Use a stable reference, 5V or 2.5V, or whatever.
Either divide it down directly using an adjustable divider to produce a 0-25mV output and buffer that with a low-offset, low-drift opamp, or use a DAC and then divide down its output with a fixed divider to produce 0-25mV, then buffer that output with a good low-offset, low-drift opamp.
hi!
thank you for your guidence. have any body any type of a milivolt power supply schtemetic digram because the thing that is woring me is this how much i can give a high resolution supply because i try to make any milivolt supply and to get it i am using supply of 1.5 or 3 volt