Digital Bandlimiting Filters for PCM Transmission Systems

Bandlimiting filtering is required at the input to p.c.m. transmission and switching systems to prevent aliasing. The required filtering can be performed by a combination of analog and digital filters or by analog filters alone. This paper discusses a combination of a simple analog filter and digital filter suitable for Large Scale Integration. Both recursive and transversal digital filters are considered each in a variety of realizations. The realizations include two filters which exploit the companded nature of the p.c.m. code by using logarithmic signal processing to simplify multiplication. Comparisons are made between the realizations and the most suitable types for Large Scale Integration are found to be a recursive look-up table filter and a transversal logarithmic filter.