How It Works
VueG8 technology is uniquely positioned to take advantage of both low cost LED and focus free laser light sources. Using high volume semiconductor manufacturing, VueG8 devices and pixel sizes can be easily scaled to meet the cost, size, and performance needs of pico projectors.
While VueG8 uses a well established Liquid Crystal on Silicon (LCOS) light modulation process, what makes VueG8 unique is its patented all digital technology for controlling the pixels. This technology is able to support Field Sequential Color (FSC) while having a small pixel mirror and a small overall device. Since VueG8 technology is 100% digital, it supports high yields and easy testing for high volume manufacturing.
VueG8 has many advantages in making pico projector microdisplays, some of which are:
- Small pixel size for high resolution in a small device
- Leverages high volume digital CMOS manufacturing to build hundreds of microdisplays on a single silicon wafer
- All digital low power CMOS design with on-display processing reduces bandwidth to the display and system power.
- Small low cost packaging
- Ready to go into low cost systems with LEDs today.
- Supports focus free operation with lasers with the ability to make small pixels to leverage the advantages of laser light.
Small Devices with High Resolution
Liquid Crystal on Silicon (LCOS) is formed by sandwiching liquid crystal (LC) between a cover glass with an optically transparent electrical coating and a silicon integrated circuit. Individual pixels are formed by the top metal layer of the integrated circuit which acts both as reflective mirrors and electrodes to control the liquid crystal above the mirror/electrode. Syndiant employs a very high speed liquid crystal, about 50 to 100 times faster than the liquid crystal found in a typical LCD television, to support Field Sequential Color (FSC).
The cover glass and silicon integrated circuit are bonded together with epoxy glue which contains spacer beads to form a very thin gap for the liquid crystal. There can be on the order of 500 VueG8 pico projector microdisplays on a single 8-inch (200mm) silicon wafer and thus about 500 devices are being formed at time, making this a very high volume and cost effective way to manufacture pico projector light modulators.
Due to the small size of the devices, the cost of materials is low. As one example, there is enough liquid crystal in a typical 17-inch monitor to fill about 20,000 VuG8 WVGA displays.
Field Sequential Color
In order to meet the size and cost requirements for a pico-projector microdisplay, Field Sequential Color (FSC) is employed. With basic FSC, a single full color image is broken down into color fields based on the the primary colors of red, green, and blue and imaged by the microdisplay individually. As each color field is imaged by the microdisplay, the corresponding led color is turned on. When these color fields are displayed in rapid sequence a full color image will be seen.
FSC has the advantage of requiring only one small microdisplay to display a full color image and can result in very small optical system. An alternative for making an LCOS microdisplays has been to use color filters, but this requires at least 3 color filtered mirror sub-pixels per pixel and thus is generally more than 3 times larger. Color filter microdisplays therefore require larger optics and display poor color quality due to electrical interaction between the color filtered sub-pixels.
Performing FSC necessitates generating the color fields at a high rate which means the device must work faster. In the case of LCOS, FSC also requires using high speed liquid crystals that can be more difficult to control.
Single Pulse Drive
The high speed liquid crystals used by VueG8 have very asymmetrical rise and fall times. They have a very fast fall to black time to support well saturated colors while the rise time is about 3 times slower. VueG8 uses a single pulse drive technique that generates a pulse width to control each color, the advantage being that a wider pulse is a brighter pulse regardless of the LC response time and the rise and fall times of the liquid crystal.
By using on-display processing, a VueG8 device efficiently generates a single pulse to control each of the many hundreds of thousands of pixels on a single device. Controlling so many pixels with a single pulse, and supporting the high field rates of field sequential color would be impractical without on-display processing.
Small Highly Parallel on Display SIMD Processing
To perform the very large number of operations required to support FSC single pulse on hundreds of thousands of pixels, VueG8 employs a very simple and small but highly parallel processor with a Single Instruction, Multiple Data Stream (SIMD). Having the processing on the silicon allows sending encoded pixel values (a much smaller amount of data) to the backplane for processing into pulse widths to drive the individual pixels.
There is a very simple bit serial processing element (PE) per column of pixels that is controlled by a single instruction controller. Each of the PE’s is running the same operation/instruction but the data that it processes is different based on the value of the pixel. The processing is split in half with half the PE’s on the top and half the PE’s on the bottom of the display array.
The scratch memory on the top and bottom of the array is used to buffer pixel data being processed. Additionally, this scratch SRAM is used to buffer data used to enable a very fast “context switch” between two colors as they sequence. The scratch SRAM memory has only a few bits per pixel and none of the bits are dedicated to any given pixel. The memory is constantly re-allocated to different pixels based on proprietary algorithms that leverage the bit serial processing to reduce the number of processing cycles and to save power and minimize the amount of on-chip SRAM memory required.
Resolution and Future Trends
The figure below shows an extreme close up picture of an actual image projected by a VueG8 display with 5.4 µM pixels so that the individual mirrors/pixels can be seen. The text in the image has single pixel stroke fonts and note that the dot in each letter “i” is formed by a single pixel. This also demonstrates that the pixels could be made smaller to support higher resolution with a small display.
VueG8 technology will soon be providing HD resolutions of 720P and 1080P on devices small enough to be embedded in a cell phone.