JPH1049107A - Liquid crystal projection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal projection device capable of reducing a vertical view angle characteristic on visual sensation with simple constitution and displaying a stable and bright video. SOLUTION: This device controls a transmissivity of light in a liquid crystal cell by applying a video signal between respective electrodes of the liquid crystal cell constituting liquid crystal panels 4R, 4G, 4B and the common electrode COM of the liquid crystal panels 4R, 4G, 4B, and transmits the light through the liquid crystal panels 4R, 4G, 4B, and projects an image formed by the liquid crystal cells with the video signal. Then, the device is constituted so as to be provided with a voltage signal formation output part 6 imparted with a vertical synchronizing signal incorporated in the video signal and forming and outputting a voltage signal synchronized with the vertical synchronizing signal and a voltage change part 2 imparted with the voltage signal from the voltage signal formation output part 6 and changing the voltage of the common electrode COM according to the voltage signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a light transmittance by applying a video signal to a liquid crystal cell constituting a liquid crystal panel, transmitting the light to the liquid crystal panel, and causing the liquid crystal cell to generate a video signal. The present invention relates to an improvement in a liquid crystal projector for projecting an image to be formed and a liquid crystal projection device used for a liquid crystal projection television or the like.

[0002]

2. Description of the Related Art A video signal contained in a video signal is applied to a liquid crystal cell constituting a liquid crystal panel to control the light transmittance, and the light is transmitted to the liquid crystal panel. In a liquid crystal projection device that projects an image to be formed, light is focused on a liquid crystal panel surface by a convex lens or the like in order to brighten a projected image. However, when the light is focused by the lens, the light does not enter the liquid crystal panel surface perpendicularly except for the optical axis. On the other hand, in a liquid crystal panel, the transmittance of light changes depending on the incident angle of light, and as the incident angle increases,
The function as a light valve is lost.

For example, as shown in the sectional view of FIG.
The angle of incidence from obliquely above the vertical LCD panel surface is negative,
Angle of incidence 0 when the angle of incidence from obliquely below is defined as positive
The characteristics (VT characteristics) of the transmittance of light versus the video voltage applied to the liquid crystal at the angles of ± 10 ° are as shown in (b), for example. That is, as the light transmittance approaches 0% (black), the influence of the incident angle increases. In addition, the portions near the upper and lower ends of the liquid crystal panel have incident angles close to + 10 ° and -10 °, so that even when the applied video voltages are equal, they exhibit different transmittances from those near the center.

In FIG. 10B, due to the optical anisotropy of the liquid crystal, different transmittances of light are shown when the incident angle is ± 10 °. In some cases, the relationship between the incident angle and the light transmittance may be reversed. In the case of a liquid crystal projection device using three liquid crystal panels for red, green, and blue, the transmittance of light further differs depending on the wavelengths of red, green, and blue light. In particular, the black portion is greenish or red. The colors will look mixed, for example.

[0005]

In the conventional liquid crystal projection device, due to the above-described characteristics, as a result, for each liquid crystal panel of each color, the portions near the upper end and the lower end where the angle of incidence on the liquid crystal panel becomes large are: Even when the applied video voltage is equal, the transmittance becomes different from that near the center,
There is a problem with the upper and lower viewing angle characteristics that the gradation of the black portion is crushed and the projected image looks mixed with greenish or reddish colors. In particular, when the luminance setting is darkened, in FIG. 10B, the video voltage shifts to the higher side and the influence of the incident angle increases, so that the gradation of the black portion is crushed and colored up to the center and the whole. May be visible.

Conventionally, as a technique for improving the upper and lower viewing angle characteristics, a video voltage applied to a liquid crystal panel is subjected to a cycle of a vertical synchronizing signal before inverting its polarity for each horizontal synchronizing signal and each vertical synchronizing signal. In some cases, the upper portion or the lower portion of the liquid crystal panel is made relatively brighter to improve the gradation collapse in a black portion. However, circuit design adjustments are made because the video voltage applied to the liquid crystal panel has its polarity inverted as described above, and the video voltage has been subjected to luminance correction such as gamma correction and white extension. Tend to be complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and provides a liquid crystal projection device capable of reducing the upper and lower viewing angle characteristics visually with a simple configuration and displaying a stable bright image. The purpose is to provide.

