User's Manual

MeiG hardware design guide
32
5.2.4. MIPI
MIPI is a high-speed signal line. Users must pay attention to protection during the layout phase, so that
they are away from the signal lines that are easily interfered. The GND processing must be performed
on the upper and lower sides, and the traces are differential pairs. 100 ohm differential impedance
matching is performed. Ensure impedance consistency and do not bridge different GND planes as
much as possible.
The MIPI interface selects a small-capacity TVS when selecting an ESD device. It is recommended
that the parasitic capacitance be less than 1pF.
The MIPI routing requirements are as follows:
 The total length of the cable does not exceed 305mm
 It is required to control 100 ohm differential impedance with an error of ±10%.
 The error of the differential line length within the group is controlled within 0.7mm.
 The length error between groups is controlled within 1.4mm.
5.2.5. USB
The module supports high-speed USB interface at a rate of 480Mbps. The user recommends adding a
common-mode inductor during the schematic design phase to effectively suppress EMI interference. If
you need to increase the static protection, please select a TVS tube with a parasitic capacitance of less
than 1pF. Please refer to the following notes when planning:
 The common mode inductor should be close to the USB connector side.
 It is required to control the 90 ohm differential impedance with an error of ±10%.
 The differential line length error is controlled within 6mm.
 If the USB has a charging function, please note that the VBUS cable is as wide as possible.
 If there is a test point, try to avoid the split line and put the test point on the path of the trace.
Table 5.1:
Pin
Signal
Length(mm)
Length Error（P-N）
14
USB_DP
26.2
0.2mm
13
USB_DM
26.5
5.2.6.Audio
The module supports 3 analog audio signals. Analog signals are susceptible to interference from high
speed digital signals. So stay away from high-speed digital signal lines. The module supports the LTE
system, and the LTE signal can interfere with the audio by coupling and conduction. Users can add
33pF and 10pF capacitors to the audio path to filter out coupling interference. The 33pF capacitor
mainly filters out the interference of the LTE band, and the 10pF capacitor mainly filters out the
interference of the WCDMA band. The coupling interference of TDD has a great relationship with the
PCB design of the user. In some cases, the LTE frequency band is more serious, and in some cases, the
interference of the WCDMA frequency band is more serious. Therefore, the user can select the
required filter capacitor according to the actual test result, and sometimes even do not need to paste the
filter capacitor.