JP6262940B2 - Liquid crystal display device and driving method thereof - Google Patents

Description

  The present invention relates to a liquid crystal display device and a driving method thereof.

  Conventionally, a method of displaying an image by driving a liquid crystal cell by a field sequential method is known.

  This method is different from the method of performing color display by providing segments of each color of R (red), G (green), and B (blue) like a color filter in a display pixel, and a light source that emits light of each color is used. The color display is performed by sequentially switching the illumination of each color in a short time.

  In this method, a liquid crystal cell having the same configuration as that of a liquid crystal cell used for monochrome display is used, and light emitting elements arranged to illuminate the liquid crystal cell from the front or the rear are, for example, R (red), G (green) ), B (blue) light of the three primary colors is emitted, and the liquid crystal cell is irradiated with these lights sequentially for a predetermined time TS. That is, for example, in the order of R (red), G (green), and B (blue), light of each color is irradiated to the liquid crystal cell for time TS, and the irradiation of these three primary colors is repeated in the same manner. The liquid crystal cell changes the light transmittance of each display pixel in synchronization with this time TS. That is, according to the color to display, the transmittance | permeability of each light of R, G, B is driven and controlled by a liquid crystal cell, and the ratio of each light which permeate | transmits a liquid crystal cell is changed. Here, by making the time TS very short, each color is not recognized as one color, but is recognized as a color mixture of each color by human eyes.

  In this method, the time TS needs to be very short, and the transmittance of the liquid crystal cell needs to be changed at high speed accordingly. Therefore, a ferroelectric liquid crystal having a higher switching speed than that of the nematic liquid crystal is suitable for this method. Ferroelectric liquid crystal switches between on and off at high speed in a bistable state, and gradation display is performed by changing the amount of transmitted light in one field by controlling the on and off times.

  FIG. 4A is a timing chart showing a state in which ideal black display (gradation 0 display), gray display (gradation 127 display), and white display (gradation 255 display) are performed. These are timing charts showing a state where ideal low gradation black display (gradation 1 display, gradation 2 display) is performed. Here, one field is formed by an active period in which an image is displayed and a passive period in which a voltage having a polarity opposite to that at the time of image display is applied in order to prevent burn-in of the display image. In the case of performing color display, three such fields are continuously provided corresponding to each color of RGB, and one image is displayed in these three fields. When only monochrome display is performed, one image is displayed in one field.

  When the light source repeats light emission (lighting) and non-light emission (light extinction) at a constant cycle, for example, when black display (gradation 0 display) is performed, ideally, light emission start timing of the light source in each RGB field By matching the timing of switching the liquid crystal from the on state to the off state, light is not transmitted and a complete black display is obtained.

  Further, when performing gray display (gradation 127 display), performing white display (gradation 255 display), or performing low gradation black display (gradation 1 display, gradation 2 display), RGB Within the active period of each field, the timing for switching the liquid crystal from the on state to the off state is delayed by a predetermined time from the light emission start timing of the light source, and during that time, a predetermined amount of transmitted light is obtained to display each gradation. . In the figure, the amount of transmitted light obtained is conceptually represented by the area of the shaded area.

  FIG. 5 is a diagram showing ideal γ (gamma) characteristics. In the state where ideal gradation display is performed as shown in FIGS. 4A and 4B, the luminance with respect to the gradation is changed from a low gradation to a high gradation as shown in FIG. It changes to increase linearly. In gradation display, it is ideal that such γ characteristics are obtained.

  FIG. 6 is a timing chart showing a state where realistic black display (gradation 0 display) is performed. A certain amount of time is required for the liquid crystal to change from the on state to the off state. Even if the ferroelectric liquid crystal has a switching speed faster than that of the nematic liquid crystal, it takes about 50 μsec or more. Even if the timing for starting the light emission of the light source and the timing for switching the liquid crystal from the on state to the off state are matched, the timing for starting the light emission of the light source and the liquid crystal are actually turned on. An error occurs between the timing when the state is completely switched to the off state. In other words, since the light source emits light before the liquid crystal is completely turned off and light is transmitted during that time, the luminance is sufficiently small with respect to the black display during black display (gradation 0 display). Therefore, there arises a problem that the contrast is lowered.

