Users Manual
40
40
'(7
The performance of a product depends largely on the PCB trace. As mentioned above, if the PCB layout is
unreasonable, it may cause interference problems such as card loss. The way to solve these interferences is often to
redesign the PCB. If you can plan a good PCB layout in the early stage, the PCB traces smoothly, saving a lot of time.
Of course, it can also save a lot of costs. This chapter mainly introduces some things that users should pay attention
to during the PCB layout stage, minimizing interference problems and shortening the user's development cycle.
The SLM756 module is an intelligent module with its own Android operating system. It includes sensitive data lines
such as high-speed USB and MIPI. It also has strict requirements on the length and impedance of the signal line. If
the high-speed signal processing is not good, it will cause serious EMI. The problem, more serious will also affect the
USB identification, LCM display, so the PCB design requirements when using the SLM756 module is much higher
than the previous 2G module, please read this chapter carefully, reduce the subsequent hardware debugging cycle.
When using the SLM756 module, the user is required to use at least 4 layers of via design for the impedance control
and signal line shielding.
(.('#3#
Before the PCB layout, first understand the pin distribution of the module, and rationally layout the relevant devices
and interfaces according to the distribution defined by the pin. Please refer to Figure 2 to determine the distribution
of the function feet of the module.
(-(0'!# & '
Several aspects of the main attention during the PCB layout phase:
&
Antenna part design, SLM756 module has a total of 5 antenna interfaces, they are: RF_MAIN, RF_DRX, RF_GPS,
RF_WIFI, RF_FM. Pay attention to component placement and RF routing:
The RF test head is used to test the conducted RF performance and should be placed as close as possible to the
antenna pins of the module;
The antenna matching circuit needs to be placed close to the antenna end;
The connection between the antenna pin of the module and the antenna matching circuit must be controlled by
50 ohm impedance;
The devices and connections between the antenna pins of the module and the antenna connec tor 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 across the entire PCB should be absolutely avoided.
If the antenna is connected by a coaxial RF line, care should be taken to avoid coaxial RF lines across the SIM card,
power circuit, and high-speed digital circuits to minimize the effects of each other.
0HL*KDUGZDUHGHVLJQJXLGH