PCB LAYOUT three special routing skills

PCB LAYOUT three special routing skills

Here from the right angle alignment, differential alignment, snake line three aspects to illustrate the PCB LAYOUT alignment:

Right-sided alignment (three aspects)

Right angle alignment of the signal is the main embodiment of the three aspects: First, the corner can be equivalent to the transmission line on the capacitive load, slow rise time, the second is the impedance of the signal will cause continuous reflection; Third, EMI, to 10GHZ above the RF design field, these small right angles may become a high-speed problem of key objects.

Differential traces ("isometric, equidistant, reference plane")

The differential signal is the drive side to send two equivalent, inverted signal, the receiver by comparing the difference between the two voltage to determine the logic state "0" or "1", and carrying the differential letter that pair of traces Called differential line alignment, differential signal and ordinary single-ended signal traces compared to the most obvious advantages of the following three aspects

1.Anti-interference ability, because the coupling between the two differential traces is very good, when there is noise outside the interference, almost simultaneously coupled to the two lines, and the receiver is only concerned about the difference between the two signals, So the external common mode noise can be completely offset.

2.Can effectively suppress EMI, the same reason, because the polarity of the two signals on the contrary, their external radiation electromagnetic field can offset each other, the closer the coupling, the less the electromagnetic energy released to the outside world.

3.Timing positioning accuracy, because the differential signal switching is located at the intersection of two signals, rather than ordinary single-ended signal to rely on low two threshold voltage to determine, and thus by the process, the impact of temperature is small, can reduce the timing error, And more suitable for low-amplitude signal circuit, the current popular LVDS refers to this small-amplitude differential signal technology.

Snake line (adjustment delay)

The main purpose of the snake line is that LAYOUT is often used. The main purpose is to adjust the delay to meet the system timing design requirements. The two most critical parameters are the parallel coupling length (LP) and the coupling distance (S). Obviously, when the signal is transmitted on the serpentine line, the coupling between the lines parallel to each other occurs in the form of differential mode. The smaller the S, the larger the LP, the greater the degree of coupling, which may cause the transmission delay to decrease , As well as due to crosstalk and greatly reduce the quality of the signal, the mechanism can refer to the common mode and differential mode crosstalk analysis.