Variable duty ratio display scanning method and system - Patents.com

Abstract

To provide a method of scanning a flat panel display using a variable duty cycle of a pixel's active interval to reduce motion artifacts.SOLUTION: A method of resetting a row of pixels in a pixel array 122 to a predetermined optical transmission level is provided, the method comprising: setting a column signal line 102 of the pixel array 122 to an initial voltage 202; asserting a row signal line 104 of the pixel array while the column signal line 102 is at the initial voltage 202; and deasserting the row signal line 112 of the pixel array prior to a change in voltage of the column signal line 102 from the initial voltage 202.SELECTED DRAWING: Figure 4

Description

Related Applications

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 278,658, filed Jan. 14, 2016, the entire teachings of which are incorporated herein by reference. [Background technology]

[0002] Flat panel displays have now almost completely replaced cathode ray tubes (CRTs) due to their many advantages in power, volume, cost, and performance. However, CRTs have one advantage that many modern displays do not have: in a CRT device, after the electron beam scans the phosphors, the phosphors naturally fade to black unless stimulated again. In contrast, the pixels of many flat panel displays maintain their bright or dark state from frame to frame. This persistence of flat panel displays can result in the perception of motion artifacts (e.g., trailing) when the entire image is viewed.

[0003] Some flat panel displays mitigate motion artifacts by inserting black frames, which requires doubling the frame rate and driving every other frame in black, which requires a higher video bandwidth to the pixel array, and therefore more power and complexity.

[0004] Liquid crystal displays (LCDs) can take a similar approach by pulsing the backlight, which causes pixels to be illuminated for shorter periods of time, but pixels near the top of the display are scanned before pixels near the bottom, which can cause non-uniformity problems due to their different phase relationships to the backlight timing.

[0005] Further mitigation may be possible by synchronizing a segmented backlight with the scanning of the pixel array, but this adds complexity and is not practical for certain applications (e.g., microdisplays) that are illuminated by a single LED backlight anyway. Other displays may achieve global blanking by controlling at least one common signal to the pixel array (e.g., to VCOM in the case of LCDs, or to the anode or cathode supply in organic light-emitting diode (OLED) displays). However, these approaches may have the same uniformity challenges as the backlight blanking approach described in the previous paragraph.

[0006] In many liquid crystal display (LCD) configurations, especially those employing the commonly used twisted nematic (TN) topology, the brightness of a pixel is varied by the voltage applied to the liquid crystal (LC) cell. This voltage affects the degree to which the LC material rotates the polarized light, thereby controlling how much light passes through the output polarizer. In other words, the LCD is a passive device that acts as a light valve. Typically, the management and control of the data to be displayed is performed by at least one circuit, commonly referred to as a display driver circuit or simply a driver.

[0007] Gray scale can be achieved by driving variable analog voltages to the LCD pixels. Analog video amplifiers are often used in the video signal path of the LCD driver circuit. When the video signal source is digital, at least one digital-to-analog converter (DAC) is typically used to convert the digital video signal to a corresponding analog video signal. Summary of the Invention [Problem to be solved by the invention]

[0008] The disclosed embodiments provide a method for scanning flat panel displays to reduce motion artifacts by using a variable duty cycle for the active period of a pixel to achieve a CRT-like effect.

[0009] One advantage of the disclosed embodiments is that the brightness of the display can be conveniently adjusted by varying the duty cycle without compromising the dynamic range. These embodiments do not require a significant increase in the video bandwidth, and there is no need to add circuitry to the pixel array to implement them. [Means for solving the problem]

[0010] In one aspect, the invention is a method of resetting a row of pixels in a pixel array to a predetermined light transmission level, the method comprising the steps of setting column signal lines of the pixel array to an initial voltage, asserting row signal lines of the pixel array while the column lines are at the initial voltage, and deasserting the row signal lines of the pixel array before the column signal lines change from the initial voltage.

