GB1161342A - Correction of Distortion Effects in Transversal Equalisers - Google Patents

Abstract

1,161,342. Transversal equalizers. WESTERN ELECTRIC CO. Inc. 25 Aug., 1966 [27 Aug., 1965], No. 38178/66. Heading H4R. The adaptive transversal equalizer of Specification 1,105,959 is modified to operate on multi-level signals where each data symbol has a number of permissible amplitude levels. In the modified apparatus, Fig. 1, the output of the transversal equalizer is applied from summer 16 to the sampler 17 which, under the control of clock 25, samples the transmitted data symbols at the appropriate time. The sampled symbol value is then passed to a multi-level slicer which converts the amplitude into a digital signal according to the reflected binary Gray code by operating on the analogue signal with a multi-level slicer, as shown in Fig. 3, which successively slices the input signal at zero level and full wave rectifies the signal before applying it to the succeeding slicer. The rectifier folds the signal about zero level and the successive slicers provide the Gray coded binary output in parallel form. One stage of rectification and slicing is provided in excess of that required for recovering the signal content of the sample and this additional digital signal, the (n + 1)<SP>th</SP> slicer output, is fed as an indication of the amplitude of the error over line 21. The actual polarity of the error is not defined by the n + 1 slicer output but is dependent on the preceding slicer outputs, lead 33 therefore provides an indication of the polarity of the digit supplied over lead 21, the Exclusive- or gate 27 then provides a signal to the delay 28 which indicates the actual polarity of the error. The remainder of the system is similar to that described in Specification 1,105,959 except that reversible counters 32 are provided in place of the low-pass filters and slicers of the previous application. The reversible counter is similar to an integrator with a long time constant in that the error signal, applied to the " EXCLUSIVE- OR " gates 31 together with the main interference component from the shift register stage 30 causes an increase, or a decrease, in the count of the appropriate counter 32. When the counter reaches a predetermined count the respective attenuator counter 15 has its count increased or decreased by one, to adjust the attenuator on the tap appropriately, and the reversible counter 32 is reset to zero.