Novel RAM cell designs based on inherent capabilities of quantum-dot cellular automata

Quantum Cellular Automata (QCA) is a novel and attractive method which enables designing and implementing high-performance and low-power consumption digital circuits at nano-scale. Since memory is one of the most applicable basic units in digital circuits, having a fast and optimized QCA-based memory cell is remarkable. Although there are some QCA structures for a memory cell in the literature, however, QCA characteristics may be used in designing a more optimized memory cell than blindly modeling CMOS logics in QCA. In this paper, two improved structures have been proposed for a loop-based Random Access Memory (RAM) cell. In the proposed methods, the inherent capabilities of QCA, such as the programmability of majority gate and the clocking mechanism have been considered. The first proposed method enjoys smaller number of cells and the wasted area has been reduced compared to traditional loop-based RAM cell. For the second proposed method, the memory access time has been duplicated in presence of smaller number of cells. Irregular placement of QCA cells in a QCA layout makes its realization troublesome. So, we have proposed alternative versions of the proposed methods that exploit regularity of clock zones in design and have compared them to each other. QCA designer has been employed for simulation of the proposed designs and proving their validity.     

Application-specific programmable control for high-performanceasynchronous circuits

The advantages of the programmable control paradigm are widely known in the design of synchronous sequential circuits: easy correction of late design errors, easy upgrade of product families to meet time-to-market constraints, and modifications of the control algorithm, even at run time. However, despite the growing interest in asynchronous (self-timed) circuits, programmable asynchronous controllers based on the idea of microprogramming have not been actively pursued. In this paper, we propose an asynchronous microprogrammed control organization (called a microengine) that targets application-specific implementations and emphasizes simplicity, modularity, and high performance. The architecture takes advantage of the natural ability of self-timed circuits to chain actions efficiently without the clock-based scheduling constraints that would be involved in comparable synchronous designs. The result is a general approach to the design of application-specific microengines featuring a programmable data-path topology that offers very compact microcode and high performance-in fact, performance close to that offered by automated hardwired controllers. In performance comparisons of a CD-player error decoder design, the proposed microengine architecture was 26 times faster than the general purpose hardware of a 280 MIPS microprocessor, over three times as fast as the special purpose hardware of a low-power macromodule based implementation, and even slightly faster than a finite state machine-based implementation     

Adiabatic-CMOS/CMOS-adiabatic logic interface circuit

This paper describes the design of an adiabatic-CMOS/CMOS-adiabatic logic interface circuit for a group of low-power adiabatic logic families with a similar clocking scheme. The circuit provides interfacing between several recently proposed low-power adiabatic logic circuits and traditional digital CMOS circuits. One advantage of this design is that it is insensitive to clock overlap. With the proposed interface circuit, both adiabatic and CMOS logic circuits are able to co-exist on a single chip, taking advantage of the strengths of each approach in the design of low power systems.     

A 0.5-GHz CMOS digital RF memory chip

In the application of digital RF memory (DRFM) chips for radar jamming, an RF signal is sampled, stored in random access memory (RAM) and later recreated from the stored data. A CMOS (l/SUB eff/=1 /spl mu/m) DRFM chip is described that integrates static RAM, control circuitry, and two channels of shift registers on a single chip. The sample rate achieved was 0.5 GHz. VLSI density was made possible by the low-power dissipation of quiescent CMOS circuits. An 8K RAM prototype chip has been built and tested.     

Fully boosted 64K dynamic RAM with automatic and self-refresh

A novel high-speed low-power 64K dynamic RAM with enough margin has been attained using a double polysilicon and 3-/spl mu/m process technologies. To obtain a low soft error rate below 1/spl times/10/SUP -6/ errors per device hour without sacrificing the high-speed and low-power operation, some novel approaches are proposed in the circuit and device designs. In particular, fully boosted circuits and the Hi-C cell structure with polysilicon bit line are designed to increase the margin of the single 5-V power supply 64K dynamic RAM. The fabricated device provides a typical access time of 90 ns and an operating power of 190 mW at 25/spl deg/C. Also, the design features of the automatic and self-refresh functions on the same chip are described.     

