Simple Analog Components
Discrete analog components tend to be physically small because they’re fundamentally simple creations (see Figure 2.4). In the early days of electronics, all components were simple analog components. Since about 1960, engineers have been combining these discrete building blocks to create ever more elaborate, integrated components that tend to be physically larger.
Some analog components are sold as small discrete components; others are combined into larger integrated analog components, seen later. Engineers designing analog products (e.g., radios and some stereo gear) sometimes like to fine-tune their designs by hand-picking each individual analog component. In contrast, engineers designing computers and other large digital products are happy to use ICs, taking their components in bulk. There’s a fair amount of finesse required to design and build complex products from discrete analog components, and engineers gifted with that talent are rare and valuable.
Resistors, capacitors, diodes, and other common analog discrete components are smaller than a penny and cost even less. These analog components are like the insects of the semiconductor world: They are amazingly plentiful and almost totally ignored.
You might sometimes hear electronics aficionados discussing linear components, especially if they’re into short-wave radios or high-end stereo gear. Linear components are a subclass of analog components. Some analog components are linear, and some are nonlinear. Linear describes how these components can take electricity and amplify (increase) or attenuate (decrease) it very smoothly without adding any “coloring” to it. In stereo gear, for example, it’s important to play the music exactly as it was recorded without adding artificial distortion.
Let’s start our tour of the analog kingdom with resistors, probably the simplest and most common type of electrical component (see Figure 2.5). Resistors do pretty much what their name implies: They resist the passage of electricity. Resistors are electronic speed bumps, bleeding off voltage and slowing the electric flow.
If you’re a fan of Newton’s Third Law of motion and Einstein’s E = mc2, you know that energy can’t be created or destroyed, only converted. Resistors convert the electricity they’re resisting into heat; the bigger the value of the resistor, the warmer it gets. Tiny resistors like those you’d find in a portable radio generate so little heat it’s not even noticeable. Some big resistors, though, need metal cooling fins to keep from overheating. In the extreme case, the whole purpose of a resistor is to generate heat. A car’s rear-window defogger or burners on an electric range are both examples of resistors that get hot on purpose.
Although slowing down electric current seems pretty pointless, clever combinations of resistors can adjust voltages to specific and desirable levels. Technically speaking, resistors aren’t really semiconductors because they’re not made from silicon. Most resistors are just powdered carbon stuffed into a hollow tube, like a tiny pencil. Big, high-voltage resistors use coils of heavy wire in place of the carbon, making them essentially electric space heaters.
Resistors are so small that it’s hard to print any markings on them, so they’re identified with colored bands. The colors are a special code that electrical engineers memorize early in their careers. Each color stands for a different number, from nine to zero: black, brown, red, orange, yellow, green, blue, violet, gray, and white.
The next-most common type of analog component is capacitors (see Figure 2.6). Again, the name gives you a hint about its function. Capacitors store small amounts of electricity, like electric shoeboxes. Electricity flows in one end of a capacitor, where it gets stored indefinitely or until the capacitor “overflows.” The bigger the capacity of a capacitor, the more electricity it holds until it overflows.
Capacitors are simply two metal plates separated by a small gap. Electricity can’t jump across this gap, so it builds up at one end of the capacitor. Finally, after enough electricity builds up on one side, the sheer force of all that juice pushes electricity away from the metal plate toward the other side. The net result is a brief time delay in the electric flow. If you’re used to repairing cars, you might remember replacing the condenser, which is just another word for capacitor. The condenser is a big capacitor that stores enough electricity to create a spark in the spark plugs.
Capacitors, like resistors, aren’t technically semiconductors because they aren’t made from silicon. Capacitors usually include two metal plates separated by a piece of plastic, paper, or sometimes just air. To make the capacitors small and compact the plates are wound up into a cylinder like cinnamon rolls.
