JP2012220632A - Electro-optical device, control method of electro-optical device and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to suppress an occurrence of a flicker even if an image for adjustment is not displayed.SOLUTION: An optical sensor 71 detects brightness of a display panel 10. A control circuit 52 detects the brightness of the display panel 10 from a signal S1 output from the optical sensor 71 and obtains a difference between an effective voltage when a pixel holds a positive polarity voltage and an effective voltage when the pixel holds a negative polarity voltage from a signal obtained by cutting a DC component of the signal S1 by a capacitor 72. The control circuit 52 controls a voltage applied to a counter electrode such that the difference between the effective voltages becomes smaller when the difference between the effective voltages becomes equal to or larger than a threshold value.

Description

  The present invention relates to a technique for suppressing the occurrence of flicker in an electro-optical device.

  A liquid crystal element used in a liquid crystal display device has a structure in which a liquid crystal is sandwiched between two electrodes. However, when a direct current component is applied, the liquid crystal deteriorates. For this reason, in a liquid crystal display device, the liquid crystal element is generally AC driven. However, a DC component may be applied to the liquid crystal only by AC driving. Specifically, in the liquid crystal display device, the pixel electrode substrate sandwiching the liquid crystal layer and the common electrode substrate have different physical structures, and a positive voltage that is higher than the common electrode is applied. The resistance value at the interface between the electrode and the alignment film or at the interface between the alignment film and the liquid crystal layer differs depending on the case where a negative polarity voltage that is low when viewed from the common electrode is applied. As a result, in the liquid crystal display device, the current amount is different between the application of the positive voltage and the application of the negative voltage even if the effective voltage to the liquid crystal layer is the same, and the amount of charge transfer is non-targeted. Arise. In addition, due to the asymmetry of the current amount, the electric charge in the liquid crystal is biased, and an internal electric field is generated by the bias of the charge. Due to the influence of the internal electric field, the voltage actually applied to the liquid crystal layer becomes asymmetric depending on the polarity of the drive voltage, and a DC voltage component is applied to the liquid crystal layer.

  When this direct current component is applied to the liquid crystal layer, flicker occurs. Therefore, there is a technique for adjusting the voltage of the common electrode in order to suppress flicker. For example, the liquid crystal display device disclosed in Patent Document 1 adjusts the voltage of the common electrode based on the difference between the luminance when a positive voltage is applied to the liquid crystal element and the luminance when a negative voltage is applied.

JP 2010-197928 A

  The liquid crystal display device disclosed in Patent Document 1 includes a pixel including a photosensor outside an active area where an input image is displayed, and an image for adjustment when adjusting the voltage of the common electrode. Is displayed on a pixel including an optical sensor, and the luminance of the pixel is detected by the optical sensor. However, with such a configuration, a liquid crystal element including an optical sensor is provided separately from the active area, and the structure of the device becomes complicated. Further, it is necessary to display an adjustment image separately from the display of the active area.

  The present invention has been made in view of the above-described circumstances, and one of its purposes is to make it possible to suppress the occurrence of flicker without displaying an adjustment image.

In order to achieve the above object, the electro-optical device according to the present invention is provided corresponding to the intersection of a plurality of scanning lines and a plurality of data lines, respectively, and when each of the scanning lines is selected, A display region having a pixel having a gradation corresponding to a voltage of a data signal supplied to the data line, the pixel being opposite to the pixel electrode to which the data signal is applied; An electro-optical device in which an electro-optical material is sandwiched between an electrode and the pixel electrode and the counter electrode, the positive electrode being a voltage corresponding to the gradation of the pixel and having a high level based on a predetermined potential A positive polarity field that supplies a positive voltage to the data line corresponding to the pixel as the data signal, and a negative polarity voltage that is a voltage corresponding to the gray level of the pixel and is lower than a predetermined potential. The pixel as a data signal In each of the negative polarity fields supplied to the corresponding data lines, the scanning line driving circuit that selects the plurality of scanning lines in a predetermined order, and one scanning line in the positive polarity field are selected. When a voltage corresponding to the gradation of the pixel is supplied to the data line corresponding to the pixel as the data signal, and the one scanning line is selected in the negative polarity field. A data line driving circuit for supplying a voltage corresponding to a gradation of the pixel to the data line corresponding to the pixel as a data signal for the pixel located on the one scanning line; and brightness of the display area Is detected to generate a signal representing the brightness, a first signal representing the direct current component of the signal, a second signal representing the alternating current component of the signal, and a first circuit generated by the detection circuit 2 signals When the wave height of the waveform is equal to or greater than a threshold value determined according to the first signal generated by the detection circuit, the effective voltage applied to the pixel in the positive polarity field so that the wave height is less than the threshold value. A control circuit for controlling a difference between a voltage and an effective voltage of the voltage applied in the negative polarity field is provided.
According to the present invention, since the brightness of the display area that changes in accordance with the difference between the effective voltage of the voltage applied in the positive polarity field and the effective voltage of the voltage applied in the negative polarity field, it is applied in the positive polarity field. The difference between the effective voltage of the first voltage and the effective voltage of the voltage applied in the negative field is detected. In addition, since the difference between the effective voltage of the voltage applied in the positive polarity field and the effective voltage of the voltage applied in the negative polarity field is adjusted so that the difference in effective voltage is less than the threshold value, The occurrence of flicker can be suppressed without displaying an image used only for display in the display area.

In the present invention, the control circuit has at least three threshold values determined according to the first signal, and when the value of the first signal is less than a predetermined first set value, When the threshold value is a first threshold value, and the value of the first signal is less than a predetermined second set value greater than the first set value and greater than or equal to the first set value, the threshold is set to the first threshold value. A third threshold value that is greater than one threshold value, and when the value of the first signal is greater than or equal to the second set value, the threshold value is a second threshold value that is greater than the first threshold value and smaller than the third threshold value. It is good.
According to this configuration, it is possible to determine the threshold more appropriately according to the brightness of the display area, and the effective voltage of the voltage applied in the positive polarity field so that the difference in effective voltage is less than the threshold, and the negative electrode The occurrence of flicker can be suppressed by adjusting the difference between the voltage applied in the sex field and the effective voltage.

In the present invention, the control circuit may be configured to determine the threshold value from the wave height of the second signal and the first signal.
According to this configuration, the threshold value can be determined more appropriately, and the effective voltage of the voltage applied in the positive field and the voltage applied in the negative field so that the difference in effective voltage is less than the threshold value. The occurrence of flicker can be suppressed by adjusting the difference from the effective voltage.

In the present invention, the control circuit controls the voltage applied to the counter electrode, whereby the effective voltage of the voltage applied to the pixel in the positive field and the negative field are applied. The difference between the effective voltage and the effective voltage may be controlled.
According to this configuration, by adjusting the potential of the counter electrode, the difference between the effective voltage of the voltage applied in the positive field and the effective voltage of the voltage applied in the negative field is adjusted, and flicker occurs. Can be suppressed.

In the present invention, the control circuit controls the ratio of the positive voltage application time and the negative voltage application time to control the voltage applied to the pixel in the positive field. The difference between the effective voltage and the effective voltage of the voltage applied in the negative field may be controlled.
According to this configuration, the difference between the effective voltage of the voltage applied in the positive polarity field and the effective voltage of the voltage applied in the negative polarity field is adjusted by adjusting the ratio of the application time, and flicker occurs. Can be suppressed.

In the present invention, the control circuit controls the ratio of the voltage applied to the counter electrode, the application time of the positive voltage, and the application time of the negative voltage to the pixel. The difference between the effective voltage applied in the positive field and the effective voltage applied in the negative field may be controlled.
According to this configuration, the difference between the effective voltage of the voltage applied in the positive polarity field and the effective voltage of the voltage applied in the negative polarity field is adjusted by adjusting the potential of the counter electrode and the application time ratio. The occurrence of flicker can be suppressed.

  The present invention can be conceptualized not only as an electro-optical device but also as a control method of the electro-optical device and an electronic apparatus having the electro-optical device.

