Jitter analysis and measurement in subthreshold source-coupled differential ring oscillators

The jitter and the phase noise of ring oscillators utilizing subthreshold source-coupled logic (STSCL) style are analyzed in this paper. Closed-form equations are derived to predict the jitter and phase noise caused by white and flicker noise. Measurement results of a test chip fabricated in a standard CMOS 90 nm technology are presented to validate these expressions. The performed analysis shows that jitter in STSCL-based ring oscillator is independent of technology parameters, as opposed to its CMOS counterparts that depend on supply voltage and parameters of technology. Based on measured results, noise on current control line can dominate the total jitter of the oscillator. Design guidelines are proposed to limit the jitter effect of ring oscillators using STSCL logic. The proposed STSCL-based ring oscillator achieves an average RMS jitter as low as 0.24 % of the oscillation period at a 1.08 MHz/μA energy efficiency, which demonstrates its suitability for ultra-low-power applications.