science

Transistor–transistor logic

Transistor–transistor logic is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Transistor–transistor logic rather than just read about it. In short: Transistor–transistor logic (TTL) is a logic family built from bipolar junction transistors (BJTs). Its name signifies that transistors perform both the logic function (the first "transistor") and the amplifying function (the second "transistor"), as opposed to earlier resistor–transistor logic (RTL) and diode–transistor logic (DTL).

Key takeaways

Transistor–transistor logic belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Transistor–transistor logic to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Transistor–transistor logic from memory before moving on to harder problems.

Reference excerpt

Transistor–transistor logic (TTL) is a logic family built from bipolar junction transistors (BJTs). Its name signifies that transistors perform both the logic function (the first "transistor") and the amplifying function (the second "transistor"), as opposed to earlier 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. After their introduction in integrated circuit form in 1963 by Sylvania Electric Products, TTL integrated circuits were manufactured by several semiconductor companies. The 7400 series by Texas Instruments became particularly popular. TTL manufacturers offered a wide range of logic gates, flip-flops, counters, and other circuits. Variations of the original TTL circuit design offered higher speed or lower power dissipation to allow design optimization. TTL devices were originally made in ceramic and plastic dual in-line package(s) and in flat-pack form. Some TTL chips are now also made in surface-mount technology packages. TTL became the foundation of computers and other digital electronics. Even after Very-Large-Scale Integration (VLSI) CMOS integrated circuit microprocessors made multiple-chip processors obsolete, TTL devices still found extensive use as glue logic interfacing between more densely integrated components.

History

Early transistor-coupled logic circuits were described in 1962 by R. H. Beeson and H. W. Ruegg of Fairchild Semiconductor in “New Forms of All-Transistor Logic,” presented at the IEEE International Solid-State Circuits Conference, where the approach was explicitly referred to as transistor–transistor logic (TTL or T²L). Around the same time, at Pacific Semiconductor (later acquired by TRW), James L. Buie described similar circuits as transistor-coupled transistor logic (TCTL), distinguishing them from diode-coupled transistor logic (DCTL). As later summarized by the Computer History Museum, these developments occurred in parallel at multiple companies during the early 1960s. In 1962, Gordon Moore, then at Fairchild, referred to this approach as T²L and noted that although it was simple and well suited to integration, it suffered from reduced noise immunity and “current hogging,” limiting fan-in and fan-out; adding the components needed to correct these shortcomings reduced its advantages. Fairchild subsequently pursued diode–transistor logic as its next production family. By the mid-1960s, a wide variety of logic families were in use, including RTL, RCTL, DCTL, LLL, CML, and DTL, with TTL emerging as an additional family. Work at Sylvania under Tom Longo refined transistor-coupled logic into a commercially supported family, introduced in 1963 as the Sylvania Universal High-Level Logic (SUHL). Patents for the design were applied for in May and June 1963. The Sylvania parts were used in applications including the controls of the Phoenix missile. Texas Instruments later standardized and popularized TTL with the 5400 series in 1964 and the 7400 series in 1966. In later oral history, Tom Longo stated that Texas Instruments’ early 54-series implementation closely followed the circuit configuration he had described publicly in 1963, while differentiating its products through relocating the power supply pins to the package corners, together with packaging, cost reduction, and manufacturing scale. The Texas Instruments 7400 family became a de facto industry standard. Compatible parts were manufactured by numerous semiconductor companies, including Motorola, AMD, Fairchild, Intel, National Semiconductor, Signetics, Siemens, and others, including manufacturers in the Eastern Bloc (Soviet Union, GDR, Poland, Czechoslovakia, Hungary, and Romania). In addition to bipolar implementations, compatible 7400-series parts were later produced using other circuit technologies. At least one major manufacturer, IBM, produced non-compatible TTL circuits for internal use; IBM employed TTL technology in systems such as the IBM System/38, IBM 4300, and IBM 3081. The term "TTL" is applied to many successive generations of bipolar logic, with gradual improvements in speed and power consumption over about two decades. The most recently introduced family 74Fxx is still sold today (as of 2019), and was widely used into the late 90s. 74AS/ALS Advanced Schottky was introduced in 1985. As of 2008, Texas Instruments continues to supply the more general-purpose chips in numerous obsolete technology families, albeit at increased prices. Typically, TTL chips integrate no more than a few hundred transistors each. Functions within a single package generally range from a few logic gates 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. The Kenbak-1, ancestor of the first personal computers, used TTL for its CPU instead of a microprocessor chip, which was not available in 1971. The Datapoint 2200 from 1970 used TTL components for its CPU and was the basis for the 8008 and later the x86 instruction set. 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. Most computers used TTL-compatible "glue logic" between larger chips well into the 1990s. Until the advent of programmable logic, discrete bipolar logic was used to prototype and emulate microarchitectures under development.

Implementation

Fundamental TTL gate

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Transistor–transistor logic

Start with the simplest possible case. Write down what Transistor–transistor logic claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Transistor–transistor logic before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Transistor–transistor logic ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Transistor–transistor logic

In research: Transistor–transistor logic appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Transistor–transistor logic in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Transistor–transistor logic is common in secondary-school and first-year university syllabi. It links to neighbouring topics Digital electronics, Logic families, so understanding it makes those chapters shorter.
In everyday life: Look for Transistor–transistor logic outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Transistor–transistor logic in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Transistor–transistor logic means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Transistor–transistor logic out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Transistor–transistor logic in simple terms?

Why does Transistor–transistor logic matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Transistor–transistor logic?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Transistor–transistor logic.