[0011] In some embodiments, the initial voltage corresponds to a transparency of each pixel of the pixel array. The transparency may be a level that blocks light (opaque) or a level between a level that blocks light (transparent). Deasserting the row signal line may cause a storage capacitor to store the initial voltage. The storage capacitor may be associated with a particular pixel such that the voltage on the storage capacitor is applied to the pixel. The steps of asserting the row signal line and deasserting the row signal line may cause a pulse on the row signal line. The pulse may be long enough to stabilize the storage capacitor at the initial voltage and short enough to block (block out) voltage changes on the column line. Asserting the row signal line may connect the column signal line to a storage capacitor of a pixel of the pixel array.

[0012] In another aspect, the invention is a method of scanning video information into a pixel array, comprising the steps of: during a first active row period, setting a column signal line to an initial voltage, asserting a first row signal line of the pixel array, setting the column signal line to a desired voltage, and deasserting the first row signal line when the column signal line is at the desired voltage, the method further comprising the steps of: during a second active row period occurring a fixed time after the first active row period, setting the column signal line to the initial voltage, asserting the first row signal line of the pixel array, and deasserting the first row signal line while the column signal line is at the initial voltage.

[0013] In yet another aspect, the invention provides a pixel matrix scanning system comprising a pixel array, a column drive subsystem and a row drive subsystem configured to set a column signal line to an initial voltage, assert a first row signal line of the pixel array, set the column signal line to a desired voltage, and deassert the first row signal line when the column signal line is at the desired voltage during a first active row period, the column drive subsystem and the row drive subsystem further configured to set the column signal line to the initial voltage, assert the first row signal line of the pixel array, and deassert the first row signal line while the column signal line is at the initial voltage during a second active row period occurring a fixed time after the first active row period.

[0014] The foregoing will become apparent from the following more detailed description of exemplary embodiments of the invention, as illustrated in the accompanying drawings. The same reference characters refer to the same structures / components throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the invention. [Brief description of the drawings]

[0015] [Figure 1A] FIG. 2 illustrates an exemplary LCD active matrix pixel circuit in accordance with an embodiment of the present disclosure. [Figure 1B] FIG. 2 illustrates an exemplary OLCD active matrix pixel circuit in accordance with an embodiment of the present disclosure. [Figure 1C] FIG. 1 illustrates an example embodiment of a pixel matrix scanning system constructed in accordance with an embodiment of the present disclosure. [Diagram 2] FIG. 1C is a timing diagram for the pixel shown in FIGS. 1A and 1B. [Diagram 3] FIG. 2 is a timing diagram according to an embodiment of the present disclosure. [Figure 4] FIG. 11 is another timing diagram according to an embodiment of the present disclosure. [Diagram 5] FIG. 1 illustrates an example methodology for scanning video information into a pixel array. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] In the following, exemplary embodiments of the present invention are described. The entire teachings of all patents, published patent applications and references cited herein are hereby incorporated by reference.

[0017] An exemplary LCD active matrix pixel circuit is shown in Figure 1A, and an exemplary OLED active matrix pixel circuit is shown in Figure 1B. In the example of Figure 1A, a signal voltage is provided to a column line 102 (COLX) and a row line 104 (ROWY) controls a switch transistor 106 that can write the column voltage to a storage capacitor 108. The OLED example uses a complementary pair of switch transistors 110 controlled by a pair of complementary row lines 112 (ROWY / ROWBY). The voltage stored on the capacitor 108 controls a liquid crystal cell 114 (LCD) or a source follower circuit 116 (OLED) to modulate the light transmitted or emitted from the pixel.

