Clock phase adaptation for precursor isi reduction

Abstract

Systems and methods of mitigating precursor ISIs for communication channels having time-variant precursor channel responses using digital circuit designs. A phase adaptation circuit is utilized in a receiver and configured to generate a phase control signal responsive to an input signal and based on the current precursor channel response. The phase control signal controls the phase shift of a recovered clock to a position where the precursor ISI at h(−1) is minimized. The phase control signal corresponds to a “feed-forward equalization (FFE) first tap weight” obtained via a digital least-mean-square (LMS) process.

Description

TECHNICAL FIELD[0001]The present disclosure relates generally to the field of communications, and, more specifically, to the field of signal processing in communications.BACKGROUND[0002]In telecommunication, high speed serial links (SerDes) transmit data over various physical media such as copper cables, backplanes, optical fibers, etc. High rate communication channels suffer many problems negatively affecting the integrity of the signals. A primary problem is intersymbol interferences (ISI), defined as a form of distortion of a signal in which one symbol interferes with other symbols in a similar effect as noise, thus making the communication less reliable. ISIs are usually caused by multipath propagation or the inherent non-linear frequency response of a channel whereby causing successive symbols to “blur” together.[0003]The presence of ISIs in the system introduces errors in the decision device at the receiver output. Therefore, in the design of the transmitting and receiving fil...

AI Technical Summary

Benefits of technology

[0006]The embodiments of the present disclosure provide systems and methods of mitigating precursor ISIs for communication channels having time-variant precursor channel responses using digital circuit designs. Embodiments of the present disclosure employ a phase adaptation circuit configured to generate a phase control signal responsive to an input signal and based on a current precursor channel response. The phase control signal is used to control the phase shift of a recovered clock to a position that the precursor ISI at h(−1) (which is usually the most significant) is minimized. In some embodiments, the phase control signal corresponds to a feed-forward equalization (FFE) first tap weight (C1) that is obtained via a digital least-mean-square (LMS) process. Thus, the precursor ISIs can be advantageously and effectively reduced using simple digital circuitry, rather than involving multiplication of analog signals as required in conventional FFEs.

Problems solved by technology

High rate communication channels suffer many problems negatively affecting the integrity of the signals.

A primary problem is intersymbol interferences (ISI), defined as a form of distortion of a signal in which one symbol interferes with other symbols in a similar effect as noise, thus making the communication less reliable.

The presence of ISIs in the system introduces errors in the decision device at the receiver output.

However, advancing the clock phase is only performed once and so it is not adapted to any variation of the precursor channel response over time.

Also, although the overall performance is improved, advancing the clock phase once causes some degradation of the received signal power of the main cursor and raises the level of the first tap weight of the decision in the DFE.

Generally speaking, conventional FFEs utilize multipliers for analog signals which make them difficult to implement.

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