Reducing waiting time jitter
First Claim
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1. A method for reducing waiting time jitter in a synchronizer, the method comprising:
- generating a sub-bit phase comparison of read and write clocks used to pass unsynchronized data through an elastic store;
selecting a threshold level based on the generated sub-bit phase comparison;
comparing read and write pointers for the read and write clocks with the threshold level; and
generating a frame of synchronized data from the data in the elastic store with a length that is dependent on the result of comparing the read and write pointers with the threshold level.
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Abstract
Circuits and methods are described which reduce waiting time jitter at a synchronizer/multiplexer by using a “sub-bit” comparison of a clock associated with an unsynchronized data stream and a clock associated with a synchronized data stream to generate a threshold level for use in determining when to stuff bits into the synchronized data stream. The term “sub-bit” means that the phase difference, as measured by, for example, the location of pointers associated with the two clocks, is precise to a fraction of a bit.
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Citations
43 Claims
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1. A method for reducing waiting time jitter in a synchronizer, the method comprising:
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generating a sub-bit phase comparison of read and write clocks used to pass unsynchronized data through an elastic store;
selecting a threshold level based on the generated sub-bit phase comparison;
comparing read and write pointers for the read and write clocks with the threshold level; and
generating a frame of synchronized data from the data in the elastic store with a length that is dependent on the result of comparing the read and write pointers with the threshold level. - View Dependent Claims (2, 3, 4, 5)
filtering the sub-bit phase comparison with a low pass filter; and
selecting between at least two threshold levels.
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5. The method of claim 4, wherein selecting between at least two threshold levels comprises selecting between −
- K, 0 and K unit intervals, wherein a magnitude of the value K is a constant.
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6. A method for reducing waiting time jitter in a synchronizer, the method comprising:
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measuring a phase difference of read and write clocks used to pass unsynchronized data through an elastic store, wherein the measured phase difference is precise to a fraction of a bit;
selecting a threshold level based on a fractional component of the measured phase difference;
comparing read and write pointers for the read and write clocks with the threshold level; and
generating a frame of synchronized data from the data in the elastic store with a length that is dependent on the result of comparing the read and write pointers with the threshold level. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14)
filtering the fractional component of the measured phase difference; and
selecting the threshold level based on the filtered fractional component of the measured phase difference;
wherein the threshold level is selected to be a positive constant if the filtered fractional component of the measured phase difference is below a first selected value;
wherein the threshold level is selected to be a negative constant if the filtered fractional component of the measured phase difference is above a second selected value;
wherein the threshold level is selected to be zero if the filtered fractional component of the measured phase difference is between the first and second selected values; and
wherein the negative constant has a magnitude equal to a magnitude of the positive constant.
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14. The method of claim 13, wherein the first selected value and the second selected value are equal.
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15. A method for reducing waiting time jitter in a synchronizer, the method comprising:
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measuring a phase difference of read and write clocks used to pass unsynchronized data through an elastic store, wherein the measured phase difference has a fractional component;
comparing read and write pointers for the read and write clocks with a threshold level;
generating a frame of synchronized data from the data in the elastic store with a length that is dependent on the result of comparing the read and write pointers with the threshold level; and
selecting the threshold level used in comparing the read and write pointers based on the fractional component of the measured phase difference. - View Dependent Claims (16, 17, 18, 19, 20, 21)
filtering the fractional component of the measured phase difference; and
selecting the threshold level based on the filtered fractional component of the measured phase difference;
wherein the threshold level is selected to be a positive constant if the filtered fractional component of the measured phase difference is below a first selected value;
wherein the threshold level is selected to be a negative constant if the filtered fractional component of the measured phase difference is above a second selected value;
wherein the threshold level is selected to be zero if the filtered fractional component of the measured phase difference is between the first and second selected values; and
wherein the negative constant has a magnitude equal to a magnitude of the positive constant.
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21. The method of claim 20, wherein the first selected value and the second selected value are equal.
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22. A method for reducing waiting time jitter in a synchronizer, the method comprising:
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generating a signal indicative of a phase difference of read and write clocks used to pass unsynchronized data through an elastic store, wherein the signal includes both a bit level component and a fractional component;
selecting a threshold level based on the fractional component of the signal;
comparing the bit level component of the signal with the threshold level; and
generating a frame of synchronized data from the data in the elastic store with a length that is dependent on the result of comparing the bit level component of the signal with the threshold level.
