1. Field of the Invention
The present invention relates to a driving method for a display device and related driving device, and more particularly to a driving method able to mitigate threshold voltage shifting of transistors in the display device and related driving device.
2. Description of the Prior Art
A liquid crystal display (LCD) is a flat panel display which has the advantages of low radiation, light weight and low power consumption and is widely used in various information technology (IT) products, such as notebook computers, personal digital assistants (PDA), and mobile phones. An active matrix thin film transistor (TFT) LCD is the most commonly used transistor type in LCD families, and particularly in the large-size LCD family. A driving system installed in the LCD includes a timing controller, source drivers and gate drivers. The source and gate drivers respectively control data lines and scan lines, which intersect to form a cell matrix. Each intersection is a cell including crystal display molecules and a TFT. In the driving system, the gate drivers are responsible for transmitting scan signals to gates of the TFTs to turn on the TFTs on the panel. The source drivers are responsible for converting digital image data, sent by the timing controller, into analog voltage signals and outputting the voltage signals to sources of the TFTs. When a TFT receives the voltage signals, a corresponding liquid crystal molecule has a terminal whose voltage changes to equalize the drain voltage of the TFT, which thereby changes its own twist angle. The rate that light penetrates the liquid crystal molecule is changed accordingly, allowing different colors to be displayed on the panel. In the prior art, the U.S. Pat. No. 8,477,092 and the U.S. Pat. No. 8,248,341 provide different methods of driving the LCD.
In order to reduce the power consumption of the LCD, the driving system of the LCD may dynamically reduce a refreshing rate. Under such a condition, a display quality of the LCD would not be affected and the power consumption of refreshing frames can be saved. When the refreshing rate of the LCD is reduced to ultra-low frequency (e.g. 1 Hz), the gate of the TFT in each cell of the LCD receives negative gate voltage for a long period of time, resulting that the threshold voltage of the TFT in each cell gradually decreases and the LCD may work abnormally. Thus, how to mitigate the shifting of the threshold voltage of the TFT becomes a topic to be discussed.
In order to solve the above issue, the present invention provides a driving method able to mitigate shifting of threshold voltage shifting of transistors in the display device and related driving device.
In an aspect, the present invention discloses a driving method for a display device with a plurality of pixels, wherein each pixel includes a plurality of transistors connected in series. The driving method comprises adjusting a first gate driving signal of a first transistor among the plurality of transistors to make the first transistor cut-off and generating compensation waveform on at least one second gate driving signal of at least one second transistor among the plurality of transistors within a compensation interval of a plurality of intervals between every two contiguous data updating periods among a plurality data updating periods; wherein the plurality of transistors of each pixel are conducted in a specific period within the plurality of data updating periods, to update a data voltage of each pixel.
In another aspect, the present invention discloses a driving device, for a display device with a plurality of pixels, wherein each pixel comprises a plurality of transistors connected in series. The driving device comprises a driving module, for generating a plurality of gate driving signals controlling the plurality of transistors in each pixel according to a control signal; and a control module, for adjusting a first gate driving signal of a first transistor among the plurality of transistors to make the first transistor cut-off and generating compensation waveform on at least one second gate driving signal of at least one second transistor among the plurality of transistors within a compensation interval of a plurality of intervals between every two contiguous data updating periods among a plurality data updating periods; wherein the plurality of transistors of each pixel are conducted in a specific period within the plurality data updating periods, to update a data voltage of each pixel.
In still another aspect, the present invention discloses a driving method for a display device with a plurality of pixels, wherein each pixel includes a plurality of transistors connected in series. The driving method comprises adjusting at least one first gate driving signal of at least one first transistor among the plurality of transistors to make the at least one first transistor cut-off and generating compensation waveform on at least one second gate driving signal of at least one second transistor among the plurality of transistors within a compensation interval of a plurality of intervals between every two contiguous data updating periods among a plurality data updating periods; wherein the plurality of transistors of each pixel are conducted in a specific period within the plurality of data updating periods, to update a data voltage of each pixel.
In yet another aspect, the present invention discloses a driving device, for a display device with a plurality of pixels, wherein each pixel comprises a plurality of transistors connected in series. The driving device comprises a driving module, for generating a plurality of gate driving signals controlling the plurality of transistors in each pixel according to a control signal; and a control module, for adjusting at least one first gate driving signal of at least one first transistor among the plurality of transistors to make the at least one first transistor cut-off and generating compensation waveform on at least one second gate driving signal of at least one second transistor among the plurality of transistors within a compensation interval of a plurality of intervals between every two contiguous data updating periods among a plurality data updating periods; wherein the plurality of transistors of each pixel are conducted in a specific period within the plurality of data updating periods, to update a data voltage of each pixel.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
Please refer to
As shown in
Because the threshold voltage shifting of the transistors correlates with light and temperature, the control module 102 utilizes the light sensing unit 108 and the temperature sensing unit 110 to sense the ambient light and temperature and to accordingly generate a light sensing signal LS and a temperature sensing signal TS as the references of controlling the driving module 100 to make the at least one first transistor cut-off and to generate the compensation waveform on the gate driving signal of the at least one second transistor within random interval between the data updating periods. Note that, the light sensing unit 108 and the temperature sensing unit 110 may be independent external components and may not be configured in the driving device 10.
