Noise
Johnson Noise
Thermal noise generated by the random motion of charge carriers in a resistive element, with power proportional to temperature and bandwidth, setting the fundamental noise floor of electronic systems
Understanding Johnson Noise
Johnson noise power is calculated as P = kTB, where k is Boltzmann's constant (1.38e-23 J/K), T is absolute temperature in Kelvin, and B is bandwidth in Hz. At room temperature (290K), this equals -174 dBm/Hz, the thermal noise floor.
Johnson noise is white noise with a flat spectral density across frequency (up to quantum limits). It exists in all resistive elements regardless of current flow and sets the fundamental sensitivity limit for RF receivers.
Common Questions
Frequently Asked Questions
What is the noise floor at room temperature?
The thermal noise floor at 290K is -174 dBm/Hz. In a 1 MHz bandwidth, this becomes -114 dBm.
How can Johnson noise be reduced?
The only way to reduce Johnson noise is to lower the physical temperature of the component, which is why cryogenic LNAs are used for the most sensitive receivers.
See Also