CN101546529B - Liquid crystal display device - Google Patents

Abstract

The invention provides a liquid crystal display device, which includes: a scanning driving circuit, an active matrix, a reset circuit and a charging circuit. The scanning driving circuit is used to output a first level and a second level; the active matrix includes a plurality of pixel units driven by the first level and the second level, and each pixel unit includes a thin film transistor , the thin film transistor is turned on when receiving the first level, and is turned off when receiving the second level, and the charging circuit is used to maintain the first level after shutdown; the reset circuit enables all outputs of the scan driving circuit to be selected the first level. The liquid crystal display device can quickly and effectively eliminate afterimage after shutdown.

Description

Liquid crystal display device

technical field

The invention relates to a liquid crystal display device.

Background technique

At present, liquid crystal display devices are widely used in desktop computers, personal digital assistants (Personal Digital Assistant, PDA), portable phones, televisions, and various office automation and audio-visual equipment. In liquid crystal display devices and related products, when the external power is turned off, since a large amount of residual charge in the liquid crystal display panel of the liquid crystal display device cannot be released in time, there will be residual images on the display screen after shutdown, that is, after-image phenomenon after shutdown.

Please refer to FIG. 1 , which is a schematic circuit diagram 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 scanning driving circuit 13 . The active matrix 15 includes a plurality of data lines 153 and a plurality of scan lines 151 vertically insulated and intersected therewith. The plurality of data lines 153 and the plurality of scan lines 151 divide a plurality of pixel units 152 . Each pixel unit 152 includes a thin film transistor 155, a pixel electrode 157 and a common electrode 150 corresponding to it, and the pixel electrode 157 is formed with the common electrode 150 and a liquid crystal layer (not shown) sandwiched between them. A capacitor is used to store the gray scale signal. The drain of the TFT 155 is connected to the pixel electrode 157 , the source is connected to the data line 153 , and the gate 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 grayscale signals for the plurality of pixel units 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 failure, and the large amount of charge remaining in the pixel electrode 157 cannot be quickly released, causing the liquid crystal display device 10 to have image sticking after power off.

Contents of the invention

In order to solve the problem of residual image after shutdown in the prior art liquid crystal display device, it is necessary to provide a liquid crystal display device that can effectively eliminate the residual image after shutdown.

A liquid crystal display device, which includes: a scan driving circuit, an active matrix, a reset circuit and a charging circuit. The scan drive circuit is used to output a first level and a second level, the active matrix includes a plurality of pixel units driven by the first level and the second level, and each pixel unit includes a thin film transistor , the thin film transistor is turned on when receiving the first level, and is turned off when receiving the second level, the scan driving circuit includes a first level input terminal and a reset terminal, the charging circuit includes a diode, a switching device and a Capacitor, the switching device is turned on when the liquid crystal display device is turned off, it has a first end and a second end, the first end is connected to the cathode of the diode, the anode of the diode is connected to a DC power supply, and the first end is simultaneously The capacitor is grounded, and the second end is connected to the first level input end. The reset circuit includes an input terminal and an output terminal, the input terminal is connected to a DC power supply, the output terminal is connected to the reset terminal of the scanning drive circuit, when the liquid crystal display device is turned off, the output terminal outputs a reset signal to the reset terminal, When the reset terminal receives a reset signal, all outputs of the scan driving circuit are selected to be at the first level.

A liquid crystal display device, which includes: a scan driving circuit, an active matrix, a reset circuit and a charging circuit. The scanning driving circuit is used to output a first level and a second level; the active matrix includes a plurality of pixel units driven by the first level and the second level, and each pixel unit includes a thin film transistor , the thin film transistor is turned on when receiving the first level, and is turned off when receiving the second level, and the charging circuit is used to maintain the first level after shutdown; the reset circuit enables all outputs of the scan driving circuit to be selected the first level.

Compared with the prior art, the above-mentioned liquid crystal display device includes a reset circuit and a charging circuit. When the liquid crystal display device is turned off, the charging circuit charges the first level so that the level continues to be maintained for a period of time after the liquid crystal display device is turned off. The reset circuit outputs a reset signal to make all the outputs of the scanning drive circuit select the first level, so that the plurality of pixel units are turned on, and residual charges are released, so as to quickly and effectively eliminate the afterimage after shutdown of the liquid crystal display device.

Description of drawings

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

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

FIG. 3 is a schematic diagram of the circuit structure of the charging circuit of the second embodiment of the liquid crystal display device of the present invention.

