Abstract: An illustrative decoder includes: a syndrome calculator, a location finder, and an error corrector. The syndrome calculator has an array of logic gates to obtain syndrome values as a product of a receive message vector and a parity check matrix, the syndrome values including at least a three ten-bit syndrome values S1, S2, and S3. The location finder derives a number of errors from the syndrome values, and uses a second array of logic gates to obtain two polynomial roots as a product of a syndrome value vector and a quadratic solution matrix when the number of errors is two, the quadratic solution matrix corresponding to a determination of a quadratic equation's trailing coefficient value s, a determination of the quadratic equation's roots, and a reversal of a variable substitution. The location finder further determines a bit index for each of the polynomial roots.

Abstract: Retimers and retiming methods may employ dual path clock forwarding to drive a transmit clock generator. One illustrative integrate retimer circuit includes: a sampling element configured to produce a digital receive signal by sampling an analog receive signal in accordance with a sampling signal; a timing error estimator configured to produce a timing error signal indicating an estimated timing error of the sampling signal relative to the analog receive signal; a clock recovery circuit configured to derive the sampling signal from the estimated timing error and a reference clock in part by determining a frequency signal; a transmitter configured to retransmit the digital receive signal in accordance with a transmit clock; and a transmit clock generator configured to derive the transmit clock. The transmit clock generator operates based on each of: the reference clock; the frequency signal; and a phase error of the transmit clock relative to the sampling signal.

Abstract: An illustrative retimer includes: an upstream interface having an upstream receiver configured to convert a downlink signal into a downlink symbol stream; a downstream interface having a downstream transmitter configured to provide a transmit signal representing the downlink symbol stream; core circuitry having a downstream path and a downstream bypass path; and a controller. The downstream path is configured to convey the downlink symbol stream from the upstream receiver to the downstream transmitter via a receive clock domain component, a core clock domain component, and a transmit clock domain component. The downstream bypass path is configurable to convey the downlink symbol stream from the upstream receiver to the downstream transmitter without any core clock domain components. The controller is configured to disable a clock signal for the transmit clock domain component of the downstream path when the downstream bypass path is enabled.

Abstract: Flash analog to digital converters and other types of integrated circuits having multiple comparators may employ calibration methods and firmware to efficiently compensate the various offset voltages of the multiple comparators. One illustrative integrated circuit includes: multiple comparators each configured to provide a comparator output signal indicating whether an input signal exceeds a reference voltage by more than an offset voltage, the multiple comparators including a current comparator and a previous comparator; and a controller configured to perform a search to select a calibration setting for each of the comparators in turn, the controller determining an initial search window for the current comparator based on a calibration setting selected for the previous comparator.

Abstract: Retimers and retiming methods may employ dual path clock forwarding to drive a transmit clock generator. One illustrative integrate retimer circuit includes: a sampling element configured to produce a digital receive signal by sampling an analog receive signal in accordance with a sampling signal; a timing error estimator configured to produce a timing error signal indicating an estimated timing error of the sampling signal relative to the analog receive signal; a clock recovery circuit configured to derive the sampling signal from the estimated timing error and a reference clock in part by determining a frequency signal; a transmitter configured to retransmit the digital receive signal in accordance with a transmit clock; and a transmit clock generator configured to derive the transmit clock. The transmit clock generator operates based on each of: the reference clock; the frequency signal; and a phase error of the transmit clock relative to the sampling signal.

Abstract: Integrated circuit transceivers having digital timing recovery loops with phase interpolation may incorporate dynamic loop gains to compensate for nonlinearities of the phase interpolation. An illustrative receiver circuit includes: a phase interpolator, a sampling element, a timing error estimator, and a feedback circuit. The phase interpolator provides a sampling signal by applying a phase shift to a clock signal in response to a phase control signal. The sampling element produces a digital receive signal by sampling an analog receive signal in accordance with the sampling signal. The timing error estimator produces a timing error signal indicating an estimated timing error of the sampling signal relative to the analog receive signal. The feedback circuit derives the phase control signal from the timing error signal using a scaling element configured to scale the estimated timing error by a scale factor that depends on the phase control signal.

