All-Digital A/D converter TAD for sensor interface over wide temperature ranges

For achieving a highly-durable sensor ASIC with high performance and low cost, an all-digital sensor ADC using a time-domain processor TAD (Time A/D converter) is presented. Generally, measuring travel time of signals (e.g., light pulses, radio and ultrasonic waves, etc.) should be done under various stringent conditions (i.e., high ambient temperature) in automobiles, heavy-machinery and resource exploration systems, for example. Therefore, to realize wide-range temperature durability, sensor ADC 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, an ADC core is implemented with 0.26 mm² in a low-cost 0.35-μm digital CMOS applying our original 2-CKES (clock edge shift) method for higher resolution. When detecting low-level noisy signals received, a high-speed sensor ADC with a voltage resolution of 10.9 mV/LSB (6.5bit, 40MS/s) is available for integrating received pulse/wave amplitude to determine signal-travel time in a wide temperature range between -40 and 125°C. In addition, the all-digital architecture TAD is suitable for porting and scaling to another silicon technology with minimal IC design term and cost. As a scaling result, using a test-IC in a 0.18-μm digital CMOS, we have also experimentally confirmed its stable operations between -40 and 125°C with a smaller active area (0.044mm²) and higher resolutions, resulting in 0.15mV/LSB (1MS/s).