Method and apparatus for eliminating dead zone in phase locked loops using binary quantized phase detectors
View Patent ↗A method and apparatus for eliminating dead zone in a phase locked loop with binary quantized detectors are described. Dead zone can be eliminated by changing the threshold used to quantize the cross point sample. A quantized cross point sample is integrated in order to set a new threshold. The integration may be performed during data transitions to eliminate threshold drift during long sequences where no transitions occur.
1. A phase locked loop having a binary quantized phase detector, comprising:
a first means for storing a reference threshold value;
a comparator having a first input for receiving a first input signal and a second input for receiving the reference threshold value, the comparator comparing the first input signal with the reference threshold value to generate an output; and
a set threshold block, comprising:
a second means for generating a constant value for level shifting the output from the comparator to produce an output whose value is 0; and
an integrator, coupled to the second means, for locating a cross point in a data-eye diagram of a data sequence, having an input for receiving the output from the comparator and an output for generating a new threshold value;
a third means for filtering the output of the second means, having a first input for receiving the quantized output and an output coupled to the integrator; and
a fourth means for determining if two values are not equal, having a first input for receiving a first input signal, a second input for receiving a second input signal, and an output coupled to a second input of the third means.
2. The phase locked loop of claim 1 , wherein the output of the second means is coupled to the input of the integrator.
3. A method for eliminating dead zone in a binary quantized phase detector, comprising:
referencing a reference data sample to locate a center of a first eye in a data-eye diagram;
receiving a first signal for a first data sample in the first center of the first eye;
receiving a second signal for a second data sample in a wandering interval caused by a dead zone;
using the reference data sample to locate a center of a second eye in the data-eye diagram;
receiving a third signal for a third data sample in the center of the second eye;
applying a first comparison to a value of the second signal and a reference threshold value;
applying a second comparison to a value of the first signal and a first reference constant;
applying a third comparison to the value of the third signal and a second reference constant; and
applying a function to a result of the second comparison and the third comparison, determining if the two comparison results are equal.
4. The method of claim 3 , wherein the two comparison results differ.
5. The method of claim 4 , further comprising: after applying the function, integrating the output result of the first comparison.
6. The method of claim 5 , further comprising: after the integrating step, setting the second signal as the new reference data sample.
7. The method of claim 5 , further comprising: after the integrating step, setting the result of the integration as the new reference threshold value.
8. The method of claim 7 , comprising: after the reference setting steps, restarting with the new reference data sample and reference threshold value.
9. The method of claim 3 , wherein the two comparison results are equal.
10. The method of claim 9 , further comprising: after applying the function, setting the second signal as the new reference data sample.
11. The method of claim 10 , comprising: after the reference setting step, restarting with the new reference data sample.
12. The method of claim 3 , wherein the first comparison step produces an output whose average value is not 0.
13. The method of claim 12 , further comprising: after applying the first comparison, level shifting the output of the first comparison to produce an output whose average value is 0.