Q.Draw the symbol and write the truth table and Boolean expression of a two-input NAND gate, and show how a NAND gate can, by itself, be used to realise a NOT gate.

A NAND gate's symbol is the AND-gate symbol with a small inversion bubble added at its output. Its truth table is the row-for-row complement of the AND gate's own table: output $Y=0$ only in the single row where $A=1$ and $B=1$, and $Y=1$ in every other row. Its Boolean equation is $Y=\overline{A\cdot B}$. To realise a NOT gate from a NAND gate ALONE, connect BOTH of its inputs to the same single signal $A$: the gate then sees $A$ on both inputs, so $Y=\overline{A\cdot A}=\overline{A}$, exactly the NOT-gate function. …

Take the AND gate's truth table and invert every output row for the NAND truth table; then set $B=A$ in the e …

• Forgetting to invert every row of the AND truth table.
• Leaving the two NAND inputs separate when trying to realise …