As documentation says, Arduino Due power supply is based on NCP1117ST33T3G regulator, which is quite precise (1%). But for scientific measurement higher precision can be required. I want to understand is it possible to provide custom reference voltage but further documentation is a bit unclear:
The analogReference() function is ignored on the Due. [ArduinoBoardDue]
Does this mean that reference voltage can not be changed? Or, the board will configure it automatically?
The AREF pin is connected to the SAM3X analog reference pin through a resistor bridge. To use the AREF pin, resistor BR1 must be desoldered from the PCB.
Can I connect precise external power supply after unsoldering the resistor (which will be quite challenging task)?
Q2.
Will change of the reference voltage affect all other voltages on the board?
@brian: Yes, JR1 needs to be desoldered off the board if you are connecting any input to AREF. I'd just slide it over onto the other side of BR1 so that it connects the external pin.
@KVA: Page 1403 in the datasheet: 250uA. It also has a specification for impedance, 14kOhm, which should be very easy to achieve. It may not be obvious, but AREF can't exceed the supply voltage of 3.3V or be negative.
Well, one use of AREF is if you have 5V sensors (like the great MPX pressure sensors from Freescale) and you have a voltage divider from the 5V rail providing the reference voltage. Then you shouldn't choose 15K resistors for your voltage divider. The reason why you would want 15K resistors is then you would waste less power providing the reference. You might then add a capacitor to lower the DC impedance, which also has the beneficial effect of increasing the AC impedance, reducing noise.
That Linear chip looks perfectly adequate. It will have an extremely low impedance, probably under 100 ohms at a guess. Fortunately there is no such thing as "too low" for this application.