High-Speed Decoder for a Multi-Pair Gigabit Transceiver

• US 20100086019A1
• Filed: 12/08/2009
• Published: 04/08/2010
• Est. Priority Date: 11/13/1998
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Kruse, David, Hatamian, Mehdi, Agazzi, Oscar E., Abnous, Arthur
• Granted Patent: US 8,259,787 B2
• Time in Patent Office: Days
• US Class Current: 375/233
• CPC Class Codes: G01R 31/3004 Current or voltage test
• CPC Class Codes: G01R 31/3008 Quiescent current [IDDQ] test or leakage current test
• CPC Class Codes: G01R 31/3016 Delay or race condition test, e.g. race hazard test
• CPC Class Codes: G01R 31/31715 Testing of input or output circuits; test of circuitry between the I/C pins and the functional core, e.g. testing of input or output driver, receiver, buffer
• CPC Class Codes: G01R 31/318502 Test of Combinational circuits
• CPC Class Codes: G01R 31/318552 Clock circuits details
• CPC Class Codes: G01R 31/318594 Timing aspects clock circuits G01R31/318552
• CPC Class Codes: H03M 13/256 with trellis coding, e.g. with convolutional codes and TCM
• CPC Class Codes: H03M 13/41 using the Viterbi algorithm or Viterbi processors
• CPC Class Codes: H03M 13/6331 Error control coding in combination with equalisation
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers
• CPC Class Codes: H04B 3/32 Reducing cross-talk, e.g. by compensating
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 1/0052 Realisations of complexity reduction techniques, e.g. pipelining or use of look-up tables
• CPC Class Codes: H04L 1/0054 Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms
• CPC Class Codes: H04L 1/0059 Convolutional codes
• CPC Class Codes: H04L 1/242 by comparing a transmitted test signal with a locally generated replica
• CPC Class Codes: H04L 2025/03363 Multilevel H04L2025/03369 takes precedence
• CPC Class Codes: H04L 2025/03369 Partial response
• CPC Class Codes: H04L 2025/03477 not time-recursive
• CPC Class Codes: H04L 2025/0349 : as a feedback filter
• CPC Class Codes: H04L 2025/03496 : as a prediction filter
• CPC Class Codes: H04L 2025/03503 : as a combination of feedback and prediction filters
• CPC Class Codes: H04L 2025/03617 : Time recursive algorithms H04L2025/03643 takes precedence
• CPC Class Codes: H04L 2025/03745 : Timing of adaptation
• CPC Class Codes: H04L 25/03038 : with a non-recursive structure H04L25/03031 takes precedence
• CPC Class Codes: H04L 25/03057 : with a recursive structure H04L25/03031 takes precedence
• CPC Class Codes: H04L 25/03146 : with a recursive structure H04L25/03127 takes precedence
• CPC Class Codes: H04L 25/03267 : with decision feedback equalisers
• CPC Class Codes: H04L 25/067 : providing soft decisions, i.e. decisions together with an estimate of reliability H04L25/068 and H04L25/069 take precedence; sequence estimation techniques H04L25/03178
• CPC Class Codes: H04L 25/14 : Channel dividing arrangements , i.e. in which a single bit stream is divided between several baseband channels and reassembled at the receiver
• CPC Class Codes: H04L 25/4917 : using multilevel codes
• CPC Class Codes: H04L 25/497 : by correlative coding, e.g. partial response coding or echo modulation coding transmitters and receivers for partial response systems transversal equalizers at the transmitter end H04L25/03343
• CPC Class Codes: H04L 7/0062 : detection of error based on data decision error, e.g. Mueller type detection
• CPC Class Codes: H04L 7/0334 : Processing of samples having at least three levels, e.g. soft decisions

Abstract

A method and a system for providing an input signal from a multiple decision feedback equalizer to a decoder based on a tail value and a subset of coefficient values received from a decision-feedback equalizer. A set of pre-computed values based on the subset of coefficient values is generated. Each of the pre-computed values is combined with the tail value to generate a tentative sample. One of the tentative samples is selected as the input signal to the decoder. In one aspect of the system, tentative samples are saturated and then stored in a set of registers before being outputted to a multiplexer which selects one of the tentative samples as the input signal to the decoder. This operation of storing the tentative samples in the registers before providing the tentative samples to the multiplexer facilitates high-speed operation by breaking up a critical path of computations into substantially balanced first and second portions, the first portion including computations in the decision-feedback equalizer and the multiple decision feedback equalizer, the second portion including computations in the decoder.

