TWI665654B - Liquid crystal display and gamma voltage correction method - Google Patents

Abstract

A gamma voltage correction method for a liquid crystal display. The ground potential of the liquid crystal display is set as a reference voltage, and then at least one of a plurality of positive gamma voltages and a plurality of negative gamma voltages is adjusted to make each pair of gammas. The zero flicker value of the voltage is equal to the reference voltage, thereby improving the screen flicker problem of the liquid crystal display.

Description

Liquid crystal display and gamma voltage correction method

The invention relates to a method for improving the flicker of a liquid crystal display screen, in particular to a method for correcting a gamma voltage of a liquid crystal display.

In a liquid crystal display, the gamma curve and the reference voltage Vcom affect the color of the liquid crystal display and the flatness of the screen. Because the liquid crystal molecules of a liquid crystal display cannot be fixed at a certain voltage for too long, the gamma voltage driving the liquid crystal molecules will be divided into positive polarity and negative polarity. When the reference voltage Vcom is at the center of the positive and negative gamma voltages, That is, when the reference voltage Vcom is equal to the center voltage value of the gamma curve, a positive gamma voltage and a negative gamma voltage having the same voltage difference as the reference voltage Vcom will have gray scales with the same brightness. In the conventional liquid crystal display, the gamma voltage is a preset fixed value and cannot be changed. Therefore, the reference voltage Vcom can only be adjusted so that the reference voltage Vcom is equal to the center voltage value of the gamma curve.

FIG. 8 shows a conventional liquid crystal display 20, which includes a gamma voltage circuit 22, a source driver 24, a reference voltage control circuit 26, a panel 28, and a panel common electrode 30. The gamma voltage circuit 22 is used to provide a plurality of positive gamma voltages. PV0-PV1023 and multiple negative gamma voltages NV0-NV1023, the source driver 24 selects the required gamma voltage from multiple positive gamma voltages PV0-PV1023 and multiple negative gamma voltages NV0-NV1023 to drive the panel 28 The reference voltage control circuit 26 provides a reference voltage Vcom to the panel common electrode 30, and the gamma voltage provided by the source driver 24 and The voltage difference between the reference voltage Vcom on the panel common electrode 30 determines the gray scale of the pixels on the panel.

Figure 1 shows a gamma curve 10 and a reference voltage Vcom. The gamma curve 10 is composed of multiple positive gamma voltages PV0-PV1023 and multiple negative gamma voltages NV0-NV1023, and multiple positive gamma voltages PV0-PV1023 and The multiple negative gamma voltages NV0-NV1023 control the gray levels D0-D1023 of the liquid crystal display. FIG. 2 shows the reference voltage control circuit 26 of FIG. 8. The reference voltage Vcom is generated and controlled by an operational amplifier 16. The operational amplifier 16 has two input terminals and an output terminal. One of the input terminals receives a feedback related to the reference voltage Vcom. Signal FB_Vcom, the other input terminal receives the set signal Vset, and the output terminal provides the reference voltage Vcom. As shown in FIG. 1, when the reference voltage Vcom 12 is not at the center voltage value 14 of the gamma curve 10, the LCD screen will flicker. At this time, the reference voltage can be adjusted by adjusting the setting signal Vset provided to the operational amplifier 16. Vcom 12 makes it equal to the center voltage value 14 of the gamma curve 10, thereby improving the screen flicker problem. However, the conventional method for adjusting the reference voltage Vcom requires an additional operational amplifier 16, and the operational amplifier 16 requires a driving current to cause additional power loss. The bandwidth of the operational amplifier 16 also limits its inability to change rapidly when the reference voltage Vcom changes. Correct the reference voltage Vcom immediately. In addition, as shown by the waveform 18 in FIG. 2, the reference voltage Vcom provided by the operational amplifier 16 oscillates up and down, which is not a constant value, which causes gray-scale flicker, thereby reducing display performance.

An object of the present invention is to provide a liquid crystal display and a gamma voltage correction method thereof.

