基于与非锥的新型FPGA逻辑簇互连结构研究

该文针对新型FPGA可编程逻辑单元与非锥(And-Inverter Cone, AIC)的结构特性,提出一系列方案以得到优化的逻辑簇互连结构,包括:移除输出级交叉矩阵,单级反相交叉矩阵,低负载电路优化,将反馈和输出选择功能分开,限制AIC输出级数的基础上移除中间级交叉矩阵,与LUT架构进行混合等。通过大量的实验,得出针对面积延时积最优的AIC簇互连结构,与Altera公司的FPGA芯片Stratix-IV结构相比,该结构逻辑功能簇本身面积减小9.06%, MCNC应用电路集在基于优化的AIC FPGA架构上实现的平均面积延时积减小40.82%, VTR应用电路集平均面积延时积减小17.38%;与原有的AIC结构相比,簇面积减小23.16%, MCNC应用电路集平均面积延时减小27.15%, VTR应用电路集平均面积延时积减小15.26%。     

LFU算法的ASIC实现

为ASIC实现内存管理中页面替换的LFU算法,基于TSMC公司0.18 μm的单元库,用标准逻辑单元库实现LFU算法.通过研究一组数中的最小值检出和最小值地址检出的逻辑规律,简化逻辑,减小了电路规模.通过控制关键路径的级数,达到了减少延迟,提高运行速度的目的.给出了版图和静态时序分析结果.     

静态时序分析及其在IC设计中的应用

讨论了静态时序分析算法及其在IC设计中的应用。首先，文章讨论了静态时序分析中的伪路径问题以及路径敏化算法，分析了影响逻辑门和互连线延时的因素。最后通过一个完整的IC设计流程介绍了静态时序分析的应用。     

基于关键路径延时检测的自适应电压缩减技术

为了减小传统的最差情况设计方法引入的电压裕量,提出了一种变化可知的自适应电压缩减(AVS)技术,通过调整电源电压来降低电路功耗.自适应电压缩减技术基于检测关键路径的延时变化,基于此设计了一款预错误原位延时检测电路,可以检测关键路径延时并输出预错误信号,进而控制单元可根据反馈回的预错误信号的个数调整系统电压.本芯片采用SMIC180 nm工艺设计验证,仿真分析表明,采用自适应电压缩减技术后,4个目标验证电路分别节省功耗12.4％,11.3％,10.4％和11.6％.     

一种降低电路泄漏功耗的多阈值电压方法

目前,多阈值电压方法是缓解电路泄漏功耗的有效手段之一。但是,该方法会加重负偏置温度不稳定性(NBTI)效应,导致老化效应加剧,引起时序违规。通过找到电路的潜在关键路径集合,运用协同优化算法,将关键路径集合上的门替换为低阈值电压类型,实现了一种考虑功耗约束的多阈值电压方法。基于45 nm工艺模型及ISCAS85基准电路的仿真结果表明,在一定功耗约束下,该方法的时延改善率最高可达12.97%,明显优于常规多阈值电压方法。电路的规模越大,抗泄漏功耗的效果越好。     

SoC设计中的低功耗逻辑综合策略

介绍了一种SoC(片上系统)电路的高效逻辑综合方法,用工具对功耗关键模块插入时钟门控单元来降低功耗,并用工具提取不带时钟门控模块的约束条件来优化相应带门控的模块,使SoC在最高主频率、面积和功耗等方面达到最优,且时序收敛较快.采用该方法对Unity805plus SoC芯片进行综合,取得比自顶向下、自底向上等传统综合方法更好的效果,在最差情况下最高频率为200 MHz,面积为8 773 410μm2,功耗为724.920 4 mW.在ULTRA60上运行时间为14h.[关键词:逻辑综合,SoC,时序收敛     

超前进位加法器的一种优化设计

描述了超前进位加法器的一种优化设计.在结构上采用按4位分组进行超前进位的方法达到并行、高速的目的.为了在高速运算的同时降低功耗,对求和式子进行了逻辑变换;在晶体管级进行优化的单元电路设计,可减小延时、降低整个电路的面积和功耗.     

