Schoelkopf, Robert J. and Zmuidzinas, Jonas and Phillips, Thomas G. and LeDuc, Henry G. and Stern, Jeffrey A. (1995) Measurements of noise in Josephson-effect mixers. IEEE Transactions on Microwave Theory and Techniques, 43 (4). pp. 977-983. ISSN 0018-9480. http://resolver.caltech.edu/CaltechAUTHORS:SCHOieeetmtt95
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We present new heterodyne receiver results obtained at 100 GHz using resistively-shunted Nb and NbN tunnel junctions. In addition, we have carried out accurate measurements of the available noise power of these devices at the L-band (1.5 GHz) IF frequency. Both the heterodyne and the output noise measurements show that the noise of these devices can be a factor of five or more higher than that predicted by the simple current-biased RSJ model. The noise approaches the appropriate thermal or thermal and shot noise limits for bias voltages where the nonlinearity is not strong (i.e., V>ICRN), but as expected from the RSJ model, can be significantly higher at the low voltages where the mixers are typically biased. The bias voltage dependence of the noise shows structure which is associated with resonances in the RF embedding circuit. Surprisingly, we find that changes in the high-frequency (100 GHz) impedance presented to the junction can dramatically affect the magnitude and voltage dependence of the low-frequency (1.5 GHz) noise. This emphasizes the necessity of very closely matching the junction to free space over a wide frequency range.
|Additional Information:||© Copyright 1995 IEEE. Reprinted with permission. Manuscript received July 15, 1994; revised November 15, 1994. This work was supported by NASA under Grant NAGW-107 and BMDO. R.J. Schoelkopf was supported by a NASA Graduate Student Researcher Fellowship. The authors would like to thank N. Dubash, R. McGrath, and T. Kerr for helping to find suppliers of microwave equipment suitable for low temperatures, J. Kooi and P. Schaffer for assistance with design and fabrication of the cryostat, and G. Ugras, E. Grossman, and T. Groesbeck for helpful discussions.|
|Subject Keywords:||Josephson effect; millimeter wave mixers; millimeter wave receivers; niobium; niobium compounds; shot noise; superconducting device noise; superconducting device testing; thermal noise|
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|Deposited On:||05 Apr 2008|
|Last Modified:||26 Dec 2012 09:55|
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