Question

The truth table for system of four NAND gates as shown in the figure is

• A. $\begin{array}{ccc}A& B& Y\\ 0& 0& 0\\ 0& 1& 0\\ 1& 0& 1\\ 1& 1& 1\end{array}$
• B. $\begin{array}{ccc}A& B& Y\\ 0& 0& 1\\ 0& 1& 1\\ 1& 0& 0\\ 1& 1& 0\end{array}$
• C. $\begin{array}{ccc}A& B& Y\\ 0& 0& 1\\ 0& 1& 0\\ 1& 0& 0\\ 1& 1& 1\end{array}$
• D. $\begin{array}{ccc}A& B& Y\\ 0& 0& 0\\ 0& 1& 1\\ 1& 0& 1\\ 1& 1& 0\end{array}$

Answer 1

The correct option is D

$\begin{array}{ccc}A& B& Y\\ 0& 0& 0\\ 0& 1& 1\\ 1& 0& 1\\ 1& 1& 0\end{array}$

Outputs of the gates are marked as $y$, $y_1$ and $y_2$:

A NAND gate gives low output when both the inputs are high, otherwise, it gives a high output. Now, the truth table is