This work describes a 4-bit Flash ADC with low power consumption. The performance metrics of a Flash ADC depend on the kind of comparator and encoder used. Hence openloop comparator and mux-based encoder are used to obtain improved performance. Simulation results show that the simulated design consumes 0.265mW of power in 90nm CMOS technology using cadence-virtuoso software. The circuit operates with an operating frequency of 100MHz and a supply voltage of 1V.