A Design Database For Stripline Interconnections

Abstract

The advancing semiconductor technologies are unabatedly raising the circuit and device performance. This, in turn, raises the demands on the signal propagation characteristics of the chip and module interconnecting systems. As these requirements become ever tighter, better design aids become indispensable. The experience with an experimental design database to form the core of a stripline CAD program is described. The design space can be covered with a sufficiently small number of points to allow instantaneous response from the necessary scanning and interpolation operations, while accuracies better thm 1 % can be achieved. A database allows the determination of electrical parameters from line cross-section geometries as well as the inverse, i.e., the establishment of line geometries for given electrical parameters, with comparable ease. The scaling properties of transmission line systems permit very efficient coverage of the design space at the cost of added intricacies in the database organization and in the scanning algorithms. A contemporary personal computer is fully adequate to run the resulting CAD program. However, more powerful machines are preferable for the one-time numerical computations for generating the database. A CAD program with swift response is an effective solution to these problems. Such a program can be developed around a database consisting of pre-computed electrical parameters for line geometries that uniformly cover the design space, i.e., the ranges of the geometrical dimensions reasonably achievable by a technology. In such an approach, the intricacies associated with numerical solutions of the boundary value problems are only faced once, during generation of the database, and can be relegated to the experts. Once the database is established, electrical parameters for given line geometries, or line geometries for given electrical parameters, can be determined by table-lookup and interpolatlon routines. These routines are fast enough to provide literally instantaneous response, making such CAD programs truly interactive. In the next section, the theory of multi-conductor transmission lines is briefly reviewed and the equations for calculating the electrical parameters of a two-conductor system are given. To illustrate the concept of a database-driven CAD program, a specific database for the two-line system is used here as an example. The inductances and capacitances were computed with the parameter extraction program UAC, developed at the University of Arizona, [I], [a] The main design considerations for the database are discussed in Section 3.