Oscillators are generally used to generate frequency signals in the form of sine waves or square waves for computers, receivers, transmitters, audio equipment, and other such devices. There are multiple types of oscillators such as crystal oscillators, Armstrong oscillators, Hartley oscillators, Colpitts oscillators, and others. This article will explain the construction, working, advantages, and applications of Colpitts oscillators.
What is the Colpitts Oscillator
The Colpitts oscillator is a type of inductor-capacitor (LC) oscillator that is very similar to the Hartley oscillator, except for the fact that it uses a capacitive voltage divider instead of an inductive voltage divider. Given below is the tank circuit of the Colpitts oscillator, in which an inductor is connected in parallel with two capacitors that are tapped from the center to generate a sinusoidal output waveform.
Assembly of Colpitts Oscillator
The main portion of Colpitts Oscillator is its tank circuit. It has two capacitors and one inductor in it. An operational amplifier or a transistor is used as an amplifier in the Colpitts oscillator circuit. The emitter of the transistor is attached or connected between the capacitors C1 and C2 where they have a common terminal.
There are two resistors, R1 and R2, that are used for stabilizing DC bias voltage to keep the transistor operating at the rated voltage. Capacitor C3 is used for smoothing of Direct Current (DC) and it is linked to the base of the transistor. A radio frequency choke is also connected in parallel with R1 to offer high reactance at oscillation frequency. Whereas capacitor C4 is used as a bypass capacitor that eliminates high-frequency noise from the output signal.
Working of Colpitts Oscillator
When power is supplied to the circuit, C1 and C2 are charged first. While the capacitors discharge, the inductor also gets charged as the electrostatic energy stored in capacitors transforms into magnetic flux. When the inductor discharges, capacitors get charged again. These cycles of charging and discharging continue to provide frequency oscillations.
These frequency oscillations are transferred to the base-emitter (BE) junction of the NPN transistor. They are then amplified when they reach the collector output. Therefore, the tank circuit acts as an energy reservoir of the Colpitts oscillator.
Oscillation Frequency of Colpitts Oscillator
The oscillation frequency of the Colpitts Oscillator can be calculated using the given formula:
Here, Ceff is the effective capacitance of C1 and C2 that is calculated through the given formula
The effective capacitance is actually the equivalent capacitance of C1 and C2 connected in parallel.
Advantages of Colpitts Oscillator
The Colpitts oscillator has the following benefits:
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- The Colpitts oscillator is very useful to generate high-frequency sinusoidal.
- It has a highly stable frequency.
- Its frequency can also be adjusted by varying the values of capacitors or using variable capacitors.
- Change in frequency does not impact the amplitude of the output signal.
Disadvantages of Colpitts Oscillator
The Colpitts oscillator possesses the following disadvantages:
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- The inductor and radio frequency choke can make the circuit bulky.
- Its design is intricate.
How is the Colpitts Oscillator Different from the Hartley Oscillator?
The Hartley Oscillator and the Colpitts Oscillator differ in the following ways.
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- The Hartley Oscillator has two inductors and one capacitor in the tank circuit, whereas the Colpitts Oscillator has one inductor and two capacitors in its tank circuit.
- The Hartley Oscillator has a less stable frequency because of two inductors used that are prone to noise interference.
- The design of the Hartley Oscillator is simpler than that of the Colpitts oscillator.
Real-Life Applications of Colpitts Oscillator
The Colpitts oscillators are used in sine wave generators that generate high-frequency sine waves. They are also used in radio receivers and radio frequency oscillators. They can be used in frequency modulation as well.
Conclusion
The Colpitts oscillator is a very convenient form of oscillator that can be used to generate pure sinusoidal of high frequency. The tank circuit of the Colpitts oscillator produces frequency oscillations that are amplified and filtered by a transistor and a capacitor, respectively. They are used in different frequency devices.
