A global process variability monitor using sensitivity-enhanced ring oscillators and modified iterative method

This paper proposes a process variation sensor for monitoring random variations in the threshold voltage. The proposed circuit monitors the pmos and nmos process variabilities independently by using two types of the inverter-based ring oscillators (RO). The nmos (pmos) type ring oscillator is designed to improve its sensitivity to the process variation of nmos (pmos) transistors. In addition, a modified iterative estimation method is used to reduce the nonlinearity of the estimated parameter and enhance the reliability of the detection. All work is in TSMC-180nm process.