circuit than the inductor.

53) what is principle of RC phase shift oscillator?
With the proper selection of R and C , the phase of the voltage at the resistor will
be advanced by 60 degree. Since each of the three RC advances the phase by 60 degree ,
this network produces precisely a phase shift of 180 degree.

54) What is clapps oscillator?
It the modified form of colpitts oscillator. In this capacitor is connected in series
with the inductor of the tank circuit.

55) What are the applications of the wien bridge oscillator?
 used in audio oscillator
 used in sine wave generator

56) What are the advantages of the wien bridge oscillator?
 good frequency stability
 good sine wave output
 overall gain is high
 high stabilized output

57) what is the disadvantages of using LC oscillator?
The frequency stability of usual LC circuit used in radio frequency oscillator is
poor. For certain applications particularly in radio transmitters frequency of
Oscillation should be stable.

58) what are the applications of crystal oscillators?
 receiving telephone
 telegraph signals

59) what are the materials used for piezo electric crystal?
 Quartz
 Tourmaline
 Roachelle salt

60) what is piezo electric effect?
A material is said to posses piezo electric effect , if a mechanical force applied on
opposite faces produces electric charge between the perpendicular faces or vice versa.

61) What is relaxation oscillator?
Oscillator circuit is designed to give an sinusoidal, square and rectangle and saw
tooth and pulse waveform is called relaxation oscillator .
62) what are the various types of relaxation oscillator?
 saw tooth generator
 blocking oscillator
 multivibrators

EC unit 4
63) How high pass RC circuit be used as a differentiator?
In some RC circuits, capacitor C stores some of the charges on each cycle ; ie it
integrate or adds the charges on each pulse until it become charged to some definite
value. RC circuits used to intgrate pulses are called RC integrator circuit or low pass
filter.

64) How low pass RC circuit be used as a integrator?
In some RC circuits, the wave form of the voltage across the capacitor is
substantially the same as that of the applied voltage, whereas the voltage across the
resistor has a new waveform which is depend upon how fast the applied voltage changes.
Because of their ablity to differentiate between rates of change of the applied voltage,
these circuits are called differentiator.

65) List the various squarewave generator circuit?
 astable multivibrator.
 monostable multivibrator.
 bistable multivibrator.
 Schmitt trigger

66) List the various sawtooth generator circuit?
 exponential charging
 miller circuit.
 Bootstrap circuit.
 Phantastron circuit.
 Inductor circuit

67) What is Clamper?
It can be explained as introducing a dc level into an ac signal or shifting the ac
signal to a predetermined dc level other than zero. These also called as dc restorers.

68) What is Clipper?
Clipping or limiter circuits are designed to reduce the positive or negative
extremities of an input waveform to a predetermined value which may zero.

69) How the frequency of oscillation varied in an astable multivibrator?
1/T = 1/ 1.38RC , so by varying the value of R or C , the frequency of oscilltaion
can be varied.

70) Give any applications of schmitt trigger?
 amplitude comparator
 as a flip – flop
 as a squaring circuit.

71) What is multivibrator?
The multivibrator is a relaxation oscillator used to produce non- sinusoidal
waveforms such as square, rectangle, sawtooth. It is basically s two stage resistance
coupled amplifier with the output of each stage coupled regeratively to the other.

72) What is dutycycle?
It is the ratio of pulse width ot the pulse period is known as duty cycle.
Duty cycle = on time / ( on + off time )

73) What is meant by Hysteresis?
It can be obsreved that output changes the state , it remains there in definitely
until the input voltage crocess any of the thershold levels. So when the output changes the
state from the low to high at UTP, it remains there till input crosses LTP and vice versa.
This characteristics of schmitt trigger is called hysteresis.

74) Discuss the application of an astable multivibrator.
 used as a square wave generator, voltage to frequency converters.
 used as a clock for binary logic signals.
 used in digital voltmeter and switched mode power supply.

75) Discuss the application of an monostable multivibrator.
 used to produce rectangular waveform
 used as a gating circuit.
 used as to introduce time delays as gate width is adjustable.
 used as to generate uniform width pulses from a variable width input pulse
train

76) Discuss the application of an bistable multivibrator.
 used for the performance of many digital operations.
 used as memory element in shift registers, counters etc.
 used in processing of pulse type waveforms.
 Can be used asa frequency divider.

