JP4613689B2 - Display device with built-in optical sensor - Google Patents

Description

  The present invention relates to a photosensitive element that responds to light input from a light source, and a photosensor (photodetection type digitizer) that includes a photosensitive circuit composed of a photosensitive element and a transistor, and more particularly to a display device incorporating a photosensor. Is.

  In the conventional liquid crystal display device with a built-in light detection type digitizer, the potential of the sensor connected to the row scanning line related to the digitizer function is given as the gate potential of the thin film transistor. The OFF state is controlled, and the signal is detected from the column scanning line related to the digitizer function (see, for example, Patent Document 1).

JP 2001-75732 A (page 7, FIG. 12)

  In the conventional liquid crystal display device with a built-in light detection type digitizer disclosed in the above-mentioned document, in order to operate the digitizer function, scanning signals composed of pulse waveforms for driving thin film transistors are sequentially input to the row scanning lines related to the digitizer function. Two scanning signals are required together with the gate wiring related to the display function. In this case, two scanning signal driver circuits are required, which increases the cost.

  An object of the present invention is to solve the above-described problems, and to obtain a display device with a built-in photosensor that does not need to sequentially input scanning signals to row scanning lines related to the photosensor function, and can reduce the cost. To do.

  In the present invention, a photosensitive circuit scanning thin film transistor, which is a second transistor, is connected in series between a thin film transistor, which is a first transistor of a photosensitive circuit related to an optical sensor function, and a signal detection wiring. The electrode is connected to the gate wiring of the display circuit related to the display function.

  The present invention makes it possible to detect the signal of the photosensitive circuit in conjunction with the scanning signal for the gate wiring of the display circuit, and to sequentially input a scanning signal different from the display circuit to the row scanning line related to the optical sensor function. Disappears.

Embodiment 1 FIG.
FIG. 1 is a circuit configuration diagram of one pixel Cij in the optical sensor built-in liquid crystal display device according to the first embodiment of the present invention. The pixel includes a display circuit related to a display function and a photosensitive circuit related to an optical sensor function.

  The display circuit is the same as a normal liquid crystal display device, and includes a gate wiring Qi, a video signal wiring Pj intersecting with the gate wiring Qi, a display circuit thin film transistor TDij used for the switching operation of the pixel electrode, and a pixel electrode and a counter electrode. And a common wiring Zi that forms an auxiliary capacitance Cs for holding charges.

  The photosensitive circuit includes a signal detection wiring Xj for extracting a signal of the photosensitive circuit outside the display area, a first potential supply wiring Yi, a common wiring Zi that also serves as a second potential supply wiring, a photosensitive element Sij, a reference element A resistor Rij, a thin film transistor Tij as a first transistor, and a photosensitive circuit scanning thin film transistor T2ij as a second transistor connected in series to the resistor Rij. The gate electrode of the photosensitive circuit scanning thin film transistor T2ij is connected to the gate wiring Qi of the display circuit. Accordingly, the signal detection of the photosensitive circuit can be performed in conjunction with the scanning signal of the liquid crystal display circuit, and it is not necessary to apply a scanning signal different from the display circuit to the first potential supply wiring Yi.

  Next, the operation principle will be described in detail. The photosensitive element Sij and the reference resistor Rij are connected in series, and connect between the first potential supply wiring Yi and the common wiring Zi that also serves as the second potential supply wiring. When the potential of the first potential supply wiring Yi is Vy, the potential of the common wiring Zi is Vz, the resistance value of the photosensitive element is Rsij, and the resistance of the reference resistance is Rrij, the photosensitive element Sij and the reference resistance Rij at position A are divided. The potential Vsij of the photosensitive element Sij is expressed by the following formula (1).

  Vsij = Vz + (Vy−Vz) · Rrij / (Rsij + Rrij) (1)

  This potential Vsij is supplied as the gate potential of the thin film transistor Tij of the photosensitive circuit. Since the potential Vsij changes according to the difference between the resistance value Rsij when the photosensitive element Sij is irradiated with light and when it is not irradiated with light, the thin film transistor Tij of the photosensitive circuit depends on the difference in the amount of light irradiated to the photosensitive element Sij. The current that flows between the source and drain changes.

  Here, in the case of an active matrix liquid crystal display device using an amorphous silicon (a-Si) thin film transistor, the photosensitive element Sij and the reference resistor Rij are preferably a-Si photodiodes. FIG. 2 shows a circuit configuration diagram of the a-Si photodiode. As shown in FIG. 2, the a-Si photodiode is formed in the same manufacturing process as the display circuit thin film transistor TDij of the display circuit, and the gate electrode and the source electrode (or drain electrode) of the a-Si thin film transistor are electrically connected. It is only a configuration. It is possible to incorporate a photosensitive circuit without adding a new process to the manufacturing process of the liquid crystal display device.

