bandgap chip temp detectors

[amic]

how are the present chip temp detectors for voltage regulators designed these days ?
do we need to essentially use both BGR voltage and PTAT voltage ? or since PTAT is already an indication of chip tempreture, could it simply be buffered and sent to an A-D converter to get tempreture digital readout ( or control signal )

thanks.

Sachin

 

[Fom]

You can use both. But if you use ADC that means you use bandgap also.
For the best resolution you should adjust temperature sensor output voltage to ADC input range.

 

[amic]

You can use both. But if you use ADC that means you use bandgap also.
For the best resolution you should adjust temperature sensor output voltage to ADC input range.

thanks fom, but could u explain why use of ADC necessitates use of BGR voltage ? can't PTAT voltage be directly the input for ADC ?

 

[Fom]

Sorry I meant IC implementation.
If you are going to implement both on the same chip you need precise voltage reference for ADC. Usually it is bandap.

 

[amic]

Sorry I meant IC implementation.
If you are going to implement both on the same chip you need precise voltage reference for ADC. Usually it is bandap.

But Fom, My Vdd is 1.8 V which I was planning to use as referance voltage for the ADC ( as opposed to 1.2 V BGR voltage ). If I use lower Vref for ADC then it would reduce the input dynamic range and increse noise sensitivity. wouln't it ??

attached is the architecture, I had in mind ....any suggestions on how should I go about ?

 

[electronrancher]

Using Vdd is a bad idea in production chips, as Vdd usually varies 10-20% from board to board. But you're right, a higher reference voltage is always nicer. If you're only going to use this chip in the lab, then using Vdd as a reference is fine else you probably do need an internal reference.