JP3326829B2 - Drive signal processing circuit for liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive signal processing circuit for a liquid crystal display device suitable for application to, for example, a liquid crystal projector.

[0002]

2. Description of the Related Art In general, as a development from a CRT (cathode ray tube) technology, an AG using a white peak has been developed.
There is known a technique for applying C (automatic gain control; automatic gain control) to prevent so-called "overexposure". In this case, “white loss” is likely to occur on a screen where the entire screen is dark and there are many white peaks.
As shown in FIG. 13, in the general contrast adjustment, the contrast is increased due to the black level clamp, and as a result, the amplitude of the video signal is increased.
In FIGS. 11 to 13, symbol P ₀ indicates a video signal, and symbol W
The "overexposure" and shows each region, the video signal P ₀ indicates that in indicated by a hatched portion "overexposure" occurs). Then, when the technology is applied to a liquid crystal projector, it is not always advisable to consider it from the viewpoint of securing the light quantity.

That is, when the surrounding environment (for example, the degree of brightness in a room) is dark, if the contrast of the video signal is appropriate, the screen is in a good state, but the surrounding environment is slightly bright. Then, light is suddenly applied to the screen, so that it is difficult to determine the display content in a dark part on the screen.

[0004] This point will be described more specifically.
As shown in the figure, when the image P is displayed on the screen 200 by the LCD (liquid crystal display) projector 100 in a state where the surrounding environment is dark, the change in the illuminance of the image P on the screen 200 is appropriate. Has become. That is, as will be understood from FIG. 15, when explaining with a curve Q indicating a change in illuminance in the qq line cross section of the screen 200, the illuminance on the screen 200 changes from a value 0 [Lux] to a value 50 [Lux]. Is properly changed and displayed.

On the other hand, as shown in FIG.
When the surrounding environment becomes bright (for example, the value 20 [Lux])
On the screen 200, as can be understood from FIG. 17, the display portion having the value of 20 [Lux] or less is buried in the surrounding light and cannot be seen. In such a case, simply increasing the brightness is not sufficient. As shown in FIG. 18, "whiteout" occurs.

Therefore, it is necessary to adjust the contrast and brightness each time to control the image so that "whiteout" is less likely to occur and the screen looks brighter, and this control is performed by the user. Is a triode CR
This is particularly remarkable in a liquid crystal pull ejector having a smaller amount of light as compared with the T method or the like. So, in a liquid crystal projector,
Measures have been proposed to reduce the need to perform such adjustment and control by increasing the amount of light.

[0007]

However, demanding such adjustment and control from the user poses a problem in terms of ease of use, and increasing the amount of light causes a problem in terms of manufacturing costs. Become.

It is an object of the present invention to provide a drive signal processing circuit for a liquid crystal display device in which the contrast of a video signal is controlled so that brightness is automatically set to an optimum state while avoiding "whiteout". It is in.

[0009]

A drive signal processing circuit for a liquid crystal display device according to the present invention comprises, for example, as shown in FIG. 1, a white reference signal set to correspond to a signal level of a luminance signal of a video signal. A white reference pulse generation circuit 15 for generating a pulse, a white reference pulse insertion circuit 13 for inserting the white reference pulse into the front porch portion of the luminance signal at a timing based on the horizontal synchronization signal, and an output from the white reference pulse insertion circuit 13 Signal processing circuits 19, 23, and 29 that at least perform a contrast adjustment process on the luminance signal and the primary color signal generated from the color difference signal of the video signal and output the result to the display device 31.
And a sample-and-hold circuit 27 for sampling and holding a white reference pulse of the output signal with respect to the output signals from the signal processing circuits 19, 23 and 29, and a reference white-hold reference voltage which does not cause overexposure. And a white-hold reference voltage generation circuit 33 that outputs the white-hold reference voltage output from the sample-hold circuit 27 and the value of the white-hold reference voltage output from the white-hold reference voltage generation circuit 33. The pedestal level of the video signal output from the signal processing circuit is varied according to the comparison result, and the black level of the video signal is controlled.