1 is a block diagram showing a configuration of an electro-optical device 1. FIG. FIG. 3 is a diagram illustrating a configuration of a display panel 10 of the electro-optical device 1. FIG. 3 shows a configuration of a pixel 110 in the display panel 10. FIG. 6 shows an operation of a scanning line driving circuit 130. FIG. 4 is a diagram showing an example of a voltage waveform of a data signal in the display panel 10. FIG. 4 is a diagram showing an example of a voltage waveform of a data signal in the display panel 10. The figure which shows transition of the writing of the pixel in a display area. FIG. 4 is a diagram illustrating characteristics of the display panel 10. The figure which showed the relationship between the voltage applied to a liquid crystal, and the transmittance | permeability. The figure which showed the relationship between the brightness of the display panel 10, and voltage difference AC. The figure which showed the relationship between the brightness of the display panel 10, voltage DC, and voltage difference AC. 5 is a flowchart showing the flow of processing of a control circuit 52. FIG. 6 shows an operation of a scanning line driving circuit 130. The figure which shows transition of the writing of the pixel in a display area. FIG. 6 shows an operation of a scanning line driving circuit 130. The figure which shows transition of the writing of the pixel in a display area. 5 is a flowchart showing the flow of processing of a control circuit 52. 5 is a flowchart showing the flow of processing of a control circuit 52. FIG. 3 is a diagram illustrating a configuration of a projector using the electro-optical device according to the embodiment.

[First Embodiment]
FIG. 1 is a block diagram showing a configuration of an electro-optical device 1 according to the first embodiment of the present invention. As shown in FIG. 1, the electro-optical device 1 is roughly divided into a display panel 10, a processing circuit 50, and a detection circuit 70. Among these, the processing circuit 50 which is a circuit module for controlling the operation of the display panel 10 includes a control circuit 52, a display data processing circuit 54, and a D / A conversion circuit 56, for example, an FPC (flexible printed circuit) substrate. Is connected to the display panel 10. The detection circuit 70 includes an optical sensor 71, a capacitor 72, and an A / D conversion circuit 73. The electro-optical device 1 is an example of a liquid crystal device that displays an image using liquid crystal.

  The control circuit 52 generates various control signals for controlling the display panel 10 in synchronization with a synchronization signal Vsync supplied from an external host device (not shown). These control signals will be described later as appropriate. The control circuit 52 generates various control signals and controls the display data processing circuit 54.

  The display data processing circuit 54 temporarily stores display data Video supplied from an external host device in an internal memory (not shown) under the control of the control circuit 52 and then reads it in synchronization with driving of the display panel 10. It is. Note that the display data Video is data that specifies the gradation of the pixels in the display panel 10, and the waveform is not particularly shown, but for one frame (period of 16.7 milliseconds (frequency 60 Hz)) (For pixel). The D / A conversion circuit 56 converts the read display data into an analog data signal Vid according to control by the control circuit 52.

  Next, the display panel 10 will be described. FIG. 2 is a diagram illustrating a configuration of the display panel 10. As shown in this figure, the display panel 10 is a peripheral circuit built-in type in which a scanning line driving circuit 130 and a data line driving circuit 140 are built around the display region 100. In the display area 100, 480 scanning lines 112 are provided so as to extend in the row (X) direction, and 640 columns of data lines 114 are provided so as to extend in the column (Y) direction. The pixels 110 are arranged so as to be electrically insulated from the scanning lines 112 and correspond to the intersections of the scanning lines 112 of 480 rows and the data lines 114 of 640 columns. Accordingly, in the present embodiment, the pixels 110 are arranged in a matrix of 480 rows × 640 columns in the display region 100, but the present invention is not limited to this arrangement.

  The configuration of the pixel 110 will be described with reference to FIG. FIG. 3 shows a total of 4 pixels of 2 × 2 corresponding to the intersection of the i row and the (i + 1) row adjacent to the i row and the j column and the j column and the (j + 1) column adjacent to the right one column. The structure of is shown. Note that i and (i + 1) are symbols for generally indicating the row in which the pixels 110 are arranged, and are integers of 1 to 480 in this description. J and (j + 1) are symbols for generally indicating a column in which the pixels 110 are arranged, and are integers of 1 to 640.

  As shown in FIG. 3, each pixel 110 includes an n-channel TFT 116 and a liquid crystal capacitor 120. Here, since each pixel 110 has the same configuration, the gate electrode of the TFT 116 in the pixel 110 in the i row and j column will be described as the pixel in the i row and j column. On the other hand, the source electrode is connected to the data line 114 in the j-th column, and the drain electrode is connected to the pixel electrode 118 which is one end of the liquid crystal capacitor 120. The other end of the liquid crystal capacitor 120 is connected to the counter electrode 108. The counter electrode 108 is common to all the pixels 110 and is applied with the voltage LCcom.

Although not specifically shown, the display panel 10 has a configuration in which a pair of substrates of an element substrate and a counter substrate are bonded together with a certain gap therebetween, and liquid crystal is sealed in the gap. Among these, the scanning line 112, the data line 114, the TFT 116, and the pixel electrode 118 are formed on the element substrate together with the scanning line driving circuit 130 and the data line driving circuit 140, while the counter electrode 108 is formed on the counter substrate. These electrode forming surfaces are bonded together with a certain gap so as to face each other. Therefore, in this embodiment, the liquid crystal capacitor 120 is configured by sandwiching the liquid crystal 105, which is an example of an electro-optic material, between the pixel electrode 118 and the counter electrode 108.
In this embodiment, if the effective voltage value held in the liquid crystal capacitor 120 is close to zero, the transmittance of light passing through the liquid crystal capacitor is maximized to display white, while the effective voltage value increases. The normally white mode in which the amount of transmitted light decreases and finally the black display with the minimum transmittance is set.

  In this configuration, a selection voltage is applied to the scanning line 112 to turn on the TFT 116, and the voltage corresponding to the gradation (brightness) is applied to the pixel electrode 118 via the data line 114 and the on-state TFT 116. When the data signal is supplied, the liquid crystal capacitor 120 corresponding to the intersection of the scanning line 112 to which the selection voltage is applied and the data line 114 to which the data signal is supplied can hold the effective voltage value corresponding to the gradation. Therefore, the light transmitted through the liquid crystal capacitor 120 can be different for each pixel, whereby an image is formed in the display region 100. The formed image is viewed directly by the user or enlarged and projected as in a projector described later.

  Note that when the scanning line 112 becomes a non-selection voltage, the TFT 116 is turned off (non-conducting). However, since the off resistance at this time is not ideally infinite, the charge accumulated in the liquid crystal capacitor 120 is small. Leak. In order to reduce the influence of off-leakage, a storage capacitor 109 is formed for each pixel. One end of the storage capacitor 109 is connected to the pixel electrode 118 (the drain of the TFT 116), while the other end is commonly connected to the capacitor line 107 over all pixels. The capacitance line 107 is maintained at a constant potential, for example, the same voltage LCcom as the counter electrode 108.

  The scanning line driving circuit 130 supplies scanning signals G1, G2, G3,..., G480 to the scanning lines 112 in the 1, 2, 3,. Here, the scanning line driving circuit 130 sets the scanning signal to the selected scanning line to the H level corresponding to the voltage Vdd, and the scanning signals to the other scanning lines to L corresponding to the non-selection voltage (ground potential Gnd). Level.

