The conventional sleep transistor sizing schemes do not consider the resonant supply noise which represents the worst-case supply disturbance. This paper investigates the impact of sleep transistor sizing on different on-chip noise components and shows that, contrary to the conventional wisdom, a larger sleep transistor is not always favored in term of performance when the resonant supply noise is taken into account. To minimize the worst-case supply noise, an optimal sizing scheme using an explicit noise and impedance model is developed and verified by benchmark circuits. Employing the proposed technique results in a reduction of the worst-case noise by 19%, as well as a saving of standby leakage and area overhead by 60% in comparison with conventional sizing scheme. In order to deal with the sporadic nature of the resonant, we propose an adaptive sleep transistor circuit which adjusts the size of sleep transistor on the fly to remove the DC noise penalty of the fixed sizing scheme. Simulation results on 32-nm CMOS technology are used to demonstrate the functionality and effectiveness of the proposed adaptive sizing circuits.

Subthreshold circuit designs have been demonstrated to be a successful alternative when ultra-low power consumption is paramount. However, the characteristics of MOS transistors in the subthreshold region are significantly different from those in strong inversion. This presents new challenges in design optimization, particularly in complex gates with stacks of transistors. In this paper, we present a framework for choosing the optimal transistor stack sizing factors in terms of current drivability for subthreshold designs. We derive a closed-form solution for the correct sizing of transistors in a stack, both in relation to other transistors in the stack, and to a single device with equivalent current drivability. Simulation results show that our framework provides a performance benefit ranging up to more than 10% in certain critical paths.

A fact that has generally been unnoticed is that sleep transistors for leakage reduction can significantly damp the resonant supply noise due to their series resistance. This paper describes an optimal sleep transistor sizing method considering the dominant resonant supply noise. We show that a smaller sleep transistor can offer a smaller worst case supply noise due to the increased damping. We also propose an adaptive sleep transistor technique which automatically dampens the resonant noise only when it is detected. Simulations in 32nm CMOS show that the resonant noise is reduced by 32% using the proposed technique.

The impact of the reverse short-channel effect (RSCE) on device current is stronger in the subthreshold region due to reduced drain-induced barrier lowering (DIBL) and the exponential dependency of current on threshold voltage. This paper describes a device-size optimization method for subthreshold circuits utilizing RSCE to achieve high drive current, low device capacitance, less sensitivity to random dopant fluctuations, better subthreshold swing, and improved energy dissipation. Simulation results using ISCAS benchmark circuits show that the critical path delay, power consumption, and energy consumption can be improved by up to 10.4%, 34.4%, and 41.2%, respectively.

Subthreshold circuit designs have been demonstrated to be a successful alternative when ultra-low power consumption is paramount. However, the characteristics of MOS transistors in the subthreshold regime are significantly different from those in strong-inversion. This presents new challenges in design optimization, particularly in complex gates with stacks of transistors. In this paper, we demonstrate a new optimal sizing scheme for subthreshold designs which takes these issues into account. We derive a closed-form solution for the correct sizing of transistors in a stack, both in relation to other transistors in the stack, and to a single transistor with equivalent current drivability. Experimental results show that our framework provides a performance improvement of up to 13.5% over the conventional logical effort method on ISCAS benchmark circuits, while one component circuit demonstrated an improvement of 33.1%.

The impact of the Reverse Short Channel Effect (RSCE) on device current is stronger in the subthreshold region due to the reduced Drain-Induced-Barrier-Lowering (DIBL) and the exponential dependency of current on threshold voltage. This paper describes a device size optimization method for subthreshold circuits utilizing RSCE to achieve high drive current, low device capacitance, less sensitivity to random dopant fluctuations, and better subthreshold swing. Simulation results using ISCAS benchmark circuits show that the critical path delay and power consumption can be improved by up to 10.4% and 34.4%, respectively.