A new readout system for bolometers with improved low frequency stability

¹ Centre d'Etude Spatiale des Rayonnements, 9 avenue du Colonel Roche, BP. 4346, F-31028 Toulouse Cedex 04, France
² Centre de Recherche des Très Basses Températures, 25 avenue des Martyrs, BP. 166, F-38042 Grenoble Cedex 09, France
³ Institut d'Astrophysique Spatiale, Université Paris XI, Bât. 121, F-91405 Orsay Cedex, France

Send offprint request to: S. Gaertner

Received: 23 December 1996
Accepted: 24 February 1997

Abstract

A new readout electronic system for bolometers is presented in this paper. The bolometer resistance is measured in a bridge with a capacitive load, using a periodic square wave bias current. The bias voltages at both ends of the bridge are balanced in order to keep the middle point around zero. Only changes around this zero value are amplified and detected synchronously with the bias signal. These features shift the measurement frequency out of the electrical low frequency noises (JFETs), and reduces the dynamics required from the amplification chain. The bias voltages are fully controlled by computer, and the lock-in detection is digital. This readout electronic has many advantages over previous ones. In particular, it proved to be able to read the total power of the radiation reaching the bolometer, and to perform measurements down to low frequencies ( Hz) without significant additional noise. These features open new observation strategies such as full sky scanning to bolometer instruments on board future submillimetre space projects having high thermal background levels (warm telescope). The different steps of the development of this new readout electronics on the ground-based Diabolo experiment are described, the performances reached are discussed, and a version suitable for the readout of the arrays of bolometers on the COBRAS/SAMBA satellite mission is presented.