All-Digital ON-Chip Process Sensor Using Ratioed Inverter-Based Ring Oscillator

摘要

In this paper, an all-digital ON-chip process sensor using a ratioed inverter-based ring oscillator is proposed. Two types of the ratioed inverter-based ring oscillators, nMOS and pMOS types, are proposed to sense process variation. The nMOS (pMOS)-type ring oscillator is designed to improve its sensitivity to the process variation in the nMOS (pMOS) transistors using the ratioed inverter that consists of only nMOS (pMOS) transistors. A compact process sensor can be realized using only these two types of ring oscillators. For a suitable ON-chip implementation, the output of the proposed process sensor is provided with a digital code. The proposed process sensor is fabricated using a 0.13-μm CMOS technology. Measurement results from 30 fabricated chips show that all chips have the same process corner. To verify whether the proposed sensor can properly sense all the process corners, the threshold voltage of the fabricated chips is shifted by body biasing. The verification results show that the measured code error compared with the postlayout simulation is less than 2.92%.