EVA-7M - Hardware Integration Manual
UBX-12003235 - R05
Production Information
Design-in
Page 17 of 42
2.9
Layout design-in checklist
Follow this checklist for the layout design to get an optimal GNSS performance.
Layout optimizations (Section 2.10)
Is the EVA-7M placed according to the recommendation in section 2.10.3?
Is the grounding concept optimal?
Has the 50 Ohm line from antenna to EVA-7M (micro strip / coplanar waveguide) been kept as short as
possible?
Assure low serial resistance in
VCC
power supply line (choose a line width > 400 um).
Keep power supply line as short as possible.
Design a GND guard ring around the optional RTC crystal lines and GND below the RTC circuit.
Add a ground plane underneath the GNSS module to reduce interference. This is especially important for the
RF input line.
For improved shielding, add as many vias as possible around the micro strip/coplanar waveguide, around the
serial communication lines, underneath the GNSS module, etc.
Calculation of the micro strip for RF input
The micro strip / coplanar waveguide must be 50 Ohms and be routed in a section of the PCB where
minimal interference from noise sources can be expected. Make sure around the RF line is only GND as well
as under the RF line.
In case of a multi-layer PCB, use the thickness of the dielectric between the signal and the 1st GND layer
(typically the 2nd layer) for the micro strip / coplanar waveguide 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.
2.10
Layout
This section provides important information for designing a reliable and sensitive GNSS system.
GNSS signals at the surface of the earth are about 15 dB below the thermal noise floor. Signal loss at the
antenna and the RF connection must be minimized as much as possible. When defining a GNSS receiver layout,
the placement of the antenna with respect to the receiver, as well as grounding, shielding and jamming from
other digital devices are crucial issues and need to be considered very carefully.
