Gate oxide leakage current analysis and reduction for VLSI circuits

In this paper we address the growing issue of gate oxide leakage current (I/sub gate/) at the circuit level. Specifically, we develop a fast approach to analyze the total leakage power of a large circuit block, considering both I/sub gate/ and subthreshold leakage (I/sub sub/). The interaction between I/sub sub/ and I/sub gate/ complicates analysis in arbitrary CMOS topologies and we propose simple and accurate heuristics based on lookup tables to quickly estimate the state-dependent total leakage current for arbitrary circuit topologies. We apply this method to a number of benchmark circuits using a projected 100-nm technology and demonstrate accuracy within 0.09% of SPICE on average with a four order of magnitude speedup. We then make several observations on the impact of I/sub gate/ in designs that are standby power limited, including the role of device ordering within a stack and the differing state dependencies for NOR versus NAND topologies. Based on these observations, we propose the use of pin reordering as a means to reduce I/sub gate/. We find that for technologies with appreciable I/sub gate/, this technique is more effective at reducing total leakage current in standby mode than state assignment, which is often used for I/sub sub/ reduction.     

粗糙集属性约简方法研究

属性约简是粗糙集理论研究的核心内容之一。传统的属性约简研究并未考虑决策信息系统的树形结构,为解决这一问题,本文基于粗糙集理论,首先给出了决策信息系统的树形表示结构,该树形结构以粗糙集理论中的不可分辨关系为基础。基于本文构建的树形表示结构,文中给出了一种判断属性是否可约简的树形结构求解方法。通过理论分析表明,本文提出的树形结构求解方法能够大大减少属性搜索的步骤,压缩属性约简所消耗的时间。因此本文提出的属性约简算法是行之有效的。     

Harmonic current reduction in three-phase bridge-rectifier circuitsusing controlled current injection

This paper describes the further development of the novel current-injection scheme devised by the authors for attenuating line current harmonics in bridge-rectifier circuits. The previous passive filters are replaced by controlled filters connected between the bridge-rectifier output and the star point of the power transformer secondary. These filters are used to inject controlled third harmonic currents into the transformer windings. Variations in bridge working conditions, due to changes in either load or bridge delay angle, lead to corresponding changes in the filter operating conditions if the harmonic attenuation is to remain optimal. The control law for the filters has been derived and the effectiveness of the new method confirmed by both simulation and laboratory tests     

Experimental determination of the ratio of injected hole current and total current in silicon nitride

In a metal-Si3N4-nSi structure, the net minority-carrier generation rate is equal to the hole injection rate into the insulator under balanced conditions. The generation rate has been determined experimentally, giving the ratio of the injected hole current and the total current in the Si3N4 film.     

Harmonic current reduction in a three-phase diode bridge rectifier

A novel method for reducing harmonic currents on the AC supply side of a three-phase bridge rectifier is presented. The principle of the method is to modify the current waveforms in the DC windings of the converter transformer by injecting a third harmonic current into the neutral point of the transformer. Passive LC filters connected between the rectifier output and the secondary neutral point act as third harmonic current sources. The effectiveness of the method is confirmed by laboratory recordings     

Leakage current mechanisms and leakage reduction techniques in deep-submicrometer CMOS circuits

High leakage current in deep-submicrometer regimes is becoming a significant contributor to power dissipation of CMOS circuits as threshold voltage, channel length, and gate oxide thickness are reduced. Consequently, the identification and modeling of different leakage components is very important for estimation and reduction of leakage power, especially for low-power applications. This paper reviews various transistor intrinsic leakage mechanisms, including weak inversion, drain-induced barrier lowering, gate-induced drain leakage, and gate oxide tunneling. Channel engineering techniques including retrograde well and halo doping are explained as means to manage short-channel effects for continuous scaling of CMOS devices. Finally, the paper explores different circuit techniques to reduce the leakage power consumption.     

