Have you ever tried to find the reason behind switching off all the electronic items while traveling in an airplane? Well, the reason is Electromagnetic Interference (EMI). If they are switched on, the radiation being emitted can enforce the communication equipment’s in the pilot’s cabin to operate strangely. This can trigger a nightmare due to wrong or no communication with the station.
The same issue persists with a high speed Printed Circuit Board (PCB) wherein the frequency of signals is 100 to 1000 Mega Hertz (MHz). Even if the board is working well, it is radiating some energy, which is known as the electromagnetic energy.
This energy results in EMI, which can be fatal. Either the source unit or another electronic item tends to absorb it to disrupt its functionality. As a rule of thumb, the higher the switching speed, the more is the radiation, which is disruptive.
Still, it is possible to alleviate this interference by following some simple design tips, which are given below.
For high-speed applications, multilayer PCBs are preferable, which come with several power and ground planes. These PCBs are capable of significantly alleviating the effects of interference, unlike the single- or double-sided designs. They also facilitate a close control over impedance on some layers, high component density, and easier routing of signals.
When it comes to constructing a layer for high speed design, symmetrical stripline geometry is considered ideal for minimizing or eradicating the interference. A layer of single signal is inserted between two ground layers for enabling the ground planes topull away almost all noise.
As a critical requirement, an efficient circuit should offer a path of low impedance to the current for returning to its source at even high frequencies. The symmetrical stripline geometry offers a stable orientation for returns.
Apt Isolation of Components
It is essential to isolate the noise-generating components from the ones that are sensitive to interference and generate less noise. Both the types of components run at different frequencies and consequently generate different waveforms. Thus, their closer proximity result in more noise.
It is sensible to isolate analog components featuring high power as well as current from the adjacent digital ones having low power as well as current.
It is also essential to isolate the transmitted signalsunderneath these two types of components to suppress noise. You may segregate an internal plane layer below the trace layers to split the power and ground layers for suitable transmission.
Preferably, analog traces should run below their analog ground plane, while digital traces should run below the digital ground plane. This keeps impedance constant and ensures a good return path for the signals.
Clock Units in the Middle
For a high speed design, clock units are vital. This unit is an important source of radiation interference. This isthe reason why you should not position it at the edge of your board. By putting them in the middle, you make a way for reducing the interference in the circuit.