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Concept about NAND GATE :-
The NAND (Not – AND) gate has an output that is normally at logic level “1” and only
goes “LOW” to logic level “0” when ALL of its inputs are at logic level “1”. The Logic
NAND Gate is the reverse or “Complementary” form of the AND gate.
The logic or Boolean expression given for a logic NAND gate is that for Logical
Addition, which is the opposite to the AND gate, and which it performs on
the complements of the inputs. The Boolean expression for a logic NAND gate is
denoted by a single dot or full stop symbol, ( . ) with a line or Overline, ( ‾‾ ) over the
expression to signify the NOT or logical negation of the NAND gate giving us the
Boolean expression of: A.B = Q .
Then we can define the operation of a 2-input digital logic NAND gate as being:
“If either A or B are NOT true, then Q is true”
TRANSISTOR NAND GATE –
A simple 2-input logic NAND gate can be constructed using RTL Resistor-transistor
switches connected together as shown below with the inputs connected directly to
the transistor bases. Either transistor must be cut-off “OFF” for an output at Q.
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