Op-Amp Based Bandgap Voltage to Current Converter

[Question]

voltage to current converter op amp

The Bandgap circuit can generate the internal PTAT current. Using current mirror architecture, this PTAT current can mirror to any value for biasing.

In most of application, designers will add a external Op-Amp and resistor to convert voltage to current (as the image) for biasing. I don't know why use this kind of architecture, and what is the advantage of this architecture? I think the PTAT current is steady and accurate.

 

[aken_lu]

this topology has lower output resistance and bigger current drivability comparing to the internal PTAT current, because you cann't introduce big PTAT curretn in Bandgap due to power dissipation issue.Furthermore, this topology use the large input resistance of Amp to eliminate the effect of load.

 

[Question]

this topology has lower output resistance and bigger current drivability comparing to the internal PTAT current, because you cann't introduce big PTAT curretn in Bandgap due to power dissipation issue.Furthermore, this topology use the large input resistance of Amp to eliminate the effect of load.

what is the issue of power dissipation that limited the PTAT current?

Thanks!

 

[simov]

your bandgap core only generate a temperature independent voltage, so you need to convert this voltage to current. Don't confuse PTAT current and temperature independent current.

 

[yibinhsieh]

the two resistor connected in the input of OP can be deleted.

I=Vbg/R, only one resistor is enough. And this current is almost indepedent to the temperature if the R is external one.

Yibin.

 

[wjx197733]

the structure of the op?
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