Find the correct combination of 
and D inputs which can cause the LED to glow.
Text Solution
Verified by ExpertsA
The LED will glow if it is forward biased, which means the potential at the p -side must be higher than the potential at the n -side.
Let 
be the output of the upper NAND gate ( p -side) and 
be the output of the lower NOR gate ( n -side).
For the LED to glow, we need 
and 
.
The upper circuit consists of two NOT gates (NOR gates with shorted inputs) followed by a NAND gate.
Output of first NOT gate is 
, and second is 
.
(using De Morgan's Law).
The lower circuit is a NOR gate with inputs 
and 
.
.
Condition 1: 
. This means at least one of 
or 
must be 1 .
Condition 2: 
. This means at least one of 
or 
must be 1 .
Checking the options:
and 
. (Satisfied)
. (Not satisfied)
. (Not satisfied)
. (Not satisfied)
Thus, the correct combination is 1101 .
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