How to Design a High Speed PCB
When designing a high speed pcb, you need to pay special attention to your copper traces and their layout. This includes following important guidelines like using proper impedance and signal return path design.
The best way to do this is to use the right CAD software with advanced options. This will allow you to view your signal propagation delay and traces simultaneously.
Spacing and Impedance
A key aspect of high speed PCB design is ensuring that your circuit can handle the required signal levels. This involves paying careful attention to component placement, layer stackup, and routing. A good PCB design company can assist with this.
Impedance control is a critical part of high speed PCB design, and it requires specific trace widths and spacing. This is because high speed signals require controlled impedance for optimal transmission and power transfer.
One way to achieve controlled impedance is to use differential pairs. This is because it helps reduce noise and improves signal integrity. Another method is to keep the traces as short as possible. This is because long traces increase parasitic capacitance and inductance, which can degrade signal quality.
Another important factor in high speed PCB design is choosing the right power high speed pcb delivery network (PDN) components. These include capacitors, resistors, and inductors. PDNs must be decoupled from other components on the board, so they don’t interfere with each other or cause EMI.
Choosing the right PDN components can help you avoid problems like ringing and transients on the circuit. Also, it’s a good idea to route your ICs in the center of the board, so you don’t have to worry about radiated EMI. The bottom line is that high speed digital designs are much more complex than traditional analog designs, and they require special care. Therefore, it’s essential to work with a PCB design firm that has the experience necessary to provide cutting-edge PCBs.
Trace Geometry
One of the main reasons for high speed signal integrity problems is incorrectly designed traces. This can result in a poor impedance of the trace, making it difficult to carry current and causing it to overheat. To avoid this, it’s important to know the correct stack-up for your board’s layers. Using a stack-up calculator tool will help you determine the minimum trace width required to meet your requirements. There are many different tools available for this online. These can be used to enter various parameters such as thickness, current, and maximum acceptable temperature rise, allowing you to find the perfect trace width for your design.
You should also pay attention to the trace geometry. For example, a digital or analog signal will require a thinner trace than a power or ground signal. The overall trace length should be as short as possible, and the traces should be spaced evenly apart to minimize interference. Moreover, the traces should be thick enough to support the current needed for their operation.
When routing high speed signals, it’s important to use GND vias (electroplated holes) on the differential layers to maintain a consistent GND reference and uniform impedance throughout the signal path. If possible, these GND vias should be positioned symmetrically close to the signal transition vias. Moreover, the corners of the traces should be rounded. Right angle corners can cause a significant difference in the baseline impedance of a copper trace at high speeds.
Vias
When constructing a high speed PCB, via structures play an important role in keeping signals clean and accurate. It is necessary to minimize stray capacitance and inductance, which can be caused by the distance between the signal source and the via point. This can lead to signal reflection and noise. It is recommended to avoid stacked vias, and use staggered vias whenever possible. This will reduce the amount of metal that is needed, and also help to reduce the aspect ratio.
In addition, when routing high-speed signals, it is important to consider the impedance of the signal at the via point. Due to the geometry of a via and High-Speed PCB Supplier the lack of a reference plane, its impedance is usually different from that of a PCB track, which can result in signal reflection and compromise signal integrity.
Fortunately, it is easy to avoid these problems by using appropriate via placement and routing techniques. For example, it is important to place vias strategically to allow for escape routing or bus routing without creating a continuous void in the ground plane that can cause the return signals to wander. This can also cause EMI and other signal quality problems. It is also important to avoid placing vias over antipads, which can create a slot in the ground plane that will block clear return paths for signals.
Ground Planes
As signal speeds increase, digital circuits tend to switch states often. This can cause noise and interference pulses in the ground circuit. These pulses can impact other parts of the circuit, especially the ones that need to return current. A PCB ground plane with a wide conducting section can help minimize these disturbances because it offers a lower impedance than a routed ground net.
To achieve this, the PCB designer must ensure that no part of the ground plane is obstructed by traces. In addition, the ground layer should be connected to vias that connect it to both the top and bottom sides of the board. This helps keep the ground loops from becoming unstructured, which can cause EMI.
The ground layer is also important for reducing crosstalk between adjacent traces. When two traces run parallel, electromagnetic field lines from one can be coupled to the other through induction. A ground plane under the signal traces can reduce this effect by containing the return currents in the area underneath.
Another way to minimize crosstalk is to separate analog and digital signal traces. This can be done by placing the devices by function and routing their signals in a separate region. This can also be accomplished by using a split-plane design. The split-plane technique uses multiple layers to split the power and ground planes, thereby limiting their interaction. However, it is more expensive than a single-sided PCB.
