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Decision feedback equalizer

  • US 5,268,930 A
  • Filed: 12/19/1991
  • Issued: 12/07/1993
  • Est. Priority Date: 12/19/1991
  • Status: Expired due to Term
First Claim
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1. An adaptive equalizer for compensating a digital signal for dynamic variations in the transfer function of a communication channel, said digital signal being transmitted via the communication channel to said equalizer, said equalizer comprising:

  • (A) first and second adaptive tapped delay lines each having an input and an output, the input of the first adaptive delay line for receiving the digital signal from the communication channel, the input of the second adaptive delay line for alternately receiving either a training signal or a decision result signal, the output of each adaptive delay line for producing an output signal which represents the product of the signal received at the respective input, delayed by a predetermined period which is a multiple a symbol period or of a fraction of the symbol period, multiplied by a preselected coefficient;

    (B) a first summer for adding the output signals from the first and second delay lines to produce a compensated digital signal;

    (C) decision means for receiving the compensated digital signal and responsively producing a decision result signal which represents an approximation of the digital signal transmitted by the transmitter;

    (D) a switch for alternately passing either the decision result signal or the training signal to an output node in response to a switch control signal;

    (E) a second summer for producing an error signal which represents the difference between the compensated digital signal and the signal present at the output node;

    (F) coefficient adjustment means for receiving the error signal and a convergence control signal and responsively adjusting the coefficients of said first and second adaptive delay line means;

    (G) an error detector for receiving the error signal and responsively producing an error decision signal which is indicative of whether the equalizer is accurately tracking changes in the communication channel'"'"'s characteristics; and

    (H) a controller for receiving the error decision signal and responsively producing said switch control signal, whereby during a data receiving mode of operation the switch passes the decision result signal to the output node and during training or retraining modes of operation the switch passes the training or retraining signal, respectively, to the output node.

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