PCB these three special alignment skills you know how much

In PCB design, wiring (Layout) is one of the most basic work skills. Good or bad alignment directly affects the performance of the entire system. In most of the high-speed design theory should ultimately be realized and verified by Layout. Therefore, it can be imagined how important wiring is a step in PCB design! Today we take a look at the right-angle alignment, differential alignment and serpentine line of these three special alignment techniques, can you master it?

The first: right-angle alignment

Right-angle alignment is one of the measures of good and bad wiring. This alignment is generally asked to avoid as much as possible, because the right-angle alignment will have a certain impact on the signal, mainly in three aspects:

1. Corners can be equated to capacitive loads on the transmission line, slowing down the rise time. 2;

2. impedance discontinuities can cause signal reflections;

3. EMI generated by right-angled tips. In the field of RF design above 10GHz, these small right angles can be the focus of high-speed problems.

Second: Differential Alignment

Differential signaling means that the driver sends two equal and inverted signals, and the receiver determines the logic state '0' or '1' by comparing the difference between these two voltages. The pair of wires carrying the differential signals is called differential wires.

Differential signals have been widely used in high-speed circuit design, and the most critical signals in the circuit are usually designed with differential structures.

Differential signals and ordinary single-ended signal alignment compared to the three most obvious advantages:

1. strong anti-jamming ability, because the coupling between the two differential alignments is very good, when there is noise interference in the outside world, is almost simultaneously coupled to the two lines. The receiving end is only concerned about the difference between the two signals, so the outside world of common mode noise can be completely canceled out.

2. can effectively inhibit EMI, the same reason, because the polarity of the two signals are opposite,2 oz copper thickness in mm they can cancel each other out of the electromagnetic field radiation. The tighter the coupling, the less electromagnetic energy leaked to the outside world. 3.

3. Timing positioning accuracy, due to differential signal switching changes are located in the intersection of the two signals, unlike ordinary single-ended signals rely on the high and low two threshold voltage judgment. Therefore, it is less affected by process and temperature, which can reduce the timing error, and it is also more suitable for low amplitude signal circuits. The currently popular LVDS (lowvoltagedifferentialsignaling) refers to this small amplitude differential signaling technology.

For PCB engineers, the most concerned about how to ensure that the actual alignment can fully utilize these advantages of differential alignment. Perhaps as long as the people who have contacted the Layout will understand the general requirements of differential alignment, that is, 'equal length, equal distance'.

Equal length is to ensure that the two differential signals at all times to maintain the opposite polarity, reducing the common mode component; equal distance is mainly to ensure that the two differential impedance is the same, reducing reflections.'' As close as possible principle' is sometimes one of the requirements of differential alignment.

The third type: snake line (regulating delay)

Snake alignment is a special kind of circuit board wiring similar to the shape of the snake alignment.plated through hole vs via Its main purpose is to adjust the delay to meet the system timing design requirements.

The two most critical parameters of the snake alignment are the parallel coupling length (Lp) and coupling distance (S). When signals are transmitted on a serpentine alignment, coupling occurs between parallel line segments, in the form of a differential mode, and the smaller S and the larger Lp are, the greater the degree of coupling. This is likely to lead to a reduction in transmission delay, as well as a significant reduction in signal quality due to crosstalk. The mechanism can be found in the analysis of common mode and differential mode crosstalk.

I have compiled a few suggestions for PCB design engineers when dealing with serpentine lines:

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