Hi,
First: you are wrong: on a high side driver, maybe it has 15V power supply. The power supply is referenced to a GND pin, then this pin is not the emitter ppin of the IGBT.
Again: look at the datasheet.
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Second you are wrong: in a typical high side driver ther is neither an Opamp, nor an ADC.
Again: look at the datasheet.
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I don't recommend you to build you own high side driver, because you don't have the electronical knowledge and it seems you don't have the knowledge about safety rules for high voltage. Don't hurt/kill yourself and don't hurt/kill others.
If you want to build a high side driver on your own you
* either use a proven schematic concept,
* or you need to develop a schematic concept of your own.
In both cases you should show us the schematic to discuss the details of the circuit.
Talking about wrong assumptions is useless.
Klaus