[0008]

A liquid crystal projector according to a first aspect of the present invention applies a video signal between each electrode of a liquid crystal cell constituting a liquid crystal panel and a common electrode of the liquid crystal panel. By controlling the light transmittance of the liquid crystal cell, transmitting the light to the liquid crystal panel, and projecting the image formed by the liquid crystal cell by the video signal, the liquid crystal projection device included in the video signal A vertical synchronizing signal is applied, a voltage signal generating output unit that generates and outputs a voltage signal synchronized with the vertical synchronizing signal, and the voltage signal is supplied from the voltage signal generating output unit, and the common electrode is supplied according to the voltage signal. And a voltage changing unit that changes the voltage of

In this liquid crystal projection device, the voltage signal generation and output section is supplied with the vertical synchronizing signal included in the video signal,
A voltage signal synchronized with the vertical synchronization signal is generated and output.
The voltage change unit changes the voltage of the common electrode of the liquid crystal panel according to the voltage signal provided from the voltage signal generation output unit. As a result, the difference voltage between the video signal and the common electrode voltage applied to the liquid crystal cells near the upper and lower ends of the liquid crystal panel is reduced, and becomes relatively bright, so that the portions near the upper and lower ends of the liquid crystal panel become brighter. Can be corrected.

In the liquid crystal projection device according to a second aspect of the invention, the voltage signal generated and output by the voltage signal generation output section is a sawtooth wave.

In this liquid crystal projection device, the voltage signal generation and output section generates and outputs a sawtooth wave voltage signal that gradually increases or decreases each time the vertical synchronization signal included in the video signal is applied. The voltage changing unit changes the voltage of the common electrode of the liquid crystal panel according to the sawtooth voltage signal provided from the voltage signal generation and output unit.

In the liquid crystal projection device according to a third aspect of the present invention, the voltage changing section is supplied with a horizontal synchronization signal included in the video signal, and inverts the polarity of the voltage of the common electrode in synchronization with the horizontal synchronization signal. It is characterized by making it.

In this liquid crystal projection device, the voltage changing section is supplied with a horizontal synchronizing signal included in the video signal, and in synchronism with the horizontal synchronizing signal, inverts the phase of the video signal to invert the polarity of the voltage of the common electrode. . Conventionally, to reduce the amplitude of the video voltage input to the LCD panel and increase the amplitude of the voltage actually applied to the LCD panel, the voltage of the common electrode of the LCD panel is synchronized with the video signal and the polarity is inverted in the opposite phase. Let me.

By superimposing a voltage signal of a gradually increasing saw-tooth wave, for example, as shown in FIG. As shown in FIG. 2B, the absolute value of the liquid crystal panel increases from the upper part to the lower part. At this time, since the voltage of the common electrode is reversed in polarity in the opposite phase to the video signal, the absolute value of the video voltage, which is the voltage difference from the video signal, is, as shown in FIG. Since the size increases from the upper part to the lower part and the upper part of the liquid crystal panel becomes relatively bright, it is possible to correct the black gradation collapse in the upper part of the liquid crystal panel. In the case of superimposing a gradually decreasing sawtooth voltage signal, the lower part of the liquid crystal panel becomes relatively bright, and black gradation collapse at the lower part of the liquid crystal panel can be corrected.

A liquid crystal projection device according to a fourth aspect of the present invention includes a luminance setting means for setting the luminance of an image formed by the liquid crystal cell, and the voltage signal creation output section outputs a signal based on the luminance set by the luminance setting means. The method is characterized in that the voltage signal is generated.

In this liquid crystal projection device, the brightness setting means sets the brightness of the image formed by the liquid crystal cell. The voltage signal creation output section creates a voltage signal based on the brightness set by the brightness setting means. Accordingly, when the luminance is set to be low in accordance with the luminance set by the operator, the black gradation collapse can be corrected more.

