A CMOS Temperature Sensor With a V oltage-Calibrated Inaccuracy of 0.15 C (3 )F r o m 55 C to 125 C

Abstract

This paper describes the design of a low pow er, en- ergy-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 inte- gration scheme is proposed that halves the conversion time, while requiring no extra supply current. To meet the stringent cost con- straints on RFID tags, a fast voltage calibration technique is used, which can be carried out in only 200 msec. After batch calibra- tion and an individual room-temper ature calibration, the sensor achieves an inaccuracy of C from C to 125 C. Over the same range, devices from a second lot achieved an inac- curacy of C in both ceram ic and plastic packages. T h es e n s o ro c c u p i e s0 . 0 8m min a 0.16 mC M O Sp r o c e s s ,d r a w s 3.4 A 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 min- imum energy dissipation of 27 nJ per conversion.