A Variation Aware Jitter Estimation Methodology in ROs Considering Over/Undershoots in NTV Regime

A time-domain jitter estimation methodology considering process-voltage-temperature (PVT) variations of the single-ended ring oscillator (SERO) at an early stage of design is presented for near-threshold voltage (NTV) regime where non-linearities dominates. For the first time, the model accounts for the jitter due to the over/undershoot region which is critical in the NTV regime. Further, the model uses effective drive current, $I_{eff}$ model. The $I_{eff}$ is obtained considering the regions of device operation, instead of using only saturation current for jitter calculation. A time-domain jitter model is developed by considering the change in transition threshold points (TTPs) whose relative values are supply independent and $I_{eff}$ of each region with the PVT variation, design parameters, and with the introduction of noise in the circuit. The model analyzes the effects of random (white noise) and deterministic (supply, substrate) noise in the NTV regime. This approach is physics/topology-based and is valid for different technologies. Post-layout simulations have been performed on parasitic extracted netlist using CADENCE and HSPICE in STM 65nm CMOS Process Design Kit (PDK) to validate the jitter model in the NTV regime.