JPH11161239A - Liquid crystal drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform recharging with an always stable degree of freedom without respect to a setting condition of a black level for an image signal by independently setting a precharge level for a liquid crystal panel. SOLUTION: A timing signal generating circuit 15 generates a timing signal for deciding a replacing duration complying with precharging, while a replacing level setting circuit 14 sets and outputs a precharge level to be exchanged for a certain signal level in a blanking period. A replacing circuit 13 performs replacing so that the signal level in the blanking period of the inputted image signal is replaced with the precharge level at the timing based on the timing signal. In this way, even when another level pulse different from the black level is inserted during the blanking period of the inputted image signal, a level according to the pulse insertion part can be replaced with the precharge level, and as a result, precharging always provided with a stable degree of freedom can be carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal driving circuit suitable for effectively performing a precharge operation required for optimally displaying an image based on an input image signal on a liquid crystal panel.

[0002]

2. Description of the Related Art In recent years, with the demand for a small-sized and lightweight display device having a large screen, a television receiver using a liquid crystal panel or a video device such as a liquid crystal projection television has attracted attention. By using a liquid crystal panel, these video devices can be made smaller and lighter than a projection type video device using a conventional CRT, and can easily realize a large-screen display. In addition, there is an advantage that troublesome convergence adjustment is not required and there is no influence of geomagnetism.

Usually, in a liquid crystal panel (hereinafter, referred to as an LCD) used in the above-described video equipment, in order to accurately reproduce a video based on the input video signal, it is necessary to drive the liquid crystal panel in response to the input video signal. A liquid crystal driving circuit having a function of amplifying a required voltage or the like is used.

When an image based on an input image signal is displayed on an LCD, such a liquid crystal drive circuit operates to write a voltage (DC) corresponding to the image to each pixel. However, if a pixel at the time of writing has a certain potential, the potential has an influence, and a voltage based on a normal video signal is not written during driving by the liquid crystal driving circuit. Therefore, the liquid crystal drive circuit is configured to perform a precharge operation of resetting the voltage of each pixel before writing a video signal so that a normal voltage is written. This precharge operation generally operates to write a certain level before writing a video signal to a pixel, and usually writes a black level of a video signal.

FIG. 5 is a signal waveform diagram for explaining a precharge operation by a conventional liquid crystal drive circuit.

In general, in a liquid crystal driving circuit, after an input video signal is converted into an RGB signal by a video signal processing circuit, for example, the polarity inversion / gamma is converted by an LCD driving processing circuit included in a video signal processing circuit in one chip. LCD drive processing such as correction is performed, and a precharge setting is performed on the obtained video signal,
Further, each pixel of the LCD is driven based on the set voltage of the video signal.

For example, assuming that a precharge operation is to be performed on a normal video signal on which a black level is superimposed during a blanking period as shown in FIG. 5, the liquid crystal drive circuit in this case has a function corresponding to the input video signal. In order to write a regular voltage, a predetermined period in the blanking period shown in the drawing is a precharge period P for performing a precharge operation, and the potential of each pixel is precharged (reset) to a black level in this period P. ). That is, the reset level is set as the precharge level. afterwards,
The liquid crystal driving circuit drives the LCD to write a voltage corresponding to the video signal shown in FIG. 5 to each pixel.

Therefore, when the black level is the same video signal as the precharge level as described above, the written video signal is directly used as the video signal level by the LCD.
If the pixel at the time of writing has a certain potential, LC
The signal level indicated by D changes. That is, by performing a precharge operation in which the level is raised by the potential as described above, a normal voltage corresponding to the input video signal can be written to each pixel, and the video based on the video signal can be improved. Can be displayed on the LCD.

However, the input video signal to be precharged may have another signal different in level from the black level superimposed during the precharge period. In particular, a specific IC (for example, a product made by Sony, RGB for LCD)
In the driver CXA1853Q), a pulse of about 1 μS is inserted into the blanking period of the video signal, that is, inserted into the precharge period P for performing the precharge operation, for use as a reference level for gamma correction and clamp operation. Will be. FIG. 6 shows an example of such a signal waveform.