The Triptych FPGA architecture

Field-programmable gate arrays (FPGAs) are an important implementation medium for digital logic. Unfortunately, they currently suffer from poor silicon area utilization due to routing constraints. In this paper we present Triptych, an FPGA architecture designed to achieve improved logic density with competitive performance. This is done by allowing a per-mapping tradeoff between logic and routing resources, and with a routing scheme designed to match the structure of typical circuits. We show that, using manual placement, this architecture yields a logic density improvement of up to a factor of 3.5 over commercial FPGAs, with comparable performance. We also describe Montage, the first FPGA architecture to fully support asynchronous and synchronous interface circuits     

Designing low-power circuits: practical recipes

The growing market of mobile, battery-powered electronic systems (e.g., cellular phones, personal digital assistants, etc.) demands the design of microelectronic circuits with low power dissipation. More generally, as density, size, and complexity of the chips continue to increase, the difficulty in providing adequate cooling might either add significant cost or limit the functionality of the computing systems which make use of those integrated circuits. In the past ten years, several techniques, methodologies and tools for designing low-power circuits have been presented in the scientific literature. However only a few of them have found their way in current design flows. The purpose of this paper is to summarize, mainly by way of examples, what in our experience are the most trustful approaches to low-power design. In other words, our contribution should not be intended as an exhaustive survey of the existing literature on low-power design; rather, we would like to provide insights a designer can rely upon when power consumption is a critical constraint. We will focus solely on digital circuits, and we will restrict our attention to CMOS devices, this technology being the most widely adopted in current VLSI systems     

Low-power synchronous-to-asynchronous- to-synchronous interlocked pipelined CMOS circuits operating at 3.3-4.5 GHz

Interlocked pipelined CMOS (IPCMOS), a new asynchronous set of clock circuits suitable for high-frequency and low-power operation, is described. In IPCMOS, the reduced power results from enabling the local clocks only when there is an operation to perform and from a simple single-stage latch. The single-stage latch can be used because the locally generated clocks driving adjacent stages are not enabled simultaneously. The combination of enabling the clocks only when there is an operation to perform and the simple latch can lower power by a factor of five to ten times in many applications. In IPCMOS, the staggered local clocks also result in a significant reduction of dynamic Ldi/dt noise. In addition to the locally generated interlocked clocks and the single-stage latch, unique circuits that combine the function of a static NOR and an input switch are key to achieving high performance and minimizing the overhead in the interlocking. In a 0.18-/spl mu/m bulk CMOS technology, these circuits drive a path through a typical 64-b multiplier stage at 3.3-4.5 GHz on an experimental chip. IPCMOS also provides a way to implement the interface between asynchronous and synchronous portions of a design, thereby giving the approach a great deal of flexibility by making it possible to drop IPCMOS into portions of an existing synchronous design.     

A low-power sub 100 ns 256K bit dynamic RAM

A 256K-word /spl times/ 1-bit NMOS dynamic RAM using 2-/spl mu/m design rules and MoSi/SUB 2/ gate technology is described. A marked low-power dissipation of 170 mW (5 V V/SUB cc/, 260-ns cycle time) has been achieved by using a partial activation scheme. Optimized circuits exhibit a typical CAS access time of 34 ns. For the purpose of optimizing circuit parameters, an electron beam tester was successfully applied to observe the internal timing of real chips. Laser repairable redundancy with four spare rows and four spare columns is implemented for yield improvement.     

Asynchronous circuits as alternative for mitigation of long-duration transient faults in deep-submicron technologies

The use of deeper-submicron technologies in integrated circuits worsens the effects of transient faults. In fact, the transient-fault durations become as important as the clock periods of synchronous circuits. Electronic systems are thus more vulnerable to failure situations. Nevertheless, this paper shows innovatively that such a worse scenario does not happen in asynchronous circuits. This additional novel benefit pushes on the asynchronous design as a better alternative to mitigate transient faults in deep-submicron technology-based circuits.     

