Simulation can be helpful for learning how electronics circuit works. Here Colpitts oscillator is simulated in proteus to learn how it works. Colpitts osccillator is one of popular oscillator which can be used for generate high frequency sinusoidal wave. An oscillator has two main network component- one is the gain network and the other is feedback network. In case of colpitts oscillator, the gain network is constructed with transistor amplifier while the feedback network is constructed with inductor(L) and capacitor(C). The gain network of the oscillator can be built using BJT transistor or FET transistor. In LC oscillator, two capacitors are used in the LC tank and the center between these two capacitor is connected to the emitter which is grounded.

Below is simulation circuit of Colpitts oscillator which shows how the voltage varies and how the current flows in the circuit.

In this example simulation the output sinusoidal signal has frequency of 22.51 KHz. The two capacitors C1 and C2 are 0.1uF each and inductor L2 is 1mH. This two capacitor and the inductor forms the LC tank. In this LC circuit charges flows between the capacitor and inductor continuously and forms a resonant tank.

The formula for calculating the **resonant frequency** is as follows.

\[f_{r} = \frac{1}{2 \pi \sqrt{LC}}\]

where,

\[C = \frac{C_1 C_2}{C_1+C_2}\]

Here C1 and C2 are 0.1uF and the total equivalent capacitance C is 0.05uF and L is 1mH. Using the above formula the resonant frequency is 22.51 KHz.

You can use the Colpitts oscillator online calculator to calculate the resonant frequency.

The graph of the output sinusoidal signal from the oscillator is shown below.

From the graph we can see that the amplitude is 1V or the peak to peak amplitude is 2V.

The Fourier transform shows us the frequency obtained from the above circuit.

From the graph above we can see that the frequency reported is 21.9KHz.

The following video demonstrates the simulation of Colpitts oscillator in Proteus.

This oscillator can be build and tested on breadboard which is illustrated in Colpitts Oscillator Design and Experiment on Breadboard. Another variant of colpitts oscillator is illustrated in Practical Colpitts Oscillator on Breadboard.