Design of 4-Stage Single-Ended Ring Oscillators with Quadrature-Phase Output

This letter presents a study of quadrature voltage controlled oscillators (V COs) and investigates the performance of existing architectures. Traditionally, even-phased ring oscillators (ROs) are implemented with differential inverters/amplifiers which require a starter circuit, and experiences latch-up and tail current issues. This article proposes five new single-ended delay cells that employ negative-skewed delay scheme to construct quadrature-phase oscillators. The proposed circuits are compared with reported topologies in literature in terms of essential characteristics such as maximum frequency, phase-noise, tuning range, power consumption, voltage swing, power-delay product (PDP), and phase-noise bandwidth product (PNBP). Extensive simulations demonstrate the possibility of novel RO architectures for even-phase outputs with high frequency and wide tuning range. Proposed Circuit-l with the regulation of supply voltage achieves the highest operating point and frequency bandwidth of 14.36 GHz and 10.70 GHz, respectively. Meanwhile, proposed circuits 4 and 5 provide 60% and 26% improvements in terms of PDP and PNBP, respectively, from existing circuits and considered best alternatives with separate frequency tuning control. The results of this study provide valuable insights for designers seeking to incorporate quadrature RO's in their integrated circuits.