Embedded power supply for low-power DSP

The use of dynamically adjustable power supplies as a method to lower power dissipation in DSP is analyzed. Power can be reduced substantially without sacrificing performance in fixed-throughput applications by slowing the clock and lowering supply voltage instead of idling when computational workload varies. This can yield a typical power savings of 30–50%. If latency can be tolerated, buffering data and averaging processing rate can yield power reductions of an order of magnitude in some applications. Continuous variation of the supply voltage can be approximated by very crude quantization and dithering: a fourlevel controller is sufficient to get within a few percent of the optimal power savings. Significant savings are possible only if the voltage can be changed on the same time scale as the variations in workload. A chip has been fabricated and tested to verify the closed-loop functionality of a variable voltage system. The controller takes only 0.4 mm and draws a maximum of 1 mW at 2 V with a 40 MHz clock. The control framework developed is applicable to generic DSP applications.