Planck-LFI CPV: Front-end amplifier bias tuning verification

Tuning of the LFI has been accomplished at several stages of integration, with different procedures. During these procedures, the system noise temperature (Tsys) and isolation have been used as the figures of merit for optimising performance, since they can be estimated with high signal-to-noise in a short period of time. In fact, for the LFI receivers, the calibrated noise and 1/f characteristics are the true indicators of scientific performance. In principle, calibrated white noise can be derived directly from the system temperature and noise effective bandwidth, but in practice there are noise contributions and other complications which make it hard to be sure that white noise predicted by Tsys and bandwidth will be achieved. With a receiver topology as complex as LFI, it is even possible that optimising Tsys and isolation may cause us to miss the actual optimum white noise bias point. With this in mind, we developed the following verification test based on the Hypermatrix tuning: set LFI for nominal operations (DAE gain and offset tuned to allow measurement of the true radiometer white noise); acquire data (30 seconds) at each of the nominal hypermatrix tuning bias points, in the same manner as was done for the hypermatrix tuning; change the 4K load temperature by a known amount; again acquire data at all the hypermatrix bias points; white noise is estimated from each 30 second period, and then calibrated using the corresponding data from the known temperature step of the 4K load.

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PL-LFI-PST-RP-071

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http://hdl.handle.net/20.500.12386/33264

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open.access

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PL-LFI-PST-RP-071-1.0.pdf

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Planck-LFI CPV: Front-end amplifier bias tuning verification

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653.5 KB

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Adobe PDF

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Planck-LFI CPV: Front-end amplifier bias tuning verification

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