Inductors are peculiar components that take advantage of magnetic fields to control the flow of electricity. They are basically coils of very fine wire looped around and around a tiny central core. The whole inductor might be only as big as a pencil eraser, but it contains yards and yards of wire. They’re useful to engineers designing radio and cellular equipment, but inductors don’t show up much in computers and other digital products. From the outside, inductors look much like capacitors.
Transistors are a major step up the evolutionary ladder from resistors, capacitors, diodes, and inductors. They’re also the first real semiconductor in our tour of the family tree. (Resistors, capacitors, and inductors are electronic components but they aren’t made from semiconducting materials.) The invention of the transistor in 1947 was a landmark event in semiconductor physics. Transistors changed the way electronic systems are built and paved the way for everything from transistor radios to microprocessors.
Transistors were once called valves, which is a pretty fair description of what they do. A transistor, like a water valve or a spigot, has a place where current flows in, a place where it flows out, and some way to control the flow. Electrically speaking, transistors adjust the “water pressure” of a flowing electric current. They allow one electrical circuit to control another, like hands on valves. You’ll find more discussion of how transistors work in Chapter 9, “Theory.”
Like a water valve, transistors can adjust the flow of electricity in variable amounts. This makes them analog components because they adjust electricity in a continuous stream. Also like a valve, transistors can turn the flow on or off completely, which would make them digital components. The fact is, they’re both. Transistors bridge the gap between analog and digital. They can be used like analog components, smoothly adjusting electrical flow, or they can be used as digital components, acting as on/off switches.
Figure 2.7 shows the first transistor ever made. The electricity flows in through the curly wire on the left and flows out through the wire on the right. The thick wire in the middle controls the flow; it’s the hand on the spigot. The triangular object attached to the wires is a chunk of semiconducting material. In this case, it’s not silicon but a different natural material called germanium. After some experimentation, silicon was found to be a better material and virtually all semiconductors today are made from silicon.
Moore’s Law—a comment made 40 years ago by one of the industry’s early pioneers—has turned out to be a surprisingly accurate prediction of how fast the entire semiconductor industry races forward.
Fairchild Semiconductor’s head of research and development, Gordon Moore, wrote an article in 1965 speculating that his company, and other electronic makers, would be able to squeeze twice as many transistors onto a silicon chip every year. Ten years later, in 1975, his prediction was right on the money. He reduced his estimate going forward, however, forecasting 18 months for each doubling. This became unofficially known as Moore’s Law, and after 30 years, his prediction is still uncannily accurate.
Moore’s Law is often misquoted or misunderstood. Moore said nothing about computer speed, microprocessors, or prices. He restricted his comments to packing transistors onto silicon. Happily, all the other benefits have come about because of the continual advances he projected.
Over the years a number of people, including Moore himself, have unsuccessfully predicted the end of Moore’s Law. Despite many informed prophecies to the contrary, semiconductor progress continues at an astounding pace.
Transistors are still sold individually like resistors and other discrete components (see Figure 2.8). It’s much more common, however, to see transistors grouped together, often by the millions, to create larger and more elaborate integrated components.
Transistors have more or less replaced vacuum tubes in radios and televisions. Like transistors, vacuum tubes used electricity to control the flow of electricity. Linking these together you could make elaborately interrelated electronic circuits. The problems with vacuum tubes were their large size, the frailty of their glass containers, the amount of electricity they used, and the heat they gave off. Transistors perform all the same functions without any of these drawbacks. Except for a few fanatical hi-fi stereo enthusiasts, nobody mourns the passing of vacuum tubes.
Strangely, transistors lead us into the world of digital electronics. This is strange because transistors are analog devices just like resistors or diodes. Electricity passes through them in smoothly varying amounts, like water through a spigot that’s being gradually opened. Yet transistors’ ability to turn the electric flow on and off—like shutting off the spigot completely—opened the door to a new kind of electronics and a new way of thinking. Digital electronics owes its existence to transistors and to the many different and unexpected things transistors can do when they’re used in large numbers.
