Patent ID: 8633746

Claim:
A semiconductor device comprising: a phase detector that detects a phase difference between a feedback signal and a reference signal and generates a phase difference value indicating a value in accordance with the phase difference, the feedback signal being obtained by feeding back an output signal; an amplifier that amplifies the phase difference value at a gain determined in accordance with an external control signal; a filter that smoothes an output value of the amplifier; an oscillator that controls a frequency of the output signal in accordance with an output value of the filter; and a control circuit that generates, at a predetermined timing, the control signal to instruct the amplifier to switch the gain so to be lower than a gain at time when the device is booted up, and to instruct the filter to switch a cutoff frequency of the filter so as to be lower than a cutoff frequency at the time when the device is booted up, wherein said cutoff frequency is determined in accordance with the control signal, and wherein the timing is set to be earlier, by a predetermined time, than a timing at which data transmission is started in a radio communication terminal in which the device is mounted.