Patent Application
20130016285
Referring to
Video data typically contains three primary colors, red (R), green (G) and blue (B)—which in a digital system are sent as three color data words of some length, e.g., N-bits each. All three color data words are transferred from the video processor IC 106 to the LDD IC 108 for each pixel, and thus, can also be referred to as color pixel data. It is also possible that more than three color data words may be transferred from the video processor IC 104 to the LDD IC 108 for each pixel. The video processor IC 106 can perform scaling and/or pre-distortion of the video signal before the signal is provided to the LDD IC 108. The video processor IC 106 may also perform gamma expansion of the video signal before the signal is provided to the LDD IC 108.
The voltage regulator 110 (e.g., a quad-output adjustable DC-DC buck-boost regulator, or a quad-output low-dropout regulator) can convert a voltage provided by a voltage source (e.g., a battery or AC supply) into the various voltage levels (e.g., four voltage levels V1, V2, V3 and V4) for powering the various components of the projector display device 100.
The LDD IC 108 is shown as including three DACs 109 and a data interface 122, which can be, e.g., an Inter-Integrated Circuit (12C) or a Serial Peripheral Interface (SPI) interface, but is not limited thereto. The LDD IC 108 also includes registers, and the like, which are not shown. The DACs 109 of the LDD IC 108 drive the light emitting elements 112, which can include, e.g., red, green and blue laser diodes, but are not limited thereto.
In the configuration shown in
The light produced by the laser diodes or other light emitting elements 112 are shown as being provided to beam splitters 114, which can direct a small percentage of the light toward one or more calibration photo-detectors (PDs) 120, and direct the remainder of the light toward projector optics 116, which include lenses, mirrors, reflection plates and/or the like. The light output by the optics 116 can be provided to one or more micro mirror(s) 118. The mirror(s) 118 can be controlled by the video processor IC 106, or another portion of the system, to raster-scan reflected light onto a surface, e.g., a screen, a wall, the back of a chair, etc.
Embodiments of the present invention are directed to a light emitting element driver integrated circuit (IC), methods for use with a light emitting element driver IC, and projector systems that include a light emitting element driver IC. In such embodiments, the light emitting element driver IC receives color data words from a video processor IC, and the light emitting element driver IC generates an analog drive signal for driving a light emitting element. The light emitting can be, e.g., a laser diode, in which case the light emitting element driver IC can be a laser diode driver (LDD) IC. Alternatively, the light emitting element can be a light emitting diode (LED), but is not limited thereto.
In accordance with an embodiment, the light emitting element driver IC receives a color data word from the video processor IC. Starting with the color data word received from the video processor IC, the light emitting element driver IC performs a gamma expansion function to thereby produce a gamma expanded digital or analog signal. Additionally, the light emitting element driver IC outputs, in dependence on the generated gamma expanded digital or analog signal, a gamma expanded analog drive signal for driving the light emitting element.
In certain embodiments, the color data word received by the light emitting element driver has not been gamma expanded by the video processor IC. In such embodiments, the gamma expansion function performed within the light emitting element driver IC can be a gamma expansion function Y=X̂c, in which case the gamma expanded analog drive signal output by the light emitting element driver IC has been gamma expanded in accordance with the gamma expansion function Y=X̂c.
In accordance with other embodiments, the color data word received by the light emitting element driver has been partially gamma expanded by the video processor IC using a first partial gamma expansion function Y=X̂a. In such embodiments, the gamma expansion function performed within the light emitting element driver IC can be a second partial gamma expansion function Y=X̂b, in which case the gamma expanded analog drive signal output by the light emitting element driver IC has been gamma expanded in accordance with the gamma expansion function Y=X̂(a*b)=X̂c. In accordance with specific embodiments, b=2, and thus, the second partial gamma expansion function is a squaring function. In such embodiments, where the desired total gamma expansion function X̂c, a=c/2, and c=a*b=(c/2)*2. In a specific embodiment, c=2.2, and a=1.1.
In accordance with some embodiments, the gamma expansion performed by the light emitting element driver IC is performed using a look-up-table (LUT) within the light emitting element driver IC that accepts an N-bit input and outputs an M-bit output, where N and M are integers, and M>N. In a specific embodiment, the gamma expanded digital or analog signal is generated at the M-bit output of the LUT, and a linear digital-to-analog converter (DAC) that includes an M-bit input accepts the M-bit output of the LUT, and outputs the analog drive signal for driving the light emitting element.
