Self-Calibrating SPAD TDC Circuit for DNL-Limited Depth Sensing

The patent applies preliminary action by performing self-calibration before actual time-of-flight measurements. The TDC circuit executes calibration sequences that pre-characterize its own timing behavior, storing calibration data that compensates for DNL and INL errors during subsequent measurements. This preliminary calibration action resolves the contradiction by preparing the system to achieve high measurement precision despite manufacturing imperfections.

The patent implements feedback through calibration sequences that measure the TDC's actual timing performance and use this information to generate correction factors. These correction factors are fed back into the measurement process to compensate for nonlinearity errors. The feedback mechanism enables the system to achieve high measurement precision by continuously correcting for manufacturing-induced DNL and INL variations.

The patent applies self-service by implementing self-calibration functionality within the TDC circuit itself. The calibration sequences are executed autonomously by the TDC using its own internal resources (phase shifters, delay elements, and control logic). This self-calibration approach improves measurement accuracy without requiring external calibration equipment or significantly increasing device complexity, as the system calibrates itself using existing circuit components.

The patent implements multi-functionality by designing the TDC circuit to perform both normal time-of-flight measurement and self-calibration functions using the same hardware resources. The phase shifters, delay elements, and control logic are utilized for both measurement and calibration purposes. This universal design improves measurement accuracy through calibration while minimizing device complexity by avoiding dedicated calibration hardware.