Hi~~
If said a ADC has 12bits,then the reference voltage = 2V
then the smallest can measured voltage = 2/(2^12) = 4.88mV (it means LSB) ,
and  if reference voltage = 1 V --> 1/(2^12) = 2.44mV ,
so the reference voltage =1 can measure smaller voltage if ADC's  bit =12

Is this statement is right?
thanks~~~

Hi,

yes, your statement is correct if your ADC is quantization noise limited. In many cases, the resolution may however be determined by the thermal noise level, in which case the lowest value to be measured is reference-independent. In that case, using the larger reference voltage maximizes your dynamic range (if we neglect distortion).

Paul