Electronics Handbook/Devices/Oscillator/Active Oscillator/Variable Frequency Oscillator or VFO/Colpitt Oscillator

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Configuration[edit | edit source]

Oscillation frequency[edit | edit source]

The ideal frequency of oscillation for the circuits in Figures 1 and 2 are given by the equation:

where the series combination of C1 and C2 creates the effective capacitance of the LC tank.

Real circuits will oscillate at a slightly lower frequency due to junction capacitances of the transistor and possibly other stray capacitances.