Low power mode control module and method for crystal oscillator, and circuit using the same

A low-power mode control module for a crystal oscillator, comprising:

• a stable output detector, configured to detect whether an oscillation output signal of the crystal oscillator is outputted stably;
• an amplitude detector, electrically connected to the stable output detector, and configured to compare an amplitude control signal with at least one of an oscillation input signal and the oscillation output signal of the crystal oscillator when the oscillation output signal is outputted stably, to determine whether to adjust the amplitude control signal;
• a programmable reference voltage generator, electrically connected to the amplitude detector, and configured to generate an upper-bound reference voltage and a lower-bound reference voltage associated with the amplitude control signal when the amplitude detector determines not to adjust the amplitude control signal;
• and
• a low-power mode controller, electrically connected to the programmable reference voltage generator, and configured to generate a low-power mode control output signal associated with a crystal oscillator enabling signal for enabling the crystal oscillator according to whether the oscillation output signal exceeds a reference voltage range of the upper reference voltage and the lower reference voltage.