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High-res display, older processor give eBooks second wind

Posted: 27 Jun 2008 ?? ?Print Version ?Bookmark and Share

Keywords:eBook? display technology? processor? user interface?

Sony Corp.'s Portable System Reader (PRS) 500 boasts a new high-contrast, high-resolution display that can be read in bright sunlight and offers a near 180 viewing angle.

Electronic readers, or eBooks, have been around for a while but never really had a significant impact on the market. The biggest complaint was that it was hard on the eyes to look at the display for long periods of time. The user interface wasn't the greatest either.

Sony Corp. thinks it has solved those problems, with the help of a key supplier, E Ink. Its Portable System Reader (PRS) 500, which recently dropped under $300, is about a half-inch thick (about 7-inch x 5-inch in length and width) and weights just 9oz. The readable display area measures 6 inches diagonally, which is about the same as one page in a paperback book.

High-res display
With E Ink's technology called Vizplex, the high-contrast (four-level grayscale), high-resolution (170 pixels/inch) display can be read in bright sunlight and offers a near 180 viewing angle.

The Vizplex imaging film is designed for high performance with black and white electronic ink pigment formulations. It's brighter and offers a faster response time compared with the previous generation active-matrix imaging film. In addition, it can be manufactured in larger sizes, up to 9.7 inches.

To create the imaging film, a microencapsulated electronic ink is coated onto an indium-tin-oxide- coated plastic substrate in a roll-to-roll process. The resulting ink film is combined with a thin adhesive and a plastic release sheet to form the Vizplex imaging film. The film is then converted into individual sheets and packaged for shipment to the TFT display manufacturer.

With Vizplex, E Ink leverages the existing infrastructure used in the manufacture of conventional active-matrix LCDs (AMLCDs), but the E Ink process flow for display-cell assembly is actually simpler. The process used to attach the Vizplex imaging film to the TFT panel is similar to polarizer lamination for AMLCDs and uses similar equipment. Other steps, such as the scribe and break processes, are identical to processes for the AMLCDs.

Memory, battery upgrade
The eBook is designed with 64Mbyte internal memory, which the company claims is enough to store about 80 books. If that's not enough, there's a slot for a Memory Stick or an SD memory card.

Battery life was a little hard to determine, as I didn't get a chance to wear the battery down completely. But Sony claims that the battery will last for up to 7,500 continuous page turns on one charge. Charge time is about 4 hours using AC power or 6 hours through USB.

The Li-ion battery is mounted to the back of the display, which I thought was a little odd, and a tribute to the E Ink technology. I would have thought that the heat generated by the battery would distort the information on the display, but obviously not.

Older processor
The processor that's inside the reader is not exactly state of the art. It's a Freescale Semiconductors' DragonBall i.MXL applications processor, also known as the MX1 (or more specifically the MC9328MXL), that was designed around 2002. It was Freescale's first ARM-based processor, incorporating a 200MHz ARM920T core. The core is surrounded by all the usual peripherals, like a UART, a memory interface and a SPI interface. It's also got an integrated Memory Stick interface, which Sony took advantage of.

While the PRS-500 is fairly new to the U.S. market, it's been available in Japan for a number of years. That likely explains the use of the older microprocessor. Even though newer version of the i.MX family is available, Sony would have had to make changes to the software if they changed processors. Some of the software could likely have been re-used, but that would depend on which processor they chose to upgrade to. While a DSP would seem to be a likely choice for a CPU upgrade, that would require a significant change to the operating system stack.

The PRS 500 is based on an older Freescale application processor, DragonBall i.MXL, designed around 2002.

For designs like the Sony eBook, Freescale is now promoting its i.MX31 microprocessor, based on the ARM11 core and runs at 533MHz. It's not the company's latest offering, but it's well suited for an eBook design.

"If they did want to switch processors, we'd probably be heavily involved," says Boris Bobrov, manager of Freescale's multimedia applications division customer projects office. "We have a customer support team in Japan that could have engaged with Sony if they needed our help. Depending on the customers' wants and needs, we can be on-site for them or not. In addition to assisting with the software, we can review schematics for the hardware or layout."

Design challenges
One of the difficult parts of this design, at least on the hardware side, came from the high-speed buses that are employed. That brings integrity issues into play, making sure that you optimize your layout. For example, care must be taken in how you connect the Mobile DDR memory bus to the microprocessor. Freescale writes some very specific application notes to help designers navigate through these trouble spots.

On the software side, Sony had to write the application on top of the OS. That can also get tricky as the proper drivers must be loaded as needed. This is where the power management comes in to play as well. You want to ensure that only the peripherals that are needed are turned on at any given time.

Some special circuitry was required due to the fact that the E Ink architecture was employed, rather than a standard LCD. The system that I took apart used a Ricoh R5C807 to enable the E Ink technology. However, I've learned that the reference design that's used by E Ink, as well as the latest eBook platforms from Sony, make use of an Actel ProASIC3 FPGA. Both devices also serve as an interface to the external memory cards.

The FPGA, which functions as a display driver interface, takes the input from the host processor and acts as a bridge interface to that processor. The FPGA is also used for various lookup tables and display and power drivers. These functions are needed to implement E Ink's "blanking" process, where they store the drivers needed to display the next "page" in the book. In other words, one page must go blank (or black) before the next one can be loaded.

Martin Mason, a senior director at Actel, admits that this was one of the more difficult challenges in the design. "It's not so much a function of the drive electronics. It's more a function of the display technology itself." Actel claims that the security and low-power features of the ProASIC3 drew Sony to the part.

- Richard Nass

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