GATE Overflow Test Series | Mixed Subjects | Test 2 | Question: 1

Question

A switch-tail ring counter is made using a single $T$ flip flop. The resulting circuit is equivalent to:

• A. SR flip flop
• B. JK flip flop
• C. T flip flop
• D. None of the above

Answer 1

In a switch-tail ring counter with a single flip flop, $\bar Q$ is connected back as the input. Since, the FF is $T,$ $Q = \bar D$ and $\bar Q = D.$

Now, if the initial value of $Q = 1, \bar Q = 0.$ In next clock, $T = 0.$ So, no toggle and $Q = 1, \bar Q = 0.$

if the initial value of $Q = 0, \bar Q = 1.$ In next clock, $T = 1.$ So, toggle and $Q = 1, \bar Q = 0.$

So, within $2$ cycles output becomes $1$ and does not change afterwards. So, correct option is D – None of the above.

Comments

I have one doubt about this question. How can we compare a single flip-flop with S-R ff and J-K ff? Since S-R produces an invalid or don’t care condition if S=1 and R=1. So how to compare both pins. If suppose we start with Q=0 $\bar{Q}$=1 and then output is invalid. But if we consider similar for JK ff and T-ff then $\bar{Q}$=1 would be connected to J suppose. then what would be the input for K pin. How to compare if we have input only for 1 pin(either J or K)? So it is like if we know the desired output, we can modify our circuits to behave like that but how to compare output of any random circuit with previously known outcomes. For example: If we consider a J-K ff then what are the input values that must be given so that the output is considered. If that is not specified, we can voluntarily choose such values to match/ not-match the circuits. Because every flip flop can be constructed from each other. So the basic doubt is the approach to these types of questions?

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but how we are comparing this to jk sr and other flip flops

what i did was i took jk flip flop and connected it in the same manner as t flip flop

i.e j&k was connected to Qcomplement this gave me the output 1  and your T switch tail ring flip flop also gave me the same output  so i selected option jk flip flop