Transistor–transistor logic 47769 225828639 2008-07-15T16:17:46Z Epbr123 1395162 Reverted edits by [[Special:Contributions/OrgasGirl|OrgasGirl]] to last version by Iridescent (using [[WP:HG|Huggle]]) [[Image:68k ttl.jpg|right|thumb|300px|A [[Motorola 68000]]-based computer with various TTL chips mounted on [[protoboard]]s.]] '''Transistor–Transistor Logic''' ('''TTL''') is a class of [[digital circuit]]s built from [[bipolar junction transistor]]s (BJT), and [[resistor]]s. It is called ''transistor–transistor logic'' because both the logic gating function (e.g., [[logical conjunction|AND]]) and the amplifying function are performed by transistors (contrast this with [[Resistor–transistor logic|RTL]] and [[Diode–transistor logic|DTL]]). It is notable for being a widespread [[integrated circuit]] (IC) family used in many applications such as [[computer]]s, industrial controls, test equipment and instrumentation, consumer electronics, [[synthesizer]]s, etc. Because of the wide use of this logic family, signal inputs and outputs of electronic equipment may be called "TTL" inputs or outputs, signifying compatibility with the voltage levels used. ==History== [[Image:TTL Clock.jpg|right|thumb|300 px|A real-time clock built of TTL chips designed about 1979.]] TTL logic was invented in 1961 by James L. Buie of [[TRW]], "particularly suited to the newly developing integrated circuit design technology."<ref> Buie, James L. “[http://www.google.com/patents?id=tZAdAAAAEBAJ&pg=PA1965&dq=3,283,170&source=gbs_selected_pages&cad=0_1 Coupling transistor logic and other circuits],” U. S. Patent 3,283,170 </ref> The first commercial integrated-circuit TTL devices were manufactured by [[Sylvania Electric Products|Sylvania]] in 1963, called the Sylvania Universal High-Level Logic family (SUHL).<ref> http://www.computerhistory.org/semiconductor/timeline/1963-TTL.html The Computer History Museum, 1963 Standard Logic Families Introduced, retrieved 2008 April 16 </ref> 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 with military temperature range in 1964 and the later [[7400 series]] of ICs, specified over a lower range, in 1966. The Texas Instruments 7400 family became an industry standard. Compatible parts were made by [[Motorola]], [[AMD]], [[Fairchild]], [[Intel]], Intersil, [[Mullard]], [[Siemens]], [[Signetics]], SGS-Thomson (STMicroelectronics Inc.), [[National Semiconductor]] and many other companies, even in the former Soviet Union. Not only did third parties make compatible TTL parts, but compatible parts were made using many other circuit technologies as well. The term "TTL" is applied to many successive generations of [[BJT|bipolar]] logic, with gradual improvements in speed and power consumption over about two decades. The last widely available family, 74AS/ALS Advanced Schottky, was introduced in 1985.<ref>{{cite web|url=http://www.ti.com/litv/pdf/sdaa010|author=Texas Instruments|title=Advanced Schottky Family}}</ref> As of [[2008]], Texas Instruments continues to supply the more general-purpose chips in numerous obsolete technology families, albeit at increased prices. Typically, TTL logic chips integrate no more than a few hundred transistors. Functions within a single package generally range from a few [[logic gate]]s to a microprocessor [[bit-slice]]. TTL also became important because its low cost made digital techniques economically practical for tasks previously done by analog methods.<ref> *Don Lancaster, "TTL Cookbook", Howard W. Sams and Co., Indianapolis, 1975, ISBN 0-672-21035-5, preface </ref> The [[Kenbak-1]], one of the first [[personal computer]]s, used TTL for its [[CPU]] instead of a [[microprocessor]] chip, which was not available in 1971.<ref>{{cite web | url = http://www.vintage-computer.com/kenbak-1.shtml | title = Kenback-1 | work = Eric Klein's Vintage Computers}}</ref> The 1973 [[Xerox Alto]] and 1981 [[Xerox Star|Star]] workstations, which introduced the [[graphical user interface]], used TTL circuits integrated at the level of ALUs and bitslices, respectively. Most computers used TTL-compatible logic between larger chips well into the 1990s. Until the advent of [[programmable logic]], discrete bipolar logic was used to prototype and [[hardware emulation|emulate]] [[microarchitecture]]s under development. ==Theory== [[Image:TTL npn nand.svg|thumb|Simplified schematic of a two-input TTL [[Sheffer stroke#NAND gate|NAND gate]].]] [[Image:7400 Circuit.svg|thumb|Standard TTL NAND, one of four in 7400]] TTL contrasts with the preceding [[resistor–transistor logic]] (RTL) and [[diode–transistor logic]] (DTL) generations by using transistors not only to amplify the output, but also to isolate the inputs. The [[p-n junction]] of a [[diode]] has considerable [[capacitance]], so changing the logic level of an input connected to a diode, as in DTL, requires considerable time and energy. As shown in the top schematic at right, the fundamental concept of TTL is to isolate the inputs by using a [[common-base]] connection, and amplify the function using a [[common