The the inductor starts discharging and capacitors gets charged again. This transfer of energy back and forth between capacitors and inductor is the basis of oscillation. Voltage across C2 is phase opposite to that of the voltage across the C1 and it is the voltage across C2 that is fed back to the transistor.
The feedback signal at the base base of transistor appears in the amplified form across the collector and emitter of the transistor. The energy lost in the tank circuit is compensated by the transistor and the oscillations are sustained. That means the input and output are in phase and it is a necessary condition of positive feedback for maintaining sustained oscillations. The frequency of oscillations of the Colpitts oscillator can be determined using the equation below.
Where L is the inductance of the inductor in the tank circuit and C is the effective capacitance of the capacitors in the tank circuit. By using ganged variable capacitors in place of C1 and C2, the Colpitts oscillator can be made variable.
Main advantage of Colpitts oscillator over Hartley oscillator is the improved performance in the high frequency region. This is because the capacitors provide a low reactance path for the high frequency signals and thus the output signals in the high frequency domain will be more sinusoidal. Due to the excellent performance in the high frequency region, the Colpitts oscillator can be even used in microwave applications. The circuit diagram of a Colpitts oscillator using opamp is shown in the figure above.
The opamp is arranged in the inverting mode where R1 is the input resistor and Rf is the feedback resistor. The gain of the opamp based oscillator can be individually set using the components Rf and R1 and it is a great advantage.
Other components such as the tank circuit elements, coupling capacitors etc have no significant effect in the gain of an opamp based Colpitts oscillator. In transistor based versions, the gain is dependent on almost all components especially the tank circuit and it is difficult to have a prediction.
The working principle and theory of operation of the opamp based Colpitts oscillator is similar to that of the transistorized version. The equation for frequency is also the same. Clap oscillator is just a modification of Colpitts oscillator. Accept Read More. Close Privacy Overview This website uses cookies to improve your experience while you navigate through the website. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website.
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