Appendix 3. 2.4 GHz Ladder 4-element RF Matching Design Steps
After the optimum termination impedance for the 2G4RF_IOP RF port is determined as Zload_opt = 23+j11.5 Ω in Chapter 2.1 the lad-
der four-element 2.4 GHz RF matching design for EFR32 chip has the following steps remaining:
1. Initial design with ideal, loss free elements and without PCB parasitics.
2. Design with parasitics using the initial design of the previous step as a starting point. The parasitics of the SMD elements and the
PCB have a significant effect at 2.4 GHz, so tuning/optimization of the design is required. Here, an optional EM simulation can be
performed for increased accuracy.
3. Bench testing and tuning.
Appendix 3.1 Initial Design with Ideal, Loss-free Elements
In this step, the ideal skeleton design of the ladder four-element match is shown with losses and parasitic-free discretes and without
PCB parasitics.
The ladder four-element match is devoted to 20 dBm applications, so the load impedance that the match should show at the IC side is:
Zload_opt = ~23+j11.5 Ω if the antenna side is terminated by 50 Ω.
A ladder four-element match can be designed in two ways: using the ladder two-element match with an additional two-element filter
section or using a four-element ma filter combo. In the latter case, all four elements take part in the impedance match, and,
thus, it is less sensitive to element spreading. Additionally, the (reactive) elements realize less phase shift, so the impedance locus
varies closer to the Smith chart center, which means a lower Q route. As a result, the loss of elements has less influence. Unfortunate-
ly, due to having multiple stages, the overall insertion loss can be higher with four elements. A possible ladder four-element design with
ideal elements is shown in the figure below. The antenna side is denoted by the 50 Ω ZL load impedance while the PA side impednace
is denoted by Zin.
Figure 3.1. Basic Ladder Four-Element Matching Technique with Ideal Lumped Elements
AN930: EFR32 2.4 GHz Matching Guide
2.4 GHz Ladder 4-element RF Matching Design Steps
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