The on-chip power supply noise sensor detects high frequency overshoots and undershoots of the power supply voltage. By creating two identical current sources and attaching a time constant circuit to only one, the high frequency transient behavior differs while the low frequency behavior is equivalent. By comparing these currents, the magnitude of very high frequency power supply noise cars be sensed and used to either set latches or add to a digital counter. This has the advantage of directly sensing the power supply noise in a matter that does not require calibration. Also, since the sensor requires only one power supply, it can he used anywhere on a chip. Finally, it filters out any lower frequency noise that is not interesting to the circuit designer and can he timed to detect down to whatever frequency is needed.