Feasibility Study of WTA Circuit for CsI(TI)-GAPD Radiation Detector

This study proposes a scalable winner-takes-all (WTA) circuit for thallium-doped cesium iodide CsI(Tl) Geiger-mode avalanche photodiode (GAPD) radiation detectors. The proposed circuit was implemented and evaluated in a proof-of-concept 4×4 CsI(Tl)-GAPD radiation detector. The uniformity of the photopeak position was assessed before and after gain correction. The performance of the radiation detector was also measured at various GAPDs bias voltages. With a trigger activation duration of 500 ns, the analog signal reset mechanism functioned effectively without significantly affecting the analog output signal. Gain correction in the gain-level adjustment block significantly improved the uniformity of the photopeak positions in the energy spectra, reducing the ratio of the highest to lowest photopeak positions from 1.3 to 1.0. As the bias voltage increased, the photopeak position linearly increased from 507.4 to 1444.7 due to the increasing gain of the GAPDs. The best energy resolution was obtained at a bias voltage of 27.8 V, which was 3.1 V above the breakdown voltage in our experimental setup. This study demonstrated the feasibility of the WTA circuit for the CsI(Tl)-GAPD radiation detector and highlighted the potential advantages of the scalable WTA circuit for developing MR-compatible radiation detectors with multiple input channels.