  In addition, the photosensitive element Sij and the reference resistor Rij can be made separately depending on whether or not the a-Si constituting the channel region of the thin film transistor constituting each is shielded. The photosensitive element Sij is not shielded so as to be irradiated with light for light detection, and the reference resistor Rij is shielded so as not to be irradiated with light.

  As a light shielding method, a black matrix is formed on a counter substrate (not shown) on the reference resistor Rij, and a black matrix is not formed on the counter substrate on a-Si constituting the channel region of the photosensitive element Sij. To do.

  Alternatively, the channel region of the reference resistor Rij may be shielded from light by a metal film such as a wiring material on the array substrate on which the display circuit and the photosensitive circuit are formed instead of the black matrix on the counter substrate.

  FIG. 3 is a voltage-current characteristic diagram of an a-Si photodiode serving as the photosensitive element Sij. The voltage-current characteristic is non-linear, and the current value increases as the voltage increases. In addition, the current value varies greatly between light irradiation and non-irradiation, and almost no current flows when light is not irradiated.

  FIG. 4 is a modification of FIG. 3 to a voltage-resistance characteristic diagram of an a-Si photodiode. The resistance value of the a-Si photodiode increases as the voltage increases. Further, the resistance value is remarkably lowered by light irradiation.

  The resistance value Rrij of the reference resistor Rij and the resistance value Rsij of the photosensitive element Sij are inversely proportional to W / L (W is the channel width and L is the channel length) of the a-Si thin film transistor that constitutes the a-Si photodiode.

  In Embodiment 1 of the present invention, the resistance value Rrij of the reference resistor Rij when no light is irradiated is set by setting the W / L of the thin film transistor constituting the reference resistor Rij to be larger than the W / L of the photosensitive element Sij. Is configured to be smaller than the resistance value Rsij of the photosensitive element Sij.

  Since the voltage is distributed to the reference resistor Rij and the photosensitive element Sij based on the equation (1), the voltage applied to the reference resistor Rij is smaller than the voltage applied to the photosensitive element Sij. Furthermore, from FIG. 4, the resistance of the a-Si photodiode is not constant, and the resistance decreases as the voltage decreases. Therefore, in the first embodiment of the present invention, when no light is irradiated, the resistance value Rrij of the reference resistor Rij is relatively smaller than the W / L ratio with respect to the resistance value Rsij of the photosensitive element Sij.

  FIG. 5 shows a light irradiation amount and potential characteristic diagram of the photosensitive element Sij showing the first embodiment of the present invention. The potential Vsij of the photosensitive element Sij formed of an a-Si photodiode is rapidly changed from the potential Vz of the common wiring Zi, which is the second potential supply wiring, to the potential Vy of the first potential supply wiring Yi depending on the amount of light irradiation.

  The reason for this is that if the photosensitive element Sij is not irradiated with light, the result is Rsij >> Rrij, so Vsij≈Vz from equation (1). The gate potential of the thin film transistor Tij in the photosensitive circuit is substantially equal to the potential Vz of the common wiring Zi on the reference resistor Rij side.

  On the other hand, when the photosensitive element Sij is irradiated with light, the resistance value Rsij of the photosensitive element Sij is significantly reduced as shown in FIG. 4, and thus becomes smaller than the resistance value Rrij of the reference resistance Rij, and Rsij << Rrij. Therefore, Vsij≈Vy from Expression (1). The gate potential of the thin film transistor Tij in the photosensitive circuit is substantially equal to the potential Vy of the first potential supply wiring Yi on the photosensitive element Sij side.

  Based on the above operation principle, the gate potential of the thin film transistor Tij of the photosensitive circuit is changed between the potential Vz of the common wiring Zi as the second potential supply wiring and the potential Vy of the first potential supply wiring Yi by the light irradiation amount to the photosensitive element Sij. Can be changed.

  Here, the dimensions of the photosensitive element Sij and the reference resistor Rij are, for example, the channel width W of the thin film transistor that constitutes the reference resistor Rij is 25 μm, the channel length L is 4 μm, and the channel width W of the thin film transistor that constitutes the photosensitive circuit Sij is 10 μm. The channel length L was set to 4 μm. As described above, the ratio of W / L between the photosensitive element Sij and the reference resistance is preferably 2 times or more, and preferably 2.5 times or more as in this example.

  Next, a signal or potential similar to that of a general liquid crystal display device may be supplied to the gate wiring Qi, the video signal wiring Pj, and the common wiring Zi of the display circuit. In the first embodiment of the present invention, for example, the gate wiring Qi is 20V when the gate is ON, -6V when the gate is OFF, the video signal wiring Pj is a signal of 0.5V to 9V corresponding to the video, and the common wiring Zi is A constant potential of 4 V that is equal to the potential of the counter electrode (not shown) was supplied.

  Further, since the first potential supply wiring Yi is not provided in a normal liquid crystal display device, −6 V, which is the same as the gate OFF potential of the gate wiring Qi, was supplied. Thereby, it is not necessary to prepare a new power supply by using the potential already prepared on the circuit board.

  In the above configuration, the gate potential of the thin film transistor Tij of the photosensitive circuit when the photosensitive element Sij is not irradiated with light is about 4V, and the gate potential of the thin film transistor Tij of the photosensitive circuit when the photosensitive element Sij is irradiated with light is about −6V.

  When the photosensitive element Sij is not irradiated with light, the thin film transistor Tij of the photosensitive circuit is turned on, and the potential Vz of the common wiring Zi is supplied to one of the source and drain of the thin film transistor T2ij for photosensitive circuit scanning connected in series. The photosensitive circuit scanning thin film transistor T2ij is also turned on in conjunction with the gate scanning signal of the gate wiring Qi, so that the common wiring Zi and the signal detection wiring Xj are electrically connected.

  When the photosensitive element Sij is irradiated with light, the thin film transistor Tij of the photosensitive circuit is turned off, and the common wiring Zi and the signal detection wiring Xj are not electrically connected regardless of the photosensitive circuit scanning thin film transistor T2ij.

  By supplying a potential 0 V to the signal detection wiring Xj and connecting an integrator (not shown), when electrically connected to the common wiring Zi as described above, the common wiring Zi to the signal detection wiring Xj. By detecting the flowing current, it is possible to determine the light irradiation of the photosensitive element Sij.

  Further, the position detection of the photosensitive element Sij can be specified by the row coordinate i of the gate wiring Qi and the column coordinate j of the signal detection wiring Xj at the timing of the scanning signal for the gate wiring of the display circuit.

  FIG. 6 shows an overall configuration diagram of the photosensor built-in display device according to the first embodiment of the present invention. The pixels of FIG. 1 are arranged in a matrix according to the display resolution, the gate driving circuit 1 is connected to the gate wiring Qi, the source driving circuit 2 is connected to the video signal wiring Pj, and the photosensor detection circuit 3 is connected to the signal detection wiring Xj. Vz (about 4V) which is a common potential is supplied to the common wiring Zi which is a two-potential supply wiring, and Vy (about -6V) which is substantially equal to the above-described gate OFF potential is supplied to the first potential supply wiring Yi.

  Although FIG. 6 shows an example in which a photosensitive circuit is provided for all the pixels, the photosensitive circuit does not need to be included in all the pixels, and a plurality of pixels are provided according to the optical position detection resolution required by the display device with a built-in optical sensor. What is necessary is just to thin and arrange every time. For example, it is possible to adopt a configuration such as one photosensitive circuit for three horizontal or vertical pixels.

Embodiment 2. FIG.
FIG. 7 is a circuit configuration diagram showing one pixel of the photosensor built-in display device according to Embodiment 2 of the present invention. In the first embodiment of the present invention, an example in which the photosensitive element Sij is arranged on the first potential supply wiring Yi side and the reference resistor Rij is arranged on the common wiring Zi side is shown, but in the second embodiment of the present invention, these are replaced. The reference resistor Rij is disposed on the first potential supply wiring Yi side, and the photosensitive element Sij is disposed on the common wiring Zi side.

  In this case, when the photosensitive element Sij is not irradiated with light, the gate potential of the thin film transistor Tij of the photosensitive circuit is in the vicinity of the potential Vy (about −6 V) supplied by the first potential supply wiring Yi. When the photosensitive element Sij is irradiated with light, the gate potential of the thin film transistor Tij of the photosensitive circuit is near the potential Vz (about 4 V) of the common wiring Zi, and only when the photosensitive element Sij is irradiated with light, the thin film transistor Tij of the photosensitive circuit is turned on. Become. That is, the ON / OFF operation of the thin film transistor Tij of the photosensitive circuit for light irradiation / non-irradiation to the photosensitive element Sij can be reversed from that of the first embodiment of the present invention.

Embodiment 3 FIG.
FIG. 8 is a circuit configuration diagram showing one pixel of the photosensor built-in display device according to Embodiment 3 of the present invention. In the first and second embodiments of the present invention, the example in which one of the source and the drain of the thin film transistor Tij of the photosensitive circuit is connected to the common wiring Zi, but may be connected to the first potential supply wiring Yi.

  In the case where 4 V is supplied to the common wiring Zi, −6 V to the first potential supply wiring Yi, and 0 V to the signal detection wiring Xj, in the first and second embodiments of the present invention, between the source and drain of the thin film transistor Tij of the photosensitive circuit The voltage Vds is about 4 V, and the gate-source voltage Vgs changes in the range of about −6 V to about 4 V depending on whether the photosensitive element is irradiated with light or not.

  On the other hand, in Embodiment 3 of the present invention, the source-drain voltage Vds of the thin film transistor Tij of the photosensitive circuit is about 6 V, and the gate-source voltage Vgs is about 0 V to about 10 V by light irradiation or non-irradiation to the photosensitive element. Varies with range. The gate-source voltage Vgs of the thin film transistor Tij of the photosensitive circuit changes in a small direction. The absolute value of the current flowing through the thin film transistor Tij of the photosensitive circuit becomes large, and the configuration of the photosensor detection circuit 3 can be simplified.

Embodiment 4 FIG.
In the first to third embodiments of the present invention, about 4 V, which is the same as the common wiring Zi, is supplied as the second potential supply wiring, and about -6 V is supplied to the first potential supply wiring Yi, which is the same as the gate OFF potential of the gate wiring Qi. Alternatively, when a power supply different from the display circuit is prepared in one of them and the potential difference between the first potential supply wiring Yi and the second potential supply wiring is increased, the current flowing through the thin film transistor Tij of the photosensitive circuit, light irradiation / non-irradiation The current ratio can be increased, and the configuration of the photosensor detection circuit 3 can be simplified.

  For example, when a voltage of about −16 V is applied to the first potential supply wiring Yi, in Embodiment 3 of the present invention, the source-drain voltage Vds of the thin film transistor Tij of the photosensitive circuit is about 16 V, and the gate-source voltage Vgs. Can be changed in a range of about 0 V to about 20 V by irradiating or not irradiating light to the photosensitive element, and a larger current can be supplied to the signal detection wiring Xj.

  In the above first to fourth embodiments of the present invention, the liquid crystal display device has been described. However, the display device is not limited to the liquid crystal, and the display device is based on other principles such as electroluminescence (EL), electrochromic, and electrophoresis. It doesn't matter.

It is a circuit block diagram of 1 pixel in the optical sensor built-in liquid crystal display device which shows Embodiment 1 of this invention. It is a circuit block diagram of an a-Si photodiode. It is a voltage-current characteristic view of an a-Si photodiode. It is a voltage-resistance characteristic view of an a-Si photodiode. It is a light irradiation amount-potential characteristic diagram of the photosensitive element showing the first embodiment of the present invention. It is a whole block diagram in the optical sensor built-in liquid crystal display device which shows Embodiment 1 of this invention. It is a circuit block diagram of 1 pixel in the optical sensor built-in liquid crystal display device which shows Embodiment 2 of this invention. It is a circuit block diagram of 1 pixel in the optical sensor built-in liquid crystal display device which shows Embodiment 3 of this invention.

Explanation of symbols

1 gate drive circuit, 2 source drive circuit, 3 photo sensor detection circuit, Cij pixel, Qij gate wiring, Pj video signal wiring, Zi common wiring (second potential supply wiring), thin film transistor of TDij display circuit, Clc liquid crystal capacitance, Cs Auxiliary capacitance, Xj signal detection wiring, Yi first potential supply wiring, Sij photosensitive element, Rij reference resistance, Tij photosensitive circuit thin film transistor (first transistor), T2ij photosensitive circuit scanning thin film transistor (second transistor).

Claims (8)

The photosensitive circuit that constitutes the optical sensor and the display circuit that constitutes the display device are provided on the same substrate,
The photosensitive circuit is between the first potential supply wiring and the second potential supply wiring.
Connected with a photosensitive element and a reference resistor connected in series with the photosensitive element;
A first transistor that switches according to the potential of the photosensitive element;
A second transistor that is connected in series with the first transistor and that performs a switching operation in conjunction with a scanning signal of the display circuit;
A signal detection wiring connected to the second transistor;
A display device with a built-in optical sensor. The display device with a built-in optical sensor according to claim 1, wherein the first transistor is connected to a first potential supply line or a second potential supply line. 3. The display device with a built-in optical sensor according to claim 1, wherein the second potential supply wiring is also used as a common wiring of the display circuit. 4. 4. The display device with a built-in photosensor according to claim 1, wherein the photosensitive element is set to a potential at which the first transistor is turned off during light irradiation. 5. 4. The display device with a built-in photosensor according to claim 1, wherein the photosensitive element is set to a potential at which the first transistor is turned on during light irradiation. 5. 6. The device according to claim 1, wherein the first potential supply wiring or the second potential supply wiring supplies a potential at which the first transistor is turned off or on. Photosensor built-in display device. The display device with a built-in optical sensor according to claim 1, wherein the photosensitive element is a photodiode made of amorphous silicon. The display device with a built-in photosensor according to claim 1, wherein the reference resistor is made of amorphous silicon and is shielded from light.

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