According to a fifth aspect of the present invention, there is provided a liquid crystal projection device comprising: contrast control means for variably controlling the contrast of an image formed by the liquid crystal cell; and the voltage signal generation / output section, based on the voltage signal, The contrast control means controls the contrast of the screen based on the applied voltage signal.

In this liquid crystal projection device, the contrast control means variably controls the contrast of the image formed by the liquid crystal cell. The voltage signal generation and output section generates and outputs a voltage signal to be applied to the contrast control means based on the voltage signal. The contrast control means controls the contrast of the screen based on the applied voltage signal. Thus, it is possible to correct a change in contrast caused by changing the voltage of the common electrode in order to correct black gradation collapse.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing an embodiment. FIG. 1 shows a first embodiment of the present invention.
It is a block diagram showing composition of an embodiment of a liquid crystal projection device concerning the 3rd invention. This liquid crystal projection device is configured to prevent a problem due to a viewing angle characteristic generated at an upper portion of a liquid crystal panel. This liquid crystal projection device includes a luminance signal Y included in a video signal and a color difference signal R of a red signal R and a luminance signal Y.
-Y and the color difference signal BY of the blue signal B and the luminance signal Y are processed and converted by the video signal processing circuit 1, and the red signal R, the green signal G, and the blue signal B are converted into an LCD interface IC (2 ).

This liquid crystal projection device is driven by a line inversion driving method which is most often employed, and inverts the polarity of a video signal for each scanning line so that charges are not accumulated in the liquid crystal. In the LCD interface IC (2), the video signals of the red signal R, the green signal G, and the blue signal B are inverted for each scanning line, and the inverted video signals are output to the output stages 3R, 3G, and 3G. The signal is supplied to the respective liquid crystal panels 4R, 4G, 4B through 3B.

On the other hand, the vertical synchronization signal and the horizontal synchronization signal extracted from the video signal by the video signal processing circuit 1 are
It is provided to the timing controller 5. The timing controller 5 generates a vertical synchronization pulse and a horizontal synchronization pulse, which are the respective synchronization pulses, from the vertical synchronization signal and the horizontal synchronization signal.
(2) and the liquid crystal panels 4R, 4G, 4B. Further, the timing controller 5 supplies the vertical synchronizing pulse to the saw-tooth waveform generating circuit 6.

The saw-tooth wave generating circuit 6 generates a saw-tooth wave voltage signal as shown in FIG. 2A every time a vertical synchronizing pulse is applied, and generates a COM (common electrode) of the LCD interface IC (2). It is given to the control terminal 8. The COM control terminal 8 can adjust the bias voltage by the variable power supply 9. From the LCD interface IC (2), a saw-tooth wave voltage signal whose polarity is inverted as shown in FIG. The signal is supplied to the common electrodes COM of the liquid crystal panels 4R, 4G, and 4B through the COM output stage 7.
The reason for inverting the polarity of the voltage applied to the common electrode COM in a phase opposite to that of the video signal is to reduce the amplitude of the video voltage input to the liquid crystal panels 4R, 4G, and 4B and to reduce the amplitude of the liquid crystal panels 4R, 4G,
4B is to increase the amplitude of the voltage actually applied.

Hereinafter, the operation of the liquid crystal projection device having such a configuration will be described. The video signal input to the video signal processing circuit 1 is separated and extracted into video signals of a red signal R, a green signal G, and a blue signal B, and a vertical synchronization signal and a horizontal synchronization signal. Red signal R, green signal G and blue signal B
Each video signal is an interface IC for LCD (2)
And the polarity is inverted for each scanning line, and is applied to the respective liquid crystal panels 4R, 4G, 4B through the respective output stages 3R, 3G, 3B.

