Micropipelined asynchronous discrete cosine transform (DCT/IDCT)processor

We describe the design and implementation of an asynchronous discrete cosine transform/inverse discrete cosine transform (DCT/IDCT) processor core compliant with the CCITT recommendation H.261. First, a micropipelined implementation with level-sensitive latches is shown. This is improved by replacing the level-sensitive latches with dual-edge triggered flip-flops to save power and using completion-detection adders in the critical stage of the pipeline to exploit the data-dependent processing delay. Gate-level simulation of extracted layouts indicates that the performance of asynchronous implementations is comparable with that of a synchronous implementation based on an identical architecture. This is because part of the penalty introduced by handshaking circuitry in an asynchronous pipeline can be recovered by exploiting data-dependent processing delays with completion-detection circuitry. In pipelines with significant arithmetic processing such as the DCT/IDCT processor, this is easily accomplished. Our results are encouraging because asynchronous designs do not employ global clocking. In the near future when clock generation, clock distribution, and the power consumed in the clock circuitry become limiting factors in the design of large synchronous application specific integrated circuits (ASICs), asynchronous implementation methodology could be pursued as a real alternative     

Pausible clocking-based heterogeneous systems

This paper describes a novel communication scheme, which is guaranteed to be free of synchronization failures, amongst multiple synchronous and asynchronous modules operating independently. In this scheme, communication between every pair of modules is done through an asynchronous first-in first-out (FIFO) channel; communication between a module and the FIFO is done using a request/acknowledge handshaking. Synchronization of handshake signals to the local module clock is done in an unconventional way-the local clock built out of a ring oscillator is paused or stretched, if necessary, to ensure that the handshake signal satisfies setup and hold time constraints with respect to the local clock. In order to validate this scheme, we implemented a test chip in 0.5-μm CMOS. This chip is designed as a ring, composed of two synchronous modules, an asynchronous module, and two asynchronous FIFOs. Each module functions as a receiver to one module and a sender to another module. Test results show that the chip functions reliably up to 456 MHz     

Practical Asynchronous Interconnect Network Design

The implementation of interconnect is becoming a significant challenge in modern integrated circuit (IC) design. Both synchronous and asynchronous strategies have been suggested to manage this problem. Creating a low skew clock tree for synchronous inter-block pipeline stages is a significant challenge. Asynchronous interconnect does not require a global clock, and therefore, it has a potential advantage in terms of design effort. This paper presents an asynchronous interconnect design that can be implemented using a standard application-specific IC flow. This design is considered across a range of IC interconnect scenarios. The results demonstrate that there is a region of the design space where the implementation provides an advantage over a synchronous interconnect by removing the need for clocked inter-block pipeline stages, while maintaining high throughput. Further results demonstrate a computer-aided design tool enhancement that would significantly increase this space. A detailed comparison of power, area, and latency of the two strategies is also provided for a range of IC scenarios.     

基于片上系统的时钟复位设计

从方法优化和电路设计入手,提出了基于片上系统(SOC)的复位方法和时钟复位电路.设计了片外按键复位电路、片内上电电路、晶振控制电路、片内RC低频时钟电路、槽脉冲产生电路、分频延时电路、时钟切换电路及异步复位同步释放电路等电路模块.以上电路模块构成了片上系统的时钟复位电路,形成了特定的电路时钟复位系统.该时钟复位系统将片外按键复位与片内上电复位结合起来,形成多重复位设计,相比单纯按键复位更智能,相比单纯上电复位则更可靠.另外,该时钟复位系统还采用了片内RC振荡时钟电路等一系列电路,借助片内RC时钟实现对芯片的延时复位,进而在保证复位期间寄存器得到正确初始化的同时,还使得芯片能够始终处在稳定的晶振时钟下正常工作.相比传统的时钟复位电路,该时钟复位系统既便捷,又保证了系统初始化和系统工作的可靠性.     

GALDS: a complete framework for designing multiclock ASICs and SoCs

A Globally Asynchronous, Locally Synchronous (GALS) system with dynamic voltage and frequency scaling can use the slowest frequency possible to accomplish a task with minimal power consumption. With the mechanism for implementing dynamic voltage scaling at each synchronous domain left up to the designer, our Globally Asynchronous, Locally Dynamic System (GALDS) provides a top-down, system-level means to maximize power reduction in an integrated circuit and facilitate system-on-a-chip (SoC) design. Our solution includes three distinct components: a novel bidirectional asynchronous FIFO to communicate between independently clocked synchronous blocks , an all-digital dynamic clock generator to quickly and glitchlessly switch between frequencies and a digitally controlled oscillator to generate the global fixed frequency clocks required by the all-digital dynamic clock generator. In addition to being capable of reducing power consumption when combined with dynamic voltage scaling, a GALDS design benefits from numerous other advantages such as simplified clock distribution, high performance operation and faster time-to-market through the modular nature of the architecture.     

