Locally Synchronous, Globally Asynchronous Design for Quantum-Dot Cellular Automata (LSGA QCA)

The concept of clocking for QCA, referred to as the four-phase clocking, is widely used. However, inherited characteristics of QCA, such as the way to hold state, the way to synchronize data flows, and the way to power QCA cells, make the design of QCA circuits quite different from VLSI and introduce a variety of new design challenges and the most severe challenges are due to the fact that the overall timing of a QCA circuit is mainly dependent upon its layout. This fact is commonly referred to as the layout-timing problem. To circumvent the problem, a novel self-timed circuit design technique referred to as the Locally Synchronous, Globally Asynchronous Design for QCA is proposed in this paper. The proposed technique can significantly reduce the layout-timing dependency from the global network of QCA devices in a circuit; therefore, considerably flexible QCA circuit design will be possible

Locally Synchronous, Globally Asynchronous Design for Quantum-Dot Cellular Automata (LSGA QCA)

The concept of clocking for QCA, referred to as the four-phase clocking, is widely used. However, inherited characteristics of QCA, such as the way to hold state, the way to synchronize data flows, and the way to power QCA cells, make the design of QCA circuits quite different from VLSI and introduce a variety of new design challenges and the most severe challenges are due to the fact that the overall timing of a QCA circuit is mainly dependent upon its layout. This fact is commonly referred to as the layout-timing problem. To circumvent the problem, a novel self-timed circuit design technique referred to as the Locally Synchronous, Globally Asynchronous Design for QCA is proposed in this paper. The proposed technique can significantly reduce the layout-timing dependency from the global network of QCA devices in a circuit; therefore, considerably flexible QCA circuit design will be possible

A Framework for Verification of Signal Propagation Through Sequential Nanomagnet Logic Devices

Nanomagnet Logic is an emerging technology for low-power, highly-scalable implementation of quantum-dot cellular automata. Feedback permits reuse of logical subroutines, which is a desired functionality of any computational device. Determining whether feedback is feasible is essential to assessing the robustness of nanomagnet logic in any pipelined computing design. Therefore, development of a quantitative approach for verification of feedback paths is critical for development of design and synthesis tools for nanomagnet logic structures. In this paper, a framework for verification of sequential nanomagnet logic devices is presented. A set of definitions for canonical alignment and state definitions for NML paths are presented, as well as mathematical operations for determining the resulting states. The simulation results are presented for quantification of the NML magnetization angles for horizontal, vertical, negative-diagonal, and positive diagonal geometric alignments. The presented framework may be used as the basis for defining a representation of signal propagation for design and verification for robust NML devices and preventing deadlock resulting from improper implementation

Feedbacks in QCA: a Quantitative Approach

In the post-CMOS scenario a primary role is played by the quantum-dot cellular automata (QCA) technology. Irrespective of the specific implementation principle (e.g., either molecular, or magnetic or semiconductive in the current scenario) the intrinsic deep-level pipelined behavior is the dominant issue. It has important consequences on circuit design and performance, especially in the presence of feedbacks in sequential circuits. Though partially already addressed in literature, these consequences still must be fully understood and solutions thoroughly approached to allow this technology any further advancement. This paper conducts an exhaustive analysis of the effects and the consequences derived by the presence of loops in QCA circuits. For each problem arisen, a solution is presented. The analysis is performed using as a test architecture, a complex systolic array circuit for biosequences analysis (Smith–Waterman algorithm), which represents one of the most promising application for QCA technology. The circuit is based on nanomagnetic logic as QCA implementation, is designed down to the layout level considering technological constraints and experimentally validated structures, counts up to approximately 2.3 milion nanomagnets, and is described and simulated with HDL language using as a testbench realistic protein alignment sequences. The results here presented constitute a fundamental advancement in the emerging technologies field since: 1) they are based on a quantitative approach relying on a realistic and complex circuit involving a large variety of QCA blocks; 2) they strictly are reckoned starting from current technological limits without relying on unrealistic assumptions; 3) they provide general rules to design complex sequential circuits with intrinsically pipelined technologies, like QCA; and 4) they prove with a real application benchmark how to maximize the circuits performance

Quantum-dot Cellular Automata: Review Paper

Quantum-dot Cellular Automata (QCA) is one of the most important discoveries that will be the successful alternative for CMOS technology in the near future. An important feature of this technique, which has attracted the attention of many researchers, is that it is characterized by its low energy consumption, high speed and small size compared with CMOS.  Inverter and majority gate are the basic building blocks for QCA circuits where it can design the most logical circuit using these gates with help of QCA wire. Due to the lack of availability of review papers, this paper will be a destination for many people who are interested in the QCA field and to know how it works and why it had taken lots of attention recentl

Exploring and exploiting wire-level pipelining in emerging technologies

Pipelining is a technique that has long since been considered fundamental by computer architects. However, the world of nanoelectronics is pushing the idea of pipelining to new and lower levels – particularly the device level. How this affects circuits and the relationship between their timing, architecture, and design will be studied in the context of an inherently self-latching nanotechnology termed Quantum Cellular Automata (QCA). Results indicate that this nanotechnology offers the potential for “free ” multithreading and “processing-in-wire”. All of this could be accomplished in a technology that could be almost three orders of magnitude denser than an equivalent design fabricated in a process at the end of the CMOS curve. 1

Fault and Defect Tolerant Computer Architectures: Reliable Computing With Unreliable Devices

This research addresses design of a reliable computer from unreliable device technologies. A system architecture is developed for a fault and defect tolerant (FDT) computer. Trade-offs between different techniques are studied and yield and hardware cost models are developed. Fault and defect tolerant designs are created for the processor and the cache memory. Simulation results for the content-addressable memory (CAM)-based cache show 90% yield with device failure probabilities of 3 x 10(-6), three orders of magnitude better than non fault tolerant caches of the same size. The entire processor achieves 70% yield with device failure probabilities exceeding 10(-6). The required hardware redundancy is approximately 15 times that of a non-fault tolerant design. While larger than current FT designs, this architecture allows the use of devices much more likely to fail than silicon CMOS. As part of model development, an improved model is derived for NAND Multiplexing. The model is the first accurate model for small and medium amounts of redundancy. Previous models are extended to account for dependence between the inputs and produce more accurate results