JPH06138845A - Drive signal processing circuit of liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide the drive signal processing circuit of the liquid crystal display device whose video signal has its contrast controlled so that the brightness is automatically placed in the best state while 'white blurring' is evaded. CONSTITUTION:A brightness signal (signal Y) inputted from an input terminal 1 is inputted to a pedestal clamp circuit 13 for white reference pulse insertion and a white reference pulse generating circuit 15 and a black expansion automatic pedestal circuit 19 are connected to the pedestal clamp circuit 13; and an LCD controller 21 is connected to the black expansion automatic pedestal circuit 19 and a liquid crystal display device drive signal processing circuit 23 to which a control amplifier 25 is connected is connected to the LCD controller 21. A primary color signal G outputted from a liquid crystal driving buffer 29 is inputted to the control amplifier 25 through a sample holding circuit 27 and a white reference voltage generating circuit 33 is connected to the control amplifier 25.

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 of a liquid crystal display device suitable for application to, for example, a liquid crystal projector.

[0002]

2. Description of the Related Art Generally, as an extension of CRT (cathode ray tube) technology, an AG using a white peak is used.
A technique is known in which C (automatic gain control; automatic gain control) is applied to prevent so-called "whiteout". In this case, "whiteout" tends to occur on a screen where the entire screen is dark and has many white peaks.
This is because, 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 increases (note that
11 to 13, the symbol P ₀ indicates a video signal, and the symbol W
Indicates the "whiteout" region, and the video signal P ₀ indicates that "whiteout" occurs in the shaded portion). When the technique is applied to a liquid crystal projector, it is not necessarily a good idea from the viewpoint of securing the light amount.

That is, when the surrounding environment (for example, the degree of brightness in the room) is dark, the screen is in a good state if the contrast of the video signal is appropriate, but the surrounding environment is slightly bright. Then, the screen is suddenly exposed to light, and it becomes difficult to distinguish the display content in the dark portion of the screen.

To explain this point more specifically, FIG.
As shown in, when the image P is displayed on the screen 200 by the LCD (liquid crystal display) projector 100 in a dark environment, the illuminance change of the image P on the screen 200 is appropriate. Has become. That is, as can be understood from FIG. 15, the curve Q showing the illuminance change in the q-q line cross section of the screen 200 will be described. The illuminance on the screen 200 is 0 [Lux] to 50 [Lux]. Is properly changed and displayed.

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

Therefore, it is necessary to adjust the contrast and brightness each time so that "whiteout" is unlikely to occur and the screen looks bright, and this control is performed by the user. Is a triode CR
This is particularly noticeable in liquid crystal projectors that emit less light than in the T type. Therefore, in the liquid crystal projector,
Measures have been proposed to increase the amount of light and reduce the need for such adjustment and control.

[0007]

However, demanding such adjustment and control from the user is problematic in terms of usability, and increasing the light quantity is problematic in terms of manufacturing cost. Become.

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

[0009]

A drive signal processing circuit of a liquid crystal display device according to the present invention, for example, as shown in FIG. 1, uses a pedestal of a video signal as a reference and a white reference pulse is a front porch of a luminance signal. The white reference pulse insertion circuit 13 inserted in the portion, the signal processing circuit 23 that performs desired signal processing on the output signal of the white reference pulse insertion circuit 13, and the output signal of the signal processing circuit 23. A sample hold circuit 27 for sampling and holding the white reference pulse and a white hold reference voltage generating circuit 15 for generating and outputting a white hold reference voltage are provided, and the value of the signal output from the sample hold circuit 27 is , To be compared with the value of the reference voltage output from the white hold reference voltage generation circuit 15. More, it is characterized in that the feedback clamping is applied to the output signal of the signal processing circuit 23.

[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. By this, a feedback clamp is applied to the output signal of the signal processing circuit, and as a result, when the surrounding environment is bright, the brightness is automatically in the best state (bright direction; The black level is raised by controlling the contrast of the video signal so that the image is in the “immediately collapsed state”.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of a drive signal processing circuit of a liquid crystal display device according to the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit configuration example of a main part 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 white reference pulse generation circuit 15 and the black expansion auto pedestal circuit 19 are connected to the pedestal clamp circuit 13 which is input to the circuit 13 and the average value detection circuit 11, and the average value detection circuit 11 is connected via a switch circuit 17. Connected to the black extension auto-pedestal circuit 19.

A color difference signal (RY) is input from the input terminal 5 and a color difference signal (RY) is input from the input terminal 7 to the black extension 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 device drive signal processing circuit 23 for performing adjustments such as γ correction, brightness adjustment, and contrast adjustment. The liquid crystal display device drive signal processing circuit 23 is connected to a control amplifier. 25 and the liquid crystal drive buffer 29 are connected, and the LCD 31 is connected to the liquid crystal drive buffer 29.

