How to route weak signal circuit boards, and how to route ordinary circuit boards PCBs like this

It's not enough for you to talk about weak signals, how weak are they? What is weak and what is strong? Both strong and weak are relative.

In my opinion, as long as it does not affect the operation of the circuit, it can be said to be a weak signal. One of the tasks of wiring is to consider how to minimize or eliminate the adverse effects between circuits. When it comes to influence, it is nothing more than influencing others or being influenced by others.

It is mainly high-frequency circuits that affect others, because it has a triggering effect. This means that they should be powered and wired separately from one end as much as possible. In addition, the high-power circuit should also be supplied and routed separately.

As mentioned above, the separate power supply does not necessarily use two power supplies, so to speak, a single circuit is drawn from the power supply. For weak or input-level circuits that are susceptible, they should also be placed aside, or a small unit should be built. The power supply should be clean.

That is, add enough filtering circuitry. It may be necessary to take recurring measures. Generally, multi-level magnification should be arranged in one word, and the most taboo is the C-word arrangement.

Leave room in mind when designing your board. In detail, it is to design a few pieces in advance where it is possible to add filter corrections when debugging. Of course, it takes a lot of experience.

The digital circuit and the analog circuit should be isolated, the power supply should be filtered cleanly, and the power supply of the analog device should be decoupled with a capacitor.

The signal processing circuit part should be as close as possible to the entrance of the signal source, and the signal lines should be spaced between more than 2 times the wire frame, and the copper grounding should be preferred in the middle.

For the corresponding circuits, digital and analog are separated, and power supply is separated, in short, a lot of experience is hard to describe.

Generally, the signal board is a line of equal width, and this kind of board in order to use the layout space, try to make the line thicker, so the use of not the line drawing method, but the copper pouring method, a piece of copper placed on the PCB. Some simple software can draw the above figures. For example, sprint-layout, but this software has other features that are inferior.

Most other PCB software can be drawn like this, but it is more troublesome, put the line a few more times, and the dislocation is superimposed, and it will be widened. Altium Designer also needs to be overlaid and widened repeatedly, or with a variety of wide and thin traces.

That's the result of applying copper where there are vacancies.

It depends on the specific line, generally the line layout is reasonable, the crosstalk between the lines is small, and the EMC characteristics are good. The power circuit, main circuit and control loop should be properly isolated. In the signal acquisition circuit, the analog circuit and the digital circuit should eliminate interference.

The reflection of the high-frequency line should be suppressed, and the address line and data line should be of equal length to reduce ringing and crosstalk. See below for specific principles.

I have been engaged in high-frequency circuit design for many years, and the following is my own summary of the ground wire layout, I hope it can be helpful.

In electronic devices, grounding is an important method of controlling interference. When grounded and shielded are used correctly, most interference problems can be solved. The ground structure in electronic equipment is roughly systematic, enclosure (shielded), digital (logical) and analog.

The following points should be paid attention to in the design of the ground wire:

1.Correct selection of single-point ground vs. multi-point grounding.

In the low-frequency circuit, the operating frequency of the signal is less than 1MHz, and its wiring and the inductance between the devices have less influence, while the circulation formed by the grounding circuit has a greater impact on the interference, so a little grounding should be used. When the signal working frequency is greater than 10MHz, the ground impedance becomes very large, and the ground impedance should be reduced as much as possible, and the nearest multi-point grounding should be used. When the working frequency is 1 10MHz, if a point grounding is used, the length of the ground wire should not exceed 1 20 of the wavelength, otherwise the multi-point grounding method should be used.

2.Separate digital circuits from analog circuits.

There are both high-speed logic circuits and linear circuits on the circuit board, and they should be separated as much as possible, and the ground wires of the two should not be mixed, and they should be connected to the ground wires of the power supply side respectively. The ground area of the linear circuit should be increased as much as possible.

3.Make the grounding wire as bold as possible.

If the grounding wire is very thin, the grounding potential will change with the change of current, resulting in the unstable timing signal level of the electronic equipment and the deterioration of noise immunity. Therefore, the ground wire should be thickened as much as possible so that it can pass through the three allowable currents located on the printed circuit board. If possible, the width of the ground wire should be greater than 3mm.

4.The grounding wire forms a closed loop.

When designing a ground wire system for printed circuit boards consisting only of digital circuits, making the ground wire into a closed loop can significantly improve the noise immunity. The reason is that: there are many integrated circuit components on the printed circuit board, especially when there are components that consume a lot of power, due to the limitation of the thickness of the grounding wire, a large potential difference will be generated on the ground junction, resulting in a decrease in noise resistance, if the grounding structure is formed into a loop, the potential difference will be narrowed, and the noise immunity of electronic equipment will be improved.

The main bai memorizes these three points, and a brief description of the hand-drawn sketch on the du is attached.

Single-point grounding: The power supply is directly connected to the digital ground, and the analog ground is connected with a magnetic bead or 0 ohm resistor.

Ground plane integrity: Specially use a layer of board as the ground plane, and keep the ground plane as complete as possible 3W principle: use copper pour on the signal line trace layer as pin grounding and protection, and the distance between the copper pour and the signal line is 3 times the width of the signal line.

Generally, there are two ways to lay ground wires, one is a circular ground and the other is a tree-shaped ground.

The most basic principle is that the signal ground and the power supply ground should be strictly separated, and it is best to draw them in different areas, and then connect them to the capacitors separately.

Generally, there are two ways to lay ground wires, one is a circular ground and the other is a tree-shaped ground.