However, some commercial applications and simulation tools will display impedance data in a Smith chart. As a graphical method for performing impedance matching, it was very useful before the time of graphical computers and simulation tools for plotting impedance. This unique type of chart was developed by Philip Smith at Bell Telephone's Radio Research Lab in the 1930s.

What Is a Smith Chart?Ī Smith chart is a type of graph used to plot the normalized impedance of a circuit, a circuit element, or an interconnect. Smith charts are a standard tool used by many RF engineers, so it pays to know how to use a Smith chart for impedance matching. Using a Smith chart might seem complicated to new designers, and one might question why it is any more or less useful than a graph in Cartesian coordinates. In some cases, such as with transmission line stub matching in RF circuits or input impedance matching to a feedline’s characteristic impedance, a graphical representation of impedance can aid impedance matching.Ī Smith chart provides just such a graphical representation of impedance, and it is a useful tool for understanding how impedance varies in different systems. In many cases, you need to measure and carefully simulate the appropriate impedance required to ensure impedance matching and prevent power reflection. High speed and high frequency systems need impedance matching to ensure efficient power transfer and prevent reflections. Impedance matching in this PCB can be determined using a Smith chart Once impedance matching requirements are determined, the results can be simulated in a SPICE-based simulation application. One popular method for plotting impedance and determining impedance matching is to use a Smith chart. Reflection coefficients can be read directly from the chart as they are unit-less parameters.There are many methods for impedance matching in your circuits.

Once an answer is obtained through the graphical constructions described below, it is straightforward to convert between normalised impedance (or normalised admittance) and the corresponding unnormalized value by multiplying by the characteristic impedance (admittance). The most commonly used normalization impedance is 50 ohms. Normalised scaling allows the Smith chart to be used for problems involving any characteristic or system impedance which is represented by the center point of the chart. These are often known as the Z, Y and YZ Smith charts respectively. The Smith chart is plotted on the complex reflection coefficient plane in two dimensions and is scaled in normalised impedance (the most common), normalised admittance or both, using different colours to distinguish between them.

Y smith chart