1. Field of the Invention
This invention generally relates to electronic color displays and, more particularly, to a system and method for generating a full range of colors using multicolor subpixels.
2. Description of the Related Art
However, the limit of three primary color pixel for each ‘display unit pixel (DUP)’ or pixel, which limits the achievable spatial resolution. In addition, most of current display technologies require strong backlight illuminations or strong emissive pixels (e.g., plasma and organic light emitting diodes (OLEDs)) for large dynamic and high contrast display effects. Those high luminous backlight sources and highly emissive pixels often require high power consumptions, which is not suitable for portable devices with power supplies from batteries.
Reflective display or color-tunable device technology is attractive primarily because it consumes substantially less power than LCDs and OLED displays. A typical LCD used in a laptop or cellular phone requires internal (backlight) illumination to render a color image. In most operating conditions the internal illumination that is required by these displays is in constant competition with the ambient light of the surrounding environment (e.g., sunlight or indoor overhead lighting). Thus, the available light energy provided by these surroundings is wasted, and in fact, the operation of these displays requires additional power to overcome this ambient light. In contrast, reflective display technology makes good use of the ambient light and consumes substantially less power.
Recently, MEMS reflective displays have been developed using interferometric light modulation three subpixel (red, green, and blue (RGB)) devices. Advantageously, these displays do not require backlighting. Other colors are generated by mixing of these three primary colors. Moreover, grayscale images can be generated using spatial or temporal addressing of the three subpixels. However, since each pixel is divided into three subpixels, the total reflectance for a primary color can be no more than 33%. It would be much more desirable if a single pixel could generate all colors with 100% reflectivity.
When a voltage is applied to each side of the parallel-plate capacitor, the movable plate is pulled toward the bottom plate by attraction of Coulomb force:
where C is the capacitance area, V is the applied voltage, g is the initial gap, and d is the displacement distance. At sufficiently small displacements, the deflection reaches an equilibrium position due to opposing Hooke's Law:
Fmech=kd
However, when the displacement of the movable plate is larger than one-third the initial gap, i.e. d>g/3, the Hooke's force is not strong enough to balance the Coulomb force attraction. Therefore at this point, known as the pull-in voltage, the movable plate eventually snaps down to the non-equilibrium state.
The pull-in voltage is expressed as the following:
where ∈ is the electrical permittivity of the material, and A is the area of the parallel-plate capacitor.
By solving the pull-in voltage issue, MEMS pixels can be designed to selectively reflect light with peak wavelengths in the whole visible spectral ranges. The peak wavelengths are tunable as the function of air gap lengths,
λPeak=f(d) Equation 1
In which λPeak is the peak wavelength, f(d) is the correlation function (depending on the MEMS design), and d is the air gap lengths for each MEMS pixel.
From Equation 1, it can be clearly seen that with just one subpixel, most of the standard colors through the visible spectral range can be generated.
The key advantage for the reflection based MEMS displays is the low power consumptions. Two major factors contribute to the low power consumptions: (1) no back light sources are required, which is the major factor; (2) for MEMS pixels, power consumptions only occur at switching transitions periods between different air space lengths, which are typically very short compared to the whole color duty cycles (decided by the frame rates) for well-designed MEMS pixels. The second factor can be explained by energy changes in capacitance during MEMS pixel operations. At stable states, the energy stored in MEMS capacitances is
E=U
2
×C(d)×0.5 Equation 2
Where E is the energy stored in the MEMS pixels, U is the biased voltages, and C(d) is the capacitance as the function of thickness d. It is clear that the power consumption is near zero (since the time derivatives of E(t) is almost zero) when the MEMS pixels are at a stable state. Only when the MEMS pixels are switched from position d1 to d2 by applied voltage changes, both U and C vary, leading to power consumptions E(d1)-E(d2). The near-zero power consumptions for stable states make the display very advantageous for showing still images (e.g., e-paper applications), as compared with other types of displays. Further it can be used for video displays due to the fast achievable switching speeds at the expense of power consumptions.
A number of other reflective display technologies have been developed, such as electrophoretic, electrowetting, and electrochromic displays. These display technologies, as well as the interference-based MEMS, all have disadvantages or challenges that must be overcome to obtain greater commercial success. Many existing technologies rely upon phenomena that are intrinsically slow. For example, electrophoretic or electrochemical techniques typically require particles to drift or diffuse through liquids over distances that create a slow response. Some other technologies require high power to operate at video rates. For example, many reflective displays must switch a large volume of material or chromophores from one state to another to produce an adequate change in the optical properties of a pixel. At video switching rates, currents on the order of hundreds of mA/cm2 are necessary if a unit charge must be delivered to each dye molecule to affect the change. Therefore, display techniques that rely on reactions to switch dye molecules demand unacceptably high currents for displaying video. The same holds true for electrochromic displays.
A second challenge for reflective displays is the achievement of high quality color. In particular, most reflective display technologies can only produce binary color (color/black) from one material set. To create a full color spectrum at least three sub-pixels, using different material sets, must be used when employing a side-by-side sub-pixel architecture with fixed colors. This limits the maximum reflected light for some colors to about ⅓, so that the pixels of this type cannot produce saturated colors with a good contrast.
