Application of dynamic time-over-threshold method to pixellated CdTe detector

We have designed, fabricated and tested a 64-channel ohmic-type CdTe detector for the gamma camera application with a conventional PHA (Pulse Height Analysis) circuit dynamic ToT based circuit. The pixel size of the detector is 2mm x 2mm and it consists of 8x8 arrays. The thickness of detectors is 1mm. Our group has been proposing the energy resolving Time over Threshold method with a dynamically changing threshold (dynamic ToT). Although the ToT is suitable for the readout circuits for multi-pixel detectors because of the binary readout and circuit simplicity, the linearity of the ToT versus the input charge is rather poor. The dynamic ToT method greatly improves the linearity and dynamic range. We have tested 64-channel CdTe detectors with a PHA method and dynamic ToT method and confirmed that dynamic ToT method is usable as a energy resolving system, and more suitable as a multi-channel individual readout system.