A simple hardware implementation of digital notch filters

Narrow band digital notch filters have their poles near the unit circle. As the sampling rate is increased, the poles move towards z = +1. Implementing such filters requires long registers to overcome the sensitivity and roundoff errors. A filter structure based on digital incremental computers is proposed, which has low sensitivity and roundoff errors, and simple hardware implementation. The filter structure can be directly used on differentially pulse-code modulated signals. Hard-ware multipliers are not required as the poles approach z = +1, and excellent results can be obtained using multipliers with very short word lengths, or with small size read-only memories.