Abstract: Fast sampling phase and frequency acquisition suitable for incorporation into various high bandwidth receivers and receiving methods. One illustrative integrated circuit receiver or “deserializer” design has: a clock circuit that provides a sample clock; an analog to digital converter that samples a receive signal in accordance with the sample clock to provide receive signal samples; and a clock recovery circuit. The clock recovery circuit includes: a phase and frequency acquisition module to determine and correct an initial frequency offset and an initial phase offset of the sample clock; and a feedback circuit to minimize timing error of the sample clock after the initial frequency offset and initial phase offset have been corrected.

Abstract: Fast sampling phase and frequency acquisition suitable for incorporation into various high bandwidth receivers and receiving methods. One illustrative integrated circuit receiver or “deserializer” design has: a clock circuit that provides a sample clock; an analog to digital converter that samples a receive signal in accordance with the sample clock to provide receive signal samples; and a clock recovery circuit. The clock recovery circuit includes: a phase and frequency acquisition module to determine and correct an initial frequency offset and an initial phase offset of the sample clock; and a feedback circuit to minimize timing error of the sample clock after the initial frequency offset and initial phase offset have been corrected.

Abstract: An illustrative decoder includes: a syndrome calculator, a location finder, and an error corrector. The syndrome calculator has an array of logic gates to obtain syndrome values as a product of a receive message vector and a parity check matrix, the syndrome values including at least a three ten-bit syndrome values S1, S2, and S3. The location finder derives a number of errors from the syndrome values, and uses a second array of logic gates to obtain two polynomial roots as a product of a syndrome value vector and a quadratic solution matrix when the number of errors is two, the quadratic solution matrix corresponding to a determination of a quadratic equation's trailing coefficient value s, a determination of the quadratic equation's roots, and a reversal of a variable substitution. The location finder further determines a bit index for each of the polynomial roots.

Abstract: Transmit-side equalization is disclosed for network devices and network communications methods employing onboard/co-packaged optics. An illustrative network device includes a substrate having a host device IC (integrated circuit) and an optical module IC connected by a short-reach link. The optical module IC having a transmit chain includes a CTLE (continuous time linear equalizer) to at least partly compensate for a channel response of the short-reach link, and a driver that amplifies an output of the CTLE for a photoemitter that couples to an optical fiber.

Abstract: Disclosed retimer modules and methods enable equalizer training during link speed negotiation. One illustrative retimer module includes: an analog to digital converter that uses a sampling clock to digitize a receive signal; an equalizer that converts the digitized receive signal into an equalized signal; a decision element that derives a receive symbol stream from the equalized signal; and a clock recovery module that derives the sampling clock based at least in part on an equalization error of the equalized signal, the sampling clock having a frequency with a range including a baud rate of the receive signal at a first supported speed and including a frequency not less than twice the baud rate of the receive signal at a second supported speed.

Abstract: An illustrative digital communications method includes: filtering a receive signal to provide a filtered receive signal; deriving symbol decisions from the filtered receive signal; detecting a baud rate of the receive signal; adapting one or more coefficients of the filter if the baud rate is above a predetermined rate; and inhibiting coefficient adaptation if the baud rate is below the predetermined rate. The method may be implemented in a receiver having: a filter to convert a receive signal into a filtered receive signal; a decision element coupled to the filter to derive symbol decisions; a baud rate detector to detect a baud rate of the receive signal; and an adaptation module to adapt one or more coefficients of the filter if the baud rate is above a predetermined rate, the baud rate detector inhibiting adaptation if the baud rate is below the predetermined rate.

Abstract: An illustrative digital communications method includes: filtering a receive signal to provide a filtered receive signal; deriving symbol decisions from the filtered receive signal; detecting a baud rate of the receive signal; adapting one or more coefficients of the filter if the baud rate is above a predetermined rate; and inhibiting coefficient adaptation if the baud rate is below the predetermined rate. The method may be implemented in a receiver having: a filter to convert a receive signal into a filtered receive signal; a decision element coupled to the filter to derive symbol decisions; a baud rate detector to detect a baud rate of the receive signal; and an adaptation module to adapt one or more coefficients of the filter if the baud rate is above a predetermined rate, the baud rate detector inhibiting adaptation if the baud rate is below the predetermined rate.

