A Mixed-Signal Micromegas Readout ASIC Prototype With Automatic Charge Measurement Range Calibration

The peak luminosity of the Super Tau-Charm Facility (STCF) proposed by the Chinese particle physics community is about an order of magnitude greater than the present Tau-Charm factory. In the STCF, the MicroPattern Gas Detector (MPGD)-based Ring Imaging CHerenkov (RICH) detector used for Particle IDentification (PID) demands a new high integration, low dead time, and high-performance Application Specific Integrated Circuit (ASIC). In this paper, the design and testing of a 32-channel mixed-signal readout ASIC prototype is presented. Each channel consists of a Charge Sensitive Amplifier (CSA) based analog signal processing circuit, a valid signal discriminator, a Switched Capacitor Array (SCA), a 10-bit Wilkinson ADC, and a digital core. The ASIC provides charge measurement ranges from 48 fC to 10 pC with automatic calibration, five programmable peaking times from 70 ns to 1 mu s, and can be operated at a sampling frequency of up to 240 MHz. The ASIC has been fabricated in a 0.18 mu m CMOS technology and all the test results meet the requirements. In the case of an input capacitance of 20 pF and a charge collection time of 100 ns, the charge resolution of the full-scale signal is better than 0.38% and the time resolution of the 1/3-scale signals is better than 0.78 ns for all charge measurement range options, while the power consumption is less than 20 mW per channel. In particular, the Equivalent Noise Charge (ENC) is 627 e + 18.8 e/pF for the 48 fC charge measurement range. Besides, the maximum repetition event rate capability per channel is up to 125 kHz.