Thanks NOVARIS.
Well for your comment in the circuit that I attached for Bandgap, at first when we our still gathering information and comparing different circuits of a bandgap we consider many factors in choosing that circuit. We found out that as much as possible we need to use or find a bandgap circuit which composed of ALL CMOS. (as you can see in the circuit) At first we didn't plan to find an ALL CMOS bandgap circuit, b'coz, as we observed many researchers in bandgap used bipolar so we decide to used a circuit which have bipolar, but at the end we accidentally found a circuit which have all cmos. And we consider the fact that it is recommended to use all CMOS in a bandgap.
And then we decide to used that circuit but in many papers and information I have now the authors/researchers never explain the importance of a bipolar and the difference of bandgap circuit that having a bipolar compare to bandgap circuit without bipolar. That's why I'm still confused of the importance of the BJT in a bandgap circuit. Do you have any idea about this fact?
Anyway thanks for the reference you gave it to me.