Colpitts Oscillator is an electronic oscillator which can produce sinusoidal signal with frequency up to 300MHz signal. There are many electronic oscillator and among them Colpitts oscillator is popular one. It is possible to generate sine wave signal using microcontrollers with filtering also but the signal frequency will be limited. An example of this was shown earlier in the tutorial One MHz sine wave with ATmega32A.Here Colpitts oscillator is designed and experimented on a breadboard.
Shown below is picture of designed Colpitts oscillator on a breadboard for purpose of experimentation.
In the above picture, the oscillator is on the smaller breadboard. The other breadboard contains frequency counter and LCD interfaces. The Colpitts oscillator circuit diagram is shown below.
The Colpitts oscillator design consist of LC tank with two capacitors and one inductor and a gain amplifier. Here we have used 2N3904 general purpose NPN transistor with bias for gain amplification of the oscillator unit. The biasing technique used in this Colpitts oscillator design is voltage divider biasing method. This gives stable DC bias circuit. The LC tank is made up of two 220pF capacitors and one 22uH inductor. We can calculate the resonant frequency using the Colpitts oscillator calculator. Using the online calculator the resonant frequency is 3.24MHz.
The Colpitts oscillator formula is as follows.
\[f_{r}=\frac{1}{2 \pi \sqrt{LC}}\]
where,
\[C=\frac{C_{1}C_{2}}{C_{1}+C_{2}}\]
The Colpitts oscillator circuit diagram shown above can also be simulated in Proteus. This was shown in Colpitts oscillator simulation in Proteus blog post.
One can experiment with this Colpitts oscillator circuit by replacing the capacitor and inductor components with different capacitance or inductance. By changing the capacitor and inductor value the resonant frequency will change. The aforementioned online oscillator calculator can also be used to find component value for desired frequency.
The following video demonstrates the working of Colpitts oscillator designed on breadboard.
Another variant of Colpitts oscillator shown in Practical Colpitts Oscillator on Breadboard.
