Logic Families Interview Question Answer - 5

Important Questions of Logic Families

In this post, some of important questions of logic families are given. It include NMOS, PMOS, advantages of CMOS, noise margin, CMOS bilateral transmission gate, CMOS bilateral switch, unidirectional gate logic devices, CMOS transmission gate, meaning of Interfacing, Two phase non – over lapping clock, interfacing logic and low input current and high output current logic.

Why the NMOS is popular than that of the PMOS? 

The NMOS is popular to that of PMOS due to following reasons

• The operating speed of the NMOS is about three times to that of the PMOS. The package density of the NMOS is twice to that of the PMOS.

Describe the advantages of the CMOS over the PMOS and the NMOS.     

Advantages of CMOS over the PMOS and the NMOS

• High speed
• Low power consumption
• Improved noise margin

What is indicated by the broken or dotted line in the symbol of the PMOS and NMOS?   

• The dotted line in the PMOS or NMOS indicates that there is no conducting channel between electrodes.

Why the fan out of the CMOS is very high?                

• The fan out of the CMOS is very high because it draws almost zero current from the driving gate.

Why the CMOS is faster than that of NMOS?  

• The CMOS is faster than that of the NMOS because its output impedance is small as compared to that the NMOS.

Describe the effect of supply voltage on the noise margin of the CMOS.     

• As the supply voltage increases the noise margin of the CMOS is also increases.

Why the CMOS is preferred in noisy environment? 

• The CMOS is preferred in noisy environment because its noise margin is only 30% of supply voltage.

Why the CMOS is also called as bilateral transmission gate or bilateral switch?         

• The CMOS is also called as bilateral switch because it transmits signals in both directions.

Name two unidirectional gate logic devices.       

• ECL and TTL

At which condition, the control transmit signal from input to output in the CMOS transmission gate?

• The control transmit signal from input to output in the CMOS gate when the CONTROL is HIGH.

Describe the effect of supply voltage and frequency on the power dissipation of the CMOS

• As the supply voltage and frequency increases the power dissipation of the CMOS increases.

Describe the effect of supply voltage on the speed of the CMOS gate.

• As the supply voltage increase the speed of the CMOS gate increases.

Why the power consumption is very low in the dynamic MOS logic?

• The power consumption of the dynamic MOS logic is very low because of inherent capacitance of the MOS transistors to store logic levels.

What do you mean by interfacing?   

Interfacing

• The interfacing means the output of the one circuit is connected to the input of the other circuit that has different characteristics.

Explain the term : Two phase non – over lapping clock     

Two phase non – over lapping clock

• The dynamic MOS inverter consists of two control signals that are used to control the transistors. 
• These two control signals together are called as two phase non – over lapping clock.

Which type of interfacing logic is used in the De – multiplexers? Why?     

• The transfer of input data in the De – multiplexer is at a faster rate and output data at slower rate therefore ECL to TTL interfacing logic is used.

Which type of interfacing logic is used when the input data handle much lower rate than the output data?

• TTL to ECL logic

Which type of interfacing logic is used for low input current and high output current logic?  

• CMOS to TTL logic

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