A 1.6MHz Swing-Boosted Relaxation Oscillator with ±0.15%/V 23.4ppm/°C Frequency Inaccuracy using Voltage-to-Delay Feedback

This paper presents a relaxation oscillator for on-chip clock reference or sensor interface application. To improve the frequency stability over temperature and supply variations, a voltage-to-delay feedback is proposed to compensate the circuit delay variation. In addition, a switch-capacitor swing boosting (SCSB) circuit is proposed to enhance the output swing for phase noise reduction. Implemented in 0.18-μm CMOS process, the proposed oscillator shows a 1.6MHz output frequency, with low frequency inaccuracy of 23.4ppm/°C across 0°C-90°C and ±0.15%/V over 1.2V-1.52V. The measured phase noise is -118.6dBc/Hz at 100kHz offset, corresponding to 156dBc/Hz FOM. The oscillator consumes 51.4μW under 1.3V supply voltage.

I. Introduction

Fully integrated on-chip relaxation oscillator has attracted significant research interests in recent years attributed to its great potentials as on-chip clock reference or sensor interface for IoT and wearable healthcare device. It is area and cost efficient compared to the bulky off-chip crystal oscillator. It is also preferred over ring oscillator for its high frequency stability, control linearity and wide tuning range [1]. However, many issues remain to be addressed when designing high performance relaxation oscillator, such as frequency variation due to circuit noise, supply fluctuation and change in environment.