Noise in Circuits: Causes & Solutions

[amaresh92]

I wonder if anyone could tell me how and why the noise is created by the any electronic circuit or clipping circuit?

thanks

 

[chaoseverlasting]

Why does any electronic circuit function? The underlying form of energy is electrical. Electrical energy may be represented by movement of electrons. When a particular signal passes through a circuit, it causes the electrons present in the devices of that circuit (R, L, C) to move in a certain way.

However, the movement of electrons in a device is also affeced by ambient conditions (temperature primarily). These conditions give the electrons present in the device some inherent energy (kinetic energy). As these electrons are already moving in a certain way, the signal reproduced at the output of the circuit is the additive sum of the input signal plus the inherent movement of the electrons. We call this inherent movement 'noise'.

 

[dlgoff]

Clipping a sine wave results in higher frequency harmonics. These extra frequencies can get into your circuit and is called "noise" albeit not like the random/thermal noise that chaoseverlasting mentioned.

Here the extra frequencies due to clipping are odd harmonics; hence the 3,5,&7.

http://hyperphysics.phy-astr.gsu.edu/hbase/audio/amp.html"

 

[Bob S]

The lower noise limit in an electronic circuit is given by the Johnson-Nyquist equation

http://en.wikipedia.org/wiki/Johnson–Nyquist_noise

where k_B is the Boltzmann constant 1.38 x 10^-23 Joules per degree Kelvin.

In addition, there is an amplifier "noise figure", representing amplifier input noise, to be added to the total circuit noise, referenced to the input.

Very nominally, the noise limit is ~ -114 dBm per MHz.

[added note]

kBT = 1.38 x 10^-23 x 10⁶ x 293 = 4.04 x 10^-12 milliwatts per MHz.

10 Log (4.04 x 10^-12) = -113.9 dBm per MHz

Bob S