[0010]

In the drive signal processing circuit of the liquid crystal display device according to the present invention, the value of the signal output from the sample hold circuit is compared with the value of the reference voltage generated and output by the white hold reference voltage generation circuit. As a result, the output signal of the signal processing circuit is feedback-clamped. As a result, when the surrounding environment is bright, the brightness is automatically adjusted to the best state (bright direction; "white" The contrast of the video signal is controlled so as to be in a state of “crushing”, and the black level is raised.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a drive signal processing circuit for a liquid crystal display device according to the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a main circuit configuration of a drive signal processing circuit of a liquid crystal display device of the present invention. A luminance signal (signal Y) input from an input terminal 1 is a pedestal clamp for inserting a white reference pulse. The pedestal clamp circuit 13 is connected to a white reference pulse generation circuit 15 and a black extension auto pedestal circuit 19, and the average value detection circuit 11 is connected to the pedestal clamp circuit 13 via a switch circuit 17. And is connected to a black extension auto pedestal circuit 19.

A color difference signal (RY) from the input terminal 5 and a color difference signal (BY) from the input terminal 7 are input to the black expansion auto pedestal circuit 19, and an LCD (liquid crystal display) controller 21 is connected. The LCD controller 21 is connected to a liquid crystal display drive signal processing circuit 23 for performing adjustments such as gamma correction, brightness adjustment, and contrast adjustment. The liquid crystal display drive signal processing circuit 23 includes a control amplifier. The LCD 31 is connected to the LCD drive buffer 29 and the LCD drive buffer 29.

The primary color signal G output from the liquid crystal drive buffer 29 is input to a control amplifier 25 via a sample hold circuit 27, and a white reference voltage generation circuit 33 is connected to the control amplifier 25.

In the circuit configuration described above, in the white reference pulse generation circuit 15, as can be understood from FIG. 2, the horizontal synchronizing signal (H signal) input from the input terminal 3 is a 2H pulse signal. Accordingly, a timing signal is generated based on the signal a) shown in FIG. Then, the sampling pulse signal SP is input from a well-known pulse generating means to the white reference pulse generation circuit 15, and the timing signal is input to the white reference pulse insertion circuit 13 and inserted into the front porch portion of the luminance signal Y. A signal c shown in FIG. This sampling pulse signal SP is also used as a sampling pulse in a sample and hold process described later.

In this case, the white reference pulse generation circuit 1
The value (unit: volt) of the white reference pulse voltage HP (signal b shown in FIG. 2) output from the luminance signal Y
Is set to a value larger than the lowest level value V (unit is volt). Also, the sampling pulse signal SP
The pulse width and the insertion position are appropriately adjusted and then inserted, and the portion where the amplitude of the sampling pulse signal SP is created is set so that the DC component of the video signal is not lost.

That is, the pedestal potential of the video signal in the luminance signal Y is sampled and held, and a voltage corresponding to the signal level of the luminance signal of the video signal is applied in a form accumulated on the sample and hold potential. Also, by setting the pedestal potential so that the amplitude is accumulated by sampling and holding, a pulse having a value V _PP is inserted with reference to the pedestal.

FIG. 3 shows a circuit configuration for inserting a pulse having a value V _PP with reference to the pedestal. The luminance signal Y input from the input terminal 2 is
The collector of the transistor 4 is connected to a power supply E having a value of 12 [volts], the emitter is grounded via a resistor 8, and the emitter of the analog switch 10 is connected via a capacitor 6. One fixed contact 10B and one fixed contact 12A of the analog switch 12 are connected.

A connection point between the capacitor 6 and the fixed contact 10B is connected to one side of a resistor 14, and the other side of the resistor 14 is connected to a power supply E. The analog switch 10 is provided with the other fixed contact 10A and the movable contact 10C.
6, the collector of the transistor 16 is connected to the power supply E, the emitter is grounded via the resistor 18, and is connected to the output terminal 20 from which the luminance signal Y is output. ing.

Further, a resistor 22, a variable resistor 24 and a resistor 26 are connected in series to the power source E and grounded. The movable element of the variable resistor 24 is grounded via a capacitor 28. At the same time, it is connected to the fixed contact 10A, and the connection point between the variable resistor 24 and the resistor 26 is grounded via the capacitor 30 and is connected to the movable contact 12B.

On the other hand, the signal b is inputted from the input terminal 32 and inputted to the flip-flop circuit 34 and the base of the transistor 36. The non-inverted output of the flip-flop circuit 34 is used as the sampling pulse signal SP. The inverted output is input to the base of a transistor 42 via a resistor 40 to which a capacitor 38 is connected in parallel. The emitter of the transistor 42 is grounded, and the collector is connected to a power supply E via a resistor 44. The analog switch 10 is switched by a signal obtained at both ends of the resistor 44.

