System and method for transferring data among transceivers substantially void of data dependent jitter
View Patent ↗A communication system, clock generation circuit, and method are provided for receiving jitter upon data and to generate a clock reference that does not contain the received jitter. The clock reference can be used either by a digital subsystem of a communication system node, or can be transmitted as substantially jitter-free data from that node to a downstream node of the communication system. Instead of recovering the clock reference from the data having jitter, a pattern is regularly defined within the data stream preferably at periodic, timed intervals. The data pattern may be made up of a series of non-transitions which, regardless of any jitter in the data itself, does not impute any jitter onto a phase-locked loop triggered from an edge of the non-transitioning data pattern. Using the edge as a reference point, a jitter-free clocking signal can be derived at the same frequency as a clocking signal which would normally be produced from the jitter-induced data.
1. A clock generation circuit, comprising:
a detection circuit coupled to receive a stream of data having a repeating pattern of data regularly interspersed within a preamble portion of the stream of data, and to generate an edge during the preamble portion, and during a time no more than one bit after which the pattern of data ends, but not during prior transitions of the pattern of data;
an oscillator coupled to generate a plurality of regularly spaced clock pulses phase synchronized to the edge;
a window state machine coupled to receive a first clock generated from the stream of data and to produce a window pulse synchronized to the first clock and having a duration that begins prior to the edge and ends after the edge; and
logic coupled to produce the edge only during times when the window pulse exist.
2. The clock generation circuit as recited in claim 1 , wherein the detection circuit is coupled to produce the edge at the same time regardless of a rate at which the data preceding the pattern of data transitions.
3. The clock generation circuit as recited in claim 1 , wherein the detection circuit is coupled to produce the edge at the same time regardless of whether the stream of data preceding the pattern of data is encoded as a logic one, logic zero, or random logic value.
4. The clock generation circuit as recited in claim 1 , wherein the detection circuit comprises:
a first logic gate coupled to output the edge independent of a polarity of the pattern of data; and
a second logic gate coupled to receive the output from the first logic gate during a window pulse that repeats at least one time during which the pattern of data repeats.
5. The clock generation circuit as recited in claim 1 , wherein the pattern of data extends for a duration exceeding the reciprocal of the cutoff frequency of a low-pass filter associated with the detection circuit.
6. The clock generation circuit as recited in claim 1 , wherein the pattern of data extends for a duration that ensures voltage output from the detection circuit achieves the same value at the end of the pattern independent of any preceding data.
7. The clock generation circuit as recited in claim 1 , wherein the pattern of data extends during the preamble portion between frames of the stream of data.
8. The clock generation circuit as recited in claim 1 , wherein the pattern of data extends for a time period indicative of a coding violation, and wherein the detection circuit is adapted to detect the coding violation.
9. The clock generation circuit as recited in claim 1 , wherein the regularly spaced clock pulses are forwarded to a digital circuit for synchronizing operation thereof.
10. The clock generation circuit as recited in claim 1 , further comprising:
a first phase-locked loop coupled to receive the stream of data and generate a first clock therefrom;
a second phase-locked loop having a phase detector that aligns at least one phase of the regularly spaced clock pulses with the edge to form a second clock therefrom; and
a buffer coupled to receive the stream of data synchronized to the first clock and to output the stream of data to a digital circuit synchronized to the second clock.
11. A communication system, comprising:
a receiver coupled to receive a repeating pattern of bit values regularly interspersed within a preamble portion of a data stream and to generate an edge during the preamble portion, and no more than one bit after each said pattern terminates, wherein one of a plurality of regular clock pulses are generated in phase with the edge;
a synchronous circuit coupled to process data synchronized to the plurality of regular clock pulses;
a window state machine coupled to produce a window pulse synchronized to a first clock generated from the data stream, beginning before the edge and ending after the edge; and
logic coupled to produce the edge only during times when the window pulse exists.
12. The communication system as recited in claim 11 , wherein the synchronous circuit comprises a transmitter coupled to transmit the data synchronized to the plurality of regular clock pulses.
13. The communication system as recited in claim 11 , wherein the synchronous circuit comprises a multimedia device.
14. The communication system as recited in claim 11 , wherein the receiver comprises a detection circuit coupled to detect logic value transitions of the data stream and to
produce a relatively variable output depending on a logic value of the data stream, and
produce a relatively fixed output at the culmination of the pattern of bit values.
15. The communication system as recited in claim 11 , wherein the pattern of bit values correspond to a coding violation.
16. The communication system as recited in claim 11 , wherein a reciprocal of the time duration of pattern of bit values is less than the cut off frequency of the receiver.
17. A method for transferring data substantially free of jitter, comprising:
generating an edge during a preamble portion of a stream of data, and at the same time relative to an end of a consistent and unchanging pattern of bit values, but not during the pattern of bit values, and not more than one bit after the pattern of data ends;
producing a window pulse synchronized to a first clock generated from the data stream, beginning before the edge and ending after the edge;
producing the edge only during times when the window pulse exists;
receiving the stream of data transitioning at a rate dependent on a logic value of the data;
compiling a first clocking signal having jitter dependent on a frequency at which the rate changes;
compiling a second clocking signal synchronized to the edge and having regularly occurring pulses transitioning at substantially the same rate as the first clocking signal; and
transferring the data synchronized to the second clocking signal.
18. The method as recited in claim 17 , wherein said receiving and compiling steps occur within a first transceiver and said transferring step occurs within a communication link coupled between the first transceiver and a second transceiver of a communication system.
19. The method as recited in claim 17 , wherein said transferring comprises operating a digital system synchronized to the second clocking signal.