RF42/43
10. Application Notes
10.1. Crystal Selection
The recommended crystal parameters are given in Table 16.
Table 16. Recommended Crystal Parameters
Frequency
ESR
CL
C0
Frequency
30 MHz
60Ω
12PF
5PF
±20 ppm
The internal XTAL oscillator will work over a range for the parameters of ESR, CL, C0, and ppm accuracy. Extreme
values may affect the XTAL start-up and sensitivity of the link. For questions regarding the use of a crystal
parameters greatly deviating from the recommend values listed above, please contact customer support.
The crystal used for engineering evaluation.
10.2. Layout Practice
The following are some general best practice guidelines for PCB layout:
■ Bypass capacitors should be placed as close as possible to the pin.
■ TX matching/layout should mimic reference as much as possible. Failing to do so may cause loss
inperformance.
■ A solid ground plane is required on the backside of the board under TX matching components
■ Crystal should be placed as close as possible to the XIN/XOUT pins and should not have VDD traces running
underneath or near it.
■ The paddle on the backside of the QFN package needs solid grounding and good soldered connection
■ Use GND stitch vias liberally throughout the board, especially underneath the paddle.
10.3. Matching Network Design
10.3.1. TX PA Matching and Filtering
Figure 43. TX Matching and Filtering for Different Bands
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