Claims

1. A method for providing an input signal to a symbol decoder, the input signal being based on a tail value and a subset of coefficient values received from a decision feedback equalizer, the method comprising the operations of:

(a) generating a set of pre-computed values in a multiple decision feedback equalizer, the pre-computed values being based on the subset of coefficient values;

(b) combining each of the pre-computed values with the tail value to generate a tentative sample; and

(c) selecting one of the tentative samples as the input signal to the symbol decoder.

2. The method of claim 1 further comprising the operations of:

(d) storing the tentative samples in a set of registers; and

(e) outputting the stored tentative samples to a multiplexer, the multiplexer selecting one of the tentative samples as the input signal to the symbol decoder;

wherein the operation of storing the tentative samples in the registers before providing the tentative samples to the multiplexer facilitates high-speed operation by breaking up a critical path of computations into substantially balanced first and second portions, the first portion including computations in the decision-feedback equalizer and the multiple decision feedback equalizer, the second portion including computations in the symbol decoder.

3. The method of claim 2 further including the operations of saturating the tentative samples and providing the saturated tentative samples to the registers.

4. The method of claim 1 wherein the decision-feedback equalizer comprises a set of ordered coefficients and the subset of coefficient values comprises values of first two lowest ordered coefficients of the decision-feedback equalizer.

5. The method of claim 1 wherein the pre-computed values are based on the subset of coefficient values and values representing levels of a multi-level alphabet.

6. The method of claim 1 wherein in operation (c) said one of the tentative samples is selected based on a symbol received from the symbol decoder.

7. A multiple decision feedback equalizer for providing an input signal to a decoder, the multiple decision feedback equalizer receiving a tail value and a subset of coefficient values from a decision-feedback equalizer, the multiple decision feedback equalizer comprising:

(a) a computing module for generating a set of pre-computed values based on the subset of coefficient values;

(b) a set of adders coupled to the computing module, the adders corresponding one-to-one to the pre-computed values, each of the adders combining the corresponding pre-computed value with the tail value to generate a tentative sample; and

(c) a multiplexer coupled to the adders, the multiplexer receiving the tentative samples, selecting and outputting one of the tentative samples as the input signal to the decoder.

8. The multiple decision feedback equalizer of claim 7 further comprising:

(d) a set of registers coupled to the set of adders to receive the tentative samples, the registers storing the tentative samples and providing the tentative samples to the multiplexer;

wherein the locations of the registers facilitate high-speed operation by breaking up a critical path of computations into substantially balanced first and second portions, the first portion including computations in the decision-feedback equalizer and the multiple decision feedback equalizer, the second portion including computations in the decoder.

9. The multiple decision feedback equalizer of claim 8 further including a set of saturators coupled to the set of adders, the saturators saturating the tentative samples and providing the saturated tentative samples to the registers.

10. The multiple decision feedback equalizer of claim 7 wherein the decision-feedback equalizer has a set of ordered coefficients and the subset of coefficient values comprises values of first two lowest ordered coefficients of the decision-feedback equalizer.

11. The multiple decision feedback equalizer of claim 7 wherein the pre-computed values are based on the subset of coefficient values and known symbol values.

12. The multiple decision feedback equalizer of claim 7 wherein the multiplexer selects said one of the tentative samples based on a symbol received from the decoder.

13. A method for decoding an input sample into a final decision corresponding to a codeword of a trellis code having N states, the method comprising the operations of:

(a) decoding a set of signal samples to generate tentative decisions and the final decision using a decoder block;

(b) providing the tentative decisions to a decision-feedback equalizer, the decision feedback equalizer having a set of low-ordered coefficients and a set of high-ordered coefficients;

(c) generating from the decision-feedback equalizer a tail value based on the tentative decisions, values of the high-ordered coefficients and the input sample;

(d) providing the tail value and values of the low-ordered coefficients to a multiple decision feedback equalizer; and

(e) generating from the multiple decision feedback equalizer the set of signal samples for the decoder.

