3.5 Bench Tuning and Measured Results
The final (fifth) step of the matching design is bench tuning with real measurements. The figure below shows the impedance and trans-
fer characteristic measurement setup. Port 1 of the VNA is connected to the soldering pad of the 2G4RF_IOP pin through a pigtail (the
EFR32 chip is removed here as only the matching network is measured). The reference plane of the S-parameter measurements is
shifted to the TX pin. Port 2 is connected to the matching 50 Ω side output through a UFL connector.
Figure 3.11. Match Impedance and Transfer Characteristic Measurement
The figure below shows the measured impedance and transfer characteristic of the ladder two-element match with the final SMD ele-
ments. As shown, the real part is very close to the targeted 20 Ω, but the reactance is slightly higher (14 Ω instead of the targeted 10
Ω). This slight deviation causes a negligible (> 0.1 dB) power drop, so the match is not tuned further.
Second harmonic suppression is only 13.7 dB, so the ladder two-element match is, as expected, only proper for the lower (< +10 dBm)
power regimes.
Figure 3.12. Measured S11 and S21 (Transfer) Characteristic of the Ladder 2-element SMD Match
The measured ladder two- and four-element spectrum plots in the middle of the band (2.45 GHz) with the 7x7 mm dual band EFR32
version is shown in in the first column of
Figure 3.13 Measured Spectrum Plots of the Dual Band 7x7 mm EFR32 with (a) a Ladder
Two-Element Match in 10 dBm Power State and (b) a Ladder Four-Element Match in 20 dBm Power State on page 15
. In the second
column, the four-element match spectrum is also given. The ladder two-element match is tested with a 10 dBm power setting, while the
four-element match is tested with a 20 dBm power setting.
In the 20 dBm power setting, the achieved fundamental power is ~19 dBm at 2.45 GHz. Large volume measurements show approxi-
mately ±1 dB variation of the output power. The average is typically ~19.5 dBm with 134 mA total IC current. Note that the loss of the
applied UFL connector is approximately 0.3–0.5dB. With direct connection, the delivered power is around 20 dBm.
AN930: EFR32 2.4 GHz Matching Guide
2.4 GHz RF Matching Design Steps
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