SI4785 데이터 시트보기 (PDF) - Silicon Laboratories
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SI4785 Datasheet PDF : 69 Pages
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Figure 12. Stub Antenna in Wire Implementation
5.1.1. Embedded Stub Antenna—Wire Implementation
A stub (wire) antenna is typically a floating wire that is approximately 10 cm in length and is embedded inside the
device with FM functionality. The antenna can be longer if the device's industrial design will accommodate it. The
material for a stub (wire) antenna can be an actual wire or a PCB trace. PCB traces can be either in flexible
packaging (flexible PCB trace) or as a trace on the PCB. The 24AWG wire has been experimentally proven to have
optimal performance.
The stub (wire) antenna should be placed such that it is not obstructed by a ground plane or shield. This
requirement can be met by placing the antenna on an extremity of the device (e.g., top or bottom) or on the
perimeter. The antenna can also be embedded in the device plastic or outside the plastic with a protective
covering. The flexible PCB antenna should be between a PCB and the device plastic such that the antenna trace is
not obstructed by a ground plane or shield. The antenna is connected to pin 4 and resonated with the on-chip
variable capacitor.
5.1.1.1. Matching
A 10 cm stub (wire) antenna has a capacitive impedance, typically more than 1~2 pF. The antenna is matched by
resonating it with a shunt inductor and the on-chip shunt variable capacitor. See Appendix B for inductor value
calculation.
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Rev. 0.8
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