J. Phys. III France
Volume 6, Numéro 1, January 1996
Page(s) 77 - 90
DOI: 10.1051/jp3:1996115
J. Phys. III France 6 (1996) 77-90

Amplification by Frequency Transposition with a Low Critical Temperature DC SQUID

O. Hubert, Y. Monfort, J. Lepaisant, C. Gunther and D. Bloyet

Groupe de Recherche en Informatique, Image et Instrument de Caen (G.R.E.Y.C.), URA CNRS 1526, ISMRA, 6 Boulevard du maréchal Juin, 14050 Caen Cedex, France

(Received 3 November 1994, accepted 5 October 1995)

The performances of a heterodyne amplifier involving a DC SQUID have been modelised and measured. This type of amplification is derived from frequency translation methods using flux modulation. The pump frequency used depends on the signal to be analysed and the translation to a fixed frequency f0 is carried out by the SQUID which is a nonlinear device. Such a system simplifies the impedance matching between the SQUID and the semiconductor preamplifier and can be operated as a spectrum analyser for signals of relatively high and variable frequency. Flux sensitivities of 5 to 10 $\mu\Phi_{0}/\sqrt{\rm Hz}$ have been measured in this configuration for frequencies ranging from 200 kHz to 2 MHz. In order to validate our model, the flux sensitivity of the SQUID in the heterodyne configuration has been compared to that given by direct measurements at the intermediate frequency f0. Our measurements are in good agreement with a theoretical model based on a simplified voltage to flux characteristic of the DC SQUID.

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