Time-over-threshold processing implementation for silicon detectors with large capacitances

Modern High Energy Physics experiments require more functionality from the multichannel readout circuits which in conjunction with strict limits on power consumption, area occupation and low noise performance set new requirements in the analog front-end electronics design. We discuss the applicability issues and design challenges of a constant-current discharge time-over-threshold (ToT) processing chain for readout of the large capacitance silicon strip detectors. The conclusions are based on measurement results of two prototype ASICs: TOTOl, TOT02. The revealed non-idealities and issues have been identified and are briefly presented in this paper. Moreover, an idea for charge amplifiaction, measurement and timestamping is proposed as a possible remedy for presented matters. This conception uses two cascaded amplifiers and exploits advantages of two different feedback circuits to eliminate the negative impact of a large detector capacitance on the performance of ToT processing while keeping the power consumption at low level.