What is the purpose of +-VREF pins in ADC?

[david90]

Regarding uC's ADC, what is the purpose of +-VREF pins?

 

[spaceaky]

vref adc

give a reference voltage。
or a max voltage

 

[Davood Amerion]

vref in adc

this pin used where FSD (full scale deflection) of input signal is lower than 5Volts.
and you need to get digit 255 for 8bit ADC, and 1023 for 10bit ADC (after ADC conversion) , for that voltage.

eg1. if maximum measure voltage is 2 volts, you connect Vref to 2 volt , to get maximum resulution.

eg2. if maximum measure voltage is 2 volts, you connect Vref to 2.56 volt , to get 0-200 digit value without allignment (in 8 bit version).

 

[david90]

vref for adc

if u connect +vref to 2v and -vref to 1V, then maximum resolution is achieved when measure voltage is 1V?

 

[philba]

dac vref

If you meant a 1V swing (from 1 to 2 V), yes. with the vreg+ and - set as above, 1V input would yield an ADC value of 0, 2V input would yield 255 or 1023 (8 or 10 bit ADC, respectively).

By the way, you probably would not see 0 and 255 (1023) due to noise but that's a whole new level of discussion.