A Time-Domain SAR Smart Temperature Sensor With Curvature Compensation and a 3σ Inaccuracy of-0.4°C ∼+0.6°C Over a 0°C to 90°C Range

This paper describes a time-domain temperature sensor based on a successive approximation algorithm. Without using any bipolar transistor, a temperature sensor composed of a temperature-dependent delay line (TDDL) is utilized to generate a delay proportional to the measured temperature. A binary-weighted adjustable reference delay line (ARDL) is adopted with an effective delay varied by a SAR control logic to approximate the TDDL delay for output coding. For linearity enhancement, a curvature compensation between both delay lines is invented to achieve the best ever accuracy among inverter-delay-based smart temperature sensors. With two-point calibration, a -0.4 degrees C similar to 0.6 degrees C inaccuracy (3) over a 0 degrees C similar to 90 degrees C temperature operation range has been measured for 23 test chips. With 10 output bits, the proposed sensor achieves a resolution better than 0.1 degrees C and a chip area of 0.6 mm(2) in a TSMC 0.35-mu m standard digital CMOS process. The sensor's average current consumption is 11.1 mu A at a conversion rate of 2 samples/s.