Incremental Sigma-Delta Modulators for 3D-Imaging: System Architecture and Signal Processing

The design of a system for measuring the time-of-flight of a pulsed light beam for 3-D imaging with 2-4 ps resolution is described. An array of Spanks determines the arrival times of a single reflected photon measured by a coarse 10 ns clock period and a fine of about 14 bit accuracy. The designed circuit uses an incremental second order SigmaDelta modulator with a current and voltage feedback DAC on the integrators. The time-of-flight integrated circuit is for a 6.25 MHz pulsed laser and a 2-D 32 times 64 pixels SPAD array. The use of four time-to-digital converters enable obtaining 25 frame/s 3-D image with 23 m measurement range and 0.3 mm resolution.