All-digital ADC/TDC using TAD architecture for highly-durable time-measurement ASIC

For achieving a highly-durable auto-lidar (light detection and ranging) time-measurement ASIC, an all-digital ADC/TDC using a time-domain processor TAD (Time A/D converter) is presented. In order to realize wide-range temperature durability, sensor ADC/TDC circuits should be fully-digital, including a ring-delay-line (RDL) driven by an input voltage V_in for its power supply, along with an RDL frequency counter, latch and encoder. In this study, ADC/TDC cores are implemented with 0.26/0.35mm², respectively, in a low-cost 0.35-μm digital CMOS by applying the same circuit architecture TAD. When the received pulse signal level is high, a 4-input terminal TDC can be used to directly digitize the round-trip time of light pulses with time-resolution 244ps/LSB (13-bit) without any AGC techniques. On the other hand, when detecting very-low-level noisy signals received, a high-speed ADC with voltage-resolution 10.9 mV/LSB (6.5bit, 40MS/s) is available for integrating received pulse amplitude to determine signal-travel time in a wide temperature range between -40 and 125°C. Finally, using the all-digital ADC/TDC, a time-measurement ASIC in a 0.35-μm CMOS for low-cost auto lidar has been developed, adapting to variable received-signal levels.