CMOS SPAD Line Sensor With Fine-Tunable Parallel Connected Time-to-Digital Converters for Raman Spectroscopy

A 256-channel single-photon avalanche diode (SPAD) line sensor was designed for time-resolved Raman spectroscopy in 110-nm CMOS technology. The line sensor consists of an
$8\times256$
SPAD array and 256 parallel connected time-to-digital converters (TDCs). The adjustable temporal resolution and dynamic range of TDCs are 25.6–65 ps and 3.2–8.2 ns, respectively. The median timing skew along 256 channels is 43.7 ps, and TDC bin boundaries can be fine-tuned at the ps-level to enable precise timing skew compensation. The sensor is capable of real-time dark count measurement (two dark measurements for each excitation pulse) that gives accurate data for dark count compensation without any increment in measurement time. The maximum excitation pulse rate with real-time dark count measurement is 680 kHz. Raman spectra of six different samples were measured to prove the performance of the sensor in time-resolved Raman spectroscopy.