Analog input: influence of the VCC changing?

[Alex Co]

Hi I read somewhere that when using internel ref for analog measurements the Vin changing does not influences the analog reading. Is that true?

Please, consider the circuit on this link:

devzone.nordicsemi.com/.../

Suppose we start with a 3.3 coin cell which will be drain more or less fast but nRF51 has a brown out of 1.8v

how can we calculate the influence (if any) in the analog conversion when using internal 1.2 ref (ADC_CONFIG_REFSEL_VBG) (and a brown out of 1.8v!) and a analoginput signal divided by 3 (ADC_CONFIG_INPSEL_AnalogInputOneThirdPrescaling)?

Can we trust in the analog conversion during all time of battery draining (until 1.8v)?

Thanks

Alex

[Alex Co]

By the way i am not planning to read analog value while driving BLE. Should i use even though a large cap in the board vin? Any schematic for that. ?