Symbol timing recovery method for low resolution multiple amplitude signals

• US 6,731,697 B1
• Filed: 10/06/2000
• Issued: 05/04/2004
• Est. Priority Date: 10/06/2000
• Status: Active Grant

• Current Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Original Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Inventors: Boccuzzi, Joseph, Hwang, Kevin, Rao, Roopa
• Primary Examiner(s): Ghayour, Mohammad H.
• Assistant Examiner(s): Nguyen, Dung X.
• Application Number:
  US09/680,909
• Time in Patent Office: 1,306 Days
• Field of Search: 375/326, 375/340, 375/346, 375/348, 375/355, 375/371, 375/320, 375/321, 375/342, 375/373, 375/375, 375/376, 375/327, 382/168, 382/170, 382/172, 382/199
• US Class Current: 375/326
• CPC Class Codes: H04L 7/007 detection of error based on maximum signal power, e.g. peak value, maximizing autocorrelation
• CPC Class Codes: H04L 7/0334 Processing of samples having at least three levels, e.g. soft decisions

Abstract

Symbol timing is performed by providing a histogram of samples of a signal for a predetermined number of symbol times. An average, weighted average, or other method is applied to determine an average timing for a max eye opening for each symbol time. The average max eye opening timing is applied to an edge detection of a currently received signal to determine timing of a sample that is most likely to occur closest to the max eye opening for the current symbol. The invention may also be practiced based on a center timing of each symbol.

Claims

1. A symbol timing device, comprising:

an ADC mechanism configured to sample a received signal at a predetermined over-sampling rate;

a detector connected to said ADC mechanism and configured to detect a symbol identified by at least one of said samples during predetermined symbol times; and

a symbol timing mechanism connected to said ADC mechanism and said detector and configured to read said samples and adjust a timing of the detection performed by said detector based on previously read samples so that the detected samples are at a most likely maximum eye opening of said samples during said predetermined symbol times;

wherein;

said symbol timing mechanism comprises,

a histogram device configured to,

store a histogram of said samples over a predetermined number of said symbol times, and

calculate a most likely max eye opening of said samples of a next symbol time based on said histogram, and

an adjustment device configured to adjust said timing of the detection performed by said detector based on the calculated most likely max eye opening.

2. The symbol timing device according to claim 1, wherein:

said over-sampling rate is N; and

said histogram device comprises,

a memory configured to store M sets of samples, each sample set comprising N samples, and each sample set corresponding to one of said predetermined symbol times, and

a calculation mechanism configured to determine said most likely eye-opening of said set of samples of a next symbol time based on the sample sets stored in said histogram.

3. The symbol timing device according to claim 1, wherein said histogram device comprises a calculator configured to calculate said most likely max eye opening by averaging max eye openings of said samples over said predetermined number of symbol times.

4. A symbol timing device, comprising:

an ADC mechanism configured to sample a received signal at a predetermined over-sampling rate;

a detector connected to said ADC mechanism and configured to detect a symbol identified by at least one of said samples during predetermined symbol times; and

a symbol timing mechanism connected to said ADC mechanism and said detector and configured to read said samples and adjust a timing of the detection performed by said detector based on previously read samples so that the detected samples are at a most likely maximum eye opening of said samples during said predetermined symbol times;

wherein;

said symbol timing mechanism comprises,

an edge detector configured to determine an edge of symbols sampled by said ADC mechanism;

a histogram configured to save samples from said ADC for a predetermined number of previous symbol times; and

a center adjustment mechanism configured to adjust a sample detected by said detector based on said histogram and edges detected by said edge detector,

said edge detector comprises,

a delay mechanism having an input connected to said ADC mechanism, and an output, and

an exclusive or device having one input connected to said ADC mechanism, a second input connected to the output of said delay mechanism, and an output connected to said histogram; and

said histogram uses the output of said exclusive or to identify samples maintained in said histogram.

5. A symbol timing device, comprising:

an ADC mechanism configured to sample a received signal at a predetermined over-sampling rate;

a detector connected to said ADC mechanism and configured to detect a symbol identified by at least one of said samples during predetermined symbol times; and

a symbol timing mechanism connected to said ADC mechanism and said detector and configured to read said samples and adjust a timing of the detection performed by said detector based on previously read samples so that the detected samples are at a most likely maximum eye opening of said samples during said predetermined symbol times;

wherein;

said symbol timing mechanism comprises,

a transition detector configured to determine an edge of symbols sampled by said ADC mechanism and output a transition detected signal,

a conversion mechanism configured to convert the transition detected signal to a pulse synched with a center of symbols corresponding to detected transitions, and

a histogram that maintains data on a predetermined number M of said pulses;

said detector is further configured to detect symbols based on the data maintained in said histogram.

