The TimberWolf placement and routing package

TimberWolf is an integrated set of placement and routing optimization programs. The general combinatorial optimization technique known as simulated annealing is used by each program. Programs for standard cell, macro/custom cell, and gate-array placement, as well as standard cell global routing, have been developed. Experimental results on industrial circuits show that area savings over existing layout programs ranging from 15 to 62% are possible.     

A performance-driven placement tool for analog integrated circuits

This paper presents a new approach toward performance-driven placement of analog integrated circuits. The freedom in placing the devices is used to control the layout-induced performance degradation within the margins imposed by the designer's specifications. This guarantees that the resulting layout will meet all specifications by construction. During each iteration of the simulated annealing algorithm, the layout-induced performance degradation is calculated from the geometrical properties of the intermediate solution. The placement tool inherently handles symmetry constraints, circuit loading effects and device mismatches. The feasibility of the approach is demonstrated with practical circuit examples     

Layout-Specific Circuit Evaluation in 3-D Integrated Circuits

In this paper, we describe a comprehensive layout methodology for bonded three-dimensional integrated circuits (3D ICs). In bonded 3D integration technology, parts of a circuit are fabricated on different wafers, and then, the wafers are bonded with a glue layer of Cu or polymer based adhesive. Using our layout methodology, designers can layout such 3D circuits with necessary information on inter-wafer via/contact and orientation of each wafer embedded in the layout. We have implemented the layout methodology in 3DMagic. Availability of 3DMagic has led to interesting research with a wide range of layout-specific circuit evaluation, from performance comparison of 2D and 3D circuits to layout-specific reliability analyses in 3D circuits. Using 3DMagic, researchers have designed and simulated an 8-bit encryption processor mapped into 2D and 3D FPGA layouts. Moreover, the layout methodology is an essential element of our ongoing research for the framework of a novel Reliability Computer Aided Design tool, ERNI-3D.     

Automatic layout synthesis of analog ICs using circuit recognition and constraint analysis techniques

A systematic method for automatic layout synthesis of analog integrated circuit modules is presented. This method uses analog circuit recognition and critical net analysis techniques to derive proper layout constraints for analog circuit performance optimization. These layout constraints are analyzed and prioritized according to the recognized analog circuit topologies and classified net sensitivities. The weighted constraints are then used to drive the physical layout generation process to obtain a high-quality custom circuit layout. An efficient, constraint-driven analog floorplanning technique based on a zone-sensitivity partitioning algorithm is specially developed to generate a slicing floorplan incorporating the layout constraints. This layout synthesis approach has three key advantages. First, it can produce a satisfactory analog circuit performance with negligible degradation due to the layout-introduced parasitic effects. Second, it allows a complete automation for netlist-to-layout synthesis so that the layout tool can be used by VLSI system designers. Finally, this method is quite general and can be applied to handle a wide variety of analog circuits. Experimental results in CMOS operational amplifiers and a comparator are presented.     

Analog circuit design optimization based on symbolic simulation andsimulated annealing

A methodology for the automatic design optimization of analog integrated circuits is presented. A non-fixed-topology approach is realized by combining the optimization program OPTIMAN with the symbolic simulator ISAAC. After selecting a circuit topology, the user invokes ISAAC to model the circuit. ISAAC generates both exact and simplified analytic expressions, describing the circuit's behavior. The model is then passed to the design optimization program OPTIMAN. This program is based on a generalized formulation of the analog design problem. For the selected topology, the independent design variables are automatically extracted and OPTIMAN sizes all elements to satisfy the performance constraints, thereby optimizing a user-defined design objective. The global optimization method used on the analytic circuit models is simulated annealing. Practical examples show that OPTIMAN quickly designs analog circuits, closely meeting the specifications, and that it is a flexible and reliable design and exploration tool     

KOAN/ANAGRAM II: new tools for device-level analog placement androuting

The authors describe KOAN and ANAGRAM II, new tools for device-level analog placement and routing. Analog layout tools that merely apply known digital macrocell techniques fall short of achieving the density and performance of handcrafted analog cells. KOAN and ANAGRAM II differ from previous approaches by using general algorithmic techniques to find critical device-level layout optimizations rather than relying on a large library of fixed-topology module generators. New placement algorithms implemented in KOAN handle complex layout symmetries, dynamic merging and abutment of individual devices, and flexible generation of wells and bulk constants. New routing algorithms implemented in ANAGRAM II handle arbitrary gridless design rules in addition to over-the-device, crosstalk-avoiding, mirror-symmetric, and self-symmetric wiring. Examples of CMOS and BiCMOS analog cell layouts produced by these tools are presented     

