Logic Families and Their Characteristics MCQs

Question 1

What is unique about TTL devices such as the 74SXX?

Accepted Answer

These devices use Schottky transistors and diodes to prevent them from going into saturation; this results in faster turn-on and turn-off times, which translates into higher frequency operation.

Answer

The gate transistors are silicon (S), and the gates therefore have lower values of leakage current.

Answer

The S denotes the fact that a single gate is present in the IC rather than the usual package of 2–6 gates.

Answer

The S denotes a slow version of the device, which is a consequence of its higher power rating.

Question 2

Which of the following logic families has the shortest propagation delay?

Accepted Answer

ECL

Answer

CMOS

Answer

BiCMOS

Answer

74SXX

Question 3

Special handling precautions should be taken when working with MOS devices. Which of the following statements is not one of these precautions?

Accepted Answer

Workers handling MOS devices should not have grounding straps attached to their wrists.

Answer

All test equipment should be grounded.

Answer

MOS devices should have their leads shorted together for shipment and storage.

Answer

Never remove or insert MOS devices with the power on.

Question 4

What should be done to unused inputs on TTL gates?

Accepted Answer

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

Answer

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.

Answer

All unused gates should be connected together and tied to V through a 1 k resistor.

Answer

All unused inputs should be connected to an unused output; this will ensure compatible loading on both the unused inputs and unused outputs.

Question 5

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?

Accepted Answer

82.5 mW

Answer

50 mW

Answer

115 mW

Answer

165 mW

Question 6

What is the major advantage of ECL logic?

Accepted Answer

very high speed

Answer

wide range of operating voltage

Answer

very low cost

Answer

very high power

Question 7

What is the range of invalid TTL output voltage?

Accepted Answer

0.4–2.4 V

Answer

0.0–0.4 V

Answer

2.4–5.0 V

Answer

0.0–5.0 V

Question 8

What is the difference between the 54XX and 74XX series of TTL logic gates?

Accepted Answer

54XX has a wider power supply and expanded temperature range.

Answer

54XX is faster.

Answer

54XX is slower.

Answer

54XX has a narrower power supply and contracted temperature range.

Question 9

Using the schematic diagram of a TTL NAND gate, determine the state of each transistor (ON or OFF) when all inputs are high.

Accepted Answer

Q1-OFF, Q2-ON, Q3-OFF, Q4-ON

Answer

Q1-ON, Q2-OFF, Q3-ON, Q4-OFF

Answer

Q1-ON, Q2-ON, Q3-OFF, Q4-OFF

Answer

Q1-OFF, Q2-OFF, Q3-ON, Q4-ON