Analysis of field-driven clocking for molecular quantum-dot cellular automata based circuits

Molecular quantum-dot cellular automaton (QCA) offers an alternative paradigm for computing at the nano-scale. QCA circuits require an external clock which can be generated using a network of submerged electrodes to synchronize information flow and provide the required power to drive the computation. In this paper, the effect of electrode separation and applied potential on the likelihood of different QCA cell states of molecular cells located above and in between two adjacent electrodes is analyzed. Using this analysis, estimates of operational ranges are developed for the placement, applied potential, and relative phase between adjacent clocking electrodes to ensure that only those states that are used in the computation are energetically favorable. Conclusions on the trade-off between cell size, cell-to-cell distance, and applied clocking potential are drawn and the temperature dependence of the operation of fundamental QCA building blocks is considered.     

Architecture for an external input into a molecular QCA circuit

A simple architecture for data input into a molecular quantum-dot cellular automata (QCA) circuit from an external CMOS circuit is proposed. A “T”-shaped interconnect, utilizing fixed-polarization cells to provide the desired polarization, is controlled via external electrodes connected to a standard CMOS input driver. The applied input signal is used to gate either the propagation of a fixed polarization, P=+1, or that of the complementary fixed polarization, P=−1, into the QCA circuit. The architecture utilizes the field-driven clocking scheme proposed in recent literature to achieve transduction between applied input voltage and a molecular configuration. The system is modelled using the coherence vector formalism with a three-state basis and simulated using the QCADesigner simulation tool.     

A comparative analysis and design of quantum‐dot cellular automata memory cell architecture

Quantum‐dot cellular automata (QCA) nanotechnology is considered as the best candidate for memory system owing to its dense packages and low power consumption. This paper analyzes the drawbacks of the previous QCA memory architectures and improves memory cell that exploits regular clock zone layout by employing two new clocking signals and a compact Read/Write circuit. The proposed layout is verified with the modified QCADesigner simulator and is analyzed by considering the noise effect. This design, occupying only a fraction of the area compared with the previous memory design, has superior performance. It is shown that the clock circuitry is very regular, helping manufacturability for physical implementation. Comparisons show that Read/Write latency of the proposed design is mitigated, the overall cell number, control cell and layout area are reduced (100%), and its performance against random charge noise is presented to be better. Copyright © 2010 John Wiley & Sons, Ltd.     

A novel quantum-dot cellular automata CLB of FPGA

Quantum-dot cellular automata (QCA) is a promising, emerging nano-technology based on single electron effects in quantum dots and molecules. This paper presents design, implementation and simulation of a configurable logic block for a field programmable gate arrays (FPGA) by QCA. Previous works focus on QCA-based FPGA that have fixed logic and programmable interconnection or programmable logic and fixed interconnection; however, proposed structures in this paper have programmable logic and programmable interconnection. The presented look-up table implemented with novel structure which has been allowed as frequently as the read/write operation occurs, also acts as a pipeline. In this paper, we presented novel decoders and multiplexers and implemented with QCA, designed with the minimum number of majority gates and cells. Finally, a new configurable logic block (CLB) is designed, implemented and simulated in the QCA, which used signal distribution network method to avoid the coplanar problem of crossing wires. Also, QCADesigner software is used for detailed layout and QCADesigner attend with HDLQ verilog are used for circuit simulation. The proposed CLB is simulated with programming by the QCADesigner software. The area and delay of QCA-based CLB presented in this paper compared to the CLB based on CMOS, nanomaterial and CNT (32 nm). Results show that proposed CLB will do the task with a minimum clock and can be configured as a FPGA.     

A novel QCA implementation of MUX-based universal shift register

QCA (Quantum-dot Cellular Automata) is an alternative technology for CMOS that has a low power consumption and high density. QCA extensively supports the new plans in the field of nanotechnology. Applications of QCA technology as an alternative method for CMOS technology in nano-scale have a hopeful future. This paper presents the successful design, implementation and simulation of 2 to 1, 4 to 1 and 8 to 1 multiplexer with the minimum area as compared to the previous models in QCA technology. In this paper, by means of 4 to 1 multiplexers including D-Flip Flop (D-FF) structure in QCA, we present an 8-bit universal shift register. The structure of the 8-bit universal register is extendable to 16-bit, 32-bit and etc. In this paper, the successful simulation of 2 to 1, 4 to 1 and 8 to 1 multiplexers, including D-FF and finally 8-bit universal register structure in QCADesigner is provided. The multiplexers and D-FF presented in this paper have the minimum complexity, area and delay compared to the previous models. In this paper, the implementation of 8-bit universal shift register, by means of 4 to 1 multiplexers and D-FF are presented in QCA technique which have the minimum complexity and delay. In the proposed design of the 8-bit universal shift register, the faults are likely to occur at 2 to 1 multiplexers and D-FF. In this article, 2 to 1 multiplexers and D-FF are investigated from the cell missing and possible defects. Considering the pipeline being the virtue of QCA, the 8-bit universal shift register has a high speed function. This 8-bit universal shift register may be used in the high speed processors as well as cryptography circuits.     