Diodes make one-way streets for electricity. Electricity can flow through a diode in one direction but not the other. This makes diodes good for controlling the flow of electricity, directing it to where it’s needed. From the outside, diodes look very much like resistors but without the colored bands.
There’s a special kind of diode that gives off light, so it’s called, obviously enough, a light-emitting diode (LED), shown in Figure 2.9. Although LEDs work just like normal diodes do, they’re more interesting for their lighting ability than for their one-way electrical characteristics. When electricity tries to pass through an LED in the “wrong” direction, it is stopped, just like a normal diode. However, when electricity passes through in the right direction, the LED glows. (For you physicists, the energy of the electricity is converted to visible light.)
LEDs come in a few different colors, but red is the most common by far. Most home electronics, like your VCR, microwave oven, television, or bedside clock probably use red LEDs. They glow red simply because the chemicals used to make LEDs happen to give off that color; it was not an intentional choice.
You might see clear or “white” LEDs from time to time. These are actually special red LEDs that have a color-filtering lens that blocks the red light, like tiny sunglasses. Filtering out colors like that is inefficient, so clear LEDs waste more electricity than colored LEDs.
Researchers have tried to make blue LEDs for a long time, with little success until recently. Why the big deal over one color? The combination of red, green, and blue LEDs would allow manufacturers to make LED television sets and dispense with big, heavy, expensive glass picture tubes. The combination of red, green, and blue (RGB) lights can create any color the eye can see. Without blue, LED TV wouldn’t be worth watching.
With different chemicals inside, LEDs can be made to glow in different colors. Yellow and green LEDs are popular, but blue LEDs are exceedingly rare and expensive. It’s hard to find a natural substance that makes good diodes that can also give off light. There are infrared LEDs that glow in colors you can’t see. These LEDs glow in “invisible light” in the infrared spectrum. The remote control for your TV probably uses one of these. Press a button on your remote control; do you see any lights blinking on the front? Probably not, because the LED in your remote emits a color of light your eye can’t see but your television can.
If you have a video camera or camcorder, try videotaping yourself as you operate the remote control for your TV. Even though you can’t see the light coming out of the infrared LED in the remote control, your video camera probably can. Play back the tape to see your remote blinking its secret signals to your television. Other remote controls (for your VCR, etc.) probably work the same way.
LEDs are now being used in car taillights, brake lamps, and city traffic lights because they’re smaller and more rugged than light bulbs. One or two LEDs in a cluster can burn out, but the traffic light will still work. LEDs also light up faster than bulbs do. Some sharp-eyed people report seeing traffic signals “flash” when they turn red because LEDs don’t warm up the way traditional bulbs do.
At the extreme end of the LED family tree are laser diodes, which are tiny lasers, no bigger than a pencil eraser. We’ve all seen laser diodes used as high-tech pointers in business presentations—they’re a kind of nerd chic—but they’re also common in the home. Every stereo CD player, DVD movie player, portable CD player, in-dash car CD player, and CD-ROM drive or DVD-ROM in a computer uses a laser diode. Most home video game systems use one, too. These little components have enabled a whole wave of consumer electronics and toys. Who would’ve thought that lasers, the preferred weapon of James Bond villains, would become ubiquitous, harmless children’s toys?
Laser diodes are different from simple LEDs because they give off a narrow beam of laser light instead of glowing in all directions. Laser light travels in a straight line and doesn’t spread out. That’s why laser pointers make a small red spot on the wall instead of lighting up the entire room the way a light bulb would. That’s also why you can’t see a laser unless it’s pointed directly at you, as opposed to an LED that’s visible from anywhere. Creating a laser requires some precision manufacturing, so laser diodes are more expensive than LEDs. The tight beam of a laser diode is just what you want for reading the tiny marks engraved on a music CD or DVD.