The vertical synchronizing signal and the horizontal synchronizing signal extracted by the video signal processing circuit 1 are given to a timing controller 5. The timing controller 5 generates a vertical synchronization pulse and a horizontal synchronization pulse, which are the respective synchronization pulses, and generates the LCD interface IC (2).
And to each of the liquid crystal panels 4R, 4G, 4B. Further, the timing controller 5 supplies the vertical synchronizing pulse to the saw-tooth waveform generating circuit 6.

The saw-tooth waveform generating circuit 6 generates a saw-tooth waveform voltage signal as shown in FIG. 2A every time a vertical synchronizing pulse is applied, and generates a COM (common electrode) of the LCD interface IC (2). It is given to the control terminal 8. The LCD interface IC (2) synchronizes with inverting the polarity of the video signal for each scanning line and in the opposite phase, and as shown in FIG. 2B, the sawtooth voltage applied to the COM control terminal 8 Outputs the signal with its polarity inverted. As a result, the saw-tooth wave voltage signal whose polarity is inverted in the opposite phase for each scanning line of the video signal is represented by C
Through the OM output stage 7, each liquid crystal panel 4R, 4G, 4B
Given to.

The liquid crystal cells of each of the liquid crystal panels 4R, 4G, and 4B have a TFT (Thin Film Transistor) as shown in FIG.
The liquid crystal cell is a type liquid crystal, and one scanning line of a video signal is sampled and applied to the sources (or drains) of the transistors of all the liquid crystal cells in the same row according to the position of the liquid crystal cell in the row.

The drain (or source) of the transistor of the liquid crystal cell is connected to one terminal of the liquid crystal. When the gate of the transistor is turned on in synchronization with the horizontal synchronization signal for each row of the liquid crystal cell, sampling is performed. The voltage of the video signal (video voltage) is applied to the liquid crystal, and the liquid crystal exhibits light transmittance according to the voltage. The other terminal of the liquid crystal is connected to the common electrode COM of the liquid crystal panel, and a voltage of a portion of the saw-tooth wave voltage signal in which the polarity is inverted in the opposite phase to one scanning line of the video signal (the portion is substantially constant). Is applied.

As a result, the video voltage applied to the liquid crystal is as shown in FIG. 2C (provided that the original video voltage is constant), and its absolute value is the voltage applied to the common electrode COM. And the light transmittance decreases.
The absolute value of the voltage applied to the common electrode COM becomes larger toward the lower part of the liquid crystal panels 4R, 4G, and 4B from the form of the sawtooth wave voltage signal.
The video voltage at the top of 4G, 4B is relatively small,
The characteristic (VT characteristic) curve in FIG. 10B is shifted to the left. Therefore, the upper portions of the liquid crystal panels 4R, 4G, 4B become relatively brighter, thereby preventing a problem due to viewing angle characteristics.

FIG. 4 is a circuit diagram showing an example of the configuration of the sawtooth wave generating circuit 6. The saw-tooth waveform generating circuit 6 applies a vertical synchronizing pulse to a series circuit including a resistor R1 and a capacitor C1, and the other end of the capacitor C1 is connected to a resistor R2 having the other end grounded and a cathode of a diode D1 having an anode grounded. And the base of the NPN transistor Tr1. The emitter of the NPN transistor Tr1 is grounded, and the collector is connected to the anode of the Zener diode D2.

The cathode of the Zener diode D2 is P
Connected to the collector of NP transistor Tr2, PNP
A power supply voltage of 15 V is applied to the emitter of the transistor Tr2 via the resistor R5. PNP transistor T
The base of r2 is connected to a resistor R4, the other of which is grounded, and the cathode of a diode D3. The anode of the diode D3 is connected to a resistor R3 to which a power supply voltage of 15 V is applied.
Is connected. The collector of the PNP transistor Tr2 is connected to the capacitor C2, the other of which is grounded, and the base of the NPN transistor Tr3. The collector of the NPN transistor Tr3 is supplied with a power supply voltage of 15 V, and the emitter is grounded via the resistor R6. .

