A Low-noise front-end readout chip integrated with a high-resolution TDC for APD-based small-animal PET

This paper presents the design of a low-noise multi-channel front-end readout chip integrated with a high-resolution TDC. It is foreseen to be used as front-end readout electronics of Avalanche Photo Diodes (APD) dedicated to a small animal Positron Emission Tomography (PET) system. The architecture of the chip is depicted. Two prototype chips, a ten-channel front-end chip and a three-channel high-resolution TDC, have been designed in AMS 0.35 μm CMOS technology. A low-noise charge-sensitive amplifier (CSA) and a shaper is integrated in each channel of the front-end chip. The designed CSA has the capability to compensate leakage current of 40 nA from detector automatically. An equivalent input noise charge of 266 e^- plus 10 e^- /pF (rms) has been obtained. The TDC chip is based on coarse-fine two-level conversion scheme. In the coarse conversion, a 10-bit counter is employed to achieve a wide range. Meanwhile, the time interpolation using an array of delay-locked loops is proposed for fine conversion. The measured range is 10 μs. The resolution has been achieved from 71 ps to 142 ps with a reference clock from 100 MHz to 50 MHz.