emitter]] connection. Note that the base of the output transistor is driven high only by the forward-biased base–collector junction of the input transistor. The second schematic adds to this a "totem-pole output". When V<sub>2</sub> is off (output equals ''1''), the resistors turn V<sub>3</sub> on and V<sub>4</sub> off, resulting in a stronger ''1'' output. When V<sub>2</sub> is on, it activates V<sub>4</sub>, driving ''0'' to the output. The [[diode]] forces the emitter of V<sub>3</sub> to ~0.7 [[Volt|V]], while R<sub>2</sub>, R<sub>4</sub> are chosen to pull its base to a lower voltage, turning it off. By removing pull-up and pull-down transistors from the output stage, this allows the strength of the gate to be increased without proportionally affecting power consumption.<ref>[http://www.siliconfareast.com/ttl.htm Transistor-Transistor Logic (TTL) - Page 1 of 2<!-- Bot generated title -->]</ref><ref>[http://www.asic-world.com/digital/gates5.html Digital Logic Gates Part-V<!-- Bot generated title -->]</ref> TTL is particularly well suited to [[integrated circuit]]s because the inputs of a gate may all be integrated into a single base region to form a multiple-emitter transistor. Such a highly customized part might increase the cost of a circuit where each transistor is in a separate package. However, by combining several small on-chip components into one larger device, it reduces the cost of implementation on an IC. As with all [[BJT|bipolar]] logic, a small amount of current must be drawn from a TTL input to ensure proper logic levels. The total current drawn must be within the capacities of the preceding stage, which limits the number of nodes that can be connected (the [[fanout]]). All standardized common TTL circuits operate with a 5-[[volt]] power supply. A TTL input signal is defined as "low" when between 0&nbsp;V and 0.8&nbsp;V with respect to the ground terminal, and "high" when between 2.2&nbsp;V and 5&nbsp;V<ref>[http://www.twysted-pair.com/74xx.htm TTL standard logic level]</Ref> (precise logic levels vary slightly between sub-types). Use of the TTL logic levels was so ubiquitous that complex circuit boards often contained chips made by many manufacturers in different logic families, selected based on availability and cost. Logic gates could often be treated as ideal Boolean devices without concern for harmful electrical incompatibilities. Like most integrated circuits of the period 1965–1990, TTL devices were usually packaged in [[through-hole]], [[dual in-line package]]s with between 14 and 24 lead wires, usually made of epoxy plastic but also commonly ceramic. Beam-lead chips without packages were made for assembly into larger arrays as hybrid integrated circuits. Parts for military and aerospace applications were packaged in flat packs, a form of surface-mount package, with leads suitable for welding or soldering to printed circuit boards. Today, many TTL-compatible devices are available in surface-mounted packages. <!-- As military and aerospace applications tend to lag the IC state of the art, MSI and TTL have remained popular longer in that industry. Reference please! --> ==Comparison with other logic families== Generally, TTL devices consume more power than an equivalent [[CMOS]] device at rest, but power consumption does not increase with clock speed as rapidly as for CMOS devices. Compared to contemporary [[Emitter coupled logic|ECL]] circuits, TTL uses less power and has easier design rules, but is typically slower. Designers can combine ECL and TTL devices in the same system to achieve best overall performance and economy. TTL was less sensitive to damage from [[electrostatic discharge]] than early CMOS devices. Due to the output structure of TTL devices, the output impedance is asymmetrical between the high and low state, making them unsuitable for driving transmission lines. This is usually solved by buffering the outputs with special line driver devices where signals need to be sent through cables. ECL, by virtue of its symmetric output structure, doesn't have this drawback. The typical "totem-pole" output structure often has a momentary overlap between the upper and lower transistors, resulting in a substantial pulse of current drawn from the supply. These pulses can couple in unexpected ways between multiple integrated circuit packages, resulting in reduced noise margin and lower performance. TTL systems usually have a [[decoupling capacitor]] for every one or two IC packages, so that a current pulse from one chip does not momentarily reduce the supply voltage to the others. Several manufacturers now supply CMOS logic equivalents with TTL compatible input and output levels, usually bearing part numbers similar to the equivalent TTL component and with the same pin-out diagrams. For example, the 74HCT00 series provides many drop-in replacements for bipolar [[7400 series]] parts, but uses [[CMOS]] technology. ==Sub-types== Successive generations of technology produced compatible parts with improved power consumption, switching speed or both. Although vendors uniformly marketed these various product lines as TTL with [[Schottky diode]]s, some of the underlying circuits, such as used in the LS family, could rather be considered [[DTL]].