Optical sensors are like the reverse of LEDs. Instead of giving off light, they detect light. These look like LEDs on the outside put perform the opposite task. Your TV remote control will have an LED on it, but your TV will have an optical sensor somewhere on the front to detect the light given off by the LED.
Optical sensors can’t really see or recognize images. They can only tell whether the light nearby is bright or dim. If the light flickers, they can tell that, too. That’s how TV remote controls work: by blinking their light off and on in various patterns like an invisible version of Morse code.
Advanced Analog Components
Digital components aren’t the only ones that are integrated into larger ICs. Analog components, too, have been combined in interesting ways. Some, like charge-coupled device (CCD) arrays, open up new kinds of markets and products once they’re integrated. Others, like micro-electrical mechanical sensors (MEMS), seem just plain weird at first glance.
CCD Image Sensors
CCD image sensors form the basis of digital cameras and other interesting image-recognition products. A CCD image sensor is a chip with individual light sensors arranged in a square pattern, or array, like tiles on a bathroom floor. The image sensor might have 100 “tiles” across and 100 up and down, or it might have thousands in each direction. Each individual sensor in this tiled array can sense one dot, or pixel, of light. Together, they can “see” an entire image. The more sensors in the array, the sharper and clearer the image will be, which is why you’ll hear camera experts bragging about how that 20-megapixel camera is better than a 3-megapixel camera.
There are other types of images sensors, such as CMOS image sensors, but they all work in basically the same way. Thousands or millions of individual light sensors are arranged in a square pattern on a chip to produce one large, clear image.
Also under the heading of sensors are temperature sensors, pressure sensors, acceleration sensors, magnetic sensors, and many more. Temperature sensors are essentially electronic thermometers, useful for household thermostats as well as many industrial uses. They work by taking advantage of the way some materials behave when they get hot (or cold). Some materials conduct electricity better when they’re warm or when they’re cool. Engineers have discovered exactly how much their properties change and can determine the temperature of the chip by measuring how much electricity it conducts.
Magnetic sensors work in somewhat the same way. Some materials behave differently in the presence of magnetic fields, so chips built around these materials can detect slight differences in magnetism. This is useful in electronic compasses (detecting the Earth’s magnetic field) or even for measuring flaws in bulk steel by sensing slight differences in its magnetic properties.
Chemistry labs and medical labs use small sensors that detect certain smells or gases. Like the temperature sensors, some materials behave differently when they’re exposed to certain gases. Engineers have measured these differences and created chips that give off tell-tale electrical impulses in the presence of, say, oxygen. Like a canary in a coal mine, these chemical sensor chips can detect very minute amounts of gas or poison before laboratory technicians can.
A/D and D/A Converters
Converters bridge the world of analog and digital electronics. There are analog-to-digital converters (usually called A/D converters, or just ADCs) and digital-to-analog converters (called D/A converters, or DACs) that go the other way. Obscure as these components might seem, they’re actually quite common. Every CD player, MP3 player, and portable music player has at least one D/A converter to convert the digital data stream into an analog signal for the headphones or speakers. Some will have two or more DACs, one for each speaker. Any “tapeless” digital telephone answering machine will include an A/D converter that records your greeting and converts it into digital data before storing it in memory chips. Any synthesized voices you might hear emanate from D/A converters.
MEMS are truly the strangest type of semiconductor. Little understood even by industry insiders, MEMS have a devoted following and a greatly confused reputation. Neither digital nor analog, MEMS aren’t even always semiconductors. They might be made of silicon but they don’t always conduct electricity in any useful way. MEMS are basically tiny mechanical devices that just happen to be built using chip-manufacturing techniques.
The term MEMS has nothing to do with memory. It’s short for micro-electrical mechanical sensor, an awkwardly technical description of how they function. MEMS use tiny gears and levers to move things or sense motion on a microscopic scale. MEMS can sniff chemicals, separate blood cells, or measure acceleration—all functions that require mechanical movement and not just electrical current. The fact that MEMS are built using silicon-processing equipment allows them to be incredibly small and relatively inexpensive (see Figure 2.10).
