Patent GB-1514829-A (GB)
Title: Transversal multi-tap equalizers
IPC: H04L25/03
Filed: 1975-08-18
Abstract: 1514829 Adaptive equalizers WESTERN ELECTRIC CO Inc 18 Aug 1975 [21 Aug 1974] 34257/75 Heading H4R In an arrangement for identifying from a plurality of data words the data word having the largest magnitude and storing the data words in address locations with the largest magnitude word at a predetermined location, particularly for locating the multiplier coefficients of a transversal equalizer in appropriate positions in a coefficient store, each data word of the plurality is fed sequentially into a second storage device and compared with a data word held in a first storage device by a comparator which causes that data word of largest magnitude to be transferred to, or held in, the first storage device. When all the data words have been compared, that data word having the largest magnitude is positioned in a selected one of the address locations. As described the arrangement is used in conjunction with a transversal equalizer of the type of Fig. 1 (not shown) which is described in Specification 1,493,466 in which during a start-up mode using a pseudorandom test sequence of length equal to the number of equalizer stages, as described in Specification 1,380,651, the maximum equalizer multiplier coefficient which has to be positioned at a reference equalizer tap. As described with respect to Fig. 2 the sets of multiplier coefficients for the inphase (I) and quadrature (Q) channels of the equalizer of Fig. 1 are derived in conventional manner on a test sequence and stored in the respective stores 19 and 20. It has been found that the positions of the maximum coefficients in the I and Q sets track each other closely enough and therefore the processing to find the largest magnitude coefficient occurs with the stores 19 and 20 connected in series to obtain the largest coefficient of both sets, which is positioned in a reference location and the other set takes up a corresponding position. Initially registers A 2  and A 4  are set to a + 0 position by initializers 21, 22, then the contents of A 2  and A 4  are transferred, via the make contacts of switches 67 and 68, to the respective registers A 3  and A 1 . The first coefficient C, and D, are fed to the stores A 2  and A 4 , and the full adders 73, 74 compare the contents of registers A 2  and A 4 , holding values C, and D 1 , with the contents of A 3  and A, respectively, holding the previous nominal maximum value, initially +0, while simultaneously transferring the contents of A 2  and A 4  i.e. C 1  and D 1 , to the respective registers A 3  and A 1  and transferring the contents of A 1  and A 3 , i.e. the previous maximum values to A 4  and A 2  respectively, and also into the respective coefficient stores, in the part of the store normally reserved for updating values which are not used during the maximum value placing operation. If the new values C 1  and D 1  are greater than the prior maximum values adders B 1  and B 2  produce a "1" which operates switches 69 and 70 to the break (or bar) position and the values stored in A, and A 3  i.e. D, and C, respectively are looped around and back into their existing locations A 1  and A 3 . If the prior maximum values are larger than the new values C, and D, switches 69 and 70 are operated to their make position (X) and the values stored in A 2  and A 4  i.e. the prior maximum values are transferred to registers A 3  and A 1  respectively. The process is repeated for each value in the stores 19 and 20, in each case the coefficients Cn and Dn in registers A 2  and A 4  being compared with the previously determined maximum value C max  and D max  held in the respective registers A 3  and A, and the maximum value of each comparison being fed to the respective registers A 3  and A 1 . Subsequently the links 55 and 56 are broken and the links 80 and 85 are made and the comparison process repeated in this condition in order to find the overall maximum tap co-efficient. Having found the overall maximum the process is stopped and then the tap coefficients are circulated at half speed in the stores 19 and 20 to bring the maximum value to the central, or other predetermined, location.