Computer Simulation of the Electrical Properties of Memory Arrays

The evolution of a simple mathematical model for pulse propagation in memory arrays and its implementation by computer programs is described. The development of the model is based initially on the properties of a simplified two-dimensional memory array using common bit-sense lines. The model is then generalized to include separate bit and sense lines. Finally, applications to three-dimensional arrays are considered. It is shown that for a wide variety of calculations nonlinear bit-storage devices such as ferrite cores, tunnel diodes, etc., can be replaced by linear equivalent circuits. With the aid of these equivalent circuits the array is characterized in the language of linear transmission-line theory. Two computer programs are described which solve the resulting differential equations. Applications of these computer programs to the analysis of sense-signal propagation, bit-sense noise, signal transfer between crossed wires, and propagation of pulses along bit lines are discussed. The mathematical theory is derived explicitly for ferrite-core memories but care is taken to point out the changes required to extend the model to other technologies. These changes can be effected in the supporting computer programs by a simple interchange of subroutines which characterize the properties of bit-storage devices.