Semiconductor Electronics

[figure] For the circuit shown above, equivalent GATE is :

1. NOT gate
2. NAND gate
3. AND gate
4. OR gate

Which of the following circuits has the same output as that of the given circuit? [figure]

1. [figure]
2. [figure]
3. [figure]
4. [figure]

[figure] In the circuit shown here, assuming threshold voltage of diode is negligibly small, then voltage VAB is correctly represented by:

1. [figure]
2. [figure]
3. VAB would be zero at all times.
4. [figure]