A 0.021mm2 PVT-Aware Digital-Flow-Compatible Adaptive Back-Biasing Regulator with Scalable Drivers Achieving 450% Frequency Boosting and 30% Power Reduction in 22nm FDSOI Technology

Abstract

A near-threshold power supply aims to operate at the minimal energy point but suffers from high-sensitivity to process, temperature and voltage variations. Adaptive voltage scaling (AVS) is a well-known strategy to adapt the power supply to die-to-die and temperature variations [1]. However, AVS needs dedicated power supplies with nonnegligible overheads, e.g. extra die area, lower power converter efficiency, and with granularity limitations or complex fine-grain integration in the power mesh. SOI-based technologies offer unique features by biasing the wells below the transistors to tune the threshold voltage ($\mathrm{V}_{\mathrm{T}\mathrm{H}}$). The well-known adaptive back-biasing (ABB) technique has already shown its capability to reduce power consumption or/and maintain operating frequency by compensating $\mathrm{V}_{\mathrm{T}\mathrm{H}}$ variability according to process corners and temperature [1–5]. However, previously published ABB architectures provide a limited overview on how to integrate the ABB seamlessly in the digital design flow with industrial-grade qualification. We propose a reusable ABB-IP for any biased digital load, from 0.4-100 mm2, with low area and power overhead, e.g. 1.2% @ 2mm2 and 0.4% @ 10mm2, respectively. We properly quantify the gain in a mass-production context with a large statistical scope analysis across 316 measured dies from different split-wafer lots and from -40 to 125°C with a representative load (a Cortex M4F). Thanks to 3V asymmetrical wells amplitude swing, our ABB-IP brings up to 30% power reduction by decreasing the minimal power supply byl00mV, while maintaining the target operating frequency (50 MHz) with a high yield. Distributed timing monitors (DTM) guarantee an accurate timing monitoring of the biased digital load, while scalable well drivers adjust to the biased well area, enabling the ABB-IP genericity.