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transistor transistor logic


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7400 TTL series.
Two input TTL-NAND Gate.
Totem-pole output stage of TTL.
Advantages –disadvantages of totem-pole.
Clamping diodes.
5400 series.
Advantages –disadvantage

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transistor transistor logic

  2. 2. CONTAIN:  7400 TTL series.  Two input TTL-NAND Gate.  Totem-pole output stage of TTL.  Advantages –disadvantages of totem-pole.  Clamping diodes.  5400 series.  Advantages –disadvanges of TTL.
  3. 3. 7400 TTL Series o TTL ICs first developed in 1965 and they are known as “standard TTL” . This version of TTL circuit is not available now. o TTL family use only transistor to perform the basic logic operations. o The standard TTL is improved to a great extent over the year. o TTL devices are still used as “glue” logic which connects more complex devices in digital system.
  4. 4. Two Input TTL-NAND Gate  The first, let us replace transistor Q1 by its equivalent circuits.  A and B are the input terminals.  The i/p voltage A and B can be either low (zero volts ideally) or High (+Vcc ideally).  A and B both low : If A and B both are connected to ground, then both the B-E junction of the transistor T1 are forward biased.
  5. 5. Totem – pole Output Stage of TTL  The arrangement of Q1 and Q2 on the output side of a TTL NAND gate is called the totem-pole arrangement.  In this circuit, the three output component Q1,Q2 and diode D1 are stacked one on the top of the other in the form of totem-pole. At any time, only one of them will be conducting.  The Totem-pole output is also known as Active pull- up.
  6. 6. Advantages and Disadvantages of Totem pole output Advantages:  1. External pull up resistor is not required  2. Operating speed is high Disadvantages:  Output of two gates cannot be tied together
  7. 7. Clamping Diodes  The TTL input should not be subjected in negative voltage.  If voltage transition are applied at the input,then there is a possibility of ringing. Due to ringing the input will be subjected to negative voltages.  To suppress this ringing, clamping diodes are generally connected externally in all the TTL circuits.  This are fast recovery diodes. They are forward during the negative half cycles of the ringing sinusoidal waveform. Hence the negative input voltage will be restricted(clamped)to -0.7 volts approximately.
  8. 8.  Clamping diodes
  9. 9. 54000 Series  The devices of 5400 series oprate over the temperature range of -55 to 125˚c and over the suppl voltage range of 4.5 to 5.5 volts.  5400 TTL series developed specially for the milatry applications.
  10. 10. ADVANTAGES of TTL  TTL circuit are fast.  Low propagation delay.  Power dissiparation is not dependent on frequency.  Compatibale to all the other families.  Latch ups do not take place.  These are not susceptible to the damage due to static charges.
  11. 11. Disadvantages of TTL  Large power dissipation.  Less component density.  Can operate only on +5 V power supply.  Poor noise immunity.