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Doctoral Defense

Design and Characterization of an Advanced Virtual Frisch-Grid Application Specific Integrated Circuit for Gamma Ray Spectroscopy and a Low Noise Multi-Amplifier Readout System for Synchrotron Applications

Emerson Vernon

June 5, 2019
12:00 PM
Light Engineering room 250
Advisor: Dr. Gianluigi De Geronimo

Compact radiation detection systems, with high channel integration, rely on low noise front-end application specific integrated circuits (ASICs) to achieve high spectral resolution. Here, a new advanced virtual Frisch-grid (AVG) ASIC is presented for security and space applications. Corresponding to each ionizing event in a 4 x 4 array of virtual Frisch-grid cadmium zinc telluride (VFG CZT) bar sensors, the ASIC measures the amplitude and timing at each anode, cathode and pad electrode on 52 input channels with configurable baselines of 250 mV and 1.2 V. With a static power dissipation of 177 mW, each channel performs low-noise charge amplification, high-order shaping, peak and timing detection along with analog storage and multiplexing. The overall channel linearity is better than ±1 %, with timing resolution down to 700 ps for charges greater than 8 fC in the 3.2 MeV range. With a 4 x 4 array of 6 x 6 x 20 mm3 VFG CZT bar sensors connected and biased, an electronic resolution of ≈270 erms was achieved for charges up to 100 fC in the 3.2 MeV range. Spectral measurements obtained with the 3D correction technique demonstrated resolutions of 1.8 % and 0.9 % FWHM at 238 keV and 662 keV respectively.

In addition, a multi-element amplifier readout system (MARS) ASIC is developed for synchrotron applications. The MARS ASIC instruments 32 configurable front-end channels, that perform signal processing on either positive or negative charge from germanium strip detectors or silicon drift detectors. At a gain setting of 3.6 V/fC and 1 μs shaping time, a resolution of 10 erms was measured without the sensor. With a linear silicon drift detector connected at biased, a resolution of 13 erms is attained at 248 K. A spectral resolution of 170 eV FWHM at 5.9 keV was obtained with an 55Fe source. The channel linearity was better than ±1 % with rate capabilities up to 40 kcps. The ASIC was fabricated in a commercial 250 nm process, with dimensions of 6.3 x 3.9 mm2 and dissipates 167 mW of static power.

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