The emitter of the transistor 36 is grounded, the collector is connected to the power supply E via a resistor 46, and the analog switch 12 is switched by a signal obtained from the collector of the transistor 36. It has been.

As described above, in the circuit configuration shown in FIG. 1, the pulse signal V _PP is inserted into the luminance signal Y, and the signal c into which the pulse signal V _PP is inserted and the color difference signal (R
-Y) and (B-Y) are subjected to a known matrix process to generate primary color signals R, G, and B.
As will be understood from the above, the pulse signal V _PP is inserted into all the primary color signals R, G, B.

That is, by inserting the pulse signal SP into all the primary color signals R, G, B, the pulse signal SP corresponds not to the amplitude of the primary color signals R, G, B but to the signal amplitude of the luminance signal Y. The level of the reference pulse can be obtained. Also, the average value detection circuit 11 adjusts the picture (image quality adjustment) according to the magnitude of the DC component in the luminance signal Y.
Can be weakly controlled, whereby the current amplitude can be controlled by a so-called ABL circuit (automatic brightness limiting circuit) on the entire amplitude of the video signal together with the inserted reference pulse.

As shown in FIG. 5, the liquid crystal drive signal is a positive / negative symmetrical AC drive with respect to the apparent center voltage V _COM , so that the value of the voltage at which “whiteout” occurs is obtained. two (voltage V _A and the voltage V _B) is present. In this case, one of the voltages to be controlled is sufficient, and the AND is generated with the flip-flop circuit 34 for generating the inverted signal (the AND of the drive signal inverting pulse and the sampling pulse is calculated with the logical circuit). ) Every other (2
The sample hold is performed as the pulse of K).

And the voltage sampled and held;
White hold reference voltage (voltage value V _A shown in FIG. 5)
And the white hold reference voltage generation circuit 3 of FIG.
3), and a feedback is applied to the brightness control terminal of the liquid crystal display device drive signal processing circuit 23 to form a DC (direct current) control loop. With this loop, the amplitude of the video signal (see FIG. 5, the portion indicated by the symbol A) changes, but the potential of the head portion of the inserted pulse is changed to the reference potential V _C that does not cause overexposure.
(V _A = V _C ).

FIG. 6 shows a circuit configuration for performing control such that V _A = V _C. The output terminal of the DC amplifier 102 to which the luminance signal Y is input is connected to the output DC amplifier 1.
The DC amplifier 102 is provided with a variable resistor 102B for adjusting the amplitude of an external signal and an input terminal 102A for a brightness adjustment signal.

The output terminal of the DC amplifier 104 is
The LCD 31 and the fixed contact 108A of the switch circuit 108 are connected. The movable contact 108B of the switch circuit 108 is connected to the fixed contact 110A of the switch circuit 110. Connected to inverting terminal. A capacitor 116 is interposed between the switch circuit 108 and the switch circuit 110, and one side of the capacitor 116 is grounded, and the switch circuit 108 outputs a signal input to the sample and hold circuit 27 in FIG. While the switching operation is performed by d, the switch circuit 110 is configured to perform the switching operation by the signal whose polarity of the signal d is inverted by the inverter 118.

Here, the inverting terminal of the differential amplifier 112 is
Its output terminal is short-circuited (voltage follower), its output terminal is connected to the non-inverting terminal of the differential amplifier 114, and the inverting terminal of the differential amplifier 114 is connected to three resistors 12
0, 122, and 124 are connected in series.
0 (controlled so that V _A = V _C ),
From the output terminal of the differential amplifier 114, V _A = V _C
The output voltage V ₀ controlled to be
2 is input to the brightness adjustment signal input terminal 102A, and a loop formed by a path from the DC amplifier 102 to the differential amplifier 114 is the DC control loop.

With the above configuration, as can be understood from FIGS. 7 to 10, the user can change only the amplitude of the video signal and change only the signal expansion component in the black direction without "whiteout". As a result, an easy-to-view image can be easily obtained. In FIGS. 7, 8 and 9, the symbol P ₀ indicates a video signal, and the insertion pulses (white hold pulses) A ₁ , A ₂ , and A ₃ indicate A ₁ <A ₂ <A
₃ is satisfied, the symbol _VH indicates a threshold hold potential at which no whiteout occurs, and the symbol W indicates a "whiteout" region.