An object of the present invention is to provide a liquid crystal display and a method for correcting a zero flicker value curve by modifying a gamma voltage so that the zero flicker value curve overlaps with a quasi-base voltage.

According to the present invention, a liquid crystal display includes a panel and a gamma voltage correction. Circuit and a source driver. The panel has a panel common electrode connected to a ground terminal, and the voltage on the panel common electrode is the reference voltage of the panel. The gamma voltage correction circuit provides multiple pairs of gamma voltages to control the gray scale of the panel, and corrects the multiple pairs of gamma voltages according to a correction signal so that the zero flicker value of each pair of gamma voltages is equal to the reference voltage. Each pair of gamma voltages includes a positive gamma voltage and a negative gamma voltage corresponding to the same gray scale, and the zero flicker value is a voltage value that makes the positive gamma voltage and the negative gamma voltage exhibit the same brightness. The source driver receives the plurality of pairs of gamma voltages from the gamma voltage correction circuit, and provides a required gamma voltage to the panel.

According to the present invention, a method for correcting a gamma voltage of a liquid crystal display includes setting a ground potential of the liquid crystal display as a reference voltage, and then adjusting a plurality of pairs of gamma voltages according to a correction signal so that each pair of gamma voltages has zero flicker. The value is equal to this reference voltage. Each pair of gamma voltages includes a positive gamma voltage and a negative gamma voltage corresponding to the same gray scale, and the zero flicker value is a voltage value that allows the positive gamma voltage and the negative gamma voltage to exhibit the same brightness.

The liquid crystal display of the present invention does not need to use an operational amplifier to adjust the reference voltage, so that cost and power loss can be reduced, and the ground potential of the liquid crystal display is a fixed value, so the reference voltage will not oscillate and cause grayscale flicker. Show performance.

10‧‧‧ Gamma Curve

12‧‧‧Reference voltage Vcom

14‧‧‧Gamma curve center voltage value 10

16‧‧‧ Operational Amplifier

17‧‧‧Zero flicker value curve

18‧‧‧ waveform of reference voltage Vcom

20‧‧‧ LCD

22‧‧‧Gamma Voltage Circuit

24‧‧‧Source Driver

26‧‧‧Reference voltage control circuit

28‧‧‧ Panel

30‧‧‧panel common electrode

32‧‧‧ LCD

34‧‧‧Gamma voltage correction circuit

36‧‧‧Control bus in real time

38‧‧‧Storage unit

40‧‧‧ Offset Controller

42‧‧‧correction unit

44‧‧‧ Adder

46‧‧‧ Digital Analog Converter

48‧‧‧output stage

50‧‧‧ feedback signal converter

FIG. 1 shows a gamma curve and a reference voltage Vcom; FIG. 2 shows a circuit for controlling the reference voltage Vcom; FIG. 3 shows a flowchart of the gamma voltage correction method of the present invention; 4 shows a circuit architecture after applying the gamma voltage correction method of the present invention; 5 shows the first embodiment of step S22 in FIG. 3; 6 shows a second embodiment of step S22 in FIG. 3; FIG. 7 shows a third embodiment of step S22 in FIG. 3; FIG. 8 shows a conventional liquid crystal display; and FIG. 9 shows that the center voltage value of the gamma curve is equal to the reference voltage Vcom 10 shows a liquid crystal display of the present invention; FIG. 11 shows a first embodiment of the gamma voltage correction circuit in FIG. 10; FIG. 12 shows a second embodiment of the gamma voltage correction circuit in FIG. 10; and FIG. 13 shows Different configurations of the circuit in FIG. 12.

FIG. 3 shows the flow of the gamma voltage correction method of the present invention. Referring to FIG. 1 and FIG. 3, the gamma voltage correction method of the present invention sets the ground potential GND of the liquid crystal display to the reference voltage Vcom, as shown in step S20. Next, step S22 adjusts at least one of the plurality of positive gamma voltages PV0-PV1023 and the plurality of negative gamma voltages NV0-NV1023 to bring the center voltage value 14 of the gamma curve 10 closer to the reference voltage Vcom to improve the screen of the liquid crystal display. Blinking problem. Preferably, the center voltage value 14 of the adjusted gamma curve 10 is equal to the reference voltage Vcom. FIG. 4 shows the circuit structure after applying the gamma voltage correction method of the present invention, which does not need to use the operational amplifier 16 again, so the cost and power loss can be reduced, and the ground potential GND of the liquid crystal display is a fixed value, so the reference voltage Vcom will not Occurrence of oscillation causes gray-scale flicker, so it has better display performance.