Detailed ways

Please refer to FIG. 2 , which is a schematic diagram of the circuit structure of the first embodiment of the 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 scanning driving circuit 23 , a reset circuit 27 and a charging circuit 28 . The scan driving circuit 23 is used to scan the active matrix 25; the data driving circuit 21 provides grayscale 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 , and release the residual charge of the active matrix 25 after the liquid crystal display device 20 is turned off.

The active matrix 25 includes a plurality of data lines 251 and a plurality of scan lines 253 vertically insulated and intersected therewith. The plurality of data lines 251 and the plurality of scan lines 253 divide a plurality of pixel units 252 . Each pixel unit 252 includes a thin film transistor 255, a pixel electrode 257, and a common electrode 250 corresponding to it. The capacitor is used to store the grayscale signal. The drain of the TFT 255 is connected to the pixel electrode 257 , the source is connected to the data line 253 , and the gate is connected to the scan line 251 .

The data driving circuit 21 transmits gray scale signals to the plurality of pixel units 252 through the plurality of data lines 253 , and the scan driving circuit 23 transmits scanning signals to the plurality of pixel units 252 through the plurality of scanning lines 251 . The scan driving circuit 23 includes a first level input terminal (not shown), a second level input terminal (not shown in the figure) and a reset terminal 231 . The first level input end receives a first level V _GH , the second level input end receives a second level V _GL , and the scanning driving circuit 23 selectively outputs the two levels to a scanning line. on line 251. The first level V _GH is about 12 volts to turn on the thin film transistor 255 ; the second level V _GL is about −2 volts to turn off the thin film transistor 255 . The scan driving circuit 23 includes a reset terminal 231 , when the reset terminal 231 receives a reset signal, all the outputs of the scan driving circuit 23 are selected as the first level 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 transistor, its source and gate are short-circuited, its gate is connected to the ground through the capacitor 287, its drain is connected to the input terminal of the first level V _GH , and its source is connected to the current limiting The resistor 283 is connected to the cathode 282 of the diode 281, and the anode 280 of the diode 280 is connected to a DC power supply AVDD, and the DC power supply AVDD 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 a 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 scanning drive circuit 23, When the input terminal 271 detects that the level of the DC power DVDD is less than 2.7 volts, the output terminal 272 outputs a reset signal. The reset circuit 27 can be implemented with a corresponding reset chip. The reset chip of model S-80927C-R is shown in FIG. 2 , and the reset signal is a low-level signal.

When the liquid crystal display device 20 works normally, the first level V _GH maintains an output of 12 volts, and the drain level of the transistor 285 is higher than the gate level, so that the transistor 285 is turned off. The level of the anode 281 is higher than the level of the cathode 282 to turn on the diode 280 , and the DC power AVDD charges the capacitor 287 through the diode 280 and the current limiting resistor 283 . The DC power DVDD detected by the reset circuit 27 maintains an output of 3.3 volts, and the reset circuit 27 has no effect on the scan driving circuit 23 at this time.

When the liquid crystal display device 20 is turned off, the DC power supply AVDD, DVDD and the first level V _GH drop rapidly, and the level of the source of the transistor 285 remains unchanged for a period of time due to the effect of the capacitor 287. When the DC power supply AVDD drops to a level lower than the source of the transistor 285, the diode 280 is turned off, and the level of the gate of the transistor 285 is higher than the level of the drain so that the transistor 285 is turned on. The first level V _GH continues to be maintained for a period of time due to the effect of the capacitor 287 . Simultaneously, when the input terminal 271 of the reset circuit 27 detects that the DC power supply DVDD drops below 2.7 volts, its output terminal 272 outputs a reset signal to the reset terminal 231 of the scan drive circuit 23, and the scan drive circuit 23 receives the reset signal Then all its outputs are selected as the first level V _GH , then the scanning drive circuit 23 outputs the first level V _GH to all scanning lines 251, so that all thin film transistors 255 are turned on, and the plurality of pixel electrodes The residual charges on 257 are released to the multiple data lines 253 via the multiple thin film transistors 255, so that the screen of the liquid crystal display device 20 can be quickly turned black, and the residual image after shutdown of the liquid crystal display device 20 can be quickly eliminated.

