There are basically four ADC technologies; flash, pipeline, successive approximation register, and sigma delta. Flash ADCs are also known as “direct conversion or parallel ADCs” and are very fast in converting an analog signal to a digital signal. The reason for the fast conversion is the single stage of 2n-1 comparators as shown in the circuit above. The comparators output a “1” when analog input voltage is higher than the reference voltage defined by its input resistor. A comparator outputs a “0” when the input is lower than its reference voltage. In parallel, the output of zeroes and ones go into a decoder and it outputs a digital code. The flash ADC’s comparator and encoder architecture is analogous to a mercury thermometer where the mercury rises to the appropriate temperature and no mercury is present above the temperature. The flash ADC has fast conversion, but on the downside, it requires a lot of well matched comparators and die area is significantly increased. A 16-bit ADC would require 65,535 comparators. Flash converters are better suited for 8-bits and less of resolution.