OSCILLATOR CIRCUIT GENERATING OSCILLATION SIGNAL RESPONSIVE TO ONE OF RESONANT ELEMENT AND EXTERNAL CLOCK SIGNAL

Disclosed herein is an oscillator circuit generating an oscillation signal in response to a resonant element in a first mode and to an external clock signal in a second mode. This oscillator circuit comprises a tri-state inverter circuit and a transfer circuit between the input and output nodes of the tri-state inverter circuit, and the output node of the tri-state inverter circuit is brought into a high impedance condition when an external clock signal is used and into an active state when the resonant element is employed.