A low voltage mixed signal ASIC for digital clinical thermometer

Abstract

This paper describes a mixed signal, low voltage, digital clinical thermometer chip. Temperature is sensed using a thermistor sensor. A modified Schmitt trigger based relaxation oscillator is used to convert thermistor resistance into a frequency signal. A ROM is used to map the Schmitt trigger frequency onto temperature. An extensive analysis of various errors in temperature measurement is provided. The chip can measure temperature to an accuracy of better than 0.1/spl deg/C down to 1.1 V battery voltage. It has a die size of 87/spl times/91 mils and is implemented in a 1.2 /spl mu/m double metal single poly CMOS process.