FIG. 4 is a timing chart showing the scanning signals G1 to G480 output from the scanning line driving circuit 130 in relation to the start pulses Dya and Dyb and the clock signal Cly. As shown in the figure, each scanning line 112 is selected twice in one frame period. Here, the frame means a period required to display one image on the display panel 10, but the display data Video is supplied with a period of 16.7 milliseconds as described above. Corresponds to 16.7 milliseconds of this period.
The control circuit 52 outputs a clock signal Cly having a duty ratio of 50% for 480 periods equal to the number of scanning lines over a period of one frame. In FIG. 4, a period of one cycle of the clock signal Cly is denoted as H. The control circuit 52 outputs start pulses Dya and Dyb having a pulse width corresponding to one cycle of the clock signal Cly when the clock signal Cly rises to the H level as follows. That is, the control circuit 52 outputs the start pulse Dya at the beginning of one frame period (that is, at the beginning of the first field), while outputting the start pulse Dyb for 240 cycles of the clock signal Cly after outputting the start pulse Dyb. Is output at a timing T at which a half period of one frame has passed. However, as will be described later, the control circuit 52 may output the start pulse Dyb with respect to the timing T to the front side or the rear side in terms of time in units of the period of the clock signal Cly.

The period from the start pulse Dya output until the start pulse Dyb is output is set as the first field in the period of one frame, and the next start pulse Dya is output after the start pulse Dyb is output. The period until is the second field.
Here, the start pulses Dya and Dyb are alternately output, and among these, the start pulse Dya is output at the start timing of one frame, that is, every 16.7 milliseconds. For this reason, when the start pulse Dya is specified, the start pulse Dyb is inevitably specified, and therefore, in FIG. 1, FIG. 2, etc., there is a case where they are described as the start pulse Dy without particularly distinguishing both.

The scanning line driving circuit 130 outputs the scanning signals G1 to G480 shown in FIG. 4 from the start pulses Dya and Dyb and the clock signal Cly. That is, when the start pulse Dya is supplied to the scanning signals G1 to G480, the scanning line driving circuit 130 sequentially sets the clock signal Cly to the H level during the L level period, while when the start pulse Dyb is supplied. The clock signal Cly is sequentially set to the H level during the H level period.
For this reason, by supplying the start pulse Dya, the scanning line extends in the order of 1, 2, 3, 4,... The clock signal Cly is selected after a half cycle period.
On the other hand, when the start pulse Dyb is supplied, the scanning line moves from the second field of a certain frame to the first field of the next frame in the downward direction of the screen in the order of rows 1, 2, 3, 4,. Thus, it is selected between selections triggered by the supply of the start pulse Dya.

  The data line driving circuit 140 includes a sampling signal output circuit 142 and n-channel TFTs 146 provided corresponding to the data lines 114, respectively. As shown in FIGS. 5 and 6, the sampling signal output circuit 142 selects one of the scanning lines 112 according to the control signal Ctrl-x from the control circuit 52, and the scanning signal supplied to the scanning line is at the H level. In this period, sampling signals S1, S2, S3,..., S640 that sequentially become H level exclusively are output so as to correspond to each of the data lines 114. Note that the control signal Ctrl-x is actually a start pulse or a clock signal, but is not directly related to the present invention, so the description is omitted. Further, the period during which the scanning signal is at the H level is actually slightly narrower than the half-period period of the clock signal Cly, as shown in FIGS.

  Meanwhile, the D / A conversion circuit 56 in FIG. 1 converts display data Video for one row of pixels located on the scanning line 112 selected by the scanning line driving circuit 130 into sampling signals S1 to S640 by the sampling signal output circuit 142. The data signal Vid having the following polarity is converted according to the output. In other words, the D / A conversion circuit 56 is positive for the data signal Vid of the pixel located in the selected row when the clock signal Cly is at the L level, and is selected when the clock signal Cly is at the H level. The data signal Vid of the pixel located at is converted into a negative polarity. Note that the positive polarity means that the voltage applied to the pixel electrode 118 is higher than the voltage applied to the counter electrode 108, and the negative polarity means that the voltage applied to the pixel electrode 118 is applied to the counter electrode 108. A case where the voltage is lower than the applied voltage.

  Next, the output timing of the start pulse Dyb will be described. The control circuit 52 controls the output timing of the start pulse Dyb. The control circuit 52 has a register that stores a value for designating the output timing of the start pulse Dyb, and changes the output timing of the start pulse Dyb in accordance with the value stored in the register.

  First, the control circuit 52 stores the display data Video supplied from the external host device in the internal memory of the display data processing circuit 54, and then selects a scanning line of a row on the display panel 10, and The display signal is read out at a speed twice the storage speed, and the sampling signal output circuit 142 is connected via the control signal Ctrl-x so that the sampling signals S1 to S640 sequentially become H level in accordance with the reading of the display data. Control. The read display data is converted into an analog data signal Vid by the D / A conversion circuit 56.

Here, the control circuit 52 supplies the start pulse Dyb at timing T when the value stored in the register is “0”. When supplying the start pulse Dyb at the timing T, the control circuit 52 selects the scanning lines 112 in the order of the 241, 241, 2, 243,..., 480, 240th rows in the first field. Is done. Therefore, the control circuit 52 controls the scanning line driving circuit 130 so that the scanning line 112 in the 241st row is selected first. Further, the control circuit 52 causes the display data processing circuit 54 to read the display data Video corresponding to the 241st row stored in the memory at double speed, and causes the D / A conversion circuit 56 to read the negative data signal. The sampling signal output circuit 142 is controlled so that the sampling signals S1 to S640 are exclusively set to the H level in this order in accordance with the reading. When the sampling signals S1 to S640 are sequentially set to the H level, the TFTs 146 are sequentially turned on, and the data signals Vid supplied to the image signal lines 171 are sequentially sampled on the data lines 114 in the 1st to 640th columns.
On the other hand, when the scanning line 112 in the 241st row is selected and the scanning signal G241 becomes the H level, all the TFTs 116 in the pixels 110 located in the 241st row are turned on. Therefore, the negative voltage of the data signal Vid sampled on the data line 114 is applied to the pixel electrode 118 as it is. For this reason, the liquid crystal capacitor 120 in the pixels of the 241st row and in the columns 1, 2, 3, 4,..., 639, 640 has a negative voltage corresponding to the gradation specified by the display data Video. Will be written and held.

Next, the control circuit 52 controls the scanning line driving circuit 130 so that the scanning line 112 in the first row is selected. In addition, the control circuit 52 causes the display data processing circuit 54 to read the display data Video corresponding to the first row stored in the memory at double speed, and causes the D / A conversion circuit 56 to output a positive data signal. The sampling signal output circuit 142 is controlled so that the sampling signals S1 to S640 are exclusively set to the H level in this order in accordance with the reading.
When the scanning line 112 in the first row is selected and the scanning signal G1 becomes H level, all the TFTs 116 in the pixels 110 located in the first row are turned on, whereby the voltage of the data signal Vid sampled on the data line 114 is turned on. Is applied to the pixel electrode 118. Therefore, a positive voltage corresponding to the gradation specified by the display data Video is written and held in the liquid crystal capacitor 120 in the pixels in the first row and in the 1st to 640th columns.

Hereinafter, in the first field, the same voltage writing operation is performed in the order of the 242nd, 2nd, 24th, 3rd,..., 480th, and 240th rows. Thereby, a positive voltage corresponding to the gradation is written to the pixels in the first to 240th rows, and a negative voltage corresponding to the gradation is written to the pixels in the 241st to 480th rows. Each will be held.
If the start pulse Dyb is supplied at the timing T, the scanning lines 112 are 1, 241, 2, 242, 3, 243, 4, 244,..., 240, 480 rows in the second field. While being selected in the order of eyes, the writing polarity in the same row is inverted. Therefore, a negative voltage corresponding to the gradation is written to the pixels in the first to 240th rows, and a positive voltage corresponding to the gradation is written to the pixels in the 241st to 480th rows. Each will be held.