Electromigration-aware analog Router with multilayer multiport terminal structures

The combined effects of current densities and temperature in the interconnects may cause the failure of a circuit due to electromigration (EM). EM becomes increasingly more relevant with the ongoing reduction in circuit sizes caused by the evolution of nanoscale integration processes. Therefore EM effects must be taken into account in the design of both power networks and signal wires of analog or mixed-signal integrated circuits (ICs), to make their impact on the circuits’ reliability negligible. In previous EM-aware analog IC routing approaches, ‘dot-models’ are assumed for the terminals, i.e. each terminal has only one port that needs to be routed; however, in practice, analog standard cells usually contain multiple electrically-equivalent locations, often distributed over different fabrications layers, where legal connections can be made, multiport terminals, which need to be properly explored. This paper describes an EM-aware routing methodology considering multiport multiterminal signal nets of analog ICs. The complete design flow is detailed and demonstrated with experimental results and also, by generating the routing for two typical analog circuit structures for the UMC 130 nm design process; the automatically generated layouts are validated using the industrial grade Calibre^® tool.     

Performance-constrained analogue layout retargeting and optimisation with geometric programming

Layout parasitic has crucial influence on the performance of analogue integrated circuits. The paper presents a performance-constrained analogue layout retargeting and optimisation scheme. Geometric programming (GP), is a kind of nonlinear optimisation problem, is used in the method, which can be transferred or fitted into a convex optimisation problem based on mathematical analyses. Then, a global optimum solution can be achieved. To achieve the desired circuit performance, performance sensitivities based on layout parasitic are carried out in the analogue layout optimisation. In addition, a central difference method is applied to control parasitic-related layout geometries by constructing a set of performance constraints subject to maximum performance deviation. At last, a two-stage Miller-compensated operational amplifier and a single-ended folded cascode operational amplifier are simulated with the proposed scheme. The automatically generated target layouts can satisfy performance constraints to ensure the desired specifications. The experimental results show that the scheme can achieve effective retargeting of analogue circuit with less layout area and better circuit performance.     

带寄生及匹配约束的CMOS模拟电路模块的STACK生成优化方法

模拟电路的性能紧密依赖于版图的寄生参数和匹配特性 .提出了用以描述分布式的寄生电容和由于工艺梯度变化而产生的寄生参数不匹配以及 STACK内连线的不匹配的模型 .基于该模型 ,一种新的 STACK生成方法用来控制版图的寄生参数和匹配特性 ,优化 STACK的形状和确保为所给出的模拟电路模块生成相映的欧拉图 .一个 OPA电路的例子说明了所提出的版图优化方法可以提高诸如单位增益带宽和相位余量等电路性能     

带寄生及匹配约束的CMOS模拟电路模块的STACK生成优化方法

模拟电路的性能紧密依赖于版图的寄生参数和匹配特性．提出了用以描述分布式的寄生电容和由于工艺梯度变化而产生的寄生参数不匹配以及STACK内连线的不匹配的模型．基于该模型,一种新的STACK生成方法用来控制版图的寄生参数和匹配特性,优化STACK的形状和确保为所给出的模拟电路模块生成相映的欧拉图．一个OPA电路的例子说明了所提出的版图优化方法可以提高诸如单位增益带宽和相位余量等电路性能．     

Reliability optimization of analog integrated circuits considering the trade-off between lifetime and area

