## 25/03/2020

### Logic Families Interview Question Answer - 1

 1 Explain the terms : Threshold voltage, Figure of merit, Propagation delay Threshold voltage It is defined as the voltage at the input of a gate which causes the state of the output from one level to the other. Figure of merit It is defined as the product of the speed – power product. Propagation delay It is time required for gate pulse to propagate from input to output. 2 Explain the terms : Power consumption, Fan in and Fan out Power consumption It is power required by the gate to operate at 50% duty cycle at a specified frequency. Fan in It is defined as the number of inputs that gate is designed to handle. Fan out It is defined as maximum number of standard loads that the output of the gate drives without affecting its normal operation. 3 Explain the terms : Noise margin and Noise Noise margin It is defined as amount of noise that digital circuit can withstand without compromising the operation of the circuit. Noise It is defined as the unwanted spurious signals. 4 Which parameter is affected by fan out of the IC? Saturation and propagation delay time 5 What is operating temperature range for IC gates? Operating temperature range for IC gates Commercial : 0 to 70 0C Industrial : 0 to 85 0C  Millitary : – 55 to 125 0C 6 Write the unit of speed power product of an IC. Watt – second 7 Which logic families are included in SSI, LSI & VLSI? SSI Transistor transistor logic ( TTL) Complementary metal oxide semiconductor logic ( CMOS ) LSI Metal oxide semiconductor logic ( MOS ) Complementary metal oxide semiconductor logic ( CMOS ) VLSI Integrated injection logic ( IIL) 8 Which is most popular and widely used digital logic IC? Transistor transistor logic ( TTL) 9 Which mode of operation is used for transistor in the TTL logic IC? Saturation mode 10 What is logic behind the name TTL? The transistors alone perform all the logic operations in the TTL therefore it is known as TTL. 11 Write the features of TTL logic IC. Features of TTL logic IC High power consumption Low cost Moderate package density Generation of noise Generation of Power transients 12 What is operating voltage range for TTL? The operating voltage for standard TTL for logic 1 is 2 to 5 voltage and that of for logic 0 is 0 to 0.8 voltages. 13 Define : Loading factor Loading factor It is defined as maximum number of standard loads that the output of the gate drives without affecting its normal operation. 14 Describe the function of diode at the input in the TTL logic IC. The diodes at the input in the TTL protect the transistor from negative spikes. 15 Describe the function of diode at the totem – pole output of the TTL logic IC. The diode at the totem – pole output of the TTL ensures conducting of any one transistor at a time.

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