Design and Development of a Front-End Readout ASIC for APD-Based STCF Electromagnetic Calorimeter

Abstract

This work presents a low-noise and high-rate front-end readout ASIC for the electromagnetic calorimeter in the super tau-charm factory. The chip is designed to process signals generated from avalanche photodiode detectors. A low-noise preamplifier and a 5th-order high-linearity shaper with controllable shaping times were proposed to decrease noise induced by the 270pF detector capacitance. A peak detect-hold circuit and a high-linearity differential analog buffer convert each peak voltage of the shaper to differential voltages with strong driving capability. A fast shaper and a discriminator are implemented to produce trigger signals, which contain the arrival timing information of the input signals. The output data can be digitized on-chip by a 12 bit 10 MS/s pipelined successive approximation ADC and a 16 bit three-stage TDC. The preliminary experimental results have been obtained. The input charge range is from 4.8fC to 400fC. The maximum count rate is up to 1Mcps at the peaking time of 200ns. The measured nonlinear error of the system is less than 2.5%. The equivalent noise charge is 898 e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> + 5.2 e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> /pF. The timing resolution is better than 632ps at an input charge of 100fC. The effective resolution of the ADC is 10.65-bit when operated at 10 MS/s. The chosen technology is a standard commercial 1P6M 0.18μm mixed-signal CMOS process and the chip area occupancy is 2.4 x 1.6 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .