A CMOS Oscillators-Based Smart Temperature Sensor for Low-Power Low-Cost Systems

This paper proposes a CMOS oscillators-based smart temperature sensor with a SAR (Successive Approximation Register) search algorithm. To reduce the cost and release the number of bits, a temperature-dependent delay circuit (TDDC) composed of a thermal ring oscillator and a fixed-gain time amplifier was used to generate a thermal sensing delay proportional to the test temperature. An adjustable reference delay circuit (ARDC) composed of another thermal compensation ring oscillator and an adjustable-gain time amplifier was used to program a reference set-point delay. For digital output coding, a SAR control logic was adopted for selecting the optimal reference delay of the ARDC to approximate the thermal delay of the TDDC through the help of a time comparator. The chip size of the proposed oscillators-based sensor with 11 output bits was 0.25 mm(2), which is less than the 0.6 mm(2) of its delay-linebased predecessor with a 10 output bits in the same 0.35-mu m TSMC CMOS process [1]. The measurement errors were within +/- 0.6 degrees C in the temperature range of 0 degrees C to 90 degrees C after two-point calibration for eight packaged chips. (C) 2012 Elsevier Ltd....Selection and/or peer-review under responsibility of the Symposium Cracoviense Sp. z.o.o.