LENA-R8 series - System integration manual
UBX-22015376 - R02
Design-in
Page 51 of 116
C1-Public
•
Add GND keep-out (clearance) on the buried metal layer below
ANT
and
ANT_GNSS
pads if the
top-layer to buried layer dielectric thickness is below 200
µ
m, to reduce parasitic capacitance to
ground, as described in the right example of
Min.
250 µm
Min. 400 µm
GND
RF pad
GND clearance
on very close buried layer
below RF pad
GND clearance
on top layer
around RF pad
Figure 32: GND keep-out area on top layer around RF pad and on very close buried layer below RF pad (ANT / ANT_GNSS)
2.4.1.2
Guidelines for RF transmission line design
Any RF transmission line, such as the ones from the
ANT
and
ANT_GNSS
pads up to the related
antenna connector or up to the related internal antenna pad, must be designed so that the
characteristic impedance is as close as possible to 50
.
RF transmission lines can be designed as a micro strip (consists of a conducting strip separated from
a ground plane by a dielectric material) or a strip line (consists of a flat strip of metal which is
sandwiched between two parallel ground planes within a dielectric material). The micro strip,
implemented as a coplanar waveguide, is the most common configuration for printed circuit boards.
and
provide two examples of suitable 50
coplanar waveguide designs. The first
example of RF transmission line can be implemented in case of 4-layer PCB stack-up herein described,
and the second example of RF transmission line can be implemented in case of 6-layer PCB stack-up
herein described.
35
µ
m
35
µ
m
35
µ
m
35
µ
m
270
µ
m
270
µ
m
760
µ
m
L1 copper
L3 copper
L2 copper
L4 copper
FR-4 dielectric
FR-4 dielectric
FR-4 dielectric
380
µ
m 500
µ
m
500
µ
m
Figure 33: Example of 50
coplanar waveguide transmission line design for the described 4-layer board layup
35 µm
35 µm
600 µm
35 µm
110 µm
110 µm
L1 copper
L2 copper
FR-4 dielectric
220 µm 500 µm
500 µm
110 µm
35 µm
35 µm
35 µm
600 µm
L3 copper
L4 copper
FR-4 dielectric
L5 copper
L6 copper
FR-4 dielectric
FR-4 dielectric
FR-4 dielectric
Figure 34: Example of 50
coplanar waveguide transmission line design for the described 6-layer board layup