Now, using a conventional liquid crystal driving circuit, FIG.
When an image signal as shown in FIG. 1 is to be displayed on the LCD, a signal having a different signal level as shown in the figure is superimposed during the precharge period P during which the precharge operation is performed. The problem that it cannot be done arises. In particular, when a pixel has a potential, a voltage corresponding to a normal input video signal cannot be written to each pixel, and as a result, an image based on the input video signal cannot be displayed well.

In the precharge operation by the liquid crystal drive circuit, as described above, if the normal black level is set to be the same as the precharge level, if a pixel at the time of writing has a certain potential, the potential is reduced by the potential. However, since the signal level displayed on the LCD only changes, this function is used in reverse to precharge the precharge level to a potential different from the black level and manage the input video signal. An image shifted by a certain level can be displayed.

Therefore, in recent years, in the precharge operation by the liquid crystal drive circuit, it is possible to separately manage and set the precharge level and the black level of the video signal, for example, by setting the precharge level to a value other than black due to a factor on the LCD side. It is desired. FIG. 7 shows a video signal waveform when the precharge level and the black level are separately set. That is, as shown in FIG.
Are set to levels different from the black level written during the normal precharge operation. By setting each of the signal waveforms to have such a signal waveform, it is possible to obtain an image shifted by a predetermined level as described above.

However, in the conventional liquid crystal driving circuit,
When the precharge level and the black level are to be set separately, there is also a problem that it is not possible to cope with them.

[0014]

As described above, in the conventional liquid crystal drive circuit, in setting the precharge level, the black level signal superimposed during the blanking period of the input video signal is usually set as the precharge level. However, if the precharge level changes due to the setting of this video signal, or if another signal different from the black level is inserted during the precharge period, a normal precharge There is a problem that the charging operation cannot be performed.

Further, since it is impossible to independently set and manage the precharge level and the black level of the video signal, there is a problem that such a case cannot be dealt with. .

In view of the above, the present invention has been made in view of the above-described problems. By making it possible to independently set the precharge level of the liquid crystal panel, the present invention is not affected by the setting state of the black level of the video signal. It is another object of the present invention to provide a liquid crystal driving circuit capable of always performing a precharge operation with a stable degree of freedom.

[0017]

A liquid crystal driving circuit according to the present invention drives a plurality of pixels of a liquid crystal panel so as to write a voltage corresponding to an input video signal, thereby forming an image based on the input video signal into a liquid crystal. A pre-charge operation for resetting the charge voltage of each pixel to a predetermined voltage before this writing, in order to display the image on the panel and write a voltage corresponding to the input video signal to each pixel of the liquid crystal panel properly. A video signal processing circuit that performs predetermined signal processing necessary for displaying the input video signal on a liquid crystal panel and outputs the input video signal, and a timing for performing the precharge operation. A timing signal generating circuit for generating and outputting a signal,
A switching level setting circuit that can arbitrarily set and output the predetermined voltage at the time of performing the precharge operation as a replacement voltage, and a voltage within a predetermined period during which the precharge operation is performed based on a timing signal from the timing generation circuit. And a switching circuit for switching to a switching voltage from the switching level setting circuit.

In the present invention, in order to write a voltage corresponding to an input video signal to each pixel of the liquid crystal panel properly, a precharge operation of resetting a charge voltage of each pixel to a predetermined voltage before this writing. A timing signal for performing the precharge operation is generated and output by a timing generation circuit, and the predetermined voltage at the time of performing the precharge operation is changed by a replacement level setting circuit. Arbitrarily set and output as a replacement voltage. As a result, the precharge level of the liquid crystal panel can be set independently, and a precharge operation with a stable degree of freedom can always be performed without being affected by the setting state of the black level of the video signal. .

[0019]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a liquid crystal drive circuit according to the present invention.

As shown in FIG. 1, the liquid crystal drive circuit 10 of the present invention has an input terminal 11 to which a video signal to be displayed on an LCD is supplied. A video signal input through the input terminal 11 is supplied to a video signal processing circuit 12, which performs a predetermined video signal processing to thereby drive the LCD for driving the LCD. It is converted into an RGB signal whose polarity is determined for each horizontal line.

