Transistor–transistor logic
TTL integrated circuits (ICs) were widely used in applications such as computers, industrial controls, test equipment and instrumentation, consumer electronics, and synthesizers.
TTL manufacturers offered a wide range of logic gates, flip-flops, counters, and other circuits.
TTL devices were originally made in ceramic and plastic dual in-line package(s) and in flat-pack form.
TTL was invented in 1961 by James L. Buie of TRW, which declared it "particularly suited to the newly developing integrated circuit design technology."
Compatible parts were made by Motorola, AMD, Fairchild, Intel, Intersil, Signetics, Mullard, Siemens, SGS-Thomson, Rifa, National Semiconductor,[5][6] and many other companies, even in the Eastern Bloc (Soviet Union, GDR, Poland, Czechoslovakia, Hungary, Romania — for details see 7400 series).
[7] The term "TTL" is applied to many successive generations of bipolar logic, with gradual improvements in speed and power consumption over about two decades.
[8] As of 2008, Texas Instruments continues to supply the more general-purpose chips in numerous obsolete technology families, albeit at increased prices.
TTL also became important because its low cost made digital techniques economically practical for tasks previously done by analog methods.
[11] The 1973 Xerox Alto and 1981 Star workstations, which introduced the graphical user interface, used TTL circuits integrated at the level of arithmetic logic units (ALUs) and bitslices, respectively.
An approximately constant current flows from the positive rail, through the resistor and into the base of the multiple emitter transistor.
The strength of the gate may be increased without proportionally affecting the power consumption by removing the pull-up and pull-down resistors from the output stage.
The driving stage must absorb up to 1.6 mA from a standard TTL input while not allowing the voltage to rise to more than 0.4 volts.
A TTL input signal is defined as "low" when between 0 V and 0.8 V with respect to the ground terminal, and "high" when between 2 V and VCC (5 V),[22][23] and if a voltage signal ranging between 0.8 V and 2.0 V is sent into the input of a TTL gate, there is no certain response from the gate and therefore it is considered "uncertain" (precise logic levels vary slightly between sub-types and by temperature).
TTL outputs are typically restricted to narrower limits of between 0.0 V and 0.4 V for a "low" and between 2.4 V and VCC for a "high", providing at least 0.4 V of noise immunity.
Beam-lead chip dies without packages were made for assembly into larger arrays as hybrid integrated circuits.
But in an integrated circuit, the additional emitters for extra gate inputs add only a small area.
[28] Compared to contemporary ECL circuits, TTL uses less power and has easier design rules but is substantially slower.
The TTL "totem-pole" output structure often has a momentary overlap when both the upper and lower transistors are conducting, resulting in a substantial pulse of current drawn from the power supply.
These pulses can couple in unexpected ways between multiple integrated circuit packages, resulting in reduced noise margin and lower performance.
Successive generations of technology produced compatible parts with improved power consumption or switching speed, or both.
Although vendors uniformly marketed these various product lines as TTL with Schottky diodes, some of the underlying circuits, such as used in the LS family, could rather be considered DTL.
[29] Variations of and successors to the basic TTL family, which has a typical gate propagation delay of 10ns and a power dissipation of 10 mW per gate, for a power–delay product (PDP) or switching energy of about 100 pJ, include: Most manufacturers offer commercial and extended temperature ranges: for example Texas Instruments 7400 series parts are rated from 0 to 70 °C, and 5400 series devices over the military-specification temperature range of −55 to +125 °C.
Before the advent of VLSI devices, TTL integrated circuits were a standard method of construction for the processors of minicomputer and midrange mainframe computers, such as the DEC VAX and Data General Eclipse; however some computer families were based on proprietary components (e.g. Fairchild CTL) while supercomputers and high-end mainframes used emitter-coupled logic.
They were also used for equipment such as machine tool numerical controls, printers and video display terminals, and as microprocessors became more functional for "glue logic" applications, such as address decoders and bus drivers, which tie together the function blocks realized in VLSI elements.
While originally designed to handle logic-level digital signals, a TTL inverter can be biased as an analog amplifier.
Handheld devices such as graphing calculators and NMEA 0183-compliant GPS receivers and fishfinders also commonly use UART with TTL.