  FIG. 7 is a timing chart showing a state in which black display (gradation 0 display) is performed using the conventional technique. The following are known as conventional driving methods for solving the above-mentioned problems. In this driving method, when black display (gradation 0 display) is performed, the liquid crystal is turned on by delaying the light emission start timing by the time TD required for the liquid crystal to change from the on state to the off state. The amount of transmitted light is prevented from being obtained during the period from when it is changed to the off state. According to this driving method, since the luminance can be sufficiently reduced during black display (gradation 0 display), high contrast can be obtained. (For example, see Patent Document 1)

JP-A-10-63225

  FIG. 8A is a timing chart showing a state where (a) an ideal low gradation black display (gradation 1 display) is performed, and (b) a low gradation black display (level) using the conventional technology. FIG. 8-2 is a timing chart showing a state in which a tone 1 display is being performed, and FIG. 8-2 illustrates a state in which (a) an ideal low gradation black display (gradation 2 display) is being performed. It is the figure which compared the timing chart which shows, and the timing chart which shows the state in which (b) low gradation black display (gradation 2 display) is performed using the prior art. In the related art, by delaying the light emission start timing of the light source, a high contrast can be obtained when performing gradation 0 display. For example, when performing low gradation display such as gradation 1 or 2, However, there is a problem that the proper light intensity cannot be obtained and the original gradation display cannot be performed due to the delay of the light emission start timing of the light source.

  That is, the ideal amount of transmitted light when performing black display of gradations 1 and 2 is represented by the shaded area in FIGS. 8-1 (a) and 8-2 (a), respectively. Is obtained because the on-time TA of the liquid crystal overlaps the light emission time TS of the light source is shortened by the amount of delay of the light emission start timing of the light source (time TD). The amount of transmitted light decreases with respect to the ideal value, as indicated by the hatched area in FIGS. 8-1 (b) and 8-2 (b), and the original gradation display is displayed accordingly. It becomes impossible to do. The on-time TA of the liquid crystal indicates a time during which a driving voltage is applied to the liquid crystal of the liquid crystal cell.

  FIG. 8C is a timing chart showing a state where (a) an ideal high gradation white display (gradation 253 display) is performed, and (b) a high gradation white display (gradation 253 using conventional technology). FIG. 8-4 is a timing chart showing a state in which an ideal high gradation white display (gradation 254 display) is performed. And (b) is a diagram comparing a timing chart showing a state in which high gradation white display (gradation 254 display) is performed using the conventional technique. Further, in the prior art, for example, when performing high gradation display such as gradations 253 and 254, an appropriate amount of transmitted light cannot be obtained due to a delay in timing at which the liquid crystal completely switches from the on state to the off state. There also arises a problem that the original gradation display cannot be performed. This problem is caused by the response speed of the liquid crystal and is not directly related to the delay of the light emission start timing of the light source, and is not limited to the conventional technique that delays the light emission start timing of the light source. It is.

  That is, the ideal transmitted light amount when performing high gradation white display of gradations 253 and 254 is represented by the area of the hatched portion in FIGS. 8-3 (a) and 8-4 (a), respectively. Actually, since it takes time to completely switch the liquid crystal from the on state to the off state, the transmitted light quantity obtained is the area of the shaded portion in FIGS. 8-3 (b) and 8-4 (b), respectively. As shown by the above, it increases with respect to the ideal value, and accordingly, the original gradation display cannot be performed.

