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What Is Mini-LED TV?

The real display news from CES 2021 isn’t rollable screens

4 min read
TCL's “ODZero” mini-LED
TCL eliminated the rounded lens and the gap that separated the LEDs from the LCD panel in their previous generation of mini-LED TV
Image: TCL

CES 2021, this year's fully virtual consumer electronics show, kicked off on Monday with Media Day and a flurry of announcements from the largest consumer electronics manufacturers. For these companies, the center of the consumer electronics world is the television—the bigger the screen the better. People generally don't replace their TVs as often as they do their mobile devices, so TV manufacturers are constantly looking for a new display technology or feature that will make that TV on the store shelf seem a lot better than the TV in the family room. Some of these efforts have been more successful than others—3D displays, for example, never caught on.

This year, the TV manufacturers' tech news coalesced around mini-LED technology. LG pitched its “quantum nanocell mini-LED," a technology it somehow turned into the acronym QNED.

TCL touted its “ODZero" mini-LED.

And Hisense, Samsung, and others are also unveiling mini-LED televisions at the show.

To understand what mini-LED is—and isn't—and why it improves the TV picture, it helps to know a bit about what came before it.

First, to be clear, mini-LED isn't a new display technology so much as a new backlight. The picture itself is generated by a liquid crystal display (LCD); how that evolved is an entirely different story.

Originally, LCD displays were lit by fluorescent tubes running behind the screens. Then, as LEDs became available at mass market prices, they replaced the fluorescent tube and the LCD TV came to be called the LED TV (a misrepresentation that still drives me a little crazy). LED has several advantages over fluorescent tubes, including energy efficiency, size, and the ability to be turned off and on quickly.

The first LED TVs used just dozens of the components, either arrayed on the edges or behind the LCD panel, but the arrays quickly grew in complexity and companies introduced what is called “local dimming." With this technology (in which groups of LEDs are turned down or even off in the darkest areas of the TV picture), contrast, a big contributor to picture quality, increases significantly.

Recalls Aaron Drew, director of product development for TCL North America: “We were an early proponent of local dimming in the U.S. market. We had the first TV with what we called contrast control zones in 2016. That array had nearly 100 zones with a total number of LEDs in the hundreds.

There is no industry definition of mini-LED. For us, I would say we introduced our first backlight using mini-LEDs, that had just over 25,000 LEDs and nearly 1000 contrast control zones."

Drew says that he's happy to see other brands join TCL with mini-LED product announcements, but points out that TCL's new display technology is interesting not just because it uses mini-LEDs, but because the company has figured out a way to eliminate the need to maintain space between the LEDs and the LCD panel; in traditional designs, he says, a little space is required to allow lenses to distribute the light evenly.

TCL mini-LED viewTCL's latest mini-LED TVs close the gap between the LED backlight and the LCD displayImage: TCL

“We have a way to precisely control the distribution of the light without a globe shape lens and optical depth," Drew says.

And that reduced optical depth (OD) feature gives the TCL technology the “OD Zero" tag.

This latest generation of TCL LED TVs contain tens of thousands of LEDs and thousands of contrast control zones, the company indicated in its announcement.

Over at LG, the Q of its QNED acronym refers to the quantum dot color film that most LED TVs use today to convert some of the blue LED light into the green and red wavelengths used in an RGB picture. The N, for NanoCell, also refers to that quantum dot layer. The company apparently dropped the L from LED to avoid confusion with its OLED TVs.

LG says these QNED TVs will have almost 30,000 LEDs and 2500 local dimming zones.

LG QNED comparisonLG's new backlight for its LCD displays uses an array of 30,000 mini LEDsImage: LG

None of the mini-LED TV announcements have included pricing to date.

Is mini-LED technology different enough to send the average consumer running to the store to replace a TV they currently own? Without actually seeing these new displays in person—the huge downside of a virtual trade show—it's impossible to tell. My guess, however, is no. But it is different enough to make a mini-LED TV display look better on a store shelf than a non-mini-LED TV parked next to it, so it's not surprising that everybody is jumping into this pool.

