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SIM900 Reference Design Guide Notes

2.4.1 Referenced circuit of headset design

Figure 9: Referenced circuit of headset

2.4.2 Referenced circuit of hand free design

Figure 10: Referenced circuit of audio PA

2.5 Antenna matching circuit design

Because the module is working under 50ohm system in RF part, so, to get the best RF

performance, the SMT module’s load impedance should be tuned to 50ohm. But in fact, the most

antenna’s port impedance is not a purely 50ohm, so, to meet the 50ohm requirement, an additional

SIM900_AN_Reference Design Guide_V1.01 01.27.2010

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Rhydo SIM 900 SIM 900 -TTL UART Dokumentacja Strona 12