colpitt oscillator its advantages and its applications

1. BY
HARSHA VARDHAN.K
COLPITT OSCILLATOR

2. Oscillator:
An oscillator is a circuit that produces
a repetitive signal from a dc
voltage.
The Colpitts oscillator is known for
using a capacitor voltage divider as
its feedback source

3. Circuit diagram:

4.  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
oscillations

5.  The output voltage is developed
across C1.
 The feedback voltage is developed
across C2

6. Frequency of oscillations

7. Conditions for Oscillation and
Startup
 Values of C1 and C2 determine the
attenuation as
or
But for Oscillation

8. 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
When Q<10, the resonant
frequency is significantly reduced

9.  To avoid this loading effect, we can use
JFET instead of BJT as it has very high
input impedance as compared to BJT.

10. Frequency Stability
 Use high stability capacitors, e.g. silver
mica, polystyrene, or teflon capacitors
and low temperature coefficient
inductors for high stable oscillators.

11. Amplitude Stability
 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
the amplitude

12. Advantages:
 Good wave purity
 Fine performer at high frequency
 Good stability at high frequency
 Wide operation range 1 to 60 MHz
Disadvantages:
 Poor isolation (Load impedance v.s. frequency)
 Hard to design

13. Applications:
 to generate the sinusodal
waveform(to generate sustained
oscillations)
 Oscillator design and simulation is
a complicated process. It is also
extremely important and crucial to
design a good and stable oscillator

14.  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