26.5 Adaptive clocking in the POWER9™ processor for voltage droop protection

Increasing transistor counts in modern processors can create instantaneous changes in current, driving nanosecond-speed supply voltage (V
_DD
) droops that require extra guardband for correct product operation. The POWER9 processor uses an adaptive clock strategy to reduce timing margin needed during power supply droop events by embedding analog voltage-droop monitors (VDMs) that direct a digital phase-locked loop (DPLL) to immediately reduce clock frequency in response.