![]() This shifts the peak in all of the models, so it seems that some get better and some get worse. ![]() Adding a fixed shunt capacitance in parallel with each matching capacitor or a fixed inductance in series with each matching inductor.The optimizer consistently pushed this toward zero, so I think I've built the miter pretty well. Adding a fixed shunt capacitance at the mitered corner to model any additional capacitance there.I've tried a lot of variations looking for a better match, including: Here is an example (using the same optimized board properties and parasitics as above) where the model matches quite well: Some component values match better than others, so the problem does not seem to be a fixed parasitic inductance/capacitance on the board. For this measurement, L15 = L5 = 2.2 nH and C16 = C13 = 1.0 pF. Solid lines show amplitude of S11 and dashed lines show phase. Here, the measured value is shown in blue and the model in red. For example, here is a plot comparing one measurement with its associated model: In particular, each set of component values shows a resonant peak at some frequency, but in my model the peak typically falls at a slightly different frequency. ![]() I have been unable to find optimized values (for board properties and parasitic elements) which match the measured S11 perfectly. Here's where I'm running into a bit of trouble. The basic dimensions for the transmission line components are specified in an equation: Note that I am using 2-port S-parameter models for each component from the manufacturer's website (Murata GRM1555 and LQG15). On the left, we have an ideal transmission line which represents the pigtail, then an inductor which represents the short length of center conductor which lies outside the dielectric of the pigtail. The Qucs model I've built for each permutation looks like this: I've made S11 measurements using 1.0 and 2.2 nH inductors and 1.0 and 2.2 nF capacitors. Here's what the board looks like with the pigtail and matching components installed. Finally, use the Qucs optimization tools to find the optimal matching component values.Use the Qucs optimization tools to find board properties and parasitics which match the measured S11 values.Build a model of the matching circuit in Qucs.Repeat steps 2-3 for several sets of component values.Place a random selection of inductors and capacitors on the board.Add a short length of semi-rigid coax where the EFR32BG13 will go.In addition to the visible layers (top and bottom), layer 2 is a solid ground plane and layer 3 is a solid VCC plane.Īs a bit of a learning opportunity, I've decided to use Qucs to select the matching components as follows: The current board layout looks like this: I am designing a matching circuit for an EFR32BG13 SoC.
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