This paper presents a fully integrated 32-MHz relaxation oscillator (ROSC) capable of sub-1-µs start-up time operation for low-power intermittent VLSI systems. The proposed ROSC employs current mode architecture that is different from conventional voltage mode architecture. This enables compact and fast switching speed to be achieved. By designing transistor sizes equally between one in a bias circuit and another in a voltage to current converter, the effect of process variation can be minimized. A prototype chip in a 0.18-µm CMOS demonstrated that the ROSC generates a stable clock frequency of 32.6 MHz within 1-µs start-up time. Measured line regulation and temperature coefficient were ±0.69% and ±0.38%, respectively.

CMOS SoCs can reduce power consumption while maintaining performance by adopting voltage scaling (VS) technologies. The operating speed of the level converter (LC) strongly affects the effectiveness of VS technologies. However, PVT variations can cause serious problems to the LC, because the state-of-the-art LC designs do not give enough attention to this issue. In this work, we proposed to analyze the impact of PVT variations on the performance of the LC using a previously developed heuristic sizing methodology. Based on the evaluation results from different operating corners with different offset voltages and temperatures, we proposed a variation-tolerant LC that achieves both high performance and low energy with a high tolerability for PVT variations.