On-chip dual-ring-oscillator-based random-fluctuation-measurement method for detecting lowest voltage in adaptive voltage scaling systems

A fully digital 40-nm-CMOS-based sensor using dual-ring oscillators for detecting random device fluctuation was developed. The sensor detects threshold voltage fluctuation of a MOSFET with precision of 1 mV with ±10% accuracy by calculating the squared sum of the differences in frequencies of the two ring oscillators. This sensing method does not require reference signals and achieves a smaller layout area than that of a conventional analog sensor.