Patent ID: 7327201

Claim:
A semiconductor integrated circuit device, comprising: a voltage controlled oscillation circuit; a maximum value detection circuit having an N-type MOSFET to detect a first value corresponding to a maximum value of an oscillation output signal of the voltage controlled oscillation circuit; a minimum value detection circuit to detect a second value corresponding to a minimum value of the oscillation output signal of the voltage controlled oscillation circuit; a first reference voltage generation circuit to generate a first predetermined voltage, the first reference voltage generation circuit being arranged to receive the first value and to output a difference between the first value and the first predetermined voltage; a bias current control circuit to regulate a bias current of the voltage controlled oscillation circuit by a control signal, the bias current control circuit being connected in series to the voltage controlled oscillation circuit; and a differential amplifier to output a feedback signal to the bias current control circuit so that the difference between the maximum value and the minimum value of the oscillation output signal may be equal to the threshold voltage of the N-type MOSFET, wherein: the voltage controlled oscillation circuit comprises a LC resonant circuit and an insulated gate field effect transistor to perform positive feedback: and the first predetermined voltage is a value corresponding to a threshold voltage of the insulated gate field effect transistor of the voltage controlled oscillation circuit.