Electrical Noise in a TES as a Resistively Shunted Conducting Junction

We present results of the analysis of electrical noise in a transition edge sensor (TES) as a resistively shunted conducting junction (the RSJ model). We derive an expression for the spectral density of voltage fluctuations taking into account weak superconductivity of a TES. We analyse and discuss differences in voltage noise in a TES compared to the familiar situation for the Josephson junction. The spectral density of voltage noise in the RSJ model has a unique analytical structure and cannot be reduced to the expression for the nonlinear Johnson noise near equilibrium.