In this paper we analyse the properties of the Bloch oscillating
transistor as a preamplifier in cryogenic devices. We consider here
especially the readout of hot electron bolometers (HEBs) based on
Normal-Superconductor-Insulator tunnel junctions, but the results also apply more generally. We show that one can get an equivalent noise voltage below 1 nV/&sqrt;Hz with a single BOT. By using N BOTs in a parallel array configuration, a further reduction by factor
&sqrt;N may be achieved.
Small Josephson junctions are known to be very susceptible to noise. We have utilized this property in developing methods to measure noise as well as environmental resonance modes in mesoscopic systems. We review recent results on tunnel junction systems and show also that higher order moments of shot noise can be addressed with the present method based on the noise-induced modification of incoherent tunneling of Cooper pairs.