A 64-channel wide dynamic range charge measurement ASIC for strip and pixel ionization detectors

In this paper we report a 64-channel ASIC for the readout of parallel plate strip and pixel ionization detectors. The detectors measure the intensity and the geometrical characteristics of a hadron beam for hadrontherapy cancer treatments. The ASIC is based on a current to frequency converter followed by a counter. It uses a charge balancing integration technique to obtain a dynamic range in excess of 10⁵ with a non-linearity of less than 1%. The ASIC has been designed in a CMOS 0.8 μm technology and it has been used for the readout of both strip ionization detectors for beam calibration and pixel detectors for beam monitoring during treatment. A new version of the chip in CMOS 0.35 μm technology which allows bipolar input currents has been designed and is currently under test.