power plane design in PCBs
A power plane is a flat layer of copper that’s connected to your PCB’s power supply. It’s a common technique used to reduce noise and common mode emissions in your circuit’s power supply. It’s used along with decoupling capacitors to help stop noise and energy from spreading between different circuits on your PCB.
A good PCB design will have a clear separation between the signal layers and power planes. This helps to prevent the power planes from being swamped with unwanted current and voltage that can cause EMI. It also ensures that your PCB has proper symmetry for effective heat dissipation.
Typically, you can use the pcb design rules to check your design and make sure there are no unwanted connections between traces. These checks can help you spot things like traces that touch each other and vias with incorrect diameters. Another technique you can use is to divide the power planes into multiple domains based on their voltage requirements. For example, you may want your MCU to sit on a separate power domain than your I/O ports, so you can give them different voltages.
What techniques are used for power plane design in PCBs?
You can also use internal power planes to provide isolation between traces. This can be useful if your signal layers have to travel long distances between the signal source and the device under test (DUT). By using power planes and decoupling capacitors, you can improve your PCB’s EMC performance and reduce its impedance.
Power planes are a common feature in multilayer PCBs. They are usually located on the outermost layers and connect to a ground plane. This provides a stable DC potential across the board and improves the signal integrity of high-speed signals. A reference plane can be added to the power plane for better stability and EMI reduction, but it’s not necessary.
In addition to power planes, a PCB can have multiple reference and control planes. These are important for maintaining a constant signal voltage and improving its impedance. These are especially beneficial in high-speed designs where the signal path might be longer than usual.
A PCB can have several different types of traces, including stripline and microstrip. These traces have shorter return paths than traditional traces and can significantly improve the signal-to-ground ratio of a circuit. They can also reduce EMI and noise. When you use a stripline or microstrip trace, it’s important to place it correctly on the PCB. For example, you should place it over a signal and power plane, and avoid placing it on top of a metal ground plane. This is because the overlapping portion of the plane will produce unwanted distributed capacitance between it and the DUT.
It’s also a good idea to have decoupling capacitors placed near the entrance of the power plane and around the DUT. This will keep the power plane’s impedance low and prevent any unwanted voltages from occurring at the entry point of the power plane or between the power plane and the DUT.
