Digital automatic line equalizer with means for controlling tap gains of transversal filter based on mean power of output from the filter

DETAILED DESCRIPTION It is an object of the present invention to provide a digital automatic line equalizer which can readily effect line equalization without use of the decided signal.
As mentioned in the preamble, a digital automatic line equalizer is used in a receiving side of a digital signal transmitted through a transmission line in a digital communication system, and comprises a transversal filter responsive to the digital signal for producing a filter output of sampled pulses.
The transversal filter has a plurality of tap gains controlled by control means so as to produce an equalized signal as the filter output.
According to the present invention, the digital automatic line equalizer comprises first multiplying means coupled to the transversal filter and responsive to a current one of the filter output for squaring the current filter output to produce a first multiplied signal, means coupled to the transversal filter for temporarily holding the filter output as a held signal, second multiplying means coupled to the transversal filter and the holding means and responsive to the current filter output for multiplying the held signal and the current filter output to produce a second multiplied signal, calculating means coupled to the first and the second multiplying means for calculating from the first and the second multiplied signals a mean power of sum of the first multiplied signal and the second multiplied signal weighed by weight to produce a mean power signal, and the control means coupled to the calculating means and responsive to the mean power signal for determining a set of values of the tap gains as a set of determined values on the base of the mean power signal to control the tap gains to be the set of determined values so that the transversal filter produces the equalized signal with the mean power being equal to a predetermined value.
In a digital communication system using a partial response code signal as the digital signal, the digital automatic equalizer further comprises a partial response filter coupled with an input side of the transversal filter for filtering the digital signal to apply the partial response code signal to the transversal filter