A CMOS temperature sensor with a voltage-calibrated inaccuracy of ± 0.15 °c (37sigma;) From-55°C to 125°C

This paper describes the design of a low power, energy-efficient CMOS smart temperature sensor intended for RFID temperature sensing. The BJT-based sensor employs an energy-efficient 2nd-order zoom ADC, which combines a coarse 5-bit SAR conversion with a fine 10-bit ΔΣ conversion. Moreover, a new integration scheme is proposed that halves the conversion time, while requiring no extra supply current. To meet the stringent cost constraints on RFID tags, a fast voltage calibration technique is used, which can be carried out in only 200 msec. After batch calibration and an individual room-temperature calibration, the sensor achieves an inaccuracy of ±0.15°C 3σ from-55°C to 125°C. Over the same range, devices from a second lot achieved an inaccuracy of ± 0.25°C (3σ) in both ceramic and plastic packages. The sensor occupies 0.08 mm² in a 0.16 μm CMOS process, draws 3.4 μA from a 1.5 V to 2 V supply, and achieves a resolution of 20 mK in a conversion time of 5.3 msec. This corresponds to a minimum energy dissipation of 27 nJ per conversion.