I need to measure about 4.5mV signal with 0.1mV - 0.05mV precision.
Arduino normal supports 0-5v.
5/1023 means about 4.8mv precision?
That means that I will need some kind of op amp for this
Do you know about good op amp circuit that would fit well into this project?
The INA125 is (was) often used with the Arduino. But there are other good OpAmps that run at 5V. It depends on what it is used for. Is it a current shunt or a wheatstone bridge ?
Which Arduino board do you have ?
Is it an Arduino Uno ?
With the internal voltage reference of 1.1V, the resolution is 1mV.