From Wikipedia, the free encyclopedia.
In telecommunication or other systems, thermal noise (Johnson noise) is the noise generated by thermal agitation of electrons in a conductor. The noise power, P , in watts, is given by P = kT Δf , where k is Boltzmann's constant in joules per kelvin, T is the conductor temperature in kelvins, and Δf is the bandwidth in hertz.
- Thermal noise power, per hertz, is equal throughout the frequency spectrum, depending only on k and T .
- For the general case, the above definition may be held to apply to charge carriers in any type of conducting medium.
Thermal noise is intrinsic to all resistors and is not a sign of poor design or manufacture, although resistors may also have excess noise. Electronics engineers often prefer to work in terms of noise voltage and noise current.
en = √ kTR Δf
in = √ kT Δf / R
