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All Digital Low Pass Filter and a Slicer

IP.com Disclosure Number: IPCOM000076314D
Original Publication Date: 1972-Feb-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Besseyre, JA: AUTHOR

Abstract

This is a transversal filter and slicer suitable for use in a modem receiver as shown in Fig. 1A. In such a receiver, time varying analog signal samples are digitally encoded 4 and applied to correlator 6) Now, the correlator output is manifest as a sequence of binary digits occurring at the same frequency rate. It is fed into the shift register 3, 5,-----15 of the transversal filter 8 in Fig. 1B. The shift register has a length of N bits; where N is an odd number. Each of the N bits is applied to the input of a majority logic gate 17. The logic gate output exhibits a binary out of a first kind, if N+1 over 2 out of N shift register positions contain binary values of the first kind. For example, if N=9, then the logic output is +1 if there are five or more inputs equal to +1.

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All Digital Low Pass Filter and a Slicer

This is a transversal filter and slicer suitable for use in a modem receiver as shown in Fig. 1A. In such a receiver, time varying analog signal samples are digitally encoded 4 and applied to correlator 6) Now, the correlator output is manifest as a sequence of binary digits occurring at the same frequency rate. It is fed into the shift register 3, 5,-----15 of the transversal filter 8 in Fig. 1B. The
shift register has a length of N bits; where N is an odd number. Each of the N bits is applied to the input of a majority logic gate 17. The logic gate output exhibits a binary out of a first kind, if N+1 over 2 out of N shift register positions contain binary values of the first kind. For example, if N=9, then the logic output is +1 if there are five or more inputs equal to +1.

This device can be decomposed into two parts: a linear part and a nonlinear part. The linear part is equivalent to a transversal filter with, in this case, weighting all 1's. The shape of the spectrum is given in Fig. 2. The nonlinear part is simply a threshold detector or a slicer 10.

It is possible to give a different weighting to the bits in the shift register. For example, with a 9-bit logic majority gate, it is possible to give weighting 0, 0, 1, 2, 3, 2, 1, 0, 0, by applying the same bit to 1, 2, 3 inputs of the logic majority gate 17 (Fig. 2). This leads to much better spectrum shaping, since a triangular window is better than a rectangular wind...