An ultra low-noise radio frequency amplifier based on a dc SQUID
- Andre, Marc-Olivier (Department of Physics, University of California, Berkeley) ;
- Kinion, Darin (Lawrence Livermore National Laboratory) ;
- Clarke, John (Department of Physics, University of California, Berkeley) ;
- Muck, Michael (Department of Physics, University of California, Berkeley)
- Published : 2000.08.16
Abstract
We have developed an extremely sensitive radio frequency amplifier based on the dc superconducting quantum interference device (dc SQUID). Unlike a conventional semiconductor amplifier, a SQUID can be cooled to ultra-low temperatures (100 mK or less) and thus potentially achieve a much lower noise temperature. In a conventional SQUID amplifier, where the integrated input coil is operated as a lumped element, parasitic capacitance between the coil and the SQUID washer limits the frequency up to which a substantial gain can be achieved to a few hundred MHz. This problem can be circumvented by operating the input coil of the SQUID as a microstrip resonator: instead of connecting the input signal open. Such amplifiers have gains of 15 dB or more at frequencies up to 3 GHz. If required, the resonant frequency of the microstrip can be tuned by means of a varactor diode connected across the otherwise open end of the resonator. The noise temperature of microstrip SQUID amplifiers was measured to be between