Functional Verification in an Interactive Symbolic Ic Design Environment

This paper describes verification techniques that have been implemented as part of an interactive symbolic IC des ign system. Circuit analysis programs perform node extraction and gate decomposition. They generate both transistor and gate level circuit desriptions which are used as input to a transistor level digital MOS timing s imulator. The extraction programs make use of an intermediate circuit description language which captures both geometric placement and circuit connectivity. All programs are written in the C programming language and run under the UNIX operating system. An example is included to demonstrate the operation of these various techniques. l. INTRODUCTION Functional verification is an important and necessary step in the design of large scale integrated circuits. It is that part of the design cycle which eliminates most, preferably all, of the human errors introduced in the forward part of the design. It is generally a two stage process consisting firstly of automatic circuit extraction, in which electrical circuit descriptions are generated from the physical layout, and secondly of functional simulation of the derived circuit. Symbolic design techniques simplify the circuit extraction task as they introduce structural or circuit information into the layout file and remove unnecessary geometrical data. Interactive design techniques, however, place additional constraints on verification in that they demand fast response in order to avoid slowing the interactive design cycle. This paper describes verification techniques that have been implemented on MULGA [ L] a UNIXt based interactive symbolic layout system. They consist of two programs which perform nodal circuit extraction and gate decomposition , and EMU a transistor level MOS timing simulator. All programs are written in the C programming Language and run under the UNIX operating system in a microcomputer based design station. 2. MULGA Symbolic layout provides a means of abstracting the detailed and often laborious task of mask design. rt offers the advantages of manual layout with regard to density, along with reduced design time and reduced likelihood of manual error . MULGA is a UNIX based interactive symbolic design system consisting of a suite of programs residing on a high performance color display station. Figure l shows the various software components of MULGA and t UNIX is a trademark of Bell Laboratories CALTECH CONFERENCE ON VLSI, Janua~y 1981 286 8 Pyan Ackland ~ nd NeiL Weste INTERACTIVE EDITOR r---r I I