  FIG. 9 is a diagram showing γ (gamma) characteristics when gradation display is performed using the conventional technique. As described above, since the appropriate transmitted light amount cannot be obtained in the prior art, the γ characteristic is a characteristic of a quadratic curve as shown by a solid line in the figure, and is ideal as shown by a broken line in the figure. A difference (characteristic (linear characteristic)) occurs. That is, the original gradation display cannot be performed by the difference.

  As described above, the problem that the ideal gradation display cannot be performed is whether the display color is color or black and white, regardless of whether the operation method is normally black mode or normally white mode. Regardless of whether the gradation is 256 gradations, and not limited to the above reasons, the same can occur when performing gradation display.

  The present invention has been made in view of the above problems, and an object thereof is to provide a liquid crystal display device capable of realizing ideal gradation display and a driving method thereof.

A liquid crystal cell; a light source that supplies light to the liquid crystal cell; a liquid crystal control circuit that controls on / off of a driving voltage for the liquid crystal cell to control light modulation operation of the liquid crystal cell; A light source control circuit for switching light emission and a light emission delay circuit for delaying a light emission start timing of the light source, and controlling a light modulation operation of the liquid crystal cell in synchronization with a light emission timing and a non-light emission timing of the light source One image is displayed in one or a plurality of field units, and an image display driving period for performing driving for displaying the image is provided in the field. In the image display driving period, the light source of the light source is provided. a light emitting period and a non-emission period, the the on and off periods of the driving voltage to the liquid crystal cell is provided, before the inter-light emission period of the light source in the image display drive period There line gradation display of the image by controlling the length between the on period of the drive voltages to the liquid crystal cell, wherein the start timing of the light emission delay circuit the image display drive period until a predetermined time elapses The light emission start timing of the light source in the image display drive period is delayed, and the delayed period becomes a non-light emission period of the light source in the image display drive period, and the non-light emission period corresponds to the liquid crystal in the image display drive period. by overlapping the on period of the drive voltage, when performing the gradation display, the liquid crystal display device caused the error of luminance between the before and after delaying the timing of the emission start of said light source, said liquid crystal cell wherein the error in luminance occurring when performing gradation display, between the on period of the drive voltage to the liquid crystal cell in the image display drive period A liquid crystal display device is corrected by changing the Is.

The liquid crystal driving time correction circuit is configured such that the light emission delay circuit performs a light emission start timing of the light source when the liquid crystal cell performs gradation display excluding the lowest gradation on a lower gradation side than a specific halftone. the error in luminance caused by delaying the may be a liquid crystal display device is corrected by prolonging during on-period of the driving voltage to the liquid crystal cell in the image display drive period.

Length between the liquid crystal drive time correction circuit, the error from the ideal value of the luminance caused by the response speed of the liquid crystal of the liquid crystal cell, on period of the drive voltage to the liquid crystal cell in the image display drive period It can be set as the liquid crystal display device which correct | amends by changing.

The liquid crystal drive time correction circuit, when performing the gradation display of high gradation side than the liquid crystal cell is a particular halftone, the error from the ideal value of the luminance caused by the response speed of the liquid crystal, the It may be a liquid crystal display device for correcting by the image display drive period to shorten the oN period of the driving voltage to the liquid crystal cell.

By controlling the light modulation operation of the liquid crystal cell in synchronization with the light emission timing of the light source, one image is displayed in units of one or a plurality of fields, and the field is driven to display the image. An image display drive period is provided, and in the image display drive period, a light emission period and a non-light emission period of the light source, and an on period and an off period of a drive voltage for the liquid crystal cell are provided. performs gradation display of the image by controlling the length between the on period of the drive voltage to the liquid crystal cell in the light emitting period of the light source, until a predetermined time elapses from the timing of the start of the image display drive period The light emission start timing of the light source in the image display driving period is delayed, and the delayed period is the non-lighting of the light source in the image display driving period. Become light period, the by overlapping the ON period of the driving voltage to the liquid crystal in the non-emission period is the image display drive period, when performing the gradation display, before and after delaying the timing of the emission start of the light source a method of driving a liquid crystal display device caused the error of luminance between, the error in luminance liquid crystal cell is produced when performing the gradation display, on the driving voltage to the liquid crystal cell in the image display drive period a method of driving a liquid crystal display device is corrected by changing the length of the period.

