Abstract:
In this brief, generalized Phase Sequence and multi-band Frequency Switching mechanisms in Multi-Loop Separately-Driven Skew-Based Ring Oscillators (MSSROs) are presented for the first time. Compared to inverter-based Conventional Ring Oscillators (CROs), MSSROs can generate high-frequency multi-phase outputs with lower noise for a fixed power budget. However, delay cell connection schemes and resulting phase sequences for achieving lower frequencies have never been explored in MSSROs, limiting their use in sampling applications. This brief provides a detailed design methodology for producing multi-phase MSSRO outputs in a wide frequency range at pre-defined sequences. These guidelines are validated with post-layout simulations in 180/65nm CMOS for MSSROs oscillating at frequencies equivalent to 3, 5, 7, and 9-stage CROs. Finally, comparisons for frequency, FoM, and PVT sensitivity between the proposed topologies and CROs pose their usefulness as a viable clocking alternative.