DES芯片抵御高阶差分功耗分析攻击方法研究

分析独特的屏蔽方法及改进方法的不足,提出了逻辑层和算法层相结合抵御高阶差分功耗分析攻击的新方法,并给出芯片半定制设计流程.芯片关键部分电路采用自定义功耗恒定逻辑单元实现,非关键部分电路采用CMOS逻辑以减少功耗和面积.整体电路采用独特的屏蔽方法自定义轮实现.结果表明芯片能够抵御高阶差分功耗分析攻击,运算速度与现有方法相当,而所需资源比现有方法少.     

DES芯片抵御高阶差分功耗分析攻击方法研究

分析独特的屏蔽方法及改进方法的不足,提出了逻辑层和算法层相结合抵御高阶差分功耗分析攻击的新方法,并给出芯片半定制设计流程.芯片关键部分电路采用自定义功耗恒定逻辑单元实现,非关键部分电路采用CMOS逻辑以减少功耗和面积.整体电路采用独特的屏蔽方法自定义轮实现.结果表明芯片能够抵御高阶差分功耗分析攻击,运算速度与现有方法相当,而所需资源比现有方法少.     

基于RTD的新型全加器设计

单双稳态转换逻辑单元(MOBILE)是基于共振隧穿二极管(RTD)电路的一个重要逻辑单元,非常适合阈值逻辑电路设计。由MOBILE可以构成阈值逻辑门(TG)和广义阈值逻辑门(GTG)等阈值逻辑电路。本文通过将三变量异或函数转化为较简单、理想的GTG输入输出函数形式,设计了由GTG构成的新型三变量异或门,并利用该三变量异或门设计了新型的全加器。通过HSPICE仿真和性能比较,该全加器不仅器件数量少,输出延时短,而且能达到较高的工作频率、更小的电路功耗与功耗-延迟积。     

Efficient subthreshold leakage current optimization - Leakage current optimization and layout migration for 90- and 65- nm ASIC libraries

Leakage current is of great concern for designs in nanometer technologies. In 90- and 65-nm technologies, subthreshold leakage current dominates total leakage current. For a typical ASIC circuit running at several hundred megahertz frequencies, the subthreshold leakage power can be as high as 60% of total power. An important method for minimizing power in ASIC libraries is reducing leakage current. In this article, a complete automated leakage optimization flow that changes channel lengths and widths with cell delay and active area constraints was discussed. Optimization results show that there is ~30% leakage current reduction with a few percent active area and delay increase. There is increase in dynamic power, but the net total power reduction is significant. A uniform increase of 10% in gate length results in ~35% leakage reduction at the cost of ~12% delay degradation. The total cell area changes are minimal in both cases. The optimization flow begins with SPICE net lists from an existing library, optimizes leakage currents subject to performance metrics and active area increase constraints, and finishes with new layout generation and characterization. Investigations indicate that the leakage optimization has little impact on cell noise margin and layout parasitic modifications do not affect optimization results. The efficient automatic layout-to-layout cell leakage optimization flow is most suitable for leakage minimization and library migration for 90- and 65-nm ASIC libraries. Future work includes applying the flow to situations where layout-dependent DFM and process variation objective functions are also optimized     

Crosstalk noise reduction in synthesized digital logic circuits

As CMOS technology scales into the deep submicrometer regime, digital noise is becoming a metric of importance comparable to area, timing, and power, for analysis and design of CMOS VLSI systems. Noise has two detrimental effects in digital circuits: First, it can destroy logical information carried by a circuit net. Second, it causes delay uncertainty: Non critical paths might become critical because of noise. As a result, circuit speed becomes limited by noise, primarily because of capacitive coupling between wires. Most design approaches address the crosstalk noise problem at the layout generation stage, or via postlayout corrections. With continued scaling, too many circuit nets require corrections for noise, causing a design convergence problem. This work suggests to consider noise at the gate-level netlist generation stage. The paper presents a simplified analysis of on-chip crosstalk models, and demonstrates the significance of crosstalk between local wires within synthesized circuit blocks. A design flow is proposed for automatically synthesizing CMOS circuits that have improved robustness to noise effects, using standard tools, by limiting the range of gate strengths available in the cell library. The synthesized circuits incur a penalty in area/power, which can be partially recovered in a single postlayout corrective iteration. Results of design experiments indicate that delay uncertainty is the most important noise-related concern in synthesized static CMOS logic. Using a standard synthesis methodology, critical path delay differences up to 18% of the clock cycle time have been observed in functional blocks of microprocessor circuits. By using the proposed design flow, timing uncertainty was reduced to below 3%, with area and power penalties below 20%.     