FIG. 5 shows an example of a voltage waveform of the data signal Vid in a period in which the (i + 240) -th scanning line and the i-th scanning line in the first field are selected.
In this figure, voltages Vb (+) and Vb (−) are positive and negative voltages corresponding to the black of the lowest gradation, respectively, and have a symmetrical relationship with respect to the reference voltage Vc. The reference voltage Vc is the center of the amplitude of the data signal Vid and is an intermediate voltage between the voltages Vb (+) and Vb (−). In the present embodiment, the ground potential Gnd is used as a voltage reference unless otherwise specified. In the present embodiment, when the decimal value of the gradation value designated by the display data Video is “0”, black of the lowest gradation is designated, and thereafter, a bright gradation is designated as the decimal value increases. Is normally white mode, so if the voltage of the data signal Vid is converted to positive polarity, it becomes a voltage swung from the voltage Vb (+) to the lower side as the gradation value increases, and the negative polarity In the case of converting to V, the voltage is swung from the voltage Vb (−) to the higher side.

In the first field, since the (i + 240) -th scanning line is selected before the i-th row, for example, the sampling signal S1 is at the H level during the period in which the scanning signal G (i + 240) is at the H level. During this period, the data signal Vid becomes a negative voltage corresponding to the gradation of the pixel in the i row and the first column, and the second, third, fourth,... It changes to a negative polarity voltage according to the gradation of the pixel.
In the i-th row that is subsequently selected, since positive polarity writing is designated, the data signal Vid is i during the period in which the scanning signal Gi is at the H level, for example, the period in which the sampling signal S1 is at the H level. It becomes a positive voltage according to the gradation of the pixel in the row 1 column, and thereafter, according to the change of the sampling signal, the positive voltage according to the gradation of the pixel in the 2, 3, 4,. Change.
In the second field, since the (i + 240) -th scanning line is selected after the i-th row, the scanning signal Gi first goes to the H level and the writing polarity is inverted, so that the data signal Vid The voltage waveform is as shown in FIG.
In FIG. 5 and FIG. 6, the vertical scale indicating the voltage of the data signal Vid is enlarged as compared with the vertical scales of other signals for convenience. In addition, the voltage corresponding to black is obtained during the period from when the sampling signal S640 changes to the L level to when the sampling signal S1 changes to the H level. This is because it does not contribute to the display even if it is written on.

Next, FIG. 7 is a diagram showing the writing state of each row with the lapse of time over successive frames when the start pulse Dyb is supplied at the timing T. FIG. As shown in this figure, in the present embodiment, negative polarity writing is performed in the pixels of 241, 242, 243,..., 480th row in the first field, and 1, 2, 3,. In the pixel on the 240th row, positive writing is performed and held until the next writing. On the other hand, in the second field, negative-polarity writing is performed on the pixels in the first, second, third,..., 240th rows, and positive-polarity writing is performed on the pixels in the 241st, 24th, 242th,. In the same manner, it is held until the next writing.
When the value of the register is “0” and the start pulse Dyb is supplied at the timing T, the period of the first and second fields is 240 periods of the clock signal Cly. The period during which the positive voltage is held and the period during which the negative voltage is held are halved.

Incidentally, as shown in FIG. 5, the voltage LCcom applied to the counter electrode 108 is set to a lower side than the reference voltage Vc at the time of factory shipment. This is because, in an active matrix electro-optical device in which the pixel electrode is driven by a TFT, so-called push-down occurs, or when the liquid crystal capacitance leak holds a positive voltage and a negative voltage. It depends on what is different.
If the voltage LCcom is made to coincide with the reference voltage Vc, the effective voltage value of the liquid crystal capacitor 120 by negative polarity writing becomes slightly larger than the effective value by positive polarity writing (when the TFT 116 is n-channel). The voltage LCcom is set to an optimum value so that this difference is offset by offsetting the voltage LCcom lower than the reference voltage Vc.

In this embodiment, when the start pulse Dyb is supplied at the timing T, the first and second field periods are equal to each other, and the positive voltage and the negative voltage are held in the liquid crystal capacitor 120 in each pixel. Since the period to be performed is half of the period of the frame, a direct current component should not be applied to the liquid crystal capacitor 120. However, when the TFT pushdown amount or the amount of leakage in the liquid crystal capacitance changes from the time of shipment from the factory due to changes over time, the voltage LCcom is no longer the optimum value, and a direct current component is applied to the liquid crystal capacitance 120, and the positive voltage Therefore, there is a difference between the effective voltage when the voltage is held and the effective voltage when the negative voltage is held, and flicker occurs.
In addition, the display panel 10 has different characteristics, and even if the register value is 0, a panel that needs to increase the voltage LCcom that minimizes flicker after a certain period of time and a voltage LCcom that minimizes flicker are displayed. There are panels that need to be reduced. In this case, even if the register value is 0, flicker occurs.

  Here, FIG. 8 is a diagram showing the value of the register and the amount of change in the voltage LCcom that minimizes the amount of flicker for the flicker that occurs after a certain time has elapsed after applying a voltage based on the value of the register. In this figure, the horizontal axis represents the register value. When the register value is positive, the positive voltage holding period is long, and when the register value is negative, the negative voltage holding period is long. ing. The vertical axis represents how much the flicker is minimized when the voltage LCcom is changed after a predetermined time has elapsed. The panel (1) in FIG. 8 is a panel in which the voltage LCcom needs to be increased in order to minimize the flicker after a certain time has elapsed when the value of the register is 0. The panel (2) in FIG. 8 is a panel in which the voltage LCcom needs to be reduced in order to minimize the flicker after a certain time has elapsed when the value of the register is 0.

  The control circuit 52 controls the voltage LCcom applied to the counter electrode 108 so that the effective voltage difference is reduced when the effective voltage difference is equal to or greater than a predetermined threshold value. This control is performed because the difference in brightness of the pixel increases as the difference between the effective voltage when the pixel holds the positive voltage and the effective voltage when the pixel holds the negative voltage increases. This is because this difference is perceived as flicker.

  The electro-optical device 1 includes a detection circuit 70 for performing this control. The optical sensor 71 of the detection circuit 70 is a sensor that detects the brightness of the display panel 10. The optical sensor 71 includes a photodiode. When light enters the photodiode, the change in the current flowing through the photodiode is converted into a change in voltage by a current-voltage conversion circuit, thereby indicating the brightness of the display panel 10. The analog signal S1 is supplied to the A / D conversion circuit 73 and the capacitor 72. In the present embodiment, the signal S1 output from the optical sensor 71 represents the brightness of the display panel 10 by the voltage value, and the voltage changes according to the detected brightness. The capacitor 72 cuts the DC component of the signal S1. The signal S2 from which the DC component has been cut by the capacitor 72, that is, the signal S2 representing the AC component of the signal S1, is supplied to the A / D conversion circuit 73. The A / D conversion circuit 73 converts the supplied analog signal S1 into a signal S11 (first signal) which is a digital signal, and supplies the signal S11 to the control circuit 52. The A / D conversion circuit 73 converts the supplied analog signal S2 into a signal S12 (second signal) which is a digital signal, and supplies the signal S12 to the control circuit 52.

  If there is no difference between the effective voltage when the pixel holds the positive voltage and the effective voltage when the pixel holds the negative voltage, the voltage of the signal S1 is displayed if the display panel 10 displays the same image. Is constant. On the other hand, as described above, when a direct current component is applied to the liquid crystal and a difference occurs between the effective voltage when the pixel holds a positive voltage and the effective voltage when the pixel holds a negative voltage, Depending on this difference, a difference in brightness occurs. When a difference occurs in the brightness of the pixels, the brightness of the display panel 10 as a whole also differs when the pixels hold a positive voltage and when the pixels hold a negative voltage. As a result, the voltage of the signal S1 differs between when the pixel holds a positive polarity voltage and when the pixel holds a negative polarity voltage, and the voltage value represented by the signal S11 and the voltage value represented by the signal S12 are also positive. This is different between when the negative voltage is held and when the negative voltage is held. Note that the difference between the brightness when the pixel holds the negative voltage and the brightness when the pixel holds the negative voltage corresponds to the difference in the effective voltage, and is obtained, for example, during one frame. The difference between the maximum value and the minimum value of the signal S12 corresponds to the difference between the effective voltage when the pixel holds the positive voltage and the effective voltage when the pixel holds the negative voltage.

