A low-power, radiation-resistant ASIC for SDD-based x-ray spectrometers

We present an Application Specific Integrated Circuit (ASIC) for high resolution x-ray spectrometers (XRS) in radiation harsh environment (such as Jovian system). The ASIC was designed to read out signals from low resistivity pixelated Silicon-Drift-Detectors (SDD) to ensure radiation hardness. The readout is done by wire-bonding the anodes to the inputs of the ASIC. The ASIC dissipates 32 mW and provides 16 channels of low-noise charge amplification, high-order shaping with baseline stabilization, discrimination, pile-up rejection, and peak detection with analog memory. The readout is sparse and based on a custom low-power tristatable low-voltage differential signaling. A unit of 64 SDD pixels, read out by four ASICs, covers an area of 12.8 cm², and dissipates less than 20 mW/cm². The ASICs were powered on and irradiated using a beam line with 200 MeV protons, to doses ranging from 0.25 Mrad to 12 Mrad. Performance degradation due to radiation-induced leakage current was observed to peak around 2 Mrad dose. Critical contributors to the degradation were identified through simulation and measurements, and corresponding circuitry was modified to address the issues. Measurements on the radiation-resistant design have shown excellent radiation resistance at doses from 1 to 8 Mrad.