Minimal Design for GR551x SoC
Note
:
The RF route should be straight and as short as possible. If a curving route is necessary for a specific structure, an
inverted arc is required for a turning, and angles at or less than 90◦ are not allowed.
RF routing at the PCB surface (the top layer or the bottom layer) helps avoid using vias or switching layers, and
is therefore preferred. Stub routes should be avoided, and the reference ground plane underneath the RF route
shall be complete. The RF route shall be of the same width as the component pad. This ensures there will not be
discontinuities in the 50 Ω transmission line due to a mismatch between the component pad size and trace size.
Taking the 4-layer PCB layout design as an example, the transmission line is routed as a coplanar waveguide using
layer-2 ground as the reference plane. The dimensions are:
•
Trace width: 559 μm
•
Spacing from trace to top layer: 178 μm
•
Spacing from top layer to layer 2: 432 μm
The design uses FR-4 dielectric and 0.5 ounce copper on the outer layer. In actual design, PCB manufacturers are
required to provide single-ended RFIO traces with an impedance of 50 Ω (+/–10%).
Ground vias should be placed along the transmission line every 1.25 mm and right next to the ground pads of the
matching components.
A PI-network should be placed close to the antenna feedpoint for antenna matching purposes. The matching network
value of antenna is adjusted according to the actual antenna used. It is recommended to use mature antenna schemes
and recommended values of antenna factories.
3.2.6 Grounding
Always provide a solid grounding for the radio IC of GR551x. Use as many vias as possible to create a solid GND under
the IC itself and connect it to inner and bottom GND layers.
For the center ground paddle (at the package bottom) of QFN packages, use a matrix of 3 x 3, 4 x 4, or other vias to
the ground-plane.
The GND of the 10 µF filter capacitor connecting to VBATL shall be close to the main GND pin, and apply copper
pouring if possible (see “
”). The ground return path of the GND pin (VSS_BUCK) of DC-DC
power shall be in good condition, which guarantees stable and secure operation of ICs.
Note
:
•
Make sure the ground-pad shape follows the shape of the paddle on chip, including the exposed paddle parts
(for QFN packages).
•
Make sure a ground via is placed right next to the TRX pin.
•
For the BGA packages, place ground vias as close as possible to the ground balls.
3.2.7 ESD Protection Design
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