Smart Machine Smart Decision
SIM2000S_Hardware_Design_V1.00
45
2014-02-27
5.2
Principle of PCB layout
During layout, attention should be paid to the following interfaces, like Antenna, power supply, RUIM 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 RUIM card, power ICs.
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 53, Pin 54, Pin 63, Pin64 and Pin65 are GND signals, and shortest layout to GND of power source
should be designed.
5.2.3
RUIM Card Interface
RUIM card holder will take large space on board, and there is no anti-EMI component inside. Thus RUIM card
interface maybe interfered, please pay more attention on this interface during layout. Ensure RUIM card holder is
far way from antenna or RF cable inside. And it is better to put RUIM card holder near the module, as near as
possible. It is better to add ESD component to protect clock, data, reset and RUIM_VDD signals which should
be far away from power and high-speed-frequency signal.
5.2.4
Audio Interface
The audio signals have to be layout according to differential signal layout rules, they should be well protected.
5.2.5
Others
It is better to trace signal lines of UART bunched, as well as signals of USB.
