Q. Parallel - flash converter?

Parallel / flash converter.

Also known as parallel A/D converter, this circuit is the simplest to understand. It's formed of a series of comparators, each one comparing input signal to a unique reference voltage. Comparator outputs connect to inputs of a priority encoder circuit that then produces a binary output. Following illustration demonstrates a 3-bit flash ADC circuit: 

Fig: FLASH ADC Circuit

Vref is a stable reference voltage provided by a precision voltage regulator as part of converter circuit, not displayed in schematic. As analog input voltage exceeds reference voltage at each comparator, comparator outputs will sequentially saturate to a high state. Priority encoder generates a binary number based on highest-order active input, ignoring all other active inputs.