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Thermal sensor: accuracy is so hard?

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neoflash

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I am designing a high accuracy temperature sensor on 130nm CMOS process. Supply voltage is about 1.5v.
Sensor need to be within +/- 2 degree accuracy, from 0 ~ 125 degree.


My difficulty is that bandgap voltage reference itself is very hard to be controlled within 3%. How can we measure temperature by so coarse ruler?

Any suggestion engineering wise?

thanks,
Neoflash
 

Basically one needs to measure delta-Vbe voltage with high accuracy.
To do it use a switched-cap auto-zeroed amplifier.
To get an accurate bandgap reference to compare with, use a similar auto-zeroed amplifier in the reference loop. Some sort of curvature correction should be added also. All this combiled should give you the necessary accuracy.
Good luck!
 

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