The emitter of the NPN transistor Tr3 is
It is connected to the COM control terminal 8 of the LCD interface IC (2) through the electrolytic capacitor C3. C
The other terminal of the OM control terminal 8 is connected to the resistor R13 to which the power supply voltage 5V is applied and the emitter of the PNP transistor Tr11, and the collector of the PNP transistor Tr11 is grounded. The anode of the electrolytic capacitor C11 whose cathode is grounded and the variable resistance terminal of the variable resistor VR1 are connected to the base of the PNP transistor Tr11. One of the terminals at both ends of the variable resistor VR1 is connected to a resistor R11 whose other end is grounded, and the other end is connected to a diode D1.
1 cathode. The anode of the diode D11 is connected to a resistor R12 to which a power supply voltage of 5 V is applied to the other end.
Is connected.

In the sawtooth wave generating circuit 6, the vertical synchronizing pulse inputted from the resistor R1 is supplied to the differentiating circuit C1,
Differentiated by R2, the transistor Tr1
Turn on. The diode D1 is for protecting the transistor Tr1. The transistor Tr2 is always turned on by the voltage division of the resistors R3 and R4, and charges the capacitor C2. Then, the charging voltage of the capacitor C2 is fixed to the Zener voltage of the Zener diode D2 each time the transistor Tr1 is turned on.

That is, in the voltage waveform of FIG.
The lowest voltage corresponds to the Zener voltage of the Zener diode D2, and the gradually increasing sawtooth voltage corresponds to the gradually increasing charging voltage, and is applied to the base of the transistor Tr3. The transistor Tr3 is applied as an emitter follower to the COM control terminal 8 of the LCD interface IC (2) via the electrolytic capacitor C3. Resistors R11, R12, R centered on transistor Tr11
13, the variable resistor VR1, the diode D11 and the electrolytic capacitor C11 are for fixing the voltage above the sawtooth wave voltage applied to the COM control terminal 8.

FIG. 5 is a block diagram showing the configuration of an embodiment of the liquid crystal projection device according to the fourth invention of the present invention. This liquid crystal projection device is also configured to prevent problems due to the viewing angle characteristics generated above the liquid crystal panel. In this liquid crystal projection device, a setting voltage for setting the luminance is supplied from the CPU 11 for controlling the entire liquid crystal projection device to the luminance setting terminal 10 of the LCD interface IC (2) via the resistor R28. The CPU 11 is supplied with a vertical synchronization signal and a horizontal synchronization signal from the timing controller 5.

A setting voltage for setting the luminance is supplied from the CPU 11 to the sawtooth waveform generating circuit 6a. A resistor R29, the other of which is grounded, is connected to the input terminal of the set voltage for setting the luminance of the sawtooth wave generating circuit 6a. Other configurations are the same as those of the above-described embodiment of the liquid crystal projection device according to the first to third aspects of the present invention, and a description thereof will be omitted.

Hereinafter, the operation of the liquid crystal projection device having such a configuration will be described. The sawtooth wave generating circuit 6a prevents the output of the sawtooth voltage signal when the luminance is maximum (bright) and the set voltage is the highest, and when the luminance is minimum (dark) and the set voltage is the lowest, A voltage signal having an output waveform as shown in FIG. 6 is applied to the COM control terminal 8 so as to output the entire sawtooth voltage signal.

The luminance is set by an operator using a volume (not shown) connected to the CPU 11. When the operator further lowers the luminance, the voltage applied to the common electrode COM becomes a sawtooth wave. From the form of the voltage signal, the absolute value decreases toward the top of the liquid crystal panels 4R, 4G, and 4B, so that the characteristic (VT characteristic) curve in FIG. 10B is shifted to the left. Therefore, the liquid crystal panels 4R, 4G,
The upper part of 4B becomes relatively brighter, thereby preventing a problem due to viewing angle characteristics. Other operations are the same as those of the first operation described above.
3 to 3 are the same as those of the embodiment of the liquid crystal projection device according to the present invention, and the description is omitted.

