Cryogenic preamplifiers for low-temperature particle detectors

Two voltage-sensitive preamplifier designs are presented for operation at 1.6K. These preamplifiers are used in conjunction with a silicon crystal acoustic detector (SiCAD), which is intended for neutrino detection. Both designs incorporate GaAs MESFETs. The carriers in GaAs do not freeze out below 77 K as with silicon. The first design has two stages including a common-source gain stage and a source follower stage. The voltage gain into 50 Ω is 7.0 dB, with the -3dB point occuring at 10 MHz. The noise of the first stage was found to dominate the total noise. The second design incorporates one cold FET, dissipating 1-5 mW, in cascode with a room-temperature bipolar transistor. The noise of this design was found to be approximately equal to that of the two-cold-stage design except for a bulge in the voltage noise centered at 13 MHz. There are two outputs with 38 and 58 dB gain, both outputs have 50 Ω output impedance. Noise measurements will be presented along with a discussion of the preamplifier designs. (author) 3 refs.; 3 figs