Noise temperature contours for high-sensitivity Squids

A simple expression is developed for the noise temperature TN of SQUID amplifiers. The expression is in terms of equivalent current and voltage noise generators in the input circuit, and is shown to contain the spectral energy resolution, which is the currently accepted figure of merit for SQUID's. It is also shown that a SQUID optimized for the best energy resolution is not necessarily optimized for the lowest noise temperature.