Relaxation Oscillator Application for the High Accuracy Clinical Thermometer Chip
Jian Wenxiang · Research & Progress of SSE Solid State Electronics · 2008
A relaxation oscillator based temperature measurement circuit has been presented in this paper.The reference/sensor frequency generation circuit is used to convert the change of thermistor sensor into frequency signal for digital processing.A RS trigger is designed which has the same function as Schmitt trigger for the relaxation oscillator.The advantage is that RS trigger reduces the dependence to the process and has better performance under low voltage and wide temperature range.This temperature measurement circuit is applied in a clinical thermometer chip,which can measure temperature with an accuracy of better than 0.05°C down to 1.1 V battery voltage with the operation current of 30 μA and quiescent current of 0.2 μA.It has a die size of 1 250 μm×1 260 μm and is fabricated in a 0.5 μm 1.5 V double metal single poly CMOS process.