An oscillating signal generator circuit includes an oscillator circuit, a feedback circuit, and a voltage regulator circuit. The oscillator circuit is configured to generate a first and second oscillating signal at a first and second output terminal according to a first reference voltage. The first and second oscillating signals are a differential pair of signals. The oscillator circuit includes a common mode sensing circuit coupled between the first and second output terminals. The common mode sensing circuit is configured to sense a common mode component of the first and second oscillating signals so as to generate a sense voltage. The feedback circuit, coupled to the common mode sensing circuit, is configured to generate a feedback voltage according to the sense voltage. The voltage regulator circuit is coupled to the oscillator circuit and the feedback circuit, and configured to regulate a supply voltage so as to generate the first reference voltage.