Broadband cryogenic preamplifiers incorporating GaAs MESFETs for use with low-temperature particle detectors

Two voltage-sensitive preamplifier designs are presented for operation at 1.6 K. Both designs incorporate GaAs MESFETs (Plessy P35-1101). The first design has two stages including a common-source gain stage and a source follower stage. The noise performance, particularly with the low-frequency noise, was found to improve with cooling. The white-noise level at low temperature is 1 nV/Hz1/2, and the low-frequency noise corner occurs at approximately 1 MHz. The voltage gain into 50 Ω is 7.0 dB, with the −3-dB point occuring at 10 MHz. The noise of the first stage was found to dominate the total noise at the output of a low-noise room-temperature post amplifier. The output impedance of the preamplifier is 50 Ω. The second design incorporates one cold FET, dissipating 1 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 due to impedance mismatching of the line to room temperature. The gain of this design is 21 dB, with the −3-dB point at 2 MHz. Cryogenic semiconductor operation is discussed, design parameters of the two preamplifiers are discussed in detail, noise measurements are presented along with a discussion of the different temperature- and bias-dependent noise sources, and an analysis of the signal-to-noise ratio and rise time for the present detection scheme is made.