Design Note DN025
3.3.1.2
Layout
The layout greatly influences the RF performance. TI recommends to always copy our
reference design [6] as closely as possible.
Figure 7. Layer 1 of CC1101 JTI 868/915 MHz Reference Design Layout
The ground from the decoupling capacitors has been divided from the remaining ground on
layer1. Tests from the lab have proven that this is not necessary and the ground can be solid
as shown in Figure 8. As previously mentioned, the most important critical part of the layout is
the positioning of the inductor L122 in order to minimize the coupling effect to the Matched
Balun Filter.
In the event that the reference design [6] can not be copied then the routing from the RF pins
RF_P & RF_N must be symmetrical to the Matched Balun Filter component, U121. The
length of the tracks should be kept to a minimum and preferably the same length that is used
in the reference design [6]. If this routing is not symmetrical; then the output power will be
reduced and the harmonics will increase.
All component ground pads should have the own ground via which should be positioned as
close as possible to the ground pad. When positioning the ground vias for the component pad
grounds it is important to try to keep the return path loop to ground as little as possible in
order to prevent unnecessary radiated emissions.
SWRA250A
Page 7 of 26
JOHANSON [ JOHANSON TECHNOLOGY INC. ]