Fuzzy set computational processes in risk analysis

An article by R. Kangari and L.S. Riggs (see ibid., vol.36, no.2, p.126-31, 1989), which dealt with the use of fuzzy sets in construction risk analysis, contains a number of errors and inconsistencies, most of which appear in examples given to clarify the concepts involved in computations related to fuzzy sets. The errors and inconsistencies are identified, and the computational results are clarified by providing the correct results for enough computations to ensure an understanding of the processes involved     

Dark current reduction in stacked-type CMOS-APS for charged particle imaging

A stacked CMOS-active pixel sensor (APS) with a newly devised pixel structure for charged particle detection has been developed. At low operation temperatures (<200 K), the dark current of the CMOS-APS is determined by the hot carrier effect. A twin well CMOS pixel with a p-MOS readout and n-MOS reset circuit achieves low leakage current as low as 5/spl times/10/sup -8/ V/s at the pixel electrode under liquid nitrogen temperature of 77 K. The total read noise floor of 0.1 mV/sub rms/ at the pixel electrode was obtained by nondestructive readout correlated double sampling (CDS) with the CDS interval of 21 s.     

粗糙集属性约简在自动装填系统故障诊断方面的应用

火炮的自动装填系统对整个火炮系统的可靠性影响很大,需要进行故障诊断的属性也比较多。根据需要设计了硬件电路,硬件电路完成了数据采集、存储、控制命令发送等功能。由于每个装填环节进行数据采集的通道数不同,为了简化故障诊断程序运行的时间,采用粗糙集进行属性约简。实验证明,采集到的数据经过粗糙集进行属性约简后,再与故障样本集进行比较,判断故障状态,大大降低了程序运行的时间,同时由于数据维数的减少,也增强了系统的可靠性。     

The current distribution and AC resistance of a microstripstructure

The AC resistance of the strip in a microstrip structure is compared with that of an isolated strip for better understanding of the conductor loss mechanism. An analysis is presented of the AC resistance in a microstrip structure for any metallization thickness by deriving the current distribution over the strip cross section. The analysis uses the separation of variables technique and the Green's function method. It shows that the skin current of the strip is concentrated toward the ground plane in a microstrip structure. In the extreme case, the AC resistance of the strip can be twice as high as the AC resistance of the same isolated strip. The imperfect ground plane also adds to the total conductor loss of a microstrip line. For a wide strip over a lossy ground plane at high frequency, the ground plane surface current distribution is concentrated directly under the strip, and the ground plane AC resistance can be as large as the strip AC resistance. Therefore, the total AC resistance at the microstrip line can be four times as high as that of an isolated strip conductor     

Level set analysis for leukocyte detection and tracking

We propose a cell detection and tracking solution using image-level sets computed via threshold decomposition. In contrast to existing methods where manual initialization is required to track individual cells, the proposed approach can automatically identify and track multiple cells by exploiting the shape and intensity characteristics of the cells. The capture of the cell boundary is considered as an evolution of a closed curve that maximizes image gradient along the curve enclosing a homogeneous region. An energy functional dependent upon the gradient magnitude along the cell boundary, the region homogeneity within the cell boundary and the spatial overlap of the detected cells is minimized using a variational approach. For tracking between frames, this energy functional is modified considering the spatial and shape consistency of a cell as it moves in the video sequence. The integrated energy functional complements shape-based segmentation with a spatial consistency based tracking technique. We demonstrate that an acceptable, expedient solution of the energy functional is possible through a search of the image-level lines: boundaries of connected components within the level sets obtained by threshold decomposition. The level set analysis can also capture multiple cells in a single frame rather than iteratively computing a single active contour for each individual cell. Results of cell detection using the energy functional approach and the level set approach are presented along with the associated processing time. Results of successful tracking of rolling leukocytes from a number of digital video sequences are reported and compared with the results from a correlation tracking scheme.     

Switching noise and shoot-through current reduction techniques for switched-capacitor voltage doubler

Switching noise and shoot-through current reduction techniques for switched-capacitor voltage doublers based on cross-coupled structure are presented. The intuitive analysis of the shoot-through current and switching noise generation processes in the doubler is first reported. Break-before-make mechanism is adopted to minimize the shoot-through current, thereby greatly reducing the no-load supply current dissipation and improving the light-load power efficiency of the voltage doubler. In addition, by employing gate-slope reduction technique at the serial power transistor during turn-on, the switching noise of the voltage doubler is significantly lowered. Two voltage doublers with and without the proposed circuit techniques have been fabricated in a 0.6-/spl mu/m CMOS process. Experimental results verify that the total supply current at no-load condition of the proposed voltage doubler is reduced by two fold and its switching noise is decreased by 2.5 times.     

