The superpositioning truncated response filter: a new filter structure for baseband or pre-modulation filtering

A novel digital filter structure is used to implement a digital finite impulse response (FIR) filter when the input is constrained to a two level non return to zero (NRZ) binary signal such as is common in digital communications systems such as digital cellular telephones. Depending on the specified filter, the structure superposes the impulse or rectangular pulse response of the filter for each bit in the NRZ signal. The superpositioning filter can be designed in either a parallel or serial configuration. The serial configuration results in the smallest hardware usage and is the preferred way of implementing the filter for minimum hardware low-power applications. A filter designed with the serial configuration will require only one summing point and no coefficient multipliers. Because there are no multipliers, this filter structure becomes very attractive for the implementation of FIR filters, when the input is a two level NRZ signal