The video signal processing circuit 12 is composed of, for example, a one-chip IC, and converts an RGB signal into an LC signal.
LCD drive processing such as polarity inversion processing for alternately writing to each electrode of D or gamma correction processing is performed and output. Thus, the output of the video signal processing circuit 12 becomes an RGB signal whose polarity is inverted for each horizontal line, which is necessary for driving the demodulated video signal to the LCD. The output of the video signal processing circuit 12 is supplied to a replacement circuit 13.

The switching circuit 13 is provided for controlling the precharge level and the black level of the video signal when performing the precharge operation by the liquid crystal drive circuit 10 independently from each other. Performs a switching operation of switching the precharge level within the precharge period P to an arbitrarily set precharge level with respect to the output of, and enables independent setting control of the precharge level. This replacement circuit 13 includes:
The switching level setting circuit 14 and the timing signal generating circuit 15 are connected.

The switching circuit 13 determines the precharge level of the RGB signal from the video signal processing circuit 12 based on the switching timing signal (two pulse signals) from the timing signal generating circuit 15 by the switching level setting circuit 13. An operation is performed to switch to the set replacement level (hereinafter, referred to as a replacement operation), and the obtained signal is written to each pixel of the LCD 16.
The switching level setting circuit 14 outputs to the switching circuit 13 a precharge level to be switched when it is desired to change the precharge level in the precharge period P during the precharge operation. The level of the precharge level is configured to be arbitrarily adjustable.

The timing generation circuit 15 generates a switching timing signal required for the switching operation by the switching circuit 13 and controls the switching operation by the switching circuit 12 using the switching timing signal. As the replacement timing signal, for example, two pulse signals (hereinafter, referred to as pulse 1 and pulse 2) are used. Pulse 1 is used to set a replacement timing time, and pulse 2 is a video signal. Since the signal (RGB signal) alternates every one horizontal scanning period (1H), it is used as a timing signal for switching the switching level every 1H.

Therefore, according to the above configuration, for example, FIG.
Even when a video based on a video signal in which another signal is inserted during the precharge period P as shown in the middle left portion is displayed on the LCD, the circuits of the switching circuit 13, the switching level setting circuit 14, and the timing signal generating circuit 15 are used. Depending on the group, other signal levels in the precharge period P can be switched to the desired precharge level and set. In this case, if the precharge level is set to be the same as a normal black level, a video signal having a signal waveform shown on the right side in FIG. 2 can be obtained. As a result, it is possible to normally perform a precharge operation necessary for optimally displaying an image based on the input image signal.

FIG. 3 is a circuit diagram showing a specific configuration example of a main circuit portion including the switching circuit 13 and the switching level setting circuit 14. The configuration of the switching circuit 13 and the switching level setting circuit 14, which are the main circuit portions of the liquid crystal driving circuit of this embodiment, will be described in detail with reference to FIG.

The replacement circuit 13 includes, for example, 1
The switching operation is performed by using a Q1 (for example, TC405B3 manufactured by Toshiba: Machiplexer or the like) as a digital switch having six connection terminals 1 to 16. This Q
In FIG. 1, a connection terminal 1 is a 1Y input terminal, and a switching terminal voltage is supplied from Q2 as a switching level setting circuit 14. Connection terminal 2 is a 0Y input terminal and G
A signal is provided. The connection terminal 3 is an IZ input terminal,
The connection terminal 4 is replaced with a Z output terminal and outputs a B signal. The connection terminal 5 is an 0Z input terminal to which a B signal is supplied. The connection terminals 6 to 8 are connected so as to be grounded. The connection terminals 9 to 11 are supplied with the pulse 1 from the timing generation circuit 15.
2 is an 0X input terminal to which an R signal is supplied. Connection terminal 13
Is a 1X input terminal to which the switching terminal voltage from Q2 is supplied. The connection terminal 14 outputs an R signal that has been switched at the X output terminal, and the connection terminal 15 outputs a G signal that has been similarly switched at the Y output terminal. The connection terminal 16 is connected to the power supply voltage V
The power supply voltage VCC is connected to the CC line.