Wherein from said than liquid crystal cell specific halftone when performing gradation display except the lowermost gray scale to a low tone, the ideal value of the luminance caused by delaying the timing of the emission start of the light source error and may be a method of driving a liquid crystal display device is corrected by prolonging during on-period of the driving voltage to the liquid crystal cell in the image display drive period.

Liquid crystal be corrected by said error from the ideal value of the luminance caused by the response speed of the liquid crystal of the liquid crystal cell, to vary the length between the on period of the drive voltage to the liquid crystal cell in the image display drive period A driving method of the display device can be obtained.

When the liquid crystal cell performs gradation display on a higher gradation side than a specific halftone, an error from an ideal luminance value caused by the response speed of the liquid crystal is caused in the liquid crystal cell during the image display driving period. it can be a method of driving a liquid crystal display device that corrects by shortening the between-on period of the driving voltage with respect.

  According to the present invention, since an error from an ideal value of luminance generated when performing gradation display can be corrected by varying the on-time of the driving voltage for the liquid crystal cell, ideal gradation display is performed. It is possible.

(A) Timing chart showing a state where ideal low gradation black display (gradation 1 display) is performed, and (b) Low gradation black display (gradation 1 display) using conventional technology. FIG. 2 is a diagram comparing a timing chart showing a state in which a low tone is displayed and (c) a timing chart showing a state in which low gradation black display (gradation 1 display) is performed using the present invention. (A) Timing chart showing a state where ideal low gradation black display (gradation 2 display) is performed, and (b) Low gradation black display (gradation 2 display) using conventional technology. And (c) a timing chart showing a state where low gradation black display (gradation 2 display) is performed using the present invention. (A) A timing chart showing a state where an ideal high gradation white display (gradation 253 display) is performed, and (b) a high gradation white display (gradation 253 display) is performed using the conventional technology. The timing chart which shows the state which is present, and (c) the timing chart which shows the state where the high gradation white display (gradation 253 display) is performed using the present invention (A) A timing chart showing a state where an ideal high gradation white display (gradation 254 display) is performed, and (b) a high gradation white display (gradation 254 display) is performed using the conventional technology. FIG. 6 is a diagram comparing a timing chart showing a state in which the display is performed and (c) a timing chart showing a state in which high gradation white display (gradation 254 display) is performed using the present invention. Timing chart showing a state where black display (gradation 0 display) and low gradation black display (gradation 1 to 4 display) are performed using the present invention Block diagram conceptually illustrating the present invention Timing chart showing a state where ideal gradation display (gradation 0, 127, 255 display) is performed Timing chart showing the state where ideal low gradation black display (gradation 1, 2 display) is performed Diagram showing ideal γ (gamma) characteristics Timing chart showing a state where realistic black display (gradation 0 display) is performed Timing chart showing a state in which black display (gradation 0 display) is performed using conventional technology (A) Timing chart showing a state where ideal low gradation black display (gradation 1 display) is performed, and (b) Low gradation black display (gradation 1 display) using conventional technology. Compared to the timing chart showing the status (A) Timing chart showing a state where ideal low gradation black display (gradation 2 display) is performed, and (b) Low gradation black display (gradation 2 display) using conventional technology. Compared to the timing chart showing the status (A) A timing chart showing a state where an ideal high gradation white display (gradation 253 display) is performed, and (b) a high gradation white display (gradation 253 display) is performed using the conventional technology. Comparison with timing chart showing (A) A timing chart showing a state where an ideal high gradation white display (gradation 254 display) is performed, and (b) a high gradation white display (gradation 254 display) is performed using the conventional technology. Comparison with timing chart showing The figure which shows the gamma (gamma) characteristic at the time of performing gradation display using conventional technology

