logic families


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logic families

  1. 1. Logic families Classification Koshys institute of management studies Bangalore
  2. 2. Logic families  Ic technology changes from time to time. The technology depends on following factors  Speed  Power dissipation  Noise immunity  Input/output interface compatibility  Cost
  3. 3. Desirable qualities  High speed  Low power dissipation  High noise immunity  Single output to be obtained from many i/p.  Compatibility : connecting the output of one device to input of other.  Interfacing: design of interconnection between circuits that shift the voltage levels and current levels to make them compatible.
  4. 4. Classification of digital Ic families  Digital IC classified as Bipolar families MOSFET families  Resistor transistor logic(RTL) PMOS Pchannel  Diode transistor logic(DTL) NMOS Nchannel  Transistor transistor logic (TTL) Complementary MOS  Emitter coupled logic (ECL)
  5. 5. TTL  TTL is most popular of ssi and msi.  TTl Uses diodes and transistors for basic NAND gates this technology is called DTL  Diodes were replaced by transistor to improve the circuit operation and this logic family was called TTL.  Built from bipolar junction transistors and resistors .  It is called TTL because both logic gating function and amplifying function is performed by transistors.
  6. 6. TTL APPLICATIONS  Most widely used logic family  In computers  Industrial controls  Test equipment's  Consumer electronics  Military and aerospace.  Ttl is an ex of SSI & LSI
  7. 7. Variation in ttl  Standard ttl  High speed ttl  Low power  Schotty  low powerSchottky  Advanced Schottky  Low voltage ttlSchottky
  8. 8. ECL  Also called as current mode logic  Obtained through bipolar transistor that compute logical functions. CHARACTERISTICS/ advantages  Change state rapidly thus operate at high speed.  Fastest of logic family since propagation time is less than nano seconds.  Does not depend on state of the circuit.  Little power noise is generated.
  9. 9. Disadvantage ,Usage-Ecl  Transistor draw current continuously  Circuit requires more power and wastage is more.  Power requirements:  TTl- 5 volts  Ecl – (-5.2v)negative power supplies.  USAGE  When high performance is required, high speed application.  Older version of Main frame computers.  Super computers and signal processors.
  11. 11. MOS  Unipolar transistor depends on only one type of carrier.  Carrier may be electrons or holes.  Used in Lsi & vlsi  Metal electrode is placed on top of oxide insulator ie the semiconductor material.  Mosfet is used where power consumption is low.
  12. 12. PMOS,NMOS,CMOS  P channel mos is referred as pmos.  P oldest and slowest obsolete.  Nmos n channel and used in circuits with one type of MOS transistor.  Nmos used in microprocessor and memories.  CMOS combination n and p channel.  Cmos is also explained as “Complementary – Symmetry”.  Cmos uses Symmetrical pairs of electronic devices p type and n type.
  13. 13. Characteristics of Cmos  High input resistance.  Compatible output of one device can be connected to another CMOS.  High noise immunity  Low static power  High density on chip  Simple  Protection circuitry  Absorb electric charges with no damage.
  14. 14. Usage Cmos  Microcontrollers, microprocessor, RAM  Image sensors, data converter and integrated transceivers and other types of communication.  Current IBM mainframes .  Digital wristwatches, calculators and portable computers. ADVANTAGE Dissipate less power . Operates on high speed. Low cost More economical operation
  15. 15. Disadvantage  Power consumption increases with clock speed.  Higher noise COMPARISONS TTL,ECL,CMOS Ttl Ecl Cmos Power consumption increase with clock speed Power consumption is high Power consumption does not increase Less sensitive elecrostatic discharge More sensitive electrostatic discharge Nand gate Nor gate Not gate