# US 11,451,417 B1 · Power-efficient nonlinear equalizers and methods > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,451,417 B1 - Document ID: US11451417B1 - Status: Granted - Kind: B1 - Application number: 17/443,078 - Filed: 2021-07-20 - Granted: 2022-09-20 - Earliest claimed: 2021-07-20 - Assignees: Credo Technology Group Limited - Applicants: Credo Technology Group Ltd - Inventors: Junqing (Phil) Sun - Web page: https://patentgrep.com/patent/US11451417B1 ## CPC - H04L 25/03057: {with a recursive structure (H04L25/03031 takes precedence)} - H04L 25/4917: {using multilevel codes} - H04L 25/03146: {with a recursive structure (H04L25/03127 takes precedence)} - H04L 25/03267: {with decision feedback equalisers} - H04L 25/03885: {adaptive} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract One illustrative equalizer converts a receive signal into a sequence of symbol decisions using: a linear filter that filters the receive signal as part of deriving a first sequence of equalized signal samples; a first decision element that derives a tentative sequence of symbol decisions from the first sequence of equalized signal samples; a nonlinear filter that, when enabled, applies nonlinear compensation to the linearly filtered receive signal as part of deriving a second sequence of equalized signal samples; a second decision element that, when enabled, derives replacement symbol decisions from the second sequence of equalized signal samples; a subtraction element that calculates an equalization error for each symbol decision in the tentative sequence; and a controller that selectively enables the nonlinear filter and the second decision element to obtain a replacement symbol decision for each symbol decision in the tentative sequence having an equalization error greater than a predetermined value. ## Claims ### Claim 1 An equalizer that converts a receive signal into a sequence of symbol decisions, the equalizer comprising: a linear filter that obtains a filtered signal from the receive signal as part of deriving a first sequence of equalized signal samples from the receive signal; a first decision element that derives a tentative sequence of symbol decisions from the first sequence of equalized signal samples; a nonlinear filter that, when enabled, operates on both the receive signal and the filtered signal as part of deriving a second sequence of equalized signal samples from the receive signal; a second decision element that, when enabled, derives replacement symbol decisions from the second sequence of equalized signal samples; a subtraction element that calculates an equalization error for each symbol decision in the tentative sequence; and a controller that selectively enables the nonlinear filter and the second decision element to obtain a replacement symbol decision for each symbol decision in the tentative sequence having an equalization error greater than a predetermined value. ### Claim 2 (depends on 1) The equalizer of claim 1, further comprising: a feedback filter that derives a feedback signal from the tentative sequence of symbol decisions; and a summer that combines the feedback signal with an output of the linear filter to provide the first sequence of equalized signal samples. ### Claim 3 (depends on 2) The equalizer of claim 2, further comprising: a second summer that combines a second feedback signal with an output of the nonlinear filter to provide the second sequence of equalized signal samples. ### Claim 4 (depends on 1) The equalizer of claim 1, wherein the predetermined value corresponds to an estimated probability of 10−2 or less. ### Claim 5 (depends on 1) The equalizer of claim 1, wherein the nonlinear filter combines an output of the linear filter with second order combinations of receive signal samples. ### Claim 6 (depends on 5) The equalizer of claim 5, wherein the nonlinear filter derives the second sequence of equalized signal samples as a weighed sum of inputs to the nonlinear filter. ### Claim 7 (depends on 5) The equalizer of claim 5, wherein the nonlinear filter includes one or more delay chains to make a pool of available second order combinations, and wherein the nonlinear filter includes multiplexers to select a subset of the available second order combinations to derive the second sequence of equalized signal samples. ### Claim 8 An equalization method that converts a receive signal into a sequence of symbol decisions, the method comprising: using a linear filter on the receive signal to obtain a filtered signal for deriving a first sequence of equalized signal samples; deriving a tentative sequence of symbol decisions from the first sequence of equalized signal samples; using a nonlinear filter that, when enabled, operates on the receive signal to derive a second sequence of equalized signal samples; using a decision element that, when enabled, derives replacement symbol decisions from the second sequence of equalized signal samples; calculating an equalization error for each symbol decision in the tentative sequence; and selectively enabling the nonlinear filter and the decision element to obtain a replacement symbol decision for each symbol decision in the tentative sequence having an equalization error greater than a predetermined value. ### Claim 9 (depends on 8) The equalization method of claim 8, further comprising: deriving a feedback signal from the tentative sequence of symbol decisions; and combining the feedback signal with an output of the linear filter to provide the first sequence of equalized signal samples. ### Claim 10 (depends on 9) The equalization method of claim 9, further comprising: combining a second feedback signal with an output of the nonlinear filter to provide the second sequence of equalized signal samples. ### Claim 11 (depends on 8) The equalization method of claim 8, wherein the predetermined value corresponds to an estimated probability of 10−2 or less. ### Claim 12 (depends on 8) The equalization method of claim 8, wherein the nonlinear filter combines an output of the linear filter with second order combinations of receive signal samples. ### Claim 13 (depends on 12) The equalization method of claim 12, wherein the nonlinear filter derives the second sequence of equalized signal samples as a weighed sum of inputs to the nonlinear filter. ### Claim 14 (depends on 12) The equalization method of claim 12, wherein the nonlinear filter selects a subset of available second order combinations to derive the second sequence of equalized signal samples. ### Claim 15 A semiconductor intellectual property core that generates circuitry for an equalizer, wherein the equalizer comprises: a linear filter that operates on a receive signal to obtain a filtered signal as part of deriving a first sequence of equalized signal samples from the receive signal; a first decision element that derives a tentative sequence of symbol decisions from the first sequence of equalized signal samples; a nonlinear filter that, when enabled, operates on the receive signal as part of deriving a second sequence of equalized signal samples from the receive signal; a second decision element that, when enabled, derives replacement symbol decisions from the second sequence of equalized signal samples; a subtraction element that calculates an equalization error for each symbol decision in the tentative sequence; and a controller that selectively enables the nonlinear filter and the second decision element to obtain a replacement symbol decision for each symbol decision in the tentative sequence having an equalization error greater than a predetermined value. ### Claim 16 (depends on 15) The semiconductor intellectual property core of claim 15, wherein the equalizer further comprises: a feedback filter that derives a feedback signal from the tentative sequence of symbol decisions; and a summer that combines the feedback signal with an output of the linear filter to provide the first sequence of equalized signal samples. ### Claim 17 (depends on 16) The semiconductor intellectual property core of claim 16, wherein the equalizer further comprises: a second summer that combines a second feedback signal with an output of the nonlinear filter to provide the second sequence of equalized signal samples. ### Claim 18 (depends on 15) The semiconductor intellectual property core of claim 15, wherein the predetermined value corresponds to an estimated probability of 10−2 or less. ### Claim 19 (depends on 15) The semiconductor intellectual property core of claim 15, wherein the nonlinear filter combines an output of the linear filter with second order combinations of receive signal samples. ### Claim 20 (depends on 19) The semiconductor intellectual property core of claim 19, wherein the nonlinear filter includes one or more delay chains to make a pool of available second order combinations, and wherein the nonlinear filter includes multiplexers to select a subset of the available second order combinations to derive the second sequence of equalized signal samples.