Highly Sensitive Indirect Time-of-Flight Distance Sensor With Integrated Single-Photon Avalanche Diode in 0.35 μm CMOS

This work describes the architecture and measured capabilities of an optical distance sensing application specific integrated circuit (ASIC) manufactured in 0.35 μm CMOS with a nominal supply voltage of 3.3 V for indirect time-of-flight. An integrated single-photon avalanche diode (SPAD) with an active diameter of 38 μm is used as detector with 6.6 V excess bias, active quenching and active resetting circuit. Phase measurement is performed using a digital correlation approach with digital counters. Due to the unmatched sensitivity of SPADs, sub-cm accuracy measurements can be performed with a received signal power in the pW range. Background light ratios up to 24.1 dB still allow sub-cm precision. Depending on the required accuracy and the received optical power, the measurement time can be adjusted freely up to several seconds only limited by digital counter depth. Compared to a pin-photodiode iTOF sensor in the same technology, this chip has a sensitivity improvement of 33.3 dB and 40.7 dB for a distance accuracy of 1 cm and 10 cm, respectively, while reducing the effective measurement time by 75% at the same time. The chip size is 1.4 mm × 1.4 mm including two correlator blocks, for simultaneous acquisition of two phase steps. The number of correlators is scalable allowing parallel measurements of phase correlations.