Design of digital filters for an all digital frequency division multiplex-time division multiplex translator

Abstract

In keeping with the trend toward greater use of digital circuits for signal processing, a project was undertaken to realize an important telecommunication function using as great a proportion of digital hardware as possible. The function in question concerns the translation between the traditional analog frequency division multiplex (FDM) format and the newer digital time division multiplex (TDM) format. This paper describes the design of the digital filters for such a translating device and discusses some of the problems encountered in the hardware realization of these filters. In particular, a concise relationship is developed between the amount of digital filter hardware required and the sample rate, clock (bit) rate, data word length, number of channels being multiplexed, and order of the filter. This relationship is then used as the basis of comparison between various methods of accomplishing the desired function.