Efficient power reduction techniques for time multiplexed address buses

Abstract

We address the problem of reducing power dissipation on the time multiplexed address buses employed by contemporary DRAMs in SOC designs. We propose address encoding techniques to reduce the transition activity on the time-multiplexed address buses and hence reduce power dissipation. The reduction in transition activity is achieved by exploiting the principle of locality in address streams in addition to its sequential nature. We consider a realistic processor-memory architecture and apply the proposed techniques on the address streams derived from time-multiplexed DRAM addresses. Although the techniques by themselves are not new, we show that a judicious combination of the existing techniques yield significant gains in power reductions. Experiments on SPEC95 benchmark programs show that our encoding techniques yield as much as 82% in transition activity compared to binary encoding. We show that these reductions amount to as much 60% reduction in the off-chip address bus power. Also since the encoder/decoder add some power overhead, we calculate the minimum off-chip bus capacitance to the internal node capacitance ratio needed to achieve power reductions.