Stuff synchronization device with reduced sampling jitter
First Claim
1. A pulse stuff synchronization device responsive to an input pulse sequence comprising input information pulses at an input bit rate for producing an output pulse sequence comprising output information pulses and stuff pulses in selected ones of consecutive pulse slots defined by a reference clock pulse sequence of an output bit rate higher than said input bit rate, said consecutive pulse slots being divisible into a succession of frames and including that at least one predetermined pulse slot in each frame in which said output pulse sequence includes a selected one of said output information pulses and said stuff pulses to arrange said input information pulses in said output pulse sequence as the respective output information pulses in synchronism with said reference clock pulse sequence, said device comprising (a) i one-bit memory cells, where i represents a predetermined natural number equal at least to two, (b) means for producing first through i-th write pulse sequences having first through i-th cyclically retarding write pulse phases, respectively, for use in storing said input information pulses cyclically in said memory cells, (c) gapping means responsive to said reference clock pulse sequence and a control pulse produced in one frame for providing a gap between the reference clock pulses at the predetermined pulse slot in a frame next succeeding said one frame to produce a gapped clock pulse sequence in response to successive control pulses, (d) means responsive to said gapped clock pulse sequence for distributing the gapped clock pulses into first through i-th read pulse sequences having first through i-th cyclically retarding read pulse phases, respectively, to produce said first through said i-th read pulse sequences, said first read pulse phase having a phase lag relative to said first write pulse phase, (e) means responsive to said first through said i-th read pulse sequences for cyclically reading as said output information pulses the input information pulses stored in said memory cells, (f) means for sampling phase lags of said first through said i-th read pulse phases relative to said first through said i-th write pulse phases, respectively, to provide sampled phase lags from time to time, (g) phase lag monitoring means coupled to said sampling means for monitoring said sampled phase lags to successively produce stuff demand pulses every time said sampled phase lags decrease below a predetermined threshold and (h) supplying means for supplying said stuff demand pulses as said successive control pulses to said gapping means, said output pulse sequence being subject to a jitter component when said sampled phase lags are sampled at a sampling interval substantially equal to i input bit periods, wherein the improvement comprises jitter reducing means for reducing said jitter component, said jitter reducing means comprising:
- a random pulse generator responsive to said reference clock pulse sequence for producing a sequence of random pulses having a pulse interval variable at random between i and (i-k) output bit periods, both inclusive, where k represents an integer preselected from natural numbers less than said predetermined natural number; and
means coupled to a selected one of said sampling means and said phase lag monitoring means and responsive to said random pulse sequence for randomizing time intervals between said sampled phase lags.
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Abstract
It has now been confirmed as regards a stuff (justification) synchronization device for each of plesiochronous input pulse sequence to be time division multiplexed that a low frequency jitter component appears in a synchronous output pulse sequence from the effect of sampling phase lags of read pulse sequences for reading the output pulse sequence for stuffing from an elastic memory (36) of the device relative to write pulse sequences for storing the input pulse sequence in the memory at a sampling interval equal to the memory capacity. The jitter is reduced (1) by selecting a prime number, preferably thirteen and more preferably seventeen or nineteen, as the memory capacity, (2) by cyclically using selected write and read pulse sequences for phase lag monitoring, or (3) by rendering the sampling interval either random or equivalently random.
32 Citations
8 Claims
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1. A pulse stuff synchronization device responsive to an input pulse sequence comprising input information pulses at an input bit rate for producing an output pulse sequence comprising output information pulses and stuff pulses in selected ones of consecutive pulse slots defined by a reference clock pulse sequence of an output bit rate higher than said input bit rate, said consecutive pulse slots being divisible into a succession of frames and including that at least one predetermined pulse slot in each frame in which said output pulse sequence includes a selected one of said output information pulses and said stuff pulses to arrange said input information pulses in said output pulse sequence as the respective output information pulses in synchronism with said reference clock pulse sequence, said device comprising (a) i one-bit memory cells, where i represents a predetermined natural number equal at least to two, (b) means for producing first through i-th write pulse sequences having first through i-th cyclically retarding write pulse phases, respectively, for use in storing said input information pulses cyclically in said memory cells, (c) gapping means responsive to said reference clock pulse sequence and a control pulse produced in one frame for providing a gap between the reference clock pulses at the predetermined pulse slot in a frame next succeeding said one frame to produce a gapped clock pulse sequence in response to successive control pulses, (d) means responsive to said gapped clock pulse sequence for distributing the gapped clock pulses into first through i-th read pulse sequences having first through i-th cyclically retarding read pulse phases, respectively, to produce said first through said i-th read pulse sequences, said first read pulse phase having a phase lag relative to said first write pulse phase, (e) means responsive to said first through said i-th read pulse sequences for cyclically reading as said output information pulses the input information pulses stored in said memory cells, (f) means for sampling phase lags of said first through said i-th read pulse phases relative to said first through said i-th write pulse phases, respectively, to provide sampled phase lags from time to time, (g) phase lag monitoring means coupled to said sampling means for monitoring said sampled phase lags to successively produce stuff demand pulses every time said sampled phase lags decrease below a predetermined threshold and (h) supplying means for supplying said stuff demand pulses as said successive control pulses to said gapping means, said output pulse sequence being subject to a jitter component when said sampled phase lags are sampled at a sampling interval substantially equal to i input bit periods, wherein the improvement comprises jitter reducing means for reducing said jitter component, said jitter reducing means comprising:
