Patent ID: 7133465

Claim:
A precoding circuit for connecting to a communication channel ( 21 , 51 , 61 , 71 ) at a transmit end ( 22 ) thereof for minimising distortion of an input signal of range +M/2 to −M/2 being transmitted through the communication channel ( 21 , 51 , 61 , 71 ) between the transmit end ( 22 ) and a receive end ( 23 ) of the communication channel ( 21 , 51 , 61 , 71 ), whereby the distortion is due to a transfer function of the communication channel ( 21 , 51 , 61 , 71 ), the precoding circuit ( 20 , 50 , 60 , 70 ) comprising: a feedback circuit ( 27 ) connected to the transmit end of the communication channel ( 21 , 51 , 61 , 71 ), and having a transfer function which is the inverse of a feedforward part of the transfer function of the communication channel, a feedforward circuit ( 31 ) connected to the transmit end of the communication channel ( 21 , 51 , 61 , 71 ), and having a transfer function which is the inverse of a feedback part of the transfer function of the communication channel ( 21 , 51 , 61 , 71 ,), a first circuit means ( 35 ) for subtracting a feedback signal of the feedback circuit ( 27 ) from a feedforward signal of the feedforward circuit ( 31 ), and for outputting a difference signal, which is the difference of the feedback and feedforward signals, a second circuit means ( 39 ) for outputting a control signal of value kM derived from the difference signal and the input signal, where k is an integer which is a positive, negative or zero, and for selecting the value of k such that when the control signal is subtracted from the input signal at the transmit end ( 22 ) the value of the signal being outputted from the precoding circuit to the communication channel ( 21 , 51 , 61 , 71 ) is minimised, and a third circuit means ( 40 ) for subtracting the control signal from the input signal upstream of the feedback and feedforward circuits ( 27 , 31 ).