Jak zlepšit rušení signálů SDRAM při návrhu desek plošných spojů?

A good PCB design is one that is free from radiation interference from SDRAM signals. You can do this by keeping the signal lines as short as possible and increasing the dielectric constant of the PCB board. Moreover, you can place magnetic beads at the connections of the wires or cables.

Increasing the dielectric constant of the PCB board

When using high-speed circuits, the need to match the impedance of traces is critical. If not, RF energy can radiate and cause EMI problems. A good way to solve this problem is to use signal termination. This will mitigate the effects of reflection and ringing, and slow down fast rising and falling edges. The materials used in PCB boards play a big role in the impedance of the traces.

The best practice is to route key signals separately and as short as possible. This minimizes the length of coupling paths for interference signals. Clock signals and sensitive signal lines should be routed first. Insignificant signal lines should be routed last. In addition, key signal routing should not exceed the space created by pad and through-hole vias.

Keeping signal lines as short as possible

Keeping signal lines short in PCB design helps to avoid EMI and crosstalk problems. The signal return path is defined as the projection of a trace on the reference plane. It is very important to keep this reference plane continuous. In some cases, the return path can be reduced by using signal switching and power layer splitting techniques. In such cases, the SDRAM signal should be placed on the inner layer of the PCB.

If the signal return path is long, it will create a large amount of crosstalk and mutual coupling. Hence, it is important to keep signal lines short as much as possible. The length of the signal line should be set as close as possible to the adjacent ground plane. It is also essential to reduce the number of parallel leads at the input and output terminals. If necessary, the distance between the two leads can be shortened or increased by adding grounding lines between them.

Using ferrite beads

Ferrite beads are used to reduce radiation interference in circuits containing sdram signals. The beads are used on individual conductors in the circuit. The use of these beads requires careful consideration. For example, single-board computer CPUs are typically operated at high frequencies, with clocks often in the hundreds of megahertz. Similarly, power rails are susceptible to RF.

The main properties of ferrite magnetic beads are that they have very low resistance to low-frequency currents and very high-frequency attenuation to high-frequency currents. These characteristics make them more effective at noise absorption than conventional inductors. For optimal results, the manufacturer should provide a technical specification. This will help the user to determine the correct impedance for the circuit.

Using ground-fill patterns

Radiation interference is a problem that can cause malfunctions in electronic equipment. It can occur in any frequency range and can cause signal quality to be compromised. Luckily, there are several ways to improve radiation interference. This article outlines some techniques that can be used.

One technique is to extend the ground traces. By doing this, the ground traces can fill up empty spaces on the PCB. In a two-layer board, for example, the ground traces should be extended from the top layer to the bottom. In addition, the ground traces should not be too long. Using ground-fill patterns in pcb design allows designers to reduce the distance between the output and input terminals.

Another method is to use via stitching to reduce the amount of radiation interference caused by traces that are too close to the edges of the board. By doing this, the board is protected from EMI by forming a ring of vias around the board’s edge. Via stitching is particularly beneficial on two and four-layer boards.

Avoiding transmission line reflections

When designing a PCB, it is crucial to avoid transmission line reflections. These are caused by changes in impedance between the source and destination signals. This can be a result of various factors, such as the dielectric constant or height of the PCB.

First of all, the PCB must be able to maintain continuity of the reference plane, as the return current needs to go through the same layer. This continuity is essential when using signal switching and power layer splitting. Another way of ensuring that the return path is as short as possible is to incorporate a capacitor on the inner layer of the PCB.

Another solution to avoid transmission line reflections is to make sure that the traces are not too close together. This will reduce the likelihood of crosstalk, which can cause serious issues for high-speed signals.