A new readout system for bolometers with improved low frequency stability

A new readout electronic system for bolome- ters is presented in this paper. The bolometer resistance is measured in a bridge with a capacitive load, using a pe- riodic 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 amplied 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 amplication 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 reach- ing the bolometer, and to perform measurements down to low frequencies ( 0:1 Hz) without signicant addi- tional noise. These features open new observation strate- gies such as full sky scanning to bolometer instruments on board future submillimetre space projects having high thermal background levels (warm telescope). The dierent 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 suit- able for the readout of the arrays of bolometers on the COBRAS/SAMBA satellite mission is presented.