The reliability of analog integrated circuits becomes a major concern for the semiconductor industry as technology continuously scales. Among the many contributing factors, manufacturing process induced parameter variations and lifetime operational-condition-dependent transistor aging are two major hurdles limiting the reliability of analog circuits. Process variations mainly influence the parametric yield value of the fresh circuits, while transistor aging due to physical effects, such as Negative Bias Temperature Instability (NBTI) and Hot Carrier Injection (HCI), will cause another yield loss during circuit lifetime. In the past decades, the two issues were mainly studied separately by various communities, but analog designers nowadays need an accurate yet efficient method to analyze and optimize their circuits during the design phase, to ensure a more robust design tolerant of such joint effects.This paper proposes an efficient method for sizing of analog circuits for reliability. It is based on the analysis and optimization of the fresh worst-case distance value for each circuit performance, which can be used to characterize the robustness of circuits considering process variations and aging effects in terms of x-sigma. The fresh and aged sizing rules as well as the maximum area constraints are checked during the optimization. The trade-off between the circuit lifetime and the price we pay in terms of layout area is studied in detail. According to the result of this trade-off analysis, a longer circuit lifetime requires more total area to be spent in layout, and designers can ensure the circuit robustness with certain layout area consumption.     

Measuring the uniqueness and variety of analog circuit design features

Analog circuit design activity is currently a less formalized process, in which the main source for innovation is the designer's ability to produce new designs by combining basic devices, sub-circuits, and ideas from similar solutions. There are few systematic methods that can fuse and transform the useful features of the existing designs into new solutions. Moreover, most automated circuit synthesis tools are still limited to routine tasks, like transistor sizing and layout design. Developing new design techniques that can combine the existing design features requires metrics that describe the uniqueness and variety of the features. This paper evaluates for analog circuits two such general-purpose metrics proposed in [1] and [2]. Three case studies are discussed on using the metrics to characterize the design features of current mirrors, transconductors, and operational amplifiers. The two metrics and the presented study is useful in producing an overall characterization of analog circuit features. This can help in enhancing the circuit design process, training of young designers, and developing new automated synthesis tools that can explore more solution space regions that are likely to include novel design features.     

Challenges and opportunities toward fully automated analog layout design

Realizing the layouts of analog/mixed-signal (AMS) integrated circuits (ICs) is a complicated task due to the high design flexibility and sensitive circuit performance. Compared with the advancements of digital IC layout automation, analog IC layout design is still heavily manual, which leads to a more time-consuming and error-prone process. In recent years, significant progress has been made in automated analog layout design with emerging of several open-source frameworks. This paper firstly reviews the existing state-of-the art AMS layout synthesis frameworks with focus on the different approaches and their individual challenges. We then present recent research trends and opportunities in the field. Finally, we summaries the paper with open questions and future directions for fully-automating the analog IC layout.     

信号流驱动的模拟电路版图综合方法

提出了一种新的基于信号流分析的模拟电路版图综合方法.电路分析子系统采用新提出的信号流分析方法再结合已有的电路拓扑分析和电路灵敏性分析方法生成布图约束控制电路性能的衰减.由于考虑了电路中有关信号流的启发式信息,该方法的复杂性较一般的纯粹性能驱动方法小.然后分别在器件生成子系统、布图子系统和布线子系统中实现这些约束,使得这些约束在最容易实现的阶段得到满足.实际的电路例子已经证明了这一方法可以获得出色的电路性能.     

Circuit layout

This paper gives a general overview of circuit layout, taking a unified approach to various styles of integrated circuits, printed circuit boards, and hybrid circuits. A lot of attention is given to the layout of large and complicated circuits, in particular, to the layout of very-large-scale-integration (VLSI) chips. Though the paper is an overview, and one could almost say a tutorial, it is intended for readers with some basic knowledge of what a circuit layout is and what some of the basic problems are. The main subjects discussed are: assignment of gates, placement methods, loose routing, final routing, and problems associated with the implementation of a hierarchical system. The emphasis is on new, not widely published methods, and on methods that seem to have potential for solving some of the current problems. Practical examples illustrate this rather personal account of circuit layout and sugsest where we may go from here.     

A Signal-Flow Driven Automatic Physical Synthesis Methodology for Analog Circuits

This paper introduces a novel automatic physical synthesis methodology for analog circuits based on the signal-flow analysis.Circuit analysis sub-system adopts the newly advanced methodology,circuit topology analysis,and circuit sensitivity analysis to generate layout constraints and control performance degradations.Considering the heuristic information about signalflow，complexity of the methodology is less than the pure performance-driven methodology.And then these constraints are implemented in device generation,placement，and routing sub-systems separately,which makes the different constraints be satisfied at most easily implemented stages.Excellent circuit performance obtained by the methodology is demonstrated by practical circuit examples.