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a random pulse generator responsive to said reference clock pulse sequence for producing a sequence of random pulses having a pulse interval variable at random between i and (i-k) output bit periods, both inclusive, where k represents an integer preselected from natural numbers less than said predetermined natural number; and means coupled to a selected one of said sampling means and said phase lag monitoring means and responsive to said random pulse sequence for randomizing time intervals between said sampled phase lags. - View Dependent Claims (2, 3, 4, 5)
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6. A pulse stuff synchronization device responsive to an input pulse sequence comprising input information pulses at an input bit rate for producing an output pulse sequence comprising output information pulses and stuff pulses in selected ones of consecutive pulse slots defined by a reference clock pulse sequence of an output bit rate higher than said input bit rate, said consecutive pulse slots being divisible into a succession of frames and including that at least one predetermined pulse slot in each frame in which said output pulse sequence includes a selected one of said output information pulses and said stuff pulses to arrange said input information pulses in said output pulse sequence as the respective output information pulses in synchronism with said reference clock pulse sequence, said device comprising (a) i one-bit memory cells, where i represents a predetermined natural number equal at least to two, (b) means for producing first through i-th write pulse sequences having first through i-th cyclically retarding write pulse phases, respectively, for use in storing said input information pulses cyclically in said memory cells, (c) gapping means responsive to said reference clock pulse sequence and a control pulse produced in one frame for providing a gap between the reference clock pulses at the predetermined pulse slot in a frame next succeeding said one frame to produce a gapped clock pulse sequence in response to successive control pulses, (d) means responsive to said gapped clock pulse sequence for distributing the gapped clock pulses into first through i-th read pulse sequences having first through i-th cyclically retarding read pulse phases, respectively, to produce said first through said i-th read pulse sequences, said first read pulse phase having a phase lag relative to said first write pulse phase, (e) means responsive to said first through said i-th read pulse sequences for cyclically reading as said output information pulses the input information pulses stored in said memory cells, (f) means for sampling phase lags of said first through said i-th read pulse phases relative to said first through said i-th write pulse phases, respectively, to provide sampled phase lags from time to time, (g) phase lag monitoring means coupled to means for monitoring said sampled phase lags to successively produce stuff demand pulses every time said sampled phase lags decrease below a predetermined threshold, said output pulse sequence being subject to a jitter component when said sampled phase lags are sampled at a sampling interval substantially equal to i input bit periods, (h) supplying means for supplying said stuff demand pulses as said successive control pulses to said gapping means, said supplying means comprising:
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holding means for holding each of said stuff demand pulses during an interval of time between a pulse slot in said one frame at which said each stuff demand pulse is produced and a pulse slot predetermined relative to said next succeeding frame and means for producing said held stuff demand pulse as said control pulse in the predetermined pulse slot in said next succeeding frame; and
(i) jitter reducing means comprising;a random pulse generator responsive to said reference clock pulse sequence for producing a sequence of random pulses having a pulse interval variable at random between i and (i-k) output bit periods, both inclusive, where k represents an integer preselected from natural numbers less than said predetermined natural number and means coupled to said holding means and responsive to each of said random pulses for lengthening said interval of time in relation to the pulse interval next preceding said each random pulse. - View Dependent Claims (7)
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8. A pulse stuff synchronization device responsive to an input pulse sequence comprising input information pulses at an input bit rate for producing an output pulse sequence comprising output information pulses and stuff pulses in selected ones of consecutive pulse slots defined by a reference clock pulse sequence of an output bit rate higher than said input bit rate, said consecutive pulse slots being divisible into a succession of frames and including that at least one predetermined pulse slot in each frame in which said output pulse sequence includes a selected one of said output information pulses and said stuff pulses to arrange said input information pulses in said output pulse sequence as the respective output information pulses in synchronism with said reference clock pulse sequence, said device comprising (a) i one-bit memory cells, where i represents a predetermined natural number equal at least to two, (b) means for producing first through i-th write pulse sequences having first through i-th cyclically retarding write pulse phases, respectively, for use in storing said input information pulses cyclically in said memory cells, (c) gapping means responsive to said reference clock pulse sequence and a control pulse produced in one frame for providing a gap between the reference clock pulses at the predetermined pulse slot in a frame next succeeding said one frame to produce a gapped clock pulse sequence in response to successive control pulses, (d) means responsive to said gapped clock pulse sequence for distributing the gapped clock pulses into first through i-th read pulse sequences having first through i-th cyclically retarding read pulse phases, respectively, to produce said first through said i-th read pulse sequences, said first read pulse phase having a phase lag relative to said first write pulse phase, (e) means responsive to said first through said i-th read pulse sequences for cyclically reading as said output information pulses the input information pulses stored in said memory cells, (f) means for sampling phase lags of said first through said i-th read pulse phases relative to said first through said i-th write pulse phases, respectively, to provide sampled phase lags from time to time, (g) phase lag monitoring means coupled to said sampling means for monitoring said sampled phase lags to successively produce stuff demand pulses every time said sampled phase lags decrease below a predetermined threshold, and (h) supplying means for supplying said stuff demand pulses as said successive control pulses to said gapping means, said output pulse sequence being subject to a jitter component when said sampled phase lags are sampled at a sampling interval substantially equal to i input bit periods, wherein the improvement is characterized in that said predetermined natural number is a selected prime number having a value greater than or equal to three, thereby reducing said jitter component.
Specification