Question

The sequential circuit shown below functions according to which of given below statement

• A. It works as a D-flip-flop
• B. It works as a T-flip-flop
• C. Output remains stable at 1
• D. Output remains stable at 0

Answer 1

The correct option is B It works as a T-flip-flop

From the combinational logic

Assuming D as input, $Q_n$ as present state and $Q_{n+1}$ as the next state, then

$R=\overline{D⨁Q},S=D⨁Q$

Characteristic equation of R - S flip flop

$Q_{n+1}=S+\overline{R}{Q}_{in}$

So, $Q_{n+1}=(D⨁Q_n)+\overline{\overline{(D⨁Q_n)}}{Q}_n$

$=(D⨁Q_n)+(D⨁Q_n)Q_n$

$=(D⨁Q_n)[1+Q_n]$

$=D⨁Q_n$

$=D{\overline{Q}}_n+\overline{D}{Q}_n$

For, $D=0;Q_{n+1}=Q_n$

$D=1;Q_{n+1}={\overline{Q}}_n$

$\text{So the circuit functions as a T- flip flop.}$