Digital Electronics Combinational Logic Circuits Questions and Answers
The Combinational Logic Circuits questions with answers focus on logic gates, Boolean algebra, K-maps, and circuit simplification techniques in digital electronics. These logical reasoning questions and answers help students understand how digital systems process information. Frequently asked in ECE exams and electronics company placements like BEL, ISRO, and TCS, these questions strengthen analytical and circuit design skills. Study the truth tables, logic expressions, and practical implementations to master this essential topic in digital design.
Digital Electronics Combinational Logic Circuits
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59 questions
11. Which of the following expressions is in the product-of-sums form?
- (A + B)(C + D)
- (AB)(CD)
- AB(CD)
- AB + CD
12. Which of the following is an important feature of the sum-of-products form of expressions?
- All logic circuits are reduced to nothing more than simple AND and OR operations.
- The delay times are greatly reduced over other forms.
- No signal must pass through more than two gates, not including inverters.
- The maximum number of gates that any signal must pass through is reduced by a factor of two.
13. An output gate is connected to four input gates; the circuit does not function. Preliminary tests with the DMM indicate that the power is applied; scope tests show that the primary input gate has a pulsing signal, while the interconnecting node has no signal. The four load gates are all on different ICs. Which instrument will best help isolate the problem?
- Current tracer
- Logic probe
- Oscilloscope
- Logic analyzer
14. The binary numbers A = 1100 and B = 1001 are applied to the inputs of a comparator. What are the output levels?
- A > B = 1, A < B = 0, A < B = 1
- A > B = 0, A < B = 1, A = B = 0
- A > B = 1, A < B = 0, A = B = 0
- A > B = 0, A < B = 1, A = B = 1
15. A logic probe is placed on the output of a gate and the display indicator is dim. A pulser is used on each of the input terminals, but the output indication does not change. What is wrong?
- The output of the gate appears to be open.
- The dim indication on the logic probe indicates that the supply voltage is probably low.
- The dim indication is a result of a bad ground connection on the logic probe.
- The gate may be a tristate device.
16. Each "1" entry in a K-map square represents:
- a HIGH for each input truth table condition that produces a HIGH output.
- a HIGH output on the truth table for all LOW input combinations.
- a LOW output for all possible HIGH input conditions.
- a DON'T CARE condition for all possible input truth table combinations.
17. Looping on a K-map always results in the elimination of:
- variables within the loop that appear only in their complemented form.
- variables that remain unchanged within the loop.
- variables within the loop that appear in both complemented and uncomplemented form.
- variables within the loop that appear only in their uncomplemented form.
18. What will a design engineer do after he/she is satisfied that the design will work?
- Put it in a flow chart
- Program a chip and test it
- Give the design to a technician to verify the design
- Perform a vector test
19. What is the indication of a short on the input of a load gate?
- Only the output of the defective gate is affected.
- There is a signal loss to all gates on the node.
- The affected node will be stuck in the LOW state.
- There is a signal loss to all gates on the node, and the affected node will be stuck in the LOW state.
20. In HDL, LITERALS is/are:
- digital systems.
- scalars.
- binary coded decimals.
- a numbering system.