Analog-to-digital-conversion (ADC) is required in Embedded Systems to deal with various analog world parameters such as current, pressure, motion, temperature, etc. An ADC is an electronic system or a module that has analog input, reference voltage input and digital outputs.
The ADC convert the analog input signal to a digital output value that represents the size of the analog input comparing to the reference voltage. It basically samples the input analog voltage and produces an output digital code for each sample taken.
This application note from Atmel describes the fundamental concepts of ADC and the associated parameters that determine the performance and accuracy of the ADC’s output. – See more at: http://embedded-lab.com/blog/?p=7843#sthash.L7xjUI5s.dpuf
For more detail: Understanding ADC parameters for accurate analog