The SIDDHARTA chip: a CMOS multi-channel circuit for Silicon Drift Detectors Readout in Exotic Atoms Research

We propose a multichannel CMOS circuit that will be used with silicon drift detectors (SDDs) for high-resolution and high peak stability X-ray spectroscopy. The circuit is developed in the framework of a project for researches on ´exotic atoms´ (e.g. kaonic hydrogen) at e-/e+ colliders. The circuit is composed of 8 identical analog channels and of a digital section. The single channel is composed of a low-noise charge preamplifier and by semigaussian shaping amplifier with four selectable peaking times. The preamplifier operates with the input JFET directly integrated on the detector itself. A low-frequency current-mode feedback loop allows to stabilize the operating point of the input JFET with respect to background and leakage current variations. The preamplifier is designed with the possibility to adjust externally its decay time in order to match the fixed time constant of the pole/zero network. A peak stretcher stores the analog value and prevents data to be lost even if another event involves the same channel before the acquisition has read the value. The 8 channel events are multiplexed to an analog bus according to a sparse readout logic. A dedicated digital section performs the peak stretcher management and bus control. A prototype has been realized in the 0.35 mum AMS technology. The chip performances have been evaluated. The energy resolution measured using the chip with a SDD of 10 mm² is of 139 eV at 6 keV with a peaking time of 3 mus.