Competition Shifts to Energy-Saving LCD TVs
Competition Shifts to Energy-Saving LCD TVs
Aug 11, 2009 00:00 Analysis Nikkei Electronics Asia — August 2009
Takuya Otani, Shinya Saeki
The competition is shifting from past battles over image quality, screen thinness and so on, to energy efficiency, marking a dramatic change in liquid crystal display (LCD) television trends. We popped open one of the products leading this trend to take a closer look at the technologies used to slash power consumption.
New energy-efficient LCD TVs are hitting the shelves in large quantity in 2009. The TV accounts for about 10% of total power consumption in the home, and TV manufacturers recognizing that low-power products will be more competitive are engaged in an intense performance competition.
One of the LCD TVs at the cutting edge of the trend is the BRAVIA, from Sony Corp of Japan. The first model to have low power consumption emphasized as a key selling point was the KDL-32JE1, a 32-inch set released in July 2008. Power consumption was only 89W, a 34% reduction from the prior model, and Sony promoted the set as the “Number One power-saving model on the market by a wide margin.” And in fact power consumption was dramatically lower than prior designs. The first 32-inch BRAVIA model, released in Oct 2005, drew 150W, while the 32-inch cathode ray tube (CRT) model of June 2000 drew 220W.
We picked up a Sony KDL-32J5, a 32-inch set released in Feb 2009 as the successor to the KDL-32JE1. The company claims this set’s power consumption is 84W (max luminance mode, all-white screen, max volume). Actual measurement of terrestrial digital broadcasting in the standard mode was 56.45W (Fig 1).
We asked a few specialists, including engineers from TV and backlight manufacturers, to join us in disassembling the set to find out how Sony did it. We discovered that the whole Sony design concept was clearly built around slashing energy consumption. During the same disassembly session, we also took apart the DY-32SDDB LCD TV, a 32-inch set from Dynaconnective Co Ltd of Japan which is stirring up excitement because of its price tag of under Yen50,000.
No Conversion to DC
We discovered two power-saving techniques through our investigation, the first of which was evident as soon as we removed the back panel from the Sony 32-inch LCD TV: there were only two circuit boards (Fig 2).
One of the boards holds the power supply and backlight inverter circuitry, and the other is the signal processor. The engineer from the backlight manufacturer pointed out that most LCD TVs use separate boards for the power supply unit and the backlight inverter circuitry. This turned out to be the case in the Dynaconnective TV, in fact (Fig 6). The boards were integrated into one in the Sony set, though, and our suspicion is that this was done to improve power utilization efficiency.
Most LCD TVs first convert the alternating current (AC) power from the home receptacle into direct current (DC) for the power supply board, which then supplies DC power to the signal processor, inverter circuits, etc. The inverter circuit board converts the DC power from the power supply into high-frequency AC, and uses it to light the cold cathode fluorescent lamp (CCFL).
By combining the power supply board and inverter circuit board, explains the backlight engineer, “AC power from the receptacle is used directly by the CCFL, without converting it back to DC first in the power supply.” While the CCFL requires one AC-DC and one DC-AC conversion in prior designs, these have been eliminated to increase power utilization efficiency. The same engineer estimates this alone cut power by about 10%.
The power supply board was separate from the inverter circuit board because of the lateral development approach used for LCD TVs. The inverter circuit board was usually purchased by the set manufacturer (or panel manufacturer) from the backlight manufacturer as a unit, complete with backlight, and optimized for use with it. The set manufacturer would then assemble all the components. By combining the two boards, says the backlight engineer, “The set developer has to consider total design interactively from the initial backlight development stages, which is very difficult in lateral development.”
Fewer CCFL Tubes Used
As we proceeded with our dissection we pulled out the LCD panel module and panel, revealing the backlight, where the second key power-cutting innovation became apparent.
We immediately noticed that there were fewer CCFL tubes than usual. The set held four U-shaped tubes, so effectively there were eight CCFLs (Fig 3a). “Most recent 32-inch LCD TVs use ten tubes,” revealed the backlight engineer. The Dynaconnective TV uses twelve (Fig 8).
Fewer lamps will of course reduce power consumption, but it is not a trivial feat because it is harder to attain the needed screen brightness, and the wider separation between tubes tends to create light and dark bars on the screen. Sony solved the problem by using functional optical components.
The optical components in the Sony TV are thought to be (starting from the lamp) a patterned diffusion sheet, a microlens diffusion sheet, a lens sheet and a polarizing sheet (Fig 3b). “The patterned diffuser helps suppress tube brightness variations. The three-ply optical sheet is quite special, like having microlenses, and makes effective use of lamp light for display brightness,” suggested the backlight engineer.
It is more common for backlight optical materials to consist of about two layers, a pattern-free diffuser and a diffusion sheet with no lenses. Sony’s backlight, on the other hand, is probably quite a bit more expensive. The backlight engineer estimated that while a standard diffusion sheet is probably a bit over Yen100, the polarizing sheet in the Sony set, for example, is at least Yen1,000. Expensive components like these make it clear that total cost is rising, regardless of how many CCFL tubes they get rid of at about Yen150 apiece. The backlight engineer suggested that Sony had accepted a higher cost in order to achieve lower power consumption.
Less Cost; Simpler Design
An in-depth investigation of the disassembled Sony TV revealed a range of measures designed to lower cost.
Apparently, engineers simplified the design as much as possible to drop costs in an effort to make up for expenses incurred in reducing power consumption.
One example is the timing controller (TCON) circuit board. As evident in the Dynaconnective TV, the most common approach in LCD TVs is to position the TCON board behind the LCD panel module (Fig 6).