Compared with the prior art, the liquid crystal display device 20 of the present invention includes a reset circuit 27 and a charging circuit 28 . When the liquid crystal display device 20 is powered off, the charging circuit 28 keeps the first level V _GH constant for a period of time; the reset circuit 27 makes all the outputs of the scanning drive circuit 23 selected as the first level _VGH . The first level V _GH is output to the gate of each thin film transistor 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 afterimage after shutdown of the liquid crystal display device 20 is rapidly eliminated.

Please refer to FIG. 3 , which is a schematic structural diagram of the charging circuit of the 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, the main difference being that the switching device 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 grounded through the capacitor 387 , and the cathode 386 thereof is connected to the input terminal (not shown) of the first level V _GH .

Compared with the liquid crystal display device of the first embodiment, the switching device of the liquid crystal display device of the second embodiment is a diode 385, and its structure is simpler than that of the transistor 285, which can simplify the circuit structure and manufacture of the liquid crystal display device process.

However, the switching device of the present invention is not limited to NMOS transistors and diodes, and other devices with switching functions such as PMOS, MOSFET and JFET can be used as the switching device of the present invention.

Claims (9)

1. liquid crystal indicator, it comprises a scan driving circuit and an active-matrix, this scan drive circuit is used for exporting one first level and one second level, this active-matrix comprises a plurality of pixel cells that driven by this first level and this second level, each pixel cell comprises a thin film transistor (TFT), conducting when this thin film transistor (TFT) receives this first level, end when receiving this second level, this scan drive circuit comprises one first a level input end and a reset terminal, it is characterized in that: this liquid crystal indicator further comprises a charging circuit and a reset circuit, this charging circuit comprises a diode, one switching device and an electric capacity, this switching device is opened when this liquid crystal indicator shutdown, it has one first end and one second end, this first end connects the negative electrode of this diode, the anode of this diode connects a direct current power supply, and by this capacity earth, this second end is connected in this first level input end to this first end simultaneously; This reset circuit comprises an input end and an output terminal, this input end connects a direct current power supply, this output terminal connects the reset terminal of this scan drive circuit, during this liquid crystal indicator shutdown, this output terminal output reset signal is to this reset terminal, when this reset terminal received reset signal, this first level was all selected in all outputs of this scan drive circuit.

2. liquid crystal indicator as claimed in claim 1 is characterized in that: this switching device is a nmos pass transistor, and the grid of this nmos pass transistor links to each other with source electrode, and its source electrode is first end, and its drain electrode is second end.

3. liquid crystal indicator as claimed in claim 1 is characterized in that: this switching device is a diode, and its anode is first end, and its negative electrode is second end.

4. liquid crystal indicator as claimed in claim 1 is characterized in that: this charging circuit also comprises a current-limiting resistance, and it is connected between the negative electrode and this switching device first end of this diode.

5. liquid crystal indicator as claimed in claim 1 is characterized in that: this reset circuit realizes that by the chip that resets the model of this chip that resets is S-80927C-R, and this reset signal is a low level signal.

6. liquid crystal indicator, it comprises a scan driving circuit and an active-matrix, this scan drive circuit is used for exporting one first level and one second level, this active-matrix comprises a plurality of pixel cells that driven by this first level and this second level, each pixel cell comprises a thin film transistor (TFT), conducting when this thin film transistor (TFT) receives this first level, end when receiving this second level, it is characterized in that: this liquid crystal indicator further comprises a charging circuit and a reset circuit, and this charging circuit is used for keeping this first level after shutdown; This reset circuit is used for making all outputs of this scan drive circuit all to select this first level.

7. liquid crystal indicator as claimed in claim 6, it is characterized in that: this scan drive circuit comprises one first level input end, it is used for receiving this first level, this charging circuit comprises a diode, a switching device and an electric capacity, this switching device is opened when this liquid crystal indicator shutdown, it has one first end and one second end, this first end connects the negative electrode of this diode, the anode of this diode connects a direct current power supply, by this capacity earth, this second end is connected in this first level input end to this first end simultaneously.

8. liquid crystal indicator as claimed in claim 6 is characterized in that: this scan drive circuit comprises a reset terminal, and when this reset terminal received reset signal, this first level was all selected in all outputs of this scan drive circuit.

9. liquid crystal indicator as claimed in claim 8, it is characterized in that: this reset circuit comprises an input end and an output terminal, this input end connects a direct current power supply, this output terminal connects the reset terminal of this scan drive circuit, during this liquid crystal indicator shutdown, this output terminal output reset signal is to this reset terminal.

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