Response-time properties of linear asynchronous pipelines

One of the potential advantages of asynchronous circuits is that they can be optimized for average-case performance rather than worst-case performance. The performance analysis of asynchronous circuits, however, is more challenging than that of synchronous circuits because of the absence of a clock. We discuss some performance measures of special asynchronous networks, viz., response-time properties of asynchronous pipelines with various handshake communications. The response times of a pipeline are the delays between requests and succeeding acknowledgments for the first cell. We derive simple formulas for the bound on worst-case response time and average-case response time of such pipelines using a variable-delay model, where delays may vary between a lower and upper bound. The properties are independent of any particular implementation of the cells of the pipeline. The formulas give insight into the role of each parameter and allow a quick back-of-the-envelope prediction of the performance of an asynchronous pipeline     

New dynamic flip-flops for high-speed dual-modulus prescaler

A fast pipeline technique using single-phase, edge-triggered, ratioed, high-speed logic flip-flops and D flip-flops is introduced and analyzed. The circuits achieve high speed by reducing the capacitive load and sharing the delay between the combination logic blocks and the storage elements. Also it is suitable for realizing high-speed synchronous counters. A divide-by-128/129 and 64/65 dual-modulus prescaler using the proposed flip-flops is measured in 0.8 μm CMOS technology with the operating clock frequency reaching as high as 1.8 GHz     

光传送网中复用映射电路的设计

为了简化光传送网中光数据单元的时钟电路设计、降低成本,提出了一种基于均匀缺口时钟的同步电路。首先,采用异步FIFO实现缺口同步时钟的生成;然后,通过带有缺口的同步时钟设计了一种复用映射电路,处理不同类型的光数据单元,实现信号频偏吸收、时钟数据恢复和前向错误纠错。并通过电路仿真证明,该方案设计的电路可达到与传统方案相同的性能,且设计和实现采用虚拟时钟替代锁相环,使电路更加简单经济。     

A synchronous approach for clocking VLSI systems

Presents a synchronous solution for clocking VLSI systems organized as distributed systems. This solution avoids the drawbacks of the self-timed approach. These VLSI systems are constituted of modules which represent synchronous areas driven by their own fast clock, interconnected by a synchronous communication mechanism driven by a slow clock. In order to avoid the risk of metastability in flip-flop between the modules and the communication mechanism, the author suggests to resynchronize the phase of each module clock on the transitions of the communication clock by a phase locked loop circuitry added to each module.     

异步系统的信号传送研究

异步电路在低功耗、低噪声、抗干扰、无时钟偏移和模块化设计等方面有较高的性能。在SOC芯片设计中,异步设计技术逐渐成为研究的热点。文中比较了同步系统和异步系统信号传递基础,介绍了多个基于异步系统的信号传递模型,讨论了专用于异步电路的数据传送方式。从应用的角度对现有的异步电路信号传递模型的结构、特点、数据信号、应用背景等方面进行了比较研究,最后总结了在实际问题中选择模型的原则。     

多时钟域的异步信号的参考解决

在ASIC设计中,不同的模块往往工作在不同的频率下,在一个芯片上采用单时钟设计基本上是不可能实现的。多时钟域的设计是SOC设计中的一个重要环节。分析了多时钟域设计中异步信号的产生以及带来的亚稳定性对整个电路性能和功能的影响,提出了采用同步器,握手通信协议,FIFO等方法减小亚稳定性概率和其影响的措施,并且给出了实用电路图并进行了实现,从而使得电路能够在多时钟域下更加健壮和稳定。     

LCD控制器中异步电路的设计

异步电路的设计能够解决功耗、系统速度、时钟偏移等问题,成为当前VLSI研究的热点.文章提出了4级灰度LCD控制器异步电路的设计方案,通过异步控制以消除无效操作从而降低功耗,经验证平均功耗仅为同步电路的23.7%：异步电路还实现了部分显示和滚屏等功能,加快了系统响应速度.     

