TWI397045B - Liquid crystal display device - Google Patents

Description

Liquid crystal display device

The present invention relates to a liquid crystal display device.

At present, liquid crystal display devices are widely used in desktop computers, personal digital assistants (PDAs), portable phones, televisions, and various office automation and audiovisual devices. In the liquid crystal display device and related products, when the external power is turned off, a large amount of residual charge in the liquid crystal display panel of the liquid crystal display device cannot be released in time, which may result in residual image on the display after the shutdown, that is, the phenomenon of shutdown and afterimage.

Please refer to FIG. 1. FIG. 1 is a schematic diagram showing the circuit structure of a prior art liquid crystal display device. The liquid crystal display device 10 includes an active matrix 15, a data driving circuit 11, and a scan driving circuit 13. The active matrix 15 includes a plurality of data lines 153 and a plurality of scan lines 151 intersecting perpendicularly thereto. The complex data lines 153 and the complex scan lines 151 define a complex pixel unit 152. Each pixel unit 152 includes a thin film transistor 155, a pixel electrode 157, and a common electrode 150 disposed corresponding thereto, the pixel electrode 157 and the common electrode 150 and a liquid crystal layer sandwiched therebetween. Not shown) a capacitor is formed for storing gray scale signals. The drain of the thin film transistor 155 is connected to the pixel electrode 157, the source thereof is connected to the data line 153, and the gate thereof is connected to the scan line 151.

The scan driving circuit 13 is connected to the plurality of scan lines 151, and outputs a scan signal to turn on or off the plurality of thin film transistors 155. The data driving circuit 11 is connected to the plurality of data lines 153, and provides a gray scale signal to the complex pixel unit 152 when the plurality of thin film transistors 155 are turned on.

However, when the liquid crystal display device 10 is turned off, the plurality of thin film transistors 155 are turned off due to power-off, and a large amount of electric charge remaining in the pixel electrode 157 cannot be quickly released, causing the liquid crystal display device 10 to have a shutdown phenomenon.

In view of this, it is necessary to provide a liquid crystal display device capable of eliminating the afterimage of shutdown.

A liquid crystal display device includes a scan driving circuit, a reset circuit and a charging circuit. The scan driving circuit is configured to output a first voltage and a second voltage, and includes a first voltage input end and a reset end. When the reset end receives the reset signal, all outputs of the scan driving circuit select the first Voltage. The charging circuit includes a diode, a switching element, and a capacitor. The switching element is turned on when the liquid crystal display device is turned off, and has a first end and a second end. The first end is connected to the diode. a cathode, the anode of the diode is connected to the power source, the first end is simultaneously grounded by the capacitor, and the second end is connected to the first voltage input end. The reset circuit includes an input end connected to the DC power supply, and the output end is connected to the reset end of the scan drive circuit. When the liquid crystal display device is turned off, the output end outputs a reset signal to the reset end.

A liquid crystal display device includes a scan driving circuit, a reset circuit and a charging circuit. The scan driving circuit is configured to output a first voltage and a second voltage; the charging circuit is configured to maintain the first voltage after shutdown; and the reset circuit is configured to select the first voltage of all outputs of the scan driving circuit.

Compared with the prior art, the liquid crystal display device includes a reset circuit and a charging circuit. When the liquid crystal display device is turned off, the charging circuit is first The voltage is charged, and the voltage is maintained for a period of time after being turned off. The reset circuit outputs a reset signal to select the first voltage of the output of the scan driving circuit, so that the plurality of pixel units are turned on, releasing residual charges, and eliminating the The shutdown phenomenon of the liquid crystal display device.

Please refer to FIG. 2 , which is a schematic structural diagram of a circuit of a first embodiment of a liquid crystal display device of the present invention. The liquid crystal display device 20 includes an active matrix 25, a data driving circuit 21, a scan driving circuit 23, a reset circuit 27, and a charging circuit 28. The scan driving circuit 23 is configured to scan the active matrix 25; the data driving circuit 21 is configured to provide gray scale signals to the active matrix 25 when it is scanned. The reset circuit 27 and the charging circuit 28 are connected to the scan driving circuit 23 for releasing the charge remaining in the active matrix 25 after the liquid crystal display device 20 is turned off.

The active matrix 25 includes a plurality of data lines 253 and a plurality of scan lines 251 intersecting perpendicularly thereto. The complex data lines 253 and the complex scan lines 251 define a complex pixel unit 252. Each pixel unit 252 includes a thin film transistor 255, a pixel electrode 257, and a common electrode 250 disposed corresponding thereto, the pixel electrode 257 and the common electrode 250 and a liquid crystal layer sandwiched therebetween. Show) forming a capacitor for storing gray scale signals. The drain of the thin film transistor 255 is connected to the pixel electrode 257, the source thereof is connected to the data line 253, and the gate thereof is connected to the scan line 251.

The data driving circuit 21 transmits a gray scale signal to the complex pixel unit 252 via the complex data line 253, and the scan driving circuit 23 transmits the scanning signal to the complex pixel unit 252 by the complex scanning line 251. The scan driving circuit 23 includes a first voltage input terminal (not shown), a second voltage input terminal (not shown), and a reset terminal 231. The first voltage input terminal receives a first voltage V _GH , the second voltage input terminal receives a second voltage V _GL , and the scan driving circuit 23 selectively outputs the two voltages to a scan line 251 . The first voltage V _GH is about 12 volts, causing the thin film transistor 255 to turn on; the second voltage V _GL is about -2 volts, causing the thin film transistor 255 to turn off. The scan driving circuit 23 includes a reset terminal 231. When the reset terminal 231 receives the reset signal, the output of the scan driving circuit 23 is all selected as the first voltage V _GH .

The charging circuit 28 includes a diode 280, a current limiting resistor 283, a transistor 285, and a capacitor 287. The transistor 285 is an NMOS type transistor, the source thereof is short-circuited with the gate, the gate thereof is grounded by the capacitor 287, and the drain is connected to the input end of the first voltage V _GH , and the source thereof is The current limiting resistor 283 is connected to the cathode 282 of the diode 281. The anode 280 of the diode 280 is connected to a DC power source AVDD, which is about 12 volts.

The reset circuit 27 includes an input terminal 271 and an output terminal 272. The input terminal 271 is connected to the DC power supply DVDD. The DC power supply DVDD is 3.3 volts. The output terminal 272 is connected to the reset terminal 231 of the scan driving circuit 23. When the input terminal 271 detects that the voltage of the DC power supply DVDD is less than 2.7 volts, the output terminal 272 outputs a reset signal. The reset circuit 27 can be implemented by a corresponding reset chip. The reset chip of the model S-80927C-R is shown in FIG. 2, and the reset signal is a low voltage signal.

When the liquid crystal display device 20 is operating normally, the first voltage V _GH maintains a 12 volt output, and the gate voltage of the transistor 285 is higher than its gate voltage, causing the transistor 285 to be turned off. The voltage of the anode 281 is higher than the voltage of the cathode 282 to turn on the diode 280, and the DC power source AVDD charges the capacitor 287 via the diode 280 and the current limiting resistor 283. The DC power supply DVDD detected by the reset circuit 27 maintains a 3.3 volt output, and the reset circuit 27 has no effect on the scan drive circuit 23 at this time.

At the moment of shutdown of the liquid crystal display device 20, the DC power sources AVDD, DVDD and the first voltage V _GH rapidly drop, and the voltage of the source of the transistor 285 remains unchanged for a period of time due to the action of the capacitor 287. When the power supply AVDD drops to a voltage less than the source of the transistor 285, the diode 280 is turned off, and the gate voltage of the transistor 285 is higher than the gate voltage thereof to turn on the transistor 285. The first voltage V _GH It continues to be maintained for a period of time due to the action of the capacitor 287. At the same time, the input terminal 271 of the reset circuit 27 detects that the DC power supply DVDD drops below 2.7 volts, and the output terminal 272 outputs a reset signal to the reset terminal 231 of the scan driving circuit 23, and the scan driving circuit 23 receives the reset signal. After the output is all selected as the first voltage V _GH , the scan driving circuit 23 outputs the first voltage V _GH to all the scan lines 251, so that all the thin film transistors 255 are turned on, and the plurality of pixel electrodes 257 are turned on. The residual charge is released to the complex data line 253 via the plurality of thin film transistors 255, so that the screen of the liquid crystal display device 20 is quickly blackened, and the shutdown image of the liquid crystal display device 20 is quickly eliminated.

The liquid crystal display device 20 of the present invention includes a reset circuit 27 and a charging circuit 28 as compared with the prior art. When the liquid crystal display device 20 is powered off, the charging circuit 28 maintains the first voltage V _GH for a period of time; the reset circuit 27 causes all of the outputs of the scan driving circuit 23 to be selected as the first voltage V _GH . The first voltage V _{GH is} output to the gate of each of the thin film transistors 255, so that all the thin film transistors 255 are turned on, so that the residual charge in the active matrix 25 is released, and the shutdown of the liquid crystal display device 20 is quickly eliminated.

Please refer to FIG. 3 , which is a structural diagram of a charging circuit according to a second embodiment of the liquid crystal display device of the present invention. The structure of the liquid crystal display device of the second embodiment is basically the same as that of the liquid crystal display device of the first embodiment, except that the switching element of the charging circuit 38 is a diode 385. The anode 384 of the diode 385 is connected to the current limiting resistor 383, and the capacitor 387 is grounded, and the cathode 386 is connected to the first voltage V _GH input terminal (not shown).

Compared with the liquid crystal display device of the first embodiment, the switching element of the liquid crystal display device of the second embodiment is a diode 385, and the structure thereof is simpler than the transistor 285, which simplifies the circuit structure of the liquid crystal display device. And its process.

However, the switching element of the present invention is not limited to the NMOS transistor and the diode, and other elements having a switching function such as a PMOS, a MOSFET, and a JFET can be used as the switching element of the present invention.

In summary, the present invention has indeed met the requirements of the invention, and has filed a patent application according to law. However, the above description is only the preferred embodiment of the present invention, and the scope of the present invention is not limited to the above-described embodiments, and equivalent modifications or variations made by those skilled in the art in light of the spirit of the present invention are It should be covered by the following patent application.

20‧‧‧Liquid crystal display device

21‧‧‧Data Drive Circuit

23‧‧‧Scan drive circuit

231‧‧‧Reset end

25‧‧‧Active Matrix

251‧‧‧ scan line

253‧‧‧Information line

252‧‧‧ pixel unit

255‧‧‧film transistor

257‧‧‧ pixel electrodes

250‧‧‧Common electrode

27‧‧‧Reset circuit

271‧‧‧ input

272‧‧‧output

28, 38‧‧‧Charging circuit

280, 385‧‧ ‧ diode

281, 384‧‧‧ first end

282, 386‧‧‧ second end

283, 383‧‧‧ Current limiting resistor

285‧‧‧Optoelectronics

287, 387‧‧‧ Charge storage unit

1 is a schematic diagram showing the circuit structure of a prior art liquid crystal display device.

2 is a schematic view showing the circuit structure of a first embodiment of a liquid crystal display device of the present invention.

3 is a schematic structural view of a charging circuit of a second embodiment of the liquid crystal display device of the present invention.

20‧‧‧Liquid crystal display device

21‧‧‧Data Drive Circuit

23‧‧‧Scan drive circuit

231‧‧‧Reset end

25‧‧‧Active Matrix

251‧‧‧ scan line

253‧‧‧Information line

252‧‧‧ pixel unit

255‧‧‧film transistor

257‧‧‧ pixel electrodes

250‧‧‧Common electrode

27‧‧‧Reset circuit

271‧‧‧ input

272‧‧‧output

28‧‧‧Charging circuit

280‧‧‧ diode

281‧‧‧ first end

282‧‧‧ second end

283‧‧‧ Current limiting resistor

285‧‧‧Optoelectronics

287‧‧‧Charge storage unit

Claims (7)

A liquid crystal display device includes: a scan driving circuit for outputting a first voltage and a second voltage, comprising a first voltage input end and a reset end, wherein the reset end receives the reset signal, the scan drive The first voltage is selected for all outputs of the circuit; a charging circuit comprising a diode, a switching element and a capacitor, the switching element being turned on when the liquid crystal display device is turned off, having a first end and a first a second end, the first end is connected to the cathode of the diode, the anode of the diode is connected to the power source, the first end is simultaneously grounded by the capacitor, and the second end is connected to the first voltage input end; a reset circuit includes an input end and an output end, the input end is connected to a DC power supply, and the output end is connected to the reset end of the scan drive circuit, and when the liquid crystal display device is turned off, the output end outputs a reset signal to the reset end. The liquid crystal display device of claim 1, wherein the switching element is an NMOS transistor, and the gate of the NMOS transistor is connected to the source, the source is extremely first, and the second end is . The liquid crystal display device of claim 1, wherein the switching element is a diode, the anode is a first end, and the cathode is a second end. The liquid crystal display device of claim 1, wherein the charging circuit further comprises a current limiting resistor connected between the cathode of the diode and the first end of the switching element. The liquid crystal display device of claim 1, wherein the The reset circuit is implemented by a reset chip, the type of the reset chip is S-80927C-R, and the reset signal is a low voltage signal. The liquid crystal display device of claim 1, wherein the liquid crystal display device further comprises an active matrix, the active matrix comprising a plurality of pixel units driven by the first voltage and the second voltage. The liquid crystal display device of claim 6, wherein each pixel unit comprises a thin film transistor, the thin film transistor is turned on when receiving the first voltage, and turned off when receiving the second voltage.