[0018] In some embodiments, the display element connecting the active matrix pixel circuits of FIG. 1A (LCD) and FIG. 1B (OLED) may be a Wide Video Graphics Array (WVGA) display manufactured by the assignee of the present application and sold under the trade name "CYBERDISPLAY® WVGALV". The display element may be a wide format color filtered active matrix liquid crystal display having a resolution of 854×480. In other embodiments, the display element may instead comprise a Super Video Graphics Array (SVGA) display manufactured by the assignee of the present application and sold under the trade name "CYBERDISPLAY® SVGALVS". The display element may be a color filtered active matrix liquid crystal display having a resolution of 800×600. Other display elements are also applicable, such as those described in detail in U.S. Patent Nos. 8,378,924 and 9,116,340, the entire contents of which are incorporated herein by reference. The disclosed embodiments are not limited to a particular display element, but are applicable to any lightweight display known in the art that uses active matrix pixel circuitry, such as that depicted in the example circuitry of Figures 1A and 1B.

[0019] 1C shows an exemplary embodiment of a pixel matrix scanning system 120 with a pixel array 122 driven by a number of data and control signals. In this simple example, pixel array 122 includes 20 columns and 16 rows of pixels for a total of 320 pixels. As noted above, pixel arrays for practical microdisplays typically include many more pixels than this.

[0020] The pixel array 122 includes a column driver 124 and a row driver 126 that together provide information to the pixel array 122. In general, the column driver 124 provides image information to the pixels, and the row driver 126 provides control information to the pixels. The column driver signal 128 for a particular pixel column 130 may include multiple signals, such as for a red-green-blue (RGB) pixel array.

[0021] Figure 2 is an example timing diagram for use with the pixel circuit of Figure 1A. Similar timing may be generated for the complementary row line 112 in the example OLED circuit of Figure 1B. At the beginning of an active row period 201, row line 104 is asserted to an active voltage 208a. All common lines are typically reset to a common voltage at the beginning of the row period to improve uniformity.

[0022] Sometime during the active row period 201, the column voltage is driven from an initial reset voltage level 202 through a transition 204 to a desired voltage 206. While the row line 104 is asserted, the pixel voltage (e.g., the voltage on the storage capacitor 108) follows the column signal from an initial voltage 210 through a transition 212 to a target voltage 214.

[0023] The drive method employed determines the column timing, and possibly the horizontal position of the pixel in the array. A row period 201 ends when the row line is deasserted, and the column line returns to the initial reset voltage 202 in preparation for the next row write cycle, except that the row line is deasserted while the column voltage is still at the desired voltage 206 (i.e. before the column voltage transitions from the desired voltage 206 to the reset voltage 202). Thus, the pixel voltage maintains its stored level 214 at this point.

[0024] However, if, as in the example embodiment of FIG. 3, the row line is briefly asserted (i.e., pulsed) to an active voltage 208b while the column voltage is at an initial reset voltage 202, and then deasserted before the column voltage begins to transition, the pixel's storage capacitor 108 will store the reset voltage 202. In this example embodiment, the reset voltage 202 is selected to achieve a black level (e.g., opaque), so pulsing provides a fast way to drive a row to black. In other embodiments, the column voltage when the row line is pulsed (208b) may be an alternative voltage to reset the pixel row to another transparency corresponding to an optical characteristic other than black.

[0025] In some embodiments, a row may operate to reset during the normal write cycle of another row. In the example of Figure 4, the row line of row y (ROWy) is asserted to an active voltage 404. When the row line of row y is lowered (406), the pixel value 408 of row y holds the column voltage value at the time the line of row y was lowered (406). After d row periods, the row line of row y is pulsed (410) while the column voltage is at the initial reset voltage 402, causing the pixel value 412 to hold the initial reset voltage 402. The example of Figure 4 shows that by performing a reset pulse on a row d row periods after it is written, the active period of the pixel is limited to d row periods. In these embodiments, after video information is written to a row, d row periods later the row is reset to black (or some other predetermined transparency depending on the column voltage at the time the pulsed row signal 410 occurs) by a pulsed row line signal 410. For vertical timing of V lines per frame, the effective duty cycle is (d / V) x 100%.

