4.2.5 RF
The main feature of SAM R21 Xplained Pro is to show the RF capability of the ATSAMR21G18A device. This device has bidirectional 100Ω differential antenna pins, which are fed through a balun (Johanson Technology, 2450BM15A0015) to create a single 50Ω unbalanced output/input. This kit has a passive analog RF switch (Skyworks Solutions Inc, AS222-92LF) connected to the unbalanced output of the balun. The switch is driven by the RFCTRL1 and RFCTRL2 pins of the ATSAMR21G18A, which feature Antenna Diversity to enable the device to automatically select the best signal from two antennas (can also be selected manually). The output of the switch is connected to a ceramic chip antenna (Johanson Technology, 2540AT18D0100) and a SMA connector for external antennas.
| Pin on SAM R21 | RF | Shared functionality |
|---|---|---|
| RFP | RF balanced output (positive) | |
| RFN | RF balanced output (negative) | |
| PA09 / RFCTRL1 | RF switch control signal (negative) | EDBG |
| PA12 / RFCTRL2 | RF switch control signal (positive) | EDBG |