2D CMOS SPAD array techniques in 1D pulsed TOF distance measurement applications

The goal of the research was to study the characteristics, performance and feasibility of a pulsed time-of-flight 1D laser radar system employing a 2D SPAD detector array in conjunction with a custom-made laser diode producing high energy and high-speed laser pulses. The research included the characterization and comparison of custom-made QW and bulk laser diodes operating in enhanced gain switching mode and producing laser pulses with a total energy of ~1–5 nJ and an FWHM of ~100 ps at pulsing rates >100 kHz. The receiver module was a purpose-built single-chip CMOS IC incorporating a 2D 9x9 SPAD array and a 10-channel TDC circuit enabling parallel SPAD-specific TOF measurements.

The key performance parameters of the laser radar system are intrinsic timing walk error ~5 cm (dynamic range ~1:100 000), linearity ± 0.5 mm, signal detection rate ~28% (target distance 34 m and reflectivity 11%) and precision ~2 cm. The total energy of a probe pulse was 0.6 nJ and the diameter of the circular receiver aperture ~20 mm. The selectable subarray feature of the receiver IC enables laser spot tracking on the detector array while maintaining a small effective field of view, thus reducing background radiation-induced noise detections, and offering prospect of walk error free measurement results. Detection time gating proved an effective means for signal-to-noise ratio improvement under conditions of high-level background radiation. Feasibility studies demonstrated high spatial accuracy of the system in practical settings when performing non-contact human heart rate measurement and when distinguishing individual free-falling snowflakes.

The implementation and performance of the 1D laser radar system demonstrated the viability of the proposed technology as an alternative along with a conventional laser radar operating in the linear detection mode for high performance, compact and cost-effective laser radar applications.