Cooler and Electronics

The detector is connected to the radiative cooler (Passive Cooling System) and to the control electronics unit. The cooler is an $\sim1$m long tube with weight of about 100 kg, directed vertically to the optical axis. The dimensions of the electronics box are 560 $\times$317 $\times$ 277 mm, and the total weight of the electronics and detector system is 33 kg.

Each detector element has its own front-end electronics channel which includes a charge-sensitive preamplifier with transistor reset feedback and a linear amplifier. The first stages of the preamplifiers (JFETs) are positioned in the detector body in order to cool them and thus reduce the noise of the FETs, which will be a dominant factor determining the energy resolution. In addition to energy signal outputs, the linear amplifiers have fast timing outputs for time-interval measurements.

The front-end electronics is grouped on three cards, and one multiplexer is used for the energy outputs from each group. The multiplexers also provide anticoincidence functions and pile-up rejection. The pulse height analyzers linked to each multiplexer use Gatti sliding scale construction.

The resulting digital information is processed by digital electronics including two independent processors (DPUs) that share the control of the available observing modes, which are described later in "Operating modes". The permanent programs and parameters are stored in an EEPROM, and the system has 4 MBytes of RAM and (at least) a 40 Mbyte hard disk for the science data.