what is the differences btw linear and non-linear ADC ?

Please help me!
i don' t know the differences between the linear and non-linear analogue to digital converter (ADC).
even though i try to surf the net about the differences but i still couldn't understand.
can somebody help me and explain it to this forum.
thanks for ur help!!

Sarah_Radzi

linear ADC => each increment of bit equals to a fixed value.. such as 1V/128 ..

non linear ADC ... each bit increment is different .. usually on log scale ... used in voice compression / A-Law/ u-law