SCALLER: Standard Cell Assembled and Local Layout Effect-Based Ring Oscillators

This letter presents a technique that enables very fine tunability of the frequency of ring oscillators (ROs). Multiple ROs with different numbers of tunable elements were designed and fabricated in a 65-nm CMOS technology. A tunable element consists of two inverters under different local layout effects (LLEs) and a multiplexer. LLEs impact the transient response of inverters deterministically and allow to establish a fine tunable mechanism even in the presence of large process variation. The entire RO is digital and its layout is standard-cell compatible. We demonstrate the tunability of multistage ROs with post-silicon measurements of oscillation frequencies in the range of 80–900 MHz and tuning steps of 90 kHz.