Yet to come to the consumer market, and likely to make a much bigger difference in picture quality, is the so-called micro-LED. These use LED components that are small enough to act as pixels themselves, not as backlights for an LCD. The upshot: They lose no brightness to filters and can be turned off individually for true blacks—and they actually deserve to be called LED TVs. While some companies have announced micro-LED displays, these are expensive and gigantic—in the over-100-inch screen size category—and aimed at commercial markets only. Samsung did announce a 110-inch micro-LED model at CES 2021 that will be available in March, but it's hard to see where such an expansive TV display would fit in most homes. Micro-LEDs will have to get even smaller (again, there is no official measurement of “micro") before the prices and the screen sizes make sense for consumers.

And now about those rollable displays. TCL in its online press conference also demonstrated flexible OLED displays; one was in the form of a phone that rolls out to extend the display (LG also teased a rollable phone). TCL's other rollable display came in the form of a scroll about the size of a folded compact umbrella. It unrolls to a 17-inch display. Had there been an in-person CES audience, these would definitely have sparked gasps and rustles in the crowd, but they are likely a long way from appearing on store shelves.

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The Inner Beauty of Basic Electronics

Open Circuits showcases the surprising complexity of passive components

5 min read
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A photo of a high-stability film resistor with the letters "MIS" in yellow.
All photos by Eric Schlaepfer & Windell H. Oskay
Blue

Eric Schlaepfer was trying to fix a broken piece of test equipment when he came across the cause of the problem—a troubled tantalum capacitor. The component had somehow shorted out, and he wanted to know why. So he polished it down for a look inside. He never found the source of the short, but he and his collaborator, Windell H. Oskay, discovered something even better: a breathtaking hidden world inside electronics. What followed were hours and hours of polishing, cleaning, and photography that resulted in Open Circuits: The Inner Beauty of Electronic Components (No Starch Press, 2022), an excerpt of which follows. As the authors write, everything about these components is deliberately designed to meet specific technical needs, but that design leads to “accidental beauty: the emergent aesthetics of things you were never expected to see.”

From a book that spans the wide world of electronics, what we at IEEE Spectrum found surprisingly compelling were the insides of things we don’t spend much time thinking about, passive components. Transistors, LEDs, and other semiconductors may be where the action is, but the simple physics of resistors, capacitors, and inductors have their own sort of splendor.

High-Stability Film Resistor

A photo of a high-stability film resistor with the letters "MIS" in yellow.

All photos by Eric Schlaepfer & Windell H. Oskay

This high-stability film resistor, about 4 millimeters in diameter, is made in much the same way as its inexpensive carbon-film cousin, but with exacting precision. A ceramic rod is coated with a fine layer of resistive film (thin metal, metal oxide, or carbon) and then a perfectly uniform helical groove is machined into the film.

Instead of coating the resistor with an epoxy, it’s hermetically sealed in a lustrous little glass envelope. This makes the resistor more robust, ideal for specialized cases such as precision reference instrumentation, where long-term stability of the resistor is critical. The glass envelope provides better isolation against moisture and other environmental changes than standard coatings like epoxy.

15-Turn Trimmer Potentiometer

A photo of a blue chip
A photo of a blue chip on a circuit board.

It takes 15 rotations of an adjustment screw to move a 15-turn trimmer potentiometer from one end of its resistive range to the other. Circuits that need to be adjusted with fine resolution control use this type of trimmer pot instead of the single-turn variety.

The resistive element in this trimmer is a strip of cermet—a composite of ceramic and metal—silk-screened on a white ceramic substrate. Screen-printed metal links each end of the strip to the connecting wires. It’s a flattened, linear version of the horseshoe-shaped resistive element in single-turn trimmers.

