Smart Machine Smart Decision
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PCB Layout
This section provides PCB layout guidelines for SIM8905A users to ensure their production against lots of issues,
and achieve the optimum performance.
Stack-up Options
At least, 4-layer through-hole PCB should be chosen for good impedance control and signal shielding.
General Placement Guidelines
Locate SIM8905A module in the center of PCB, rather than in the corner.
Digital devices and traces should not be placed near sensitive signals like RF and clock.
Keep SPKR and MIC away from sensitive RF lines.
PCB Layout Guideline Details
RF Trace
RF connector should be placed close to the module’s antenna pin.
Antenna matching circuit should be placed close to the antenna.
Keep the RF traces at 50
Ω
.
Maintain a complete and continuous reference ground plane from antenna pin to the RF connector.
The RF traces should be far away from any other noisy traces.
Keep the RF traces as short as possible.
If using a coaxial RF cable to connect the antenna, please avoid spanning on USIM cards, power circuits and
high-speed digital circuits to minimize the impact of each other.
Power/GND
Both VBAT and return path should be as short and wide as possible to minimize the IR drop
The VBAT current should go through Zener diode, capacitors, then VBAT pins
Must have a solid ground plane throughout the board as the primary reference plane for most signals
USIM Card
Ensure USIM card holder is far way from antenna or RF signal
