Patent ID: 7005936
Filing Date: 2006-02-28
Classification: H03C

Abstract:
1. A direct frequency modulation apparatus comprising: a voltage-controlled oscillator which comprises a first voltage-variable capacitive circuit that is so constituted as to change a capacitance value by a first voltage applied to a first control terminal, and a second voltage-variable capacitive circuit that is so constituted as to change a capacitance value by a second voltage applied to a second control terminal, and oscillates at frequencies corresponding to the first and second voltages applied to the first and second control terminals; a phase-locked loop which is connected to the first control terminal, locks an oscillation frequency of the voltage-controlled oscillator to a predetermined frequency, and then holds the first voltage applied to the first control terminal; and a voltage generation circuit which is connected to the second control terminal, applies the second voltage to the second control terminal during a locking period of the phase-locked loop, and after the locking period of the phase-locked loop, generates a modulation voltage obtained by changing the second voltage by a third voltage in accordance with input data, the second voltage being applied to the second control terminal, wherein temperature dependency of the second voltage is higher than temperature dependency of a potential difference between two terminals of an element which provides a capacitance value in the second voltage-variable capacitive circuit.