A multichannel integrated readout circuit for high throughput X-ray spectroscopy with Silicon Drift Detectors

In this paper we describe a front-end ASIC for the readout of multi-elements SDDs specifically designed for high count-rate X-ray applications. In particular, the focus of this design is the maximization of the throughput, keeping a high energy resolution. The readout of the detector by means of 8 separate channels enables to increase the maximum count-rate of the system, while the custom design of the front-end ASIC allows to handle the number of channels within a very compact architecture of the detection system and maintaining excellent noise performance. The use of a very-fast high-order processing filter and of an efficient pile-up rejection strategy enables to minimize the pile-up probability and maximize the throughput of the single channels for a given processing time. As it will be shown, the developed 3-phase peak-stretcher, together with a fast output multiplexer, does not introduce additional dead-time during the valid-data acquisition with respect to the pure pile-up limitation of the shaper. The ASIC is designed with the possibility to operate with the input JFET integrated on the detector itself as well as to operate in combination with an external CMOS preamplifier. The measured noise-contribution added by the front-end ASIC at 1.8 μs shaping time is only 2.9 electrons and just 4.1 electrons ENC exploiting at best the speed capability using the shortest 600 ns peaking time. In X-ray spectroscopy measurements, the ASIC connected to a SDD has allowed to achieve an energy resolution of 126 eV at 1.5 μs peaking time and 115 kcps/channel input rate, and 144 eV at 600 ns peaking time and 800 kcps/channel input rate.