Some reflective displays face reliability problem over a long lifetime. In particular, to sustain video rate operation for a few years requires at least billions of reversible changes in optical properties. Achieving the desired number of cycles is particularly difficult in reflective displays using techniques based on chemical reactions, techniques that involve mixing and separation of particles, or MEMS technology that involves repeated mechanic wear or electric stress.
Retuning to
It would be advantageous if a practical pixel design existed that permitted a wider range of colors.
It would be advantageous if a pixel were able to generate a full gamut of colors using less than three subpixels.
It would be advantageous if a pixel were able to generate a broader range of combination colors by using more than 3 primary colors.
Provided herein are a system and method that permit a reflective display pixel to generate a larger color gamut, while consuming less power. For higher resolution applications where a primary combination color is required, the two primary color subfields are generated using either one or two subpixels sequentially multiplexed in time division multiplexing (TDM) mode. For lower resolution applications, neighboring subpixels simultaneously generate primary colors in a spatial division multiplexing (SDM) mode. Even in the low resolution modes, the achievable spatial resolution for each pixel is still higher than for a conventional three-subpixel display. The TDM mode requires constant switching of the subpixels to create colorful images, and consumes more energy than the SDM mode. In the SDM mode, once an image is set, it can be held for long time without consuming power, making this mode good for static displays, such as book readers and other e-paper.
Accordingly, a display device is presented that utilizes a method for generating a full color gamut. In one aspect, a display includes a plurality of pixels, and each pixel includes a single subpixel. A pixel, as defined herein, is a physical element occupying a space (i.e. a spatial element) capable of showing any color needed to display image. A subpixel is a physical element occupying a space that forms a part of a pixel, able to generate at least one primary color. In the present device, a single subpixel is able to sequentially generate a plurality of (e.g.; at least three) primary colors. A primary color exhibits a single wavelength peak in the visible spectrum of light. As a result of the single subpixel, the display is able to supply a gamut of colors including at least 3 primaries colors. For example, the sequential generation of the 3 primary colors may involve operating the subpixel in a time division multiplex (TDM) mode, and a primary combination color is supplied in response to the subpixel generating 2 primary colors in respective TDM subframes. A primary combination color is the “in-between” color perceptible to human vision as the result of “merging” two primary colors. To take a simple example, the primary combination color of orange resulting from the primary colors of red and yellow.
In another aspect, the pixel includes at least two neighboring subpixels which can be operated in the spatial division multiplex (SDM) mode, and primary combination colors can be supplied in response to the first and second subpixels simultaneously generating primary colors in the SDM mode. If the first subpixel is capable of sequentially generating at least 2 primary colors, then it can also be operated the TDM mode, and a primary combination color can be supplied in response to the first subpixel generating 2 primary colors in respective TDM subframes. If the second subpixel capable of sequentially generating 2 primary colors, then a primary combination color can be supplied in response to the first subpixel generating 2 primary colors in respective TDM subframes, the second subpixel generating 2 primary colors in respective TDM subframes, the first and second pixels each generating a primary color in respective TDM subframes, or the first and second subpixels generating primary colors in the SDM mode.
Additional details of the above-described method and multicolor gamut display are provided below.
Each subpixel 604 in the display 600 is capable of sequentially generating at least 3 primary colors, although more than 3 primary colors are possible. For example, each subpixel may be capable of generating red, green, and blue (RGB) primary colors, or cyan, magenta, and yellow (CMYK) primary colors. Each subpixel 604 is capable of operation in a time division multiplex (TDM) mode. Then, each pixel 602 is able to supply primary combination colors in response to the subpixel 604 generating 2 primary colors in respective TDM subframes. A primary combination color is the “in-between” color perceptible to human vision as the result of “merging” two primary colors. To take a simple example, the primary combination color of orange results from the primary colors of red and yellow. A subframe or subfield is a temporal slice of a frame (or field), so that multiple subframes=1 frame. A frame or field is one entire spatial image. For example, a display image that changes over a time interval (e.g., multiple frame intervals) may be referred to as a video image.
In another aspect, the first subpixel 604a is capable of generating 2 primary colors in respective TDM subframes and the second subpixel 604b is also capable of generating 2 primary colors in respective TDM subframes. Then, each pixel 602 supplies primary combination colors in response to the first subpixel 604a generating 2 primary colors in respective TDM subframes, the second subpixel generating 2 primary colors in respective TDM subframes, and the first and second subpixels each generating a primary color in respective TDM subframes.
Further, the first and second subpixels 604a/604b may be capable of operation in the spatial division multiplex (SDM) mode, and each pixel 602 additionally supplies primary combination colors in response to the first and second pixel elements simultaneously generating a primary color in the SDM mode. It should also be noted that the display of
Referencing either
Each subpixel 604 is capable of changing the primary color being generated in response to the framing signals. For simplicity a single control interface is shown for each row of the display. However, it should be understood that each pixel may be individually controlled using a combination row and column (not shown) control interfaces to create an XY control matrix, as is well understood in the art.
