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Clapp Oscillator

The Clapp oscillator has exceptional frequency stability. It is a simple variation of the Colpitts oscillator. The total tank capacitance is the series combination of C1 and C2. The effective inductance L of the tank is varied by changing the net reactance by adding and subtracting capacitive reactance via CT from inductive reactance of LT. Usually C1 and C2 are much larger than CT,

while LT and CT are series resonant at the desired frequency of operation. C1 and C2 determine the feedback ratio, and they are so large compared with CT that adjusting CT has almost no effect on feed back.The Clapp oscillator achieves its reputation for stability since stray capacitances are swamped out by C1 and C2 meaning that the frequency is almost entirely determined by LT and CT. The frequency of operation is determined by