7400 TTL series.
Two input TTL-NAND Gate.
Totem-pole output stage of TTL.
Advantages –disadvantages of totem-pole.
Advantages –disadvanges of TTL.
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
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.
Two Input TTL-NAND Gate
The first, let us replace transistor Q1 by its equivalent
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.
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
The Totem-pole output is also known as Active pull-
Advantages and Disadvantages of Totem
1. External pull up resistor is not required
2. Operating speed is high
Output of two gates cannot be tied together
The TTL input should not be subjected in negative
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.
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
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
Disadvantages of TTL
Large power dissipation.
Less component density.
Can operate only on +5 V power supply.
Poor noise immunity.