A low noise APD readout ASIC for electromagnetic calorimeter in HIEPA

Abstract This paper presents a 4-channel avalanche photodiode readout ASIC for the electromagnetic calorimeter in the 2-7 GeV high intensity electron positron accelerator. A large detector capacitance of the avalanche photodiode will increase equivalent noise charge and extend rise time of the front-end preamplifier, resulting in attenuated energy and time resolution of the ASIC. A low-noise preamplifier and a 5th-order high-linearity shaper were proposed to decrease the noise induced by a 270 pF detector capacitance. The ASIC is fabricated using a standard 0.18- μ m CMOS technology, and the die size of the prototype chip is 1.1 mm × 2.4 mm. The input charge range of the ASIC is from 4.8 fC to 400 fC. The event rate of the ASIC can achieve 400k count/s. Nonlinear error of the shaper is less than 2%. The measured signal to noise ratio is better than 7.8 at a shaping time of 800 ns. The timing resolution of the ASIC is better than 300 ps at an input charge of 100 fC.