High Speed PCB – How to Avoid Common PCB Design Issues
High speed pcb is a special PCB design that requires specialized considerations for layout and routing. The key to achieving high speed is avoiding common PCB design issues, such as crosstalk and signal integrity.
Signal timing occurs when signals fail to reach their destination in time and get interpreted as a 1 instead of a 0. Signal noise is caused by random fluctuations that affect other signals.
Impedance control
Signals that travel through PCBs are vital for connecting parts in electronic devices. They transfer electrical signals that control functions such as power, clocking, and timing. Those signals do not travel freely, however, and must overcome the resistance and capacitance of the copper traces. This process requires careful design to ensure the integrity of high speed digital and analog signals. Signal distortion can cause ringing, crosstalk, reflections, and ground bounce. These problems are exacerbated at higher speeds.
High speed signals require a special type of board to maintain their quality and performance. The board must have a specialized laminate material to reduce insertion loss and provide a consistent impedance. Spread glass and PTFE laminates are ideal for this application, but they are not the only options. In addition, the PCB must have rounded corners and smooth bends. These features will help prevent the signal from traveling through the traces and losing its energy.
The PCB’s controlled impedance depends on its design, layout, and layer buildup. To determine this, you can use a formula or calculator with field solver functionality. The size of the transmission line and its distance from surrounding power or ground plane layers will also impact impedance. Ensure that the transmission lines have a uniform characteristic impedance, and place GND vias close to differential pairs.
Differential pairs
Differential pairs are an important part of any high-speed PCB design. They can help reduce noise and EMI in a signal, as well as withstand ground offsets. However, they must be routed correctly to ensure that these benefits are retained. A differential pair requires two conductors to carry a signal, and it is important that high speed pcb they are closely spaced. Using too wide a spacing between the traces will result in impedance mismatches that can cause noise and EMI.
Another issue that can occur with differential pairs is crosstalk. This occurs when the differential pair transmits a pulse that is correlated with the same single-ended signal on another trace. This can be difficult to prevent, but it can be reduced by ensuring that the signals are not transmitted to the same location.
The main advantage of differential signaling is the ability to cancel out incoming and outgoing noise. This is because the pair’s two conductors create a magnetic field that counteracts each other. However, it is important to note that this effect is only effective when the traces are very close together. If the traces are too far apart, they will not be able to cancel out incoming and outgoing noise.
Fortunately, many modern PCB design tools, such as EasyEDA, Eagle, and Altium, have built-in features for routing differential pairs. These tools can automatically manage the widths and spacing of the pairs as they are routed. They can also manage the skew between the traces.
Vias
The PCB board’s vias are an important part of the signal path, but they can also be a source of interference. The right type of via is important for High-Speed PCB Supplier high-speed signal integrity, as it can minimize parasitic capacitance and inductance. In addition, the via size must be matched to the signal waveform. For example, a large via can increase the transmission loss, while a small one may reduce it.
In addition, high-speed signals require impedance matching, which is a process of ensuring that the signal path has a constant impedance throughout its length. This is done to prevent signal reflections that can corrupt the signal. The PCB designer can calculate a target impedance in the CAD tool based on the track width, copper height, and distance from the ground plane.
It is also important to avoid routing signals over overlapping layers, as this can cause crosstalk between different components. It is best to keep the signal transition vias symmetrical within 200 mils of each other, or use stitching vias.
A good way to avoid these problems is to restrict high-speed routing to a single layer. This method can be expensive because it requires extra production steps, but it is often more cost-effective than adding return vias. In addition, it improves performance by reducing the number of resonant frequencies.
Component location
In high speed PCBs, it is important to pay close attention to the location of components. For example, you should separate analog components from digital ones and place them away from each other. This will help you avoid EMI issues and improve the quality of the signal on your board. You should also keep traces short to reduce parasitic capacitance and inductance, which can affect signal integrity.
The location of components becomes a real challenge when you are dealing with a small circuit board. The size of the board is very limited, and the components have to be placed in a way that does not compromise the functionality of the board. This is not an easy task, but it can be done with a little planning and careful execution.
Another issue in high speed PCB design is the proximity of signals to each other. If the tracks are too close, they can cause a delay in the transmission of the signal. The resulting signal distortion can affect the device’s performance and lead to errors in data processing. To avoid this, it is important to use rounded corners for the copper traces on your PCB.
In addition to this, you should avoid routing tracks over cutouts in the polygon and over polygon-splits. Doing so can cause extra EMI, signal propagation delays, signal integrity violations and generate electromagnetic interference. Moreover, you should avoid placing components that relate to high speed interfaces near the edge of your PCB. This will have a negative impact on the quality of the signal.