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23. A method for reducing waiting time jitter in a synchronizer, the method comprising:
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generating a signal indicative of a phase difference of read and write clocks used to pass unsynchronized data through an elastic store, wherein the signal includes both a bit level component and a fractional component;
filtering the fractional component of the signal;
selecting a threshold level based on the filtered fractional component of the signal, wherein the threshold level has a first level if the filtered fractional component is above a first selected value, the threshold level has a second level different from the first level if the filtered fractional component is below a second selected value, and the threshold level has a third level if the filtered fractional component is between the first selected value and the second selected value;
comparing the bit level component to the signal with the selected threshold level;
sending a short frame of synchronized data from the data in the elastic store if the bit level component of the signal exceeds the threshold level; and
sending a long frame of synchronized data from the data in the elastic store if the threshold level exceeds the bit level component of the signal. - View Dependent Claims (24, 25, 26)
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27. A method for reducing waiting time jitter in a synchronizer, the method comprising:
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generating a first phase comparison of read and write clocks used to pass an unsynchronized data stream through an elastic store;
generating a second phase comparison of a divided down write clock with a frame synchronization signal using a lead-lag counter, wherein the frame synchronization signal is associated with a synchronized data stream output from the synchronizer;
varying a threshold level based on the second phase comparison;
inserting stuff bits into a frame of synchronized data from the data in the elastic store when the first phase comparison exceeds the threshold level; and
deleting stuff bits from a frame of synchronized data from the data in the elastic store when the threshold level exceeds the first phase comparison. - View Dependent Claims (28, 29, 30, 31, 32, 33)
filtering the second phase comparison with a low pass filter; and
selecting between at least two threshold levels based on a value of the filtered second phase comparison.
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31. The method of claim 30, wherein selecting between at least two threshold levels comprises selecting between −
- K, 0 and K unit intervals, wherein a magnitude of the value K is a constant.
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32. The method of claim 31, wherein selecting between at least two threshold levels comprises selecting −
- K unit intervals when the filtered second phase comparison is above a first selected value, selecting 0 unit intervals when the filtered second phase comparison is between the first selected value and a second selected value, and selecting K unit intervals when the filtered second phase comparison is below the second selected value.
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33. The method of claim 32, wherein the first selected value and the second selected value are equal.
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34. A method for reducing waiting time jitter in a synchronizer, the method comprising:
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generating a phase comparison of read and write clocks used to pass unsynchronized data through an elastic store, wherein the phase comparison includes a bit level component and a fractional component;
varying a threshold level based on the fractional component of the phase comparison;
inserting stuff bits into a frame of synchronized data from the data in the elastic store when the bit level component of the phase comparison exceeds the threshold level; and
deleting stuff bits from a frame of synchronized data from the data in the elastic store when the threshold level exceeds the bit level component of the phase comparison. - View Dependent Claims (35, 36, 37, 38, 39)
filtering the fractional component of the phase comparison with a low pass filter; and
selecting between at least two threshold levels based on a value of the filtered fractional component of the phase comparison.
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37. The method of claim 36, wherein selecting between at least two threshold levels comprises selecting between −
- K, 0 and K unit intervals, wherein a magnitude of the value K is a constant.
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38. The method of claim 37, wherein selecting between at least two threshold levels comprises selecting −
- K unit intervals when the value of the filtered fractional component of the phase comparison is above a first selected value, selecting 0 unit intervals when the value of the filtered fractional component of the phase comparison is between the first selected value and a second selected value, and selecting K unit intervals when the value of the filtered fractional component of the phase comparison is below the second selected value.
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39. The method of claim 38, wherein the first selected value and the second selected value are equal.
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40. A method for reducing waiting time jitter in a synchronizer, the method comprising:
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generating a phase comparison of read and write clocks used to pass unsynchronized data through an elastic store, wherein the phase comparison includes a bit level component and a fractional component;
filtering the fractional component of the phase comparison;
varying a threshold level to have a first level if the filtered fractional component is above a first selected value, a second level different from the first level if the filtered fractional component is below a second selected value, and a third level if the filtered fractional component is between the first selected value and the second selected value;
inserting stuff bits into a frame of synchronized data from the data in the elastic store when the bit level component of the phase comparison exceeds the threshold level; and
deleting stuff bits from a frame of synchronized data from the data in the elastic store when the threshold level exceeds the bit level component of the phase comparison. - View Dependent Claims (41, 42, 43)
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Specification