  Further, the signal S1 before the AC component is cut has a low voltage value when the display panel 10 is dark, and the voltage value becomes high as the display panel 10 becomes brighter. For this reason, the voltage value represented by the signal S11 represents the brightness of the display panel 10. Note that the brightness of the display panel 10 changes according to the displayed image, and is dark when there are many black pixels, and becomes brighter as the number of halftone pixels and white pixels increases. It can be said that the brightness is 10 and the content of the displayed image.

  The control circuit 52 obtains an average value of the voltage value represented by the signal S11 supplied during a predetermined n frames (n is an integer of 1 or more) triggered by the start pulse Dy, and displays the obtained average value. It is assumed that the voltage DC represents the brightness of the panel 10. Further, the control circuit 52 sets the maximum and minimum values of the voltage value represented by the signal S12 for the signal S12 supplied during a predetermined n frames (n is an integer of 1 or more) triggered by the start pulse Dy. (Wave height of the waveform of the signal S12) is obtained, and the obtained difference (wave height) is defined as a voltage difference AC.

  Note that the value of the voltage difference AC changes according to the difference in effective voltage, but the voltage difference AC varies depending on the gradation of the pixel even if the difference in effective voltage applied to the pixel is approximately the same. FIG. 9 is a diagram showing the relationship between the applied voltage (V) and the transmittance (T) of the liquid crystal 105. In the present embodiment, since the liquid crystal 105 is in a normally white mode, it is represented by characteristics as shown in FIG. In order to make the pixel 110 have a transmittance according to the gradation level specified by the data signal Vid, a voltage corresponding to the gradation level should be applied to the liquid crystal. However, when a direct current component is applied to the liquid crystal, the voltage acting on the liquid crystal differs when a negative voltage is applied and when a positive voltage is applied.

For example, even when the voltage V1 is applied to the pixel electrode 118, if a direct current component is applied to the liquid crystal, the voltage acting on the liquid crystal is the voltage V11 between when a positive voltage is applied and when a negative voltage is applied. And voltage V12. In the intermediate gradation, since the change in transmittance is large when the voltage applied to the liquid crystal changes, the transmittance when the voltage V11 is applied to the liquid crystal and the transmittance when the voltage V12 is applied to the liquid crystal. The difference is large, and the transmittance difference (pixel brightness difference) is ΔC1 as shown in FIG.
On the other hand, for example, when the voltage V2 that makes the pixel white is applied to the pixel electrode 118, even if the same DC component is applied to the liquid crystal, the voltage acting on the liquid crystal is the same as that applied when the positive voltage is applied. At that time, the voltage V21 and the voltage V22 are obtained. Here, the voltage difference between the voltage V21 and the voltage V22 and the voltage difference between the voltage V11 and the voltage V12 are the same, but in the range where the transmittance is close to the maximum, even if the voltage acting on the liquid crystal changes, the voltage difference is transmitted. Since the change in the rate is small, the difference between the transmittance when the voltage V21 is applied to the liquid crystal and the transmittance when the voltage V22 is applied to the liquid crystal is small, and the difference in transmittance (difference in pixel brightness) Becomes ΔC2 smaller than ΔC1.
In this way, even when the voltage difference acting on the liquid crystal is the same between when the positive voltage is applied and when the negative voltage is applied, the difference in brightness of the pixels is different. The difference in brightness differs depending on the content of the image, and the voltage difference AC also differs between when a bright image is displayed and when a dark image is displayed.

FIG. 10 shows the voltage difference AC for each image content when the effective voltage difference reaches a predetermined value. FIG. 11 shows the relationship between the brightness of the display panel 10 and the voltage DC and the difference in effective voltage when displaying an image in which the gradation of all the pixels in the display area 100 is the same gradation. It is the figure which showed the relationship between the brightness of the display panel 10 when it reached | attained, and voltage difference AC.
Even if the difference in effective voltage is the same, when the display panel 10 displays a dark image, the voltage difference AC is small as shown in FIG. In addition, when the display panel 10 displays a bright image, the voltage difference AC is small as shown in FIG. Further, when the display panel 10 displays a halftone image, the voltage difference AC increases as shown in FIG.

In the present embodiment, since the voltage difference AC changes according to the difference in effective voltage, the voltage LCcom is controlled by determining that the effective voltage difference is equal to or greater than a predetermined value when the voltage difference AC is equal to or greater than a threshold value. . However, since the voltage difference AC differs depending on the brightness of the display panel 10 as described above even if the effective voltage difference is the same, if the threshold value is one, whether the effective voltage difference from the voltage difference AC is equal to or greater than the threshold value. I cannot judge whether or not.
Therefore, in the present embodiment, as shown in FIG. 10, an image with a large brightness (such as an image with many white pixels) and an image with a small brightness (such as an image with many black pixels) are included in the voltage DC range. ), Divided into three ranges, such as medium-brightness images (half-tone images, etc.), and measured the voltage difference AC (AC1 to AC3 in FIG. 10) when the effective voltage is a predetermined value for each range In addition, a LUT (Look Up Table) 52A in which each image is associated with the measured voltage difference AC is stored. The control circuit 52 specifies a display image from the obtained voltage DC, and acquires a voltage difference associated with the specified image from the LUT 52A. The control circuit 52 uses the voltage difference acquired from the LUT 52A as a threshold value, and controls the voltage LCcom applied to the counter electrode 108 so that the voltage difference AC becomes smaller when the voltage difference AC obtained from the signal S12 becomes equal to or larger than the threshold value.
This threshold value is set to a value that is not recognized as flicker when the user looks at the display panel 10. In this embodiment, the voltage DC1 and the voltage DC2 are determined in advance as a reference for determining the brightness of the image (where voltage DC1 <voltage DC2), and when the voltage DC <voltage DC1, the brightness is small. It is determined that the brightness is medium when voltage DC1 ≦ voltage DC <voltage DC2, and it is determined that the brightness is large when voltage DC2 ≦ voltage DC. Each threshold value obtained from the LUT 52A is the voltage difference AC1 when the brightness is small (when the voltage DC <the voltage DC1), and when the brightness is medium (when the voltage DC1 ≦ the voltage DC <the voltage DC2). ) Is the voltage difference AC3, and when the brightness is large (voltage DC2 ≦ voltage DC), the voltage difference AC2. As shown in FIG. 10, the voltage difference AC has a magnitude relationship of voltage difference AC3> voltage difference AC2> voltage difference AC1, and therefore, the threshold magnitude relationship is greatest when the brightness is medium and the brightness is high. The case where the voltage is small is the smallest, and the brightness is large, the voltage DC is between the middle and the voltage DC is low.

  Next, an operation when the control circuit 52 controls the voltage LCcom will be described. FIG. 12 is a flowchart showing the flow of processing performed by the control circuit 52. When the drive of the display panel 10 is started, the control circuit 52 stores “0” in the register in order to specify the output timing of the start pulse Dyb. Further, the control circuit sets the voltage of the counter electrode 108 to a predetermined voltage LCcom as the voltage at the time of starting the driving of the counter electrode 108. Next, in the electro-optical device 1, when the synchronization signal Vsync and the display data Video are supplied from the external host device to the processing circuit 50, the data signal Vid is supplied to the display panel 10. Further, the control circuit 52 drives the display panel 10 in accordance with the supplied synchronization signal Vsync. Here, since the value stored in the register is “0”, the control circuit 52 outputs the start pulse Dyb at the timing T.

  When the display panel 10 is driven, the brightness of the display panel 10 is measured by the optical sensor 71, and the signal S 1 is supplied to the capacitor 72 and the A / D conversion circuit 73. From the capacitor 72, the signal S2 obtained by cutting the DC component of the signal S1 is supplied to the A / D conversion circuit 73. The A / D conversion circuit 73 converts the supplied signal S1 into a signal S11 and supplies the signal S11 to the control circuit 52. The A / D conversion circuit 73 converts the supplied signal S2 into a signal S12 and supplies the signal S12 to the control circuit 52.

