MeiG Smart product technical information
SLM500
Hardware Design Guide
Page 57
must be controlled by 50 ohm impedance;
The device and wiring between the antenna pin and the antenna connector of the module
must be 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:
-speed
signal lines, and the SIM card should not be too long;
module to make the GND equipotential between the two.
SIM_CLK.
to place a 100nF capacitor on the SIM_VDD signal line near the SIM
card holder;
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
