Mumbai University > COMPS > Sem 3 > Digital Logic Design and Analysis

Marks: 8 M

Year: Dec 2014

TTL- Transistor Transistor Logic

• This logic family basic TTL gate has improvence over standard DTL gate.
• TTL gate has 3 different type of output configurations:
  1. open collector output
  2. totem pole output
  3. three state output (tristate)
• Totem pole provide less power dissipation, high speed of operation and high fanout
• Standard TTL series of logic families starts with 7404,74586 &74ALs161

• The other two families are for military and industrial application

  54-military

  84-industrial

ECL- Emitter Coupled Logic

• ECL is based on use of current steering switch realised using differential transistor pair.
• ECL is fastest logic family among all and this is due to avoidance of saturation region for application
• Following are characteristics of ECL logic family
  1. Propagation rate is about 1 to 2ns
  2. Noise immunity and power dissipation is worst of all the logic families.
  3. High Level is 0.8V and Low Level 1.8V
  4. it has differential input amplifier, internal temperature and voltage compensated bias network; either follower output
• ECL gate provide both true as well as complemented outputs

CMOS – Complementary Mental Oxide Semicoductor

• MOS logic families has more delay as compared to transistor logic familities
• Following are the typical feature of CMOS
  1. lowest power dissipation
  2. excellent noise immunting
  3. high parking density
  4. wide range of power supply
  5. highest fanout among all logic familes
• Difference