What is electrical noise?

[drewdavis]

Hello,

I have heard several people talk about "noise" but I don't know what it is. Could somebody explain? Also, why do capacitors in front of analog inputs solve the problem?

Thanks,
Drew

[BulletMagnet83]

Electrical noise is unwanted signals causing undesired operation. Imagine if you're trying to listen to a faint tone against a background of loud static... in simplest terms it's a little bit like that.

EDIT: Here's a thing on RC filters to get you started.

http://www.youtube.com/watch?v=OBM5T5_kgdI

[drewdavis]

Thanks that helped!

[patduino]

Great explanation.  The noise can come from external signals or even from the chip itself. The clock can introduce noise into your circuits, too.

[Grumpy_Mike]

Electronic noise is any fluctuation in voltages that you don't want.
It could be from the operation of a chip, capacitors help smooth this.
Here is one example of noise being generated and being suppressed.
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

Noise can also be generated by thermal agitation of electrons, this is know as thermal noise. There are other mechanisms that generate noise but in digital electronics this is normally too small to be a problem.

Noise can also be injected into a circuit through radiation when the circuit is acting unintentionally like a radio receiver.

[retrolefty]

And sometimes electrical noise is a desirable trait as in pink and white noise generators used to output wide spectrum audio signals to measure frequency response of circuits or components, or as when wanting a hardware noise generator to be used as a source of random number generators.

All electrical circuits and components generate noise to some degree just by the energy of electron movement. One does not eliminate electrical noise, but one can manage it in a circuit such that it does not effect the desired function(s) of the device or circuit.

http://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise

Lefty

[MarkT]

Often audio amplifiers and equipment use a small-valued capacitor across the input(s) to present a virtual short-circuit
to radio-frequency signals - this really helps prevent the unintended radio-receiver effect (the non-linear elements in
the amplifier circuit can inadvertantly act like an amplitude-modulation detector at radio frequencies).

Even quite a small value capacitor like 100pF can severely attenuate radio frequencies (MHz and above) without doing much
at all at audio frequencies.

Often the source of unwanted noise is from the cables (which here can be acting as radio aerials / antennas).   Mains
wiring often has sporadic noise spikes (clicks) when switches and thermostats are operated - main wiring is everywhere in
buildings and thus tends to inject such noise into any other wiring running near it.

[A4kash]

Often audio amplifiers and equipment use a small-valued capacitor across the input(s) to present a virtual short-circuit
to radio-frequency signals - this really helps prevent the unintended radio-receiver effect (the non-linear elements in
the amplifier circuit can inadvertantly act like an amplitude-modulation detector at radio frequencies).

Even quite a small value capacitor like 100pF can severely attenuate radio frequencies (MHz and above) without doing much
at all at audio frequencies.

Often the source of unwanted noise is from the cables (which here can be acting as radio aerials / antennas).   Mains
wiring often has sporadic noise spikes (clicks) when switches and thermostats are operated - main wiring is everywhere in
buildings and thus tends to inject such noise into any other wiring running near it.

stuck in virtual short circuit. can we create virtual short circuit?or it is the feature of capacitor?

[A4kash]

Electronic noise is any fluctuation in voltages that you don't want.
It could be from the operation of a chip, capacitors help smooth this.
Here is one example of noise being generated and being suppressed.
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

Noise can also be generated by thermal agitation of electrons, this is know as thermal noise. There are other mechanisms that generate noise but in digital electronics this is normally too small to be a problem.

Noise can also be injected into a circuit through radiation when the circuit is acting unintentionally like a radio receiver.

here + and - denotes the source but i failed to understand how the IC'S here are  producing the varying current and here it is shown that the varying current is going to the ICA and thus the other current going to ICB  and ICcare also changing due to changing current produced by ICA .

[drewdavis]

Thanks for all the explanations. I have learned so much from everybody on this forum.

[Grumpy_Mike]

but i failed to understand how the IC'S here are  producing the varying current and here it is shown that the varying current is going to the ICA and thus the other current going to ICB  and ICcare also changing due to changing current produced by ICA .

Any digital IC works by switching things on and off inside. The current taken in the on states different to that taken in the off state. The connections between the ICs are not zero ohms, the resistance is small butnot zero. So a varying current into the IC produces a varying voltage across it. If the power to the ICs is chained like shown hear the next IC sees the power supply as not constant but having a small ammount of ripple on it or noise.that makes the effect on the second IC even greater. Because it is taking a varying current and is being driven by a varying voltage. And so it goes on down the line until the ICs stop working or work only intermittently.