一种层次式加载BUFFER的时钟网布线

多级时钟树构造是解决时钟布线问题的关键。本文提出一种新的层次式布线策略,它将拓扑生成,绕障碍ＤＭＥ及ＢＵＦＦＥＲ定位同时进行考虑,避免了布线的盲目性,减少了后处理工作。首先,对时钟汇点进行层次式均匀划分,在各个局域区域同时进行时钟子树的拓扑生成和ＤＭＥ嵌入;     

高速多级时钟网布线

提出了一种新的加载缓冲器的时钟布线算法 .该算法根据时钟汇点的分布情况 ,在时钟布线之前对缓冲器进行预先布局 ,并将时钟树的拓扑生成及实体嵌入和层次式的缓冲器布局方法有机结合起来 ,使布线情况充分反映缓冲器对时钟网结构的影响 .实验证明 ,与将缓冲器插入和布局作为后处理步骤相比 ,缓冲器预先插入和布局在很大程度上避免了布线的盲目性 ,并能更加有效地实现各时钟子树的延迟和负载的平衡 .     

Clock Buffer Polarity Assignment for Power Noise Reduction

Power/ground noise is a major source of VLSI circuit timing variations. This work aims to reduce clock network induced power noise by assigning different signal polarities (opposite switchings) to clock buffers in an existing buffered clock tree. Three assignment algorithms are proposed: 1) partitioning; 2) 2-coloring on minimum spanning tree; and 3) recursive min-matching. A post-processing of clock buffer sizing is performed to achieve desired clock skew. SPICE based experimental results indicate that our techniques could reduce the average peak current and average delay variations by 50% and 51%, respectively.      

合理偏差驱动的时钟线网构造及优化

提出了一种新的时钟布线算法 ,它综合了 top- down和 bottom- up两种时钟树拓扑产生方法 ,以最小时钟延时和总线长为目标 ,并把合理偏差应用到时钟树的构造中 .电路测试结果证明 ,与零偏差算法比较 ,该算法有效地减小了时钟树的总体线长 ,并且优化了时钟树的性能     

时钟延时及偏差最小化的缓冲器插入新算法

本文提出了以最小时钟延时和时钟偏差为目标的缓冲器插入新算法.基于Elmore延时模型,我们得到相邻缓冲器间的延时是缓冲器在时钟树中位置的凸函数.当缓冲器布局使所有缓冲器间延时函数具有相同导数值时,时钟延时达到最小;当所有源到各接收端点路径的延时函数值相等时,时钟偏差达到最小.对一棵给定的时钟树,我们在所有从源点到各接收端点路径上插入相同层数的缓冲器,通过优化缓冲器的位置实现时钟延时最小;通过调整缓冲器尺寸和增加缓冲器层数,实现时钟偏差最小.     

Pattern-matching-based X-architecture zero-skew clock tree construction with X-Flip technique and via delay consideration

As IC fabrication technologies get into nanometer era, clock routing gradually dominates chip performance indicated by delay, cost, and power consumption. X-architecture can be applied for routing metal wires in diagonal and rectilinear directions to overcome the above challenges due to wirelength reduction. In this paper, we present a clock routing algorithm, called PMXF, to construct an X-architecture zero-skew clock tree with minimum delay. An X-pattern library is defined for simplifying the merging procedure of the DME approach, an X-Flip technique is proposed for reducing the wirelength between the paired points, and a wire sizing technique is applied for achieving zero skew. In terms of clock delay, wirelength, power consumption, and via count listed in the experimental results on benchmarks, the proposed PMXF algorithm can respectively achieve more reductions compared with other previous X-architecture clock routing algorithms.     

基于精确时延模型考虑缓冲器插入的互连线优化算法

随着VLSI电路集成度增大和特征尺寸的不断减小,连线的寄生效应不可忽略,互连线的时延在电路总时延中占了很大的比例,成为决定电路性能的主要因素.在互连时延的优化技术中,缓冲器插入是最有效的减小连线时延的方法.本文提出了一个在精确时延模型下,在布线区域内给定一些可行的缓冲器插入位置,对两端线网进行拓扑优化,并同时插入缓冲器以优化时延的多项式时间实现内的算法.我们的算法不但可以实现时延的最小化,也可以在满足时延约束的条件下,最小化缓冲器的插入数目,从而避免不必要的面积和功耗的浪费.     

