News Column

"Display Circuitry with Reduced Pixel Parasitic Capacitor Coupling" in Patent Application Approval Process

September 11, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- A patent application by the inventors Roudbari, Abbas Jamshidi (Sunnyvale, CA); Chang, Shih-Chang (Cupertino, CA); Chang, Ting-Kuo (Cupertino, CA); Yu, Cheng-Ho (Cupertino, CA), filed on February 6, 2014, was made available online on August 28, 2014, according to news reporting originating from Washington, D.C., by VerticalNews correspondents.

This patent application is assigned to Apple Inc.

The following quote was obtained by the news editors from the background information supplied by the inventors: "This relates generally to electronic devices, and more particularly, to electronic devices with touch screen displays.

"Touch screen displays are prevalent in many applications, including consumer electronics devices such as smartphones, tablet devices, and laptop and desktop computers. The display function in such devices is typically performed by a liquid crystal display (LCD), plasma, or organic light emitting diode (OLED) display element array that is connected to a grid of source (data) and gate (select) metal traces. The display element array is often formed on a transparent panel such as a glass panel, which serves as a protective shield. The data and select lines of the display element array may be driven by a display driver integrated circuit (IC). The driver IC receives an image or video signal, which it then decodes into raster scan pixel values (color or gray scale) and writes them to the display element array during each frame, by driving the data and select lines. This process is repeated at a high enough frame rate so as to render video.

"The touch gesture detection function in such devices is typically performed using a capacitance sensing subsystem in which a touch transducer grid structure overlays the display element array. The touch transducer structure is stimulated and sensed by touch controller circuitry. A touch stimulus signal is applied to the row segments of the grid, while simultaneously sensing the column segments (to detect a single-touch or a multi-touch gesture). Touch detection is typically performed during a blanking interval portion of the frame, while the display function is performed during a display interval portion of the frame.

"The touch transducer grid structure can be implemented as a light transparent electrode plate that covers the display element array and may be formed on a rear surface of the protective panel. In some cases, the transparent electrode plate is also connected to the display elements, serving to deliver a 'common voltage' to the display elements from a voltage source circuit often referred to as a Vcom conditioning circuit. The Vcom conditioning circuit helps improve the display function by adjusting a voltage on the transparent conductor plate that changes the light modulation characteristics of the connected display elements (during the display interval). As such, the transparent electrode plate is dual purposed in that it is used for both the display function and as the touch transducer grid structure."

In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventors' summary information for this patent application: "An electronic device having a liquid crystal display (LCD) is provided. The liquid crystal display may include display pixel circuitry formed on a glass substrate. Thin-film transistor structures may be formed on the glass substrate.

"Each display pixel may include a first thin-film transistor (TFT) and a second thin-film transistor coupled in series between a data line and a storage capacitor. The first TFT may have a gate terminal that receives a gate line signal from a gate line, whereas the second TFT may have a gate terminal that receives an enable signal from a control line. The gate line and the control line may be formed in different dielectric layers over the glass substrate. The gate line may be orthogonal to the control line. During data loading operations, the gate line signal may be asserted for a first period of time to turn on the first TFT, and the enable signal may be asserted for a second period of time that is substantially greater than the first period of time to turn on the second TFT (e.g., the second period of time may be at least two times longer than the first period of time, at least ten times longer than the first period of time, at least 100 times longer than the first period of time, at least 1000 times longer than the first period of time, etc.).

"In one suitable arrangement, the first transistor is a top-gate TFT, whereas the second transistor is a bottom-gate TFT. In this arrangement, an electrically floating conductive member may be formed over the second TFT. In another suitable arrangement, the first and second transistors are top-gate TFTs. In either arrangement, an electrically floating light shield structure may be formed directly beneath the first TFT to prevent backlight from affecting the operation of the first TFT. If desired, a third transistor having a gate that also receives the gate line signal may be stacked in series with the first transistor to help reduce leakage.

"In general, the LCD display includes many display pixels arranged in rows and columns. In some embodiments, the second transistor in each display pixel in a first column of the display pixels may be coupled to the control line via a first active circuit, whereas the second transistor in each display pixel in a second column of the display pixels may be coupled to the control line via a second active circuit. The first and second active circuits may be implemented using inverting circuits or using a first pass transistor that passes a positive power supply voltage and a second pass transistor that passes a ground power supply voltage. If desired, the second transistor in each display pixel in a third column of display pixels may also be coupled to the control line via the first active circuit (e.g., adjacent pixels of the same color may be coupled to the control line via a shared active circuit).

"Further features of the present invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 is a perspective view of an illustrative display such as a liquid crystal display in accordance with an embodiment of the present invention.

"FIG. 2 is cross-sectional side view of an illustrative display in accordance with an embodiment of the present invention.

"FIG. 3 is an illustrative diagram showing how a display may be provided with image pixel structures and touch sensor elements in accordance with an embodiment of the present invention.

"FIG. 4 is a top view of a portion of a display showing how cross-lines may be used in implementing touch functionality in accordance with an embodiment of the present invention.

"FIG. 5 is a diagram of a conventional display pixel element.

"FIG. 6 is a circuit diagram of an illustrative display pixel element having at a decoupling bottom-gate thin-film transistor in accordance with an embodiment of the present invention.

"FIG. 7 is a timing diagram showing the behavior of display control signals in accordance with an embodiment of the present invention.

"FIG. 8 is a top layout view of the display pixel of FIG. 6 in accordance with an embodiment of the present invention.

"FIG. 9 is a cross-sectional side view showing an illustrative dielectric stack-up arrangement that can be used in forming display pixel structures in accordance with an embodiment of the present invention.

"FIG. 10 is a circuit diagram of an illustrative display pixel element having a decoupling top-gate thin-film transistor in accordance with an embodiment of the present invention.

"FIG. 11 is a circuit diagram of an illustrative display pixel element having stacked gate line thin-film transistors and a decoupling bottom-gate thin-film transistor in accordance with an embodiment of the present invention.

"FIG. 12 is a top layout view of the display pixel of FIG. 11 in accordance with an embodiment of the present invention.

"FIG. 13 is a top layout view of a display pixel of the type shown in FIG. 11, where the decoupling transistor is implemented using a top-gate thin-film transistor in accordance with an embodiment of the present invention.

"FIG. 14 is a diagram showing additional loading components that can be interposed in light shield lines to reduce power consumption in accordance with an embodiment of the present invention.

"FIG. 15 is a diagram illustrating how the use of the additional loading components of FIG. 14 helps reduce power consumption in accordance with an embodiment of the present invention.

"FIGS. 16A and 16B show two different possible implementations of the additional loading components in accordance with an embodiment of the present invention.

"FIG. 17 is a diagram showing how adjacent sub-pixels of the same color may be routed to a common light shield line loading component in accordance with an embodiment of the present invention."

URL and more information on this patent application, see: Roudbari, Abbas Jamshidi; Chang, Shih-Chang; Chang, Ting-Kuo; Yu, Cheng-Ho. Display Circuitry with Reduced Pixel Parasitic Capacitor Coupling. Filed February 6, 2014 and posted August 28, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4740&p=95&f=G&l=50&d=PG01&S1=20140821.PD.&OS=PD/20140821&RS=PD/20140821

Keywords for this news article include: Apple Inc.

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Source: Politics & Government Week


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