Methods and systems to detect droop events on-chip, which may include a sensor circuit located adjacent to a voltage node to convert a corresponding voltage to a digital count or value indicative of the voltage. The sensor circuit may include an n-stage ring oscillator and an asynchronous counter. The sensor circuit may include circuitry to capture and convert a phase associated with a count to a binary fractional value to increase voltage resolution. Multiple counts associated with the node may be evaluated at the node to identify minimum and maximum counts and corresponding time stamps. More complex evaluation and control circuitry may be shared amongst a plurality of sensor circuits and may include circuitry to generate and compare counts to one or more variable thresholds, circuitry to average counts over time, and memory to store state values associated with the sensors.