77) what is pulse circuits?
The word pulse circuits refer to the active and passive circuits intended to handle,
generate shape and store pulse signals. The different pulse signals and circuits to generate
some of them are discussed .
78) what are the different types of clipper?
* positive clipper - series and shunt.
* negative clipper - series and shunt.
 biased clipper
 combined clipper.

79) what are the different types of clipper?
 positive clamper
 negative clamper

80) define stable state of the bistable multivibrator.
It signifies a circuit which can exist indefinitely in either of two stages. It can be
made to make an abrupt transistion to the other by an external excitation called triggering
signal but after transistion, it remains in the new state.

81) what are the triggering methods?
 symmetrical trigggering
 un symmetrical trigggering
 positive edge trigggering
 negative edge trigggering
 input edge trigggering
 output edge trigggering

82) what is the schmitt trigger?
Special form of bistable multivibrator but has the following difference:
 there is a feedback through the communicating capacitors in only one
 The reverse feedback is through R2

83) what does the triggering rate depend on monostable multivibrator?
 duration T of a quasi stable state.
 The recovery phenomenon.

EC UNIT 5
84) What is ‘peak inverse voltage ‘? What is its value for the HWR?
The peak inverse voltage is the peak voltage across the diode in the reverse
direction ie when the diode reverse biased . HWR when the diode is reverse biased and
hence the maximum value of voltage that can exist across the diode is nothing but Em.

85) Draw the block diagram of DC power supply
ac i/p       Transforme              Rectifie         Filter        Regulator     dc o/p
r                       r

86) what is rectifier?
Rectifier is a device which convert a.c voltage to pulsating d.c voltage , using one
or more pn junction.

87) What are the important characteristics of the rectifier ?
 wave form of the load current
 regulation of the output voltage
 rectifier efficiency
 peak value of the current in the rectifier circuit.
 PIV
 Ripple factor

88) What is ripple factor?
The output of the rectifier is of pulsating DC type. The amount of AC content in
the output can be mathematically expressed by a factor called ripple factor.
Its value is 1.211 for the HWR
Its value is 0.48 for the FWR

89) What is rectifier efficiency?
It is defined as the ratio of output DC power to the input AC power
= Pdc / Pac

90) What is TUF?
The factor which indicates how much is the utilization of the transformer in the
circuit is called Transformer utilization factor.
Its value is 0.287 for the HWR
Its value is 0.812 for the FWR

91) What is the disadvantages of the HWR?
 ripple factor is high. The output contain lots of varying component
 rectification efficiency is 40%
 low TUF, transformer is not fully satisfied.
 Cost high.

92) What is the advantages of the bridge rectifier?
 the current of the transformer flows for the entire cycle, so cost low, more
power output, small size of the transformer.
 AC voltage can be directly applied to the transformer.
 Circuit is suitable for the large power is required .
 Used for high voltage application.

93) What is the need of filter circuit?
An AC input is applied to the filter circuit , there will be DC and ripple voltage
present , which is the input to the filter. Ideally the output of the filter should be pure DC.
Practically the filter circuit will try to minimize the ripple at the output, as far as possible.

94) What are the basic types of the filter circuit?
 capacitor input filter
 chock input filter

95) Name the type of circuit used to regulate the supply.
 linear electronic voltage regulator
 switch mode power supply.

96) Name the types of linear voltage regulator
 Transistor Series regulator
 Transistor Shunt regulator
 Zener regulator

97) What are the disadvantages of linear regulator?
 input step down transformer is bulky and expensive.
 Due to low frequency large value of filter capacitor is required.
 Efficiency is low
 More power dissipation.

98) what are the components of SMPS?
 voltage source
 switching transistor
 pulse generator
 filter

99) what are the types of SMPS?
 step down switching regulator
 step up switching regulator
 inverting switching regulator

100) What is bleeder resistor?
Resistance R connected across the output of the filter is known as a bleeder
resistor and its main purpose is to place a minimum load across the rectifier during the
time. Prevent dangerous shocks.

101) compare capacitor input filter and chock input filter

capacitor input filter                           chock input filter
DC voltage is higher                             DC voltage is comparatively lower
Voltage regulation is poor                       Voltage regulation is much better
Ripple is less and increases with increasing     Ripple is independent of load current