CARTS 1995 Paper

These electrical simulation programs have grown out of SPICE. SPICE is an acronym that stands for Simulation Program for IC Emulation. This is a tool originally intended to aid in the understanding of the performance of integrated circuits (ICs). Today, SPICE modeling has moved well beyond integrated circuit emulation to full circuit emulation with some packages also allowing for environmental effects. This tool is seen by many as an effective means of reducing cycle time from circuit design to manufacturing by eliminating most of the prototype work needed in circuit board design. However good the software, its practical application may be hindered because individual components often do not always behave as predicted by ideal models. Discussions with our customers affirmed their need for more realistic models. Much performance information on capacitors already existed in our files, so our primary objective was to reduce this empirical data to a “SPICE-friendly” format. We desired to purchase a SPICE software package that was popular and used models that were compatible with other software packages. However the software available today is so numerous and different that the “most popular” category was never definable. Their differences also eliminated generating models on a universal basis. However, most software did allow creation of sub-circuits that could be substituted for components, or the importing of frequency related data that would allow a component to be created. Discussing with SPICE practitioners who were interested in realistic capacitor emulation directed us to the use of a general mathematical software for the capacitor models. We started our analysis by using Mathcad® software to generate the frequency responses necessary. In addition, we could use this software to generate ASCII table listings of Frequency, Impedance, ESR (effective series resistance), Capacitance, DF (dissipation factor or resistance divided by reactance), and Phase Angle throughout the chosen frequency spectrum. These could then be imported into many other packages, including spreadsheet software. The simple RLC model (Figure 1) is often considered as a good representative of the component in varying frequency applications. Many papers and charts have depicted this model as representative of a capacitor’s behavior over frequency and some newer instruments have capability of defining the elements in a component under test. However, things are never as simple as they seem. For example, the resistive elements change with frequency, and electrolytic capacitors have a fairly steep capacitance roll-off at higher frequencies. These reactions now make the ESR and capacitance frequency dependent. These dependencies can be handled as mathematical dependencies, or the complexity of the model could be increased to a more complex circuit representation. We have used both methods in our models.