In other embodiments, a multiplying digital-to-analog converter (DAC) within the light emitting element driver IC performs the gamma expansion function and outputs the analog drive signal for driving the light emitting element.
In certain embodiments, a segmented DAC within the light emitting element driver IC implements the gamma expansion function as a piecewise linear transfer function and outputs the analog drive signal for driving the light emitting element.
In further embodiments, a linear DAC (within the light emitting element driver IC) accepts the color data word received from the video processor IC, and an analog output state (within the light emitting element driver IC) receives an analog signal output by the linear DAC and performs the gamma expansion function within the light emitting element driver IC, and outputs the analog drive signal for driving the light emitting element.
This summary is not intended to summarize all of the embodiments of the present invention. Further and alternative embodiments, and the features, aspects, and advantages of the embodiments of the invention will become more apparent from the detailed description set forth below, the drawings and the claims.
As mentioned above in the discussion of
Referring back to
In accordance with specific embodiments of the present invention, the number of bits per color data word that is to be transferred from a video processor IC to a driver IC is reduced by performing at least some of the gamma correction (i.e., all of, or part of, the gamma expansion) within the driver IC, as will now be described with reference to
Referring to
The use of alternative light emitting elements, such as light emitting diodes (LEDs), etc., is also possible. It is also possible that the LDD IC 308 drive more than three light emitting elements. More generically, the LDD driver 308 can be referred to as a light emitting element driver IC 308, or simply as a driver IC 308. However, for the remainder of this discussion the light emitting elements 112 will sometimes be referred to as laser diodes, but as just noted, can alternatively be other types of light emitting elements. Further, for the remainder of this discussion, the driver IC 308 will sometimes be referred to as an LDD driver IC, but can be a light emitting diode (LED) driver IC or any other type of light emitting element driver IC.
In some embodiments, each gamma expansion and D/A conversion block 310 includes a sub-block that performs the function Y=X̂2.2, and includes a DAC that converts Y from a digital value to an analog current (or voltage). The sub-block that performs the function Y=X̂2.2 can be a software, firmware and/or hardware that performs the actual exponential function. Alternatively, the sub-block that performs the function Y=X̂2.2 can be or a look-up-table (LUT), e.g., 6-bit input/14-bit output LUT (also known as a 64×14-bit LUT). The LUT can be stored, e.g., in ROM, but is not limited thereto. More generically, the gamma expansion function can be Y=X̂c.
The gamma expansion performed by the driver IC 308 can include all of, or at least some of, the exponential (also referred to as power-law) expansion that is typically performed within a video processor IC (e.g., the video processor IC 106). Additionally, the gamma expansion performed by the driver IC 308 can also provide at least a portion of brightness correction, white balance correction, noise filtering and/or compensation for the transfer function of the light emitting elements 112 being driven by the analog outputs of the driver IC 308, but are not limited thereto. Other portions of brightness correction, white balance correction, and/or compensation for the transfer function of the light emitting elements 112 can be performed using a calibration feedback loop that includes one or more calibration PDs 120.
In other embodiments, partial gamma expansion is performed for each color data word by the video processor IC 306, and the remainder of the gamma expansion is performed by the gamma expansion and D/A conversion blocks 310 of the LDD IC 308. In a specific embodiment, the video processor IC 306 performs the function Y=X̂1.1 for each color; and each gamma expansion and D/A conversion block 310 includes a sub-block that performs the function Y=X̂2, and includes a DAC that converts Y from a digital value to an analog current (or voltage). This will result in each color data word being gamma expanded using the function Y=X̂2.2, since {X̂1.1}̂2=X̂2.2. The partial gamma expansion performed by the video processor IC 306 can be referred to as front-end partial gamma expansion (with the function more generically Y=X̂a), and the remainder of the gamma expansion performed by the LDD driver 308 can be referred to as back-end partial gamma expansion (with the function more generically Y=X̂b, where a*b=c).