FIG. 7 is a circuit diagram showing an example of the configuration of the sawtooth wave generating circuit 6a. The sawtooth wave generation circuit 6a is an NPN
The collector of the transistor Tr3 is an electrolytic capacitor C3
Is connected to the base of the NPN transistor Tr4. The base of the NPN transistor Tr4 is connected to a resistor R8 having a power supply voltage of 15 V applied to the other end and a resistor R9 having the other end grounded.

The collector of the NPN transistor Tr4 is
The power supply voltage 1 together with the collector of the NPN transistor Tr5
5 V is applied, and the respective emitters are commonly connected to a resistor R10 whose other end is grounded. The anode of the diode D4 is connected to the common connection node of each emitter, and the cathode is connected to the base of the NPN transistor Tr5. The base of the NPN transistor Tr5 is connected to one of the resistors R27. Resistance R2
The other terminal 7 is connected to a luminance setting voltage terminal T1 to which a voltage for setting luminance is supplied from the CPU 11 and a capacitor C4 whose other terminal is grounded. The common connection node between the emitters of the NPN transistors Tr4 and Tr5 is N
It is connected to the base of the PN transistor Tr6, and its emitter is grounded via the resistor R12.

The collector of the NPN transistor Tr6 is
On the other hand, a resistor R13 to which a power supply voltage of 15 V is applied and NP
It is connected to the base of N transistor Tr7. N
A power supply voltage of 15 V is applied to the collector of the PN transistor Tr7.
Is applied and the other end of the resistor R1 is grounded.
4 and a COM control terminal 8 via an electrolytic capacitor C5. The other circuit configuration is the same as the circuit configuration of the sawtooth wave generating circuit 6 described above (FIG. 4).
Description is omitted.

In the circuit of the sawtooth wave generating circuit 6a, the amplitude of the sawtooth wave is determined by the resistors R6 and R7, and the transistor Tr is set by the electrolytic capacitor C3 and the resistors R8 and R9.
4 has been reset. This resetting is in accordance with a change in the voltage for setting the luminance, which is provided through the resistor R11. The voltage of the emitter of the transistor Tr4 is controlled by the voltage for setting the luminance from the transistor Tr5. When the voltage for setting the luminance at the maximum luminance is high, the transistor Tr4 does not output a saw-tooth wave. When the voltage for setting the luminance at the minimum luminance is low, the entire sawtooth wave is output.

The level at which the sawtooth wave is output and the maximum level to which the voltage changes for setting the luminance from the minimum luminance to the maximum luminance are determined by the gain of the inverting and amplifying transistor Tr3. And the transistor Tr4
And the base voltage. The sawtooth voltage signal inverted by the transistor Tr3 is again inverted by the transistor Tr6, and is applied to the COM control terminal 8 of the LCD interface IC (2) via the electrolytic capacitor C5 at the emitter follower of the transistor Tr7. Other operations are the same as the operations of the sawtooth wave generating circuit 6 described above, and thus the description thereof is omitted.

FIG. 8 is a block diagram showing the configuration of an embodiment of the liquid crystal projection device according to the fifth invention of the present invention. This liquid crystal projection device has a C for controlling the entire liquid crystal projection device.
A setting voltage for setting the luminance is supplied from the PU 11a to the luminance setting terminal 10 of the LCD interface IC (2) via the resistors R32 and R30. Also, C
A voltage signal for controlling the contrast is supplied from the PU 11a to the contrast control terminal 12 of the LCD interface IC (2). A vertical synchronization signal and a horizontal synchronization signal are supplied from the timing controller 5 to the CPU 11a.

The connection node between the resistors R32 and R30 is connected to a resistor R31 whose other end is grounded. CPU 11a
, A setting voltage for setting the luminance is applied to the sawtooth wave generating circuit 6b. A voltage signal for controlling the contrast is also supplied to the contrast control terminal 12 from the saw-tooth wave generation circuit 6b. Other configurations are
Since it is the same as the embodiment of the liquid crystal projection device according to the fourth invention described above, the description is omitted.