交流特高压线路下电场强度的改善

提高杆塔高度即提高导线对地高度是控制交流特高压输电线路地面电场的主要方式之一,但特高压线路跨越距离长,大范围提高杆塔高度工程成本很高,而在某些环境敏感区域,降低杆塔高度使地面电场强度增大,有可能超过国家相应标准,故研究降低线路地面场强的措施,如架设接地屏蔽线的方法等是交流特高压工程中急需考虑的技术问题。为此针对屏蔽线的不同架设方式试验研究了线路地面电场,通过分析比较各种屏蔽线架设方案下的场强水平,提出最优的屏蔽线架设方案。     

Fabrication of a conductive molecular wire using the ionization‐assisted evaporation method

Organic molecules are interesting materials with potential for use in next‐generation optical and electronic devices. It is important to prepare highly oriented molecular wires, since the optical and electrical properties of organic films strongly depend on their molecular orientation. The charge‐transfer‐complex wire of TTF‐TCNQ has been studied for application to molecular wires having quasi‐one‐dimensional conductivity. We have prepared highly oriented TTF‐TCNQ grains using the ionization and electric‐field‐assisted deposition method, and have investigated the growth mechanism of TTF‐TCNQ grains. These results demonstrate that needle‐like TTF‐TCNQ grain growth near the electrodes is controlled both by the electric field between the electrodes and by the ionization of evaporated molecules. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 8–15, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10015     

Innovative design methodologies in quantum‐dot cellular automata

Current transistor‐based IC fabrication technology faces many trivial issues such as those of excess power dissipation, expensive fabrication and short channel effects at very low device size [1]. Quantum‐dot cellular automata (QCA)‐based digital electronics on the other hand provide scope for further development in the future by shrinking the device size. Current QCA logic circuits are based on logic synthesis using Inverters and (three or five input) Majority Gates. In this paper, a new design methodology has been described that can be used to create circuits with even greater device substrate densities than what are currently achieved in existing QCA designs. Based on the proposed methodology, a new QCA inverter is proposed. It is further tested through simulations on QCA Designer. Through the simulations, it is subsequently proved to be much more reliable and robust than the presently used common QCA inverter(s). In the second section of this paper, simple QCA circuits such as ring oscillators using odd number of inverters in daisy chains are described and designed using the proposed inverter design. Copyright © 2013 John Wiley & Sons, Ltd.     

Design and simulation of modular 2n to 1 quantum‐dot cellular automata (QCA) multiplexers

In this paper a novel design of a quantum‐dot cellular automata (QCA) 2 to 1 multiplexer is presented. The QCA circuit is simulated and its operation is analyzed. A modular design and simulation methodology is developed, which can be used to design 2ⁿ to 1 QCA multiplexers using the 2 to 1 QCA multiplexer as a building block. The design methodology is formulated in order to increase the circuit stability. Copyright © 2009 John Wiley & Sons, Ltd.     

采用屏蔽线降低架空线线下场强的研究

采用等效电荷法对架空线下的场强进行分析。通过对架空线线下架设屏蔽线后线下场强的计算,可知屏蔽线架设位置、数量对降低线下场强的效果有明显的影响。工程实践也证明, 在输电导线下方安装屏蔽线来降低地面电场, 既经济, 又实用。建议: 同杆双回线路采用屏蔽线时, 架设宽度以与输电线基本等宽为宜; 屏蔽线架设高度在离最低相导线下方3m 左右屏蔽效果较好; 采用2～3 根屏蔽线为宜。     

QCA技术在递归盒式滤波器中的应用

量子点元胞自动机(quantum dot-cellular automata, QCA)因其延迟时间短、功耗低以及占用面积小等优点被当作代替CMOS的新型技术之一。针对CMOS器件尺寸日益减小导致的高功耗和电容寄生及串扰问题,本文首次利用QCA技术构建了一种递归盒式滤波器。其中,提出了一种全新的QCA全加器,较已提出的QCA全加器减少了55%的电路面积;少使用了56.7%的元胞数;量子成本也降低了10%以上。并以此为基础设计了一种高效的行波进位加法器(ripple carry adder, RCA)以及一种高效的进位选择加法器(carry select adder, CSA)来构成盒式滤波器的加法单元。以此构建的盒式滤波器较一般QCA盒式滤波器节省了32.6%的硬件资源;减少20%的电路运行时间;减少了48.7%的功耗。并使用QCA Designer仿真,结果表明,本设计完全可以代替实现传统的盒式滤波器功能,并在效率、功耗、电路面积、资源占用方面均有显著降低。     