Enhancing sensitivity-based power reduction for an industry IC design context

For many years, discrete gate sizing has been widely used for timing and power optimization in VLSI designs. The importance of gate sizing optimization has been emphasized by academia for many years, especially since the 2012/2013 ISPD gate sizing contests [1, 2]. These contests have provided practical impetus to academic sizers through the use of realistic constraints and benchmark formats. At the same time, due to simplified delay/power Liberty models and timing constraints, the contests fail to address real-world criteria for gate sizing that are highly challenging in practice. We observe that lack of consideration of practical issues such as electrical and multi-corner constraints – along with limited sets of benchmarks – can misguide the development of contest-focused academic sizers. Thus, we study implications of the “gap” between academic sizers and product design use cases. In this paper, we note important constraints of modern industrial designs that are generally not comprehended by academic sizers. We also point out that various optimization techniques used in academic sizers can fail to offer benefits in product design contexts due to differences in the underlying optimization formulation and constraints. To address this gap, we develop a new robust academic sizer, Sizer, from a fresh implementation of Trident [3]. Experimental results show that Sizer is able to achieve up to 10% leakage power and 4% total power reductions compared to leading commercial tools on designs implemented with foundry technologies, and 7% leakage power reduction on a modern industrial design in the multi-corner multi-mode (MCMM) context.     

Active mode leakage reduction using fine-grained forward body biasing strategy

Leakage power minimization has become an important issue with technology scaling. Variable threshold voltage schemes have become popular for standby power reduction. In this work we look at another emerging aspect of this potent problem which is leakage power reduction in active mode of operation. In gate level circuits, a large number of gates are not switching in active mode at any given point in time but nevertheless are consuming leakage power. We propose a fine-grained forward body biasing (FBB) scheme for active mode leakage power reduction in gate level circuits without any delay penalty. Our results show that our optimal polynomial time FBB allocation algorithm results in 70.2% reduction in leakage currents. We also present an exact standard-cell placement driven FBB allocation algorithm that effectively reduces the area penalty using the post-placement area slack and results in 56.5%, 62.8% and 66.1% reduction in leakage currents for 0%, 4% and 8% area slack, respectively. Furthermore, we present a heuristic to solve the standard-cell placement driven FBB allocation problem that is computationally efficient and results in leakage within 2% of that from the exact formulation.     

Supply Switching With Ground Collapse: Simultaneous Control of Subthreshold and Gate Leakage Current in Nanometer-Scale CMOS Circuits

Power gating has been widely used to reduce subthreshold leakage. However, the efficiency of power gating degrades very fast with technology scaling, which we demonstrate by experiment. This is due to the gate leakage of circuits specific to power gating, such as storage elements and output interface circuits with a data-retention capability. A new scheme called supply switching with ground collapse is proposed to control both gate and subthreshold leakage in nanometer-scale CMOS circuits. Compared to power gating, the leakage is cut by a factor of 6.3 with 65-nm and 8.6 with 45-nm technology. Various issues in implementing the proposed scheme using standard-cell elements are addressed, from register transfer level to layout. These include the choice of standby supply voltage with circuits that support it, a power network architecture for designs based on standard-cell elements, a current switch design methodology, several circuit elements specific to the proposed scheme, and the design flow that encompasses all the components. The proposed design flow is demonstrated on a commercial design with 90-nm technology, and the leakage saving by a factor of 32 is observed with 3% and 6% of increase in area and wirelength, respectively.     

