Electronics/Noise in electronic circuits

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Electrical Noise
any unwanted form of energy tending to interfere with the proper and easy reception and reproduction of wanted signals.

Classification[edit | edit source]

Based on Origin[edit | edit source]

  1. External noise
    1. Atmospheric
    2. Extraterrestrial
      1. solar
      2. Cosmic
    3. Industrial
  2. Internal noise
    1. Thermal Agitation Noise
    2. Shot Noise
    3. Transit Time Noise
    4. Flicker Noise
    5. Miscellaneous Sources

Thermal noise[edit | edit source]

Thermal Agitation Noise
Also known as Johnson noise or White noise.

where k = Boltzmann's constant = 1.38x10-23J/K

T = absolute temperature, K = 273 + °C
δ f = bandwidth of interest
Pn = maximum noise power output of a resistor

Shot Noise[edit | edit source]

where in = r.m.s. shot-noise current

e = charge of an electron = 1.6x10-19C
ip = direct diode current
δ f = bandwidth of system

Noise Calculations[edit | edit source]

Addition due to several sources[edit | edit source]

noise voltages:

, ...and so on, then

where Rtot = R1+R2+...

Addition due to Cascaded Amplifier stages[edit | edit source]

Req = R1+R'2

Analog Noise Models[edit | edit source]

CMOS[edit | edit source]

BJT[edit | edit source]

Noise in digital circuits:[edit | edit source]

Methods of reducing noise[edit | edit source]

Differential signaling[edit | edit source]

Differential signaling is a method of transmitting information electrically by means of two complementary signals sent on two separate wires. The technique can be used for both analogue signaling, as in some audio systems, and digital signaling, as in RS-422, RS-485, PCI Express and USB.

Good grounding[edit | edit source]

An ideal signal ground maintains zero voltage regardless of how much electrical current flows into ground or out of ground.

When low-level signals travel near high currents, their return currents shouldn't be allowed to flow in the same conductor. Otherwise, noise such as AC ripple on the high current will modulate the low-level signal.

References[edit | edit source]

Kennedy, George 'Electronic Communication Systems' , 3rd Ed. ISBN 0-07-034054-4