Quartz Colpitts oscillator with varactor diode - is able to pull frequency over wide range and oscillates at higher harmonic

摘要

The quartz Colpitts oscillator can be pulled over a width frequency range and oscillates at a higher harmonic. An inductor (L1) is coupled in series with the quartz crystal (Q). The inductor forms a series resonant circuit with the varactor diode used for frequency pulling and with a capacitive voltage divider (C1,C2). The resonant circuit is tuned to the diode average capacitance. A damping resistor is coupled in parallel with the crystal and is larger than the series resonant resistance of the crystal at the working harmonic but still low enough to prevent the crystal from being excited at its fundamental.