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I was trying to understand the ripple effect in asynchronous counter and I came across this figure:-

enter image description here

In all the problems solved in my book, they consider the minimum clock period required for proper functioning of counter as the sum of the delays caused due to these flip flops.

If we consider each delay as 5ns in the figure then the answer would be 15ns (minimum clock period time) according to my book.

My doubt is if it is exactly 15ns, then after 15ns, Q0 will toggle and we would get "1". So at the end we can't get 1000 as output as by that time Q0 would have toggled and we would get 1001 skipping 1000.

So I don't understand how clock period of 15ns would solve the problem of rippling.

Can someone please help me understand this concept?

ref:- https://www.allaboutcircuits.com/textbook/digital/chpt-11/asynchronous-counters/

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  • \$\begingroup\$ add the clock signal to the diagram \$\endgroup\$ – jsotola Nov 14 '17 at 7:06
  • \$\begingroup\$ I am not able to understand what will be the time period of the clock signal(thats my doubt). How can I add it? I edited the question with the reference link from where I took the diagram. \$\endgroup\$ – Zephyr Nov 14 '17 at 7:27
  • \$\begingroup\$ If the ceiling is exactly your height, are you going to bump your head on it? \$\endgroup\$ – Brian Drummond Nov 14 '17 at 7:33
  • \$\begingroup\$ @BrianDrummond *Takes a blunt* Woaaah maaan. So deep dude. Duuuuude. \$\endgroup\$ – Harry Svensson Nov 14 '17 at 7:39
  • \$\begingroup\$ @Zephyr, the first timing diagram on the web page shows the clock rising edge being the clocking signal for the first flip-flop. .... as per diagram on the bottom, the outputs are allowed to update in the receiving circuit when the clock goes low. therefore the clock has to stay high until the last flip-flop output is valid. .... for your example, the clock high has to be more than 15ns .... draw the clock into the diagram above .... rising when Q0 goes low and falling just after Q3 goes high \$\endgroup\$ – jsotola Nov 14 '17 at 8:12

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