Method of fast tracking and jitter improvement in asynchronous sample rate conversion
View Patent ↗A method for fast tracking and jitter improvement in an asynchronous sample rate conversion includes a digital phase locked loop (DPLL) for an asynchronous sample rate conversion (ASRC) device. A control apparatus in the DPLL includes a gain controller that sets and maintains gains (K i , K p ) of two branches of the control apparatus at a fixed value, which enables searching of a desired value by the DPLL to determine a neighborhood of the desired value, and reduces the gains when the number of samples reaches a predetermined number. Processing units in the DPLL generate and process first and second input signals based on an input clock, an output clock, and a system clock. The second input signal is processed using two branches. Signals resulting from the two branches are re-aligned according to a changed status of the first processed input signal such that the signals resulting from the two branches are sampled in the same input clock interval.
1. A control apparatus in a digital phase locked loop (DPLL), comprising:
a counter that counts a number of samples; and
a gain controller, in communication with the counter, that sets and maintains gains of two branches of the control apparatus at a fixed value, which enables searching of a desired value by the DPLL to determine a neighborhood of the desired value, and reduces the gains when the number of samples counted in the counter reaches a predetermined number.
2. The control apparatus of claim 1 , further comprising:
a subtractor that subtracts a feedback signal from an input signal to generate a predicted input signal;
a first gain amplifier that amplifies the predicted input signal with a first gain to generate a first amplified signal;
a second gain amplifier that amplifies the predicted input signal with a second gain to generate a second amplified signal;
a first integrator, connected to the first gain amplifier, that integrates the first amplified signal to generate a first integrated signal;
a summer, connected to the first integrator and the second gain amplifier, that sums the first integrated signal and the second amplified signal to generate a summed signal; and
a second integrator, connected to the summer, that integrates the summed signal when an output clock is asserted and generates the feedback signal;
wherein the gain controller determines whether an absolute value of the predicted input signal is larger than a predetermined threshold in order to set the first gain and the second gain at the fixed value if the absolute value of the predicted input signal is larger than the predetermined threshold, to maintain the first and the second gains at the fixed value to enable the DPLL searching to located the neighborhood of the desired value, and to reduce the first and the second gains when the number of samples counted in the counter reaches the predetermined number.
3. The control apparatus of claim 1 , wherein the fixed value of the gains is 1.
4. The control apparatus of claim 1 , wherein the predetermined number of samples is at least 4 samples.
5. A digital phase locked loop (DPLL) for an asynchronous sample rate conversion (ASRC) device, comprising:
a first processing unit that generates and processes a first input signal to produce a first processed input signal based on an input clock and an output clock;
a second processing unit that generates and processes a second input signal to produce a second processed input signal based on the input clock, the output clock, and a system clock;
a first summer, connected to the first and second processing units, that sums the first and second processed input signals to produce a summed input signal; and
a closed loop control unit connected to the first summer, wherein the closed loop control unit comprises a counter that counts a number of samples and a gain controller that sets and maintains gains of two branches of the closed loop control unit at a fixed value to enable searching by the DPLL to locate a neighborhood of a desired value, and reduces the gains of the two branches when the counted number of samples reaches a predetermined number.
6. The DPLL of claim 5 , further comprising:
a subtractor, connected to the first summer, that subtracts a feedback signal from the summed input signal to generate a predicted input signal;
the closed loop control unit further comprising:
a first gain amplifier, connected to the subtractor, that amplifies the predicted input signal with a first gain to generate a first amplified signal;
a second gain amplifier, connected to the subtractor, that amplifies the predicted input signal with a second gain to generate a second amplified signal;
a first integrator, connected to the first gain amplifier, that integrates the first amplified signal to generate a first integrated signal;
a second summer, connected to the first integrator and the second gain amplifier, that sums the first integrated signal and the second amplified signal to produce a summed amplified signal;
wherein the gain controller determines whether an absolute value of the predicted input signal is larger than a predetermined threshold, sets the first and second gains at the fixed value if it is determined that the absolute value of the predicted input signal is larger than the predetermined threshold, maintains the first and second gains at the fixed value to enable the DPLL searching to locate the neighborhood of the desired value, and reduces the first and the second gains when the number of samples counted in the counter reaches the predetermined number; and
a second integrator, connected to the second summer, that integrates the summed amplified signal when the output clock is asserted to generate the feedback signal.
7. The DPLL of claim 5 , wherein the second input signal is processed in two branches of the second processing unit, and signals resulting from the two branches are re-aligned according to a changed status of the first processed input signal before producing the second processed input signal such that the signals resulting from the two branches are sampled in the same input clock interval.