<ref>{{cite web|url=http://people.seas.harvard.edu/~jones/es154/lectures/lecture_7/pdfs/215ln04.pdf|author=John Emerson Ayers|title=UConn EE 215 lecture 4|accessdate=2008-05-11}}</ref> Variations of and successors to the basic TTL family, which has a typical gate propagation delay of 10ns and a power dissipation of 10mW per gate, for a power-delay product (PDP) or switching energy of about 100 [[joule|pJ]], include: * Low-power TTL (L), which traded switching speed (33ns) for a reduction in power consumption (1mW) (now essentially replaced by [[CMOS]] logic) * High-speed TTL (H), with faster switching speed than standard TTL (6ns) but significantly higher power dissipation (22mW) * Schottky TTL (S), introduced in 1969, which used [[Schottky diode]] clamps at gate inputs to prevent charge storage and speed switching time. These gates operated more quickly (3ns) but had higher power dissipation (19mW) * Low-power Schottky TTL (LS) — used the higher resistance values of low-power TTL and the Schottky diodes to provide a good combination of speed (9.5ns) and reduced power consumption (2mW), and PDP of about 20 pJ. Probably the most common type of TTL since these were used as glue logic in microcomputers; essentially replacing the former H, L, and S sub-families. * Fast (F) and Advanced-Schottky (AS) variants of LS from Fairchild and TI, respectively, circa 1985, with "[[Miller effect|Miller]]-killer" circuits to speed up the low-to-high transition. These families achieved PDPs of 10 pJ and 4 pJ, respectively, the lowest of all the TTL families. * 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. * [[Radiation hardening|Radiation-hardened]] devices are offered for space applications * Special quality levels and high-reliability parts are available for military and aerospace applications. * Low-voltage TTL (LVTTL) for 3.3-volt power supplies and memory interfacing. ==Inverters as analog amplifiers== While designed for use with logic-level digital signals, a TTL inverter can be biassed to be used as an analog amplifier. Such amplifiers may be useful in instruments that must convert from analog signals to the digital domain, but would not ordinarily be used where analog amplification is the primary purpose. <ref> Darold Wobschall, ''Circuit Design for Electronic Instrumentation: Analog and Digital Devices from Sensor to Display'', Second edition, McGraw Hill, New York, 1987 ISBN 0-07-071232-8, pp. 209-211 </ref> TTL inverters can also be used in [[crystal oscillator]]s where their analog amplifcation ability is significant in analysis of oscillator performance. ==Applications== Before the advent of [[Very-large-scale integration|VLSI]] devices, TTL integrated circuits were a standard method of construction for the processors of mini-computer and mainframe processors; such as the [[Digital Equipment Corporation|DEC]] [[VAX]] and [[Data General]] [[Data General Eclipse|Eclipse]], and for equipment such as machine tool numerical controls, printers, and video display terminals. As [[microprocessor]]s became more functional, TTL devices became important for "glue logic" applications, such as fast bus drivers on a motherboard, which tie together the function blocks realized in VLSI elements. == See also == * [[Resistor–transistor logic]] (RTL) * [[Diode–transistor logic]] (DTL) * [[Emitter-coupled logic]] (ECL) * [[Positive emitter-coupled logic]] (PECL) * [[CMOS|Complementary metal–oxide–semiconductor]] (CMOS) * [[Integrated injection logic]] (I2L) * [[Digital circuit]] * [[Logic family]] ==References== <references /> *Jacob Millman, "Microelectronics Digital and Analog Circuits and Systems", McGraw-Hill Book Company, New York, 1979 ISBN 0-07-042327-X *Paul Horowitz and Winfield Hill, "The Art of Electronics 2nd Ed. " Cambridge University Press, Cambridge, 1989 ISBN 0-521-37095-7 *The Engineering Staff, "The TTL Data Book for Design Engineers", 1st Ed., Texas Instruments, Dallas Texas, 1973, no ISBN *Fairchild Semiconductor, "[http://www.fairchildsemi.com/an/AN/AN-368.pdf Application Note 368]" (for relative ESD sensitivity of TTL and CMOS) ==External links== *[http://focus.ti.com/logic/docs/techdocs.tsp?sectionId=452&tabId=1989&techDoc=1&familyId=1&documentCategoryId=1&viewType=1&techFamId=0 Texas Instruments logic family application notes] [[Category:Digital electronics]] [[Category:Logic families]] [[cs:TTL (logika)]] [[de:Transistor-Transistor-Logik]] [[es:Tecnología TTL]] [[fr:Transistor-Transistor logic]] [[ko:트랜지스터-트랜지스터 논리]] [[it:Transistor-transistor logic]] [[nl:Transistor-transistorlogica]] [[ja:Transistor-transistor logic]] [[pl:Transistor-Transistor Logic]] [[pt:Transistor-Transistor Logic]] [[ru:Транзисторно-транзисторная логика]] [[simple:Transistor-transistor logic]] [[fi:TTL (logiikka)]] [[sv:Transistor-Transistor Logic]] [[uk:ТТЛ-логіка]] [[zh:電晶體—電晶體邏輯]]