Bandgap reference circuit is used to supply a fixed dc voltage or current that has little dependence on temperature and power supply. It's a basic block circuit in Analog IC design.
For IC design, the process, temperature variation degrade the yield of product. bandgap reference is such a block with minimum dependence on temperature. Normally use it to provide voltage or current bias for other blocks.
Bandgap reference is a precision voltage reference that has a lowest temperature coeffiecient .It can supply a fixed voltage that equate silicon bandgap voltage.Generallly bandgap reference is regarded as the reference of other circuit block.So the independence of bandgap reference is the most key!
The bandgap reference has little temperature dependence since it combines positive temp dependence of thermal voltage with negative temp dependence of forward diode voltage.