Fast start-up crystal oscillator and fast start-up method thereof

A crystal oscillator (XO), comprising:

• a XO core circuit, configured to generate a XO signal having a XO frequency;
• a frequency synthesizer, comprising:
• a voltage control oscillator (VCO), configured to generate a VCO clock having a VCO frequency;
• and
• a divider, coupled to the VCO, configured to generate a divided clock having a divided frequency, wherein the VCO frequency is divided by a divisor of the divider to obtain the divided frequency;
• and
• an interfacing circuit, coupled between the XO core circuit and the frequency synthesizer, configured to transmit the divided clock to the XO core circuit, and generate a reference clock having the XO frequency according to the XO signal, wherein the VCO frequency is calibrated according to the reference clock;
• wherein the frequency synthesizer further comprises:
• a controller, coupled to the VCO and the divider, configured to control the VCO frequency according to a counting result from the divider, and the counting result indicates whether a count of cycles of the VCO clock within a counting period reaches a target value or not.

A start-up method of a crystal oscillator (XO), comprising:

• utilizing a voltage control oscillator (VCO) to generate a VCO clock having a VCO frequency;
• utilizing a divider to generate a divided clock having a divided frequency, wherein the VCO frequency is divided by a divisor of the divider to obtain the divided frequency;
• and
• utilizing an interfacing circuit to transmit the divided clock to a XO core circuit;
• utilizing the XO core circuit to generate a XO signal having a XO frequency with aid of the divided clock;
• and
• utilizing the interfacing circuit to generate a reference clock having the XO frequency according to the XO signal, wherein the VCO frequency is calibrated according to the reference clock;
• wherein utilizing the interfacing circuit to transmit the divided clock to the XO core circuit comprises utilizing a driver of the interfacing circuit to inject energy into the XO signal by transmitting the divided clock to the XO core circuit;
• and utilizing the interfacing circuit to generate the reference clock having the XO frequency according to the XO signal comprises utilizing a rectangular wave generator of the interfacing circuit to generate the reference clock by converting the XO signal into a rectangular wave, wherein the rectangular wave represents the reference clock.

A start-up method of a crystal oscillator (XO), comprising:

• utilizing a voltage control oscillator (VCO) to generate a VCO clock having a VCO frequency;
• utilizing a divider to generate a divided clock having a divided frequency, wherein the VCO frequency is divided by a divisor of the divider to obtain the divided frequency;
• and
• utilizing an interfacing circuit to transmit the divided clock to a XO core circuit;
• utilizing the XO core circuit to generate a XO signal having a XO frequency with aid of the divided clock;
• utilizing the interfacing circuit to generate a reference clock having the XO frequency according to the XO signal, wherein the VCO frequency is calibrated according to the reference clock;
• and
• controlling the VCO frequency according to a counting result from the divider, wherein the counting result indicates whether a count of cycles of the VCO clock within a counting period reaches a target value or not.