14. The method of claim 13 wherein operation (a) comprises:

(1) providing the set of signal samples to a Viterbi decoder;

(2) computing path metrics for each of the N states of the trellis code based on the set of signal samples;

(3) computing decisions corresponding to the N states based on the path metrics; and

(4) providing the decisions to a path memory module, the path memory module having a number of depth levels corresponding to consecutive time instants, each of the depth levels having N registers corresponding to the N states of the trellis code;

(5) updating decisions stored in the registers of all depth levels; and

(6) selecting a best decision at each of selected depth levels, the best decision at the last depth level being the final decision, the best decisions at other selected depth levels being the tentative decisions.

15. The method of claim 13 wherein the input sample is an L-dimensional sample.

16. The method of claim 13 wherein each of the tentative decisions and the final decision corresponds to a codeword of the trellis code.

17. The method of claim 13 wherein the decision-feedback equalizer includes a delay line and wherein operation (b) comprises the operation of inputting the tentative decisions into the decision-feedback equalizer at various locations of the delay line.

18. The method of claim 14 wherein operation (f) comprises the operation of selecting the best decisions at the first three depth levels of the path memory module as the tentative decisions.

19. The method of claim 13 wherein the set of low-ordered coefficients comprises the first two coefficients of the decision-feedback equalizer.

20. The method of claim 13 wherein operation (e) comprises the operations of:

(1) generating a set of pre-computed values based on the values of the low-ordered coefficients;

(2) combining each of the pre-computed values with the tail value to generate a tentative sample using a set of adders; and

(3) selecting one of the tentative samples as one of the signal samples using one of N multiplexers corresponding to the N states.

21. The method of claim 20 wherein operation (e) further comprises the operations of:

(4) storing the tentative samples in a set of registers; and

(5) outputting the stored tentative samples to the multiplexer;

wherein the operation of storing the tentative samples in the registers before providing the tentative samples to the multiplexer facilitates high-speed operation by breaking up a critical path of computations into substantially balanced first and second portions, the first portion including computations in the decision-feedback equalizer and the multiple decision feedback equalizer, the second portion including computations in the decoder.

22. The method of claim 21 wherein the multiple decision feedback equalizer further comprises a set of saturators coupled to the set of adders to receive the tentative samples, the saturators saturating the tentative samples and providing the saturated tentative samples to the registers.

23. The method of claim 20 wherein the pre-computed values are computed based on values of the set of low-ordered coefficient and known symbol values.

24. The method of claim 20 wherein, in operation (3), for each of the N states, one of the received tentative samples is selected by the corresponding multiplexer based on at least one decision outputted from the decoder.

25. A decision-feedback sequence estimation block for decoding an input sample into a final decision corresponding to a codeword of a trellis code having N states, the decision-feedback sequence estimation block comprising:

(a) a decoder block decoding a set of signal samples to generate tentative decisions and the final decision;

(b) a decision-feedback equalizer coupled to the decoder block for receiving the tentative decisions, the decision feedback equalizer having a set of low-ordered coefficients and a set of high-ordered coefficients, the decision-feedback equalizer generating a tail value based on the tentative decisions, values of the high-ordered coefficients and the input sample; and

(c) a multiple decision feedback equalizer coupled to the decision-feedback equalizer for receiving the tail value and values of the low-ordered coefficients, the multiple decision feedback equalizer generating the set of signal samples for the decoder block.

26. The decision-feedback sequence estimation block of claim 25 wherein the decoder block comprises:

(1) a Viterbi decoder for receiving the set of signal samples, the Viterbi decoder computing path metrics for each of the N states of the trellis code and outputs decisions based on the path metrics; and

(2) a path memory module coupled to the Viterbi decoder for receiving the decisions, the path memory module having a number of depth levels corresponding to consecutive time instants, each of the depth levels including N registers for storing decisions corresponding to the N states, each of selected depth levels including a multiplexer for selecting a best decision from corresponding N registers, the best decision at the last depth level being the final decision, the best decisions at other selected depth levels being the tentative decisions.

