An Indirect Time-of-Flight Sensor with Adaptive Multiple Sampling for High Depth Precision

A CMOS indirect time-of-flight (iToF) sensor with a multiple sampling scheme for suppressing depth noise is presented. A 10-b column-parallel single-slope analog-to-digital converter (SS-ADC) with five folded ramps is proposed to sample pixel voltages several times, improving signal quality in the digital domain. A conversion time is constant regardless of the ramps because the number of folding in the ramps is dependent on the signal level. In addition, a foreground calibration for matching the ramp slopes is conducted on a chip, enhancing linearity. The prototype iToF sensor fabricated in a 110-nm BSI process achieves a high depth precision of 0.72% from 0.6 m to 6.0 m at 25 MHz modulation frequency.