GB1395944A - Adaptive equalizer - Google Patents

Abstract

1395944 Adaptive equalizers INTERNATIONAL BUSINESS MACHINES CORP 11 Aug 1972 [20 Aug 1971] 37526/72 Heading H4R An adaptive transversal equalizer, Fig. 1, has its attenuation coefficients C adjusted in response to an error signal e(t) derived from the equalizer output y(t). The equalizer output is sampled by a sampler S1 under the control of a clock generator Q whose frequency is adjusted in accordance with information associated with a given tap of the equalizer filter. As described, errors in sampling frequency cause the main sample to move from the reference tap position. shown at the centre of delay line L, and so the equalizer attenuation coefficient connected to the reference tap will reduce. The attenuation coefficeint is compared in a comparator P2 with a threshold level and the change in output will cause a latch T2 to change state causing a divider D to switch from one division ratio to a second division ratio. Divider D is connected to a high frequency oscillator Q to provide at the divider output the sampling clock frequency. The divider ratios are such that one of them gives an output signal slightly higher than nominal while the other gives an output slightly lower than nominal clock frequency. Latch T2 causes continual switching from one division ratio to the other so that the main peak of the response is located on the centre tap position, and the average sampling frequency is equal to the incoming signal clock frequency. In an alternative arrangement, Fig. 2 (not shown), the divider switching signal is derived from a correlator (CL) correlating the output signal of the equalizer with the signal at the centre, or reference tap of the equalizer, with the correlator output, after integration (at I) fed to a threshold device and latch &c. as in the embodiment of Fig. 1. (For Figure see next page.)