I think the confusion between you and pedja089. The first way you need two external pins from the ADC or comparator.
One of the pins is tied to an external vref source and the other is your analog input. There is no voltage reference in the 683
VCFG bit or ADCON0.6 either connects the ADC vref(input) to VDD internally or connects it to and external (pin) reference you provide. .
The second way only one external pin is needed. (pic12F1822) has an internal reference diode which can be configured to be the vref source for the adc or comparator.