An oscillator is an electronic circuit that generates an alternating current signal through feedback and amplification. The oscillator contains a feedback path where part of the output signal is fed back to the input. For oscillation to be sustained, the feedback signal must be larger than and in phase with the input signal. Common waveforms produced by oscillators include sinusoidal and square waves. Oscillators are classified by the waveform type and frequency range. Sine wave oscillators use inductors and capacitors (LC oscillators) or crystals to control frequency, while relaxation oscillators produce square waves. Oscillators are essential components in electronic devices and are used as stable frequency sources in applications like timers, calculators, and oscilloscopes.

1. ASSIGNMENT
ICE251(ELECTRONIC CIRCUITS)
SUBMITTED TO
Mohammad Arif Iftekhar
Lecturer
Department of ECE
East West University
SUBMITTED BY
Taslima Yasmin Tarin
ID: 2015-2-50-022
East West University
Submission Date: 09.08.2017

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Definition of Oscillator
An oscillator is a circuit that generates an RF output signal through feedback and amplification.
The oscillator contains a path whereby part of the output signal is fed back to the input. A circuit
containing an active device with feedback elements must have the feedback signal larger than,
and in-phase with, the input signal for the oscillator to sustain oscillation. The most common
types of waveforms produced by an oscillator are sinusoidal and square.
Oscillator Circuits
Energy needs to move back and forth from one form to another for an oscillator to work. You
can make a very simple oscillator by connecting a capacitor and an inductor together. both
capacitors and inductors store energy. A capacitor stores energy in the form of an electrostatic
field, while an inductor uses a magnetic field .if you charge up the capacitor with a battery and
then insert the inductor into the circuit, here's what will happen:
 The capacitor will start to discharge through the inductor. As it does, the inductor will
create a magnetic field.
 Once the capacitor discharges, the inductor will try to keep the current in the circuit
moving, so it will charge up the other plate of the capacitor.
 Once the inductor's field collapses, the capacitor has been recharged (but with the
opposite polarity), so it discharges again through the inductor.
This oscillation will continue until the circuit runs out of energy due to resistance in the wire. It
will oscillate at a frequency that depends on the size of the inductor and the capacitor.
History
Probably the first people to observe an effect due to an electrical oscillator were Auguste Arthur
de la Rive, who observed a hissing arc in 1846,] and David Edward Hughes, who observed the
humming telephone effect in 1878.Mathematical conditions for feedback oscillations, now called
the Barkhausen criterion, were derived by Heinrich Georg Barkhausen in 1921. In 1969 K.
Kurokawa derived necessary and sufficient conditions for oscillation in negative resistance
circuits,which form the basis of modern microwave oscillator design.
Transistor as Oscillator
Oscillator is an electronic circuit that produces a periodic, oscillating signal often a square wave
and a sine wave. It basically converts direct current from a power supply to an alternating current

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signal here we are going to put some shadow on how we use
a transistor as an oscillator, its mechanisms and types.
When we use a transistor in a circuit, it continuously produces
undamped oscillations at the output terminals of the circuit. Here we
can explain you how to use a transistor as an oscillator with the help
of circuit diagram.
Types of Oscillator
Oscillators may be classified by the type of signal they produce.
o SINE WAVE OSCILLATORS produce a sine wave output.
o RELAXATION OSCILLATORS and ASTABLE MULTIVIBRATORS produce Square
waves and rectangular pulses.
o SWEEP OSCILLATORS produce sawtooth waves.
Sine wave oscillators can also be classified by frequency, or the type of frequency control they
use. RF (radio frequency) oscillators working at frequencies above about 30 to 50kHz use LC
(inductors and capacitors) or Crystals to control their frequency. These may also be classified as
HF, VHF, and UHF oscillators, depending on their frequency.LF (low frequency) oscillators are
generally used for generating frequencies below about 30kHz and are usually RC oscillators, as
they use resistors and capacitors to control their frequency.Square wave oscillators such as
relaxation and astable oscillators may be used at any frequency from less than 1Hz up to several
GHz and are very often implemented in integrated circuit form.
Sine Wave Oscillators
These circuits ideally produce a pure sine wave output having a
constant amplitude and stable frequency. The type of circuit used
depends on number of factors, including the frequency required.
Designs based on LC resonant circuits or on crystal resonators are used
for ultrasonic and radio frequency applications, but at audio and very
low frequencies the physical size of the resonating components, L and
C would be too big to be practical. combination of R and C is used to a
control frequency.
LC oscillators
Inductors and capacitors are combined in a resonating circuit that produces a very good shape of
sine wave and has quite good frequency stability. That is, the frequency does not alter very much

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for changes in the D.C. supply voltage or in ambient temperature, but it
is relatively simple, by using variable inductors or capacitors, to make a
variable frequency (tuneable) oscillator
RC (or CR) oscillators
At low frequencies such as audio the values of L and C needed to
produce a resonating circuit would be too large and bulky to be
practical.therefore resistors and capacitors are used in RC filter type
combinations to generate sine waves at these frequencies, however it
is more difficult to produce a pure sine wave shape using R and C.
These low frequency sine wave oscillators are used in many audio
applications and different designs are used having either a fixed or
variable frequency.
Crystal oscillators
At radio frequencies and higher, whenever a fixed frequency with very high degree of frequency
stability is needed, the component that determines the frequency of
oscillation is usually a quartz crystal, which when subjected to an
alternating voltage, and as well as being used to generate very accurate
frequency carrier waves in radio transmitters, they also form the basis of
the very accurate timing elements in clocks, watches, and computer
systems
Relaxation oscillators
These oscillators work on a different principle to sine wave oscillators.
They produce a square wave or pulsed output and generally use two
amplifiers, and a frequency control network that simply produces a timing
delay between two actions. An alternative name for this type of oscillator

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is an "astable multivibrator.Relaxation oscillators can be built using several different designs and
can work at many different frequencies.
Sweep oscillators
A sweep waveform is another name for a saw-tooth wave. This has a linearly changing (e.g
increasing) voltage for almost the whole of one cycle followed by a
fast return to the wave’s original value. This wave shape is useful for
changing (sweeping) the frequency of a voltage-controlled oscillator,
which is an oscillator that can have its frequency varied over a set
range by having a variable ‘sweep’ voltage applied to its control
input. At a given point the capacitor is rapidly discharged to return the signal voltage to its
original value.
Application
o Oscillators are a common element of almost all electronic circuits. They are used in various
applications, and their use makes it possible for circuits and subsystems to perform numerous
useful functions.
o In oscillator circuits, oscillation usually builds up from zero when power is first applied
under linear circuit operation.
o The oscillator’s amplitude is kept from building up by limiting the amplifier saturation and
various non-linear effects.
o Oscillator design and simulation is a complicated process. It is also extremely important and
crucial to design a good and stable oscillator.
o Oscillators are used as stable frequency sources in a variety of electronic applications.
o Oscillator circuits are used in computer peripherals, counters, timers, calculators, phase-
locked loops, digital multi-metres, oscilloscopes, and numerous other applications.
o Oscillators are important in many different types of electronic equipment.A quartz
watch uses a quartz oscillator to keep track of what time it is.
References
http://electronics.howstuffworks.com/oscillator2.htm
https://www.slideshare.net/soudipsahelilove/oscillators-in-various-types
http://www.learnabout-electronics.org/Oscillators/osc10.php
http://www.learnabout-electronics.org/Oscillators/osc10.php

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Index
Content Page no
Definition of Oscillator
1
OscillatorCircuits
1
History
1
Transistoras Oscillator
1
Types of Oscillator
2
Application
4
References
4

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