The Research On The Design Automation Methods Of Analog Integrated Circuits

With the rapid growth of VLSI technology, the design of application specific integrated circuits (ASIC) moves steadily towards integration of complete systems into a single chips. This involves the implementation of both analog and digital circuits. The digital part of mixed-signal system can be efficiently designed with a low effort using modern automation tools. In contrast, there is a lack of synthesis environments for analog circuits. Analog IC design continues to seize a considerable portion of the total design time and cost for mixed-signal systems. Slow analog automation design technologies and tools become the bottleneck in the mixed analog/digital design.In this paper, Design characteristics and limitations inherent in analog circuits are discussed, which are the main reasons that the development of analog CAD tools has lagged far behind that of digital CAD tools. Hierarchical decomposition technique in digital domain also permeates the analog domain. The modes of analog circuits are hierarchically divided into different levels including the behavior level, the construction level, the function level, the circuit level, the device level and layout level etc, which is very useful to solve the difficulties in the analog circuits design automation.Performance evaluation and optimization engine are two important modules in the analog integrated circuit automation synthesis. Two approaches based on SPICE and circuits equations are proposed to evaluate circuits' performance. The paper presents an improved method, which can tackle performance evaluation gracefully. Mathematical model for optimization-based technique of analog synthesis is studied; analog design problem can be regarded as a minimization problem in multidimensional continuous space with an objective function. Two mathematical optimization algorithms including simplex method and simulated annealing are used to solve the constraint optimization problems. Besides, to speed up the global convergence and decrease computational cost, a method combined simplex method and simulated annealing is discussed in detail.The analog synthesis process consists of two subprocesses: high-level synthesis and physical synthesis, high-level synthesis is divided into construction level synthesis and circuit level synthesis in the paper. The necessities and advantages of VHDL-AMS in the design of mixed signal IC are explained through its theoretical basis and its application scopes. Approaches of topology selection including hierarchical decomposition, rule-based, algorithmic-based and fixed-topology are discussed in detail, and devices sizing techniques are also discussed. Two methods includingequation-based method and simulation-based method are used to synthesis analog cells.The optimization-based technique for layout synthesis of analog systems is discussed in the paper, a method is proposed which can combine block parameter exploration, block placement and global interconnect routing while maintaining an accurate perspective on the layout parasitics.