Line current harmonics reduction in multipulse connection of asymmetrically loaded rectifiers

This paper proposes a new arrangement for the multipulse connection of asymmetrically loaded six-pulse rectifiers. This arrangement is, therefore, particularly suitable for implementing the dc voltage sources of hybrid multilevel inverters in applications with active power transfer, such as medium-voltage adjustable-speed drives. A new design methodology is proposed to determine the phase shifts among the secondaries of the isolation transformer, even when the active power levels processed by each rectifier and their input and output impedances are different. A set of phase angles is obtained to minimize, and even to eliminate, undesired low-order harmonics of the input current, in particular, the 5th harmonic, because this harmonic component presents an amplitude considerably higher than the amplitude of the other harmonics. In consequence, the proposed design methodology increases the input power factor and reduces the input current total harmonic distortion. Simulation and experimental results are presented to demonstrate the feasibility of the proposed structure.     

Dark current reduction in nano-avalanche photodiodes by incorporating multiple quantum barriers

Multiple quantum barriers have been used to suppress the dark current of nanoscale avalanche photodiodes (APDs). The n⁺–π–p⁺-structured Si–3C-SiC heterojunction-based multiple quantum barrier (MQB) APDs are considered and a detailed model of dark current has been developed from the self-consistent solution of the coupled Schrödinger–Poisson equations. Four major types of electron–hole pair (EHP) generation mechanisms such as (1) thermal generation, (2) band-to-band tunnelling generation, (3) trap-assisted tunnelling generation and (4) avalanche generation are considered for calculating variation of the total dark current with reverse bias voltage. It is observed that the dark current can be suppressed significantly by increasing both the number and thickness of quantum barriers. However, the authors have also admitted that both the number and thickness of quantum barriers cannot be increased indefinitely, since it will cause deterioration in spectral response of the device in near-infrared range (λ < 1100 nm).     

变电站设计中短路电流的计算与分析

变电所设计中,为了电气设备、载流导体的选择、继电保护、自动化装置的整定、限制短路电流措施确定等目的,往往都需要先进行短路电流的计算。准确地进行短路电流计算就能根据变电站电力系统的实际情况合理地确定限制短路电流的方案,或者限制某种运行方式的出现,得到既可靠又经济的主接线方案。短路电流主要包含有三相短路电流、两相短路电流和单相短路电流。本论文通过某工厂变电所的设计,详细地介绍了短路电流的计算原则,得出了一种切实可行的短路电流计算方法。     

Torque-ripple reduction in PM synchronous motor drives using repetitive current control

The paper deals with the torque-ripple reduction in a permanent magnet synchronous motor (PMSM) drive with distorted back electromotive force. A smooth torque is obtained by tracking a modified current reference which is periodic over one-sixth of the electrical time period in the synchronous reference frame. An accurate tracking involves, however, very high current loop bandwidth, which is usually not achievable with conventional linear controllers. In order to improve current tracking in the presence of periodic reference signals and disturbances, the paper proposes the application of repetitive techniques to the current control in a field-oriented PMSM drive, where the q-axis current reference has been modified to achieve constant torque. The paper investigates the advantages and pitfalls of the method, through a mathematical analysis and an experimental validation obtained on a laboratory prototype. Particular emphasis is placed on the adjustments that have been specifically studied to enhance the overall system performance.     

Evolutionary approach for line current harmonic reduction in AC/DCconverters

This letter explains the application of genetic algorithms (GAs) for line current harmonic reduction in a buck-type converter. Harmonic reduction/elimination is redrafted as an optimization problem and steps of the GA are applied. Compared to conventional optimization techniques, the steps of the GA are very simple and global optimum is guaranteed in most cases. Theoretical and experimental results are provided to validate the method     

Artifact reduction for set theoretic super resolution imagereconstruction with edge adaptive constraints and higher-orderinterpolants

In this paper, we propose to improve the POCS-based super-resolution reconstruction (SRR) methods in two ways. First, the discretization of the continuous image formation model is improved to explicitly allow for higher order interpolation methods to be used. Second, the constraint sets are modified to reduce the amount of edge ringing present in the high resolution image estimate. This effectively regularizes the inversion process.     

High-level asymptotic variation of transistor base resistance and current gain

Using a finite-section model for bipolar transistors with current-dependent base resistance and gain, high-current asymptotic variations of base resistance, gain and effective emitter width are studied, and useful analytic formulas are presented.