7400 series parts were constructed using bipolar transistors, forming what is
referred to as transistor-transistor
logic or TTL. Newer series, more or less compatible
in function and logic level with the original parts,
use CMOS technology or a combination of the two (BiCMOS). Originally the bipolar circuits provided higher speed but consumed more power than the competing 4000 series of CMOS devices. Bipolar devices
are also limited to a fixed power supply voltage, typically 5 V, while CMOS parts often support a range of supply voltages.
devices for use in extended temperature conditions are available
as the 5400 series. Texas Instruments also manufactured radiation-hardened devices with the
prefix RSN, and the company offered
beam-lead bare dies for integration into hybrid circuits with a BL prefix designation.
Regular-speed TTL parts were also available for a time in the
6400 series - these had an extended industrial temperature range
of -40 oC to +85 oC. While companies such as Mullard listed
parts in 1970 data sheets, by 1973 there was no mention of the 6400 family in the Texas Instruments TTL Data Book. Some companies have also offered industrial extended temperature range variants using the
regular 7400 series part numbers with a prefix or suffix to indicate the temperature grade.
As integrated circuits in the 7400 series were made in different
technologies, usually compatibility was retained with the original
TTL logic levels and power supply voltages. An integrated circuit
made in CMOS is not
a TTL chip, since it uses field-effect transistors (FETs) and not bipolar junction transistors, but similar part numbers are retained to identify similar logic functions and electrical (power and I/O voltage) compatibility in
the different subfamilies. Over 40 different logic subfamilies use this standardized part number scheme.
Many parts in the CMOS HC, AC, and FC families are also offered
in "T" versions (HCT, ACT, and FCT) which have input thresholds
that are compatible with both TTL and 3.3 V CMOS signals. The
parts have conventional CMOS input thresholds.
The 74H family is the same basic design as the 7400 family with
resistor values reduced. This reduced the typical propagation
delay from 9 ns to 6 ns but increased the power
consumption. The 74H family provided
a number of unique devices for CPU designs in the 1970s. Many designers of military and aerospace equipment used this family over a long period and as they need exact replacements, this family is still produced by
The 74S family, using Schottky circuitry, uses more power
than the 74, but is faster. The 74LS family of ICs is a
lower-power version of the 74S family, with slightly higher speed
but lower power dissipation than the
original 74 family; it became the most popular variant once it was widely available.
The 74F family was introduced by Fairchild Semiconductor and adopted by other manufacturers; it is faster than the 74, 74LS and 74S families.
Through the late 1980s and 1990s newer versions of this family
were introduced to support the lower operating voltages used in
newer CPU devices.
Copyright © 2008- Ted J. Mieske
All Rights Reserved.