If the video processor IC 306 performs Y=X̂1.1 front-end partial gamma expansion on three 6-bit color data words within the video processor IC 106, then three 7-bit partially gamma expanded color data words would need to be transferred from the video processor IC 306 to the LDD IC 108 for each pixel (assuming there was no reduction in color resolution). The sub-block that performs the back-end partial gamma expansion function Y=X̂2 can be software, firmware and/or hardware that performs the actual exponential function, or a LUT, e.g., 7-bit input/14-bit output LUT (also known as a 128×14-bit LUT). It is believed that the color resolution can be reduced from 14-bits down to 12-bits while still achieving good color reproduction without undesirable color banding. In such an embodiment, each DAC can be a 12-bit DAC.
In accordance with another embodiment, the back-end partial (or only) gamma expansion can be performed using a multiplying DAC, an example of which is shown in
In still other embodiments, each gamma expansion and D/A conversion block 310 includes a DAC followed by an analog squaring output stage, as shown in
Referring to
In some of the embodiments described above, all of the gamma expansion to the color data words (e.g., R, G and B color data words) is performed within the light emitting element driver IC after the driver IC receives non-gamma expanded color data words from the video processor IC. In still other embodiments, back-end partial gamma expansion to color data words is performed within the light emitting element driver IC after the driver IC receives partially gamma expanded color data words from the video processor IC. In specific embodiments described above, the front-end partial gamma expansion performed by the video processor IC was described as using the function Y=X̂1.1, while the back-end partial gamma expansion performed by the light emitting element driver IC was described as using the function Y=X̂2. Such embodiments can be readily implemented because it is relatively easy to implement digital and analog squaring functions. Nevertheless, it is also within the scope of the present invention that the gamma expansion be divided between front-end and back-end partial expansions in other manners. For example, the video processor IC can perform front-end gamma expansion using the function Y=X̂1.375, while the back-end partial gamma expansion performed by the light emitting element driver IC uses the function Y=X̂1.6. It is also possible that the total desired gamma expansion is a function other than X̂2.2. In other words, while a commonly used decoding gamma is 2.2, use of other decoding gammas is also within the scope of the present invention. More specifically, in accordance with specific embodiments, the decoding gamma (γ) is any value greater than 1 and less than or equal to 3, i.e., 1≦γ≦3.
Referring back to
One or more of the light emitting elements 112 can have a substantially linear current to output power transfer function above the lasing threshold, e.g., where a light emitting element is a solid state laser diode, such as, but not limited to, a Diode-pumped solid-state (DPSS) laser diode. It is also possible that one or more light emitting elements can have a substantially non-linear current to output power transfer function, e.g., where a light emitting element is a second harmonic generation (SHG) laser diode, which is sometimes used as the green (G) light emitting element 112. In accordance with embodiments of the present invention, the transfer function of the light emitting element being driven by the output of a block 310 should be considered when specifying (e.g., designing and implementing) the transfer function for the block 310 so that the overall transfer function implemented by a color channel (which includes the video processor IC 306, the block 310 of the light emitting element driver IC 308, and the light emitting element 112) is the desired transfer function (e.g., including gamma expansion, interpolation and/or predistortion, but not limited thereto). For example, where a light emitting element has a non-linear transfer function, the non-linear transfer function of the light emitting element can be used to achieve part of the gamma expansion desired for the channel.
In FIGS. 3 and 4A-4E, the gamma correction and D/A conversion blocks 310 of the driver IC 308 are shown as parallelly receiving color data words from the video processor IC 306 over a parallel data bus. In alternative embodiments, where the video processor is configured to transfer each of the color data words serially over a serial data bus, the gamma correction and D/A conversion blocks 310 of the driver IC 308 can serially receive color data words from the video processor IC. In such alternative embodiments, performing all or part of the gamma expansion within the driver IC 308 may not achieve the pin count efficiencies for the driver IC 308 mentioned above, but will still advantageously help to mitigate the data transfer bandwidth between the video processor IC 306 to the driver IC 308. Further, if the video processor IC 306 is configured to transfer each of the color data words serially over a serial data bus after full gamma expansion is performed within the video processor IC 306, this may necessitate relatively fast clock speeds within the video processor IC and the driver IC (to handle the high data transfer bandwidth). Advantageously, performing all or part of the gamma expansion within the driver IC 308 can allow for reductions in such clock speeds. Regardless of whether the color data words are transferred serially or in parallel between the video processor IC 306 to the driver IC 308, it would be beneficial to use a high speed data transfer technique, such as, but not limited to, low-voltage differential signaling (LVDS) and/or double data rate (DDR).
