Excess Noise Ratio

Excess Noise Ratio (ENR) is a way of describing the Power Spectral Density (PSD) of noise with respect to the thermal noise floor.

The available noise power delivered to a conjugated matched load at standard temperature of 290K is Pav = kTB and thus noise power density equal to -174 [dBm/Hz].

k = 1.38 x 10-23 joule / k

T= Temperature (Kelvin)

B = Bandwidth (Hz)

ENR[dB]=10 log (10^PSD[dBm/Hz]/10^-174[dBm/Hz] -1)

For cases where PSD >> -174 dBm/Hz ENR can be simply approximated by

ENR[dB]=PSD[dBm/Hz]-(-174[dBm/Hz])

For ENR >= 16 dB, the error due to the simpler approximation <= 0.11 dB

For example: when my noise source has an ENR of 44 [dB] around a certain frequency, the PSD of the noise is 44 - 174 = -130 [dBm/Hz], or -70 [dBm/MHz].