CADRE: An Asynchronous Embedded DSP for Mobile Phone Applications

Asynchronous design techniques have a number of compelling features that make them suited for complex system on chip designs. However, it is necessary to develop practical and efficient design techniques to overcome the present shortage of commercial design tools. This paper describes the development of CADRE (Configurable Asynchronous DSP for Reduced Energy), a 750K transistor, high performance, low-power digital signal processor IP block intended for digital mobile phone chipsets. A short time period was available for the project, and so a methodology was developed that allowed high-level simulation of the design at the earliest possible stage within the conventional schematic entry environment and simulation tools used for later circuit-level performance and power consumption assessment. Initial modeling was based on C behavioral models of the various data and control components, with the many asynchronous control circuits required automatically generated from their specifications. This has enabled design options to be explored and unusual features of the design, such as the Register Bank which is designed to exploit data access patterns, are presented along with the power and performance results of the processor as a whole.     

New concepts of worst-case delay and yield estimation in asynchronous VLSI circuits

Estimation of asynchronous circuit performances, such as speed, is one of the major reasons that still keeps that design style undeservedly unpopular. A simple logic simulator would be very useful in overcoming this problem if it is used for evaluating the worst-case delays in the paths of an asynchronous circuit using. In this paper a method for timing analysis of the asynchronous circuits using a VHDL simulator is presented. It is capable to deal with both non-sequential and sequential asynchronous circuit. An appropriate extension of the standard logic simulation process enables all worst-case delays for all paths in a digital circuit to be obtained with only one run of the simulation. High levels of accuracy are achieved using extensive gate modelling while statistical analysis of the results was also used to evaluate part of the parametric yield loss related to the delay. Due to the lack of asynchronous benchmark circuits, the method is verified on a set of asynchronous circuit selected by the authors.     

Hybrid asynchronous circuit generation amenable to conventional EDA flow

This work proposes a new method of synthesizing asynchronous circuits targeting its practical usability. The key contribution of this work is finding an effective technique of inter-mixing the two design principles namely handshaking based single-rail and timing annotated (i.e., quasi-delay insensitive (QDI)) dual-rail of asynchronous circuits. Precisely, we propose a clever way of partitioning an input (synchronous) circuit to transform it into a circuit with single-rail and dual-rail sub-circuits and of designing seamless interface to stitch the sub-circuits. Our proposed synthesis flow closely links to industrial design automation tools with standard cell libraries to enhance the practicality and productivity. Experimental results show that the designs produced by our approach expose partial or full combinations of high-performance, low-power consumption, great immunity to delay and noise variability, and mitigation to the side-channel attacks in hardware security.     

A Low-Power Digital IC Design Inside the Wireless Endoscopic Capsule

This paper proposes an architecture of the wireless endoscopy system for the diagnoses of whole human digestive tract and real-time endoscopic image monitoring. The low-power digital IC design inside the wireless endoscopic capsule is discussed in detail. A very large scale integration (VLSI) architecture of three-stage clock management is applied, which can save 46% power inside the capsule compared with the design without such a low-power design. A stoppable ring crystal oscillator with minimal overhead is used in the sleep mode, which results in about 60-muW system power dissipation in sleep mode. A new image compression algorithm based on Bayer image format and its corresponding VLSI architecture are both proposed for low-power, high-data volume. Thus, 8 frames per second with 320*288 pixels can be transmitted with 2 Mb/s. The digital IC design also assures that the capsule has many flexible and useful functions for clinical application. The digital circuits were verified on field-programmable gate arrays and have been implemented in 0.18-mum CMOS process with 6.2 mW     

A Hi-CMOSII 8K/spl times/8 bit static RAM

A Hi-CMOSII static RAM with 8K word by 8 bit organization has been developed. The RAM is fabricated using double polysilicon technology and p- and n-channel transistors having a typical gate polysilicon length of 2 /spl mu/m. The device was realized using low-power high-speed-oriented circuit design and a new redundancy circuit that utilizes laser diffusion programmable devices. The new RAM has an address access time of 65 ns, operating power dissipation of 200 mW, and standby dissipation of 10 /spl mu/W.     

