Exploiting resonant behavior to reduce inductive noise

Inductive noise in high-performance microprocessors is a reliability issue caused by variations in processor current (di/dt) which are converted to supply-voltage glitches by impedances in the power-supply network. Inductive noise has been addressed by using decoupling capacitors to maintain low impedance in the power supply over a wide range of frequencies. However, even well-designed power supplies exhibit (a few) peaks of high impedance at resonant frequencies caused by RLC resonant loops. Previous architectural proposals adjust current variations by controlling instruction fetch and issue, trading off performance and energy for noise reduction. However, the proposals do not consider some conceptual issues and have implementation challenges. The issues include requiring fast response, responding to variations that do not threaten the noise margins, or responding to variations only at the resonant frequency while the range of high impedance extends to a resonance band around the resonant frequency. While previous schemes reduce the magnitude of variations, our proposal, called resonance tuning, changes the frequency of current variations away from the resonance band to a non-resonant frequency to be absorbed by the power supply. Because inductive noise is a resonance problem, resonance tuning reacts only to repeated variations in the resonance band, and not to isolated variations. Reacting after a few repetitions allows more time for the response and reduces unnecessary responses, decreasing performance and energy loss.