A 700 MHz amplifier
In an usual RF-SET system, the SET is the first-stage amplifier and a high electron mobility transistor (HEMT) works as a second stage amplifier. The noise temperature of the HEMT amplifier should be in the subkelvin range in order to reach the physical limit of the RF-SET, set by the shot-noise of the SET.
We have designed a cryogenic, 700 MHz HEMT amplifier, based on Agilent ATF35143. We used cryogenic measurement data on S-parameters in conjunction with the Pospiezalski noise model to build an amplifier that shows a noise temperature of ~ 3 K.
Technologically, noise temperatures of cryogenic HEMT amplifiers seem to be limited to a few Kelvins. In order to decrease the noise temperature of the GHz amplifiers by an order of magnitude, DC-SQUID based amplifiers have been constructed. However, there are open issues related to their input match and stability to be solved before they can be used as general-purpose amplifiers in the GHz range.
- Design of cryogenic 700 MHz amplifier
L. Roschier and P.J. Hakonen
Cryogenics 44, 783 (2004)