Transceiver circuit and self-calibration method

1. A transceiver circuit configured to couple an oscillation crystal, wherein the transceiver circuit comprises:

a local oscillator comprising a capacitive element, wherein the local oscillator is configured to generate a phase locked loop signal based on an oscillation frequency of the oscillation crystal and a capacitance value of the capacitive element;

a filter circuit configured to generate a filtered signal according to the phase locked loop signal;

a control circuit configured to adjust the capacitance value to be an adjusted capacitance value according to the filtered signal and the phase locked loop signal, wherein the local oscillator is further configured to generate a calibrated local oscillation signal according to the oscillation frequency and the adjusted capacitance value; and

a radio frequency signal generator circuit configured to generate a radio frequency signal according to the calibrated local oscillation signal and a baseband signal.

2. The transceiver circuit of claim 1 , wherein the filter circuit is a band-pass filter.

3. The transceiver circuit of claim 2 , wherein the band-pass filter is implemented by a transmission line.

4. The transceiver circuit of claim 1 , wherein the control circuit comprises:

a frequency mixer configured to perform a frequency mixing process on the filtered signal and the phase locked loop signal to generate a direct-current signal;

a comparator circuit configured to compare the direct-current signal with a maximum direct-current voltage to generate a comparison result; and

a driver circuit configured to adjust the capacitance value to be the adjusted capacitance value according to the comparison result.

5. The transceiver circuit of claim 4 , wherein the capacitive element is corresponding to a plurality of capacitance values, the capacitance values are corresponding to a plurality of direct-current voltages, and the maximum direct-current voltage is a maximum one among the direct-current voltages.

6. The transceiver circuit of claim 1 , wherein the local oscillator comprises:

a phase locked loop circuit configured to generate a calibrated phase locked loop signal based on the oscillation frequency and the adjusted capacitance value; and

a frequency divider configured to perform a frequency dividing process on the calibrated phase locked loop signal to generate the calibrated local oscillation signal.

7. The transceiver circuit of claim 1 , wherein the radio frequency signal generator circuit comprises:

a baseband circuit configured to generate the baseband signal;

a frequency mixer configured to perform a frequency mixing process on the calibrated local oscillation signal and the baseband signal to generate a frequency mixing signal; and

a radio frequency circuit configured to generate the radio frequency signal according to the frequency mixing signal.

8. The transceiver circuit of claim 1 , wherein the capacitive element comprises a switched capacitor array.

9. A self-calibration method, comprising:

generating, by a local oscillator, a phase locked loop signal based on an oscillation frequency of an oscillation crystal and a capacitance value of a capacitive element;

generating, by a filter circuit, a filtered signal according to the phase locked loop signal;

adjusting, by a control circuit, the capacitance value to be an adjusted capacitance value according to the filtered signal and the phase locked loop signal;

generating, by the local oscillator, a calibrated local oscillation signal according to the oscillation frequency and the adjusted capacitance value; and

generating, by a radio frequency signal generator circuit , a radio frequency signal according to the calibrated local oscillation signal and a baseband signal.

10. The self-calibration method of claim 9 , wherein the filter circuit is a band-pass filter.

11. The self-calibration method of claim 10 , wherein the band-pass filter is implemented by a transmission line.

12. The self-calibration method of claim 9 , further comprising:

performing, by a frequency mixer of the control circuit, a frequency mixing process on the filtered signal and the phase locked loop signal to generate a direct-current signal;

comparing, by a comparator circuit of the control circuit, the direct-current signal with a maximum direct-current voltage to generate a comparison result; and

adjusting, by a driver circuit of the control circuit, the capacitance value to be the adjusted capacitance value according to the comparison result.

13. The self-calibration method of claim 12 , wherein the capacitive element is corresponding to a plurality of capacitance values, the capacitance values are corresponding to a plurality of direct-current voltages, and the maximum direct-current voltage is a maximum one among the direct-current voltages.

14. The self-calibration method of claim 9 , further comprising:

generating, by a phase locked loop circuit of the local oscillator, a calibrated phase locked loop signal based on the oscillation frequency and the adjusted capacitance value; and

performing, by a frequency divider of the local oscillator, a frequency dividing process on the calibrated phase locked loop signal to generate the calibrated local oscillation signal.

15. The self-calibration method of claim 9 , further comprising:

generating, by a baseband circuit of the radio frequency signal generator circuit, the baseband signal;

performing, by a frequency mixer of the radio frequency signal generator circuit, a frequency mixing process on the calibrated local oscillation signal and the baseband signal to generate a frequency mixing signal; and

generating, by a radio frequency circuit of the radio frequency signal generator circuit, the radio frequency signal according to the frequency mixing signal.

16. The self-calibration method of claim 9 , wherein the capacitive element comprises a switched capacitor array.