Appendix 4.1 EM Simulations of the Tline Match
More accurate tuning can be done with EM simulations.
Figure 4.5 EM Simulation of the Tline Match on page 31
part a. shows the
EM simulated layout with 3.5 mm long and 0.2 mm wide transmission line. As the first design step, the C1 capacitor with 1 pF value
(Murata GRM155 series S-parameter file) is connected between Ports 7 and 8 as shown in part B of the following figure.
Figure 4.5. EM Simulation of the Tline Match
The simulated transfer characteristic and the impedance at the TX pin (Port 2 in the layout) is shown in
Figure 4.6 Steps 1 and 2 of the
Design: Setting C1 to Have Self-Resonance at the Third Harmonic and Setting the Tline Length to Get Good Impedance at the
2G4RF_IOP Pin on page 32
. The impedance falls very close to the target, which ensures that the Tline length is properly tuned and
makes Step 2 unnecessary.
For Step 3, a proper C0 value is chosen to suppress the second harmonic (4.9 GHz). This C0 value is approximately 2.2 pF (using the
S-parameter data given by the vendor).
For Step 4, a proper L0, connected between Ports 5 and 6, as shown in
Figure 4.5 EM Simulation of the Tline Match on page 31
part
a., value is chosen, which resonates with C0 close to the fundamental frequency, results in low insertion loss, and, if possible, also
tunes the impedance further towards the optimum. The best L0 value found is 1.2 nH (using the LQG15HS type S-parameters from
Murata) but, as can be seen in
Figure 4.6 Steps 1 and 2 of the Design: Setting C1 to Have Self-Resonance at the Third Harmonic and
Setting the Tline Length to Get Good Impedance at the 2G4RF_IOP Pin on page 32
part b., due to the L0 parasitics the impedance is
not exactly optimal. Unfortunately, the LQG series inductors are available only in E12 series discrete values. As a result, the optimum
impedance usually cannot be fully reached, and some deviation remains. As mentioned before, some fine tuning can be done by insert-
ing a proper series parasitic inductance, such as a proper short trace between the inductor and the ground metal. However, the devia-
tion from the optimum impedance is so small that the power degradation is negligible (from the load-pull curves) and, as a result, fine
tuning is not required
AN930: EFR32 2.4 GHz Matching Guide
Transmission Line (Tline) Match for Minimal BOM Solutions (U.S. Patent US9780757B1)
silabs.com
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