What is a logic gate?
A logic gate is a device that performs a Boolean function, a logical operation on one or more binary inputs that produces a single binary output.
What are the seven basic logic gates?
NOT, OR, NOR, AND, NAND, XOR, and XNOR.
What does the AND gate output?
The AND gate outputs 1 only if all its inputs are 1; otherwise it outputs 0.
What does the OR gate output?
The OR gate outputs 1 if at least one of its inputs is 1; it outputs 0 only if all inputs are 0.
What does the NOT gate do?
The NOT gate inverts its input: it outputs 1 if the input is 0, and 0 if the input is 1.
What is the output of a NAND gate?
A NAND gate is the negation of AND: it outputs 0 only when all inputs are 1; otherwise it outputs 1.
What is the output of a NOR gate?
A NOR gate is the negation of OR: it outputs 1 only when all inputs are 0; otherwise it outputs 0.
What is the output of an XOR gate?
An XOR (exclusive OR) gate outputs 1 if the number of 1 inputs is odd; for two inputs, it outputs 1 when exactly one input is 1.
What is the output of an XNOR gate?
An XNOR gate is the negation of XOR: it outputs 1 when the number of 1 inputs is even; for two inputs, it outputs 1 when both inputs are the same.
What is a truth table?
A truth table lists all possible combinations of inputs and shows the corresponding output for a logic gate or circuit.
Draw the truth table for a 2-input AND gate.
A B | Q
0 0 | 0
0 1 | 0
1 0 | 0
1 1 | 1
Draw the truth table for a 2-input OR gate.
A B | Q
0 0 | 0
0 1 | 1
1 0 | 1
1 1 | 1
Draw the truth table for a NOT gate.
A | Q
0 | 1
1 | 0
How can logic gates be combined?
Logic gates can be cascaded (connected in series or parallel) to form circuits that implement more complex Boolean functions.
What are some devices built from logic circuits?
Logic circuits include multiplexers, registers, arithmetic logic units (ALUs), computer memory, and complete microprocessors.
What is the fundamental concept behind all electronic digital computers?
Using electrical switches to implement logic, based on switching circuit theory, which showed that two-valued Boolean algebra can describe switching circuits.
What are the two common sets of symbols for logic gates?
The 'distinctive shape' set (traditional schematics) and the 'rectangular shape' set (ANSI/IEEE and IEC standards).
What is the standard that defines logic gate symbols?
ANSI/IEEE Std 91-1984 and its supplement 91a-1991, plus IEC 60617-12.
What is a compound logic gate? Give an example.
A compound logic gate combines multiple basic gates into one circuit, e.g., AND-OR-invert (AOI) and OR-AND-invert (OAI).
Why are compound logic gates often used?
Because their construction using MOSFETs is simpler and more efficient than the sum of individual gates.
What is the primary way of building logic gates today?
Using MOSFETs (metal–oxide–semiconductor field-effect transistors) as electronic switches.
Who refined the binary number system and when?
Gottfried Wilhelm Leibniz, published in 1705.
Who described logical operations using electrical switching circuits in 1886?
Charles Sanders Peirce.
Who invented the first modern electronic AND gate in 1924?
Walther Bothe, inventor of the coincidence circuit.
What is the output of a 2-input XOR gate when both inputs are 1?
0, because XOR outputs 1 only when the inputs are different.