25 March 2020

Logic Families Interview Question Answer - 3


31
What is power consumption of the low power TTL as compared to standard TTL?


One tenth ( 1/10 ) times


32
What is meaning of 74L, 74H series of TTL?


74 L : Low power TTL
74 H : High power TTL

33
Why the speed of the standard TTL is very low?


Speed of the TTL
  • The standard TTL operates in the saturation mode.
  • The excess charge carriers in the saturation mode are stored in the base region of the transistor and they must be removed before the transistor is turned off. 
  • The speed of the TTL is very low due to storage time delay.


34
Why the speed of the schottky TTL is faster than the standard TTL?


Speed of Schottky TTL
  • The transistor does not allow operating in the full saturation mode in the schottky TTL therefore the speed of the schottky TTL is faster than the standard TTL.


35
Which type of TTL has lowest power product in the TTL series family?


74ALS ( Advance low power schottky TTL)

36
What is other name of the I2L logic?


Current injection logic

37
Which semiconductor device is used for fabrication of the I2L logic?


Bipolar transistors

38
Describe the advantages and disadvantages of the I2L logic.


Advantages
  • No transients
  • It can be easily integrated on same chip.
  • The power dissipation and propagation delay can be varied over wide range by programming the injector current.

Disadvantages
  • Manufacture process complicated than that of MOS technology


39
Describe the Principle of operation of the ECL logic.


Principle of ECL logic
  • The operation of the ECL logic is based on the current switching in which fixed bias current is switched from collector of one transistor to other transistor.


40
What is the other name of the ECL logic?


Current steering logic or current mode logic

41
Why the ECL is called as fastest of all logic family?


The ECL is the faster logic due to following reasons
  • It has limited voltage swing
  • The charging and discharging of the stray capacitance can be done quickly.
  • The transistor in the ECL does not allow going in the saturation mode therefore the time delay is eliminated.


42
What is reason behind the name ‘ECL’?


The BJTs which are used in the ECL are joined together at the transistor’s emitters ( E ).

43
Describe the advantages and disadvantages of the ECL logic.


Advantages
  • Low switching transients
  • Limited voltage swing

Disadvantages
  • Comparatively high power consumption
  • It is difficult to achieve good noise immunity
  • High cost
  • Cooling problem


44
Why the ECL logic is also called as CML?


The ECL is called as CML ( current – mode logic ) because the fixed bias current switches from collector of one transistor to other transistor.

45
Why the ECL logic is also called as CSL?


The current is steered from one device to other in the ECL therefore it is called as CSL ( Current steering logic ).


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