A pixel detector asic for dosimetry using time-over-threshold energy measurements

Abstract

In this work we present the design of a chip which provides the readout of a highly segmented diode array, in which signals induced by individual X-ray photons are processed discretely. There are several benefits to this approach, including the ability to achieve a high signal to noise ratio due to the inherently low sensor capacitance, and the suppression of background noise ( e.g . dark current) using an analogue threshold. The segmentation also ensures a linear behaviour even at very high dose rates. A time over threshold (ToT 1 1 ToT: Time over threshold. ASIC: Application-specific integrated circuit. APS: Active pixel sensor. DAC: Digital to analogue convertor. CSA: Charge sensitive preamplifier. ENC: Equivalent noise charge. ) energy measurement technique provides an immediate digital value corresponding to the energy deposited onto the diode by each individual photon. Deadtime-free operation is achieved by reading out a subset of the detector segments at a time while the rest of the detector continues to process signals. This paper describes the application-specific integrated circuit (ASIC) chip which was designed to provide pre-processing of photo-induced signals in the detector and readout of the processed digital data. ► We have designed the ASIC of a hybrid pixel detector for photon dosimetry. ► The pulse processing circuits measure the time over threshold of discrete photons. ► Each pixel automatically sorts ToT measurements into 16 digital energy bins. ► The binned data is used to reconstruct the charge spectrum and dose in real time.