Question

A 4 bit modulo 16 ripple counter uses jk flip flops. If the propagation delay of each flip flop is 50nanosecond , the maximum clock frequency that can be used is equal to

Answer 1

td is 50ns

total propagtion delay is 4x50ns =200ns  (4 is number of flops in modulo 16)

then maximum clock frequency is given by

F=1/200x10^-9

F=5 MHz

Answer 2

Concept:

• To get the overall delay in the counter, the propagation delays of all flip-flops are added
• The following clock pulse must arrive when all the carry's formed are propagated through all flip-flops and there is a stable output.
• Tclk≥n(tpd)FF
• fclk≤1/n(tpd)FF

Given:

• 4 bit modulo 16 ripple counter uses 5JK flip flops
• propagation delay = 50 nanosecond

Find:

• The maximum clock frequency that can be used

Solution:

Total propagation delay = 4*50 = 200 nanoseconds

Maximum frequency = 1/n(tpd)FF = 1/200 nanoseconds = 5 Mega Hz

5MHz is the maximum clock frequency that can be used.

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