Airbags are probably the most popular use of MEMS. These tiny sensors have microscopic mechanical levers etched into their silicon surface. The lever bends ever so slightly if the chip is knocked hard enough, as in a serious automobile accident. If the lever bends enough it completes an electrical circuit that isused to ignite an explosive charge and inflate the airbag. These miniature accelerometers are very reliable, very small, very inexpensive, and easy to manufacture in high volume, making them a perfect fit for auto industry mass production.
Medium-Scale Digital Chips
Once engineers discovered that transistors could be used as on/off switches for electricity, a whole new field of digital electronics was born. Digital components work by treating electricity as if it were Morse code. Instead of dots and dashes, digital components switch tiny amounts of electricity on and off. Other digital components receiving these transmissions can decode them, like a telegraph operator receiving a telegram. A string of digital components working together can create long chains of elaborate functions as each link adds its ability to that of the others. With enough of these links you can create seemingly intelligent electronic devices, such as computers.
Certain combinations of transistors were useful enough to prepackage them into the first digital ICs. These, in turn, led to more highly integrated ICs, and so on. Digital chips span the scale of complexity from a few hundred transistors per chip to tens of millions of transistors per chip, with many steps along the way.
Logic gates are the starting point for digital electronics. They’re one level up the evolutionary ladder from transistors and the fundamental building blocks for digital clocks, video games, personal computers, and a million other products. A logic gate consists of a few transistors, plus perhaps a few resistors or capacitors. As a general rule of thumb, one logic gate is equivalent to about six transistors.
Gates are so named because they gate, or control, the flow of electricity. Barnyard gates control the flow of cattle; logic gates control pulses of digital electronics. Logic gates aren’t smart but they are logical. They make very simple decisions based on very simple inputs. For example, one type of logic gate is called an inverter. It simply passes its input to its output, but reversed. In Morse code, this would be like converting all the dots to dashes and all the dashes to dots. This is not spectacularly challenging, but it is useful for certain electronic functions.
Other types of logic gates are OR gates (that’s the word “or,” not the letters O-R); AND gates, and exclusive-OR gates. From these come variations such as the NAND (negative-AND) gate, the NOR (negative-OR) gate, and XNOR (exclusive-negative-OR) gate. Buffers, inverters, and the curiously named flip-flop round out the rogues’ gallery of logic gates. If you’d like to know more about logic gates and what they do, take this as an invitation to skip ahead to Chapter 9, “Theory.”
There’s a whole branch of mathematics devoted to the OR, AND, NOR, and other logic functions. Named after English mathematician George Boole, Boolean algebra underpins all computers and digital logic chips. Ask any computer programmer or engineer and they’ll tell you that Boolean logic was the first thing they had to learn.
Boole’s work was later enhanced by Claude Shannon, John Venn (he of the Venn diagram), and Charles Dodgson, an English deacon and part-time mathematician who also wrote children’s books under the name Lewis Carroll.
Logic gates are simple and small so they’re not sold individually. You can buy small chips with collections of AND, OR, XOR, or NAND gates in them for a few pennies (see Figure 2.11). Hobbyists and students often use these small chips to build simple electronic projects.
Highly Integrated Digital Chips
Once the trend toward integrating transistors and other discrete components into larger integrated components was under way, there was no stopping it. Today, big chips contain millions of gates of logic, which implies millions of transistors, resistors, diodes, capacitors, and other basic components all rolled together.
Such highly integrated chips are generically called VLSI components. There’s no specific test for a chip to be considered a VLSI device; anything more than about a million transistors probably qualifies. By that measure, most new chips qualify as VLSI components.
