A method includes receiving an input signal at a filter, where the filter includes a plurality of filter taps, and where each of a first filter tap and a second filter tap has a weighting coefficient. The method also includes shutting down the first filter tap based on the weighting coefficient of the first filter tap being below a threshold and the weighting coefficient of the second filter tap being below the threshold, where the second filter tap is next to the first filter tap.

A first sequence of data bits is shifted into storage elements of a signal receiver during a first sequence of bit-time intervals, and a memory access command indicates that a second sequence of data bits is to be received within the signal receiver during a second sequence of bit-time intervals. Contents of the shift-register storage elements are conditionally overwritten with a predetermined set of seed bits, depending on whether one or more bit-time intervals will transpire between the first and second sequences of bit-time intervals. Equalization signals generated based, at least in part, on contents of the shift-register storage elements are used to adjust respective signal levels representative of one or more bits of the second sequence of data bits.

A decision-feedback equalizer (DFE) includes a combining circuit and a feedback filter. The combining circuit combines an input signal and at least one feedback signal to generate an equalized signal. The feedback filter generates the at least one feedback signal according to the equalized signal, and includes a controllable delay circuit. The controllable delay circuit receives an output signal that is derived from the equalized signal, and applies at least one delay amount to generate at least one delay signal, wherein the at least one feedback signal is derived from the at least one delay signal.

A PAM-4 DFE receives an input signal distorted by inter-symbol interference (ISI) and expressing a series of symbols each representing one of four pulse amplitudes to convey two binary bits of data per symbol. High-order circuitry resolves the most-significant bit (MSB) of each two-bit symbol, whereas low-order circuitry 115 resolves the immediate least-significant bit (LSB). An immediate value of the MSB is used to select a set of ISI offsets used to resolve the LSB. Resolved values of the prior values of the MSB and LSB are then used to select the ISI offset for the immediate symbol.

A decision feedback equalizer for generating an output signal according to an input signal includes: a feedforward equalizer, a feedback equalizer and a weight coefficient control unit. The feedforward equalizer includes a plurality of tapped delay lines and is controlled by a set of first weight coefficients. The feedback equalizer includes a plurality of tapped delay line and is controlled by a set of second weight coefficients. The weight coefficient control unit is employed to selectively adjust at least one of the set of first weight coefficients and determine a set of first boundary values for at least one of the set of second weight coefficients. When the at least one of the set of second weight coefficients does not exceed the set of first boundary values, the weight coefficient control unit increments the at least one of the set of first weight coefficients.

Described are methods and circuits for margin testing digital receivers. These methods and circuits prevent margins from collapsing in response to erroneously received data and can thus be used in receivers that employ historical data to reduce intersymbol interference (ISI). Some embodiments detect receive errors for input data streams of unknown patterns and can thus be used for in-system margin testing. Such systems can be adapted to dynamically alter system parameters during device operation to maintain adequate margins despite fluctuations in the system noise environment due to e.g. temperature and supply-voltage changes. Also described are methods of plotting and interpreting filtered and unfiltered error data generated by the disclosed methods and circuits. Some embodiments filter error data to facilitate pattern-specific margin testing.

A communication system includes: a transmission device including a transmission data generator, a pattern generator, a transmitter, and a control signal receiver, the transmission data generator that is configured to generate transmission data, the pattern generator that is configured to generate an alternate pattern alternating at every lapse of a predetermined time, the transmitter that includes a first equalization circuit and is configured to transmit a transmission signal including the transmission data and the alternate pattern, the first equalization circuit that is configured to adjust equalization characteristics on the basis of first instruction information, and the control signal receiver that is configured to receive the first instruction information; and a reception device including a receiver, a first detector, and a control signal transmitter, the receiver that is configured to receive the transmission signal, the first detector that is configured to detect a frequency component corresponding to the predetermined time of the alternate pattern included in the transmission signal, and the control signal transmitter that is configured to generate the first instruction information on the basis of a result of detection by the first detector and is configured to transmit the first instruction information.

Disclosed is a device that multiplies a first signal outputted from a CTLE and a second signal obtained by delaying the first signal by a predetermined time interval; produces a specific signal reflecting a temporal sum of the multiplied signal; determines gain control signal in a manner such that the difference between the specific signal and a predetermined target level is reduced; and provides the determined gain control signal to the CTLE so as to be applied to high-band boosting thereof. The time interval to be delayed corresponds to N (N is an integer equal to or greater than one) times a unit interval that is occupied by one symbol in the first signal.

Some implementations provide a passive equalizer section configured to filter an input signal, the passive equalizer section including: a first passive filter that comprises: a first resistor characterized by a first resistance, and a first reactive component characterized by a first reactance, wherein the first resistor and the first reactive component are in series and connected at a first connection node; and a second passive filter that comprises: a second resistor characterized by a second resistance, and a second reactive component characterized by a second reactance, wherein the second resistor and the second reactive component are in series and connected at a second connection node; and a signal mixing section comprising a plurality of transistors to mix signals with different frequency response characteristics.

Embodiments of the disclosure include signal processing methods to reduce crosstalk between signal lines of a channel bus using feed forward equalizers (FFEs) configured smear pulse response energy transmitted on signal lines of the channel to reduce pulse edge rates. The coefficients for the FFE may be based on crosstalk interference characteristics. Smearing or spreading pulse response energy across a longer time period using a FFE increases inter-symbol interference (ISI). To counter increased inter-symbol interference caused by smearing pulse response energy, receivers configured to recover symbol data transmitted on the channel bus may each include respective decision-feedback equalizers (DFEs) that are configured to filter ISI from transmitted symbols based on previous symbol decisions of the channel. The combination of the FFE configured to smear pulse responses and the DFE to filter ISI may improve data eye quality for recovery of transmitted data on a channel bus when crosstalk dominates noise.