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Proceedings Paper

Evaluation of controllers for tuning digitizers in the ALMA interferometer
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Paper Abstract

In radio astronomy interferometers where the number of stations is large (in the ALMA case 66 antennas, where 8 digitizers are deployed in each antenna) tuning the digitizers parameters: thresholds and bias, is a process which needs to be repeated several times, therefore finding an algorithm that allows to speed up this process is a critical task. It is quite important to keep the digitizers properly adjusted in order to reach the maximal efficiency of the correlator, specially in a regime of coarse quantization (88% for 2 bits, 96% for 3 bits), and also is critical for avoiding signal artifacts which can degrade the collected data (DC bias or harmonics). This work presents a set of different approaches for automatically tuning the digitizers primary selected as: PID by using a proportional/integrative/derivative controller and defining a system to process a coupled MIMO system as an uncoupled SISO; Fuzzy Logic by making extensive advantage of the expert operator knowledge; and finally an hybrid scheme combining PID and Fuzzy Logic for a rapid and accurate tuning process. The aim of the present work is to evaluate the performance of each tuning method based on metrics like: required tuning time, stability and robustness under different extreme boundary conditions. In addition, we suggest the means for collecting the needed information considering an usual interferometer architecture. Furthermore, we provide an automated approach to find the best sampler's clock timing profile. The aim of this work is to provide a guideline for implementing an algorithm which allows to tune a large set of digitizers under different conditions in a fast and precise automated process. The produced report will come in handy for integration into interferometer projects comprising a large number of individual stations (ALMA, SKA, VLA, CHIME, MeerKAT).

Paper Details

Date Published: 9 July 2018
PDF: 18 pages
Proc. SPIE 10708, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy IX, 107080Y (9 July 2018); doi: 10.1117/12.2312958
Show Author Affiliations
Daniel Herrera, ALMA Observatory (Chile)
Alejandro Saez, ALMA Observatory (Chile)

Published in SPIE Proceedings Vol. 10708:
Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy IX
Jonas Zmuidzinas; Jian-Rong Gao, Editor(s)

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