# Logic Families and Miscellaneous

 Question 1
The logical gate implemented using the circuit shown below where, $V_1 \; and \; V_2$ are inputs (with 0 V as digital 0 and 5 V as digital 1) and $V_{OUT}$ is the output is
 A NOT B NOR C NAND D XOR
GATE EE 2017-SET-1   Digital Electronics
Question 1 Explanation:

When $V_1=$ high 5 V, $Q_1$ on, $V_{out}=0$
$V_2=$ high 5 V, $Q_2$ on, $V_{out}=0$
Thus when any $V_1$ or $V_2$ is high then, $V_{out}=0$

Thus, it is a NOR gate.
 Question 2
In the circuit shown below, $Q_{1}$ has negligible collector-to-emitter saturation voltage and the diode drops negligible voltage across it under forward bias. If $V_{cc}$ is +5 V, X and Y are digital signals with 0 V as logic 0 and $V_{cc}$ as logic 1, then the Boolean expression for Z is
 A XY B $\bar{X}Y$ C $X\bar{Y}$ D $\overline{XY}$
GATE EE 2013   Digital Electronics
Question 2 Explanation:

$\Rightarrow \;\;Z=\bar{X}Y$
 Question 3
The TTL circuit shown in the figure is fed with the waveform X (also shown). All gates have equal propagation delay of 10 ns. The output Y of the circuit is
 A A B B C C D D
GATE EE 2010   Digital Electronics
Question 3 Explanation:

 Question 4
A TTL NOT gate circuit is shown in figure. Assuming $V_{BE}$=0.7 V of both the transistors, if $V_{i}$=3.0 V, then the states of the two transistors will be
 A $Q_{1}$ ON and $Q_{2}$ OFF B $Q_{1}$ reverse ON and $Q_{2}$ OFF C $Q_{1}$ reverse ON and $Q_{2}$ ON D $Q_{1}$ OFF and $Q_{2}$ reverse ON
GATE EE 2006   Digital Electronics
Question 4 Explanation:
When $V_i=3 V$ then $Q_1$ will be in reverse active mode i.e. reverse ON and $Q_2$ will be ON.
 Question 5
If $X_{1}$ and $X_{2}$ are the inputs to the circuit shown in the figure, the output Q is
 A $\overline{X_{1} + X_{2}}$ B $\overline{X_{1}\cdot X_{2}}$ C $\overline{X_{1}}\cdot X_{2}$ D $\overline{X_{2}}\cdot X_{1}$
GATE EE 2005   Digital Electronics
Question 5 Explanation:
$Y_1=\bar{X_1}$
Output, $Q=\overline{Y_1+X_2}=\overline{(\bar{X_1}+X_2)}$
$Q=X_1\cdot \bar{X_2}$
There are 5 questions to complete.