A sequential circuit using D flip-flop and logic gates is shown in the figure, where X and Y are the inputs and Z is the output. The circuit is

In the figure, the J and K inputs of all the four Flip-Flops are made high. The frequency of the signal at output Y is

The number of comparators in 4-bit flash ADC is

For the 4 bit DAC shown in Figure, the output voltage $${V_0}$$ is