MIPI bus is widely used in LCD or camera applications of mobile devices such as smartphones/tablets. As a hardware engineer, whether it's checking or routing, it's a basic job. Here are the 6 key rules for checking MIPI routing based on personal experience summary:

1. Equal length

MIPI is an interface for high-speed differential signals, and in order to ensure signal synchronization and consistency, it is necessary to ensure that MIPI DP/DN remains of equal length. Whether it is between pairs or between DP/DN of a single signal group, the following length rules generally need to be followed:

Camera pair to pair 100mil between groups: 25mil

LCD pair to pair 200mil, 60mil between single groups

2. Equidistant

When routing MIPI cables, it is generally necessary to maintain equidistant DP/DN during the routing process to ensure a certain degree of coupling. However, when it is necessary to clarify, the priority of equidistant cables is higher than equidistant cables.

And when routing, a distance of 2W should be maintained between the wire pairs.

3. Reference layer

MIPI routing should maintain a continuous reference layer, preferably in the geological layer. If this condition cannot be met, it is necessary to ensure that the width of the reference layer can reach 4W. In order to prevent ESD and interference, MIPI routing is best done in the inner layer.

4. Drill holes and change layers

MIPI should try to drill as few holes as possible, and it is necessary to note that when drilling and changing layers, DP/DN must be drilled and changed layers at the same time, and more ground holes must be drilled around to ensure signal backflow;

5. Stay away from interference

Stay away from interference sources such as RF and switching power supplies

6. Impedance requirements

MIPI has impedance requirements, generally requiring a differential impedance of 100 ohms;

The requirement for MIPI's wiring impedance of 100 ohms is defined based on the LVDS (Low Voltage Differential Signaling) level.

The maximum amplitude of LVDS differential signal PN two wires is 350mV, and the internal constant current source current is 3.5mA So the terminal matching resistor is 100Ohm

That is to say, the equivalent impedance between PN is 100 ohms. This is what the agreement stipulates.

If it is less than 100 ohms, the amplitude of the terminal output level is insufficient and the loss increases.

If it is greater than 100 ohms, the current source's pull-out power (driving capability) is insufficient and easily interfered with