Bio: J.P. Halter is an academic researcher from University of Illinois at Urbana–Champaign. The author has contributed to research in topics: Low-power electronics & Electronic circuit. The author has an hindex of 1, co-authored 1 publications receiving 298 citations.
••05 May 1997
TL;DR: The proposed design changes consist of minimal overhead circuitry that puts the circuit into a "low leakage standby state", whenever it goes into standby, and allows it to return to its original state when it is reactivated.
Abstract: In order to reduce the power dissipation of CMOS products, semiconductor manufacturers are reducing the power supply voltage. This requires that the transistor threshold voltages be reduced as well to maintain adequate performance and noise margins. However, this increases the subthreshold leakage current of p and n MOSFETs, which starts to offset the power savings obtained from power supply reduction. This problem will worsen in future generations of technology, as threshold voltages are reduced further. In order to overcome this, we propose a design technique that can be used during logic design in order to reduce the leakage current and power. We target designs where parts of the circuit are put in "standby" mode when not in use, which is becoming a common approach for low power design. The proposed design changes consist of minimal overhead circuitry that puts the circuit into a "low leakage standby state", whenever it goes into standby, and allows it to return to its original state when it is reactivated. We give an efficient algorithm for computing a good low leakage power state. We demonstrate this method on the ISCAS-89 benchmark suite and show leakage power reductions of up to 54% for some circuits.
10 Sep 2007
TL;DR: Is your memory hierarchy stopping your microprocessor from performing at the high level it should be?
Abstract: Is your memory hierarchy stopping your microprocessor from performing at the high level it should be? Memory Systems: Cache, DRAM, Disk shows you how to resolve this problem. The book tells you everything you need to know about the logical design and operation, physical design and operation, performance characteristics and resulting design trade-offs, and the energy consumption of modern memory hierarchies. You learn how to to tackle the challenging optimization problems that result from the side-effects that can appear at any point in the entire hierarchy.As a result you will be able to design and emulate the entire memory hierarchy. . Understand all levels of the system hierarchy -Xcache, DRAM, and disk. . Evaluate the system-level effects of all design choices. . Model performance and energy consumption for each component in the memory hierarchy.
10 Aug 1998
TL;DR: Results on a large number of benchmarks indicate that proper input selection can reduce the standby leakage power by more than 50% for some circuits.
Abstract: Low supply voltage requires the device threshold to be reduced in order to maintain performance. Due to the exponential relationship between leakage current and threshold voltage in the weak inversion region, leakage power can no longer be ignored. In this paper we present a technique to accurately estimate leakage power by accurately modeling the leakage current in transistor stacks. The standby leakage current model has been verified by IISPICE. We demonstrate that the dependence of leakage power on primary input combinations can be accounted for by this model. Based on our analysis we can determine good bounds for leakage power in the standby mode. As a by-product of this analysis, we can also determine the set of input vectors which can put the circuits in the low-power standby mode. Results on a large number of benchmarks indicate that proper input selection can reduce the standby leakage power by more than 50% for some circuits.
••06 Aug 2001
TL;DR: A model that predicts the scaling nature of this leakage reduction effect is presented and use of stack effect for leakage reduction and other implications of this effect are discussed.
Abstract: Technology scaling demands a decrease in both V/sub dd/ and V/sub t/ to sustain historical delay reduction, while restraining active power dissipation. Scaling of V/sub t/ however leads to substantial increase in the sub-threshold leakage power and is expected to become a considerable constituent of the total dissipated power. It has been observed that the stacking of two off devices has smaller leakage current than one off device. In this paper we present a model that predicts the scaling nature of this leakage reduction effect. Device measurements are presented to prove the model's accuracy. Use of stack effect for leakage reduction and other implications of this effect are discussed.
TL;DR: Two runtime mechanisms for reducing the leakage current of a CMOS circuit are described and a design technique for applying the minimum leakage input to a sequential circuit is presented, which shows that it is possible to reduce the leakage by an average of 25% with practically no delay penalty.
Abstract: The first part of this paper describes two runtime mechanisms for reducing the leakage current of a CMOS circuit. In both cases, it is assumed that the system or environment produces a "sleep" signal that can be used to indicate that the circuit is in a standby mode. In the first method, the "sleep" signal is used to shift in a new set of external inputs and pre-selected internal signals into the circuit with the goal of setting the logic values of all of the internal signals so as to minimize the total leakage current in the circuit. This minimization is possible because the leakage current of a CMOS gate is strongly dependent on the input combination applied to its inputs. In the second method, nMOS and pMOS transistors are added to some of the gates in the circuit to increase the controllability of the internal signals of the circuit and decrease the leakage current of the gates using the "stack effect". This is, however, done carefully so that the minimum leakage is achieved subject to a delay constraint for all input-output paths in the circuit. In both cases, Boolean satisfiability is used to formulate the problems, which are subsequently solved by employing a highly efficient SAT solver. Experimental results on the combinational circuits in the MCNC91 benchmark suite demonstrate that it is possible to reduce the leakage current in combinational circuits by an average of 25% with only a 5% delay penalty. The second part of this paper presents a design technique for applying the minimum leakage input to a sequential circuit. The proposed method uses the built-in scan-chains in a VLSI circuit to drive it with the minimum leakage vector when it enters the sleep mode. The use of these scan registers eliminates the area and delay overhead of the additional circuitry that would otherwise be needed to apply the minimum leakage vector to the circuit. Experimental results on the sequential circuits in the MCNC91 benchmark suit show that, by using the proposed method, it is possible to reduce the leakage by an average of 25% with practically no delay penalty.
TL;DR: This work reviews circuit behavior at low voltages, specifically in the subthreshold (Vdd < Vth) regime, and suggests new strategies for energy-efficient design, and discusses the energy benefits of techniques such as multiple-threshold CMOS and adaptive body biasing.
Abstract: Energy efficiency has become a ubiquitous design requirement for digital circuits. Aggressive supply-voltage scaling has emerged as the most effective way to reduce energy use. In this work, we review circuit behavior at low voltages, specifically in the subthreshold (Vdd < Vth) regime, and suggest new strategies for energy-efficient design. We begin with a study at the device level, and we show that extreme sensitivity to the supply and threshold voltages complicates subthreshold design. The effects of this sensitivity can be minimized through simple device modifications and new device geometries. At the circuit level, we review the energy characteristics of subthreshold logic and SRAM circuits, and demonstrate that energy efficiency relies on the balance between dynamic and leakage energies, with process variability playing a key role in both energy efficiency and robustness. We continue the study of energy-efficient design by broadening our scope to the architectural level. We discuss the energy benefits of techniques such as multiple-threshold CMOS (MTCMOS) and adaptive body biasing (ABB), and we also consider the performance benefits of multiprocessor design at ultralow supply voltages.