VOLTAGE CONTROLLED OSCILLATOR

摘要

PROBLEM TO BE SOLVED: To improve the linearity of the voltage controlled oscillator by applying a control voltage between a terminal of a voltage variable capacitive element and a terminal of a constant voltage source and by decreasing a voltage across the voltage variable capacitive element more than the control voltage to obtain a large capacitance change in the voltage variable capacitive element. SOLUTION: The level of the anode of the voltage variable capacitive diode 4 is increased through the provision of the constant voltage source E and a control voltage VX is applied to a point between the voltage variable capacitive diode 4 and the constant voltage source E. Then the control voltage VX can be cancelled by the constant voltage E and a voltage VY across the voltage variable capacitive diode 4 is smaller than the control voltage VX (VY=VX-E). Thus, the capacitance characteristic of the voltage variable capacitive diode 4 with respect to the control voltage VX shows a curve resulting from shifting the substantial characteristic toward a higher voltage by the constant voltage E. According to the method of this voltage application, a reference voltage for a compensation voltage to set an oscillated frequency at room temperature can be set to a voltage where the linearity in the voltage capacitance characteristic of the voltage variable capacitive diode 4 is high, resulting that a large capacitance change with respect to the input control voltage can be obtained.