Smart Machine Smart Decision
SIM800H_Hardware_Design_V1.01
56
2013-08-20
5.2
Principle of PCB layout
During layout, attention should be paid to the following interfaces, like Antenna, power supply, SIM card
interface, audio interface, and so on.
5.2.1
Antenna Interface
The basis principle is that, the length of trace between pin output and connector should be as short as possible, in
order to avoid coupling issue. Do not trace RF signal over across the board. Even the RF cable must be put over
the board, it should be far away from SIM card, power ICs.
There are FM antenna interface and Bluetooth antenna interface. If product equips these antennas as well, do pay
attention to the distance between each single antenna.
5.2.2.
Power Supply
Not only VBAT but also return GND are very important in layout. The positive line of VBAT should be as short
and wide as possible. The correct flow from source to VBAT pin should go though Zener diode then huge
capacitor. Pin 2, Pin 43, Pin 44 and Pin45 are GND signals, and shortest layout to GND of power source should
be designed.
There are 12 GND pads in middle of module, these pads could enhance the GND performances. On the upper
layer of these pads, do not trace any signal if possible.
5.2.3
SIM Card Interface
SIM card holder will take large space on board, and there is no anti-EMI component inside.Thus SIM card
interface maybe interfered, please pay more attention on this interface during layout. Ensure SIM card holder is
far way from antenna or RF cable inside. And it is better to put SIM card holder near the module, as nearer as
possible. It is better to add ESD component to protect clock, data, reset and VSIM signals which should be far
away from power and high-speed-frequency signal.
5.2.4
Audio Interface
In order to avoid TDD noise, or current noise, or some other noise, the signal trace of audio should far away from
antenna and power. And do not let audio trace and VBAT trace parallel.
5.2.5
Others
It is better to trace signal lines of UART bunched, as well as signals of USB and LCM.