On general zero-skew clock net construction

We propose a simulated annealing based zero-skew clock net construction algorithm that works in any routing spaces, from Manhattan to Euclidean, with the added flexibility of optimizing either the wire length or the propagation delay. We first devise an O(log n) tree grafting perturbation function to construct a zero-skew clock tree under the Elmore delay model. This tree grafting scheme is able to explore the entire solution space asymptotically. A Gauss-Seidel iteration procedure is then applied to optimize the Steiner point positions. Experimental results have shown that our algorithm can achieve substantial delay reduction and encouraging wire length minimization compared to previous works     

一种高效时钟树综合实现方法

针对ASIC芯片设计中时钟树综合效率和时序收敛的问题,提出了一种高效的时钟树综合方法,特别适用于现代先进深亚微米工艺中的高集成度、高复杂度的设计中。改进了传统时钟树综合方法,通过采用由下至上逐级分步综合的方法实现。该设计方法在SMIC 0.18μm eflash工艺下的一款电力线载波通信芯片中成功流片验证,结果表明分步综合能够在实现传统设计功能的前提下,在完成时序收敛时有效减少不必要的器件插入,从而减小芯片面积,降低整体功耗,有效改善绕线拥塞度。     

一种非零偏差时钟网布线算法

特定的非零偏差时钟网比零偏差时钟网更具优势,它有助于提高时钟频率、降低偏差的敏感度.文章提出了一种新的非零偏差时钟树布线算法,它结合时钟节点延时和时钟汇点位置,得到一个最大节点延时次序合并策略,使时钟树连线长度变小.实验结果显示,这种算法与典型的最邻近选择合并策略相比较,可以减少20%～30%的总连线长度.     

A High-Speed Variation-Tolerant Interconnect Technique for Sub-Threshold Circuits Using Capacitive Boosting

This paper describes an interconnect technique for subthreshold circuits to improve global wire delay and reduce the delay variation due to process-voltage-temperature (PVT) fluctuations. By internally boosting the gate voltage of the driver transistors, operating region is shifted from subthreshold region to super-threshold region enhancing performance and improving tolerance to PVT variations. Simulations of a clock distribution network using the proposed driver shows a 66%-76% reduction in 3sigma clock skew value and 84%-88% reduction in clock tree delay compared to using conventional drivers. A 0.4-V test chip has been fabricated in a 0.18-mum 6-metal CMOS process to demonstrate the effectiveness of the proposed scheme. Measurement results show 2.6times faster switching speed and 2.4times less delay sensitivity under temperature variations.     

百万门系统级芯片的时钟树设计

层次化设计是片上集成芯片开发采用的主流方法,它是一种自底向上的流程。但层次化设计也带来了时钟树设计难以掌握的问题。针对一款复杂So C系统芯片时钟树设计,详细分析了层次化时钟树综合需要解决的关键点,并提出有效的解决方案。实验表明该方案可以迅速实现时钟树收敛,提高设计效率。     

A Low-Power Delay Buffer Using Gated Driver Tree

This paper presents circuit design of a low-power delay buffer. The proposed delay buffer uses several new techniques to reduce its power consumption. Since delay buffers are accessed sequentially, it adopts a ring-counter addressing scheme. In the ring counter, double-edge-triggered (DET) flip-flops are utilized to reduce the operating frequency by half and the C-element gated-clock strategy is proposed. A novel gated-clock-driver tree is then applied to further reduce the activity along the clock distribution network. Moreover, the gated-driver-tree idea is also employed in the input and output ports of the memory block to decrease their loading, thus saving even more power. Both simulation results and experimental results show great improvement in power consumption. A 256$,times,$8 delay buffer is fabricated and verified in 0.18 $mu {hbox {m}}$ CMOS technology and it dissipates only 2.56 mW when operating at 135 MHz from 1.8-V supply voltage.      

Discharge-path-based antenna effect detection and fixing for X-architecture clock tree

Antenna effect is a phenomenon in the plasma-based nanometer process and directly influences the manufacturing yield of VLSI circuits. Because antenna-critical metal wires have sufficient charges to damage the thin gate oxides of the clock input ports connected by a clock tree, the standard cells or IPs cannot be driven by the clock source synchronously. For a given X-architecture clock tree that connects n clock sinks, we consider the antenna effect in the clock tree and propose a discharge-path-based antenna effect detection method. To fix the antenna violations, we use the jumper insertion technique recommended by foundries. Furthermore, we integrate the layer assignment technique to reduce the inserted jumper and via counts. Differing from the existing works, the delay of vias is considered in delay calculation, and a wire sizing technique is applied for clock skew compensation after fixing the antenna violations. Experimental results on benchmarks show that our algorithm runs in O(n²) to averagely insert 48.21% less jumpers and reduce 20.35% in vias compared with other previous algorithms. Moreover, the SPICE simulation further verifies the correctness of the resulting clock tree.     

