UC Davis

Power and thermal limits have become increasingly significant for integrated circuits as the scale of integration keeps growing. Ultra-Thin Body and Buried Oxide (UTBB) Fully Depleted Silicon-on-Insulator (FD-SOI) is a technology aimed at improving the device performance and power efficiency at the same time. A thin buried oxide (BOX) layer is introduced to not only lower the leakage currents, but also enable an strong back biasing (BB) voltage that is adjustable through front-side contacts. As a result, the threshold voltage is tunable to achieve high performance across a wide range of supply voltages. A 28 nm UTBB FD-SOI Low Threshold Voltage (LVT) technology from STMicroelectronics provides transistors that operate normally across a wide supply voltage range.

It is a common practice that digital circuits are throttled according to their real-time workload to conserve power and reduce heat generation. This is achieved by introducing a dynamic voltage and frequency scaling (DVFS) circuit which optimizes the supply voltage and clock frequency automatically.

In this thesis, the 28 nm UTBB FD-SOI technology is characterized through transistor-level circuit simulations. A DVFS controller design that supports two supply voltages and two back-bias voltages targeting the aforementioned technology to optimize circuit performance and reduce power consumption is proposed. Power gates are used to switch between voltages and shut down unused components. The DVFS controller suggests clock frequencies and voltages dynamically based on workload to maximize power efficiency without significantly sacrificing performance. Additionally, the controller’s output is manually configurable to accommodate user control. In a simulation conducted on inverter chains, BB provides as much as 17% reduction in propagation delay versus no BB at 1.0 V nominal supply voltage, and a maximum 56% reduction at 0.5 V. The DVFS design contributes to an average of 20.5% and a maximum of 56.3% reduction in total energy consumed in the simulated applications versus no DVFS while maintaining 96% of the throughput.