Oscillator and self-calibration method thereof

1. An oscillator, comprising:

an oscillation unit for generating an oscillation signal;

a converting unit for converting frequency of the oscillation signal into a voltage signal;

a comparison unit for comparing the voltage signal with a first voltage corresponding to a higher frequency and a second voltage corresponding to a lower frequency, and outputting a comparison result signal;

an adjusting unit for storing a calibration value, adjusting the calibration value based on the comparison result signal and outputting a calibration signal corresponding to the adjusted calibration value;

a calibration unit for calibrating the frequency of the oscillation signal based on the calibration signal;

a control unit for generating a time window for calibration; and

a latch unit for latching the calibration signal, wherein the calibration unit is configured to determine whether there is a time window for calibration, and if yes, the calibration unit calibrates the frequency of the oscillation signal based on the calibration signal, and if not, the latch unit latches the calibration signal.

2. The oscillator according to claim 1 , wherein the comparison unit is configured to: output a first comparison result signal if the voltage signal is lower than the second voltage, output a second comparison result signal if the voltage signal is higher than the second voltage and lower than the first voltage, and output a third comparison result signal if the voltage signal is higher than the first voltage.

3. The oscillator according to claim 2 , wherein the adjusting unit is configured to: add 1 to the calibration value if the comparison unit outputs the first comparison result signal, keep the calibration value unchanged if the comparison unit outputs the second comparison result signal, and subtract 1 from the calibration value if the comparison unit outputs the third comparison result signal.

4. The oscillator according to claim 1 , wherein the control unit is a pulse counter which generates the time window for calibration by counting the number of the oscillation signal.

5. The oscillator according to claim 1 , wherein the converting unit comprises a frequency-to-digital converting unit for converting the oscillation signal into a digital signal based on the frequency of the oscillation signal, and a digital-to-analogue converting unit for converting the digital signal into the voltage signal.

6. The oscillator according to claim 1 , wherein the comparison unit comprises: a first operational amplifier, a second operational amplifier and a first inverter, where positive terminals of the first and second operational amplifiers are coupled to the voltage signal, a negative terminal of the first operational amplifier is coupled to the first voltage, a negative terminal of the second operational amplifier is coupled to the second voltage, an output terminal of the second operational amplifier is coupled to an input terminal of the first inverter, and the comparison result signal is outputted based on signals from output terminals of the first operational amplifier and the first inverter.

7. A self-calibration method for an oscillator, comprising:

generating an oscillation signal;

converting frequency of the oscillation signal into a voltage signal;

comparing the voltage signal with a first voltage corresponding to a higher frequency and a second voltage corresponding to a lower frequency, and outputting a comparison result signal;

adjusting a calibration value based on the comparison result signal and outputting a calibration signal corresponding to the adjusted calibration value;

calibrating the frequency of the oscillation signal based on the calibration signal; and

determining whether there is a time window for calibration before calibrating the frequency of the oscillation signal based on the calibration signal, if yes, calibrating the frequency of the oscillation signal based on the calibration signal, and if no, latching the calibration signal.

8. The method according to claim 7 , wherein comparing the voltage signal with the first voltage and the second voltage, and outputting the comparison result signal comprises: outputting a first comparison result signal if the voltage signal is lower than the second voltage, outputting a second comparison result signal if the voltage signal is higher than the second voltage and lower than the first voltage, and outputting a third comparison result signal if the voltage signal is higher than the first voltage.

9. The method according to claim 8 , wherein adjusting the calibration value based on the comparison result signal comprises: adding 1 to the calibration value if the first comparison result signal is outputted, keeping the calibration value unchanged if the second comparison result signal is outputted, and subtracting 1 from the calibration value if the third comparison result signal is outputted.

10. The method according to claim 7 , wherein the time window for calibration is generated by counting the number of the oscillation signal.

11. The method according to claim 7 , wherein converting frequency of the oscillation signal into a voltage signal comprises: converting the frequency of the oscillation signal into a digital signal; and converting the digital signal into the voltage signal.