On-Chip Temperature and Process Variation Sensing using a Reconfigurable Ring Oscillator

This paper proposes a temperature monitoring scheme using a reconfigurable ring oscillator that has been proposed to estimate process variation. New circuit configurations, whose delay characteristics are sensitive to leakage current, are proposed to exploit the exponential dependence of the leakage current to temperature. Based on transistorlevel simulation assuming a 65 nm process technology, the oscillation frequency of the proposed circuit topology shows the temperature sensitivity of 5.0 %/degrees C at 20 degrees C and 2.9 %/ degrees C at 80 degrees C with low voltage sensitivity of 0.28 degrees C/10 mV at 25 degrees C and a supply voltage of 0.9 V. Estimation error of a 65 nm test chip ranges from -0.6 degrees C to 0.4 degrees C after two-point calibration. We also proposed a method to estimate the process variation and the temperature at the same time.