  The control circuit 52 acquires the signal S11 and the signal S12 (step SA1). When acquiring the signals S11 and S12, the control circuit 52 obtains the voltage DC and the voltage difference AC (step SA2). Specifically, the control circuit 52 obtains an average value of the voltage value represented by the signal S11 supplied during a predetermined n frames triggered by the start pulse Dy, and the obtained average value is displayed on the display panel 10. A voltage DC representing brightness is used. Further, the control circuit 52 obtains the voltage difference AC from the maximum value and the minimum value of the signal S12 supplied during a predetermined n frames with the start pulse Dy as a trigger.

  The control circuit 52 displays an image displayed from the obtained voltage DC, such as an image having a large brightness (such as an image having many white pixels), an image having a small brightness (such as an image having many black pixels), and the brightness. Is identified as a medium image (halftone image or the like), and the voltage difference AC associated with the identified image is acquired from the LUT 52A and set as a threshold value (step SA3). The control circuit 52 compares the threshold acquired from the LUT 52A with the obtained voltage difference AC, and determines whether the voltage difference AC is equal to or greater than the threshold. If the obtained voltage difference AC is less than the threshold value (NO in step SA4), the process flow returns to step SA1. Note that the control circuit 52 may return the processing flow to step SA1 after a predetermined time has elapsed (for example, several seconds to several minutes).

  On the other hand, when the obtained voltage difference AC is equal to or larger than the threshold value (YES in step SA4), the control circuit 52 increases the voltage applied to the counter electrode 108 so that the difference in effective voltage is reduced (step SA5). . For example, when the difference between the effective voltage when applying the negative voltage and the effective voltage when applying the positive voltage when the voltage difference AC reaches the threshold is 50 mV, the voltage LCcom applied to the counter electrode 108 is 50 mV. Add to

  Here, when the effective voltage at the time of applying the positive polarity voltage is larger than the effective voltage at the time of applying the negative polarity voltage, the difference between the effective voltage at the time of applying the positive polarity voltage and the effective voltage at the time of applying the negative polarity voltage becomes small. The difference AC is less than or equal to the threshold value. On the other hand, when the effective voltage at the time of applying the positive voltage is smaller than the effective voltage at the time of applying the negative voltage, the difference between the effective voltage at the time of applying the positive voltage and the effective voltage at the time of applying the negative voltage is further increased. The difference AC is further increased.

  Next, the control circuit 52 acquires the signal S11 and the signal S12 (step SA6). When acquiring the signals S11 and S12, the control circuit 52 obtains the voltage DC and the voltage difference AC in the same manner as in step SA2 (step SA7). Further, the control circuit 52 acquires a threshold value as in step SA3 (step SA8). The control circuit 52 compares the threshold acquired from the LUT 52A with the obtained voltage difference AC, and determines whether the voltage difference AC is equal to or greater than the threshold. If the obtained voltage difference AC is less than the threshold value (NO in step SA9), the process flow returns to step SA1. Here, the control circuit 52 may return the processing flow to step SA1 after a predetermined time has elapsed (for example, several seconds to several minutes).

  On the other hand, when the obtained voltage difference is equal to or larger than the threshold (YES in step SA9), that is, when the determination is YES in step SA4, the effective voltage when the positive voltage is applied is smaller than the effective voltage when the negative voltage is applied. If the voltage difference AC increases as a result of increasing the voltage of the counter electrode 108 in step SA4, the control circuit 52 decreases the voltage applied to the counter electrode 108 (step SA10). For example, when the difference between the effective voltage when the negative voltage is applied and the effective voltage when the positive voltage is applied when the voltage difference AC becomes the threshold is 50 mV, the voltage LCcom applied to the counter electrode 108 is 100 mV. Minus. Here, the difference between the effective voltage when the positive voltage is applied and the effective voltage when the negative voltage is applied is reduced, and the voltage difference AC is equal to or less than the threshold value. When finishing the process of step SA9, the control circuit 52 returns the process flow to step SA1.

  According to the present embodiment, even if there is a difference in effective voltage between when a positive voltage is applied and a negative voltage is applied by applying a direct current component to the liquid crystal, there is a difference in effective voltage. Since the voltage LCcom of the counter electrode 108 is controlled so as to decrease, the occurrence of flicker can be suppressed. Further, in this embodiment, since it is possible to determine whether or not there is a difference in effective voltage with the light sensor 71 that detects the brightness of the display panel 10 without providing a light sensor in the pixel, the light sensor is provided in the pixel for adjustment. Compared with the configuration that displays the screen, it is possible to suppress the occurrence of flicker with a simple configuration.

[Second Embodiment]
Next, an electro-optical device 1 according to a second embodiment of the invention will be described. The electro-optical device 1 according to the second embodiment has the same hardware configuration as that of the first embodiment. The electro-optical device 1 according to the second embodiment is different from the electro-optical device 1 according to the first embodiment in that processing performed by the control circuit 52 is different. Therefore, in the following, this difference will be mainly described.

In the first embodiment, the effective voltage difference is reduced by controlling the voltage LCcom applied to the counter electrode 108. In the present embodiment, in addition to the control of the voltage LCcom, the timing of the start pulse Dyb. Also, the difference in effective voltage is reduced by controlling also. In order to control the timing of the start pulse Dyb, the control circuit 52 stores a predetermined first setting value and second setting value as setting values for designating the output timing of the start pulse Dyb. In the present embodiment, the first set value is a negative integer value, and the second set value is a positive integer value. The control circuit 52 changes the output timing of the start pulse Dyb according to the value stored in the register. Hereinafter, the output timing of the start pulse Dyb will be described.
Note that the second setting value, which is a setting value for designating the output timing of the start pulse Dyb, is the second setting value shown in FIG. 8, and for both the panels (1) and (2), a fixed time. In order to minimize the flicker after the lapse, the voltage LCcom needs to be reduced. Further, the first setting value, which is a setting value for designating the output timing of the start pulse Dyb, is the first setting value shown in FIG. 8, and is constant for both the panels (1) and (2). In order to minimize the flicker after the lapse of time, the voltage LCcom needs to be increased.

  In this embodiment, in order to reduce the difference in effective voltage, the timing of the start pulse Dyb is changed according to the value of the set value stored in the register, and the application time of the positive voltage and the application time of the negative voltage By controlling the ratio, the application of a direct current component to the liquid crystal capacitor 120 is controlled. For example, when the value stored in the register is “−1”, the control circuit 52 sets the start pulse Dyb earlier than the timing T by one cycle of the clock signal Cly as shown in FIG. Change to (-1) and output. Then, the period of the first field is 239 periods of the clock signal Cly, while the period of the second field is 241 periods of the clock signal Cly. Accordingly, as shown in FIG. 14, the holding period of the negative voltage written by the selection triggered by the supply of the start pulse Dyb is the holding period of the positive voltage written by the selection triggered by the supply of the start pulse Dya. Longer than the period. Therefore, in the pixel, the effective voltage value held at the negative voltage is increased, and the effective voltage value held at the positive voltage is lowered.

  When the voltage effective value held at the negative voltage becomes higher than the voltage effective value held at the positive voltage, the pixel becomes brighter when holding the negative voltage, and darkened when holding the positive voltage. Change. If the value stored in the register is “−2”, the control circuit 52 changes the start pulse Dyb to a timing earlier than the timing T by two cycles of the clock signal Cly and outputs the result. Then, in the pixel, the voltage effective value held at the negative voltage is further increased and the voltage effective value held at the positive voltage is further reduced as compared with the case where the value stored in the register is “−1”.

  On the other hand, when the value stored in the register is “+1”, the control circuit 52 delays the start pulse Dyb by one cycle of the clock signal Cly from the timing T, as shown in FIG. Change to 1) and output. Then, the period of the first field is 241 periods of the clock signal Cly, while the period of the second field is 239 periods of the clock signal Cly. Accordingly, as shown in FIG. 16, the holding period of the negative voltage written by the selection triggered by the supply of the start pulse Dyb is the holding of the positive voltage written by the selection triggered by the supply of the start pulse Dya. Shorter than the period. Therefore, in the pixel, the effective voltage value held at the positive voltage is increased, and the effective voltage value held at the negative voltage is lowered.

