If your latest PCB works very well, but when someone comes to ask you, you don't want to look too confident, just complain about noise. If there is a problem with your printing circuit board and you don't know why, then you are blamed on noise. The noise is always guilty until it is proven to be innocent.
What is noise?
If you want to go, this question is a bit difficult to answer, because you will eventually enter the philosophical field, in the face of "why life is so complicated?" Or "Why can't the total entropy be reduced once every other time?" If you are satisfied with the superficial processing of this theme, the electrical noise is straightforward.
The following is a definition of electrical noise from the perspective of circuit design: noise is a universal word, which refers to changes in voltage or current, usually random, relatively low amplitude, and always unwell.
The following comments should help explain this definition:
Electromagnetic noise is an important factor in circuit design, but the definition of my limited voltage and current is that the effect of electromagnetic noise is manifested through current and voltage changes in the circuit environment.
I said that "frequent" is random to consider predictable or periodic noise signals, such as 60 Hz interference. However, this article focuses on the basic phenomenon of noise, which is randomly (or more accurately, they are random for humans).
The range of noise signals may be very large, but in this case, I think that large transients, lightning strikes, or severe electromagnetic interference are separate categories.
Sometimes we may intentionally create noise (trembling), but I think that if we limit it to unnecessary signals, the definition above will be more consistent. In my opinion, intentional useful noise is called“Noise” only because it looks like noise; intentional noise is more of a“Signal” category, at least if it is judged by its source and use, because it was created by the designer according to the needs of the system.
Reasons for noise
The goal here is to find the root cause. The noise may be "from" anywhere: air, power supply, LDO, switch regulator, resistance ... we hope to deeply understand the source of the noise itself, rather than the component or path of the noise entering the circuit.
Hot noise, also known as Johnson noise
This is a basic facts related to the resistance of electronic flow. Unless we start using superconducting design circuits, we will always have hot noise, because there is at least a little resistance.
Thermal noise is manifested as random voltage changes; it is related to temperature, resistance and bandwidth. Higher temperature and higher resistance cause higher noise amplitude. The "bandwidth" here refers to the frequency range related to circuit. If you contain more frequencies in analysis, you will see more thermal noise.
Scattered noise
Electronics does not actually "flow" the conductor. They hit around to a certain extent, and the potential energy is constantly accumulated, and then the electrons must be transformed into kinetic energy each time the electrons must cross the obstacle. (Imagine a ball rolling up a series of raised -as the energy moves back and forth between the potential energy domain and the kinetic energy domain, the speed continues to change.)
These random changes in electronic movements lead to the corresponding random changes in the current. In other words, noise. Sanda noise is more prominent than the conductor in semiconductors, because semiconductors have more potential barriers. The higher the current, the greater the noise of the scattered granules, and the wider the bandwidth wider (the same, the higher the frequency, the greater the noise).
1/f noise, also known as flashing noise
Flashing noise is generated by most electronic components, and its amplitude will decrease with frequency. The name "1/F" (that is, "inversely proportional to the frequency") reminds us that the relationship between amplitude and frequency is a significant feature of flashing noise. Like scattered noise, higher currents can cause more flashing noise.
Flash noise decreases as the frequency, so thermal noise is dominant at a certain point. The picture is taken from the publisher ADI company.
Sudden noise, also known as popcorn noise
This noise only appears in semiconductors, but this is not much helpful for us, because semiconductor is now everywhere. The defects of semiconductor materials can lead to voltage or current mutation. Quick conversion contains high -frequency energy, but the pulse frequency generated by these conversion is actually quite low.
If the polluting signal is enlarged and it is sent to the speaker, it may hear unexpected noise, which sounds like a popcorn explosion. Due to the advancement of semiconductor manufacturing technology, it is not a big problem for sudden noise.
in conclusion
This covers the most important noise source in the electronic circuit. I hope you now have a better understanding of the physical phenomenon that causes electrical engineers so panic. You can't eliminate noise, but the information above gives you some ideas that reduce noise problems. For example, in order to reduce thermal noise, you can use a smaller resistor or add a filter to limit the bandwidth. Low -current bias technology can reduce scattered noise and flash noise.
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