Speaker
Description
We present a novel digital acquisition and processing architecture for high-count-rate X-ray spectroscopy based on the direct digitization of transistor-reset preamplifier outputs. The proposed approach overcomes the limitations of conventional analog reshaping techniques, which suffer from baseline distortions and pile-up effects at high event rates, by employing a high-resolution 20-bit successive approximation register (SAR) ADC with a 6 V input range and a least significant bit of approximately 5 µV. This enables the accurate measurement of millivolt-scale signal steps superimposed on the large voltage ramp characteristic of reset-type charge-sensitive preamplifiers, achieving an effective dynamic range exceeding 1:1,000,000.
To reach the sampling rates required for fast signal processing, four identical 20-bit ADCs operating at 40 Msps are combined in an interleaved configuration, providing an effective sampling rate of 160 Msps. Precise phase alignment, gain matching, and offset correction are achieved through a mixed analog-digital calibration scheme managed by a Zynq System-on-Chip, which also implements real-time digital trapezoidal filtering, baseline estimation, trigger generation, and spectrum building. A dedicated calibration procedure based on a multi-phase sinusoidal injection and Levenberg–Marquardt fitting is used to compensate interleaving mismatches at 20-bit resolution.
The system has been prototyped on a custom acquisition board and experimentally validated using the ARDESIA multipixel silicon drift detector. Preliminary measurements obtained with a single ADC channel demonstrate an energy resolution of 128 eV FWHM at 2 µs peaking time and 140 eV FWHM at an event rate of 1 Mcps with fast shaping. These results confirm the effectiveness of the proposed direct-sampling architecture and demonstrate its suitability for high-rate, high-resolution X-ray spectroscopy in advanced detector systems.