Stabilization for thermomagnetic instability of CuNi/NbTi superconducting wire in spatially distributed magnetic field

Thermomagnetic instability in superconducting wires composing multistrand cables is a problem in the development of cables with large current capacity. This paper elucidates the quenching properties of ac superconducting wires in a distributed magnetic field applied to the strands in the cable, and the stabilization of the ac superconducting wires considering the effect of the longitudinal magnetic field or the fraction of copper embedded in each strand. First, the degradation of the quench current of CuNi/NbTi superconducting wires in a distributed magnetic field is exhibited with simple test samples. Second, the quench properties of the strand in a (6 + 1)³ cable and the optimal twist pitch of the cable for high stabilization are discussed. Last, the effect of copper on the quench properties of the strand and the appropriate fraction of copper for suppression of quench current degradation in a distributed magnetic field are discussed. © 2001 Scripta Technica, Electr Eng Jpn, 135(4): 26–34, 2001     

Towards the design of hybrid QCA tiles targeting high fault tolerance

The increasing fabrication cost of CMOS-based computing devices and the ever-approaching limits of their fabrication have led to the search for feasible options with high device density and low power waste. Quantum-dot cellular automata (QCA) is an emerging technology with such potential to match the design target beyond the limits of state-of-the-art CMOS. But nanotechnologies, like QCA are extremely susceptible to various forms of flaws and variations during fabrication at nano scale. Thus, the exploration of ingenious fault tolerant structure around QCA is gaining high importance. This work targets a new robust QCA tile structure hybridizing rotated and non-rotated cell together resulting lesser kink energy. Different QCA logic primitives (majority/minority logic, fanout tiles, etc.) are made using such hybrid cell structure. The functional characterization using the kink energy and the polarization level of such QCA structures under different cell defects have been thoroughly investigated. The results suggest that the proposed QCA logic primitives have achieved high fault tolerance of 97.43 %. Also, 100 % fault tolerance can be ascertained if the proposed logic circuit drives the correct output with the application of \(\langle \)001, 011\(\rangle \) as a primitive test vector only. A comparative performance of the proposed logic over existing structure makes it more reliable.     

Quantitative evaluation of perpendicular‐field losses in stacked high‐Tc superconducting tapes

The influence of stacks of Bi‐2223 multifilamentary tape‐shaped wires without twisting on AC losses observed in an external magnetic field perpendicular to their wide faces is investigated. The perpendicular‐field losses decrease with increasing number of tapes in the range of small field amplitudes. At larger amplitudes, on the other hand, the AC losses have little dependence on the stack number. This can be attributed to the effect of magnetic interaction between wires. By taking into account effective demagnetization factors on the basis of theoretical consideration, the perpendicular‐field losses are plotted on a master curve for the maximum magnetic field applied to the wires. Furthermore, the perpendicular‐field losses measured as a function of the field amplitude are well reproduced by the numerical evaluation of AC losses for a slab with infinitely wide surfaces. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(3): 50–57, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10050     

特高压交直流并行输电线路混合电场分布

为了降低交直流并行线路混合电场在输电走廊附近民房及金属支架上产生的静电感应影响,在交直流线路并行区域民房平台上搭建平行于线路的屏蔽线,分别测量了平行线路方向的工频电场和直流合成场分布,分析了屏蔽线架设高度、根数等对线路混合电场的屏蔽效果。在并行区域地面搭建了葡萄架模型,测量了不同网架结构的感应电压分布。结果表明,架设屏蔽线能够有效改善导线下方空间混合电场且存在最佳屏蔽方式,葡萄架感应电压受架设方式和长度的影响较大,最大感应电压对人体无电击刺痛感。     

A study of the electric-field intensity of conductors of a 500-kV air line

Electrostatic-field intensities have been obtained by mathematical simulations of the electric field of AS conductors of a 500-kV air line (AL) and numerical analysis based on the finite-element method using the Ansoft Maxwell software. The irregularity of the wire surface of an air line and the inhomogeneities of surface of the last cable layer have been taken into account in the study. The latter lead to a local increase in the field intensity, which, in turn, results in a loss of useful power. Phase splitting is used to decrease the electric- field intensity on air lines. Furthermore, the intensity on the individual wire decreases and, as a result, loss of power is reduced with respect to the corona discharge and line inductive reactance. Thus, to decrease loss of power of wires and to prolong the lifetime of wires, it is necessary to determine correctly the cross section of wires and kind of phase splitting. A 2D mathematical model of the AL electrostatic field has been developed that takes into account the inhomogeneity of the shape of the wire surface. The analytical solution of the initial problem has been considered, and the numerical and analytical results for a cylindrical wire surface have been compared. The fields for four cases of an AS conductor with different versions of splitting have been studied. The curves of field intensities near a conductor surface as a function of the cross section and number of wires in the AL phase have been plotted.     

