All-Digital Circuit-Level Dynamic Variation Monitor for Silicon Debug and Adaptive Clock Control

A 45 nm microprocessor integrates an all-digital dynamic variation monitor (DVM) to continuously measure the impact of dynamic parameter variations on circuit-level performance to enhance silicon debug and adaptive clock control. The DVM consists of a tunable replica circuit, a time-to-digital converter, and multiplexers to measure circuit delay or frequency changes with less than a 1% measured resolution error while capturing clock-to-data correlations. In validating the DVM with microprocessor maximum clock frequency (FMAX) measurements, an on-die noise injector circuit induces a supply voltage (VCC) droop at a particular cycle in the test program. The FMAX measurement is then repeated for over a thousand iterations while shifting the droop placement to a different cycle per iteration. Silicon measurements demonstrate the DVM capability of tracking the worst case FMAX reduction to within 1% for a wide range of VCC droop profiles. Furthermore, silicon measurements reveal that FMAX is highly sensitive to the placement and magnitude of a high-frequency VCC droop during program execution, thus highlighting the value of the DVM for silicon debug. In addition, the DVM interfaces with an adaptive clock control circuit to dynamically adjust the clock frequency by changing the divide ratio in the phase-locked loop in response to persistent variations, enabling the microprocessor to adapt to the operating environment for maximum efficiency.