These large-scale digital chips take many forms, from memory chips to microprocessor chips. These are the most complex and elaborate semiconductor components ever created, and their profitability reflects their advancements. Top-of-the-line microprocessor chips can sell for more than $1,000 each. They use the most advanced silicon manufacturing technology and take teams of engineers many years to design and develop.
Memory chips are the most plentiful kind of large-scale digital chips because so many products use so many of them. Your PC probably has at least eight memory chips inside, but it could have 64 or more. Microwave ovens, CD players, alarm clocks, and nearly any other electronic device you can think of, probably all have at least one memory chip inside them.
The world’s semiconductor makers produce about 10 billion memory chips every year. As complex as they are, memory chips are nearly commodities, priced very aggressively and sold in enormous volumes. Prices for memory chips fluctuate daily in electronics markets, and analysts track memory prices like treasured stock portfolios. Over the years, memory production gradually moved from the United States to Japan, and then to Korea, Taiwan, and Singapore. Because memory chips are so price sensitive, their production tends to shift to the cheapest labor pool able to manufacture them.
What do memory chips do? Obviously, they remember, or store, electrical information. That’s not as eerie or as complicated as it sounds. Memory chips are basically arrays of tiny capacitors, those simple analog components for storing electricity. Because the capacitors are very small and arranged in very tight rows, memory chips can hold millions of separate electrical charges at once.
Memory chips come in many different subtypes, which are covered in Chapter 7, “Essential Guide to Memory.” That chapter also explains more about how memory chips work. The two major memory classifications are RAM and ROM. RAM chips can be erased and reused to store different data, whereas ROM chips are permanent, holding data forever.
Communications chips handle data communications between computers, satellites, and buildings. They were once simple “bit pumps” that had no intelligence of their own; they just squirted data down a wire under the control of a computer. Now communications chips have become like microprocessors in their own right, with the intelligence to format, buffer, and massage data before it’s transmitted or unpacking data as it’s received. As the world’s desire for instant communication has increased, the newest generations of communications chips have risen to the challenge.
You’ll find specialized communications chips atop telephone poles and in cellular base station antenna “trees.” They compress and decompress voice conversations on the fly, converting our voices into densely packed (and sometimes encrypted) data packets before sending them down copper wire or optical fiber. On the return trip, these same chips decompress (and decrypt) our friends’ voices and reconstitute them into audio form. As these communications chips get more advanced, telephone companies are able to squeeze more and more simultaneous conversations onto the same wires or fibers.
With the rise of the Internet and the Web, the market for communications chips has taken off. So much data is now transferred through the Internet that intelligent and specialized chips are required at several steps along the way to make sure your e-mail gets to the right place. Some chips perform a sort of Internet triage, separating the high-priority data traffic (e.g., a streaming video broadcast) from the low-priority ones (e.g., e-mail spam). Other chips are used for security, encrypting and decrypting credit card numbers as they pass through the network. The list of communications chips is almost endless and the business of creating them is volatile and fast moving.
Graphics and 3D chips have surged to become a major part of the PC components business since the 1990s. As PCs are used more and more for games, DVD video, and other television-like tasks, the importance of graphics chips has risen. The latest graphics chips are amazingly complex and powerful, using millions of transistors and rivaling some microprocessors for performance and intricacy. In many live-action computer games, the 3D graphics chip works harder than the microprocessor in the PC. Avid PC gamers agonize over what 3D graphics chip to buy and diligently read every product review that comes out.
Apart from PCs, graphics chips are used in home electronics, such as DVD players. High-end computer systems use graphics chips to render complex information for weather forecasting; aircraft design; stress analysis; jet simulation; or nuclear, chemical, and medical research.
The performance and capabilities of graphics chips have risen dramatically over the years. Early graphics chips were little more than a D/A converter and some memory. The computer put data into the memory and the D/A converter turned it into an analog electrical signal for the screen. Now 3D graphics chips rival the microprocessor they’re serving. They render 3D images from mathematical models, generate millions of colors, calculate angles of refraction based on light sources and intensities, hide overlapping objects behind one another, and fade distant objects into the background. The mathematics involved in creating 3D scenes is complex and arcane, and the circuitry involved in making all this happen 60 times per second is impressive. It’s a lot of technology all devoted to entertainment.
