An oscillator circuit that outputs a signal which is double the input frequency. The circuit may use any NPN transistor that operates at the frequency of the input signal. Other circuit names; Frequency Doubler, Frequency Multiplier or in this case a Second Harmonic Generator.  Frequency Doubler Circuit Circuit Operation: [the links in the text are definitions] The transistor is operated in its Active region as a Class C Amplifier, neither full-on or full-off [not in saturation]. A sine-wave of some frequency is applied to the Base input, the frequency just has to be within the [frequency] operating range of the transistor. The Base of the transistor is biased by resistor R1, and AC coupled by capacitor C1. The value of Capacitor C1 does need to be selected so that it does not attenuate the incoming sine wave. The values of the tank circuit L1 and C2 are chosen for the desired frequency. Collector current flows each time the transistor is biased on. However the collector voltage is a sine-wave based on the tank circuit. The frequency of the output is F = 1 / (2 * pie * (L*C)1/2) A Tank Circuit is also called a Parallel Resonant Circuit, as in C2 is in parallel with L1. Related Manufacturing Links; |