SPAD ToF Imager Paper

IEEE JSSC publishes an open access paper "A 32 x 128 SPAD-257 TDC Receiver IC for Pulsed TOF Solid-State 3-D Imaging" by Sahba Jahromi, Jussi-Pekka Jansson, Pekka Keränen, and Juha Kostamovaara from University of Oulu, Finland.

"A single-chip receiver for pulsed laser direct time-of-flight 3-D imaging applications has been realized in a 0.35-μm HV CMOS technology. The chip includes a 32 x 128 single-photon avalanche diode (SPAD) array [35% fill factor (FF)] and 257 time-to-digital converters (TDCs) with a ~78-ps resolution. Two adjacent rows (2 x 128 SPADs) at a time can be selected for simultaneous measurement, i.e., 16 measurement cycles are needed to cover the whole array. SPADs are capable of operating in a gated mode in order to suppress dark and background light-induced detections. The IC was designed to be used in a solid-state 3-D imaging system with laser illumination concentrated in both time (short sub-ns pulses) and space (targeting only the active rows of the SPAD array). The performance of the receiver IC was characterized in a solid-state 3-D range imager with flood-pulsed illumination from a laser diode (LD)-based transmitter, which produced short [~150-ps full-width at half-maximum (FWHM)] high-energy (~3.8-nJ pulse/~14-W peak power) pulses at a pulsing rate of 250 kHz when operating at a wavelength of 810 nm. Two detector/TDC ICs formed an 8k pixel receiver, targeting a field-of-view of ~42° x 21° by means of simple optics. Frame rates of up to 20 fps were demonstrated with a centimeter-level precision in the case of Lambertian targets within a range of 3.5 m."