Patent ID: 8044731

Claim:
An oscillator circuit comprising: a current source; a resonant unit; an oscillation amplification unit connected to the current source and connected in parallel to the resonant unit; a feedback resistor connected in parallel to the oscillation amplification unit; a switch unit having a first end connected to the current source side of the oscillation amplification unit; a replica circuit connected between a second end of the switch unit and a ground side of the oscillation amplification unit and having a configuration identical to a configuration of the oscillation amplification unit; and a level detecting unit that detects an input voltage of the oscillation amplification unit, and, when the detected input voltage is higher than a bias voltage level at a time of oscillation by an amount equal to or greater than a predetermined amount, or when the detected input voltage is lower than a bias voltage level at the time of the oscillation by an amount equal to or greater than a predetermined amount, outputs to the switch unit a control signal used to allow a current from the current sources to bypass through the replica circuit, to prevent a voltage level of a connection point of the current source and the oscillation amplification unit from exceeding a breakdown voltage of the oscillation amplification unit.