Voltage controlled oscillator having an oscillation frequency variation minimized in comparison with a power supply voltage variation

摘要

A voltage controlled oscillator comprises an oscillator connected between a power supply line and a low potential power supply voltage and having an output node for outputting an oscillation signal having a frequency changed in accordance with a voltage difference between the power supply line and the low potential power supply voltage. An nMOS transistor is connected at its drain to a high low potential power supply voltage and at its source connected to the power supply line of the oscillator. A gate electrode of the nMOS transistor is connected to receive a control signal so that a source voltage of the nMOS transistor is determined by a voltage of the control signal and is supplied to the power supply line of the oscillator, with the result that the oscillation frequency of the oscillator is controlled by the voltage of the control signal. A level converter is connected between the high potential power supply voltage and the low potential power supply voltage and has an input node connected to the output node of the oscillator and an output terminal for outputting an output signal. The level converter converts an amplitude of the oscillation signal to an amplitude of the output signal corresponding to a voltage difference between the high and low potential power supply voltages. Thus, a voltage controlled oscillator having an excellent insensibility to a power supply voltage variation can be realized.