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Viewer turns iPod video into big virtual hit

Posted: 13 Dec 2007 ?? ?Print Version ?Bookmark and Share

Keywords:virtual display glasses? iPod video teardown? white LED?

Virtual display glasses are nothing new, but improvements have slimmed the package considerably and brought costs to levels more simpatico with consumer budgets. At $199, Myvu's Solo brings iPod video viewing front and center. It weighs in at a modest 118g, a good portion of which is contributed by cables connecting the device to a host iPod.

Once connected, the Myvu Solo is worn like a pair of glasses and has an earbud dangling from each swing-out earpiece. The glasses provide both virtual-display video images and a smoked-plastic viewing window to the "real world" in front of the glasses. The aim is to provide a reasonably immersive video viewing experience while not blinding wearers to the world outside.

There is no diopter adjustment to compensate for imperfect vision. Rather, Myvu has teamed with French ophthalmic optical company Essilor to provide optional "clip on" glasses for those needing correction. Perhaps the design objective of a slimline set of glasses allowed no internal compensation.

iPod goes virtual
The optical path of the imaging for each eye consists of a white LED for illumination, a polarizer film, a microdisplay LCD element and a molded plastic lens block that allows the view from outside to pass through orthogonally to the microdisplay image, which is ultimately reflected at a 45? and presented in the field of vision adjacent to the outside-world view. In normal conditions, the displayed video image dominates the eye's attention; outside images are visually muted and nondistracting.

Among the pieces in the optical path, the microdisplay takes center stage. The small transmissive color LCD panel comes from Kopin Corp., a long-term pioneer in the arena of small LCDs for virtual display applications. Kopin's display is made by a silicon lift-off process. In its finished form, the Kopin panel has much the same layer stack-up as a traditionally manufactured TFT LCD panel; but, untraditionally, Kopin builds the display layers on a silicon wafer and then transfers the finished circuitry to a glass host panel.

Kopin claims that on-wafer manufacturing allows for both a smaller pixel size and a faster TFT response because of the transistor's crystalline silicon makeup. The conventional LCD is made on large glass panels (with amorphous or low-temperature polysilicon-based transistors), yielding either large displays or a large number of displays per panel. In contrast, Kopin's semiconductor substrate size relegates the technology to the manufacture of "chip sized" displays (no problem here, since the target is a small LCD for portable eyewear).

The glasses themselves contain both left- and right-eye optics and LCDs connected by a long flex cable running across the length of the glasses.

XSA-0720S

At $199, Myvu's Solo brings iPod video viewing front and center.
(Click to view teardown.)

Smart interface
The remote control "pod" inside the Solo's connecting cable houses most of the control electronics. The iPod's video output cannot directly drive the LCDs, and still more power is needed to drive the white LEDs. Although all necessary power is drawn from the host iPod, conversion of voltage and video format must be housed in the pod.

Three discrete chips are used for power conversion: two DC/DC converters from RichTek and a charge pump regulator from Advanced Analogic. The RichTek #RT9285 DC/DC converter fine-tunes the drive voltage for each white LED.

Two devices are needed to interface iPod video output and the Kopin microdisplays. Techwell's #TW9910 converts the iPod's composite video output to the ITU-R 601 YCbCr (4:2:2) format used by the Kopin display system. It may also perform some video scaling to the QVGA resolution used by the Kopin panels. A custom microdisplay controller chip from Kopin, the #KCD-A210-BA, takes the Techwell output and performs additional signal control along with what appears to be bias voltage management based on the die topology. The Kopin ASIC provides the final interface to the two microdisplay panels.

Line-level audio output from the iPod dock is not sufficient to drive the Myvu Solo's earbuds. A Maxim #MAX9723 stereo amplifier is used to boost output.

A TI #MSP430F2131 mixed-signal MCU, with ~8Kbytes of flash and 256bytes of RAM, completes the electronics system, serving both internal control needs and providing the interface to the Solo's six control buttons.

The Solo lessens the microdisplay's cost, size and power requirements, but the ability to shoehorn a similar display into an ultrasmall cellphone may have to wait for the advent of more-compact lensing techniques.




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