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

1. TRANSISTOR TRANSISTOR LOGIC(TTL)

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. 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. 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. 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. 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. 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.  Clamping diodes

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. 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. Disadvantages of TTL
 Large power dissipation.
 Less component density.
 Can operate only on +5 V power supply.
 Poor noise immunity.