Signal characteristics and signal processing in read-out electronics for radiation detectors

The most common form of read-out electronics for radiation detection at the pixel basis can be described as a signal processing channel consisting off: detector pixel, preamplifier, pulse shaper and A/D converter. The signal generation starts when a photon interacts with a detector, resulting in a charge which amount is proportional to the photon energy. The charge is further processed by either a current or a charge preamplifier. The advantages of the charge over the current preamplifiers for radiation detectors for bio-medical applications are explained, focusing on the differences between signal and noise gains. Two most common amplifier topologies, differential amplifier and folded cascode, are discussed and compared. The pulse shaper roles are noise reduction and shaping the output signal into forms suitable for further processing. Factors that affect signals of the preamplifier and the pulse shaper are elaborated. The final stage of the channel is an A/D converter. The paper explains why the flash ADC is the most common choice. The key advantages and drawbacks of CMOS technology for detector applications are presented, including radiation effects. Detrimental effects, such as pile-ups and charge sharing, which are caused by the random properties of photons, are also briefly explained.