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What Is an Analog Integrated Circuit (IC)?

By Geisha A. Legazpi
Updated May 16, 2024
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An analog integrated circuit (IC) is a basic component in most electronic devices, the most basic circuit that is a part of a larger electronic circuit. Examples of analog integrated circuits are operational amplifiers, power management circuits, and sensors; the most well-known and long-lived analog integrated circuits are the 741 operational amplifier and the 555 timer. An analog integrated circuit is what makes computers, cell phones, and digital devices work, and it can be found inside almost every consumer electronics available to mankind today. It is still used when there is a need for higher power applications and wideband signals that need sampling rate requirements, and for user interface with a transducer.

An analog integrated circuit involves an output signal that follows a continuous input signal. In the initial stage, known as the input stage, the voltage or signal is received from a source. The second stage, or the gain stage, is when amplification occurs that boosts the signal received so it can be processed more effectively. The outgoing signal is either limited or expanded in the last stage, called the output stage.

Depending on the design of the IC, the open loop voltage gain does not need to be in the upper range. These continuous signals perform functions like amplification, mixing, demodulation, and active filtering. An analog integrated circuit will be made up of semiconductors, inductors, capacitors, and resistors. For most electronic companies as well as their engineers and designers, an analog integrated circuit helps by having an available circuit on hand instead of making one. Rather than make an analog circuit from scratch, they can choose from the various options that circuit designers have already made.

This does not mean, however, that all analog integrated circuits are good enough on every electronic device. Some problems have to be resolved first before making the device. Most of these problems occur because the signal value will always change, which is more or less 20% of the original voltage or signal value. One particular problem though is that each processed semiconductor wafer is different on each electronic device.

A circuit designer can simply use a board-level design to select and test devices based on industry values. On the other hand, an analog integrated circuit will have the designer try to find that perfect balance before incorporating it to the electronic device. Currently, more circuit designs adapt mixed signal processing by which the designer replaces some analog functions with digital logic elements to allow the chip to “talk” with the microprocessor.

A Quick History of Analog Integrated Circuits

The invention of the integrated circuit ushered in a world of innovation. Computers, smartphones, medical diagnostic equipment, digital cameras, many kitchen appliances, space exploration technologies, and even modern digital wristwatches would not be possible without it.

With all the devices that use ICs, it almost feels like they’ve been with us forever. That’s not true, of course, but they do have a significant history. From the humble transistor to modern ICs, the story of integrated circuit development is fascinating indeed.

Transistors and Solid-State Electronics

The story of the analog integrated circuit’s development really begins with the creation of the transistor in 1947. The key was controlling the flow of electricity through a crystal, which allowed solid-state electronics to develop. Solid-state components are smaller, cheaper, and more durable than vacuum tubes — important features that eventually led to the creation of integrated circuits.

The First Integrated Circuit

The quest to make smaller circuits birthed the first integrated circuit in 1958. Jack Kilby, its inventor, was an engineer at Texas Instruments. As he thought about circuit design, he stumbled on a groundbreaking idea. Silicon wasn’t just for making transistors: It could be used to make every part of a circuit.

Building an entire circuit out of one crystal seems simple to us now, but it was an extraordinary idea back in the late 1950s. Smaller circuits would be easier to mass-produce. Kilby explained the idea to his manager, who then told him to build one. Kilby’s working model of the monolithic integrated circuit was completed by September. Texas Instruments filed its patent on the invention in February 1959.

Kilby wouldn’t be the only one creating integrated circuits in the late 1950s. At Fairchild Semiconductor, physicist Robert Norton Noyce also considered how to create an entire circuit on a single chip. Noyce used a different approach to connect the individual components, which resulted in an invention called a unitary circuit. Noyce knew about TI’s patent, so he wrote extremely detailed documentation about his new circuit. In 1961, the U.S Patent Office approved Noyce’s application.

Because Kilby’s patent was still in review, Noyce received an integrated circuit patent first. Texas Instruments launched a patent war in response. It was finally resolved in 1966 with a cross-licensing agreement.

The Development of Analog Integrated Circuits

Analogue integrated circuit design as we know it dates to the early 1960s. The first commercial version, the Fairchild µA702 operational amplifier, was created by engineers David Talbert and Robert Widlar in 1964. The two-person team followed up with its successor, the µA709, in 1965. A few years later, they’d moved to National Semiconductor and created the LM101. This groundbreaking operational amplifier boasted improved gain plus lower input current and protective measures against short-circuiting.

Not to be outdone, Fairchild Semiconductor debuted a new op-amp in 1967: the µA741, designed by Scottish engineer David Fullagar. He added extra transistors to the LM101, resulting in smoother and more constant amplification. As the company’s successor to the µA709, the µA741 would set the standard for everything after it.

A Time-Tested Innovation

Believe it or not, Fullagar’s design is still in use today. You’ll find the µA741 operational amplifier in equipment such as audio mixers. Texas Instruments is one of the primary producers of the µA741 op-amp. As for the 555 timer, it was first developed by Hans Camenzind for Signetics Corporation in 1971. Camenzind’s final analogue integrated circuit design swapped the 9 pins and constant current source in his original version for an 8-pin setup and direct resistance. The 555 timer is used in many of today’s security systems, especially those with motion detectors and sound-operated timers. It also features in touch-free equipment such as water fountains and bathroom faucets.

Analog Vs. Digital Integrated Circuits

There are a few things you should understand about analog and digital integrated circuits. With analogue integrated circuit design, the IC operates on continuous varying signals ranging from zero to full power supply voltage. Thanks to this broad signal range, they’re sometimes referred to as linear circuits. This capability makes them useful in circuits built for amplifiers and voltage comparators.

On the flip side, digital circuits are considered nonlinear. They operate on discontinuous signals — either “on” or “off,” hence their binary nature. No other values in between are possible. Unlike analog ICs, digital versions do not need external components to work. Digital ICs are often used in microprocessors, memory chips, and many other computing applications.

One key invention helped pave the way for widespread IC production: MOSFET. The metal—oxide—semiconductor field-effect transistor was developed by Bell Labs engineers Mohamed Atalla and Dawon Kahng in 1959. MOSFET enabled higher manufacturing capacity plus the advent of LSI chips, which hold more than 10,000 transistors each.

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Discussion Comments

By nony — On Nov 15, 2011

@allenJo - I was never an electronics guy myself but I did mess around with audio and home theater systems.

In the early days, and I mean long ago, amplifiers used to be made up of tubes. Those amplifiers were big things to lug around but they got the job done.

Then came transistors and then the IC chips. I’ve never understood the electronic theories behind the circuitry but judging from the article I can see where the IC chip is suitable as an amplifier circuit.

Another thing I’ve noticed is that nowadays these chips can be super small, yet have more transistors on them than comparable chips twenty years ago. So we are getting more bang for the buck in our amplification, and I think this translates into greater power for small devices like cell phones.

By allenJo — On Nov 14, 2011

I used to mess around with electronics years ago before I got into personal computers. I never came up with circuits on my own but just followed schematic diagrams from books and built the circuits according to the specifications.

But how well do I remember the 555 timer IC chip. This timer is the most popular of its kind; at least it was when I was building circuits. It was very versatile, and you could use it to create timer based circuits that operated at intervals from a few milliseconds to a whole year in duration.

That’s right, you could create an “alarm” that would go off in a year’s time. What was also neat is that the IC chip didn’t need many connections for it to work properly. It was just a few connections and you were good to go.

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