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Home Digital Electronics Logic Families and Their Characteristics Comments

  • Question
  • What should be done to unused inputs on TTL gates?


  • Options
  • A. They should be left disconnected so as not to produce a load on any of the other circuits and to minimize power loading on the voltage source.
  • B. All unused gates should be connected together and tied to V through a 1 k Ω resistor.
  • C. All unused inputs should be connected to an unused output; this will ensure compatible loading on both the unused inputs and unused outputs.
  • D. Unused AND and NAND inputs should be tied to VCC through a 1 kΩ resistor; unused OR and NOR inputs should be grounded.

  • Correct Answer
  • Unused AND and NAND inputs should be tied to VCC through a 1 kΩ resistor; unused OR and NOR inputs should be grounded. 


  • Logic Families and Their Characteristics problems


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    • 1. The output current capability of a single 7400 NAND gate when HIGH is called ________.

    • Options
    • A. source current
    • B. sink current
    • C. IOH
    • D. source current of IOH
    • Discuss
    • 2. Why is a pull-up resistor needed when connecting TTL logic to CMOS logic?

    • Options
    • A. to increase the output LOW voltage
    • B. to decrease the output LOW voltage
    • C. to increase the output HIGH voltage
    • D. to decrease the output HIGH voltage
    • Discuss
    • 3. Fan-out is determined by taking the ________ result(s) of ________.

    • Options
    • A. smaller,
    • B. larger,
    • C. smaller,
    • D. average,
    • Discuss
    • 4. Assume that a particular IC has a supply voltage (Vcc) equal to +5 V and ICCH = 10 mA and ICCL = 23 mA. What is the power dissipation for the chip?

    • Options
    • A. 50 mW
    • B. 82.5 mW
    • C. 115 mW
    • D. 165 mW
    • Discuss
    • 5. If all inputs to a TTL NAND gate are low, what is the ON, OFF condition of each transistor in the circuit?

    • Options
    • A. Q1-ON, Q2-OFF, Q3-ON, Q4-OFF
    • B. Q1-ON, Q2-ON, Q3-OFF, Q4-OFF
    • C. Q1-OFF, Q2-OFF, Q3-ON, Q4-ON
    • D. Q1-OFF, Q2-ON, Q3-OFF, Q4-ON
    • Discuss
    • 6. The time needed for an output to change from the result of an input change is known as:

    • Options
    • A. noise immunity
    • B. fan-out
    • C. propagation delay
    • D. rise time
    • Discuss
    • 7. Why are the maximum value of VOL and the minimum value of VOH used to determine the noise margin rather than the typical values for these parameters?

    • Options
    • A. These are worst-case conditions.
    • B. These are normal conditions.
    • C. These are best-case conditions.
    • D. It doesn't matter what values are used.
    • Discuss
    • 8. The term buffer/driver signifies the ability to provide low output currents to drive light loads.

    • Options
    • A. True
    • B. False
    • Discuss
    • 9. Using the schematic diagram of a TTL NAND gate, determine the state of each transistor (ON or OFF) when all inputs are high.

    • Options
    • A. Q1-ON, Q2-OFF, Q3-ON, Q4-OFF
    • B. Q1-ON, Q2-ON, Q3-OFF, Q4-OFF
    • C. Q1-OFF, Q2-OFF, Q3-ON, Q4-ON
    • D. Q1-OFF, Q2-ON, Q3-OFF, Q4-ON
    • Discuss
    • 10. When is a level-shifter circuit needed in interfacing logic?

    • Options
    • A. A level shifter is always needed.
    • B. A level shifter is never needed.
    • C. when the supply voltages are the same
    • D. when the supply voltages are different
    • Discuss


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