27. The decision-feedback sequence estimation block of claim 25 wherein the input sample is an L-dimensional sample.

28. The decision-feedback sequence estimation block of claim 25 wherein each of the tentative decisions corresponds to a codeword of the trellis code.

29. The decision-feedback sequence estimation block of claim 25 wherein the decision-feedback equalizer includes a delay line and the tentative decisions are inputted into the decision-feedback equalizer at various locations of the delay line.

30. The decision-feedback sequence estimation block of claim 26 wherein the tentative decisions are generated from the first three depth levels of the path memory module.

31. The decision-feedback sequence estimation block of claim 25 wherein the set of low-ordered coefficients comprises the first two coefficients of the decision-feedback equalizer.

32. The decision-feedback sequence estimation block of claim 25 wherein the multiple decision feedback equalizer comprises:

(1) a computing module for generating a set of pre-computed values based on the values of the low-ordered coefficients;

(2) a set of adders coupled to the computing module, the adders corresponding one-to-one to the pre-computed values, each of the adders combining the corresponding pre-computed value with the tail value to generate a tentative sample; and

(3) N multiplexers corresponding to the N states of the trellis code, each of the N multiplexers being coupled to the adders for receiving the tentative samples, each of the N multiplexers selecting and outputting one of the received tentative samples as one of the signal samples to the decoder block.

33. The decision-feedback sequence estimation block of claim 32 wherein the multiple decision feedback equalizer further comprises:

a set of registers coupled to the set of adders to receive the tentative samples, the registers being located between the adders and each of the N multiplexers, the registers providing the tentative samples to the multiplexers; and

wherein the locations of the registers facilitate high-speed operation by breaking up a critical path of computations into substantially balanced first and second portions, the first portion including computations in the decision-feedback equalizer and the multiple decision feedback equalizer, the second portion including computations in the decoder block.

34. The decision-feedback sequence estimation block of claim 33 wherein the multiple decision feedback equalizer further comprises a set of saturators coupled to the set of adders to receive the tentative samples, the saturators saturating the tentative samples and providing the saturated tentative samples to the registers.

35. The decision-feedback sequence estimation block of claim 32 wherein the pre-computed values are based on values of the set of low-ordered coefficients and known symbol values.

36. The decision-feedback sequence estimation block of claim 32 wherein each of the N multiplexers selects one of the received tentative samples based on at least one decision received from the decoder block.

37. A receiver for demodulating a received signal, the received signal resulting from information signals being encoded in accordance with a multi-state encoding scheme and modulated in accordance with a multi-level modulation alphabet before transmission, the receiver comprising:

a symbol decoder receiving a set of ISI compensated signal samples representing the received signal and corresponding to the plurality of states of the encoding scheme, the symbol decoder evaluating the signal samples in accordance with the multi-level modulation alphabet, decoding the evaluated signal samples in accordance with the multi-state encoding scheme, and outputting tentative decisions; and

an ISI compensation circuit coupled to the symbol decoder to receive the tentative decisions, the ISI compensation circuit comprising a single decision feedback equalizer, the single decision feedback equalizer providing an ISI compensation to the received signal based on tentative decisions and providing the set of ISI compensated signal samples to the symbol decoder.

38. The receiver according to claim 37, wherein the symbol decoder comprises:

a symbol detector receiving the set of ISI compensated signal samples, computing path metrics for each of the states of the multi-state encoding scheme and outputting decisions based on the path metrics;

a path memory module coupled to the symbol detector to receive decisions, the path memory module including a plurality of sequential registers arranged in sets such that each of the sets of registers corresponding to a respective one of consecutive time intervals and, in each of the sets of registers, the registers storing decisions corresponding to respective ones of the states of the multi-state encoding scheme; and

a decision module selecting a best decision from a corresponding set of the sets of registers, the best decision from a distal set of the sets of registers defining a final decision, the best decision from an intermediate set of the sets of registers defining a tentative decision.

