All-digital-ADC TAD in sensor digitization for scaling over wide temperature ranges

To achieve a highly-durable sensor ASIC/SoC with distinctive scalability for IoT (Internet-of-Things)-applications, an all-digital sensor ADC using TAD (Time A/D converter) in bulk CMOS is presented. Generally, sensors in automotive subsystems have to work under various stringent conditions (i.e., high ambient temperature). 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 Vin for its power supply, along with an RDL frequency counter, latch and encoder. In the present study, first, an ADC core is implemented with 0.26 mm2 in a low-cost 0.35-μm digital CMOS with a voltage resolution of 10.9 mV/LSB (6.5bit, 40MS/s) in a wide temperature range between -40 and 125°C. Next, using a lower-cost 1.5-μm digital CMOS, a digital-type rotation-rate sensor with TAD has been developed over a wide temperature range between -40 and 150°C. Furthermore, other practical automotive sensors with TAD are introduced. Finally, thanks to the all-digital architecture, TAD is definitely suitable for scaling and porting to another silicon technology with minimal IC design term and cost. As scaling/porting results, using prototype ICs in 0.18/0.65-μm digital CMOS, we have experimentally confirmed their stable operation between -40 and 125°C with smaller/larger areas (0.044/0.29mm2) and higher/lower resolutions [(0.15mV/LSB)/(1.0mV/LSB) at 1MS/s,] respectively.