SINUSOIDAL AND NONSINUSOIDAL OSCILLATORS

Objective Questions

Short notes

Objective questions (Answers are given below)

An electronic oscillator is
(a) just like an alternator
(b) nothing but an amplifier
(c) an amplifier with feedback
(d) a converter of ac to dc energy.
The frequency of oscillation of an elementary
LC oscillatory circuit depends on
(a) coil resistance
(b) coil inductance
(c) capacitance
(d) both (b) and (c).
For sustaining oscillations in an oscillator
(a) feedback factor should be unity
(b) phase shift should be 0°
(c) feedback should be negative
(d) both (a) and (b).
If Barkhausen criterion is not fulfilled by an oscillator
circuit, it will
(a) stop oscillating
(b) produce damped waves continuously
(c) become an amplifier
(d) produce high-frequency whistles.
In a transistor Hartley oscillator
(a) inductive feedback is used
(b) untapped coil is used
(c) entire coil is in the output circuit
(d) no capacitor is used
A Hartley oscillator is used for generating
(a) very low frequency oscillation
(b) radio-frequency oscillation
(c) microwave oscillation
(d) audio-frequency oscillation

A Colpitts oscillator uses
(a) tapped coil
(b) inductive feedback
(c) tapped capacitance
(d) no tuned LC circuit
In RC phase-shift oscillator circuits.
(a) there is no need for feedback
(b) feedback factor is less than unity
(c) pure sine wave output is possible
(d) transistor parameters determine osci- llation
frequency.
Wien bridge oscillator is most often used whenever
(a) wide range of high purity sine waves is to
be generated
(b) high feedback ratio is needed
(c) square output waves are required
(d) extremely high resonant frequencies are
required.
The RC network
shown in
Fig 65.40 can
provide a maximum
theoretical
phase shift
of
(a) 90° (b) 180° (c) 270° (d) 360°
(UPSC Engineering Services 2002)
A CE amplifier can be converted into oscillator
by
(a) providing adequate positive feedback
(b) phase shifting the output by 180° and feeding
this phase-shifted output to the input.
(c) using only a series tuned circuit as a load
on the amplifier
(d) using a negative resistance device as a load
on the amplifier
(e) all of the above
(UPSC Engineering Service, 2002)
The primary advantage of a crystal oscillator is
that
(a) it can oscillate at any frequency
(b) it gives a high output voltage
(c) its frequency of oscillation remains almost
constant
(d) it operates on a very low dc supply voltage.
Non-sinusoidal waveforms
(a) are departures from sine waveform
(b) have low mark-to-space ratio
(c) are much easier to generate
(d) are unfit for digital operation.
A relaxation oscillator is one which
(a) has two stable states
(b) relaxes indefinitely
(c) produces non-sinusoidal output
(d) oscillates continuously.
A square pulse has a mark-to-space ratio of
(a) 1 : 1 (b) 1 : 2 (c) 2 : 1 (d) 1 : 4.
Apart from a dc power source, the essential requirements
of a sawtooth generator are
(a) a resistor (b) a capacitor
(c) a switching device (d) all of the above.
Which of the following statement is WRONG ?
In a multivibrator
(a) output is available continuously
(b) feedback between two stages is 100%
(c) positive feedback is employed
(d) when one transistor is ON, the other is OFF.
An MMV circuit
(a) has no stable state
(b) gives two output pulses for one input trig
ger pulse
(c) returns to its stand-by states automatically
(d) has no energy-storage element.
A BMV circuit
(a) has two unstable states
(b) has one energy-storage element
(c) switches between its two states automatically
(d) is not an oscillator.
The digital circuit using two inverters shown in
Fig. 65.42 will act as
(a) a bistable multi-vibrator
(b) an astable multi-vibrator
(c) a monostable multi-vibrator
(d) an oscillator