All-digital cost-efficient CMOS pulse-expanded temperature sensor with digital set-point programming

This study presents a cost-efficient complementary metal-oxide-semiconductor (CMOS) pulse-expanded temperature sensor (PETS), which is the first all-digital time-domain temperature sensor (TS) architecture to feature digital set-point programming. The design utilizes a shared core and pulse expansion to achieve a highly compact structure. Unlike conventional time-domain TS's with digital set-point programming that require dual-core architectures, the PETS significantly reduces hardware complexity by employing a single cyclic delay line as the shared core. For temperature sensing, a simple D-type flip-flop is cleverly integrated to simultaneously perform temperature-sensing generation and built-in offset-error cancellation, thereby significantly simplifying the sensing path complexity and reducing hardware costs. For the programmable reference time, a programmable set-point time is innovatively generated using a programmable counter with a digital input, based on an all-digital pulse-expanded approach that replaces the analog temperature-compensated circuits required by previous time-domain TS's. The final time comparison is achieved using a time comparator for a binary comparison. The prototype, fabricated in a Taiwan Semiconductor Manufacturing Company (TSMC) 0.35-μm CMOS process, occupies a core area of only 0.021 mm2, demonstrating excellent cost efficiency. To the best of our knowledge, the proposed PETS achieves the most compact architecture among related studies with set-point capability. The maximum inaccuracy is within ±1 °C in the range of 0-100 °C, with a sensor resolution of 0.23 °C per least significant bit (LSB). The proposed sensor successfully functions by reducing both circuit complexity and area, while its completely all-digital architecture ensures straightforward portability and scalability for advanced CMOS nodes.