  When the effective voltage value held at the positive voltage becomes higher than the effective voltage value held at the negative voltage, the pixel becomes brighter when holding the positive voltage and darker when holding the negative voltage. To do. If the value stored in the register is “+2”, the control circuit 52 changes the start pulse Dyb to a timing later than the timing T by two cycles of the clock signal Cly and outputs it. Then, in the pixel, the effective voltage value held at the positive polarity is further increased and the effective voltage value held at the negative polarity is further reduced as compared with the case where the value stored in the register is “+1”.

  Next, the flow of processing performed by the control circuit 52 according to the second embodiment will be described using the flowchart shown in FIG. In the control circuit 52 according to the present embodiment, the processing from the start of driving of the display panel 10 to step SA9 is the same as that in the first embodiment, and thus description thereof is omitted.

When determining NO in step SA9, control circuit 52 increases the application time of the positive voltage (step SA12). Specifically, the second set value is stored in the register. When the second set value is stored in the register, the output timing of the start pulse Dyb becomes later than the timing T, the application time of the positive voltage becomes longer, and the application time of the negative voltage becomes shorter.
On the other hand, if YES is determined in step SA9, the control circuit 52 decreases the voltage applied to the counter electrode 108 (step SA10). In addition, the control circuit 52 increases the application time of the negative voltage. Specifically, the first set value is stored in a register. When the first set value is stored in the register, the output timing of the start pulse Dyb becomes earlier than the timing T, the application time of the negative voltage becomes longer, and the application time of the positive voltage becomes longer.

  According to the present embodiment, even if there is a difference in effective voltage between when a positive voltage is applied and a negative voltage is applied by applying a direct current component to the liquid crystal, there is a difference in effective voltage. Since the voltage LCcom of the counter electrode 108 and the application time of the positive voltage and the application time of the negative voltage are controlled so as to decrease, the occurrence of flicker can be suppressed. Also in this embodiment, since it is possible to determine whether or not there is a difference in effective voltage with the light sensor 71 that detects the brightness of the display panel 10 without providing a light sensor in the pixel, a light sensor is provided in the pixel for adjustment. Compared with the configuration that displays the screen, it is possible to suppress the occurrence of flicker with a simple configuration.

[Third Embodiment]
Next, an electro-optical device 1 according to a third embodiment of the invention will be described. The electro-optical device 1 according to the third embodiment has the same hardware configuration as that of the first embodiment. The electro-optical device 1 according to the third embodiment is different from the electro-optical device 1 according to the first and second embodiments in that processing performed by the control circuit 52 is different. Therefore, in the following, this difference will be mainly described.

  FIG. 18 is a flowchart showing a flow of processing performed by the control circuit 52 according to the third embodiment. In the control circuit 52 according to the present embodiment, the processing from the start of driving the display panel 10 to step SB4 is the same as the processing from the start of driving to step SA4 in the first embodiment. Therefore, the description is omitted.

  If the control circuit 52 determines NO in step SB4, it determines whether the value stored in the register is the first set value. When the value stored in the register is not the first set value (NO in step SB5), the control circuit 52 stores the first set value in the register (step SB7). On the other hand, if “YES” is determined in the step SB4, the control circuit 52 stores the second set value in the register.

  In this embodiment, the voltage LCcom of the counter electrode 108 is not controlled, but the effective voltage and the negative polarity when the positive voltage is applied are controlled by controlling the application time of the positive voltage and the application time of the negative voltage. Since the difference from the effective voltage when the voltage is applied is controlled, the occurrence of flicker can be suppressed. Also in this embodiment, since it is possible to determine whether or not there is a difference in effective voltage with the light sensor 71 that detects the brightness of the display panel 10 without providing a light sensor in the pixel, a light sensor is provided in the pixel for adjustment. Compared with the configuration that displays the screen, it is possible to suppress the occurrence of flicker with a simple configuration.

[Fourth Embodiment]
Next, an electro-optical device 1 according to a fourth embodiment of the invention will be described. The electro-optical device 1 according to the fourth embodiment has the same hardware configuration as that of the first embodiment. The electro-optical device 1 according to the fourth embodiment is different from the electro-optical device 1 according to the first to third embodiments in that processing performed by the control circuit 52 is different. Therefore, in the following, this difference will be mainly described.

  In the embodiment described above, the image displayed on the display panel 10 is specified from the voltage DC. For example, in the case of an image in which half of the screen is black and the other half is white, the specification by the voltage DC specifies an image with a medium brightness. In this case, in the above-described embodiment, the threshold value is AC3 shown in FIG. However, when the difference in effective voltage reaches a predetermined value, only the white pixel and the black pixel are present on the screen, so that the voltage difference AC does not increase to the threshold value but is less than AC3 shown in FIG. In this case, the voltage difference AC does not reach the threshold value AC3 although the effective voltage difference has reached the predetermined value, so that control for reducing the effective voltage difference is not performed.

  Therefore, in the present embodiment, an image displayed on the display panel 10 is specified using not only the voltage DC but also the voltage difference AC. For example, when the voltage DC is a voltage that represents an image with medium brightness, when the voltage difference AC is less than AC3 and greater than or equal to AC2 shown in FIG. Is a large image. In this case, the threshold value is AC2. When the voltage difference AC is less than AC2 shown in FIG. 10, it is determined that the displayed image is an image having a small brightness. In this case, the threshold value is AC1.

  Note that in the case of an image in which white pixels and black pixels are mixed, it is considered that the voltage DC = the ratio of the pixels to the white area, so that threshold = (voltage DC / voltage DC when the pixels are all white) × all pixels May be white and the voltage difference AC when the effective voltage difference reaches a predetermined value may be used.

[Electronics]
Next, an example of an electronic apparatus using the electro-optical device according to the above-described embodiment will be described. FIG. 19 is a plan view showing a configuration of a three-plate projector using the display panel 10 of the electro-optical device 1 described above as a light valve. In this projector 2100, the light to be incident on the light valve is supplied with three primary colors of R (red), G (green), and B (blue) by three mirrors 2106 and two dichroic mirrors 2108 arranged inside. And led to the light valves 100R, 100G and 100B corresponding to the respective primary colors. Note that B light has a longer optical path than other R and G colors, and therefore, in order to prevent the loss, B light passes through a relay lens system 2121 including an incident lens 2122, a relay lens 2123, and an exit lens 2124. Led.

  Here, the configuration of the light valves 100R, 100G, and 100B is the same as that of the display panel 10 in the above-described embodiment, and image data corresponding to each color of R, G, and B supplied from an external host device (not shown). Are driven respectively. The lights modulated by the light valves 100R, 100G, and 100B are incident on the dichroic prism 2112 from three directions. In the dichroic prism 2112, the R and B light beams are refracted at 90 degrees, while the G light beam travels straight. Therefore, after the images of the respective colors are combined, they are projected in the normal rotation and enlarged by the lens unit 2114, so that a color image is displayed on the screen 2120.

  The transmitted images of the light valves 100R and 100B are projected after being reflected by the dichroic prism 2112, whereas the transmitted image of the light valve 100G is projected as it is, and thus the images formed by the light valves 100R and 100B The image formed by the light valve 100G has a left-right reversal relationship.