6. The symbol timing device according to claim 5, wherein said center adjustment mechanism is further configured to adjust time that said symbol is detected by said detector is based on an average of past pulses.

7. The symbol timing device according to claim 5, wherein said center adjustment mechanism is further configured to adjust time that said symbol is detected by said detector is based on a weighted average of past pulses.

8. The symbol timing device according to claim 5, wherein:

said conversion mechanism comprises,

an inverter connected to said transition detector and configured to invert the transition detect signal such that the inverted signal is now synched with a center of a symbol that caused the transition detection and

a rising edge detect mechanism connected to said inverter and configured to convert the synched signal to a pulse by said rising edge detect mechanism.

9. A method of symbol timing recovery, comprising the steps of:

sampling a received signal at a predetermined over-sampling rate;

determining a timing for detection of a specific one or set of said samples based on historical data of previous to said specific one or set of samples;

detecting said specific one or set of samples based on the determined timing; and

maintaining a histogram of sample sets, each set comprising a predetermined number of samples for each of a predetermined number of symbol times;

wherein said step of determining a timing comprises the steps of,

averaging a max eye opening of each set of samples maintained in said histogram, and

calculating a most likely max eye opening for a next set of samples based on the average max eye opening.

10. The method according to claim 9, wherein said step of averaging comprises performing a weighted average of said max eye openings of each set of samples maintained in said histogram.

16. The method according to claim 9, wherein:

said method is embodied in a set of computer instructions stored by a computer readable media;

said computer instructions, when loaded into a computer, cause the computer to perform the steps of said method.

17. The method according to claim 16, wherein said computer instructions are compiled computer instructions stored as an executable program by said computer readable media.

11. A method of symbol timing recovery, comprising the steps of:

sampling a received signal at a predetermined over-sampling rate;

determining a timing for detection of a specific one or set of said samples based on historical data of previous to said specific one or set of samples;

detecting said specific one or set of samples based on the determined timing; and

maintaining a histogram comprising a running average of timing of a max eye opening of samples for each of a predetermined number of symbol times;

wherein said step of determining a timing for detection of a symbol comprises using the running average.

12. A method of symbol timing recovery, comprising the steps of:

sampling a received signal at a predetermined over-sampling rate;

determining a timing for detection of a specific one or set of said samples based on historical data of previous to said specific one or set of samples;

detecting said specific one or set of samples based on the determined timing; and

maintaining a histogram indicating timings from an edge detection to max eye opening of the sampled signal during past symbol times;

averaging the timings of past symbol time max eye openings; and

detecting an edge of a symbol contained in the current sampled signal;

wherein said step of determining a timing comprises, applying the averaged past symbol max eye opening timing to a timing of the detected symbol edge of the current sampled signal.

13. The method according to claim 12, wherein said step of detecting an edge comprises the steps of:

delaying the received signal by one symbol time;

comparing a currently received signal and the delayed signal; and

signaling an edge detection if the compared signals are at different logic levels.

14. The method according to claim 12, further comprising the steps of:

inverting the detected edge so that the rising edge of the inverted signal corresponds to a center of a symbol time of the symbol for which the edge was detected;

converting the inverted signal into a pulse; and

wherein;

said step of determining a timing comprises applying each pulse as a timing for detecting said specific one or set of said samples.

15. The method according to claim 14, further comprising the step of:

adjusting a timing of said pulse based on data contained in said histogram.

18. A symbol timing device, comprising:

an ADC device configured to detect a received signal at a predetermined over-sampling rate;

a detection device configured to detect a symbol identified by at least one of said samples during a predetermined symbol time; and

a symbol timing mechanism configured to read said samples and adjust a timing of the detection performed by the detection device based on previously read samples so that the detected samples are at a most likely maximum eye opening of said samples;

wherein;

said symbol timing mechanism comprises,

a histogram device configured to store sets of said samples in a histogram and determine a most likely max eye opening of said samples based on an average max eye opening in each of the sample sets in said histogram, and

an adjustment device configured to adjust said timing of the detection performed by the detection device based on said histogram device determined most likely max eye opening.

19. A method of symbol timing recovery, comprising the steps of:

sampling a received signal at a predetermined over-sampling rate;

determining a timing for detection of a specific one or set of said samples at a most likely maximum eye opening based on historical data previous to said specific one or set of samples;

detecting said specific one or set of samples based on the determined timing; and

adjusting said timing based on newly acquired samples;

wherein;

said method is embodied in a set of computer readable instructions stored in an electronic signal;

the historical data comprises a plurality of sets of said samples; and

said step of determining comprises an average max eye opening in each of the plurality of sample sets and using the average max eye opening as the most likely maximum eye opening.