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A $4$ bit ripple counter and a $4$ bit synchronous counter are made using flip-flops having a propagation delay of $10$ ns each. If the worst case delay in the ripple counter and the synchronous counter be $R$ and $S$ respectively, then

  1. $R = 10$ ns, $S = 40$ ns
  2. $R = 40$ ns, $S = 10$ ns
  3. $R = 10$ ns, $S = 30$ ns
  4. $R = 30$ ns, $S = 10$ ns
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2 Answers

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In Ripple counter each FF waits for its previous FF's output...R = 4*10 = 40ns 

In Synchronous counter all FF are triggered by same clock so at a time all four FF will give output...S = 10ns

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ans is option B 

 for ripple counter time = n * propogation delay 

for synchronous counter time = Tff + T(combinational circuit) 

 T(combinational circuit ) not given so take it as 0 

finally ans will be  :-----

for ripple counter time = 40 

for synchronous counter time = 10 

Answer:

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