  The liquid crystal display device according to the present invention is configured as, for example, a reflective liquid crystal display device. For example, the reflective liquid crystal display device includes, as optical elements, a reflective liquid crystal cell, a light source for supplying light to the liquid crystal cell, and light having a polarization plane in a specific direction among the light emitted from the light source. A first polarizing filter that transmits only the light, and the light transmitted through the first polarizing filter is reflected toward the liquid crystal cell, and the polarization plane of the light reflected by the liquid crystal cell is reflected by the light modulation of the liquid crystal cell. And a second polarizing filter that transmits only light whose direction has been converted to another direction, and as an electrical element, light source control that switches light emission (lighting) and non-light emission (lighting off) at a predetermined timing A circuit and a liquid crystal control circuit for causing the liquid crystal of the liquid crystal cell to perform a light modulation operation (switching operation) by switching on and off the drive voltage at a predetermined timing.

  The first polarizing filter is composed of, for example, an absorption polarizing plate or a reflective polarizing plate, and the second polarizing filter is composed of, for example, a reflective polarizing plate.

  In the liquid crystal display device that displays a color image, the light source is configured by an LED that individually emits RGB light, but in the liquid crystal display device that displays only a monochrome image, the light source is configured by an LED that emits white light. Is done.

  The liquid crystal cell is composed of, for example, a ferroelectric liquid crystal cell using a ferroelectric liquid crystal having a high switching speed.

  In the above reflective liquid crystal display device, the liquid crystal control circuit controls the switching operation of the liquid crystal in synchronization with the light emission and non-light emission timings of the light source, so that the optical image signal is output from the liquid crystal cell. It is output as an image through two polarizing filters.

  In addition, the liquid crystal control circuit controls the on / off time of the driving voltage for the liquid crystal cell in each of the RGB fields, and gradation display is performed by changing the amount of transmitted light.

  The liquid crystal display device according to the present invention includes a light emission delay circuit that delays the light emission start timing of the light source, as in the prior art. The light emission delay circuit delays the light emission start timing of the light source until a predetermined time elapses from the start (start) timing of each field of RGB. The time TD for which the light emission delay circuit delays the light emission start timing of the light source is, for example, the same time as the time required for the liquid crystal to be completely turned off from the on state, but is shorter or longer than that. Can also be selected.

  By delaying the light emission start timing of the light source, it is possible to prevent a decrease in contrast during gradation 0 display due to the response speed of the liquid crystal, but particularly when performing low gradation display and high gradation display. There is a new problem that an appropriate amount of transmitted light cannot be obtained and ideal gradation display cannot be performed.

  Therefore, the liquid crystal display device according to the present invention further includes a liquid crystal driving time correction circuit for the purpose of solving the problem. The liquid crystal driving time correction circuit corrects an error from an ideal value of the transmitted light amount (luminance) generated by the light emission delay circuit delaying the light emission start timing of the light source, and obtains an appropriate transmitted light amount of RGB. In each field, the ON time of the drive voltage for the liquid crystal cell is changed. In other words, if the light transmission start time is delayed and the transmitted light amount is insufficient, the on-time of the liquid crystal is changed so that the transmitted light amount increases, and conversely, the transmitted light amount becomes excessive. For example, the on-time of the liquid crystal is changed so that the amount of transmitted light is reduced.

  FIG. 1-1 shows (a) a timing chart showing a state in which an ideal low gradation black display (gradation 1 display) is performed, and (b) a low gradation black display (floor) using a conventional technique. A timing chart showing a state in which a tone 1 display is being performed, and a timing chart showing a state in which a low gradation black display (gradation 1 display) is being performed using the present invention (c) FIG. 1-2 is a timing chart showing a state in which (a) ideal low gradation black display (gradation 2 display) is performed, and (b) low gradation black display using conventional technology ( A timing chart showing a state in which (gradation 2 display) is performed is compared with a timing chart (c) showing a state in which low gradation black display (gradation 2 display) is performed using the present invention. FIG.

