Contents I. Introduction
With the increasing demands for the ultra-low-power Internet of Things (IoT) applications, an on-chip low-power clock generator is required to reduce the cost. Compared with LC and ring oscillators, relaxation oscillators (RC) are more attractive in the kilohertz-megahertz frequency range because of their smaller area and lower power consumption. However, they suffer from the poor frequency stability over process-voltage-temperature (PVT) variations and become worse with reduced power budget. To design a robust low-power clock over PVT variation is still a great challenge [1]-[9]. [1] eliminated the comparator offset by adding up two cycles, but the effect of path delay is ignored. [7] proposed a feedforward method to compensate the path delay, yet the period controller occupies additional area and the problem of the comparator offset still exists. [8] and [9] proposed switched-capacitor reference (SCR) to achieve low power consumption, the reference and supply voltage are strongly correlated which makes it vulnerable to supply and temperature variations. In this work, we propose a low-power RC oscillator with chopping for offset cancellation and via a replica path to extract the delay for path delay cancellation. Hence, a more robust clock signal is achieved against temperature and supply variations.
