1

Describe the function
of oscillator or tank circuit?


Oscillator
 The function of the oscillator
circuit is to generate sinusoidal or non – sinusoidal oscillation of desired
frequency.

2

Is the oscillator an
energy converter circuit? True or false?


 Yes, The oscillator is an energy
converter circuit. It receives DC energy at the input and converts it to AC
energy of desired frequency.
 The output frequency depends upon the constant
of the oscillator circuit.

3

Which type of
feedback circuit is used in the oscillator?


Positive feedback

4

Describe the effect
of the value of inductance and capacitance on the oscillator frequency.


Effect of inductance and
capacitance
 The frequency of oscillation of the
tank circuit is inversely proportional to the inductance and capacitance.
 Lower value of inductance and capacitance, higher the oscillation frequency.
 The period of oscillation will be
large if the higher value of capacitance is used.
 The time requires for the
complete one cycle of oscillation depends upon value of inductance.
 Higher
value of inductance means more time requires for completing one cycle.

5

Explain the following
terms : Damped oscillation and Un 
damped oscillation


Damped oscillation
 It is an electrical oscillation
whose magnitude goes on decreasing with time is called as damped oscillation.
Undamped oscillations
 It is an electrical oscillation
whose magnitude remains constant with respect to time is called as undamped
oscillation.

6

Why the amplitude of
damped oscillations decreases with time?


The amplitude of damped
oscillations decreases with respected to time because some energy is lost and
energy losses take place during each oscillation.

7

How the damped
oscillations are converted into undamped oscillations?


 The oscillator circuit produces
damped oscillation.
 If some energy is supplied at correct time intervals to
meet the energy losses by means of external electronics circuit, the damped oscillations
convert into undamped oscillations.

8

What is Barkhausen
criterion?


Barkhausen Criterion
The following relation is called as
Barkhausen criterion:
m_{v}A_{v }= 1
Where m_{v }= Feedback
fraction ( 0 < m_{v } < 1 )
A_{v }= Voltage gain of
the amplifier without feedback
The above relation must be
satisfied in order to produce continuously Un  damped oscillations.

9

Describe the
significance of the Barkhausen Criterion.


Significance of Barkhausen Criterion
 The voltage gain of the positive
feedback amplifier is infinite if the product of
m_{v }A_{v} = 1
A_{vf }=
1 / ( 1 – m_{v}A_{v })
 However it is not possible to
achieve infinite voltage gain. It means that definite value of output voltage
is achieved even if input signal is zero.
 Therefore once the oscillator
circuit gets input it will generate oscillations at the output even if the
input reduced to zero.

10

What are the
essential conditions to produce oscillations?


The following are the essential
conditions for producing oscillations
 Tank circuit
 Amplifier circuit and
 Feedback circuit

11

Describe the name of
different types of oscillators.


Classification of oscillators
 Colpitt oscillator
 Hartley oscillator
 Wien bridge oscillator
 Phase shift oscillator
 Crystal oscillator

12

Describe the
disadvantages of Hartley and Colpitt oscillators.


Disadvantages of Hartley and
Colpitt oscillators
 The Hartley and Colpitt oscillators
cannot be used for very low frequency because They become bulky and expensive
due higher rating of inductance and capacitance.
 They suffer from distorted
waveforms and frequency in stability.

13

Describe the working Principle
of RC phase shift oscillator.


Principle of RC Phase shift
oscillator
 The phase shift 180^{0} in
the RC phase shift oscillator is produced by series combination of the RC
circuit and other phase shift of 180^{0} is produced by the
transistor circuit.
 ( The RC phase shift oscillator consists of series
combination of R and C, instead of conventional inductance and capacitance. The value of R is varied such that voltage
across R is lead by C by angle 60. There are three section of RC series
circuit produces total phase difference of 180 degree. )

14

Describe the
advantages of RC phase shift oscillator.


Advantages of RC phase shift
oscillators
 It produces good stability.
 It can be used for very low
frequency.
 Inductor or capacitor is not
required therefore it is less bulky than Hartley and Colpitt oscillator.

15

State the
applications of Piezo electric crystal.


Applications of Piezo electric crystal
 The Piezo electric crystal is
useful where frequency is nearly constant with low tolerance.
 The broadcasting stations have frequencies
which are very close to each other.
 The frequency of the crystal oscillator
remains constant with respect to temperature changes.
 Therefore the Piezo
electric crystal is more reliable than RC / LC oscillators.

16

In which type of
oscillator both positive and negative feedback circuits are used?


Wien bridge oscillator

17

Describe the
disadvantages of Wien bridge oscillator.


Disadvantages of Wien bridge
oscillator
 It is not used for high frequency.
 It requires large number of
components as well as two transistors.

18

What are the
limitations of the LC and RC oscillators?


Limitations of LC and RC
oscillators
 The frequency dependent parameter L
and C changes with variation of frequency and temperature.
 The operating
frequency changes if any component of the feedback network is changed.

19

Which materials have
property of Piezo electric crystal?


The Quartz, Rochelle salt and
tourmaline have property of Piezo electric crystal.

20

Describe the Principle
of operation of Piezo electric crystal.


Principle of Piezo  electric Crystal
 When alternating voltage is applied
to Piezo electric crystal it will vibrate at the frequency of the applied
voltage and vice versa ( It means that when crystal is compressed or placed
under mechanical strain, it produce alternating voltage.)

21

Which parameters
greatly affect the frequency of the crystal?


 The
frequency of the crystal inversely proportional to thickness of the crystal.
 Lesser the thickness of the crystal, greater the frequency and vice versa.

22

Describe the
advantages and disadvantages of crystal oscillators.


Advantages
 High frequency stability
 High quality factor as compared to
LC tank circuit
Disadvantages
 Only used for low power
applications
 The frequency of oscillation cannot
be changed

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