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Patent Issued for Display Device with Image Pickup Function, Driving Method, and Electronic Device

July 22, 2014



By a News Reporter-Staff News Editor at China Weekly News -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Omori, Hideyuki (Aichi, JP); Yamanaka, Go (Kanagawa, JP); Senda, Michiru (Aichi, JP); Nakajima, Yoshiharu (Kanagawa, JP), filed on November 2, 2010, was published online on July 8, 2014.

The assignee for this patent, patent number 8773415, is Japan Display West Inc. (Aichi-Ken, JP).

Reporters obtained the following quote from the background information supplied by the inventors: "The present application relates to a display device which incorporates an image pickup function for optically detecting an external proximity object, a method of driving the same, and an electronic device including the same.

"In recent years, a display device in which information input is enabled has attracted attention. In this display device, a touch detecting function detecting a contact of a finger or the like is equipped in a display device such as a liquid crystal display device, and various button images are displayed on that display device, instead of using typical mechanical buttons. In the display device having such a touch detecting function, since an input device such as a keyboard, a mouse, and a keypad is not necessary, there is a tendency that use of the display device is expanded in a portable information terminal such as a portable phone in addition to a computer.

"There are several methods in touch detecting methods, and one of them is an optical method. In the display device having such an optical touch detecting function, for example, there is a display device in which light emitted from the display device, and reflected by the external proximity object in the vicinity of a display surface is detected by a photo-detector incorporated in the display device, and the external proximity object is detected based on a light amount. For example, in Japanese Unexamined Patent Publication No. 2008-205870, the display device which incorporates the image pickup function is proposed. In that image pickup function, a photoelectric conversion element is used as the photo-detector, and electric charges supplied from the photoelectric conversion element are stored for charging in a capacitor during a predetermined period, thereby detecting the external proximity object based on the amount of electric charges."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "However, in the display device incorporating the above-described image pickup function, for example, there is a risk that a so-called crosstalk noise is mixed into an image pickup element (capacitor) from wiring or the like which transmits a display signal, through a parasitic capacity. In this case, the S/N ratio of a touch detecting signal obtained from an output signal of the image pickup element, and corresponding to the existence of the external proximity object is deteriorated. Therefore, for example, there is a risk that the sensitivity of a touch sensor to the external proximity object is changed depending on a display image. Alternatively, even when the external proximity object is not existed, there is a risk of malfunction that the touch sensor is reacted according to content of the display image, or the like.

"To suppress the influence of such a crosstalk noise, for example, the method in which the image pickup element and signal wiring are shielded is considered. However, in this case, since the external proximity object is detected through a shield, there is a risk that the sensitivity of the touch sensor is deteriorated, and there is a risk that the power consumption of a drive circuit is increased due to the parasitic capacity of the signal wiring. Further, since the thickness of the display device itself is increased by adding the shield, there is a risk that the size reduction becomes difficult. Therefore, in the display device incorporating the image pickup element, it is desirable to minimize an adverse effect to the image pickup element caused by the crosstalk noise, without newly providing the shield. In other words, it is desirable to improve the resistance to the crosstalk noise.

"In view of the foregoing, it is desirable to provide a display device with an image pickup function capable of minimizing an adverse effect given to an operation of a touch sensor by a display signal acting as a noise while the device size and the power consumption are suppressed from increasing, a driving method, and an electronic device.

"According to an embodiment, there is provided a display device with an image pickup function including: a plurality of pixel signal lines each supplied with a pixel signal; a plurality of display pixels each performing a display operation based on the pixel signal; and a plurality of image pickup elements. Each of the plurality of image pickup elements includes a photo-detector and a capacitor, the photo-detector generating a current of a magnitude corresponding to a photo-detection amount, the capacitor performing a discharging operation which follows a charging operation with the current from the photo-detector to output a charged voltage for a read operation. Control is performed so that a voltage level of the pixel signal line during the discharging operation is equal to a voltage level of the pixel signal line during the reading operation.

"According to another embodiment, there is provided a method of driving a display device with an image pickup function. The method includes steps of, when the display device with the image pickup function having the above-described structure is driven, in the individual image pickup elements, performing a discharging operation of the capacitor which follows a charging operation of the capacitor with the current to output a charged voltage for a read operation, the current being supplied from the photo-detector in response to photo-detection, and performing control so that a voltage level of the pixel signal line during the discharging operation is equal to a voltage level of the pixel signal line during the reading operation.

