Credo Technology Group Limited

Marvell International Limited

Junqing Phil Sun

Haoli Qian

Kok-Wui Cheong

Shaoan Dai

Zhenzhong Gu

Fang Cai

Yu Liao

Xing Wu

Danjin Wu

William Lo

Tianchen Luo

Meng Zeng

Xiong Fang

Baohua Chen

Hung Phi Nguyen

Yasuo Hidaka

Venugopal Balasubramonian

Tao Yu

Arshan Aga

Lawrence Chi Fung Cheng

Hung-Yi Chen

James Bartenslager

Don Barnetson

Sanket Shah

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.

PCIe retimer with reduced power low latency mode

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.

Dynamic timing loop gain to compensate phase interpolation nonlinearities

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.

Receivers and method with fast sampling phase and frequency acquisition

An illustrative integrated receiver circuit includes: a sampling element that produces a digital receive signal by sampling an analog receive signal in accordance with a sampling signal; a timing error estimator that produces a timing error signal indicating an estimated timing error of the sampling signal relative to the analog receive signal; a first feedback path that controls a sampling signal phase to optimize the timing error signal, the first feedback path having an associated loop delay that causes a residual phase error; and a loop-delay cancellation circuit that buffers the sampling signal phase to reduce the residual phase error.

Clock recovery with loop delay cancellation

Receivers, methods, and cores, can provide decision feedback equalization with efficient burst error correction. An illustrative receiver includes: a decision feedback equalizer that derives symbol decisions from a receive signal; a subtractor that determines an equalization error for each said symbol decision; and a post-processor that operates on the symbol decisions and equalization error to detect and correct symbol decision errors. An illustrative receiving method includes: using a decision feedback equalizer to derive symbol decisions from a filtered receive signal; determining an equalization error for each said symbol decision; and processing the symbol decisions and equalization error to detect and correct symbol decision errors. An illustrative semiconductor intellectual property core generates circuitry for implementing a receiving and method as described above.

Decision feedback equalization with efficient burst error correction

Receivers and receiving methods having maximum likelihood sequence detection with pseudo partial response equalization. One illustrative receiver includes: a feedforward equalizer that produces an equalized receive signal by diminishing a receive signal's intersymbol interference; a decision element that derives initial symbol decisions from samples of the equalized receive signal; and a filter that applies a partial response to the equalized receive signal or to an equalization error signal to produce input for a maximum likelihood sequence detector (MLSD). The MLSD may be a reduced complexity detector that derives a final sequence of symbol decisions by evaluating state metrics only for each initial symbol decision and its competing symbol decision.

Receiver using pseudo partial response maximum likelihood sequence detection

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. The host device IC includes: a parallel-to-serial converter that produces a digital symbol stream; a digital to analog converter that supplies an analog signal to the short-reach link; and a pre-equalizer coupling the parallel-to-serial converter to the digital-to-analog converter, the pre-equalizer filtering the digital symbol stream to at least partly compensate for a channel response of a combined channel that includes the short-reach link, the CTLE, the driver, and the photoemitter.

Onboard/co-packaged optics with transmit-side equalization

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.

Retimer training during link speed negotiation and link training

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.

Equalizer training during link speed negotiation

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. In an illustrative receiver, the filter is coupled to a decision element that derives a sequence of symbol decisions.

Digital filtering using combined approximate summation of partial products

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.

Parallel channel skew for enhanced error correction

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.

Systems and methods for testing jitter tolerance

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.

Clock recovery using between-interval timing error estimation

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.

Digital equalizer with overlappable filter taps

An illustrative integrated circuit and method providing on-chip jitter evaluation. One illustrative integrated circuit embodiment includes a digital receiver having a timing recovery circuit that determines a phase offset signal from estimated timing errors of previous sampling instants; and an on-chip memory that captures the phase offset signal, the on-chip memory being coupled to a processor that derives one or more jitter measurements from the phase offset signal. For initial calibration, the processor may configure the receiver for loop back operation, and thereafter the calibration values may enable evaluation of remote transmitter clock jitter.

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Cupertino, CA, United States of America

Junqing Phil Sun