Transistor Clapp Oscillator
Author: Leonard Krugman
The transistor equivalent of the Clapp oscillator is illustrated in Fig. 6-3 (A). The operating frequency is set by the series resonant circuit in the collector circuit. Feedback is taken from the voltage divider consisting of capacitors C1 and C2. The upper frequency limit depends largely on the transistor in use, and can be increased considerably by careful selection of the unit. Upper frequencies as high as 3 mc can be attained using typical junction types in this basic circuit. The numerical values shown are based on the average of a group of Raytheon CK720 transistors. If crystal control is used, the frequency stability is improved, and there is also a considerable increase in the upper frequency limit of the oscillator. One method of achieving crystal control in this circuit is to replace the collector resonant circuit by a crystal.
Fig. 6-3. (A) Transistor Clapp oscillator.