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# Partial Conductor and Cell Assignment Algorithm for Capacitance Programs

IP.com Disclosure Number: IPCOM000085133D
Original Publication Date: 1976-Feb-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 44K

IBM

## Related People

Brennan, PA: AUTHOR [+2]

## Abstract

The application of capacitance computation programs to integrated circuits, the method for which is described in reference [1], have supplied accurate answers for many problems. There are two types of geometries which have remained unresolved until now. One of these problems referred to as the "near conductor problem", is due to an approximation of the charge distribution on the conductors. The second problem, which is referred to as the "small coupling" problem, occurs due to subtraction of almost equal numbers in the matrix inversion to obtain the solution for the charges.

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Partial Conductor and Cell Assignment Algorithm for Capacitance Programs

The application of capacitance computation programs to integrated circuits, the method for which is described in reference [1], have supplied accurate answers for many problems. There are two types of geometries which have remained unresolved until now. One of these problems referred to as the "near conductor problem", is due to an approximation of the charge distribution on the conductors. The second problem, which is referred to as the "small coupling" problem, occurs due to subtraction of almost equal numbers in the matrix inversion to obtain the solution for the charges.

Sometimes negative capacitances are obtained in this error prone process. The usual remedy for the first problem is to choose a larger number of cells on the conductors for a more accurate representation of the charge, while the solution to the small coupling problem is to minimize the number of cells involved, to minimize the number of subtractions in the solution process.

An algorithm is described herein which solves the near conductor problem using a small number of cells, and thus the small coupling problem is minimized at the same time. It is first noted that the near coupling problem occurs when conductors are very close together and overlapping. Two examples are shown in Figs. 1a and 1b.

A large number of experiments were conducted on geometries like this and the following effective remedy has been found. Whenever the edge of one conductor is close to the surface of another co...