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Step 1 of 2 8.028E The circuit of the 4-bit ripple down counter using four D flip-flops is shown in Figure 1. D & D D D 2² Figure 1 Considering the propagation delays, the waveform will be delayed to the right (skewed) by the propagation of the first flip-flop. The 2¹ waveform will be skewed to the right from the waveform, and the waveform will be skewed to the right from the 2¹ waveform, and the 2³ waveform will be skewed to the right from waveform. This is a cumulative effect that causes the 2³ waveform to be skewed to the right of the original waveform by four propagation delays. Propagation delay for 74HCT D flip-flop: Since, the propagation delay for 74HCT D flip-flop is 16 Calculate the maximum propagation delay from clock to output. =4(16ns) Therefore, the maximum propagation delay is - Propagation delay for 74AHCT D flip-flop: Since, the propagation delay for 74AHCT D flip-flop is 5 ns. Calculate the maximum propagation delay from clock to output. =4(5ns) Therefore, the maximum propagation delay is - Step 2 of 2 Propagation delay for 74LS74 D flip-flop: Since, the propagation delay for 74LS74 D flip-flop is 40 ns. Calculate the maximum propagation delay from clock to output. Therefore, the maximum propagation delay is 160 ns -