On the other hand, Q2 is used as the replacement level setting circuit 14 as described above.
Has eight connection terminals 1 to 8 as shown in FIG. 3 and is provided with a changeover switch function necessary for switching and outputting a replacement level supplied to the replacement circuit 13. In this Q2, the connection terminal 1 is an output terminal for outputting a switching level voltage supplied via a switch function formed inside, and supplies this switching level voltage to the connected Q1 input terminals 1, 2, 13 connected thereto. I do. The connection terminals 2, 3, and 4 are connected to be grounded, and the connection terminal 5 is supplied with the pulse 2 from the timing generation circuit 15. Further, the connection terminals 6 and 7 of Q2 are connected to a circuit group for switching a switching level, so that switching levels having different levels are supplied.

The circuit group includes, as shown in the figure,
One of the circuits connected to the connection terminal 6 has an emitter connected to the connection terminal 16, a collector connected to the power supply voltage line, and a base connected between the resistors R1 and R2.
Q3 which is a PN transistor, and an emitter of Q3
The power supply voltage Vcc is supplied to the resistors R1 and R2 and the collector. The other circuit connected to the connection terminal 6 receives a resistor R4 connected to the connection terminal 6 and a current flowing through the resistor R4 as an emitter current. The collector is grounded and the base is connected to the resistor R5. , R6 connected between the resistors R4 and R5.
, R6 are supplied with a power supply voltage VCC. That is, by using these circuit groups, the switching level voltage can be switched.

The connection terminal 8 of Q2 is connected to a power supply voltage line so that the power supply voltage VCC is supplied.

Therefore, by using the switching circuit 13 and the switching level setting circuit 14 having such a configuration, the pulses 1 and 2 from the timing signal generating circuit 15 can be used.
, It is possible to easily perform a switching operation in which another signal level in the precharge period P is switched to a desired precharge level and set.

Next, the operation of the replacement circuit 13 and the replacement level setting circuit 14 shown in FIG. 3 will be described in detail with reference to FIG. For the sake of simplicity, only the R signal of the input RGB signals will be described, and the case where the precharge level is set to be the same as the normal black level will be described.

FIGS. 4A and 4B are output waveform diagrams for explaining the operation. FIG. 4A shows an R input signal, and FIG.
4C is a pulse 2 signal, FIG. 4D is an output signal of the connection terminal 1 of Q2 which is a switching level setting circuit 14, and FIG. 4E is an R output signal supplied to the switching circuit 13. Are respectively shown.

Now, it is assumed that the RGB signals converted by the video signal processing circuit 12 shown in FIG. 1 are supplied to the switching circuit 13, and a switching process for performing a precharge operation is performed on the RGB signals. At this time, if another different signal is inserted during the blanking period, for example, the R signal has a signal waveform shown in FIG. 4A, and such an R signal is replaced with the signal shown in FIG. The circuit 13 is supplied to the 0X input terminal 1 of Q1.

In the switching level setting circuit Q2, the terminal voltage set by the circuit group connected to the connection terminals 6, 7 is supplied to the connection terminals 6, 7, and
2 The terminal voltage selected by the internal switch function, that is, the switching level voltage is output from the output terminal 1. Therefore, the determined replacement level voltage is supplied to the 1X input terminal 13 of Q1.

Then, Q1 as the replacement circuit 13
Is the pulse 1 (FIG. 4) supplied from the connection terminals 9 to 11.
In the ethics of (b), by switching between 0X and 1X, an R output signal having a signal waveform as shown in FIG. 4E is obtained, and this R output signal is output from the Z output terminal of Q1 to FIG.
Is output to the LCD 16 shown in FIG.

