The format used to present the logic output for the various combinations of logic inputs to a gate is called a(n):
Answer: C
Correct answer: truth table
A truth table is the standard tabulation of a gate's output for every combination of its inputs. A Boolean variable is a single symbol and a Boolean constant is 0 or 1.
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The power dissipation, PD, of a logic gate is the product of the ________.
Answer: B
Correct answer: dc supply voltage and the average supply current
Power dissipation is
\[ P_D = V_{CC}\times I_{CC(avg)} \]
The average current is used because the current drawn varies as the gate switches; the peak value would overstate the power, and the supply is dc, not ac.
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If a 3-input AND gate has eight input possibilities, how many of those possibilities will result in a HIGH output?
Answer: A
Correct answer: 1
An AND output is HIGH only when every input is HIGH, and of the eight combinations of three inputs exactly one has all three at 1.
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The Boolean expression for a 3-input AND gate is ________.
Answer: B
Correct answer: X = ABC
AND is written as a product, so a three-input AND is the product of all three variables. The plus sign would make it an OR, and \( AB+C \) mixes the two operations.
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A CMOS IC operating from a 3-volt supply will consume ________.
Answer: A
Correct answer: less power than a TTL IC
CMOS draws significant current only while switching, so its static dissipation is minute compared with TTL, which draws current continuously through its output stage. Lowering the supply to 3 V reduces it further still, since dynamic power varies with the square of the supply voltage.
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What does the small bubble on the output of the NAND gate logic symbol mean?
Answer: C
Correct answer: The output is inverted.
The bubble is the standard symbol for inversion wherever it appears, on an output or an input. On the output of an AND symbol it makes NAND; on an OR symbol it makes NOR.
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What are the pin numbers of the outputs of the gates in a 7432 IC?
Answer: C
Correct answer: 3, 6, 8, and 11
The 7432 is a quad two-input OR in a 14-pin package, laid out so that each gate takes two adjacent input pins and the next pin is its output. That gives outputs at 3, 6, 8 and 11, with pin 14 for VCC and pin 7 for ground - the same pinout as the 7408 and 7400.
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The output of a NOT gate is HIGH when ________.
Answer: A
Correct answer: the input is LOW
A NOT gate produces the complement of its input, so its output is HIGH exactly when the input is LOW. The presence of supply power is a precondition for the gate working at all, not a logical input.
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How many inputs of a four-input AND gate must be HIGH in order for the output of the logic gate to go HIGH?
Answer: D
Correct answer: all four inputs
AND requires every input to be HIGH; a single LOW input forces the output LOW however many other inputs are HIGH.
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If the output of a three-input AND gate must be a logic LOW, what must the condition of the inputs be?
Answer: C
Correct answer: At least one input must be LOW.
AND gives 0 whenever any input is 0. That covers seven of the eight input combinations, so the condition is at least one LOW rather than all of them.
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