  For example, in a liquid crystal display device operating in a normally black mode, the ideal transmitted light amount when performing low gradation black display of gradations 1 and 2 is shown in FIGS. 1-1 (a) and 1-2 (2), respectively. a) In the case where the same display is performed using the conventional technique for delaying the light emission start timing of the light source, the light emission start timing of the light source is delayed (time TD). ), The period in which the on-time TA of the liquid crystal overlaps the light emission time TS of the light source is shortened, and thus the obtained transmitted light amount is the area of the hatched portion in FIGS. 1-1 (b) and 1-2 (b), respectively. As shown, the value decreases with respect to the ideal value.

  Therefore, in the present invention, when the above display is performed, as shown in FIGS. 1-1 (c) and 1-2 (c), the timing at which the liquid crystal starts to switch from the on state to the off state is set for each field of RGB. The on-time TS of the liquid crystal is extended from the head timing of each RGB field more than usual by delaying the head timing by a predetermined time. By doing so, the period in which the on-time TA of the liquid crystal overlaps the light emission time TS of the light source is lengthened, and the amount of transmitted light obtained is increased correspondingly, and FIGS. 1-1 (c) and 1-2 (c), respectively. An ideal amount of transmitted light as indicated by the area of the hatched portion inside is obtained, and ideal gradation display is performed.

  The time for delaying the timing at which the liquid crystal starts to switch from the on state to the off state, that is, the time for extending the liquid crystal on time TA (correction time) may be appropriately set according to the error from the ideal value of the transmitted light amount. When displaying a gradation 1 using a ferroelectric liquid crystal, it is about 30 μsec. The correction time suitable for each gradation can be obtained by an experimental method or a computational method.

  FIG. 2 is a timing chart showing a state in which black display (gradation 0 display) and low gradation black display (gradation 1 to 4 display) are performed using the present invention. When the light emission start timing of the light source is delayed, the γ (gamma) characteristic becomes, for example, a quadratic curve characteristic as shown in FIG. 9, and an ideal characteristic (linear characteristic) as shown in FIG. Similarly, the error occurring between the two also shows a quadratic curve characteristic. For this reason, the amount (correction time) for changing the on-time of the liquid crystal is not necessarily constant between the respective gradations. However, even when low-gradation black display such as gradations 3 and 4 is performed, these levels are corrected. As shown in FIG. 2, an ideal gradation display is performed by applying a correction time suitable for the tone and extending the on-time TA of the liquid crystal to a predetermined length from the start timing of the field. On the other hand, when black display (gradation 0 display) is performed, normal driving is performed without changing the on-time TS of the liquid crystal in order to obtain high contrast. Note that the γ characteristic shown in FIG. 9 is merely an example, and when the γ characteristic is different from the γ characteristic, the on-time of the liquid crystal is appropriately changed so that an error corresponding to the characteristic is corrected.

  FIG. 1-3 shows (a) a timing chart showing a state where an ideal high gradation white display (gradation 253 display) is performed, and (b) a high gradation white display (gradation 253 using conventional technology). FIG. 1 is a diagram comparing a timing chart showing a state where display is performed and a timing chart showing a state where (c) high gradation white display (gradation 253 display) is performed using the present invention. -4 is a timing chart showing a state in which (a) an ideal high gradation white display (gradation 254 display) is performed, and (b) a high gradation white display (gradation 254 display) using the conventional technology. FIG. 6 is a diagram comparing a timing chart showing a state in which high-tone white display (tone 254 display) is being performed using the present invention.

  For example, in a liquid crystal display device that operates in a normally black mode, ideal transmitted light amounts when performing high gradation white display of gradations 253 and 254 are shown in FIGS. 1-3A and 1-4A, respectively. ) In the case of the same display using a liquid crystal cell with a slow response speed of the liquid crystal, the liquid crystal cell is not limited to the prior art that delays the light emission start timing of the light source. Since it takes a relatively long time to completely switch from the on state to the off state, the amount of transmitted light obtained is the shaded portion in FIGS. 1-3 (b) and 1-4 (b), respectively. It increases with respect to the ideal value as expressed by the area of.

