Decision feedback adaptive equalizer acting on zero states following a non-zero state
AssigneeNorthern Telecom Limited
InventorEphraim Arnon
Life of this patent
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Abstract
In an adaptive equalizer of the decision feedback type for reducing intersymbol interference in subscriber loops of a telephone system, the corrected digital signal is applied to means for detecting the occurrence in the signal of a zero state following a non-zero state. When that occurs, a correlator samples the signal during the "zero" bit period and applies the sample to an integrator. The integrator output varies the coefficients of the feedback signal applied to the input means for addition to the incoming digital signal to provide the corrected signal. The equalizer may have several stages, each for detecting a "zero" state in a different bit period following the original pulse. Also the circuitry may be duplicated for each polarity if the input signal is bipolar.
Claims20
An adaptive equalizer for a digital communications system having decision means, for comparing a digital signal, in a bit period, with a threshold level and providing an output having either a non-zero or a zero state in dependence upon whether or not said signal exceeds the threshold, said equalizer comprising:
- (a) input means, for summing a digital input signal and a feedback signal to provide a corrected digital signal, said corrected digital signal being applied to said decision means;
- (b) sequence detection means for detecting the occurrence in said corrected signal of a sequence comprising a non-zero state in a first bit period and at least one zero state in a later bit period and providing a gating signal for each such sequence;
- (c) at least one feedback stage comprising:
- (i) correlator means responsive to said gating signal from said sequence detection means for sampling said corrected signal during a corresponding said later bit period;
- (ii) integrator means for integrating such corrected signal samples to provide a control signal, and (iii) feedback signal means responsive to said control signal for controlling said feedback signal so as to reduce the amplitude of said corrected signal during said later bit period.
A method of adaptively equalizing intersymbol interference in a digital communications system having decision means, for comparing a digital signal, in a bit period, with a threshold level and providing an output having either a non-zero or a zero state in dependence upon whether or not said signal exceeds the threshold, said method comprising:
- summing a digital input signal and a feedback signal to provide a corrected digital signal, said corrected digital signal being applied to said decision means;
- providing a gating signal indicative of the occurrence in said corrected signal of a sequence comprising a non-zero state in a first bit period and at least one zero state in later bit periods;
- in response to said gating signal, sampling said corrected signal during said later bit period;
- integrating such corrected signal samples to provide a control signal;
- and
- in response to said control signal controlling said feedback signal so as to reduce the amplitude of said corrected signal during said later bit period.
Dependencies are inferred from the claim text.