带偏差约束的时钟线网的拓扑构造和优化

提出了一种新的拓扑构造和优化方法,综合考虑了几种拓扑构造方法的优点,总体考虑偏差约束,局部进行线长优化.实验结果表明,它可以有效控制节点之间的偏差,同时保证减小时钟布线树的整体线长.     

Optimization of buffer stages in bipolar VLSI systems

Discusses the power-delay optimization of emitter followers, of level shifters used in cascode emitter coupled logic (CECL) VLSI systems, and of Darlington buffers. Quasi-linear large-signal circuit models are developed. From these, analytical delay expressions for all these buffer stages in high-speed operation, where the driving capability is substantially reduced, are extracted. In addition, the critical bias current for minimum power-delay product is determined. Basically, the same delay expressions apply also to BiCMOS buffers. The simplicity of these expressions allows a fast optimization procedure, with little loss of accuracy, as the calculation results deviate from simulation mostly less than 5%.<>     

低偏斜、高变化容忍的层次化无缓冲谐振时钟分布网络

无缓冲谐振时钟分布网络能够最小化同步系统的时钟功耗。但由于没有缓冲器,时钟网络的偏斜受到多方面因素的影响,例如时钟互连线寄生参数的差异,非平衡时钟负载以及工艺、电压温度变化。本文提出了一种层次化的两相无缓冲谐振时钟互连网络结构,将网格型和树型结构的各自优点相结合。在TSMC 65nm标准CMOS工艺下,通过一个流水线乘法器电路分析了该结构时钟网络的偏斜及变化容忍特性。版图后仿真结果表明,层次化时钟网络的偏斜分别比纯网格和纯H树结构时钟网络降低超过75%和65%,而且在非平衡时钟负载或工艺、电压温度变化的情况下,时钟网络偏斜最高小于7ps,不超过整个时钟周期（约760ps）的1%。     

Self-Timed Regenerators for High-Speed and Low-Power On-Chip Global Interconnect

In this paper, we propose a new circuit technique called self-timed regenerator (STR) to improve both speed and power for on-chip global interconnects. The proposed circuits are placed along global wires to compensate the loss in resistive wires and to amplify the effect of wire inductance in the wires to enable transmission line like behavior. For different wire widths, the number of STR and sizing of the transistors are optimized to accelerate the signal propagation while consuming minimum power. In 90-nm CMOS technology, STR design achieved a delay improvement of 14% over the conventional repeater design. Furthermore, 20% power reduction is achieved for iso-delay, and 8% delay improvement for iso-power compared with the repeater design. The proposed technique has also been applied to a clock distribution network, reducing clock power by 26%.     

Combinatorial Algorithms for Fast Clock Mesh Optimization

Clock mesh has been widely used to distribute the clock signal across the chip. Clock mesh is driven by a top-level tree and a set of mesh buffers. We present fast and efficient combinatorial algorithms to simultaneously identify the candidate locations as well as sizes of the buffers driving the clock mesh. We show that such a sizing offers a better solution than inserting buffers of uniform size across the mesh. Due to the high redundancy, a mesh architecture offers high tolerance toward variations in clock skew. However, such a redundancy comes at the expense of mesh wire length and power dissipation. Based on survivable network theory, we formulate the problem to reduce the clock mesh by retaining only those edges that are critical to maintain redundancy. Such a formulation offers designer the option to tradeoff between power and tolerance to process variations. We present efficient postprocessing techniques to reduce the size of the mesh buffers after mesh reduction. Experimental results indicate that our techniques can result in power savings up to 28% with less than 3.3% delay penalty. We also present driver models that can help in simulating the clock mesh. Such models achieve near-HSPICE accuracy with significant speedup in run time.      

基于Encounter的低功耗时钟树综合研究

以基于Cadence CCOPT引擎设计时钟树为例,介绍了以降低时钟树功耗为主要目的,使用门控技术,以及选择合适缓冲器、反相器构建时钟树的方法。通过完成物理设计动态仿真和功耗分析的数据表明,在保证时序收敛的前提下,使用门控技术和选用不同缓冲器、反向器对整个时钟树的功耗及性能影响进行分析。实验结构表明,对使用门控技术芯片的功耗在不同的操作条件下,整个时钟树上的功耗节省约50%;适合使用缓冲器和方向器构建时钟树。同时,在使用达到相同驱动的能力缓冲器和反相器情况下,使用缓冲器的时钟树较使用反相器的时钟树节省30%。