  Therefore, in the present invention, when performing the above-described display, as shown in FIGS. 1-3 (c) and 1-4 (c), the timing at which the liquid crystal starts to switch from the on state to the off state is set for each field of RGB. The on-time TS of the liquid crystal is shortened from the start timing of each field of RGB by a predetermined time earlier than the normal timing. By doing so, the period in which the liquid crystal on-time TA overlaps with the light emission time TS of the light source is shortened, and the amount of transmitted light obtained is reduced accordingly, and FIGS. 1-3 (c) and 1-4 (c) respectively. An ideal amount of transmitted light as indicated by the area of the hatched portion inside is obtained, and ideal gradation display is performed.

  The time for advancing the timing at which the liquid crystal starts to switch from the on state to the off state, that is, the time for reducing the liquid crystal on time TA (correction time) may be appropriately set according to the error from the ideal value of the transmitted light amount. When displaying gradation 254 using ferroelectric liquid crystal, it is about 30 μsec. The correction time suitable for each gradation can be obtained by an experimental method or a computational method.

  FIG. 3 is a block diagram conceptually showing the present invention. In the present invention, data (correction data) indicating how much the on-time TS of the liquid crystal should be changed when performing each gradation display is stored in advance in a storage device in the liquid crystal display device, for example. The control circuit (driving circuit) reads out necessary correction data from timely, creates a corrected image signal in which the on-time TS of the liquid crystal is adjusted based on the correction data and the input normal image signal, An ideal gradation display is performed by driving the liquid crystal based on the corrected image signal.

  As described above, since the gradation correction is performed by correcting the image signal itself input to the liquid crystal driving circuit, it can be realized relatively easily even when the liquid crystal driving circuit is already completed. Is possible.

  Further, the liquid crystal display device of the present invention can further incorporate a circuit for performing normal γ (gamma) correction. In this case, as shown in FIG. 3, an arbitrary γ correction can be further applied to the image whose gradation is corrected according to the present invention.

  The present invention is not limited to a liquid crystal display device that operates in a normally black mode, but can also be applied to a liquid crystal display device that operates in a normally white mode.

  The liquid crystal display device is not limited to a reflective liquid crystal display device using a reflective liquid crystal cell, but may be a transmissive liquid crystal display device using a transmissive liquid crystal cell.

  In the above embodiment, the light emission start timing of the light source is delayed. However, the present invention can also be applied to a liquid crystal display device having a configuration in which the light emission start timing of the light source is not delayed. That is, the present invention can be applied only for the purpose of correcting only the error from the ideal luminance value caused by the response speed of the liquid crystal, and conversely, the light emission start timing of the light source is set. The present invention can also be applied for the purpose of correcting only the error from the ideal luminance value caused by the delay, and further, the error from the ideal luminance value caused by other factors is corrected. For this purpose, the present invention can be applied.

TS Light emission time of light source TD Light emission delay time of light source TA On time of liquid crystal (application time of drive voltage)

Claims (8)