Performance analysis of slotted ring protocols in HSLANs

The performance of a number of slotted-ring protocols supporting integration of synchronous and asynchronous traffic in high-speed local area networks (HSLANs) is evaluated. They are the Cambridge fast ring, a variant of the Cambridge fast ring, and Orwell. The performance of their basic access mechanisms is compared and contrasted with that of the multiple-token ring. The effect of a uniframe scheme for supporting synchronous traffic is examined. A delay analysis of the integrated-services slotted-ring protocols is presented     

一种基于虚拟地址页的异步FIFO的FPGA设计与实现

为了实现异步时钟域之间数据高速、稳定的传输,文章设计了一个基于FPGA的异步FIFO.采用格雷码作为地址编码,引入虚拟地址页来产生标志位.并用Verilog HDL语言描述了深度为16的异步FIFO,在ALTERA的Cyclone系列FP-GA上对电路进行了验证.根据逻辑分析仪观测的结果可知,设计的异步FIFO可以稳定工作在100MHz时钟,达到了高速电路的设计要求.最后对设计进行了最坏情况的理论分析,证明了设计很好地避免了亚稳态问题.     

A "flying-adder" architecture of frequency and phase synthesis with scalability

Most of today's digital designs, from small-scale digital block designs to system-on-chip (SoC) designs, are based on "synchronous" design principle. Clock is the most important issue in these designs. Frequency and phase synthesis is closely related to the clock generation. A frequency and phase synthesis technique based on phase-locked loop is proposed in that delivers high performance, easy integration, and high stability. However, there are problems associated with this architecture, such as: 1) its highest deliverable frequency is limited by the speed of the accumulator and 2) the phase synthesis circuitry will not work well in certain ranges (dead zone) and in certain conditions (dual stability). This paper presents an improved architecture that addresses these problems. The new frequency synthesis circuitry has scalability for higher output frequency. It also has an internal node whose frequency is twice that of output signal. When duty cycle is not a concern, this signal can be used directly as clock source. The new phase synthesis circuitry is free of "dead zone" and "dual stability." The improved architecture has better performance, is simpler to implement, and is easier to understand.     

异步复位设计中的亚稳态问题及其解决方案

尽管异步复位是一种安全可靠复位电路的方法，但如果处理不当的话，异步复位释放可能会导致亚稳态（metastability）的问题。本文分析了这个问题产生的原因和后果，给出了一种可能的解决方案。在设计中加入复位同步器逻辑和复位分配缓冲树。这种方法综合了同步复位设计与异步复位设计的优点，解决了异步复位设计中的亚稳态问题。     

异步式逻辑保障片上网络传输可靠性的研究

随着Si技术的持续发展,片上系统(SoC)的规模和复杂度的增长给传统的片上互连,如总线结构,带来了前所未有的挑战。片上网络[1-2]是片上系统的一种新设计方法,是目前公认应对这种挑战较为有效的解决方案。半导体工艺进入深亚微米时代后,片上网络的可靠性也越来越成为人们关注的问题。将在研究如何应用异步式逻辑保障片上网络互连数据传输的可靠性和服务质量,提出了一个异步式片上网络的架构。通过实验证明,异步式逻辑将极大提高集成电路在应对电源不稳定性、导线间串扰、电磁干扰(EMI)、时钟偏斜和软错误方面的可靠性。采用全局异步局部同步的时钟机制,该方法带来了一种全新的片上通信方法,显著改善了传统总线式系统的性能。     

RTD-HBT高速低功耗环形振荡器的分析

RTD与HBT是高频高速器件,共振隧穿二极管-异质结晶体管(RTD-HBT)环形振荡器有很好的应用前景.详细介绍了RTD-HBT高速低功耗环形振荡器的工作原理,建立了RTD,HBT及RTD-HBT环形振荡器的等效电路模型,并对RTD-HBT环形振荡器用Pspice模拟软件进行了电路模拟.模拟结果与预期结果一致,有助于指导该电路的设计.     

Architectural Design Issues in a Clockless 32‐Bit Processor Using an Asynchronous HDL

As technology evolves into the deep submicron level, synchronous circuit designs based on a single global clock have incurred problems in such areas as timing closure and power consumption. An asynchronous circuit design methodology is one of the strong candidates to solve such problems. To verify the feasibility and efficiency of a large‐scale asynchronous circuit, we design a fully clockless 32‐bit processor. We model the processor using an asynchronous HDL and synthesize it using a tool specialized for asynchronous circuits with a top‐down design approach. In this paper, two microarchitectures, basic and enhanced, are explored. The results from a pre‐layout simulation utilizing 0.13‐μm CMOS technology show that the performance and power consumption of the enhanced microarchitecture are respectively improved by 109% and 30% with respect to the basic architecture. Furthermore, the measured power efficiency is about 238 μW/MHz and is comparable to that of a synchronous counterpart.