Patent ID: 7279998
Filing Date: 2007-10-09
Classification: H03B

Abstract:
1. A voltage-controlled oscillator comprising: an amplifier, which includes an inverter and a feedback resistor; a piezoelectric, vibrator which is connected to input and output terminals of the amplifier; a variable capacitive element, which includes a variable capacitor and first and second DC cut capacitors of which one end is respectively connected to both terminals of the piezoelectric vibrator and which serve as load capacitors between the terminals of the piezoelectric vibrator, wherein the variable capacitor includes: first and second MOS transistors, in which a drain terminal is connected to the other end of the first and second DC cut capacitors, source and backgate terminals are shorted to each other, and a gate terminal is shorted; first and second high-frequency elimination resistors in which one end thereof is connected to each of a source-backgate terminal of the first and second MOS transistors; and third and fourth high-frequency elimination resistors in which one end thereof is respectively connected to each of the drain terminals of the first and second MOS transistors and the other end is connected to each other, and an oscillation frequency is controlled by a first control signal which is formed by a static capacitance generated between the drain and gate terminals of the first MOS transistor and a static capacitance generated between the drain and gate terminals of the second MOS transistor and is input to the gate terminals connected to the first and second MOS transistors when an oscillation voltage is applied to the drain terminals of the first and second MOS transistors, and a second control signal which is input to each drain terminals of the first and second MOS transistors through the third and fourth high-frequency elimination resistors, respectively, and is input to the source-backgate terminals of the first and second MOS transistors through the first and second high-frequency elimination resistors, respectively.