ZOE-M8 series - Hardware integration manual
UBX-16030136 - R09
Design-in
Page 19 of 34
Production information
Ensure an optimal ground connection to all ground pins of the ZOE-M8 GNSS SiPs.
Choose the required serial communication interfaces (UART, SPI or DDC) and connect the
appropriate pins to your application.
If you need hot or warm start in your application, connect a backup battery to V_BCKP and add an
RTC circuit.
2.11
Layout design-in checklist
Follow this checklist for the layout design to get an optimal GNSS performance.
Layout optimizations (see section 2.12)
Is the ZOE-M8 GNSS SiP placed according to the recommendation in section 2.12.3?
Is the grounding concept optimal?
Are all the GND pins well connected with GND?
Is the 50 Ohm line from the antenna to the SiP (micro strip / coplanar waveguide) as short as
possible?
Assure low serial resistance in VCC power supply line (choose a line width > 400 µm).
Assure all VCC pins are well connected with the power supply line.
Keep the power supply line as short as possible.
If DC/DC is used on the ZOE-M8Q, ensure the inductor and capacitor are connected close to the
ZOE-M8Q V_CORE and V_DCDC_OUT pins and the capacitor has a good GND connection.
Design a GND guard ring around the optional RTC crystal lines and GND below the RTC circuit.
Add a ground plane underneath the GNSS SiP 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 SiP, and so on.
Calculation of the micro strip for RF input
The micro strip / coplanar waveguide must be 50 Ohms and 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.
2.12
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.
