US 8,804,809 B2Granted

Techniques for setting feedback coefficients of a PAM-N decision feedback equalizer

AssigneeTranSwitch Corporation

InventorsDan Raphaeli, Yaron Slezak

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Abstract

A decision feedback equalizer (DFE) for equalizing PAM-N signals comprises a coefficient setting unit for setting a first group of most significant feedback coefficients of the DFE to a predefined value selected from a group of predefined values; a coefficients computation unit coupled to the coefficient setting unit for computing values of feedback coefficients of a second group of feedback coefficients other than the first group of most significant feedback coefficients; a feedback (FB) unit for mitigating, using a complete group of feedback coefficients, effects of interference from data symbols that are adjacent in time to an input data symbol, wherein most significant feedback coefficients of the first group are set to an optimal value computed during an initialization of the DFE and feedback coefficients of the second group are computed by the coefficients computation unit.

Claims23

Dependent claims

A decision feedback equalizer (DFE) for equalizing N-pulse amplitude modulation (PAM-N) signals, comprising:

a coefficient setting unit for setting a first group of most significant feedback coefficients of the DFE to a predefined value selected from a group of predefined values;
a coefficients computation unit coupled to the coefficient setting unit for computing values of feedback coefficients of a second group of feedback coefficients other than the first group of most significant feedback coefficients;
a feedback (FB) unit for mitigating, using a complete group of feedback coefficients, effects of interference from data symbols that are adjacent in time to an input data symbol, wherein the most significant feedback coefficients of the first group are set to an optimal value computed during an initialization of the DFE and the feedback coefficients of the second group are computed by the coefficients computation unit, and wherein the complete group of feedback coefficients includes the first and second groups of feedback coefficients;
an error-and-decision unit for at least computing an error value indicating the sum of errors of an input symbol of the input data symbol from optimal positions of the voltage levels of the PAM-N signals;
and
a calibration unit for computing, based on the error value, the voltage levels of the PAM-N signals and a value of a quality parameter utilized to determine the optimal value for the feedback coefficients in the first group of most significant feedback coefficients.

3 more elements

A method for adjusting the feedback coefficients of a N-pulse amplitude modulation (PAM-N) decision feedback equalizer (DFE), comprising:

inputting to the DFE a PAM-2 signal having two voltage levels;
iteratively, for each predefined value in a group of predefined values performing:
setting at least one most significant feedback coefficient to a predefined value selected from the group of predefined values;
computing values of feedback coefficients of a second group of feedback coefficients, wherein the at least one most significant feedback coefficient and the second group of feedback coefficients are feedback coefficients utilized by the DFE to equalize the PAM-2 input signal;
computing first voltage levels of the PAM-2 signal, the first voltage levels are being used as crossing points by the DFE;
waiting for the computed values of feedback coefficients of the second group of feedback coefficients and the first voltage levels to converge;
measuring converged values of the first voltage levels;
computing second voltage levels of the PAM-N signal as new crossing points of the DFE, the second voltage levels are computed with a deliberate offset;
waiting for the computed values of the second voltage levels to converge;
measuring converged values of feedback coefficients of the second group of feedback coefficients and the second voltage levels;
computing a value of a quality parameter based on the converged values of the first voltage levels and the converged values of the second voltage levels;
and
determining the predefined value selected from the group of predefined values of the at least one most significant feedback coefficient that results in a minimal value of the computed quality parameter as an optimal value for the at least one most significant feedback coefficient, wherein the minimal value of the quality parameter ensures a minimum error at the output of the DFE.

10 more elements

Dependencies are inferred from the claim text.