[0026] 5 illustrates an example method 500 for scanning video information into a pixel array. The method begins (502) and includes, during a first active row period, steps 504, 506, 508, 509, and 510, respectively, of setting a column signal line to an initial voltage, asserting a first row signal line of the pixel array, setting the column signal line to a desired voltage, and deasserting the first row signal line when the column signal line is at the desired voltage. During a second active row period that occurs a fixed time after the first active row period, steps 512, 514, 515, and 516, respectively, of setting the column signal line to the initial voltage, asserting a first row signal line of the pixel array, and deasserting the first row signal line while the column signal line is at the initial voltage.

[0027] Although the present invention has been particularly shown and described with reference to illustrative embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as encompassed by the appended claims. The present invention includes the following embodiments. [Aspect 1] 1. A method of resetting a row of pixels in a pixel array to a predetermined light transmission level, comprising the steps of: setting column signal lines of the pixel array to an initial voltage; asserting a row signal line of the pixel array while the column signal line is at the initial voltage; deasserting the row signal line of the pixel array before the column signal line changes from the initial voltage; A method comprising: [Aspect 2] 2. The method of claim 1, wherein the initial voltages correspond to a transmittance of each pixel of the pixel array. [Aspect 3] The method of claim 2, wherein the transmittance is at a light-tight level. Aspect 4 2. The method of claim 1, wherein deasserting the row signal line causes a storage capacitor to hold the initial voltage. Aspect 5 2. The method of claim 1, wherein asserting the row signal line and deasserting the row signal line cause a pulse on the row signal line. Aspect 6 2. The method of claim 1, wherein asserting the row signal line connects the column signal line to a storage capacitance of a pixel of the pixel array. Aspect 7 1. A method for scanning video information into a pixel array, comprising: During the first active row period: setting the column signal lines to an initial voltage; asserting a first row signal line of the pixel array; setting the column signal lines to desired voltages; deasserting the first row signal line when the column signal line is at the desired voltage; In a second active row period that occurs a certain time after the first active row period, setting the column signal lines to the initial voltage; asserting the first row signal line of the pixel array; deasserting the first row signal line while the column signal line is at the initial voltage; A method comprising: Aspect 8 8. The method of claim 7, wherein the initial voltages correspond to a transmittance of each pixel of the pixel array. Aspect 9 9. The method of claim 8, wherein the transmittance is at a light-tight level. Aspect 10 8. The method of claim 7, wherein deasserting the row signal line causes a storage capacitor to hold the initial voltage. Aspect 11 8. The method of claim 7, wherein asserting the row signal line and deasserting the row signal line cause a pulse on the row signal line. Aspect 12 8. The method of claim 7, wherein asserting the row signal line connects the column signal line to a storage capacitance of a pixel of the pixel array. Aspect 13 The method of embodiment 7, further comprising: asserting a second row signal line during the second active row period; A method comprising: Aspect 14 The method of embodiment 13, further comprising: maintaining the second row signal line asserted for a predetermined period of time after deasserting the first row signal line; A method comprising: Aspect 15 A pixel array; 1. A pixel matrix scanning system comprising a column driving subsystem and a row driving subsystem, the column driving subsystem and the row driving subsystem During the first active row period: Set the column signal lines to an initial voltage, Asserting a first row signal line of the pixel array; Setting the column signal lines to a desired voltage; deasserting the first row signal line when the column signal line is at the desired voltage; In a second active row period that occurs a certain time after the first active row period, setting the column signal lines to the initial voltage; Asserting the first row signal line of the pixel array; the pixel matrix scanning system being configured to deassert the first row signal line while the column signal line is at the initial voltage. Aspect 16 16. The system of claim 15, wherein the initial voltage corresponds to a transmittance of each pixel of the pixel array. Aspect 17 16. The system of claim 15, wherein deasserting the row signal line causes a storage capacitor to hold the initial voltage. Aspect 18 16. The system of claim 15, wherein asserting the row signal line connects the column signal line to a storage capacitance of a pixel in the pixel array. Aspect 19 16. The system of claim 15, wherein the column driving subsystem and the row driving subsystem are configured to assert a second row signal line during the second active row period. Aspect 20 In the system of aspect 19, the column driving subsystem and the row driving subsystem are further configured to maintain the asserted state of the second row signal line for a predetermined period of time after deasserting the first row signal line.

