## S Stands for Smith

For many electrical engineers, the complex s-plane, where upon the plotting of Laplace transforms take place, is something very familiar. Often, it’s used to plot the poles and zeros of a transfer function, be it open or closed loop. For a feedback amplifier circuit to be stable, for example, the open loop poles must be located on the left half of the s-plane. The s-plane can be used to plot the root locus of a transfer function, something that is useful in analyzing a loop’s stability. It’s also good for plotting impedances of circuit structures or components. For example, passive devices lives entirely on the right side of the s-plane since real-life passive devices can only have positive real impedances. This last point is important and I’ll return to it later in the post. What’s less familiar to most electrical engineers is the Smith chart. In fact, some EEs I’ve…