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Description
The super tau-charm facility (STCF) is a proposed e+e- collider producing a data sample 100 times higher than present tau-charm factory (BEPCII). The inner tracker (ITK) of STCF should have high position resolution, low-material and high rate with fast readout. Under these requirements, the monolithic active pixel sensor (MAPS) is selected as one of alternative options for the ITK. Several prototype chips based on the TowerJazz 180 nm CIS process have been developed and are currently under fabrication. To minimize power consumption of MAPS chip (for low-material), large sensors are used to reduce the scale of the readout circuitry, while ensuring position resolution requirement is satisfied. Each pixel is equipped with an open-loop front-end circuit and priority readout logic. According to simulations, the equivalent noise charge (ENC) of the front-end circuit is 11.4 e-, and the threshold dispersion is 5.7 e-. The readout circuit can also provide time of arrival (ToA) and charge information based on time-over-threshold (ToT) measurement, with a least significant bit (LSB) of 50 ns. The information and addresses of fired pixels are read out to the peripheral circuit at a 20 MHz clock frequency. The peripheral circuit performs operations including correcting the ToA of the fired pixels, data aggregation, caching, framing, 8b10b encoding, and serialization. According to simulation, the power consumption for a full-scale chip is about 50 mW/cm2.
