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.

Photograph of the amplifier without cover. The coaxial rf-connections are made with SMA-connectors. The scale units at the bottom are centimeters.
Measured noise temperature TN with error estimate (gray area) and the result from the simulation (solid line). The dashed lines denote reference noise temperatures of two amplifiers (taken from Bradley RF. Nucl Phys B 72, 137 (1999)). Amplifier gain S21 is denoted by a dash-dotted line.

Related publications

  • Design of cryogenic 700 MHz amplifier

L. Roschier and P.J. Hakonen

Cryogenics 44, 783 (2004)