Hereinafter, the operation of the liquid crystal projection device having such a configuration will be described. The sawtooth wave generating circuit 6b prevents the output of the sawtooth voltage signal when the luminance is maximum (bright) and the set voltage is the highest, and when the luminance is minimum (dark) and the set voltage is the lowest, A voltage signal having an output waveform as shown in FIG. 6 is applied to the COM control terminal 8 so as to output the entire sawtooth voltage signal. On the other hand, the sawtooth wave generating circuit 6b supplies a voltage signal proportional to the voltage signal supplied to the COM control terminal 8 to the contrast control terminal 12 as a voltage signal for controlling contrast.

By the way, in the above-described first to fourth embodiments of the present invention, the VT characteristic (FIG. 10B) is merely shifted. When the video voltage shift amount is set with emphasis, gradation may be lost in a white portion. In particular, when the change in the transmittance is sharp relative to the change in the video voltage, the contrast is changed. Therefore, it is necessary to reduce the amplitude of the video voltage from white to black in accordance with the shift amount. Therefore, the sawtooth wave generating circuit 6b supplies a voltage signal proportional to the voltage signal (shift amount) supplied to the COM control terminal 8 to the contrast control terminal 12 as a voltage signal for controlling the contrast, and outputs the white signal of the video voltage.振幅 The amplitude of black is reduced according to the shift amount.

The contrast is determined by the operator using the CPU 11a.
In the fifth invention, the VT characteristic (FIG. 10) is set by a volume (not shown) connected to
In accordance with the shift of (b), the change range of the video voltage is also controlled, and the light transmittance changes from 0 to 100% (white to black) over the entire surface from the upper part to the lower part of the liquid crystal panel. Thus, the upper and lower viewing angle characteristics are corrected. Other operations are the same as those of the above-described embodiment of the liquid crystal projection device according to the fourth aspect of the present invention, and a description thereof will be omitted.

FIG. 9 is a circuit diagram showing an example of the configuration of the sawtooth wave generating circuit 6b. The sawtooth wave generation circuit 6b is an NPN
When the collector voltage of the transistor Tr6 is
The voltage is divided by 15 and supplied to the base of the NPN transistor Tr7. Further, the collector voltage of the NPN transistor Tr6 is divided by the resistors R17 and R18 and applied to the base of the NPN transistor Tr7.
The emitter of the NPN transistor Tr7 is connected to a resistor R19, the other of which is grounded, and an electrolytic capacitor C6.
It is connected to the contrast control terminal 12 of the D interface IC (2). Contrast control terminal 12
Is connected to the emitter of the PNP transistor Tr12 and the other end to the resistor R24 to which the power supply voltage 5V is applied.

The collector of the PNP transistor Tr12 is grounded, and the base is connected to a resistor R26 whose other side is grounded.
A resistor R25 to which a signal for adjusting the level of the voltage signal applied to the contrast control terminal 12 is provided to the other side is connected. The rest of the circuit configuration is the same as the circuit configuration of the sawtooth wave generation circuit 6a described above (FIG. 7), and thus the description is omitted.

In the circuit of the sawtooth wave generating circuit 6b, the sawtooth wave voltage signal divided by the resistors R14 and R15 is supplied to the LCD interface IC via the electrolytic follower C5 at the emitter follower of the transistor Tr7.
It is applied to the COM control terminal 8 of (2). On the other hand, the same sawtooth voltage signal is divided by the resistors R17 and R18, and the LCD interface IC is connected to the emitter follower of the transistor Tr8 via the electrolytic capacitor C6.
It is applied to the contrast control terminal 12 of (2). Other operations are the same as the operations of the sawtooth wave generating circuit 6a described above, and thus the description thereof is omitted.

Each of the above-described embodiments is configured to prevent the problem caused by the viewing angle characteristic generated at the upper part of the liquid crystal panel. The sawtooth voltage signal may be inverted. In that case, in the latter two embodiments, one inverting circuit can be reduced, so that the circuit configuration can be simplified. In addition, if a voltage signal having a convex central portion such as a triangular wave or an arc wave is used instead of the sawtooth wave voltage signal, problems due to viewing angle characteristics occurring at the upper and lower portions of the liquid crystal panel can be prevented at the same time. be able to.

