A LOW-POWER-DISSIPATION BROAD-BAND CRYOGENIC PREAMPLIFIER UTILIZING GAAS-MESFETS IN PARALLEL

A voltage sensitive preamplifier design is presented for operation at 1.6 K. The active device is a Sony 3SK164 dual-gate GaAs metal-semiconductor field-effect transistor (MESFET), which was chosen for its low-frequency noise performance, stability against oscillations, and the inclusion of a gate protection diode. Active devices made from GaAs operate at cryogenic temperatures without carrier ''freeze out.'' The main design goal was to keep the power dissipation in the cryostat minimal, while maintaining high bandwidth and low noise. This was achieved by operating four parallel MESFETs at cryogenic temperatures in cascode with a room-temperature Si JFET. Parallel operation gives a higher transconductance-to-power dissipation ratio than with a single device. The input cascode is followed by high-speed, low-noise operational amplifiers. The low-frequency noise comer occurs at 100 kHz. The white voltage noise of the preamplifier referred to the input is < 0.9 nV/Hz1/2 at 1 MHz with 2 mW dissipated in the cryogenic stage. The power dissipation can be reduced to 1 mW with a moderate increase in noise. The preamplifier noise was found to be dominated by the cryogenic stage. There are two 50-OMEGA outputs with gains of 39 dB and 59 dB, and the -3 dB points occur at 500 Hz and 10 MHz. The design of the preamplifier is discussed in detail. Noise measurements under a variety of bias conditions are presented along with an analysis of the different noise sources.