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Electrical Noise and Interference
4 questions By Tony R. Kuphaldt
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Question 1 of 4
Define what noise means, in the electrical sense of the word. How does electrical noise compare and contrast with audible noise?
Reveal answerElectrical noise consists of random voltage and/or current signals, usually having a broad range of frequencies.
Notes:For a good overview of electrical noise, consult Texas Instruments’ online manual, Op Amps For Everyone, sections 10-1 through 10-12.
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Question 2 of 4
Define the following noise types, according to how each one is generated in electronic circuits:
- Shot noise
- Thermal (“Johnson”) noise
- Flicker (or 1/f) noise
Also, identify the major factor responsible for the amplitude of each noise type.
Reveal answerShot noise is generated by individual electrons “jumping” across some sort of barrier potential as they travel through a conducting substance. Shot noise is proportional to the amount of electric current going through a conductor.
Thermal noise, also known as Johnson noise, is caused by the random motion of electrons due to thermal energy. As one might guess, this type of noise is proportional to conductor temperature.
Flicker noise, or 1/f noise, is characterized by a magnitude that is inversely proportional to frequency. Little is known about the origins of this type of noise, but it is proportional to the amount of DC current, just like shot noise, and so may be mitigated using the same controls.
Notes:Noise is a very complex subject in electrical engineering, and most likely beyond the scope of your students’ coursework. This question is really just scratching the surface of noise theory.
For a good overview of electrical noise, consult Texas Instruments’ online manual, Op Amps For Everyone, sections 10-1 through 10-12.
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Question 3 of 4
What is the difference between white noise and pink noise?
White noise in the audio range is generally considered to be pleasing to the human ear. Identify one source of “white” noise that anyone can readily experience for themselves.
Reveal answerThe difference has to do with the distribution of noise amplitude compared to noise frequency. Hint: compare red-colored light with “white” light.
With regard to white noise, everyone has heard it at least one in their lives, but most people don’t know what to call it!
Notes:Explain to your students that other colors are used to categorize spectral distributions of different noise types:
- Purple = f2 (directly proportional to square of frequency)
- Blue = f (directly proportional to frequency)
- White = 1 (constant amplitude)
- Pink = 1/f (inversely proportional to frequency)
- Red/Brown = 1/f2 (inversely proportional to square of frequency)
And, of course, there are such noises that do not neatly fall into any of these categories.
For a good overview of electrical noise, consult Texas Instruments’ online manual, Op Amps For Everyone, sections 10-1 through 10-12.