Abstract: Digital filters and filtering methods may employ truncation, internal rounding, and/or approximation in a summation circuit that combines multiple sets of bit products arranged by bit weight. One illustrative digital filter includes: a summation circuit coupled to multiple partial product circuits. Each partial product circuit is configured to combine bits of a filter coefficient with bits of a corresponding signal sample to produce a set of partial products. The summation circuit produces a filter output using a carry-save adder (“CSA”) tree that combines the partial products from the multiple partial product circuits into bits for two addends. The CSA tree has multiple lanes of adders, each lane being associated with a corresponding bit weight. The adders in one or more of the lanes associated with least significant bits of the filter output are approximate adders that trade accuracy for simpler implementation.

Abstract: Digital communication transmitters, systems, and methods can introduce skew into parallel transmission channels to enhance the performance of forward error correction (FEC) decoders. One illustrative serializer-deserializer (SerDes) transmitter embodiment includes: a block code encoder configured to convert a sequence of input data blocks into a sequence of encoded data blocks; a demultiplexer configured to distribute code symbols from the sequence of encoded data blocks to multiple lanes in a cyclical fashion, the multiple lanes corresponding to parallel transmission channels; a skewer configured to buffer the multiple lanes to provide respective lane delays, the lane delays differing from each other by no less than half an encoded data block period; and multiple drivers, each driver configured to transmit code symbols from one of said multiple lanes on a respective one of said parallel transmission channels.

Abstract: Digital filters and filtering methods may employ truncation, internal rounding, and/or approximation in a summation circuit that combines multiple sets of bit products arranged by bit weight. One illustrative digital filter includes: a summation circuit coupled to multiple partial product circuits. Each partial product circuit is configured to combine bits of a filter coefficient with bits of a corresponding signal sample to produce a set of partial products. The summation circuit produces a filter output using a carry-save adder (“CSA”) tree that combines the partial products from the multiple partial product circuits into bits for two addends. The CSA tree has multiple lanes of adders, each lane being associated with a corresponding bit weight. The adders in one or more of the lanes associated with least significant bits of the filter output are approximate adders that trade accuracy for simpler implementation.

Abstract: A method of assessing the ability of one or more multi-die circuit elements to tolerate the presence of jitter in intra-package. The method includes: providing a first die having a set of transmitters for digital communications, the set of transmitters comprising a first transmitter and a second transmitter; providing a second die having a set of receivers for digital communications; providing a performance monitor; coupling, using an intra-package trace, a first transmit signal from the first transmitter to a receiver of the set of receivers; coupling a second transmit signal from the second transmitter to an external pin; supplying an input signal that induces jitter in the first and second transmit signals; measuring jitter in the second transmit signal via the external pin; and determining, using the performance monitor, a performance characteristic of the second die.

Abstract: A method of assessing the ability of one or more multi-die circuit elements to tolerate the presence of jitter in intra-package. The method includes: providing a first die having a set of transmitters for digital communications, the set of transmitters comprising a first transmitter and a second transmitter; providing a second die having a set of receivers for digital communications; providing a performance monitor; coupling, using an intra-package trace, a first transmit signal from the first transmitter to a receiver of the set of receivers; coupling a second transmit signal from the second transmitter to an external pin; supplying an input signal that induces jitter in the first and second transmit signals; measuring jitter in the second transmit signal via the external pin; and determining, using the performance monitor, a performance characteristic of the second die.

Abstract: Disclosed clock recovery modules provide improved performance with only limited complexity and power requirements. In one illustrative embodiment, a clock recovery method includes: oversampling a receive signal to obtain mid-symbol interval (MSI) samples and between-symbol interval (BSI) samples; processing at least the MSI samples to obtain symbol decisions; filtering the symbol decisions to obtain BSI targets; determining a timing error based on a difference between the BSI samples and the BSI targets; and deriving from the timing error a clock signal for said oversampling.

Abstract: In one illustrative embodiment, an equalizer includes: a shift register, an array of multipliers, an array of multiplexers, and a summer. The shift register provides receive signal samples at each tap. Each multiplier in the array multiplies one of said receive signal samples by a respective coefficient to produce a product, with at least one of said multipliers coupled to a fixed tap. Each multiplexer in the array supplies an associated one of said multipliers with a receive signal sample from a selectable tap. The summer sums the products to produce a filtered output signal. To reduce hardware requirements, coefficient multipliers may be multiplexed to a reduced set of taps, and the dynamic range of the coefficients may be increased by overlapping the sets for different multipliers. Methods of tap selection and coefficient adaptation are disclosed.