Referring to
In accordance with some embodiments, the color data word received at step 802 has not been gamma expanded by the video processor IC. In such embodiments, the gamma expansion function performed at step 804, within the light emitting element driver IC, can be generically referred to as a gamma expansion function Y=X̂c. This results in the gamma expanded analog drive signal, output at step 806, having been gamma expanded in accordance with the gamma expansion function Y=X̂c.
In accordance with other embodiments, the color data word received at step 802 has been partially expanded by the video processor IC using a first partial gamma expansion function Y=X̂a. In such embodiment, the gamma expansion function performed at step 804, within the light emitting element driver IC, is a second partial gamma expansion function Y=X̂b. This results in the gamma expanded analog drive signal, output at step 806, having been gamma expanded in accordance with the gamma expansion function Y=X̂(a*b)=X̂c. In specific embodiments, b=2, and thus, the second partial gamma expansion function is a squaring function, which is relatively easy and efficient to implement. In such embodiments, where the desired gamma expansion is X̂c, a=c/2. For a specific example, a=1.1, b=2 and c=2.2.
To illustrate the above described embodiments, assume that the color data word received at step 802 is an N-bit color data word. Also assume that the N-bit color data word received at step 802 would include at least M-bits if the N-bit color data word was already fully gamma expanded by the video processor IC to have the gamma expansion function Y=X̂c, wherein M>N. Using the embodiments described herein, rather than requiring the M-bits be transferred from the video processor IC to the driver IC per color data word, N-bits can instead be transferred from the video processor IC to the driver IC per color data word, where N<M. Using such embodiments, the fully gamma expanded analog drive signal output at step 806 can be substantially equal to an analog drive signal that would be generated if an M-bit fully gamma expanded color data word was received by the driver IC and was converted to an analog drive signal using a linear digital-to-analog converter (DAC) of the driver IC.
In accordance with certain embodiments described above with reference to
In other embodiments described above with reference to
In still other embodiments, described above with reference to
In still further embodiments, step 804 is preformed using a linear DAC and an analog output stage within the light emitting element driver IC. The linear DAC accepts the color data word received from the video processor IC, and outputs an analog signal that is indicative of (e.g., directly proportional to) the color data word received from the video processor IC. The analog output stage receives the analog signal output by the linear DAC and performs the gamma expansion function within the light emitting element driver IC. Here, the gamma expanded analog drive signal, output at step 806, is the output of the analog output stage. In specific embodiments, the analog output stage comprises an analog squaring output stage, which is relatively easy and efficient to implement. An exemplary analog squaring output stage was described with reference to
As mentioned above, the gamma expansion function performed by the light emitting element driver IC at step 804 can include all of, or at least some of, the exponential (also referred to as power-law) expansion that is typically performed within a video processor IC, as well as brightness correction, white balance correction, and/or compensation for the transfer function of the light emitting elements being driven by the analog outputs of the driver IC, but are not limited thereto.
Embodiments of the present invention have been described above with the aid of functional building blocks illustrating the performance of specified functions and relationships thereof. The boundaries of these functional building blocks have sometimes been defined herein for the convenience of the description. Unless otherwise specified, alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. Any such alternate boundaries are thus within the scope and spirit of the claimed invention. While portions of the invention can be implemented using hardware, other portions of the invention can be implemented using software and/or firmware. Such software and/or firmware can be implemented as a non-transitory computer readable medium, including instructions stored thereon which when read and executed by one or more processors, cause the one or more processors, but not limited thereto, to perform and/or control specific steps described above. Such processor(s) can also be used to implement certain blocks discussed above, or portions thereof.
The forgoing description is of the preferred embodiments of the present invention. These embodiments have been provided for the purposes of illustration and description, but are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to a practitioner skilled in the art. Embodiments were chosen and described in order to best describe the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention. Slight modifications and variations are believed to be within the spirit and scope of the present invention. It is intended that the scope of the invention be defined by the following claims and their equivalents.
This application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application No. 61/506,588, filed Jul. 11, 2011, entitled LIGHT EMITTING ELEMENT DRIVER IC IMPLEMENTING GAMMA EXPANSION (Attorney Docket No. ELAN-01262US0), which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61506588 | Jul 2011 | US |
