BEE Digital Circuits 5 — Questions and Answers
Question 1: What is the purpose of a schmitt trigger in digital circuits?
- To amplify analog signals
- To provide hysteresis for clean switching on noisy or slow-transition inputs (Correct answer)
- To convert TTL levels to CMOS levels
- To store one bit of data
Correct answer: To provide hysteresis for clean switching on noisy or slow-transition inputs
A Schmitt trigger uses two different threshold voltages (hysteresis) to produce a clean, bounce-free digital output from noisy or slowly changing input signals.
Question 2: In which number system is the addition 1011 + 1101 performed, and what is the result?
- Decimal; result is 24
- Binary; result is 11000 (Correct answer)
- Hexadecimal; result is 18
- Octal; result is 30
Correct answer: Binary; result is 11000
1011₂ (11) + 1101₂ (13) = 11000₂ (24) in binary arithmetic.
Question 3: Which type of ROM can be erased by exposing it to ultraviolet light?
- PROM
- EEPROM
- EPROM (Correct answer)
- Mask ROM
Correct answer: EPROM
EPROM (Erasable Programmable ROM) is erased by UV light shone through its quartz window, resetting all cells to 1.
Question 4: A synchronous 3-bit up counter is currently in state 110. What is the next state?
- 101
- 000
- 111 (Correct answer)
- 011
Correct answer: 111
110₂ = 6; the next count is 7 = 111₂ in a standard 3-bit synchronous up counter.
Question 5: Which logic expression represents the output of an XNOR gate for inputs A and B?
- A·B + Ā·B̄ (Correct answer)
- A⊕B
- A·B̄ + Ā·B
- Ā+B̄
Correct answer: A·B + Ā·B̄
XNOR outputs 1 when both inputs are the same: A·B (both 1) or Ā·B̄ (both 0), which is the complement of XOR.
Question 6: What is the key advantage of synchronous circuits over asynchronous circuits?
- Lower power consumption
- Easier hazard-free design and predictable timing (Correct answer)
- Fewer gates required
- Faster operation at all frequencies
Correct answer: Easier hazard-free design and predictable timing
Synchronous circuits clock all state changes to a common clock edge, making timing analysis, hazard avoidance, and design verification significantly simpler.
Question 7: How many address lines are required to access each location in a 64K × 8 memory chip?
- 8
- 13
- 16 (Correct answer)
- 64
Correct answer: 16
64K = 2¹⁶ locations, so 16 address lines are needed to uniquely address each of the 65,536 memory locations.
BEE Digital Circuits 5
What is the purpose of a schmitt trigger in digital circuits?