Smart Machine Smart Decision
SIM800_Hardware Design_V1.10
51
2018-08-13
5.
PCB Layout
Usually, most electronic products with good performance are based on good PCB layout. Poor PCB layout will
lead to lots of issues, like TDD noise, SIM card undetected, etc. The final solution for these problems is to
redesign PCB layout. Making good PCB layout will save developing schedule and cost as well.
This section will give some guidelines on PCB layout, in order to eliminate interfere or noise by greatest degree,
and save product development period.
5.1
PIN Assignment
Before the placement of the PCB design, customer should learn well about PIN assignment in order to get
reasonable layout with so many external components. Please refer to figure 2 for the details.
5.2
Principle of PCB Layout
During layout, we should pay attention to the following interfaces, like Antenna, power supply, SIM card
interface, audio interface, and so on.
5.2.1
Antenna
There are some suggestions for components placing and routing of GSM and Bluetooth RF traces:
The RF connector is used for conducted test, so keep it as close to the GSM_ANT pin as possible;
Antenna matching circuit should be closed to the antenna;
Keep the RF traces as 50
Ω
；
The RF traces should be kept far away from the high speed signals and strong disturbing source.
If using a RF cable, kept it far away from SIM card, power ICs;
It is recommended that GSM antenna and Bluetooth antenna be placed as far as better.
5.2.2.
Power Supply
Not only VBAT but also power ground is very important in layout. The positive line of VBAT should be as
shorter and wider as possible. The correct flow from source to VBAT pin should go though Zener diode then
huge capacitor. PIN 62, 63, 64, 65 are GND signals, and should be designed shortest layout to GND of power
source.
5.2.3
SIM Card Interface
SIM card holder will take much more space on board, and there has no anti-EMI component inside, so, SIM card
interface always be interfered. So, pay attention to this interface during layout. Ensure SIM card holder far way
from antenna or RF cable. And it’s better to put SIM card holder near module, And it’s better to add ESD
component to protect clock, data, reset and SIM_VDD signals which should be far away from power and
high-speed signal.
