Transistor–transistor logic

Transistor–transistor logic (TTL) is a class of digital circuits built from bipolar junction transistors (BJTs) and resistors. It is called transistor–transistor logic because transistors perform both the logic function (e.g., AND) and the amplifying function (compare with resistor–transistor logic (RTL) and diode–transistor logic (DTL)).

TTL integrated circuits (ICs) were widely used in applications such as computers, industrial controls, test equipment and instrumentation, consumer electronics, and synthesizers. The designation TTL is sometimes used to mean TTL-compatible logic levels, even when not associated directly with TTL integrated circuits, for example as a label on the inputs and outputs of electronic instruments.

After their introduction in integrated circuit form in 1963 by Sylvania, TTL integrated circuits were manufactured by several semiconductor companies. The 7400 series (also called 74xx) by Texas Instruments became particularly popular. TTL manufacturers offered a wide range of logic gate, flip-flops, counters, and other circuits. Several variations of the original TTL circuit design were developed. The variations offered interchangeable functions that had higher speed or lower power dissipation to allow design optimization. TTL devices were originally made in ceramic and plastic dual-in-line (DIP) packages, and flat-pack form. TTL chips are now also made in surface-mount packages.

TTL became the foundation of computers and other digital electronics. Even after much larger scale integrated circuits made multiple-circuit-board processors obsolete, TTL devices still found extensive use as the glue logic interfacing more densely integrated components.

TTL was invented in 1961 by James L. Buie of TRW, which declared it, "particularly suited to the newly developing integrated circuit design technology." The original name for TTL was transistor-coupled transistor logic (TCTL). The first commercial integrated-circuit TTL devices were manufactured by Sylvania in 1963, called the Sylvania Universal High-Level Logic family (SUHL). The Sylvania parts were used in the controls of the Phoenix missile. TTL became popular with electronic systems designers after Texas Instruments introduced the 5400 series of ICs, with military temperature range, in 1964 and the later 7400 series, specified over a narrower range and with inexpensive plastic packages, in 1966.

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