FIG. 5 shows a first embodiment of step S22 in FIG. 3, which includes setting an offset value Vos in step S24, and then offsetting a plurality of positive gamma voltages PV0-PV1023 and a plurality of negative gamma according to the offset value Vos in step S26. At least one of the gamma voltages NV0-NV1023 to adjust the center voltage value 14 of the gamma curve 10. For example, you can offset only the maximum positive gamma voltage PV1023 or the minimum Negative gamma voltage NV1023 to adjust the center voltage value 14 of the gamma curve 10, or offset all the positive gamma voltages PV0-PV1023 and negative gamma voltage NV0-NV1023 at the same time to offset the center voltage value of the gamma curve 10. 14. In the known art, existing circuits and methods can obtain the difference between the gamma voltage and the reference voltage Vcom, and an appropriate offset value Vos can be set as long as the difference is used.

FIG. 6 shows a second embodiment of step S22 in FIG. 3, which includes a step S28 of calculating an average value Vavg between the maximum positive gamma voltage PV1023 and the minimum negative gamma voltage NV1023. Next, as shown in step S30, a difference Vdif between the average value and the reference voltage Vcom is obtained. Finally, step S32 is performed to offset all the positive gamma voltages PV0-PV1023 and the negative gamma voltages NV0-NV1023 according to the difference Vdif, so as to offset the center voltage value 14 of the gamma curve 10. In other embodiments, only a part of the positive gamma voltage PV0-PV1023 and the negative gamma voltage NV0-NV1023 may be shifted.

FIG. 7 shows a third embodiment of step S22 in FIG. 3, which includes step S34 of calculating a plurality of positive gamma voltages PV0-PV1023 and a plurality of negative gamma voltages NV0-NV1023 by an inter-integrated circuit Respective offset values, and accordingly adjust a plurality of positive gamma voltages PV0-PV1023 and a plurality of negative gamma voltages NV0-NV1023. In the known technology, it is possible to calculate the difference between each gamma voltage and the reference voltage Vcom by using the original internal integrated circuit, so an appropriate offset value can be set for individual gamma voltages. In other embodiments, only a part of the positive gamma voltage PV0-PV1023 and the negative gamma voltage NV0-NV1023 may be shifted.

FIG. 9 shows a gamma curve 10. In an ideal state, when each pair of gamma voltages PV0 and NV0, PV1 and NV1 ... PV1023 and NV1023 average voltage (PV0 + NV0) / 2, ..., (PV1023 + NV1023) / 2 is equal to the reference When the voltage is Vcom, it corresponds to the positive gamma voltage and Negative gamma voltages (for example, the positive gamma voltage PV0 and the negative gamma voltage NV0 corresponding to the gray level D0) will show the same brightness. This can make a pair of gamma voltages show the same brightness value and is called "zero flicker value". . However, in fact, the feed-through effect of thin-film transistors (TFTs) of different panels will affect the zero flicker value to different degrees, so that the actual zero flicker value curve will deviate from the reference voltage Vcom. As shown in the actual zero flicker value curve 17 shown in FIG. 9, the zero flicker value Vzf0 corresponding to the gray voltages PV0 and NV0 of the gray level D0 is higher than the center voltage value 14, and the zero corresponding to the gamma voltages PV1023 and NV1023 of the gray level D1023. The flicker value Vzf1023 is lower than the center voltage value of 14. One object of the present invention is to modify the zero flicker value curve 17 by modifying the gamma voltage so that the zero flicker value curve 17 overlaps the quasi-base voltage Vcom.