In the Sony design, however, we noted an unused screw hole right where the TCON circuit board would have normally been mounted. The TCON circuit itself has been integrated into the interface board, which is positioned behind the LCD panel module (Fig 4). The TV manufacturer engineer commented, “I haven’t seen many examples of integrating the TCON circuit into the interface board. My suspicion is they did it to reduce the parts count and improve productivity, hoping to cut cost. The unused screw hole suggests they used the sheet metal from an older model in another attempt to reduce cost.”
We looked at the main board next, and noticed that the biggest chip on it is clearly marked with an NEC logo (Fig 5).
This is almost certainly the image processing integrated circuit (IC), the core of the BRAVIA Engine 2 picture enhancement technology. The TV engineer who pointed out that the picture showed little evidence of Sony’s care in perfecting the imagery, analyzed the situation thus: “I’ve heard that Sony has outsourced a portion of its image processing IC fabrication, but even so it wouldn’t be at all unusual for the chip to have a Sony logo. While I can’t say for sure, my guess is that they simplified the image processing functionality that TV manufacturers have been so concerned about in recent years.”
In addition, the main board also mounts the silicon tuner module for terrestrial digital broadcasting reception (Fig 5). This is another cost-reduction change, compared to the conventional CAN tuner.
Brightness Competition
One important point in cutting power consumption was hidden from us during our disassembly: luminance. Before we began taking them apart we displayed a test image on both the Sony and Dynaconnective sets in the standard mode.
The TV engineer promptly pointed out that the Sony picture was distinctly dimmer. The Dynaconnective TV has a luminance of 500cd/m2, which is pretty standard for LCD TVs. Sony’s PR Center, however, explained they haven’t disclosed nominal luminance since 2008.
This is not to say that lower luminance indicates that TV performance is in any way inferior. In fact, until now LCD TV makers have been overly conscious of the “spec war,” standing out in the mass merchandiser and other issues, often setting brightness higher than necessary for home viewing. Now that the main thrust of competition is shifting towards saving energy, a review of excessively high luminance would seem to be a perfectly reasonable direction for evolution.
Why so Inexpensive?
A 32-inch LCD TV with a built-in digital videodisc (DVD) player, for only Yen49,800: how?
Distribution giant Aeon Co Ltd of Japan began sale of the DY-32SDDB 32-inch LCD TV with internal DVD player, manufactured by Dynaconnective, from Feb 20, 2009. The sale was limited to only 15,000 units, and the price was between Yen30,000 and Yen40,000 less than the general price level set for similar LCD TVs by major domestic manufacturers. The performance of the LCD panel was pretty standard, though, with 1,366 x 768 pixels resolution, 500cd/m2 luminance and a 3000:1 contrast ratio.
Dynaconnective achieved the low price by procuring LCD panels from Samsung Electronics Co Ltd of Korea at very low cost, and manufacturing the sets in Korea, where costs are lower than in Japan. We wondered if the secret to the lower cost could be found in components other than the LCD panel, though, and took it apart to find out with the help of an engineer from a domestic manufacturer.
ST Reference Design
When we opened the back of the Dynaconnective TV the first thing the TV engineer noticed was that there were a lot of cables, messily arranged (Fig 6). There were six circuit boards, or three times the number in the Sony KDL-32J5.
The signal processing board, tuner circuit board, power supply board, backlight inverter circuit board and LCD panel TCON circuit board were all located behind the LCD panel, while the slot board for the Broadcast Satellite-Conditional Access Systems (B-CAS) card was mounted on the rear of the case. As a result there were considerably more cables than in the Sony design, with complex routings. The TV engineer pointed out that productivity must be very low in assembly, and that no domestic manufacturer would ever consider such a design.
Next we looked at the signal processing board and tuner circuit board, where the key functions of the LCD TV are located (Fig 7). In LCD TVs from domestic manufacturers, advised the engineer, “A single board is used for both, in most cases.” Apparently the Dynaconnective is designed with separate boards deliberately so that it can be shipped to nations with a variety of broadcast standards. In order to handle the Integrated Services Digital Broadcasting Terrestrial (ISDB-T) digital broadcasting standard used in Japan, the tuner module is from Alps Electric Co Ltd of Japan, and the orthogonal frequency division multiplexing (OFDM) IC is from Toshiba Corp of Japan.
Of the other chips, a lot were from STMicroelectronics, a joint Italian-French venture: five types in all, including the Moving Picture Coding Experts Group Phase 2 (MPEG-2) decoding IC, the image processing IC and NOR Flash memory. Seeing these, the TV engineer said, “The signal processing circuit configuration is just about identical to the STMicroelectronics reference design. They didn’t use any custom chips, focusing strictly on lower manufacturing cost and meeting their delivery deadlines instead of trying to make the set stand out through superior display performance.”
Old-Style Backlight
We took apart the LCD backlight used in the Dynaconnective set, probably purchased cheaply from Samsung Electronics (Fig 8), and looked inside. There were four optical sheets, namely a diffusion plate, a lens sheet and two diffusion sheets. The backlight engineer commented, “The configuration is pretty standard for an LCD TV. Some models cut costs even more by using only one diffusion plate and two diffusion sheets in the backlight. Dynaconnective probably added the lens sheet to boost brightness.”
The backlight light source is twelve 3mm CCFL tubes. Compared to the Sony model the tubes are much smaller in diameter, and there are more of them. The backlight engineer added that the design was pretty common among domestic manufacturers two or three years ago.