As described above, in this embodiment, the value V of the signal output from the sample and hold
_A is generated by the white hold reference voltage generation circuit 15
By being compared with the output reference voltage value V _C ,
Since a feedback clamp is applied to the video signal output from the signal processing circuit 23, even when the surrounding environment is bright, the video is automatically adjusted to the best state while avoiding “white loss” while avoiding “white loss”. As a result, the black level is raised and an easy-to-view screen can be obtained.

The present invention is not limited to the above-described embodiment, and can adopt various other configurations without departing from the gist of the present invention.

[0032]

In the drive signal processing circuit of the liquid crystal display device according to the present invention, the value of the signal output from the sample hold circuit is compared with the value of the reference voltage generated and output by the white hold reference voltage generation circuit. As a result, a feedback clamp is applied to the output signal of the signal processing circuit, so that when the surrounding environment is bright, the video signal is automatically adjusted to the best condition while avoiding “white loss” As a result, the black level is raised to provide an easy-to-view screen.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a preferred embodiment of a drive signal processing circuit of a liquid crystal display device according to the present invention.

FIG. 2 is an explanatory diagram showing a procedure for inserting a white reference pulse.

FIG. 3 is a circuit configuration diagram for generating an insertion pulse.

FIG. 4 is a waveform diagram of a primary color signal.

FIG. 5 is an explanatory diagram showing a procedure for performing a sample hold.

FIG. 6 is a circuit diagram of a main part of a DC control loop.

FIG. 7 is an explanatory diagram showing a video signal before contrast adjustment.

FIG. 8 is an explanatory diagram showing a video signal when the contrast is increased.

FIG. 9 is an explanatory diagram showing a video signal when the contrast is increased.

FIG. 10 is an explanatory diagram of a curve Q showing illuminance when “whiteout” has not occurred.

FIG. 11 is an explanatory diagram showing a video signal before “whiteout”.

FIG. 12 is an explanatory diagram illustrating a video signal in a case where “white loss” has occurred.

FIG. 13 is an explanatory diagram illustrating a video signal in a case where “white underexposure” is further worsened.

FIG. 14 is an explanatory diagram of a state in which an image is displayed when the surrounding environment is dark.

FIG. 15 is an explanatory diagram showing an illuminance change curve when the surrounding environment is dark.

FIG. 16 is an explanatory diagram of a state in which an image is displayed when the surrounding environment is relatively bright.

FIG. 17 is an explanatory diagram showing an illuminance change curve when the surrounding environment is relatively bright.

FIG. 18 is an explanatory diagram showing a change in illuminance in a case where “white loss” has occurred.

[Explanation of symbols]

1, 3, 5, 7 input terminal 11 average value detection circuit 13 pedestal clamp circuit for white reference pulse insertion 15 white reference pulse generation circuit 17 switch circuit 19 black extension auto pedestal circuit 21 LCD controller 23 liquid crystal display device drive signal processing circuit 25 Control amplifier 27 Sample hold circuit 29 Liquid crystal drive buffer 29 31 LCD (liquid crystal display) 33 White hold reference voltage generation circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G09G 3/00-3/38 H04N 5/66-5/74 G02F 1/133 505-580

Claims (1)

(57) [Claims] 1. A white reference pulse generating circuit for generating a white reference pulse set so as to correspond to a signal level of a luminance signal of a video signal, and a front porch for the luminance signal at a timing based on a horizontal synchronization signal. A white reference pulse insertion circuit to be inserted into the portion, and at least a contrast adjustment process is performed on a primary color signal created from the luminance signal output from the white reference pulse insertion circuit and the color difference signal of the video signal, and the display device A signal processing circuit for outputting; a sample and hold circuit for sampling and holding a white reference pulse of the output signal with respect to an output signal from the signal processing circuit; And a white-hold reference voltage generation circuit, The level of the white reference pulse output from the sample hold circuit is compared with the value of the white hold reference voltage output from the white hold reference voltage generation circuit, and is output from the signal processing circuit according to the comparison result. A drive signal processing circuit for a liquid crystal display device, wherein a black level of the video signal is controlled by changing a pedestal level of the video signal.