X-ray imaging demonstration of glass GEM detector with dynamic time-over-threshold-based readout

Large-scale detection is one of the important roles for gaseous detectors to play in high-energy physics. In many cases, energy resolving multi-channel readout is required. Recent micro-pattern gaseous detectors (MPGDs) have finer pitches or pixels; hence, large-sized detectors have thousands of readout channels. In those cases, it becomes important to reduce the scale and complexity of the readout circuit while keeping its energy resolving capability. The signal processing technique called dynamic time-over-threshold (dynamic ToT, dToT) achieves both the good conversion linearity from analog to digital signal and the compact circuit scale compared with conventional analog-to-digital-converter (ADC)-based readout. In this study, we developed and demonstrated a dToT-based readout circuit for glass gas electron multiplier (glass GEM, G-GEM). The readout circuit showed better linearity than that of normal ToT. We demonstrated the readout circuit by X-ray imaging with the charge-division scheme. The good linearity of the readout circuit enabled imaging over a 100 x 100 mm(2) area with small distortion. We expect that the dToT-based readout would be a promising candidate for the future readout of large-scaled MPGDs.