[0052]

According to the liquid crystal projection devices according to the first to third aspects of the present invention, it is possible to correct black gradation collapse by relatively brightening portions near the upper and lower ends of the liquid crystal panel. Thus, the upper and lower viewing angle characteristics can be visually reduced with a simple configuration, and a stable bright image can be displayed.

According to the liquid crystal projection device of the fourth aspect, when the luminance setting is low in accordance with the set luminance,
Black gradation collapse can be more greatly corrected, and upper and lower viewing angle characteristics can be visually reduced with a simple configuration, and a stable bright image can be displayed.

According to the liquid crystal projection device of the fifth aspect, it is possible to correct the change in contrast caused by changing the voltage of the common electrode in order to correct the black gradation collapse, and to improve the vertical viewing angle characteristics. Can be reduced visually with a simple configuration, and a stable bright image can be shown.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a liquid crystal projection device according to first to third inventions.

FIG. 2 is an explanatory diagram for explaining a voltage waveform of each part of the liquid crystal projection device according to the present invention.

FIG. 3 is an explanatory diagram for explaining a configuration of a liquid crystal cell.

FIG. 4 is a circuit diagram showing a configuration example of a saw-tooth wave generation circuit.

FIG. 5 is a block diagram showing a configuration of an embodiment of a liquid crystal projection device according to a fourth invention.

FIG. 6 is an explanatory diagram for explaining a saw-tooth wave voltage signal.

FIG. 7 is a circuit diagram illustrating a configuration example of a saw-tooth wave generation circuit.

FIG. 8 is a block diagram showing a configuration of an embodiment of a liquid crystal projection device according to the fifth invention.

FIG. 9 is a circuit diagram showing a configuration example of a saw-tooth wave generation circuit.

FIG. 10 is an explanatory diagram for explaining vertical viewing angle characteristics.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Video signal processing circuit 2 LCD interface IC (voltage change part, brightness setting means, contrast control means) 4R, 4G, 4B Liquid crystal panel 6, 6a, 6b Sawtooth wave forming circuit (voltage signal forming output section) 7 COM output Stage 11 CPU (brightness setting means) 11a CPU (contrast control means) COM Common electrode R, G, B Video signal

Claims (5)

[Claims] 1. A liquid crystal cell comprising: a liquid crystal panel comprising a liquid crystal panel and a liquid crystal panel. The video signal is applied between respective electrodes of the liquid crystal cell and a common electrode of the liquid crystal panel to control light transmittance of the liquid crystal cell. In a liquid crystal projection device that transmits light to a panel and projects an image formed by the liquid crystal cell by the video signal, a vertical synchronization signal included in the video signal is provided, and a voltage signal synchronized with the vertical synchronization signal is provided. A liquid crystal comprising: a voltage signal generation output unit for generating and outputting the voltage signal; and a voltage change unit that receives the voltage signal from the voltage signal generation output unit and changes the voltage of the common electrode according to the voltage signal. Projection device. 2. The liquid crystal projection device according to claim 1, wherein the voltage signal generated and output by the voltage signal generation output section is a sawtooth wave. 3. The voltage change unit according to claim 1, wherein a horizontal synchronization signal included in the video signal is supplied, and the voltage of the common electrode is inverted in synchronization with the horizontal synchronization signal. LCD projector. 4. A brightness setting means for setting a brightness of an image formed by the liquid crystal cell, wherein the voltage signal creation output unit comprises:
The liquid crystal projection device according to claim 1, wherein the voltage signal is created based on the luminance set by the luminance setting unit. 5. Contrast control means for variably controlling the contrast of an image formed by the liquid crystal cell, wherein the voltage signal creation output means creates and outputs a voltage signal to be applied to the contrast control means based on the voltage signal. Wherein the contrast control means controls the contrast of the screen based on the applied voltage signal.
5. The liquid crystal projection device according to any one of 4.