User Manual

AT02876: Atmel REB212BSMA Hardware User Manual [APPLICATION NOTE]
Atmel-42097B-WIRELESS-AT02876-REB212BSMA-Hardware-User-Manual_ApplicationNote_062014
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To estimate the effective output power for the SMA connector reference plane, insertion losses of the balun and
the transmission line have to be taken into account. Therefore, the SMA connector output power can be up to
1.5dB below the AT86RF212B datasheet value, according to specification of the balun. Insertion loss data for the
individual components can be obtained from associated datasheets. Please check the part reference inside the
BOM in Appendix A.3.
5 PCB Layout Description
This section describes critical layout details to be carefully considered during a PCB design. The PCB design
requires taking care of the following topics:
• Create a solid ground plane as a stable reference for the transceiver, the antenna and the transmission
lines. The PCB has to be considered as a part of the antenna; it interacts with the radiated electromagnetic
wave
• Isolate digital noise from the antenna and the radio transceiver to achieve optimum range and RF
performance
• Isolate digital noise from the 16MHz reference crystal to achieve optimum transmitter and receiver
performance
• Reduce any kind of spurious emissions below the limits set by the individual regulatory organizations
The REB212BSMA PCB design further demonstrates a low-cost, two-layer PCB solution without the need of an
inner ground plane.
5.1 Balanced RF Pin Fan Out
Figure 5-1. Board Layout – RF Pin Fan Out
The Atmel AT86RF212B antenna port should be connected to a 100Ω load with a small series inductance of app.
3nH. This is achieved with the connection fan out in between the IC pins and the filter balun combination B1. The
trace width is kept small at 0.15mm for a length of approximately 2.5mm. The REB212BSMA is a two-layer FR4
board with a thickness of 1.5mm. Therefore, the distributed capacitance between top and bottom is low, and
transmission lines are rather inductive.
The distance between balun and transceiver also allows GND vias for pin 3 and pin 6 of the AT86RF212B. The
GND connection in a low distance has a small parasitic inductance and is therefore desirable for the RF port.