Peripheral chips are so named because they are used around the outside edges, or periphery, of computers. Peripheral chips are the gatekeepers or customs agents of a computer, channeling incoming data where it belongs and sending outgoing data on its way.
Peripheral chips control printers, keyboards, speakers, mice, joysticks, or anything else you might plug into your computer. Each peripheral chip specializes in one type of plug-in, so a well-equipped computer will include several different peripheral chips. In addition to computers, peripheral chips are also used in industrial and scientific systems, or anywhere there’s a computer connected to something outside in the real world.
The number and type of peripheral chips change over time as people invent new ways to use computers. Keyboard chips have been available for a long time, but chips for controlling joysticks came later. A few years ago, chips for universal serial bus (USB) and FireWire, two new PC connections, entered the market. Although peripheral chips are fairly complicated, they’re also pretty inexpensive. They’re considered little better than commodities by computer makers, so their prices tend to be low and their life spans short.
Custom Chips: ASICs and ASSPs
Big teams of engineers working at huge semiconductor companies design most large-scale chips. Chip design is difficult work, and the costs are high. However, over the past 10 years or so, the barriers to chip design have crumbled, little by little. Designing a chip is still not easy by any means, but it’s not the mysterious black art it once was. It’s now within the realm of possibility for a medium-sized company to consider designing its very own chip.
Why would you want to? Well, maybe none of the major chip-making companies produce just the chip you’re looking for. Maybe you want a memory chip with a certain capacity, or a communications chip that transmits data a certain way, or a security chip that encrypts information using your special password or code system. There are as many reasons for making a custom chip as there are companies considering it.
The term for these custom chips is application-specific integrated circuit (ASIC). An ASIC is a general term for any chip that is custom designed, as opposed to a chip that’s mass-produced by one of the major chip companies. You don’t have to sell your custom ASIC to anyone. In fact, that’s usually the point. An ASIC gives a competitive advantage to the company that makes it; it’s a secret weapon inside the television, microwave oven, or antilock brake system.
What does “application-specific” mean? The word application in this sense means product. It’s another unfortunate case of a common English word that’s been perverted somewhat by the technical community. Application-specific means the chip is intended for some particular type of product, like elevators or steam whistles. It also implies the chip isn’t very useful outside of that specific market.
ASICs by their nature are custom, so every one is different. An ASIC can be big or small, complex or (relatively) simple. It might include any combination of components from the family tree near the beginning of this chapter. An ASIC might have one or more microprocessors inside, some memory, some analog components, some programmable logic, or nearly anything else.
Designing and building an ASIC isn’t cheap, so companies don’t undertake the task lightly. It can easily cost $1 million in engineering time, materials, and services before the first chip is ready. Companies want some guarantee that the benefits of their ASIC will outweigh the risks and costs of its development. For starters, that means ASICs are created only for high-volume products like digital cameras, cell phones, automobiles, and so forth.
When an ASIC is designed for sale, as opposed to internal use, it’s called an application-specific standard product (ASSP). The “standard product” part implies that the chip is available to anyone who wants to buy it, a sort of noncustom custom chip. There’s no technical difference at all between an ASIC and an ASSP; the distinction is purely economic.
In addition to ASIC and ASSP, custom chips are sometimes called a system-on-a-chip (SoC). This term doesn’t have any specific meaning; it’s used to vaguely describe a particularly large or complex ASIC that includes everything the final product will need, all in a single chip. The world of ASICs, ASSPs, and SoCs is mapped out in more detail in Chapter 8, “Essential Guide to Custom and Configurable Chips.”
