Subthreshold conduction

About: Subthreshold conduction is a research topic. Over the lifetime, 6343 publications have been published within this topic receiving 131957 citations. The topic is also known as: Subthreshold leakage.

An Area and Power-Efficient Analog Li-Ion Battery Charger Circuit

Abstract: The demand for greater battery life in low-power consumer electronics and implantable medical devices presents a need for improved energy efficiency in the management of small rechargeable cells. This paper describes an ultra-compact analog lithium-ion (Li-ion) battery charger with high energy efficiency. The charger presented here utilizes the tanh basis function of a subthreshold operational transconductance amplifier to smoothly transition between constant-current and constant-voltage charging regimes without the need for additional area- and power-consuming control circuitry. Current-domain circuitry for end-of-charge detection negates the need for precision-sense resistors in either the charging path or control loop. We show theoretically and experimentally that the low-frequency pole-zero nature of most battery impedances leads to inherent stability of the analog control loop. The circuit was fabricated in an AMI 0.5-μm complementary metal-oxide semiconductor process, and achieves 89.7% average power efficiency and an end voltage accuracy of 99.9% relative to the desired target 4.2 V, while consuming 0.16 mm2 of chip area. To date and to the best of our knowledge, this design represents the most area-efficient and most energy-efficient battery charger circuit reported in the literature.

Maximum leakage power estimation for CMOS circuits

Abstract: Low supply voltage requires the device threshold to be reduced in order to maintain performance. As the device threshold voltage is reduced, it results in an exponential increase of leakage current in the subthreshold region. The leakage power is no longer negligible in such low voltage circuits. Estimates of maximum leakage power can be used in the design of the circuit to minimize the leakage power. The leakage power is dependent on the input vector. This input pattern dependence of the leakage power makes the problem of estimating the maximum leakage power a hard problem. In this paper, we present graph based algorithms for estimating the maximum leakage power. These algorithms are pattern-independent and do not require simulation of the circuit. Instead the circuit structure and the logic functionality of the components in the circuit are used to create a constraint graph. The problem of estimating the maximum leakage power is then transformed to an optimization problem on the constraint graph. Efficient algorithms on the graph are used to estimate the maximum leakage power dissipated by a circuit. We also present comparisons with exhaustive/long simulations for MCNC/ISCAS-85 benchmark circuits to verify the accuracy of the method.

A comprehensive study of corner effects in tri-gate transistors

Abstract: We have performed extensive 2D and 3D device simulations to assess the impact of gate and drain voltages, channel doping, discrete impurity effects, and the device dimensions on the electron density accumulation in the corner regions of tri-gate transistors. For channel doping concentrations higher than 10/sup 18/ cm/sup -3/, these 'corner effects' are found to dominate the device behavior. They are most pronounced in the subthreshold regime and significantly reduced in short devices with rounded corners, thin gate oxides, and narrow channels.

Threshold voltage compensation circuits for low voltage and low power CMOS integrated circuits

Abstract: A compensation circuit for transistor threshold voltages in integrated circuits is described. The compensation circuit includes a transistor, current source, and gate reference voltage supply. The transistor is biased to provide a well bias voltage, or backgate voltage VBG, which is coupled to transistors provided on a common integrated circuit. This compensation circuit eliminates the need for gate biasing capacitors, and provides flexibility in setting threshold voltages in low voltage circuits. The gate reference voltage and current source are established to provide a desired backgate voltage VBG. Compensation circuits are described for both n-channel and p-channel transistors. A memory device is described which includes compensation circuits for controlling threshold voltages of transistors provided therein.