MAX-7 / NEO-7 / LEA-7 - Hardware Integration Manual
GPS.G7-HW-11006-1
Design
Page 16 of 55
3.1.2
Layout checklist
See section 3.3.
Is the GPS/GNSS module located according to the recommendation?
Has the grounding concept been followed?
Has the micro strip been kept as short as possible?
Add a ground plane underneath the GPS/GNSS module to reduce interference.
For improved shielding, add as many vias as possible around the micro strip, around the serial
communication lines, underneath the GPS/GNSS module etc.
Have appropriate EOS/ESD/EMI protection measures been included? This is especially important for
designs including wireless modules.
3.1.3
Antenna checklist
The total noise figure should be well below 3 dB.
If a patch antenna is the preferred antenna, choose a patch of at least 15x15x4 mm for standalone
GPS/QZSS, or choose a patch of at least 25x25x4 mm for GPS + GLONASS. For smaller antennas, an LNA
with a noise figure <2 dB is recommended. (MAX-7Q, NEO-7N)
Make sure the antenna is not placed close to noisy parts of the circuitry. (E.g. micro-controller, display,
etc.)
To optimize performance in environments with out-of band jamming sources, use an additional SAW
filter.
The micro strip must be 50
Ω
and be routed in a section of the PCB where minimal interference from
noise sources can be expected.
In case of a multi-layer PCB, use the thickness of the dielectric between the signal and the first GND layer
(typically the 2nd layer) for the micro strip calculation.
If the distance between the micro strip and the adjacent GND area (on the same layer) does not exceed 5
times the track width of the micro strip, use the “Coplanar Waveguide” model in AppCad to calculate
the micro strip and not the “micro strip” model see section 3.3.5
Use an external LNA if your design does not include an active antenna when optimal performance is
important.
For information on ESD protection for patch antennas and removable antennas, see section 5.3.3 and if
you use GPS for design in combination with GSM or other radio then check sections 5.3.5 to 5.3.7.
For more information dealing with interference, issues see the GPS Antenna Application Note [5].
3.2
Design considerations for minimal designs
For a minimal design with a u-blox 7 GPS/GNSS module, the following functions and pins need consideration:
•
Connect the Power supply to
VCC
.
•
Connect
VCC_IO
to
VCC
or to the corresponding voltage.
•
Assure an optimal ground connection to all ground pins of the module.
•
Connect the antenna to
RF_IN
over a 50
Ω
line and define the antenna supply (
V_ANT
) for active antennas
(internal or external power supply).
•
Choose the required serial communication interface (UART, USB, SPI or DDC) and connect the appropriate
pins to your application.
•
If you need improved start-up or use AssistNow Autonomous in your application, connect a backup supply
voltage to
V_BCKP
.
