ADC internal voltage reference for DUE ?

Hardware Arduino Due
1

The UNO has 1.1v internal voltage reference for ADC, and the ARM-based Maple has a 1.2v interval voltage for ADC (ADC1, channel 17). Reading the SAM3X8E reference manual, I don't think the DUE has an internal voltage reference for ADC. Is this true?

The DUE's ADC does have a gain that can be configured to trade precision for range.

2

Yes that is right it only has a pin Vref input.

Have you read the application note on the A/D, document number 11106A
www.atmel.com/Images/doc11106.pdf
That tells you all about it.