The Colpitts oscillator is a type of oscillator that uses an LC circuit in the feedback loop. The feedback network is made up of two capacitors (C1 and C2) tapped on an inductor L. The output voltage is developed across C1, while the feedback voltage is developed across C2. For oscillations to occur, the loop gain must be greater than unity. Colpitts oscillators have good wave purity and stability at high frequencies, making them well-suited for applications like communication circuits and frequency sources. However, they can be difficult to design and have poor isolation between load impedance and oscillation frequency.

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