Claims

1. 1. A method for scanning video information into a pixel array, comprising: During the first active row period: setting the column signal lines to an initial voltage selected to achieve a black level; asserting a first row signal line of the pixel array while the column signal line is at the initial voltage; after the first row signal line is asserted, driving the column signal line from the initial voltage through a transition to a first desired voltage while the first row signal line remains asserted; deasserting the first row signal line before the column signal line changes from the first desired voltage; In a second active row period that occurs a certain time after the end of the first active row period, setting the column signal lines to the initial voltage; asserting the first row signal line of the pixel array while the column signal line is at the initial voltage; asserting a second row signal line of the pixel array while the column signal line is at the initial voltage; deasserting the first row signal line before the column signal line changes from the initial voltage; driving the column signal line from the initial voltage through a transition to a second desired voltage while the second row signal line is in an asserted state; deasserting the second row signal line before the column signal line changes from the second desired voltage; A method comprising:

2. The method of claim 1 , wherein the initial voltage corresponds to a transparency of each pixel of the pixel array.

3. The method of claim 2 , wherein the degree of transmission is a light-tight level.

4. 2. The method of claim 1, wherein the step of deasserting the row signal line causes a storage capacitor to hold the initial voltage.

5. 2. The method of claim 1, wherein the steps of asserting a row signal line and deasserting a row signal line produce a pulse on the row signal line.

6. 2. The method of claim 1, wherein asserting the row signal line connects the column signal line to a storage capacitor of a pixel of the pixel array.

7. The method of claim 1 further comprising: asserting a second row signal line during the second active row period; A method comprising:

8. The method of claim 7 further comprising: maintaining the second row signal line asserted for a predetermined period of time after deasserting the first row signal line; A method comprising:

9. A pixel array; 1. A pixel matrix scanning system comprising a column driving subsystem and a row driving subsystem, the column driving subsystem and the row driving subsystem During the first active row period: setting the column signal lines to an initial voltage selected to achieve a black level; asserting a first row signal line of the pixel array while the column signal line is at the initial voltage; driving the column signal line through a transition from the initial voltage to a first desired voltage after the first row signal line is asserted; deasserting the first row signal line before the column signal line changes from the first desired voltage; In a second active row period that occurs a certain time after the end of the first active row period, setting the column signal lines to the initial voltage; asserting the first row signal line of the pixel array while the column signal line is at the initial voltage; asserting a second row signal line of the pixel array while the column signal line is at the initial voltage; deasserting the first row signal line before the column signal line changes from the initial voltage; driving the column signal line through a transition from the initial voltage to a second desired voltage while the second row signal line is in an asserted state; A pixel matrix scanning system configured to deassert the second row signal line before the column signal line changes from the second desired voltage.

10. 10. The system of claim 9, wherein the initial voltage corresponds to a transparency of each pixel of the pixel array.

11. 10. The system of claim 9, wherein deassertion of the first row signal line causes a storage capacitor to hold the initial voltage.

12. 10. The system of claim 9, wherein the first row signal line is asserted to connect the column signal line to a storage capacitor of a pixel in the pixel array.

13. 10. The system of claim 9, wherein the column driver subsystem and the row driver subsystem are configured to assert the second row signal line during the second active row period.

14. 14. The system of claim 13, wherein the column driver subsystem and the row driver subsystem are further configured to maintain the second row signal line in an asserted state for a predetermined period of time after the first row signal line is deasserted.

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