8. The DPLL of claim 7 , wherein:
the first processing unit comprises:
a first latch that latches the first input signal based on the input clock when the output clock is asserted;
the second processing unit comprises:
a second latch that latches the second input signal based on the input clock and the system clock when the output clock is asserted;
a third latch that latches the second input signal when an output enabled (OEN) signal is asserted or the input and an output clock rising edges occur in a master clock interval;
a fourth latch that latches an output signal of the third latch when the output clock is asserted;
means for re-aligning an output signal of the second latch with an output signal of the fourth latch according to the changed status of an output signal of the first latch, such that the output signal of the second latch and the output signal of the fourth latch are sampled in the same input clock interval; and
means for performing a division with respect to the re-aligned output signals from the second latch and the fourth latch and outputting the second processed input signal.
9. The DPLL of claim 8 , wherein the second processing unit further comprises a fifth latch that generates the OEN signal, wherein the OEN signal is asserted when the output clock is asserted and no rising edge of the input clock occurs at the master clock interval.
10. The DPLL of claim 5 , wherein the fixed value of the gains is 1.
11. The DPLL of claim 5 , wherein the predetermined number of samples is at least 4 samples.
12. A digital phase locked loop (DPLL) for an asynchronous sample rate conversion (ASRC) device, comprising:
a first processing unit that generates and processes a first input signal to produce a first processed input signal based on an input clock and an output clock;
a second processing unit that generates and processes a second input signal to produce a second processed input signal based on the input clock, the output clock, and a system clock, wherein the second processing unit includes two branches for processing the second input signal, and signals resulting from the two branches are re-aligned according to a changed status of the first processed input signal before producing the second processed input signal such that the signals resulting from the two branches are sampled in the same input clock interval;
a first summer, connected to the first and second processing units, that sums the first and second processed input signals to produce a summed input signal; and
a closed loop control unit having an input including the difference between the summed input signal and a feedback signal generated by the closed loop control unit.
13. The DPLL of claim 12 , wherein the closed loop control unit comprises:
a counter that counts a number of samples; and
a gain controller that sets and maintains gains of the two branches of the second processing unit at a fixed value to enable the DPLL searching to located a neighborhood of a desired value, and reduces the gains when the number of samples counted in the counter reaches a predetermined number.
14. The DPLL of claim 13 , further comprising:
a subtractor, connected to the first summer, that subtracts a feedback signal from the summed input signal to generate a predicted input signal;
the closed loop control unit further comprising:
a first gain amplifier, connected to the subtractor, that amplifies the predicted input signal with a first gain to generate a first amplified signal;
a second gain amplifier, connected to the subtractor, that amplifies the predicted input signal with a second gain to generate a second amplified signal;
a first integrator, connected to the first gain amplifier, that integrates the first amplified signal to generate a first integrated signal;
a second summer, connected to the first integrator and the second gain amplifier, that sums the first integrated signal and the second amplified signal to produce a summed amplified signal;
wherein the gain controller determines whether an absolute value of the predicted input signal is larger than a predetermined threshold, sets the first and second gains at the fixed value if it is determined that the absolute value of the predicted input signal is larger than the predetermined threshold, maintains the first and second gains at the fixed value to enable the DPLL searching to locate the neighborhood of the desired value, and reduces the first and the second gains when the number of samples counted in the counter reaches the predetermined number; and
a second integrator, connected to the second summer, that integrates the summed amplified signal when the output clock is asserted to generate the feedback signal.
15. The DPLL of claim 13 , wherein the fixed value of the gains is 1.
16. The DPLL of claim 13 , wherein the predetermined number of samples is at least 4 samples.
17. The DPLL of claim 12 , wherein:
the first processing unit comprises:
a first latch that latches the first input signal based on the input clock when the output clock is asserted;
the second processing unit comprises:
a second latch that latches the second input signal based on the input clock and the system clock when the output clock is asserted;
a third latch that latches the second input signal when an output enabled (OEN) signal is asserted or the input and an output clock rising edges occur in a master clock interval;
a fourth latch that latches an output signal of the third latch when the output clock is asserted;
means for re-aligning an output signal of the second latch with an output signal of the fourth latch according to the changed status of an output signal of the first latch, such that the output signal of the second latch and the output signal of the fourth latch are sampled in the same input clock interval; and
means for performing a division with respect to the re-aligned output signals from the second latch and the fourth latch and outputting the second processed input signal.
18. The DPLL of claim 17 , wherein the second processing unit further comprises a fifth latch that generates the OEN signal, wherein the OEN signal is asserted when the output clock is asserted if no rising edge of the input clock occurs at the master clock interval.