Applications of asynchronous circuits

A comparison with synchronous circuits suggests four opportunities for the application of asynchronous circuits: high performance, low power; improved noise and electromagnetic compatibility (EMC) properties, and a natural match with heterogeneous system timing. In this overview paper each opportunity is reviewed in some detail, illustrated by examples, compared with synchronous alternatives, and accompanied by numerous pointers to the literature. Conditions for applying asynchronous circuit technology, such as the existence and availability of computer-aided design (CAD) tools, circuit libraries, and effective test approaches, are discussed briefly. Asynchronous circuits do offer advantages for many applications, and their design methods and tools are now starting to become mature     

A 3.5-ns, 500-mW, 16-kbit BiCMOS ECL RAM

A 16-kbit BiCMOS ECL SRAM with a typical address access time of 3.5 ns and 500-mW power dissipation was developed. The RAM was fabricated using half-micrometer, triple-poly, and triple-metal BiCMOS technology. The fast access time with moderate power dissipation has been achieved using new circuit techniques: a grounded-gate, nonlatching-type level converter with a wired-OR predecoder and a direct column sensing scheme having a cascode differential amplifier. As a result of extensive use of high-speed bipolar ECL circuits with self-aligned bipolar transistors, the RAM attains high-speed performance without degrading the low-power BiCMOS RAM characteristics.<>     

Timing of Multi-Gigahertz Rapid Single Flux Quantum Digital Circuits

Rapid Single Flux Quantum (RSFQ) logic is a digital circuit technology based on superconductors that has emerged as a possible alternative to advanced semiconductor technologies for large scale ultra-high speed, very low power digital applications. Timing of RSFQ circuits at frequencies of tens to hundreds of gigahertz is a challenging and still unresolved problem. Despite the many fundamental differences between RSFQ and semi- conductor logic at the device and at the circuit level, timing of large scale digital circuits in both technologies is principally governed by the same rules and constraints. Therefore, RSFQ offers a new perspective on the timing of ultra-high speed digital circuits.This paper is intended as a comprehensive review of RSFQ timing, from the viewpoint of the principles, concepts, and language developed for semiconductor VLSI. It includes RSFQ clocking schemes, both synchronous and asynchronous, which have been adapted from semiconductor design methodologies as well as those developed specifically for RSFQ logic. The primary features of these synchronization schemes, including timing equations, are presented and compared.In many circuit topologies of current medium to large scale RSFQ circuits, single-phase synchronous clocking outperforms asynchronous schemes in speed, device/area overhead, and simplicity of the design procedure. Synchronous clocking of RSFQ circuits at multigigahertz frequencies requires the application of non-standard design techniques such as pipelined clocking and intentional non-zero clock skew. Even with these techniques, there exist difficulties which arise from the deleterious effects of process variations on circuit yield and performance. As a result, alternative synchronization techniques, including but not limited to asynchronous timing, should be considered for certain circuit topologies. A synchronous two-phase clocking scheme for RSFQ circuits of arbitrary complexity is introduced, which for critical circuit topologies offers advantages over previous synchronous and asynchronous schemes.     

Efficient algorithms for multilevel power estimation of VLSI circuits

This paper presents a methodology for calculating highly accurate mean power estimates for integrated digital CMOS circuits. A complementary calibration scheme for ASIC library cells to extract the power relevant parameters is proposed. The circuit models presented allows the prediction of mean power dissipation of gate-level designs in CMOS technologies with an accuracy that is comparable to a SPICE simulation but up to 10 000 times faster. The outlined approach is capable of handling complex circuits consisting of more than 20 000 cells and thousands of memory elements. Very large sets of input data with several millions of patterns can, thus, be simulated in an efficient way. This allows the prediction of mean power dissipation of VLSI circuits in a realistic functional context which provides new assessment possibilities for digital CMOS low-power design methods. Experimental results for some benchmark circuits are detailed in order to demonstrate the significant improvements in terms of performance, accuracy, and flexibility of this approach compared to state-of-the-art power estimation methods     

Low-Power Impulse UWB Architectures and Circuits

Ultra-wide-band (UWB) communication has a variety of applications ranging from wireless USB to radio-frequency (RF) identification tags. For many of these applications, energy is critical due to the fact that the radios are situated on battery-operated or even batteryless devices. Two custom low-power impulse UWB systems are presented in this paper that address high- and low-data-rate applications. Both systems utilize energy-efficient architectures and circuits. The high-rate system leverages parallelism to enable the use of energy-efficient architectures and aggressive voltage scaling down to 0.4 V while maintaining a rate of 100 Mb/s. The low-rate system has an all digital transmitter architecture, 0.65 and 0.5 V radio-frequency (RF) and analog circuits in the receiver, and no RF local oscillators, allowing the chipset to power on in 2 ns for highly duty-cycled operation.