[asac] [almanews] ALMA Memo 401 Released

[Stacy Oliver]

ALMA Memo #401		

Saturation by Noise and CW Signals in SIS Mixers

A. R. Kerr (NRAO/Charlottesville, VA)

14 December 2001

Keywords:  Superconductor-Insulator-Superconductor mixers, saturation,
gain compression, dynamic range.

In ALMA Memo 321, Plambeck points out that saturation (gain compression)
is likely to be a significant factor limiting the calibration accuracy
of ALMA observations.  In this memo, saturation by broadband noise and
CW signals is analyzed for representative SIS receivers operating at
different frequencies.  Many SIS mixers in current use are expected to
exhibit a significant degree of gain compression when connected to a
room-temperature source.  Previous analyses of saturation in SIS mixers
have applied only to CW signals.  To analyze saturation by noise, the
statistics of the output voltage are derived from those of the input
signal.  A single constant, applicable to all SIS mixers, is determined
experimentally by fitting the predicted CW gain compression curve to
measured data.

View a pdf version of ALMA Memo 401.
http://www.alma.nrao.edu/memos/html-memos/alma401/memo401.pdf

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