Voltage controlled oscillator having constant tuning bias voltage

摘要

Disclosed is a local oscillator using a dielectric coaxial resonator (27), which is availably used as a fixed local oscillator in double-spot tuners and CATV converters, and which is arranged so that an AFC voltage is applied to a variable-capacitance diode (23) from an output terminal (E) of a frequency control circuit through a first resistor (35), the variable-capacitance diode having its one end being connected to a center conductor of a dielectric coaxial resonator (27) through a capacitor (25) and its other end being AC grounded, and that a first reference potential (VA) lower than a source voltage (VCC) by a predetermined value is given to the variable-capacitance diode (23), the one end of the variable-capacitance diode (23) being connected to the source voltage (VCC) through a second resistor (22), whereby the voltage impressed across the variable-capacitance diode (23) can be kept constant regardless of a variation in the source voltage to thereby prevent the oscillation frequency from fluctuating.