Programmable Logic Chips
Many companies would like to develop their own ASIC but don’t have the stomach—or the deep pockets—for it. For them, there is a middle ground, a kind of semicustom chip. These chips are called programmable logic devices (PLDs). Different PLD companies use different terminology, so you’ll also hear them called complex programmable logic devices (CPLDs) and field-programmable gate array (FPGA). These and other types of custom chips are covered in Chapter 8, “Essential Guide to Custom and Configurable Chips.”
Programmable logic chips are like electronic Etch-a-Sketches, ready to use but not really finished. Customers imprint their own design onto them, making their own semicustom chips. Customizing a programmable logic chip is nowhere near as difficult as designing and building a “real” ASIC chip from scratch. Like an Etch-a-Sketch, you can erase the chip and start over any time you want, so there’s no risk.
Programmable logic chips look like normal chips on the outside but they’re “blank” on the inside. They give designers and engineers a chance to play “what if” with theoretical chip designs. In the space of an afternoon, you can create and test half a dozen different chip designs on the same programmable logic chip. PLDs provide a blank canvas for engineers to be creative, and a washable one, too, because a single programmable logic chip can be used over and over. When the design is finally complete, the chip can be permanently installed into a product, where it will operate like any other chip.
There are downsides to all this flexibility. For one, programmable logic chips are slower than other chips. The exact same chip design will run slower in a PLD than it would in an ASIC manufactured by the normal means. Programmable logic chips are also more expensive than their ASIC counterparts. Companies that expect to ship thousands and thousands of chips shy away from using PLDs because of their higher unit price. On the plus side, there’s no million-dollar development cost for a PLD. So although PLDs are definitely cheaper in the beginning, they might be more expensive in the long run.
Microprocessors are the pinnacle of semiconductor development, or at least that’s what the microprocessor makers will tell you. They are the “computer on a chip” so beloved by the popular press. There’s no denying that microprocessors are the most complex and elaborate of all semiconductors or that they’ve forever altered our economic, social, and scientific worlds.
Microprocessors have enabled cheap, anywhere, anytime computing. Computers used to be large, noisy machines owned by governments and tended by teams of scientists in white lab coats. Now they’re in every modern home, car, and telephone, ubiquitous to the point of invisibility. Computers can be cheaper than the batteries they run on. All of this has happened in the span of one human generation.
The first microprocessor was invented in 1971; now 1 billion are sold every few months. Surprisingly, almost none of those microprocessor chips are used in computers. Most people equate microprocessors with PCs but that’s far from the whole picture. Computers are just a tiny fraction of what microprocessor chips are used for. Microprocessors have made a far greater impact in totally unrelated household, entertainment, security, and industrial uses than anyone could have predicted. The computer on a chip actually has very little to do with computers anymore.
Microprocessors have shown themselves to be amazingly adaptable. Like tiny robots, they can be commanded (programmed) to do any number of chores from the mundane to the complex. Instead of predicting the weather or calculating missile trajectories, microprocessors are used more commonly to cook food, turn on the furnace, open garage doors, play music, or blast imaginary space aliens. The average household has about two dozen microprocessors or more, without even counting home computers. The average car includes another dozen microprocessors; some have more than 60. Nearly anything that plugs into the wall or uses batteries is likely to have a microprocessor chip in it.
Microprocessors come in all shapes and sizes, and not all of them are the big, fast chips we see advertised on television. In fact, few microprocessor chips cost more than $5. The overwhelming majority of microprocessor chips are squirreled away inside everyday household appliances and toys. Microprocessor makers have started to specialize, so some chips are good for home appliances, some are for automobiles, some are for video games, and so on. Each variation has its own name or abbreviation.
There are different types of microprocessors, and they all have three-letter abbreviations like CPU, MPU, MCU, DSP, or NPU. For now we’ll treat them all the same and just call them microprocessors. For more in-depth information, turn to Chapter 6, “Essential Guide to Microprocessors,” to see what these chips are all about.