A 0.9V 2MHz 6.4x-Slope-Boosted Quadrature-Phase Relaxation Oscillator with 164.2dBc/Hz FoM and 62.5ppm Period Jitter in 0.18μm CMOS

Abstract

As a low-cost, small-sized alternative to crystal oscillators, RC oscillators have emerged and are used for on-chip reference clocks [1-3] and time-based sensor nodes [4]. Since these types of oscillators operate with the time period defined by an RC time constant, it is inherently advantageous in frequency stability, energy efficiency, and period jitter. These oscillators utilize a predefined reference voltage level to convert the RC charging/discharging voltage waveform into its output time-domain clock. in this process, any added delay causes frequency instability, and circuit voltage noises are converted into the period jitter. DLL-based [1] and FLLbased [2-3] structures suppress this delay using their loop dynamics, but their low-power timing-detection circuits lead to increase voltage noise. The swing-boosted technique [3-5] can improve this period jitter performance by reducing the voltage-noise-to-jitter conversion ratio. However, the maximum swing of these structures is limited by supply rail and high-voltage stress to transistor gates. To overcome these limits, this paper presents a quadrature-phase swing-boosted RC oscillator consisting of multiple inter-operating RC oscillator cells. The proposed quadrature RC oscillator achieves an excellent period jitter performance of 62. 5ppm and the best-ever-reported FoM of 164. 2dBc/Hz, which is 2dB higher than the state-of-the-art. This concept can be extended to an N-phase swing-boosting technique to manipulate the RC charging/discharging waveform by adjusting N.