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We describe the last stage of a readout for bolometric detectors consisting of a source follower Si-JFET held at its optimum temperature of operation and a room temperature second stage. Stringent limits on both white and low frequency noise are required. We present our design solution for the second-stage differential amplifier operated at room-temperature. A special circuit has been employed to achieve very low series noise. Possible noise sources from the power supply have been addressed and rejected. The amplifier features a white noise floor of about 400 pV/√Hz and low-frequency noise of 850 pV/√Hz at 1 Hz.
Date of Publication: Dec. 2011