Method and apparatus for reducing waiting time jitter in pulse stuffing synchronized digital communications
First Claim
1. A method of synchronizing an asynchronous signal to produce a synchronized signal comprising the steps of:
- (a) performing a comparison of phases of the asynchronous signal and the synchronized signal to produce a stuff control signal and controllably stuffing the asynchronous signal with pulses at a ratio of stuffs per stuffing opportunity in dependence upon said stuff control signal; and
(b) controllably adjusting the frequency of said synchronized signal in accordance with said ratio of stuffs per stuffing opportunity.
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Abstract
A jitter/wander reduction mechanism monitors the ratio of pulse stuffing, to detect whenever the pulse stuffing ratio is proximate a prescribed undesirable ratio of stuffs per stuffing opportunity, which causes the wander to be a large number of unit intervals. A stuffing pulse accumulator-controlled frequency shift control circuit monitors the signal produced by a multiplexer (and demultiplexer for full duplex mode) control logic circuit and incrementally adjusts, as necessary, the frequency of a synchronized clock signal input to the multiplexer (and demultiplexer). The magnitude of the incremental frequency shift is sufficient to drive the synchronized clock away from the frequency associated with the undesired stuff ratio to a frequency that is sufficiently separated from the undesired value to produce a stuffing ratio other than the undesired value and reduce the jitter/wander.
25 Citations
20 Claims
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1. A method of synchronizing an asynchronous signal to produce a synchronized signal comprising the steps of:
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(a) performing a comparison of phases of the asynchronous signal and the synchronized signal to produce a stuff control signal and controllably stuffing the asynchronous signal with pulses at a ratio of stuffs per stuffing opportunity in dependence upon said stuff control signal; and (b) controllably adjusting the frequency of said synchronized signal in accordance with said ratio of stuffs per stuffing opportunity. - View Dependent Claims (2, 3, 4, 5)
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6. An apparatus for synchronizing an asynchronous digital signal to produce a synchronized digital signal comprising:
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an elastic store into which successive components of said asynchronous digital signal are written by a write clock coupled to said elastic store, and from which successive components of said synchronized digital signal are read out by a read clock coupled to said elastic store; a phase comparator to which said write and read clocks are coupled and which is operative to produce an output representative of the phase difference between said write and read clocks; an output multiplexer which is coupled to receive said synchronized digital signal and stuff pulses, and is operative to controllably multiplex said stuff pulses with components of said synchronized signal in accordance with a control signal to produce a stuffed synchronous output signal having a number of stuffs per stuffing opportunity; and a stuff controller which is operative to generate said control signal in accordance with the output of said phase comparator, said stuff controller controllably adjusting the frequency of said synchronized signal in accordance with said ratio of stuffs per stuffing opportunity. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification