Method and apparatus for SerDes jitter tolerance improvement
View Patent ↗Apparatus and methods detect the presence of an isolated pulse in a communications signal, such as a data signal carrying data for a serializer/deserializer (SerDes). An example of an isolated pulse is a “1” pulse preceded and followed by “0” pulses, or a “0” pulse preceded and followed by a “1” pulse. These isolated pulses can exhibit a narrow pulse width, and under severe jitter conditions, may not align with a baud sample point, which can cause the isolated pulse to be missed, resulting in a data decoding error. By detecting the presence of these isolated pulses and determining the most likely baud period to which they belong, jitter tolerance can be improved for many channel conditions. This can improve jitter tolerance of a SerDes receiver for links that suffer from various sources of Deterministic Jitter (DJ) such as Duty Cycle Distortion (DCD) and Inter-Symbol Interference (ISI).
1. A method of asynchronously receiving a data signal having embedded therein data symbols, the method comprising:
oversampling and slicing the received data signal to generate multiple 1-bit raw samples per data symbol;
identifying a data sample per data symbol from the multiple raw samples; and
changing the value of one of two consecutive data samples to an opposite value when the two consecutive data samples have the same value and if there are one or more raw samples having an opposite value to that of the two consecutive data samples, wherein the one or more raw samples are interposed between the two consecutive data samples.
2. The method of claim 1 , further comprising filtering the raw samples with a majority filter, and using the filtered raw samples in determining whether there are one or more raw samples having an opposite value to that of the two consecutive data samples.
3. The method of claim 1 , wherein changing the value further comprises:
counting the one or more raw samples having the opposite value;
comparing the count to a threshold value, wherein the threshold value is at least two; and
changing the value of one of the two consecutive data samples only when the count is greater than or equal to the threshold value.
4. The method of claim 1 , wherein changing the value further comprises:
wherein the two consecutive data samples comprise a first data sample and a second data sample;
determining which of the first data sample or the second data sample is closer to the one or more raw samples having the opposite value; and
changing the value of the closer of the first data sample or the second data sample.
5. The method of claim 4 , further comprising when the first data sample and the second data sample are equidistant to the one or more data samples having the opposite value, selecting the one of the first data sample or the second data sample to change based on the value of the one or more data samples.
6. The method of claim 1 , wherein changing the value further comprises:
wherein the two consecutive data samples comprise a first data sample and a second data sample;
counting the one or more raw samples having the opposite value;
comparing the count to a threshold value, wherein the threshold value is at least two;
determining which of the first data sample or the second data sample is closer to the one or more raw samples having the opposite value; and
changing the value of one of the first data sample or the second data sample only when the count is greater than or equal to the threshold value, wherein the one that is changed is closer to the one or more raw samples having the opposite value.
7. The method of claim 6 , further comprising selecting which of the first data sample or the second data sample to change based on the value of the one or more data samples when the first data sample and the second data sample are equidistant to the one or more data samples having the opposite value.
8. The method of claim 1 , further comprising performing the method in a serializer/deserializer (SerDes).
9. The method of claim 1 , wherein changing the value is performed by firmware or software executed by a processor in real time.
10. An apparatus for asynchronously receiving a data signal having embedded therein data symbols, the apparatus comprising:
means for oversampling and slicing the received data signal to generate multiple 1-bit raw samples per data symbol;
means for identifying a data sample per data symbol from the multiple raw samples; and
means for changing a value of one of two consecutive data samples to an opposite value when two consecutive data samples have the same value and if there are one or more raw samples having an opposite value to that of the two consecutive data samples, wherein the one or more raw samples are interposed between the two consecutive data samples.
11. An apparatus for asynchronously receiving a data signal having embedded therein data symbols, the apparatus comprising:
a slicer configured to oversample and slice the received data signal to generate multiple 1-bit raw samples per data symbol;
a timing control circuit configured to identify a data sample per data symbol from the multiple raw samples; and
an isolated pulse detector configured to change a value of one of two consecutive data samples to an opposite value when two consecutive data samples have the same value and if there are one or more raw samples having an opposite value to that of the two consecutive data samples, wherein the one or more raw samples are interposed between the two consecutive data samples.
12. The apparatus of claim 11 , further comprising a majority filter, wherein the majority filter is configured to filter the raw samples, and wherein the isolated pulse detector is configured to analyze the filtered raw samples to determine whether there are one or more raw samples having an opposite value to that of the two consecutive data samples.
13. The apparatus of claim 11 , wherein the isolated pulse detector is further configured to:
count the one or more raw samples having the opposite value;
compare the count to a threshold value, wherein the threshold value is at least two; and
change the value of one of the two consecutive data samples only when the count is greater than or equal to the threshold value.
14. The apparatus of claim 11 , wherein the two consecutive data samples comprise a first data sample and a second data sample, wherein the isolated pulse detector is further configured to:
determine which of the first data sample or the second data sample is closer to the one or more raw samples having the opposite value; and
change the value of the closer of the first data sample or the second data sample.
15. The apparatus of claim 14 , wherein the isolated pulse detector is further configured to select the one of the first data sample or the second data sample to change based on the value of the one or more data samples when the first data sample and the second data sample are equidistant to the one or more data samples having the opposite value.
16. The apparatus of claim 11 , a wherein the two consecutive data samples comprise a first data sample and a second data sample, wherein the isolated pulse detector is further configured to:
count the one or more raw samples having the opposite value;
compare the count to a threshold value, wherein the threshold value is at least two;
determine which of the first data sample or the second data sample is closer to the one or more raw samples having the opposite value; and
change the value of one of the first data sample or the second data sample only when the count is greater than or equal to the threshold value, wherein the one that is changed is closer to the one or more raw samples having the opposite value.
17. The apparatus of claim 16 , wherein the isolated pulse detector is further configured to select which of the first data sample or the second data sample to change based on the value of the one or more data samples when the first data sample and the second data sample are equidistant to the one or more data samples having the opposite value.
18. The apparatus of claim 11 , wherein the apparatus is embodied in a serializer/deserializer (SerDes).