A CMOS imager with digital phase readout for fluorescence lifetime imaging

This paper presents a novel CMOS image sensor with direct digital phase output for fluorescence lifetime imaging applications. The phase-shift between intensity modulated excitation signal and emitted fluorescence is extracted utilizing a zero-crossing detection algorithm as a time-domain delay signal. A Time-to-Digital Converter (TDC) is subsequently used to quantize the time delay into digital output. A prototype sensor chip consisting of 32×32 passive pixel array, row-parallel phase extraction circuitry, and a global TDC is fabricated in 65nm low-power CMOS technology. The chip occupies 4mm×4mm silicon area with 1.2mW power consumption. Extensive characterization and phase image reconstruction results demonstrate both high sensitivity and good linearity performance of the digital phase readout. The TDC features 110ps temporal resolution over 414μs dynamic range. The proposed imager architecture offers an attractive solution for developing low-cost, low-power, and highly-integrated fluorescence lifetime imaging devices.