This survey presents an overview of recent advances in the state of the art for computer-aided design (CAD) tools for analog and mixed-signal integrated circuits (ICs). Analog blocks typically constitute only a small fraction of the components on mixed-signal ICs and emerging systems-on-a-chip (SoC) designs. But due to the increasing levels of integration available in silicon technology and the growing requirement for digital systems to communicate with the continuous-valued external world, there is a growing need for CAD tools that increase the design productivity and improve the quality of analog integrated circuits. This paper describes the motivation and evolution of these tools and outlines progress on the various design problems involved: simulation and modeling, symbolic analysis, synthesis and optimization, layout generation, yield analysis and design centering, and test. This paper summarizes the problems for which viable solutions are emerging and those which are still unsolved.

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Computer-aided design of analog and mixed-signal integrated circuits

We describe a new method for determining component values and transistor dimensions for CMOS operational amplifiers (op-amps). We observe that a wide variety of design objectives and constraints have a special form, i.e., they are posynomial functions of the design variables. As a result, the amplifier design problem can be expressed as a special form of optimization problem called geometric programming, for which very efficient global optimization methods have been developed. As a consequence we can efficiently determine globally optimal amplifier designs or globally optimal tradeoffs among competing performance measures such as power, open-loop gain, and bandwidth. Our method, therefore, yields completely automated sizing of (globally) optimal CMOS amplifiers, directly from specifications. In this paper, we apply this method to a specific widely used operational amplifier architecture, showing in detail how to formulate the design problem as a geometric program. We compute globally optimal tradeoff curves relating performance measures such as power dissipation, unity-gain bandwidth, and open-loop gain. We show how the method can he used to size robust designs, i.e., designs guaranteed to meet the specifications for a variety of process conditions and parameters.

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Optimal design of a CMOS op-amp via geometric programming

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. >

Analog circuit design optimization based on symbolic simulation and simulated annealing

This tutorial paper gives an overview of the history and present state of the art in symbolic analysis of electronic circuits at the so-called circuit level. Symbolic analysis is defined as a technique generating a closed-form analytic expression for a circuit characteristic with the circuit's elements represented by symbols. Such analytic information complements the results from numerical simulations. The paper then describes the different application areas of symbolic analysis for the design of analog circuits. Symbolic analysis is mainly used as a means to obtain insight into a circuit's behavior, to generate analytic models for automated circuit sizing, and in applications requiring the repetitive evaluation of circuit characteristics. Next, the present capabilities and limitations of symbolic analysis, both in functionality and efficiency, are discussed. The major symbolic analysis methods are presented, and algorithmic details are provided for symbolic approximation, hierarchical decomposition, and symbolic distortion analysis. Finally, existing symbolic simulators are compared, and directions for future research are pointed out. >

Symbolic analysis methods and applications for analog circuits: a tutorial overview

Platforms have become an important concept in the design of electronic systems. We present here the motivations behind the interest shown and the challenges that we have to face to make the Platform-based Design method a standard. As a generic term, platforms have meant different things to different people. The main challenges are to distill the essence of the method, to formalize it and to provide a framework to support its use in areas that go beyond the original domain of application.

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Benefits and challenges for platform-based design

This paper discusses the realization of an analogue module generator that forms part of a mixed analogue/digital design environment. It is able to design analogue functional modules such as like amplifiers, filters, etc., either in an automatic or in an interactive session, starting from performance specifications over topology selection, parameter optimization and simulation/verification down to lay-out. the analogue module generator is integrated in a commercial EDA framework. Practical design results show the capabilities and efficiency of the system.

An analogue module generator for mixed analogue/digital asic design

In this paper, the program DONALD is presented. DONALD constitutes a new approach to the use of numerical computation in circuit sizing. The program is able to numerically invert an analytic design model of an analog circuit in any arbitrary direction. It is therefore possible to answer with DONALD both design questions, analysis questions, as well as technology questions. To accomplish this, the program uses a new, heuristic algorithm for detection of minimal clusternodes is bipartite graphs. A graphical, mouse oriented user interface allows the user to make strategic and optimum moves through a circuit's design space.

DONALD: a workbench for interactive design space exploration and sizing of analog circuits

An intelligent design methodology for the design of analog functional blocks such as op-amps, comparators, etc. is described. The representation of design knowledge in design equations and the appropriate manipulation of this knowledge by the program DONALD results in a flexible approach which can easily be extended to new circuit topologies. The methodology is based on the recognition that analog design is essentially a reasoning process in the mathematical domain and that advanced symbolic and numerical simulation techniques are required to mimic this reasoning process. >

An intelligent analog IC design system based on manipulation of design equations

The ARIADNE approach to computer-aided synthesis and modeling of analog circuits is presented. It is a mathematical approach based on the use of equations. Equations are regarded as constraints on a circuit’s design space and analog circuit design is modeled as a constraint satisfaction problem. To generate and efficiently satisfy constraints, advanced computational techniques such as constraint propagation, interval propagation, symbolic simulation, and qualitative simulation are applied. These techniques cover design problems such as topology construction, modeling, nominal analysis, tolerance analysis, sizing and optimization of analog circuits. The advantage of this approach is the clear separation of design knowledge from design procedures. Design knowledge is modeled in declarative equation-based models (DEBMs). Design procedures are implemented into general applicable CAD tools. The ARIADNE approach closely matches the reasoning style applied by experienced designers. The integration of synthesis and modeling into one frame and the clear separation of design knowledge from design procedures eases the process of extending the synthesis system with new circuit topologies, turning it into an open design system. This system can be used by both inexperienced and experienced designers in either interactive or automated mode.

ARIADNE: a constraint-based approach to computer-aided synthesis and modeling of analog integrated circuits

A new design methodology for the design of arbitrary analogue functional blocks (op amps, comparators . . .) is presented. The method combines symbolic simulation, numerical optimization and knowledge-based techniques and covers the whole design path from analytic modeling over optimal circuit sizing down to layout. This path is repeatedly passed through on different hierarchical levels for higher-level blocks. The main advantage of the new CAD system is that it is not limited to a fixed set of circuit topologies. It can automatically design any new circuit by the introduction of artificial intelligence techniques: building block recognition, design equation manipulation, self-learning capabilities. . . These features make it an intelligent and flexible analogue design system. >

K. Swings

Papers

An analogue module generator for mixed analogue/digital asic design

DONALD: a workbench for interactive design space exploration and sizing of analog circuits

An intelligent analog IC design system based on manipulation of design equations

ARIADNE: a constraint-based approach to computer-aided synthesis and modeling of analog integrated circuits

An intelligent design system for analogue integrated circuits