Synthesis of Low Power Folded Programmable Coefficient Fir Digital Filters

A novel low-power synthesis technique is presented for the design of folded or time-multiplexed programmable-coefficient FIR filters where storage area is traded-off for lowering power consumption. A systematic technique is developed for low power mapping of FIR filters to architectures with arbitrary number of multipliers and adders. Power consumed in multipliers is reduced by reducing switching activity at both the data-input as well as the coefficient input. In order to increase common inputs to multipliers the transpose-form representation of the FIR filter is used. As opposed to the direct-form the transpose-form representation exposes common data inputs of a filter in an explicit manner. Switching activity at the data-input is reduced by first unfolding the FIR filter and then mapping the words with same input signal to a multiplier unit. Within each multiplier unit the switching activity for the coefficient input is further reduced by using a traveling salesperson problem (TSP) formulation for finding a low power schedule. Unfolding leads to increase in memory requirements for the folded filter. The increase in memory requirements varies linearly with the unfolding factor. Depending on the memory modules employed there exists an optimum unfolding factor that results in minimum power consumption. The unfolding factor can also be restricted by area constraints due to the linear increase in memory requirements. Simulation results are obtained for folding 65 and 129 tap bandpass FIR filters. The average power consumed in a multiplier for a fixed number of hardware multipliers with varying unfolding factors is compared. It is observed that most of the gains due to unfolding are obtained for relatively small unfolding factors and therefore for relatively small memory area overhead. Depending on the unfolding factor employed the average power consumed in a multiplier is seen to reduce anywhere from 54.75% to 81.73% when transpose FIR filters are synthesized as opposed to synthesizing direct-form FIR filters with no unfolding.