Colpitts Oscillator with resonant frequency of 812KHz is designed on a breadboard. In the previous Colpitts Oscillator Design and Experiment on Breadboard blog post, a Colpitts oscillator was designed with the feedback from the LC tank into the base. The oscillator was designed to resonant at frequency of 3.24MHz. Here the oscillator is designed with feedback from LC circuit into the emitter of the BJT amplifier.
The following picture shows a practical Colpitts oscillator implemented on a breadboard.
In the above Colpitts oscillator design, inductor value is 100uH, the two capacitor value is 2.2nF for the upper and 330pF for the lower capacitor. The amplifier transistor used was 2n3904. The resistor value used for biasing was 33KOhm(R1), 10KOhm(R2) and 560Ohm(Re). The supply voltage used was 5V.
Below picture shows the measured resonant frequency of the oscillator.
In this Colpitts oscillator design experiment the resonant frequency obtained on the breadboard was 812KHz. This is close to the theoretical value of resonant frequency which is 804KHz. The resonant frequency of the Colpitt oscillator can be calculated using the following equation.
\[f_{r}=\frac{1}{2 \pi \sqrt{LC}}\]
where,
\[C=\frac{C_{1}C_{2}}{C_{1}+C_{2}}\]
Here in this Colpitts oscillator design, L = 100uH, C1 = 2.2nF and C2 = 330pF. The Colpitts Oscillator Calculator can be used to calculate the resonant frequency.
The Colpitts oscillator circuit diagram for this practical design on breadboard is shown below.