Turning the adjustment screw moves a plastic slider along a track. The wiper is a spring finger, a spring-loaded metal contact, attached to the slider. It makes contact between a metal strip and the selected point on the strip of resistive film.

Ceramic Disc Capacitor

A cutaway of a Ceramic Disc Capacitor
A photo of a Ceramic Disc Capacitor

Capacitors are fundamental electronic components that store energy in the form of static electricity. They’re used in countless ways, including for bulk energy storage, to smooth out electronic signals, and as computer memory cells. The simplest capacitor consists of two parallel metal plates with a gap between them, but capacitors can take many forms so long as there are two conductive surfaces, called electrodes, separated by an insulator.

A ceramic disc capacitor is a low-cost capacitor that is frequently found in appliances and toys. Its insulator is a ceramic disc, and its two parallel plates are extremely thin metal coatings that are evaporated or sputtered onto the disc’s outer surfaces. Connecting wires are attached using solder, and the whole assembly is dipped into a porous coating material that dries hard and protects the capacitor from damage.

Film Capacitor

An image of a cut away of a capacitor
A photo of a green capacitor.

Film capacitors are frequently found in high-quality audio equipment, such as headphone amplifiers, record players, graphic equalizers, and radio tuners. Their key feature is that the dielectric material is a plastic film, such as polyester or polypropylene.

The metal electrodes of this film capacitor are vacuum-deposited on the surfaces of long strips of plastic film. After the leads are attached, the films are rolled up and dipped into an epoxy that binds the assembly together. Then the completed assembly is dipped in a tough outer coating and marked with its value.

Other types of film capacitors are made by stacking flat layers of metallized plastic film, rather than rolling up layers of film.

Dipped Tantalum Capacitor

A photo of a cutaway of a Dipped Tantalum Capacitor

At the core of this capacitor is a porous pellet of tantalum metal. The pellet is made from tantalum powder and sintered, or compressed at a high temperature, into a dense, spongelike solid.

Just like a kitchen sponge, the resulting pellet has a high surface area per unit volume. The pellet is then anodized, creating an insulating oxide layer with an equally high surface area. This process packs a lot of capacitance into a compact device, using spongelike geometry rather than the stacked or rolled layers that most other capacitors use.

The device’s positive terminal, or anode, is connected directly to the tantalum metal. The negative terminal, or cathode, is formed by a thin layer of conductive manganese dioxide coating the pellet.

Axial Inductor

An image of a cutaway of a Axial Inductor
A photo of a collection of cut wires

Inductors are fundamental electronic components that store energy in the form of a magnetic field. They’re used, for example, in some types of power supplies to convert between voltages by alternately storing and releasing energy. This energy-efficient design helps maximize the battery life of cellphones and other portable electronics.

Inductors typically consist of a coil of insulated wire wrapped around a core of magnetic material like iron or ferrite, a ceramic filled with iron oxide. Current flowing around the core produces a magnetic field that acts as a sort of flywheel for current, smoothing out changes in the current as it flows through the inductor.

This axial inductor has a number of turns of varnished copper wire wrapped around a ferrite form and soldered to copper leads on its two ends. It has several layers of protection: a clear varnish over the windings, a light-green coating around the solder joints, and a striking green outer coating to protect the whole component and provide a surface for the colorful stripes that indicate its inductance value.

Power Supply Transformer

A photo of a collection of cut wires
A photo of a yellow element on a circuit board.

This transformer has multiple sets of windings and is used in a power supply to create multiple output AC voltages from a single AC input such as a wall outlet.

The small wires nearer the center are “high impedance” turns of magnet wire. These windings carry a higher voltage but a lower current. They’re protected by several layers of tape, a copper-foil electrostatic shield, and more tape.

The outer “low impedance” windings are made with thicker insulated wire and fewer turns. They handle a lower voltage but a higher current.

All of the windings are wrapped around a black plastic bobbin. Two pieces of ferrite ceramic are bonded together to form the magnetic core at the heart of the transformer.

This article appears in the February 2023 print issue.

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