MeiG_SLM550_Hardware Design Manual
MeiG Smart Technology Co., Ltd
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away from high-speed signal lines and strong interference sources to avoid crossing or parallel with any
signal lines in adjacent layers.
The length of the RF cable between the antenna pin of the module and the antenna connector should
be as short as possible. The situation of crossing the entire PCB should be absolutely avoided.
If the antenna is connected by a coaxial RF line, care should be taken to avoid the coaxial RF line
spanning the SIM card, power supply circuit, and high-speed digital circuits to minimize the effects of
each other.
5.2.2 Power Supply
Power traces must consider not only VBAT, but also the return GND of the power supply. The trace of
the VBAT positive must be short and thick, the trace must first pass through the large capacitor, Zener
diode and then the power PIN of the module. There are multiple PAD exposed copper at the bottom of
the module. Make sure that the GND path of these exposed copper areas to the power supply is the
shortest and smoothest. This ensures that the current path of the entire power supply is the shortest
and the interference is minimal.
5.2.3 SIM Card
The SIM card has a large area and does not have an anti-EMI interference device. It is relatively
susceptible to interference. Therefore, in the layout, first ensure that the SIM card is away from the
antenna and the antenna extension cable inside the product. Place it as close as possible to the
module. When the PCB is routed, pay attention to it. The SIM_CLK signal is protected, and the
SIM_DATA, SIM_RST, and SIM_VDD signals of the SIM card are away from the power source and
away from the high-speed signal line. If the processing is not easy, it may cause problems such as not
knowing the card or dropping the card. Therefore, please follow the following principles when designing:
⚫
Keep the SIM card holder away from the GSM antenna during the PCB layout phase;
⚫
SIM card routing should be as far away as possible from RF line, VBAT and high-speed signal
lines, and the SIM card should not be too long;
⚫
The GND of the SIM card holder should be in good communication with the GND of the module to
make the GND equipotential between the two.
⚫
To prevent SIM_CLK from interfering with other signals, it is recommended to protect SIM_CLK.
⚫
It is recommended to place a 100nF capacitor on the SIM_VDD signal line near the SIM card
holder;
⚫
Place TVS near the SIM card holder. The parasitic capacitance of the TVS should not exceed
50pF, and the 51Ω resistor in series with the module can enhance ESD protection.
⚫
The SIM card signal line increases the capacitance of 22pF to ground to prevent radio frequency
interference.
⚫
The return path of VBAT has a large current, so the SIM card trace should avoid the return path of
VBAT as much as possible.
5.2.4 MIPI
MIPI is a high-speed signal line. Users must pay attention to protection during the layout stage, so that
they are away from the signal lines that are easily interfered. The GND processing must be performed
on the upper and lower sides, and the traces are differential pairs. 100 ohm differential impedance
matching is performed. Ensure impedance consistency and do not bridge different GND planes as
