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.

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