As to details of the control module 102 controlling the driving module 100 to control the transistors in the pixel units within the intervals between the data updating periods please refer to the followings. Please refer to
When the display device operates, the gate driving signals GA and GB are increased to a gate high voltage VGH in the data updating periods of updating the data voltage on the capacitors CPIX to conduct the transistors MA and MB and are kept at a gate low voltage VGL outside the data updating periods to make the transistors MA and MB cut-off. The computing unit 104 controls the control module 100, via the control signal CON, to make one of the transistors MA and MB cut-off and to output the compensation waveform to another one of the transistors MA and MB in the interval between the data updating periods of updating the data voltage of capacitor CPIX, to prevent the transistors MA and MB from receiving the gate low voltage VGL for a long period of time. In an example, the compensation waveform is a square wave whose maximum voltage is VGM that is greater than the minimum voltage of the display device (e.g. greater than the gate low voltage VGL). Because the gates of the transistors MA and MB avoid receiving the gate low voltage VGL indicating the cut-off state for a long period of time, the threshold voltage shifting can be mitigated. In addition, the data voltage of the capacitor CPIX is approximately unchanged because the driving module 100 makes one of the transistors MA and MB cut-off in the interval. Thus, the image displayed by the display device does not blink when adopting the abovementioned method to prevent the threshold voltages of the transistors MA and MB in the pixel unit PIX from deviating from the designed values.
Please refer to
Thus, the computing unit 104 controls the driving module 100 generate a square wave (i.e. the compensation waveform), whose period is TSW1 and the maximum voltage is VGM1, on the gate driving signal GA within the interval between the data updating periods PU1 and PU2 in the example shown in
Similarly, the square wave, whose period is TSW1 and the maximum voltage is VGM1, is generated on the gate driving signal GB within an interval between the data updating periods PU2 and PU3, to prevent the threshold voltage of the transistor MB from shifting. Within the interval between the data updating periods PU2 and PU3, the gate driving signal GA is kept at the gate low voltage VGL. Since the transistor MA is cut-off within the interval between the data updating periods PU2 and PU3, the data voltage of the capacitor CpPIX remains the same.
As can be seen from
Please refer to
In the example shown in
Next, the square wave, whose period is TSW2 and the maximum voltage is VGM2, is generated on the gate driving signal GB within the interval between the data updating periods PU2 and PU3, to prevent the threshold voltage of the transistor MB from shifting. Within the interval between the data updating periods PU2 and PU3, the gate driving signal GA is kept at the gate low voltage VGL. Since the transistor MA is cut-off within the interval between the data updating periods PU2 and PU3, the data voltage of the capacitor CPIX remains unchanged.
Note that, the compensation waveform shown in
In an example, the computing unit 104 adjusts the frequency of generating the compensation waveform during the period of multiple data updating periods. For example, the computing unit 104 may controls the driving module 100 to generate the compensation waveform on the gate driving signal GA or GB in one of multiple contiguous intervals between every two contiguous data updating periods. Please refer to
Note that, the compensation waveform shown in
The compensation waveform on the gate driving signals GA and GB within the interval between the data updating periods may be appropriately altered. For example, the voltages VGM1 and VGM2 can be altered according to physical features of the display device as long as the voltages VGM1 and VGM2 are greater than the gate low voltage VGL. In addition, the periods TSW1 and TSW2 maybe appropriately changed when the compensation waveform shown in
Note that, the threshold voltage shifting of the transistors MA and MB is affected by the light and the temperature. Thus, the computing unit 104 receives the light sensing signals LS and the temperature sensing signal TS related to the ambient environment conditions and accordingly determines whether to output the compensation waveform within the intervals among the data updating periods. In an example, because the threshold voltage of the transistors MA and MB shifts more seriously when the transistors MA and MB receive external light, the computing unit 104 generates the corresponded control signal CON to adjust the waveform of the gate driving signals GA and GB and to prevent the threshold voltages of the transistors MA and MB from deviating when determining light flux indicated by the light sensing signal LS exceeds a illumination threshold. In another example, because the threshold voltage of the transistors MA and MB shifts more seriously when the ambient temperature is higher, the computing unit 104 generates the corresponded control signal CON to adjust the waveform of the gate driving signals GA and GB and to prevent the threshold voltages of the transistors MA and MB from deviating when determining the temperature indicated by the temperature sensing signal TS exceeds a high temperature threshold.