Referencing
It should be noted that when the subpixels of
N=(700 nm−400 nm)/Δλ Equation 3
Further, as described above, hybrid TDM and SDM methods can select primary colors from λ1, λ2, . . . , λN as primary colors used to further generate primary combination colors.
In principle, almost any color in the wider gamut can be decomposed into the combinations of two primary colors that can be created directly by the tuning of reflection spectra of MEMS pixels. However, due to the limited number of digitalization of wavelengths (as shown by Equation 3), only certain color combinations can fully reconstruct the desired colors. For example, as shown in
Step 1302 provides a display with at least one pixel, where each pixel includes a single subpixel. The subpixels may be a tunable plasmonic device or tunable interferometric modulation (MEMS) device. However, the method is applicable to any subpixel capable of generating more than one primary color. Using the single subpixel, Step 1304 sequentially generates a plurality of primary colors (e.g., at least 3 primary colors), where a primary color exhibits a single wavelength peak in the visible spectrum of light. Step 1306 supplies a gamut of colors including at least 3 primaries colors. When Step 1304 operates the subpixel in the TDM mode, Step 1306 is capable of supplying a primary combination color in response to the subpixel generating 2 primary colors in respective TDM subframes. As shown in
In one aspect, Step 1302 provides a pixel with two (or more) subpixels. Then, Step 1305 operates the two subpixels in the SDM mode, and Step 1306 supplies primary combination colors in response to the first and second subpixels simultaneously generating primary colors in the SDM mode. As shown in
Alternately, the two subpixels may be used in just the TDM mode. If Step 1302 provides a pixel with a first subpixel capable of sequentially generating at least 2 primary colors and a second subpixel capable of generating at least 1 primary color, then Step 1306 is capable of supplying a primary color combination in response to the first subpixel generating 2 primary colors in respective TDM subframes, or the first and second subpixels each generate a primary color in respective subframes.
If Step 1302 provides a pixel with both the first and second subpixels capable of sequentially generating 2 primary colors, then Step 1306 is capable of supplying a primary combination color in response to the first subpixel generating 2 primary colors in respective TDM subframes, the second subpixel generating 2 primary colors in respective TDM subframes, and the first and second pixels each generating a primary color in respective TDM subframes.
In addition to using the two subpixels in the TDM mode, Step 1305 may operate the two subpixels in a SDM mode, and Step 1306 additionally supplies a primary combination color in response to the first and second subpixels simultaneously generating a primary color in the SDM mode.
In one aspect, Step 1302 provides a display where each pixel has a control interface to receive framing signals, where each framing signal includes commands for selecting a subpixel primary color. Then, supplying the gamut of colors (Step 1306) includes the first and second subpixels generating a primary color in the SDM mode for a duration lasting a plurality of frames, in response to a single control signal.
A system and method are provided for creating a full color range display using multicolor subpixels. Explicit details of MEMS device structures have been used to illustrate the invention. However, the invention is not limited to merely this example. For example, plasmonic devices may be used as subpixels. Other variations and embodiments of the invention will occur to those skilled in the art.
The application is a Continuation-in-Part of a pending application entitled, MULTIPLEXED DISPLAY USING MULTICOLOR PIXELS, invented by Aki Hashimura et al., Ser. No. 12/646,585, filed on Dec. 23, 2009, Attorney Docket No. SLA2686; which is a Continuation-in-Part of a pending application entitled, PLASMONIC DEVICE TUNED USING LIQUID CRYSTAL MOLECULE DIPOLE CONTROL, invented by Tang et al., Ser. No. 12/635,349, filed on Dec. 10, 2009, Attorney Docket No. SLA2711; which is a Continuation-in-Part of a pending application entitled, PLASMONIC DEVICE TUNED USING ELASTIC AND REFRACTIVE MODULATION MECHANISMS, invented by Tang et al., Ser. No. 12/621,567, filed on Nov. 19, 2009, Attorney Docket No. SLA2685; which is a Continuation-in-Part of a pending application entitled, COLOR-TUNABLE PLASMONIC DEVICE WITH A PARTIALLY MODULATED REFRACTIVE INDEX, invented by Tang et al., Ser. No. 12/614,368, filed on Nov. 6, 2009, Attorney Docket No. SLA2684. The instant application is also a Continuation-in-Part of a pending application entitled, FULL COLOR RANGE INTERFEROMETRIC MODULATION, invented by Aki Hashimura et al., Ser. No. 12/568,522, filed on Sep. 28, 2009, Attorney Docket No. SLA2620. All the above-referenced applications are incorporated herein by reference.
Number | Date | Country | |
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Parent | 12646585 | Dec 2009 | US |
Child | 12750495 | US | |
Parent | 12635349 | Dec 2009 | US |
Child | 12646585 | US | |
Parent | 12621567 | Nov 2009 | US |
Child | 12635349 | US | |
Parent | 12614368 | Nov 2009 | US |
Child | 12621567 | US | |
Parent | 12568522 | Sep 2009 | US |
Child | 12614368 | US |