LECTOR: a technique for leakage reduction in CMOS circuits

In CMOS circuits, the reduction of the threshold voltage due to voltage scaling leads to increase in subthreshold leakage current and hence static power dissipation. We propose a novel technique called LECTOR for designing CMOS gates which significantly cuts down the leakage current without increasing the dynamic power dissipation. In the proposed technique, we introduce two leakage control transistors (a p-type and a n-type) within the logic gate for which the gate terminal of each leakage control transistor (LCT) is controlled by the source of the other. In this arrangement, one of the LCTs is always "near its cutoff voltage" for any input combination. This increases the resistance of the path from V/sub dd/ to ground, leading to significant decrease in leakage currents. The gate-level netlist of the given circuit is first converted into a static CMOS complex gate implementation and then LCTs are introduced to obtain a leakage-controlled circuit. The significant feature of LECTOR is that it works effectively in both active and idle states of the circuit, resulting in better leakage reduction compared to other techniques. Further, the proposed technique overcomes the limitations posed by other existing methods for leakage reduction. Experimental results indicate an average leakage reduction of 79.4% for MCNC'91 benchmark circuits.     

On gate level power optimization using dual-supply voltages

In this paper, we present an approach for applying two supply voltages to optimize power in CMOS digital circuits under the timing constraints. Given a technology-mapped network, we first analyze the power/delay model and the timing slack distribution in the network. Then a new strategy is developed for timing-constrained optimization issues by making full use of stacks. Based on this strategy, the power reduction is translated into the polynomial-time-solvable maximal-weighted-independent-set problem on transitive graphs. Since different supply voltages used in the circuit lead to totally different power consumption, we propose a fast heuristic approach to predict the optimum dual-supply voltages by looking at the lower bound of power consumption in the given circuit. To deal with the possible power penalty due to the level converters at the interface of different supply voltages, we use a “constrained F-M” algorithm to minimize the number of level converters. We have implemented our approach under an SIS environment. Experiment shows that the resulting lower bound of power is tight for most circuits and that the predicted “optimum” supply voltages are exactly or very close to the best choice of actual ones. The total power saving of up to 26% (average of about 20%) is achieved without degrading the circuit performance, compared to the average power improvement of about 7% by the gate sizing technique based on a standard cell library. Our technique provides the power-delay tradeoff by specifying different timing constraints in circuits for power optimization     

Statistical timing and leakage power analysis of PD-SOI digital circuits

This paper presents a fast statistical static timing and leakage power analysis in Partially-Depleted Silicon-On-Insulator (PD-SOI) CMOS circuits in BSIMSOI3.2 100 nm technology. The proposed timing analysis considers floating body effect on the propagation delay for more accurate timing analysis in PD-SOI CMOS circuits. The accuracy of modeling the leakage power in PD-SOI CMOS circuits is improved by considering the interactions between the subthreshold leakage and the gate tunneling leakage, the stacking effect, the history effect, and the fanout effect. The proposed timing and leakage power analysis algorithms are implemented in Matlab, Hspice, and C language. The proposed methodology is applied to ISCAS85 benchmarks, and the results show that the error is within 5% compared with random simulation results.     

Process Variation-Aware Timing Optimization for Dynamic and Mixed-Static-Dynamic CMOS Logic

The advancement in CMOS technology with the shrinking device size towards 32 nm has allowed for placement of billions of transistor on a single microprocessor chip. Simultaneously, it reduced the logic gate delays to the order of pico seconds. However, these low delays and shrinking device sizes have presented design engineers with two major challenges: timing optimization at high frequencies, and minimizing the vulnerability from process variations. Answering these challenges, this paper presents a process variation-aware transistor sizing algorithm for dynamic CMOS logic, and a process variation-aware timing optimization flow for mixed-static-dynamic CMOS logic. Through implementation on several benchmark circuits, the proposed transistor sizing algorithm for dynamic CMOS logic has demonstrated an average performance improvement in delay by 28%, uncertainty from process variations by 32%, while sacrificing an area of 39%. Also, through implementation on benchmark circuits and a 64-b parallel binary adder, the proposed timing optimization flow for mixed-static-dynamic CMOS logic has demonstrated a performance improvement in delay by 17% and uncertainty from process variations by 13%.