Design of a reversible structure for memory in quantum-dot cellular automata

Complementary metal oxide semiconductor (CMOS) technology has limitations in reducing the area and size of circuits. The disadvantages of this technology include high power consumption and temperature problems. Quantum-dot cellular automata (QCA) is a new technology that can overcome these shortcomings. Reversible logic is technology used to reduce the power loss in QCA. QCA can be used to design memories that require high operating speed. In this paper, we propose a structure for the reversible memory in QCA. The proposed structure utilizes three-layer technology, which has a significant impact on circuit size reduction. The proposed structure for the reversible memory has 63% improvement in cell number, a 75% improvement in area occupancy, and a 60% reduction in delay compared to the previous best structure.     

Robust QCA full-adders using an efficient fault-tolerant five-input majority gate

Quantum-dot cellular automata (QCA) is considered as a top candidate for nanoscale technologies with unique features such as very low occupancy and ultralow power consumption. Despite the potential benefits of QCA technology over CMOS technology, QCA circuits are highly prone to defects. Therefore, a demand has risen in designing fault-tolerant circuits. In this research, a novel fault-tolerant five-input majority gate is first suggested, and then it is evaluated by implementing a variety of faults such as cell omission, cell displacement, and extra-cell deposition. The evaluation results reveal that the proposed structure is 100%, 51.85%, and 18.8% fault-tolerant under extra-cell deposition, single-cell omission, and double-cell omission, respectively. Moreover, two single-layer and coplanar fault-tolerant QCA full-adders are offered using the suggested fault-tolerant structure. The stability of the presented single-layer full-adder has also been investigated under single and double cell omission defects. The evaluation outcomes show that the suggested fault-tolerant single-layer full-adder has a high stability in Sum and C_out outputs compared with other full-adders. In order to validate the functionality of the suggested fault-tolerant five-input majority gate, a number of physical investigations are given. The QCADesigner 2.0.3 software has been used to evaluate the simulation results.     

New approaches for modeling and simulation of quantum-dot cellular automata

In order to further development of the microelectronic systems and to achieve the circuits with higher speed, higher density and lower power consumption, new technologies to replace the conventional CMOS technology must be introduced. Quantum-dot cellular automata (QCA) is an emerging nanotechnology that provides a new method for computation at the nanoscale regime. In this paper, two methods e.g. artificial neural network and a mathematical algorithm based on the QCA cell–cell response function named Tansig method are used for the modeling and simulation of QCA circuits at the cell level. The accuracy and performance of the proposed methods are analyzed through few circuits. The results of these two approaches are compared with each other and QCADesigner software. The results show the feasibility and acceptable accuracy of these types of simulations. Also, these methods enable the simulation of large QCA circuits at the cell level with acceptable precision in a short time with the ability to implement in other circuit simulators such as HSPICE and so on.     

Electrostatic performance of EHV overhead lines with asymmetrical bundles

This study deals with the computation of the electric potential and field in the vicinity of overhead extra high voltage (EHV) power transmission lines with asymmetrical bundles. The values of the electric field at the surface of the bundles as well as at the ground wires and the ground surface will also be obtained. The computer model is based on finding the potential coefficients and then solving a set of complex equations, whose number depends on the number of subconductors per phase, number of 3-phase circuits involved and the number of existing ground wires. The method is applied to a 6-bundle, 750 KV, single circuit line with flat configuration and two ground wires, resulting in a total of 20 complex equations to be solved, in order to get the charge on each of the subconductors and ground wires. The electrostatic potential and the electric field at any point can then be readily found. A comparison of the subconductor field of both symmetrical and asymmetrical bundles is made. It will be shown that the use of asymmetrical bundles will result in a reduction of the surface gradients at the bottom subconductors. At the same time, however, the field at the surface of the other subconductors will increase. This indicates that the suggested application of these asymmetrical lines for reducing the audible noise due to the line corona activity should be investigated more critically. No general statement is possible on this issue, since the numerical values of the subconductor fields will largely depend on the particular geometrical data of the line under consideration.