The Colpitts oscillator is a type of
oscillator that uses an LC circuit in
the feed-back loop.
The feedback network is made up
of a pair of tapped capacitors (C1
and C2) and an inductor L to
produce a feedback necessary for
The output voltage is developed
The feedback voltage is developed
Conditions for Oscillation and
Values of C1 and C2 determine the
But for Oscillation
For the oscillator to be self starting,
Loading Effect on FeedbackCircuit
Input impedance of the amplifier acts as a load on the
resonant feedback circuit and reduces the quality
factor of the circuit
When Q<10, the resonant
frequency is significantly reduced
To avoid this loading effect, we can use
JFET instead of BJT as it has very high
input impedance as compared to BJT.
Use high stability capacitors, e.g. silver
mica, polystyrene, or teflon capacitors
and low temperature coefficient
inductors for high stable oscillators.
In order to start the oscillation, the loop
gain is usually slightly greater than unity.
LC oscillators in general do not require
amplitude stabilization circuits because
of the selectivity of the LC circuits.
In RC oscillators, some non-linear
devices, e.g. NTC/PTC resistors, FET or
zener diodes can be used to stabilized
Good wave purity
Fine performer at high frequency
Good stability at high frequency
Wide operation range 1 to 60 MHz
Poor isolation (Load impedance v.s. frequency)
Hard to design
to generate the sinusodal
waveform(to generate sustained
Oscillator design and simulation is
a complicated process. It is also
extremely important and crucial to
design a good and stable oscillator
Oscillators are commonly used in
communication circuits. All the
communication circuits for different
modulation techniques—AM, FM, PM—the use
of an oscillator is must.
Oscillators are used as stable frequency sources
in a variety of electronic applications.
Oscillator circuits are used in computer
peripherals, counters, timers, calculators,
phase-locked loops, digital multi-metres,
oscilloscopes, and numerous other applications