Some questions about current steering DAC

In the architecture of DAC ,analog part usually use a bandgap voltage, and then ,transfer the voltage to current,where use a voltage to current circuit.
As for the graph below,it uses a op and a external resistor.
SO,i want to ask why it directly use the bandgap current? i think it is more convenient to realise.
if these v-i structure has some advantages for changing the input current through changing the resistor?

The only thing that the bandgap truly generates is a voltage. When you talk about a bandgap current is probably a current that is generated using an internal resistor. Because of that, the current will have the resistance corner variation which can be as high as 30% or even more.

You use an external resistor, so your current does not include resistance corner variation.

PaloAlto said:

The only thing that the bandgap truly generates is a voltage. When you talk about a bandgap current is probably a current that is generated using an internal resistor. Because of that, the current will have the resistance corner variation which can be as high as 30% or even more.

You use an external resistor, so your current does not include resistance corner variation.

Click to expand...

Thanks for your reply!
But when you design a bandgap voltage, you also use internal resistor ,and how to consider these resistor effect? So bandgap current and bandgap voltage all have resistor ,more, bandgap current uses less resistor than voltage.

For the bandgap voltage you use a resistor ratio which has high accuracy. So, no corner variation. For current you always need resistor nominal value.

PaloAlto said:

For the bandgap voltage you use a resistor ratio which has high accuracy. So, no corner variation. For current you always need resistor nominal value.

Click to expand...

OH~
Thank you very much for your reply.
i understand your meaning .