"According to another embodiment, there is provided an electronic device including: the above-described display device with the image pickup function of the present application, and the electronic device corresponds to, for example, a television device, a digital camera, a personal computer, a video camera, or a mobile terminal device such as a mobile phone.

"In the display device with the image pickup function, the method of driving the same, and the electronic device according to the an embodiment, light corresponding to an existence of an external proximity object is incident on the image pickup element. The photo-detector in the image pickup element generates the current of the magnitude corresponding to the photo-detection amount, and the charging operation to the capacitor is performed with that current. This charging operation is started after the discharging operation of the capacitor, and electric charges charged to the capacitor is read as the voltage after a passage of a predetermined time. This read voltage has a value corresponding to the existence of the external proximity object, and the external proximity object is detected based on a voltage difference of the capacitor between the discharging operation and the reading operation.

"At that time, when a display signal for the display operation is applied to the pixel signal line, a crosstalk noise caused by the display signal is mixed from the pixel signal line to the image pickup element (capacitor). However, since the signals having the voltage levels equal to each other are applied to the pixel signal line during the discharging operation and the reading operation of the capacitor, amounts of the crosstalk noise from the pixel signal line to the image pickup element are approximately equal to each other during the discharging operation and the reading operation. As a result, influence of the crosstalk noise is approximately canceled in both the discharging operation and the reading operation, and the voltage difference of the detected capacitor is suppressed from changing by being influenced by the display signal.

"The display pixel may be driven, for example, by a horizontal line sequential drive. In this case, the discharging operation is performed in a certain horizontal blanking period, and the reading operation is desirably performed in the different horizontal blanking period after the passage of the predetermined period of a display operation period over one or a plurality of horizontal lines.

"For example, in the case where the display is performed by using a time-divisionally multiplexed signal in which the pixel signals are time-divisionally multiplexed, by providing a plurality of first switching elements, and turning on/off the plurality of first switching elements, the individual pixel signals are demultiplexed from the supplied time-divisionally multiplexed signal, and these pixel signals are supplied to the plurality of pixel signal lines, respectively.

"As a specific example to equal the voltage levels of the pixel signal lines during the discharging operation and the reading operation, for example, the following two methods may be used. In a first method, a signal including a period of a predetermined-level voltage in a timing position which is synchronized with the horizontal blanking period is used as the time-divisionally multiplexed signal to be supplied, and all the first switching elements turn on in the horizontal blanking period, and therefore the predetermined-level voltage is supplied to all the plurality of pixel signal lines. In this method, the voltage levels of all the pixel signal lines are equal to each other in all the horizontal blanking periods. As a result, the voltage levels of the pixel signal lines are equal to each other during the discharging operation and the reading operation.

"In a second method, a plurality of second switching elements which may turn on/off a supply of a predetermined signal are provided, all the first switching elements turn off, and all the second switching elements turn on in the horizontal blanking period, and therefore the predetermined-level signal is applied to all the plurality of pixel signal lines. A DC level signal having a constant voltage level is utilized as the predetermined signal. Also in this method, in the same manner as the above-described first method, the voltage levels of all the pixel signal lines are equal to each other in all the horizontal blanking periods. As a result, the voltage levels of the pixel signal lines are equal to each other during the discharging operation and the reading operation. In addition, as the predetermined signal, an existing signal (for example, a common signal applied to a common electrode (opposite electrode) in the polarity inversion drive of a liquid crystal display device) having the same voltage level during the discharging operation and the reading operation may be used.

"According to the display device with the image pickup function, the method of driving the same, and the electronic device of the an embodiment, since the voltage levels applied to the pixel signal lines are set to be equal to each other during the discharging operation and the reading operation of the image pickup element, it may be possible to minimize an adverse effect given to an operation of a touch sensor by a display signal acting as a noise, while the device size and the power consumption are suppressed from increasing.

"Additional features and advantages are described herein, and will be apparent from the following Detailed Description and the figures."

For more information, see this patent: Omori, Hideyuki; Yamanaka, Go; Senda, Michiru; Nakajima, Yoshiharu. Display Device with Image Pickup Function, Driving Method, and Electronic Device. U.S. Patent Number 8773415, filed November 2, 2010, and published online on July 8, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8773415.PN.&OS=PN/8773415RS=PN/8773415

Keywords for this news article include: Asia, Japan Display West Inc.

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Source: China Weekly News


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