Do you take the fastest route, the shortest route, the one that is most scenic, the cheapest route, the one you have traveled before and with which you are comfortable, or one where you can stop along the way and see some sites? Consider an analogy: you need to travel from point A (the source impedance) to point B (the load impedance). But the choice of “best” topology among the possible ones is a function of design priorities. Certainly, the component values can be worked out for a given matching-circuit topology. Q: Why is this difficult? Isn’t this just a matter of detailed calculations which can be automated?Ī: Yes and no. There are many topologies for implementing networks that can do this, but determining the specific values of the components within these networks is very difficult. Q: Once you know the source and load impedance, what’s the next step?Ī: The next step is to devise a matching network so that the source sees an impedance equal to its complex conjugate, and the load sees a source with an impedance equal to its own complex conjugate. The difficulty of assessing these impedances increases with frequency.Ī: A sophisticated test instrument called a vector network analyzer (VNA), as well as a test suite are used ( Figure 1.) The VNA sweeps across the frequency range of interest, measures the impedance, and then provides a table or graphical representation of the results.

In these cases, impedances must be measured. In many cases, impedances must be determined by a detailed model of the circuit and its many elements, which is a difficult task for high-frequency RF. In some cases, such as individual components, the vendor provides this data however, parasitics and other in-circuit factors will change these values. Q: What are the challenges in impedance matching?Ī: The first challenge is figuring out what the source output impedance and load impedance actually are. The Smith chart is a very helpful graphical tool for developing the matching network. It may seem that doing a few calculations using a software package is all that is needed, but the reality is far more complicated. Once the need for an impedance-matching network is determined - and it is very likely needed - the next challenge is defining and creating this network. Part 1 looked at impedance matching and the need for a complex conjugate impedance at the load, compared to the source impedance.

Impedance matching smith chart