Patent ID: 7443214

Claim:
A PLL circuit comprising: a phase shifter including a transconductance amplifier (referred to as an “OTA”) and a capacitor, said phase shifter receiving an alternating current (AC) signal with a predetermined frequency as an input signal and outputting a signal obtained by shifting a phase of the input signal by a predetermined phase; a phase comparator for receiving the input signal fed to said phase shifter and an output signal from said phase shifter and outputting a signal corresponding to a phase difference between the received signals; a loop filter for receiving the output signal from said phase comparator and outputting a direct current (DC) voltage; and a differential amplifier for receiving and differentially amplifying the output voltage of said loop filter and a reference voltage; wherein an output voltage of said differential amplifier or a signal obtained by converting the output voltage to a current by a voltage-to-current converter circuit is fedback to said phase shifter as a control signal and a transconductance (gm) of the OTA constituting said phase shifter is controlled based on said control signal so as to make the phase difference given by said phase shifter become a constant value; and wherein the reference voltage is set to be less than a half of a power supply voltage.