Area-Efficient Mixed-Signal Time-to-Digital Converter Integration for Time-Resolved Photon Counting

Area of Science:

• Photonics and Semiconductor Devices
• Integrated Circuit Design
• Biomedical Engineering

Background:

• Time-resolved measurements using single-photon avalanche diode (SPAD) sensors generate numerous timestamp signals, necessitating efficient histogram generation.
• Conventional methods for digital histogram generation require substantial storage, limiting integration in large SPAD arrays.

Purpose of the Study:

• To develop an area-efficient mixed-signal time-to-digital converter (TDC) with analog storage for SPAD-based time-resolved measurements.
• To reduce the physical footprint of TDCs for seamless integration into large-scale SPAD sensor arrays.

Main Methods:

• Designed and fabricated a mixed-signal TDC utilizing an analog storage technique.
• Integrated the TDC using a 150 nm CMOS process, achieving a prototype area of 18.3 µm × 36.5 µm.
• Validated the TDC's performance in a point-of-care (PoC) device for fluorescence lifetime measurements.

Main Results:

• Achieved a highly compact TDC prototype with a size reduction compared to conventional designs.
• Demonstrated excellent linearity with integral nonlinearity (INL) of 0.35/0.14 LSB and differential nonlinearity (DNL) of 0.14/-0.12 LSB.
• Successfully distinguished fluorescence lifetimes of Alexa Fluor dyes and Quantum Dots, validating its application in fluorescence lifetime measurements.

Conclusions:

• The proposed analog storage TDC offers a novel, area-efficient solution for SPAD-based systems.
• This technology enables high-performance histogram generation for time-resolved measurements, with potential applications in medical diagnostics.
• The compact design facilitates integration into large SPAD arrays, advancing time-resolved sensing capabilities.