FIG. 10 shows a liquid crystal display 32 according to the present invention, which includes a panel 28, a gamma voltage correction circuit 34, and a source driver 24. The common electrode 30 of the panel 28 is connected to a ground, so the voltage on the common electrode 30 of the panel 28 is fixed at the ground potential GND. In other words, the reference voltage Vcom of the panel 28 is the ground potential GND. The gamma voltage correction circuit 34 provides multiple positive gamma voltages PV0-PV1023 and multiple negative gamma voltages NV0-NV1023. Multiple positive gamma voltages PV0-PV1023 and multiple negative gamma voltages NV0-NV1023 are used to control. The gray scale of the LCD, each gray scale D0-D1023 corresponds to a pair of gamma voltages PV0 and NV0, PV1 and NV1 ... PV1023 and NV1023, and the gamma voltage correction circuit 34 can correct multiple pairs of gamma voltages according to a correction signal Sc The photovoltaic voltages PV0 and NV0, PV1 and NV1 ... PV1023 and NV1023 make the zero flicker value Vzf0-Vzf1023 of each pair of gamma voltages equal to the reference voltage Vcom, wherein the correction signal Sc can be provided from the outside of the liquid crystal display 32 or by The circuits inside the liquid crystal display 32 are calculated immediately. After the source driver 24 receives multiple positive gamma voltages PV0-PV1023 and multiple negative gamma voltages NV0-NV1023, it supplies the required positive gamma voltage or negative gamma voltage to the panel 28 as needed to determine the Grayscale. phase Compared with the traditional liquid crystal display that cannot adjust the gamma voltage after leaving the factory, the liquid crystal display 32 of the present invention can correct the gamma voltage through the correction signal Sc. Therefore, even after the liquid crystal display 32 is shipped from the factory, zero flicker value is caused by environmental or other factors When Vzf0-Vzf1023 changes and flicker occurs, the liquid crystal display 32 can also correct the zero flicker value Vzf0-Vzf1023 by using a correction signal Sc provided from the outside or generated internally to improve the flicker problem.

FIG. 11 shows a first embodiment of the gamma voltage correction circuit 34 in FIG. 10. The gamma voltage correction circuit 34 in FIG. 11 includes a storage unit 38, an offset controller 40, a correction unit 42, a digital analog converter 46, and an output stage. 48. The storage unit 38 stores and outputs a plurality of voltage data Gvd. The offset controller 40 receives the correction signal Sc in real time from the outside of the liquid crystal display 32 or the internal circuit of the liquid crystal display 32 through the real-time control bus 36, and determines a plurality of offset data Ofd according to the correction signal Sc. The correction unit 42 receives a plurality of voltage data Gvd from the storage unit 38 and a plurality of offset data Ofd from the offset controller 40, and corrects the plurality of gamma voltage data Gvd according to the multi-offset data Ofd to generate a plurality of correction voltage data. Cvd. The correction unit 42 may be constituted by an adder 44 which adds the corresponding gamma voltage data Gvd and the offset data Ofd to generate a correction voltage data Cvd. The digital analog converter 46 is used to convert a plurality of correction voltage data Cvd into a plurality of analog positive gamma voltages PV0-PV1023 and a plurality of negative gamma voltages NV0-NV1023. The output stage 48 is used to store a plurality of positive gamma voltages PV0-PV1023 and a plurality of negative gamma voltages NV0-NV1023 output by the digital analog converter 46, and a plurality of positive gamma voltages PV0-PV1023 and a plurality of negative gamma The voltages NV0-NV1023 are output to the source driver 24.