39. The receiver according to claim 38, wherein the single decision feedback equalizer receives a selected set of tentative decisions from the path memory module, the decision feedback equalizer having a set of low-ordered coefficients and a set of high-ordered coefficients, the decision feedback equalizer generating a first ISI component based on the selected set of tentative decisions and the set of high-ordered coefficients.

40. The receiver according to claim 39, wherein the ISI compensation circuit further comprising a multiple decision feedback equalizer, including a convolution engine, coupled between the decision feedback equalizer and the symbol decoder, the convolution engine receiving low-ordered coefficients from the decision feedback equalizer and combining the low-ordered coefficients with values corresponding to levels of the multi-level modulation alphabet to produce a second ISI component.

41. The receiver according to claim 40, wherein the ISI compensation circuit combines the first and second ISI components with the received signal to generate the ISI compensated signal samples.

42. The receiver according to claim 37 wherein the receiver is implemented as an integrated circuit.

43. A method for ISI compensating and decoding a received signal, the received signal resulting from information signals being encoded in accordance with a multi-state encoding scheme and modulated in accordance with a multi-level modulation alphabet before transmission, the method comprising the operations of:

receiving a set of ISI compensated signal samples representing the received signal with ISI substantially cancelled;

evaluating the ISI compensated signal samples in accordance with the multi-level modulation alphabet and with the multi-state encoding scheme in a symbol decoder;

outputting tentative decisions from the symbol decoder;

generating the ISI compensated signal samples from the received signal and the tentative decisions using a single decision feedback equalizer; and

providing the ISI compensated signal samples to the symbol decoder.

44. The method according to claim 43, wherein the single decision feedback equalizer includes a set of low-ordered coefficients and a set of high-ordered coefficients, and wherein the operation of generating the ISI compensated signal samples comprises:

combining the tentative decisions with values of the set of high-ordered coefficients to produce a partial ISI component; and

combining the partial ISI component with the received signal to generate a partially ISI compensated intermediate signal.

45. The method according to claim 44, wherein the operation of generating the ISI compensated signal samples further comprises:

providing values of the low-ordered coefficients to a multiple decision feedback equalizer;

combining the values of the low-ordered coefficients with a set of values representing levels of the multi-level modulation alphabet to generate a plurality of convolution result terms; and

combining the partially ISI compensated intermediate signal with each of the plurality of convolution result terms to produce a set of potential signal samples for each of a plurality of states of the multi-state encoding scheme, the sets of potential signal samples corresponding one-to-one to the states of the multi-state encoding scheme.

46. The method according to claim 45, wherein the operation of generating the ISI compensated signal samples further comprises:

selecting for each of the states of the multi-state encoding scheme one of the potential signal samples included in a corresponding set of potential signal samples, the selected potential signal samples being the ISI compensated signal samples.

47. The method according to claim 46, wherein the operation of evaluating the ISI compensated signal samples comprises:

slicing the ISI compensated signal samples in accordance with the multi-level modulation alphabet;

computing path metrics for each of the states of the multi-state encoding scheme;

computing decisions corresponding to each of the states of the multi-state encoding scheme based on the path metrics;

storing the decisions in a path memory module, the path memory module having a number of depth levels corresponding to consecutive time intervals, each of the depth levels having a number of registers corresponding to the number of states of the multi-state encoding scheme;

updating decisions stored in the registers of all depth levels; and

selecting a best decision at each of selected depth levels, the best decision at the last depth level defining a final decision, the best decisions at other selected depth levels defining tentative decisions.

48. The method according to claim 47, wherein the multi-state encoding scheme is a trellis code.

49. The method according to claim 48, wherein the multi-level modulation alphabet corresponds to a five-level Pulse Amplitude Modulation constellation.

50. The method according to claim 49, wherein the method is performed in a bidirectional communication system transmitting and receiving signals over an Ethernet communication channel, the communication channel being characterized by four twisted wire pairs of cable, disposed in parallel configuration, each of the four twisted wire pairs of cable transporting signals.