A/D converters are available in a wide variety of conversion methods, which differ mainly in their conversion speed and resolution. Parallel converters, also known as flash converters, are A/D converters with bit-parallel conversion. Compared to other methods such as successive approximation( SAR), they have the advantage that they operate much faster and require only one clock signal for conversion.
Parallel converters consist of many comparators and a corresponding number of voltage dividers. The input voltage is applied to all comparators. The reference voltage derived from the voltage divider is applied to the second input of each comparator. For a dual code of 3 bits, the input voltage range must be divided into '2^3', i.e. 8 quantization intervals. This requires seven comparators and voltage dividers. The logic levels of the comparators are recoded to the number '3' by code conversion before they are converted to binary code.
The number of comparators and voltage dividers depends on the resolution of the parallel converter and is calculated from '2^2-1'. A D/A converter with a resolution of 5 bits thus consists of 31 comparators, one with 8 bits resolution of 255 and one with 16 bits of 65,535 comparators.
Each comparator receives its own reference voltage via the resistor matrix. Since the accuracy of the voltage dividers directly affects the accuracy of the D/A conversion, the resolution of parallel converters, also called flash converters, rarely exceeds 10 bits. On the other hand, the conversion speed is very high because only one clock pulse is needed for full resolution. With each clock signal, the analog input voltage is converted into a digital signal with the corresponding resolution (depending on the number of comparators).