We present a new synthesis strategy that can automate fully the path from an analog circuit topology and performance specifications to a sized circuit schematic. This strategy relies on asymptotic waveform evaluation to predict circuit performance and simulated annealing to solve a novel unconstrained optimization formulation of the circuit synthesis problem. We have implemented this strategy in a pair of tools called ASTRX and OBLX. To show the generality of our new approach, we have used this system to resynthesize essentially all the analog synthesis benchmarks published in the past decade; ASTRX/OBLX has resynthesized circuits in an afternoon that, for some prior approaches, had required months. To show the viability of the approach on difficult circuits, we have resynthesized a recently published (and patented), high-performance operational amplifier; ASTRX/OBLX achieved performance comparable to the expert manual design. And finally, to test the limits of the approach on industrial-sized problems, we have synthesized the component cells of a pipelined A/D converter; ASTRX/OBLX successfully generated cells 2-3/spl times/ more complex than those published previously.

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Synthesis of high-performance analog circuits in ASTRX/OBLX

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

This paper introduces an automated circuit design system for the evolution and subsequent invention of CMOS amplifiers. The proposed system relies on a mix of genetic programming and a new topology-independent design optimization method referred to as current-flow analysis. Genetic programming evolves new circuit topologies from the collection of primitive devices and basic building blocks. Current-flow analysis screens and corrects circuits using topology-independent design rules. Experimental results show a promising improvement on the design of operational amplifiers that make the automated analog design environment using genetic programming a lot more practical.

The invention of CMOS amplifiers using genetic programming and current-flow analysis

We present a methodology for automated sizing of analog cells using statistical optimization in a simulation based approach. This methodology enables us to design complex analog cells from scratch within reasonable CPU time. Three different specification types are covered: strong constraints on the electrical performance of the cells, weak constraints on this performance, and design objectives. A mathematical cost function is proposed and a bunch of heuristics is given to increase accuracy and reduce CPU time to minimize the cost function. A technique is also presented to yield designs with reduced variability in the performance parameters, under random variations of the transistor technological parameters. Several CMOS analog cells with complexity levels up to 48 transistors are designed for illustration. Measurements from fabricated prototypes demonstrate the suitability of the proposed methodology.

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Global design of analog cells using statistical optimization techniques

Symbolic analog-circuit analysis has many applications, and is especially useful for analog synthesis and testability analysis. In this paper, we present a new approach to exact and canonical symbolic analysis by exploiting the sparsity and sharing of product terms. It consists of representing the symbolic determinant of a circuit matrix by a graph---called determinant decision diagram (DDD)---and performing symbolic analysis by graph manipulations. We showed that DDD construction and DDD-based symbolic analysis can be performed in time complexity proportional to the number of DDD vertices. We described a vertex ordering heuristic, and showed that the number of DDD vertices can be quite small --- usually orders-of-magnitude less than the number of product terms. The algorithm has been implemented. An order-of-magnitude improvement in both CPU time and memory usages over existing symbolic analyzers ISAAC and Maple-V has been observed for large analog circuits.

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Symbolic analysis of large analog circuits with determinant decision diagrams

An analog design automation system is presented. The system is capable of designing, analyzing and optimizing analog circuits in MOS, bipolar or BiCMOS technologies. Its main feature is that it is open to the user's expertise. The expertise that can be introduced is knowledge concerning the topology and functionality of a customer circuit, which can be complemented with knowledge about its device sizing sequence. Due to the fact that it is open, it assists and encourages designers in storing their expertise in a structured way, so that it can be reused. The tool includes Monte-Carlo analysis algorithms which ensure an extensive verification and characterization of the design. >

An open design tool for analog circuits

An open analog design system is presented that can generate layouts of analog cells and subsystems starting from desired functional specifications and a technology description which can be CMOS, bipolar, or BICMOS The design system includes model parameter verification, symbolic analysis, design, optimization, and automatic documentation of cells The schematics of the analog cells can be selected out of a library or can be entered by the designer Either a full description of the schematic is given or a new schematic is composed starting from a library of subblocks The layout generator, which is process portable, handles typical analog layout constraints during placement and routing All tools can be used in a full automatic mode or can be used interactively to allow more experienced designers to impose their point of view >

The ADAM analog design automation system

A design environment allowing the design analysis and optimization of analog building blocks, such as amplifiers, voltage references, etc., has been developed. There are two main programs: IDAC 3, which performs the design, and ILAC, which performs the layout. Two approaches are possible. The synthesis approach is an imitation of human designers; the design is done following predefined heuristics that may include iterations. The optimization approach uses the downhill simplex numerical optimization algorithm. The relative merits and disadvantages of numerical optimization versus analytical design strategies are discussed. >

J. Litsios

Papers

An open design tool for analog circuits

The ADAM analog design automation system

Design strategies versus numerical optimization for analog circuits