A Selection Method of Ring Oscillators for An On-Chip Digital Temperature And Voltage Sensor

An on-chip digital sensor using three types of ring oscillators (ROs: Ring Oscillators) has been proposed to measure temperature and voltage of a VLSI. Each RO has inherent frequency characteristics with respect to temperature and voltage, which differ from those of the other two ROs. Measurement accuracy of the sensor depends on the combination of the ROs. This paper proposes a RO-selection method for the sensor with high accuracy. The proposed method takes particular note of temperature or voltage sensitivity as well as linearity of the RO characteristics. Evaluation experiments with SPICE simulation in 65 nm CMOS technology show that the temperature and voltage accuracies of the sensor are 2.744 °C and 3.825 mV, respectively, and the selected combination was a nearly optimal from a menu of many different ROs.