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http://hdl.handle.net/20.500.12386/33725
Title: | Multiplexing read out for SPICA TES microcalorimeter: FLL with Double Loop and Cryogenic feedback | Authors: | MACCULI, CLAUDIO PIRO, LUIGI Bastia, P. Torrioli, G. Colasanti, L. |
Issue Date: | 2009 | Abstract: | The concept of the “Double Loop FLL” (DL-FLL) arises from the necessity to multiplex tens of pixels, to properly work in the MHz range by applying the Frequency Division Multiplexing (FDM) technique. In the standard FDM technique the position of each pixel in a column is coded by biasing the pixels at different frequencies. It is therefore clear that, for a given signal bandwidth, the number of pixels will increase with the maximum bias frequency allowed by the system. On the other hand, the utilization of SQUID as readout requires a feedback with substantial gain, in order to cope with the intrinsic non linearity of these devices. The feedback return path through cables suffers from delays (phase rotation), that have to be kept within safe margins, to avoid instability, i.e. negative feedback turning into a positive feedback. In practice, for a given cable length, this effect limits the maximum frequency, hence the number of pixels that can be multiplexed. To circumvent this limitation, the Double Loop FLL implements a loop at cryogenic temperatures at the typical frequencies of the signal. In this way, the cable length can be kept very short, therefore recovering a large maximum frequency and number of pixels. A second feedback loop is implemented at low frequencies (DC) for keeping the SQUID working point. This second loop can therefore adopt long cables (warm) and its gain can be independently chosen at high values, for maximizing the SQUID stability. | URI: | http://hdl.handle.net/20.500.12386/33725 | Fulltext: | reserved |
Appears in Collections: | 4.03 Rapporti di progetto |
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SPICA_IT_DLFLL.pdf | [Administrators only] | 435.04 kB | Adobe PDF |
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