Sub sampling phase locked loop (SSPLL) with wide frequency acquisition
A sub-sampler phase locked loop (SSPLL) system having a frequency locking loop (FLL) and a phase locked loop (PLL) is disclosed. The FLL is configured to detect frequency variations between a phase locked loop (PLL) output signal and a reference frequency and automatically generate a pulsed correction signal upon the detected frequency variations and apply the pulsed correction signal to a voltage controlled oscillator (VCO) control voltage. The PLL is configured to generate the PLL output signal based on the VCO control voltage.
1. A sub-sampler phase locked loop (SSPLL) system comprising:
a phase locked loop (PLL) configured to generate a PLL output signal based on a voltage controlled oscillator (VCO) control voltage, wherein the PLL comprises a sub-sampler configured to generate an alias frequency based on a difference between a frequency of the PLL output signal and a multiple N of a reference frequency;
a frequency locking loop (FLL) configured to automatically generate a pulsed correction signal based on the alias frequency and combine the pulsed correction signal with a phase difference signal to generate the VCO control voltage.
2. The system of claim 1 , wherein the PLL comprises a voltage controlled oscillator (VCO) configured to generate the PLL output signal based on the VCO control voltage.
3. The system of claim 1 , wherein the PLL is configured to apply a phase correction to the VCO control voltage.
4. The system of claim 1 , wherein the FLL comprises a polarity detector configured to determine and select a polarity for the pulsed correction signal.
5. The system of claim 4 , wherein the polarity detector comprises a counter configured to generate a plurality of count values based on the alias frequency and a digital circuit configured to determine the polarity based on the plurality of count values.
6. The system of claim 4 , wherein the polarity detector comprises a phase detector configured to determine the polarity based on I and Q phases/components.
7. The system of claim 1 , wherein the FLL comprises a coarse tuning loop configured to apply coarse frequency tuning to the pulsed correction signal.
8. The system of claim 1 , wherein the FLL comprises a frequency detector configured to detect frequency variations based on the PLL output signal and the reference frequency.
9. The system of claim 1 , wherein the FLL comprises a pulse generator configured to apply pulses to the correction signal based on rising edges of an alias frequency signal.
10. The system of claim 1 , wherein the FLL is automatically activated when there are detected frequency variations.
11. The system of claim 1 , wherein the FLL is automatically deactivated when there are no detected frequency variations.
12. The system of claim 10 , further comprising a sub-sampler configured to generate an alias frequency signal having I and Q phases/components based on the reference frequency and the output signal.
13. A method of operating a sub-sampling phase locked loop (SSPLL) system, the method comprising:
generating an alias frequency signal by determining a difference between a multiple of a reference frequency and an output signal of a phase locked loop (PLL);
determining whether there is frequency drift based on the alias frequency signal; and
automatically generating a frequency correction signal upon determining that there is frequency drift by the FLL and combining the frequency correction signal and a phase difference signal to generate a voltage controlled oscillator (VCO) control voltage.
14. The method of claim 13 , further comprising adjusting the output signal based on the frequency correction signal by a circuit.
15. The method of claim 13 , further comprising adjusting the output signal based on a phase correction signal by the circuit.
16. The method of claim 13 , further comprising adjusting a coarse frequency of the output signal based on a coarse control loop of the FLL.