When Q1 is input, the R input signal is as shown in FIG.
As shown in (1), the black level changes every 1H, so that the black level changes every 1H. Therefore, it is necessary to alternate the replacement voltage every 1H. Therefore, in this example, in Q2 as the replacement level setting circuit 14, the terminal voltage set at the connection terminals 6 and 7 is applied to the pulse 2 from the timing signal generation circuit 15 supplied to the terminal connection 5 (see FIG. Based on the timing of (c), the output is switched to the output terminal 1 every 1H, and supplied to Q1 as a replacement voltage. The switching voltage of Q2 at this time has the signal waveform shown in FIG. 4D, that is, the high level is the potential of the terminal voltage of the connection terminal 6, and the low level is the potential of the terminal voltage of the connection terminal 7. They have a relationship.

Therefore, by operating as described above, for example, even when the R signal has a signal waveform in which another different signal is inserted in the blanking period as shown in FIG. As shown in FIG. 4 (e), it is possible to obtain an R output signal in which the pulse portion of the blanking period of the R signal is switched to the replacement voltage set by Q2, that is, the precharge level.
The precharge operation written to each pixel of the LCD 16 can be performed normally. In the above description of the operation, only the R input signal has been described. Of course, the other G input signal and B input signal are similarly switched, so that another pulse signal is generated in each blanking period. Even when the signal is inserted, it is possible to obtain an output signal having a signal waveform necessary for performing the precharge operation normally.

Therefore, according to this embodiment, the precharge level of the liquid crystal panel can be set independently by using the switching circuit 13, the switching level setting circuit 14, the timing generation circuit 15, and the like. Therefore, it is possible to always perform the precharge operation with a stable degree of freedom without being affected by the setting state of the black level of the video signal. As a result, an effect is obtained that an image based on the input image signal can be favorably displayed on the LCD.

[0041]

As described above, according to the present invention,
Since the precharge level of the liquid crystal panel can be set independently with a simple configuration, the precharge operation always has a stable degree of freedom without being affected by the setting state of the black level of the video signal. It becomes possible. As a result, an effect is obtained that an image based on the input image signal can be favorably displayed on the LCD.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a liquid crystal drive circuit according to the present invention.

FIG. 2 is a circuit configuration diagram showing an example of a replacement circuit and a replacement level setting circuit of FIG. 1;

FIG. 3 is an output waveform diagram for explaining the operation.

FIG. 4 is a view showing an output waveform obtained by the circuit of FIG. 1;

FIG. 5 is an explanatory diagram for explaining a precharge operation.

FIG. 6 is a diagram showing a pulse superimposed video signal used in a specific IC.

FIG. 7 is an explanatory diagram for explaining a conventional problem.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Liquid crystal drive circuit, 11 ... Input terminal, 12 ... Video signal processing circuit, 13 ... Replacement circuit, 14 ... Replacement level setting circuit, 15 ... Timing signal generation circuit, 16 ... Liquid crystal panel (LCD).

Claims (3)

[Claims] An image display apparatus according to claim 1, further comprising: driving a plurality of pixels of the liquid crystal panel so as to write a voltage corresponding to the input video signal so that an image based on the input video signal is displayed on the liquid crystal panel; A liquid crystal driving circuit capable of performing a precharge operation of resetting a charge voltage of each pixel to a predetermined voltage before the writing in order to write a corresponding voltage to each pixel of the liquid crystal panel properly; A video signal processing circuit that performs predetermined signal processing required to display an input video signal on a liquid crystal panel and outputs the signal; a timing signal generation circuit that generates and outputs a timing signal for performing the precharge operation; A switching level setting circuit that can arbitrarily set and output the predetermined voltage at the time of the precharge operation as a switching voltage And a switching circuit for switching a voltage within a predetermined period for performing a precharge operation based on a timing signal from the timing generating circuit to a switching voltage from the switching level setting circuit. . 2. The black level signal when the liquid crystal drive circuit performs a precharge operation of resetting to a voltage based on a black level signal inserted during a blanking period of a video signal. 2. The liquid crystal driving circuit according to claim 1, wherein a voltage based on the switching is switched to a switching voltage from the switching level setting circuit. 3. When a signal different from the black level is inserted during a blanking period of the input video signal, the switching circuit switches the voltage based on a portion where the pulse is inserted. 2. The liquid crystal drive circuit according to claim 1, wherein the voltage is changed to a voltage.