A liquid crystal cell;
A light source for supplying light to the liquid crystal cell;
A liquid crystal control circuit for controlling the light modulation operation of the liquid crystal cell by controlling on and off of the drive voltage to the liquid crystal cell;
A light source control circuit for switching light emission and non-light emission of the light source;
A light emission delay circuit for delaying the light emission start timing of the light source ,
By controlling the light modulation operation of the liquid crystal cell in synchronization with the light emission and non-light emission timings of the light source, one image is displayed in one or more field units, and the image is displayed in the field. An image display driving period for performing driving for the liquid crystal cell is provided, and in the image display driving period, a light emitting period and a non-light emitting period of the light source, and an on period and an off period of the driving voltage for the liquid crystal cell are provided, There line gradation display of the image by controlling the length between the on period of the drive voltage to the liquid crystal cell between light emission period of the light source in the image display drive period,
The light emission delay circuit delays the light emission start timing of the light source in the image display drive period until a predetermined time elapses from the start timing of the image display drive period, and the delayed period is in the image display drive period. becomes the non-light emission period of the light source, by which the non-light emitting period overlap with the oN period of the driving voltage to the liquid crystal in the image display drive period, when performing the gradation display, the timing of emission start of the light source in the liquid crystal display device caused the error of luminance between the before and after delaying,
Wherein said error luminance liquid crystal cell may occur in performing the gradation display, the image display liquid crystal drive time correction for correcting the driving period by changing the length between the ON period of the driving voltage to the liquid crystal cell A liquid crystal display device comprising a circuit. The liquid crystal driving time correction circuit is configured such that the light emission delay circuit performs a light emission start timing of the light source when the liquid crystal cell performs gradation display excluding the lowest gradation on a lower gradation side than a specific halftone. the error in luminance caused by delaying the liquid crystal display device according to claim 1, characterized in that to correct by prolonging between on-period of the driving voltage to the liquid crystal cell in the image display drive period . Length between the liquid crystal drive time correction circuit, the error from the ideal value of the luminance caused by the response speed of the liquid crystal of the liquid crystal cell, on period of the drive voltage to the liquid crystal cell in the image display drive period the liquid crystal display device according to claim 1 or 2, characterized in that to correct by changing the. The liquid crystal drive time correction circuit, when performing the gradation display of high gradation side than the liquid crystal cell is a particular halftone, the error from the ideal value of the luminance caused by the response speed of the liquid crystal, the the liquid crystal display device according to claim 3, characterized in that to correct by shortening the between-on period of the drive voltage to the liquid crystal cell in the image display drive period. By controlling the light modulation operation of the liquid crystal cell in synchronization with the light emission timing of the light source, one image is displayed in units of one or a plurality of fields, and the field is driven to display the image. An image display drive period is provided, and in the image display drive period, a light emission period and a non-light emission period of the light source, and an on period and an off period of a drive voltage for the liquid crystal cell are provided. It performs gradation display of the image by controlling the length between the on period of the drive voltage to the liquid crystal cell in the light emitting period of the light source,
The light emission start timing of the light source in the image display drive period is delayed until a predetermined time has elapsed from the start timing of the image display drive period, and the delayed period is a non-light emission of the light source in the image display drive period Before and after delaying the light emission start timing of the light source when performing the gradation display by overlapping the non-light emission period with the ON period of the drive voltage for the liquid crystal in the image display drive period. in the method for driving a liquid crystal display device error of the luminance occurs,
And characterized in that the correction by the liquid crystal cell is the error in luminance occurring when performing the gradation display, to change the length between the ON period of the driving voltage to the liquid crystal cell in the image display drive period For driving a liquid crystal display device. Than said liquid crystal cell is a particular halftone when performing gradation display except the lowermost gray scale to a low tone, the error in luminance caused by delaying the timing of the emission start of said light source, said method for driving a liquid crystal display device according to claim 5, characterized in that to correct by prolonging between on-period of the driving voltage to the liquid crystal cell in the image display drive period. Be corrected by the error from the ideal value of the luminance caused by the response speed of the liquid crystal of the liquid crystal cell, to vary the length between the on period of the drive voltage to the liquid crystal cell in the image display drive period A driving method of a liquid crystal display device according to claim 5 or 6 . When the liquid crystal cell performs gradation display on a higher gradation side than a specific halftone, an error from an ideal luminance value caused by the response speed of the liquid crystal is caused in the liquid crystal cell during the image display driving period. method for driving a liquid crystal display device according to claim 7, characterized in that to correct by shortening the between-on period of the driving voltage with respect.

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