The configurations of the optical sensors 71R, 71G, and 71B are the same as those of the optical sensor 71 in the above-described embodiment. The optical sensor 71R is a sensor that is sensitive to R light. The optical sensor 71G is a sensor sensitive to G light, and the optical sensor 71B is a sensor sensitive to B light. The optical sensors 71R, 71G, and 71B are disposed in the dichroic prism 2112, and the optical sensor 71R detects R leakage light from the dichroic prism 2112. The optical sensor 71 </ b> G detects G leakage light from the dichroic prism 2112, and the optical sensor 71 </ b> B detects B leakage light from the dichroic prism 2112.
The signal S1 output from the optical sensor 71R is supplied to the condenser 72 and the A / D conversion circuit 73 provided in the electro-optical device 1 including the light valve 100R. The signal S1 output from the optical sensor 71G is supplied to the condenser 72 and the A / D conversion circuit 73 included in the electro-optical device 1 including the light valve 100G, and the signal S1 output from the optical sensor 71B is the light The electric power is supplied to the condenser 72 and the A / D conversion circuit 73 included in the electro-optical device 1 including the valve 100B.

  In addition to the electronic device described with reference to FIG. 19, the rear projection type television or direct view type, for example, a mobile phone, a personal computer, a video camera monitor, a car navigation device, a pager, an electronic device Examples include notebooks, calculators, word processors, workstations, videophones, POS terminals, digital still cameras, and devices with touch panels. Needless to say, the electro-optical device according to the present invention is applicable to these various electronic devices.

[Modification]
As mentioned above, although embodiment of this invention was described, this invention is not limited to embodiment mentioned above, It can implement with another various form. For example, the present invention may be implemented by modifying the above-described embodiment as follows. In addition, you may combine each of embodiment mentioned above and the following modifications.

  In each of the above-described embodiments, the normally white mode in which white is displayed in a state in which no voltage is applied is used. However, a normally black mode in which black is displayed in a state in which no voltage is applied may be used.

In the embodiment described above, the voltage difference AC is obtained by cutting the DC component of the signal S1 by the capacitor 72. However, the voltage difference AC may be obtained from the signal S1 without using the capacitor 72.
In the above-described embodiment, the DC component of the signal S1 is cut by the capacitor 72. However, the DC component of the signal S1 may be cut by a high-pass filter.

  In the embodiment described above, the brightness of the display panel 10 is divided into three stages, and the threshold value of the voltage difference AC is determined in each stage. However, the threshold value of the voltage difference AC is determined in each stage by dividing into four or more stages. It may be.

DESCRIPTION OF SYMBOLS 1 ... Electro-optical apparatus, 10 ... Display panel, 50 ... Processing circuit, 52 ... Control circuit, 52A ... LUT, 54 ... Display data processing circuit, 56 ... D / A conversion circuit, 70 ... Detection circuit, 71, 71R, 71G , 71B ... optical sensor, 72 ... condenser, 73 ... A / D conversion circuit, 100R, 100G, 100B ... light valve, 100 ... display area, 105 ... liquid crystal, 107 ... capacitance line, 108 ... counter electrode, 109 ... storage capacitance , 110 ... pixels, 112 ... scanning lines, 114 ... data lines, 116 ... TFTs, 118 ... pixel electrodes, 120 ... liquid crystal capacitors, 130 ... scanning line driving circuits, 140 ... data line driving circuits, 142 ... sampling signal output circuits, 146 ... TFT, 2100 ... Projector, 2106 ... Mirror, 2108 ... Dichroic mirror, 2112 ... Dichroic prism , 2114 ... lens unit, 2120 ... screen, 2121 ... relay lens system, 2122 ... entrance lens, 2123 ... relay lens, 2124 ... exit lens

Claims (8)

A plurality of scanning lines and a plurality of data lines, respectively, corresponding to the intersections of the plurality of scanning lines and the plurality of data lines, each having a gradation according to a voltage of a data signal supplied to the data line when the scanning line is selected; A display region including a pixel, the pixel including a pixel electrode to which the data signal is applied, a counter electrode facing the pixel electrode, and an electro-optical material between the pixel electrode and the counter electrode An electro-optical device that holds
A positive field that supplies a positive voltage, which is a voltage corresponding to the gray level of the pixel and is higher than a predetermined potential, to the data line corresponding to the pixel as the data signal; and the gray level of the pixel In each of the negative polarity fields that supply a negative polarity voltage that is a low voltage with reference to a predetermined potential as a data signal to the data line corresponding to the pixel, A scanning line driving circuit to select in order;
When one scanning line is selected in the positive polarity field, a voltage corresponding to the gradation of the pixel is applied to the data line corresponding to the pixel as the data signal for the pixel located on the one scanning line. When the one scanning line is selected in the negative field, the voltage corresponding to the gray level of the pixel corresponds to the pixel as the data signal for the pixel located on the one scanning line. A data line driving circuit for supplying to the data line to be
A detection circuit that detects the brightness of the display area and generates a signal representing the brightness, and generates a first signal that represents a DC component of the signal and a second signal that represents an AC component of the signal;
When the wave height of the waveform of the second signal generated by the detection circuit is greater than or equal to a threshold value determined according to the first signal generated by the detection circuit, the wave height is less than the threshold value with respect to the pixel. An electro-optical device comprising: a control circuit that controls a difference between an effective voltage of a voltage applied in a positive polarity field and an effective voltage of a voltage applied in the negative polarity field. The control circuit includes:
Having at least three threshold values determined according to the first signal;
When the value of the first signal is less than a predetermined first set value, the threshold is set as the first threshold,
If the value of the first signal is less than a predetermined second set value greater than the first set value and greater than or equal to the first set value, the threshold is set to a third threshold greater than the first threshold. age,
The threshold value is a second threshold value that is greater than the first threshold value and smaller than the third threshold value when the value of the first signal is greater than or equal to the second set value. Electro-optic device. The electro-optical device according to claim 1, wherein the control circuit determines the threshold value from a wave height of the second signal and the first signal. The control circuit controls the voltage applied to the counter electrode, thereby controlling the effective voltage of the voltage applied to the pixel in the positive field and the effective voltage of the voltage applied to the negative field. The electro-optical device according to claim 1, wherein a difference between the electro-optical device and the difference is controlled. The control circuit controls an effective voltage of a voltage applied to the pixel in the positive polarity field by controlling a ratio of an application time of the positive polarity voltage and an application time of the negative polarity voltage, and 4. The electro-optical device according to claim 1, wherein a difference between an effective voltage and a voltage applied in the negative polarity field is controlled. 5. The control circuit controls the ratio of the voltage applied to the counter electrode, the application time of the positive voltage, and the application time of the negative voltage in the positive field with respect to the pixel. The electro-optical device according to any one of claims 1 to 3, wherein a difference between an effective voltage of an applied voltage and an effective voltage of a voltage applied in the negative field is controlled. A plurality of scanning lines and a plurality of data lines, respectively, corresponding to the intersections of the plurality of scanning lines and the plurality of data lines, each having a gradation according to a voltage of a data signal supplied to the data line when the scanning line is selected; A display region including a pixel, the pixel including a pixel electrode to which the data signal is applied, a counter electrode facing the pixel electrode, and an electro-optical material between the pixel electrode and the counter electrode A method of controlling an electro-optical device,
In each of the positive and negative fields, the plurality of scanning lines are selected in a predetermined order,
When one scanning line is selected in the positive polarity field, the voltage corresponding to the gray level of the pixel is higher than the pixel positioned on the one scanning line with reference to a predetermined potential. Supply the voltage of either the positive polarity or the negative polarity, which is lower, to the data line corresponding to the pixel as the data signal,
When the one scanning line is selected in the negative polarity field, the voltage corresponding to the gradation of the pixel is set to the positive polarity or the negative polarity with respect to the pixel located on the one scanning line. Supply the voltage of the other polarity as the data signal to the data line corresponding to the pixel,
Detecting the brightness of the display area and generating a signal representing the brightness; generating a first signal representing a DC component of the signal; and generating a second signal representing an AC component of the signal;
When the wave height of the waveform of the second signal is equal to or greater than a threshold value determined according to the first signal, the effective voltage applied to the pixel in the positive polarity field so that the wave height is less than the threshold value. A method for controlling an electro-optical device, comprising: controlling a difference between a voltage and an effective voltage of a voltage applied in the negative field.   An electronic apparatus comprising the electro-optical device according to claim 1.

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