Introduction to VLSI Systems
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The random logic portion of a chip Implementing a set of Boolean functions and sequential circuits usually represents a major contribution to chip area. Obviously, there are many circuits which realize the same Boolean function. Unfortunately, at present there is no general theory that provides designers (and design automation programs) with lower bounds for total area, for gate oxide area, and for delay time of logic Implementations in Integrated systems. Therefore, the main task for the computer optimization program appears In choice of the circuit with the most convenient layout. DIADES is a design automation system with register-transfer level description on its Input and CIF file on output [5]. The digital circuit can be described in both behavioral and structural mode. A set of successive compilations and hardware implementing and optimizing transformations create the description of the network on the level of logic gates and pass transistors. As the output of hardware compilation from the higher level, this description is usually nonoptimal and thus is next optimized by recursive technology independent transformations based on Boolean algebra (like A*O &equil; O, A*A &equil; A, etc.). Inverters are also inserted into long chains of AND or OR gates, being the results of iterative circuits' compilation [4]. The next stages are: technology dependant optimization of the logic network, and network's layout. It is assumed that the resultant network is multilevel, consists of complex negative gates, and is realized in semiregular Weinberger-style gate matrix layout. The logic minimization method intended for layout minimization is described in this paper. It is assumed in our silicon compiler, that logic is constructed of n-channel, polysilicon gate MOSFET ratioless complex gates, performing any negative function. By negative function we understand negation of positive function, while positive function is any combination of AND and OR functors [1]. Functions for evaluation of circuit's performance parameters such as total area, area of gate oxide, and gate delay time are used. These functions are defined in terms of basic technology and selected topology parameters. The method can be adapted to other technologies.