2. (Total 30 points) Consider the counter with parallel-load capability in Fig.
ID: 3706570 • Letter: 2
Question
2. (Total 30 points) Consider the counter with parallel-load capability in Fig. 5.24 in textbook. For the D flip-flops, assume that the setup time tsi, is 4 ns, the hold time th is 4 ns, and the clock-to-Q propagation delay tcg is 3 to 4 ns. Assume that the propagation delays for AND gates, XOR gates and 2-to-1 multiplexers are 3 ns, 3 ns and 5 ns, respectively S11 (20 points) What is the maximum clock frequency for which the circuit will operate correctly? Please show your calculations (10 points) Does the circuit have hold time violation? Briefly, explain your answer (a) (b)Explanation / Answer
Solution:
Given:
tsu= 4 ns
th= 4 ns
tcq= 3 to 4 ns
tand= 3 ns
txor= 3 ns
tmux= 5 ns
a)
The longest delay in the circuit is the path from the output of the first flip-flop to the input of the fourth flip-flop
The path includes 5 gates
so tlong= 3*tand + 1 * txor + 1 8 tmux
= 3*3 + 1*3+1*5 = 17 ns
the minimum period for which the circuit will be operating reliably
Tmin = tlong + tsu + th
= 17 + 4 + 4 = 25 ns
The maximum frequency will be
1/Tmin = 1/25 ns = 40000000
= 40MHz
b)
No, there is no hold time violation.
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