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# Characteristics of single-ended signals, differential signals and pseudo-differential signals

1. Single-ended signal

As shown in the figure, the characteristic is that a signal line is enough. The reference voltage of the reference is ground. When the voltage is greater than VH, it is 1 (high level); if it is less than VL, it is 0 (low level), why high and low levels are not equal to Is a certain value greater than/less than? This is easy to understand, the output voltage fluctuates in a small range,

It is impossible that the low level is 0mv, it may be 1mv, more than ten mv or even greater! If it is equal to 0mv, it is low level, it is estimated that it is all high level, and between VL~VH is high-impedance state, depending on how peripherals are interpreted, some hardware registers will indicate high-impedance state, some indicate 0 or 1.

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Required conditions: a. Reference place 　　 b. VH/VL threshold 　　 c. Continuous level of clock cutting (whether continuous high level represents one 1 or multiple 1)

Advantages: Less wiring and simple and convenient

Disadvantages: Poor anti-interference; On the one hand, the ground potential difference is as close as possible, otherwise the low level output at one end is 0mv, but the receiving end is 10mv, and VL=8mv, then it becomes a high level (assuming extreme cases)

On the other hand, external electromagnetic interference makes the signal line have an interference voltage of 20mv, if VL=8mv, it must be high level

Precautions: It is necessary to consider the problem of terrain difference and the value range of VL/VH has sufficient tolerance

Second, the differential signal

Generally, in high-speed signals, the voltage amplitude is relatively low. Like the MIPI DSI specification, low-speed amplitude = 1200mv, and high-speed amplitude = 200mv, so the use of the above single-ended wiring is really poor in anti-interference ability, so high speed (low amplitude) Most use differential signals. As shown:

Required conditions: a. Reference place 　　 b. VH/VL threshold 　　 c. Continuous level of clock cutting (whether continuous high level represents one 1 or multiple 1)

Advantage: Strong anti-interference; D+ /D- difference is fixed, not subject to topography or external interference. As for the high and low levels, D+/D- is compared (the above is that D+ is greater than D- for high level), and there is no need to refer to the ground and the VH/VL threshold!

High sensitivity, because it is a relative difference, the amplitude can be very low, reducing the power consumption of the device in communication

Disadvantages: Signal lines increase wiring difficulty and interference

Note: The wiring of D+ and D- should be consistent, otherwise the electromagnetic interference is inconsistent; also because the electromagnetic interference is inconsistent, the difference between the two lines should not be too small during design

(For example, D+=50mv, D-=30mv, the difference is 20mv, the interference on D++10mv finally D+=60, and the interference on D-+20mv finally D-=50mv, the difference becomes 10mv!)