Those who have experienced electromagnetic interference and those who have not. With the increase of PCB routing express, emc design is a problem that we electronic engineers have to consider. For a design, there are five important attributes to consider when conducting EMC analysis of a product and design:
(1) key device size: the physical size of the emitting device that generates radiation. An RF (radio frequency) current will create an electromagnetic field that will leak out of the housing. The routing length on the PCB as the transmission path has a direct effect on the rf current.
(2) impedance matching: the impedance of the source and receiver and the transmission impedance between them.
(3) time characteristics of the interference signal: whether the problem is a continuous (periodic signal) event, or only exists in a specific operation cycle (for example, a single time may be a key operation or power on interference, periodic disk drive operation or network burst transmission).
(4) the intensity of the interference signal: how strong is the source energy level, and what is its potential to generate harmful interference.
(5) frequency characteristics of the interference signal: use the spectrum analyzer to observe the waveform, and find out where the observed problem is in the spectrum.
In addition, some low-frequency circuit design habits need to be noted. For example, my usual single-point grounding is very suitable for low-frequency applications, but I found it is not suitable for rf signal occasions when chatting with the company’s Daniel, because there are more EMI problems in the rf signal occasions. It is believed that some engineers apply single-point grounding to all product designs without realizing that the use of this grounding method may cause more or more complex electromagnetic compatibility problems.
We should also pay attention to the current flow in the circuit components. With circuit knowledge, we know that current flows from places with high voltages to places with low voltages, and that current always flows through one or more paths in a closed-loop circuit, so a minimal loop and a very important law. For those directions in which the interfering current is measured, modify the PCB wiring so that it does not affect the load or the sensitive circuit. Applications that require a high impedance path from the power supply to the load must consider all possible paths through which the return current can flow.
There is also a PCB wiring problem. The impedance of a wire or conductor includes resistance R and inductance, and at high frequencies there is no reactance. When the wiring frequency is above 100kHz, the wire or wiring becomes inductance. Wires or wiring that work above audio may become radio frequency antennas. According to EMC regulations, no wire or wiring is allowed to work below a specified frequency for lambda /20 (the antenna’s design length is equal to a specified frequency for lambda /4 or lambda /2,). When accidentally designed that way, the wiring becomes a highly efficient antenna, which makes later debugging even more difficult.
The layout problem that soft board factory says PCB finally. First, consider the size of the PCB. When the size of PCB is too large, with the growth of wiring, the anti-interference ability of the system decreases and the cost increases, while too small size will easily cause problems of heat dissipation and interference. Second, determine the position of special components (such as clock components) (clock routing is best around the unpaved floor and do not walk above and below the key signal line, to avoid interference). Third, according to the circuit function, the PCB overall layout. In the layout of components, related components should be as close as possible, so as to achieve better anti-interference effect.