VIP-PIX: A low noise readout ASIC for pixelated CdTe gamma-ray detectors for use in the next generation of PET scanners

In this paper a low noise and low power consumption pixel readout electronics with digital output for pixelated Cadmium Telluride (CdTe) gamma-ray detectors is presented. The implemented smart-pixel will be part of a 2D pixel-array detector that will be connected, via solder bump bond, to the readout integrated circuit (ROIC) for use in various types of nuclear medicine imaging devices such as positron-emission tomography (PET) scanners, Compton gamma cameras, and positron-emission mammography (PEM) scanners. When a voxel of the CdTe detector is hit by a photon, the connected pixel readout provides the energy deposited with to-bit resolution. Simultaneously, the self-triggered pixel that is connected to a global time-to-digital converter (TDC) with 1 ns resolution provides the hit event's time stamp. The analog front-end and the analog to digital converter (A DC) from the pixel readout have been fabricated with TSMC 0.25 Ilm mixed-signal CMOS technology and characterized with external test pulse. Every pixel readout electronics consumes 200 IlW from 2.5 V supply. It offers 4 switchable gains from ±10 mV/fC to ±40 mV/fC and an input charge dynamic range up to ±70 fC for the minimum gain for both polarities. Based on noise measurements, the expected equivalent noise charge (ENC) is 65 eRMS at room temperature and a bump-bonded detector's capacitance of 100 fF.