Abstract: An oscillator circuit. A gain stage element is coupled between both terminals of the crystal. The gain stage element provides a transconductance for oscillation according to a current provided by a current source, and outputs a periodic signal through an output terminal. A bias element is coupled between an input terminal and the output terminal of the gain stage element to bias the gain stage element. A first capacitor is coupled to the input terminal of the gain stage element. A second capacitor is coupled to the output terminal of the gain stage element. A controller detects the periodic signal, and adjusts the current when the periodic signal is obtained.