Dedicated readout ASIC for dual modality probe

The bimodal diagnostic systems like ultrasound/scintigraphic ones have the benefit of providing both morphological and physiological information. In the case in which it intends to develop a compact bimodal probe it is important that, as the readout electronics are doubled, the acquisition system is the most compact possible. In this paper we present the characterization and preliminary measurements on a multi-channel readout ASIC for PSPMTs. The chip is equipped with 32 readout channels, as different works show that single channel readout allows to exploit the performances of a gamma detector, especially for linearity. Each single channel readout is composed by a variable capacitor CSA, a sample&hold and a variable gain amplifier (VGA). The possibility to change the gain of the amplifier allows to compensate for the differences in gain of the anodes of the PSPMT, while the possibility of changing the integrator capacitor allows to adapt the input dynamic of the chip depending on the PMT used (BA or SBA photocatode) and on the scintillation crystal coupled to the PMT itself. The preliminary measurements show that a 200 kHz maximum sampling rate is achievable, with 1 V input dynamic and an overall linearity of the whole channel with respect to the input charge impulse of than 2%. To validate the performances of the ASIC different operative measurement was made in two configurations: with a single chip and two R11265-M16 PMTs, and, parallelizing two chips with a single PMT H8500. The tubes were coupled with scintillation crystals with different response speeds, from CsI to LaBr3.