GB1459465A - Equalizer - Google Patents

Abstract

1459465 Active filters; adaptive equalizers INTERNATIONAL BUSINESS MACHINES CORP 13 June 1974 [12 July 1973 (2)] 26231/74 Headings H3U and H4R An equalizer for equalizing an input signal r(t) comprises two filters having impulse responses h 1 (t), h 2 (t), a Hilbert transformer having an impulse response g(t) and a summing circuit arranged to give two quadrature outputs y(t) and y(t) where In a first embodiment, Fig. 4, the input signal is fed to a first delay 10 and via a Hilbert transformer 9 to a second delay 13, the inputs to the delays being sampled at a rate 1/T. The outputs from tappings along the delays are weighted by four sets of weighting coefficients M<SP>1</SP> 0 ... M<SP>1</SP> 2N , M<SP>2</SP> 0 ...M<SP>2</SP> 2N , M<SP>3</SP> 0 ... M<SP>3</SP> 2N , M<SP>4</SP> 0 ... M<SP>4</SP> 2N the outputs from which are summed in four adders 11, 12, 14, 15. The outputs from 11, 14 are then differenced to provide the output y(t) and the outputs from 12, 15 are summed to provide the output #y(t). In a second embodiment, Fig. 5 (not shown) the number of multipliers is reduced but the number of delay tappings and the sampling rate is increased. Only one set of outputs is taken from each delay, and the #y(t) output is derived from the y(t) output by means of a second Hilbert transformer (24). In a third embodiment, Fig. 8, the input is fed in parallel to the two filters (which may share a common delay) and their outputs are applied to respective Hilbert transformers 42, 43. The y(t) output is then formed by differencing the output from one filter with the Hilbert transformed output from the other in circuit 44, and the #y(t) output is formed by adding the other output to the transformed output from the first in circuit 45. The filters may be made adaptive by feeding the y(t) and #y(t) signals to error detecting circuits which produce control signals for adjusting the multiplication coefficients of the filters, Figs. 6, 9 (not shown).