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Noise-Bandwidth of Diffusion Cooled Hot-Electron Bolometers

Authors:
Peter J. Burke, R.J. Schoelkopf, D.E. Prober, 4:13 PM 6/3/2009A. Skalare, W.R. McGrath, B. Karasik, M. Gaidis, B. Bumble, H.G. LeDuc
Abstract:
In recent years, superconducting hot-electron bolometers have demonstrated promising performance as low-noise mixers in THz receivers. Already, excellent results have been attained at rf frequencies of 0.5 THz, 1.2 THz, and 2.5 THz. An important technological issue is the intermediate frequency gain and noise bandwidth for these mixers. We have therefore measured the spectrum of the output noise as well as the conversion gain for devices of several different lengths to study how the mixer noise of hot-electron bolometers depends on the intermediate frequency. The gain-bandwidth, the frequency at which the conversion gain drops by 3 dB relative to its low frequency value, is given by l/tthermal. The output noise at low intermediate frequencies is dominated by thermal fluctuation noise, while at high intermediate frequencies Johnson noise dominates the output noise. Since the spectrum of the output noise at low frequencies (where thermal fluctuation noise dominates) has the same dependence on frequency as the conversion gain, the mixer noise (Tmix (DSB) T=out/2[eta], with [eta] =SSB conversion efficiency) will be independent of frequency up to the crossover where the Johnson and thermal fluctuation noise are comparable. Therefore, the noise-bandwidth, the frequency at which the mixer noise is 3 dB higher than its low frequency value, can be larger than the gain-bandwidth.
Categories:
Hot Electron Bolometers
Year:
1997
Session:
5
Full-text:
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Page Number(s):
272