The method of the computing unit outputting the compensation waveform to mitigate the threshold voltage shifting of the transistors in the pixel unit can be summarized into a process 60 shown in
According to the process 60, the driving device adjusts at least one first gate driving signal of at least one first transistor among the plurality of transistors to make the first transistor cut-off within a compensation interval among a plurality of intervals between every two contiguous data updating periods among a plurality of data updating periods. For example, the driving device may adjust the at least one first gate driving signal to the minimum voltage of the display device to make the at least one first transistor cut-off. Within the compensation interval, the driving device generates compensation waveform on at least one second gate driving signal of at least one second transistor among the plurality of transistors. Because the at least one first transistor is cut-off within the compensation interval, the data voltage of each pixel unit is kept unchanged. The image displayed by the display device does not blink, therefore.
As to detailed operations of the process 60 please refer to the followings. In an example, each pixel unit in the display device comprises 3 series transistors M1-M3, wherein the transistor M1 is coupled to a data line, the transistor M3 is coupled to liquid crystal component of the pixel unit, and the transistor M2 is coupled between the transistors M1 and M3. In an example, the driving device adjusts the gate driving signal of the transistor M1 to make the transistor M1 cut-off and generates the compensation waveform on at least one of the gate driving signals of the transistors M2 and M3 in a compensation interval, to prevent the threshold voltage of at least one of the transistors M2 and M3 from shifting. In another compensation interval, the driving device adjusts the gate driving signal of the transistor M2 to make the transistor M2 cut-off and generates the compensation waveform on at least one of the gate driving signals of the transistors M1 and M3 in a compensation interval, and so on. In this example, because at least one of the transistors M1-M3 is cut-off in each compensation interval, the data voltage of each pixel unit is kept unchanged. The image displayed by the display device does not blink, therefore.
In another example, the driving device adjusts the gate driving signals of the transistors M1 and M2 to make the transistors M1 and M2 cut-off and generates the compensation waveform on the gate driving signals of the transistor M3 in a compensation interval, to prevent the threshold voltage of the transistor M3 from shifting. In another compensation interval, the driving device adjusts the gate driving signals of the transistors M2 and M3 to make the transistors M2 and M3 cut-off and generates the compensation waveform on the gate driving signal of the transistor M1 in a compensation interval, and so on. In this example, because two of the transistors M1-M3 are cut-off in each compensation interval, the data voltage of each pixel unit is kept unchanged. The image displayed by the display device does not blink, therefore.
In an example, the compensation waveform may be a square wave whose maximum voltage is a positive voltage. Based on different applications and designed concepts, the period and the maximum voltage of the square wave can be appropriately altered. For example, the period of the square wave may be smaller than the interval between the updating periods. Under such a condition, the gate driving signal of the second transistor switches to the maximum voltage of the square wave multiple times in single interval (e.g. the example shown in
In an example, the driving device generates the compensation waveform on the second gate driving signal in one of a plurality contiguous intervals between every two data updating periods.
In an example, the driving device receives environment sensing signals (e.g. the light sensing signals LS and the temperature sensing signals TS) to determine whether to output compensation waveform. When the environment sensing signals indicate that the ambient environment conditions satisfy the compensation condition, the driving device generates the compensation waveform on the second gate driving signals.
The method of the computing unit 104 determining whether to adjust the gate driving signals according to the light sensing signal LS and the temperature sensing signal TS can be summarized into a process 70 shown in
According to the process 70, the driving device receive at least one environment sensing signal related to the ambient environment conditions of the display device, to determine whether the ambient environment conditions of the display device need to perform compensation. When the at least one environment sensing signal satisfies at least one compensation conditions, the driving device output a compensation waveform on the gate driving signal of one of a plurality transistors connected in series (e.g. the transistors MA and MB shown in
In an example, the driving device performs the process 70 when the display device starts to operate (e.g. when the display device begins to display images), and stops performing the process 70 when the display device stops operating (e.g. when the display device is shut down).
The driving device of the present disclosure makes one of the transistors connected in series in each pixel unit cut-off and outputs the compensation waveform on the gate driving signal of at least one of remaining transistors within the intervals between every two data updating periods, to mitigate the threshold voltage shifting of the transistors. Further, the driving device detects the ambient environment conditions and outputs the compensation waveform when the ambient environment conditions satisfy certain compensation conditions. The power consumption is reduced, therefore.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
This application claims the benefit of U.S. Provisional Application No. 62/289,356 filed on Feb. 1, 2016 and U.S. Provisional Application No. 62/339,057 filed on May 19, 2016, the contents of which are incorporated herein in their entirety.
Number | Date | Country | |
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62289356 | Feb 2016 | US | |
62339057 | May 2016 | US |