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Time Multiplexing of Delta Transversal Filter

IP.com Disclosure Number: IPCOM000076347D
Original Publication Date: 1972-Feb-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Falcoz, AM: AUTHOR [+2]

Abstract

Time Multiplexing of filter taps permits buildup of a delta transversal filter without the need for any multiplier or adder, if the coefficients of the filter happen to be integers. For instance, such a technique may be used to synthesize a cosine filter, since its coefficients are +1, -1 and +1. The transfer function of such a filter, which for instance rejects 600 Hz and 3000 Hz, is equal to H{omega} = e/-j omega tau/ (-1+2cos omega tau) where tau = 1/3600.

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Time Multiplexing of Delta Transversal Filter

Time Multiplexing of filter taps permits buildup of a delta transversal filter without the need for any multiplier or adder, if the coefficients of the filter happen to be integers. For instance, such a technique may be used to synthesize a cosine filter, since its coefficients are +1, -1 and +1. The transfer function of such a filter, which for instance rejects 600 Hz and 3000 Hz, is equal to H{omega} = e/-j omega tau/ (-1+2cos omega tau) where tau = 1/3600.

As shown in Fig. 1, the input signal is delta encoded first. The delay line is replaced by two shift registers SR1 and SR2, each 40 bits long, so that the elementary delay tau is equal to 1/3600, since the delta encoder operates at 144 KHz. A third of the sampling period is assigned to each of the three filter taps, by gating the signal which come from the input and output of SR1 and SR2. The signals which control the opening of AND gates A1, A2 and A3 are time delayed by theta = T/3, where T is the sampling period of the delta encoder. Since the second coefficient is equal to -1, an inverter 1 has been inserted between the output of SR1 and gate A2. The digital signals coming from gates A1, A2 and A3, are summed in an OR gate, and then delta decoded.

When synthesizing filters using this technique, errors occur due to the fact that the contributions of the various filter taps are not summed up simultaneously as they should be.

In this case the transfer function w...