Time-of-flight (ToF) image sensors must operate across a wide span of reflected-light intensities, from weak diffuse reflections to extremely strong retroreflections. We present a signal-intensity range-extension technique that linearizes the linear–logarithmic (Lin–Log) pixel response for short-pulse multi-tap indirect ToF (iToF) sensors. Per-pixel two-region (2R) and three-region (3R) models covering the linear, transition, and logarithmic regimes are derived and used to recover a near-linear signal. Compared with a two-region approach that does not linearize the transition region, the 3R method substantially improves linearity near the knee point if extremely high linearity is required. Experiments with a six-tap iToF imager validate the approach. Depth imaging shows that linearization with common parameters reduces average error but leaves pixel-wise deviations, whereas pixel-wise 3R linearization yields accurate and stable results. Range measurements with a retroreflective target moved from 1.8–13.0 m in 0.20 m steps and achieved centimeter-level resolution and reduced the linearity-error bound from ±6.7%FS to ±1.5%FS. Residual periodic deviations are attributed to small pulse-width mismatches between the illumination and demodulation gates. These results demonstrate that Lin–Log pixels, combined with pixel-wise three-region linearization, enable robust ToF sensing over an extended dynamic range suitable for practical environments with large reflectance variations.

This paper evaluates the effectiveness of a backside illumination (BSI) structure in a short-pulse indirect time-of-flight (SP-iToF) sensor employing 6-tap pixels. Impulse response measurements comparing 6-tap iToF pixels fabricated with both front-side illumination (FSI) and BSI structures demonstrate that the BSI configuration yields a significantly faster response to near-infrared (NIR) light at 850 nm. Specifically, the time constants near the response peak and tail are 0.35 ns and 0.93 ns, respectively—approximately half those observed in the FSI counterpart. Demodulation contrast (DC) measurements further highlight the advantages of the BSI structure. The BSI pixel achieves a DC of 99.5% with a gating pulse width (PW) of 10 ns, which decreases only slightly to 95.3% at a PW of 3 ns. In contrast, the FSI pixel shows a DC of 97.0% at 10 ns, but drops markedly to 80.0% at 3 ns. These improvements are primarily attributed to the thinner substrate used in the BSI sensor. The implemented 6-tap ToF sensor exhibits excellent depth linearity (<±0.8% full scale) and high resolution (<2%) across an indoor measurement range of 3 to 28 m.