9618 · 3.2
Logic Gates and Logic Circuits flashcards
Revision flashcards for Cambridge 9618 Logic Gates and Logic Circuits (syllabus 3.2). Flip, recall, then mark a real past-paper question.
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What is a logic gate?
An electronic component that performs a basic logical function, taking one or more binary inputs (0 or 1) to produce a single binary output.
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What is the function of a NOT gate?
It inverts its single input. A 1 becomes a 0, and a 0 becomes a 1. It is also known as an inverter. Boolean expression: $X = \neg{A}$.
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What is the function of an AND gate?
It produces a 1 output only if ALL of its inputs are 1. Otherwise, the output is 0. Boolean expression: $X = A \cdot B$.
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What is the function of an OR gate?
It produces a 1 output if AT LEAST ONE of its inputs is 1. The output is 0 only if all inputs are 0. Boolean expression: $X = A + B$.
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What is the function of an XOR gate?
The 'exclusive OR' gate. It produces a 1 output if its inputs are different (e.g., one is 1, the other is 0). Boolean expression: $X = A \oplus B$.
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What is the function of a NAND gate?
A 'NOT AND' gate. It is an AND gate followed by a NOT gate. The output is 0 only when all inputs are 1. Boolean expression: $X = \neg{(A \cdot B)}$.
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What is the function of a NOR gate?
A 'NOT OR' gate. It is an OR gate followed by a NOT gate. The output is 1 only when all inputs are 0. Boolean expression: $X = \neg{(A + B)}$.
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What does it mean for a gate to be 'universal'?
A universal gate (like NAND or NOR) can be used to construct any other type of logic gate. This is efficient for manufacturing, as only one type of gate needs to be produced.
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State De Morgan's Law for an AND expression.
The negation of a conjunction is the disjunction of the negations. In Boolean algebra: $\neg{(A \cdot B)} = \neg{A} + \neg{B}$.
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State De Morgan's Law for an OR expression.
The negation of a disjunction is the conjunction of the negations. In Boolean algebra: $\neg{(A + B)} = \neg{A} \cdot \neg{B}$.
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What is a truth table?
A table that shows all possible input combinations and the corresponding output for a logic gate or circuit.
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What is the Boolean expression for an XOR gate using AND, OR and NOT?
$X = (A \cdot \neg{B}) + (\neg{A} \cdot B)$. This shows how more complex gates can be built from simpler ones.