FIG. 12 shows a second embodiment of the gamma voltage correction circuit 34 in FIG. 10. The gamma voltage correction circuit 34 in FIG. 12 also includes a storage unit 38, an offset controller 40, a correction unit 42, and a digital analogy. Converter 46 and output stage 48, in addition to the gamma voltage calibration of Figure 12 The positive circuit 34 also includes a feedback signal converter 50. The feedback signal converter 50 receives and stores a feedback signal Sfb, and the feedback signal converter 50 generates a correction signal Sc to the offset controller 40 according to the feedback signal Sfb. The feedback signal Sfb can be provided by the panel 28, and the feedback signal Sfb can be generated by detecting the brightness generated by each of the gamma voltages PV0-PV1023 and NV0-NV1023, so that the correction signal Sc can be controlled in real time, thereby real-time correction Zero flicker values Vzf0-Vzf1023. FIG. 13 shows different configurations of the circuit of FIG. 12. In FIG. 13, the feedback signal converter 50 is arranged outside the gamma voltage correction circuit 34 and transmits the correction signal Sc to the gamma voltage correction circuit through the real-time control bus 36. 34.

Claims (9)

A liquid crystal display includes: a panel having a common electrode of the panel connected to a ground terminal, and the voltage on the common electrode of the panel is a reference voltage of the panel; a gamma voltage correction circuit provides a plurality of pairs of gamma voltages for control Gray level of the panel, and correct the pairs of gamma voltages according to a correction signal so that the zero flicker value of each pair of gamma voltages is equal to the reference voltage, wherein each pair of gamma voltages includes a positive value corresponding to the same gray level A gamma voltage and a negative gamma voltage, and the zero flicker value is a voltage value that allows the positive and negative gamma voltages to exhibit the same brightness; and a source driver connected to the panel and the gamma voltage correction circuit To receive the plurality of pairs of gamma voltages and provide the required gamma voltages to the panel. For example, the liquid crystal display of claim 1, wherein the gamma voltage correction circuit includes: a storage unit that stores and outputs a plurality of voltage data; an offset controller that determines a plurality of offset data according to the correction signal; a correction unit, Connected to the storage unit and the offset controller, and corrected the plurality of voltage data according to the plurality of offset data to generate a plurality of corrected voltage data; a digital analog converter connected to the correction unit to convert the plurality of corrected voltage data to generate The plurality of pairs of gamma voltages; and an output stage connected to the digital analog converter, storing the plurality of pairs of gamma voltages, and outputting the plurality of pairs of gamma voltages to the source driver. For example, the liquid crystal display of claim 2, wherein the gamma voltage correction circuit further includes a feedback signal converter connected to the panel and the offset controller, and generates the correction signal to the offset according to a feedback signal from the panel. Controller. For example, the liquid crystal display of claim 1 further includes a feedback signal converter connected to the panel and the gamma voltage correction circuit, and generates the correction signal to the gamma voltage correction circuit according to a feedback signal from the panel. For example, the liquid crystal display of claim 1, wherein the reference voltage is not controlled or adjusted by an output terminal of an operational amplifier, and the operational amplifier has an input terminal for receiving a feedback signal related to the reference voltage. A method for correcting a gamma voltage of a liquid crystal display. The liquid crystal display has a plurality of pairs of gamma voltages for controlling a gray scale of a panel of the liquid crystal display. The method for correcting the gamma voltage includes the following steps: setting a ground potential of the liquid crystal display to A reference voltage; and adjusting the pairs of gamma voltages according to a correction signal so that the zero flicker value of each pair of gamma voltages is equal to the reference voltage, wherein each pair of gamma voltages includes a positive gamma corresponding to the same grayscale Voltage and a negative gamma voltage, and the zero flicker value is a voltage value that makes the positive gamma voltage and the negative gamma voltage exhibit the same brightness. The gamma voltage correction method for a liquid crystal display according to claim 6, wherein the step of adjusting the pairs of gamma voltages according to a correction signal includes: providing a plurality of voltage data; determining a plurality of offset data according to the correction signal; The plurality of offset data corrects the plurality of voltage data to generate a plurality of correction voltage data; and the plurality of pairs of gamma voltages are generated according to the plurality of correction voltage data. The gamma voltage correction method of the liquid crystal display of claim 6, further comprising generating the correction signal according to a feedback signal from the panel. For example, the gamma voltage correction method for a liquid crystal display of claim 6, wherein the reference voltage is not controlled or adjusted by an output terminal of an operational amplifier, and the operational amplifier has an input terminal for receiving a feedback signal related to the reference voltage .