Noise in Circuits: Causes & Solutions

In summary, electronic circuits create noise due to the movement of electrons and ambient conditions, which is known as inherent noise. Clipping a sine wave adds higher frequency harmonics, also known as noise. The lower noise limit in a circuit is determined by the Johnson-Nyquist equation, and there is an amplifier "noise figure" that must be added to the total circuit noise. Overall, the noise limit in electronic circuits is approximately -114 dBm per MHz.
  • #1
amaresh92
163
0
I wonder if anyone could tell me how and why the noise is created by the any electronic circuit or clipping circuit?

thanks
 
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  • #2
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'.
 
  • #3
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.

amp2.gif


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"
 
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  • #4
The lower noise limit in an electronic circuit is given by the Johnson-Nyquist equation

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

where kB 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
 
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1. What is noise in circuits?

Noise in circuits refers to unwanted electrical signals that can interfere with the desired signals in a circuit. These signals can come from various sources such as electromagnetic interference, thermal noise, and shot noise.

2. What are the common causes of noise in circuits?

The main causes of noise in circuits include external sources such as power lines, radio waves, and other electronic devices. Internal sources can also contribute to noise, such as imperfect components, temperature changes, and fluctuations in power supply.

3. How does noise affect circuit performance?

Noise can have a significant impact on circuit performance, especially in sensitive systems. It can cause errors, distortions, and reduce the signal-to-noise ratio, making it difficult to distinguish between the desired signal and the noise. In extreme cases, noise can even lead to circuit failure.

4. What are some ways to reduce noise in circuits?

There are several solutions to reduce noise in circuits, depending on the source of the noise. Some common techniques include using shielding, filtering, and grounding to minimize external interference. For internal noise, using high-quality components, proper circuit layout, and decoupling capacitors can help reduce noise levels.

5. How can I measure and analyze noise in circuits?

There are various methods to measure and analyze noise in circuits, such as using an oscilloscope, spectrum analyzer, or noise meter. These tools can help identify the type and level of noise present in a circuit, allowing for targeted solutions to reduce noise and improve circuit performance.

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