Deterministic clock gating for low power VLSI design

The demand for power-sensitive design has grown significantly in recent years due to tremendous growth in portable applications. Consequently, the need for power efficient design techniques has grown considerably. Several efficient design techniques have been proposed to reduce both dynamic as well as static power in state-of-the-art VLSI circuit applications. With the scaling of technology and the need for higher performance and more functionality, power dissipation is becoming a major bottleneck for microprocessor designs. Clock power is significant in high-performance processors. Deterministic Clock Gating (DCG) technique effectively reduces the clock power. DCG is based on the key observation that for many of the pipelined stages of a modern processor, the circuit block usage in the near future is known a few cycles ahead of time. DCG exploits this advance knowledge to clock-gate the unused blocks. Because individual circuit usage varies within and across applications, not all the circuits are used all the time, giving rise to power reduction opportunity. By ANDing the clock with a gate-control signal, clock-gating essentially disables the clock to a circuit whenever the circuit is not used, avoiding power dissipation due to unnecessary charging and discharging of the unused circuits. Results show that DCG is very effective in reducing clock power. 25 – 33 % power consumption is reduced by using this method. As high-performance processor pipelines get deeper and power becomes a more critical factor, DCG’s effectiveness and simplicity will continue to be important.