Credo Technology Group Limited

Fang Cai

Haoli Qian

Junqing Phil Sun

Junqing (Phil) Sun

Hung-Yi Chen

Tianchen Luo

Ashwin Upadhya

In-band communication methods and transceivers are provided to enable protocol-agnostic management channel. One illustrative in-band communications method includes: buffering an outbound data stream from a host-side receiver with a data stream buffer, the outbound data stream having a first bit rate; and providing a line-side data stream representing the outbound data stream with an additional word after every N words of the outbound data stream, the line-side data stream having a second bit rate derived from a fill level of the data stream buffer, the additional words including message words and idle words with adjacent message words potentially separated by a predetermined number of idle words.

SerDes method and device having a protocol-agnostic in-band management channel

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

Accordingly, there are disclosed herein receivers and receiving methods that provide a graceful transition from PAM2 to PAM4 signaling. One illustrative method includes: negotiating a link speed having PAM4 signaling; performing adaption of at least one gain or filter coefficient during PAM2 signaling; switching to PAM4 detection before receiving PAM4 signaling; disabling said adaptation before said switching to PAM4 detection; detecting PAM4 signaling using at least one statistic of detected PAM4 symbols; and enabling said adaptation after PAM4 signaling is detected. Another illustrative method includes: negotiating a link speed having PAM4 signaling; adapting at least one of gain and filter coefficients during PAM2 signaling; monitoring for a change in at least one signal characteristic while performing PAM2 detection; and transitioning to PAM4 detection after detecting said change.

Transitioning between signal constellations

Equalization methods and equalizers employing discrete-time filters are provided with dynamic perturbation effect based adaptation. Tap coefficient values may be individually perturbed during the equalization process and the effects on residual ISI monitored to estimate gradient components or rows of a difference matrix. The gradient or difference matrix components may be assembled and filtered to obtain components suitable for calculating tap coefficient updates with reduced adaptation noise. The dynamic perturbation effect based updates may be interpolated with precalculated perturbation effect based updates to enable faster convergence with better accommodation of analog component performance changes attributable to variations in process, supply voltage, and temperature.

Equalizer with perturbation effect based adaptation

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

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

Decision feedback equalizers and equalization methods may employ fractional tap unrolling and/or probability-based decision threshold placement. One illustrative fractional tap unrolling equalization method embodiment includes: tracking preceding symbol decisions; converting an equalized signal into tentative symbol decisions with a precompensation unit; and selecting from the tentative symbol decisions based on the preceding symbol decisions. The precompensation unit has a decision element for each combination of a first number of speculative preceding symbols, with comparators in each decision element using a first type of symbol decision threshold that accounts for trailing intersymbol interference from the corresponding combination, and with an additional comparator in at least one of the decision elements using a second type of symbol decision threshold that accounts for trailing intersymbol interference from a second number of speculative preceding symbols, the second number being greater than the first.

Decision feedback equalizer with fractional tap unrolling

Precompensator-based quantization techniques offer a way to reduce the complexity and power requirements of clock recovery modules while offering improved timing recovery performance relative to a bang-bang scheme operating in a lossy channel. One illustrative method embodiment includes: (a) obtaining a receive signal having a sequence of symbols from a symbol set, the receive signal exhibiting trailing intersymbol interference; (b) operating on the receive signal with a precompensation unit having a set of comparators to produce, for each sampling instant, a set of comparator results representing a quantized receive signal value, the set of comparators applying a set of threshold values that at least partly compensate for the trailing intersymbol interference; (c) deriving a symbol decision from each set of comparator results; (d) combining the symbol decisions with said quantized receive signal values to determine an estimated timing error for each sampling instant; and (e) filtering the estimated timing errors to generate a sampling clock.

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Milpitas, CA, United States of America

Fang Cai