DAC's output voltage managment on Arduino Due

what is really not clear to me, how one can achieve make ADC sense smaller amounts of milivolts?? say if my ADC range is 0-4 Volts, then the minimum voltage it can sense is 4/4095=0.97miliVolts. I need to make this value something 0.5-0.3 miliVotls.

any ideas what could make that come ture= ? :confused: