A 3-stage ripple counter has Flipflop with propagation delay of 2
A 3-stage ripple counter has Flipflop with propagation delay of 25 nsec and pulse width of strobe input 10 nsec. Then the maximum operating frequency at which counter operates reliably is
A. 16.67 MHz
B. 17.6 MHz
C. 12.67 MHz
D. 11.76 MHz
Please scroll down to see the correct answer and solution guide.
Right Answer is: D
SOLUTION
Concept:
In case of ripple or asynchronous counter total propagation delay Tpd = n tpd
Where n = no. of flip flops
tpd = propagation delay of each flip flop
If the strobe signal is given, the pulse width of the strobe is also added, i.e.
Tpd = n tpd + Ts
Calculation:
Given:
n = 3, tpd = 25 nsec, Ts = 10 nsec
Tpd = 3 × 25 + 10
Tpd = 75 + 10
Tpd = 85 ns
Maximum frequency at which counter operates will be:
\({f_{max}} = \frac{1}{{{T_{pd}}}}\)
Putting on the value, we get:
\(= \frac{1}{{85 \times {{10}^{ - 9}}}}\)
\(= \frac{{{{10}^3}}}{{85}}MHz = 11.76\;MHz.\)
fmax ≈ 11.76 MHz