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

In the above circuit configuration, in the white reference pulse generation circuit 15, as can be understood from FIG. 2, a horizontal synchronizing signal (H signal; a 2H pulse signal in this embodiment) input from the input terminal 3. Therefore, a timing signal is generated based on the signal a) shown in FIG. 2, and the sampling pulse signal SP input from a predetermined circuit to the white reference pulse generation circuit 15 is used as a timing with the timing signal as a timing. 2 and is inserted into the front porch portion of the luminance signal Y.
Signal c shown in FIG.

In this case, the white reference pulse generation circuit 1
The value (unit: volt) of the white reference pulse voltage V _A (signal b shown in FIG. 2) output from the reference numeral 5 is the luminance signal Y.
Is set to a value higher than the lowest level value V _B (unit: volt) of the value V _{A by the} value V _A. In addition, the pulse width and the insertion position of the sampling pulse signal SP are appropriately adjusted before being inserted.
The portion where the amplitude of 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 the voltage is applied in such a manner that the pedestal potential is accumulated on the sample and hold potential.
Even if the pedestal varies, the pedestal potential is sampled and held so that the amplitude is accumulated, so that a pulse having a value of 1 V _PP is inserted with the pedestal as a reference.

FIG. 3 shows a circuit configuration for inserting a pulse having a value of 1 V _PP with reference to the pedestal, and a luminance signal Y input from the input terminal 2 is shown.
Is input to the base of the transistor 4, and the collector of the transistor 4 is connected to the power supply E having a value of 12 [volt],
The emitter is grounded via a resistor 8 and is also connected via a capacitor 6 to one fixed contact 10B of the analog switch 10 and one fixed contact 12A of the analog switch 12.

Further, one side of the resistor 14 is connected to the connection point between the capacitor 6 and the fixed contact 10B, and the other side of the resistor 14 is connected to the power source E. The analog switch 10 is provided with the other fixed contact 10A and the movable contact 10C, and the movable contact 10C is the transistor 1
6, the collector of the transistor 16 is connected to the power source E, the emitter is grounded through the resistor 18, and the output terminal 20 from which the luminance signal Y is output is connected. ing.

A resistor 22, a variable resistor 24 and a resistor 26 are sequentially connected in series to the power source E and grounded, and a mover of the variable resistor 24 is grounded via a capacitor 28. In addition to being connected to the fixed contact 10A, the connection point between the variable resistor 24 and the resistor 26 is grounded via the capacitor 30 and is also connected to the movable contact 12B.

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

The emitter of the transistor 36 is grounded, the collector is connected to the power source E through the resistor 46, and the analog switch 12 is switched by the signal obtained at the collector of the transistor 36. It is said that.

As described above, in the circuit configuration shown in FIG. 1, the pulse signal SP is inserted into the luminance signal Y, and the signal c into which the pulse signal SP is inserted and the color difference signal (R-
When the known matrix processing is performed on Y) and (B-Y) to create the primary color signals R, G, B, as can be understood from FIG. 4, all primary color signals R, The pulse signal SP is inserted into G and B.

That is, by inserting the pulse signal SP into all the primary color signals R, G, B, the primary color signals R,
It is possible to obtain the level of the reference pulse corresponding to the signal amplitude of the luminance signal Y, not to the amplitudes of G and B. Further, the average value detection circuit 11 makes it possible to weakly control the picture (image quality adjustment) according to the magnitude of the DC component in the luminance signal Y, whereby the entire amplitude of the video signal together with the inserted reference pulse can be controlled. And so-called A
There is an advantage that the current can be controlled by the BL circuit.

Further, as shown in FIG. 5, since the liquid crystal drive signal is AC drive of positive and negative symmetry type with respect to the apparent center voltage V _COM , the value of the voltage at which “whiteout” occurs. two (voltage V _A and the voltage V _B) is present. In this case, either one of the voltages to be controlled is sufficient, and the AND is taken with the flip-flop circuit 34 for generating the inverted signal (the AND for the drive signal inversion pulse and the sampling pulse is taken on the logic circuit). ) Every other (2
The sample hold is performed as a pulse of K).

Then, the sampled and held voltage,
White hold reference voltage (voltage value V _A shown in FIG. 5
And the white hold reference voltage generation circuit 3 of FIG.
3) is generated, and a DC (direct current) control loop is configured by feeding back to the brightness control terminal of the liquid crystal display device drive signal processing circuit 23. This loop forms an amplitude of the video signal (Fig. 5), the potential of the head portion of the pulse to be inserted is controlled to be always equal to the set potential V _C (V _A = V _C ), even when the portion indicated by the symbol A in FIG. It will be.

FIG. 6 shows a circuit configuration in which the control of V _A = V _C is performed. The output DC amplifier 1 is provided on the output terminal side of the DC amplifier 102 to which the luminance signal Y is input.
04 is connected, and 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 is connected to the fixed contact 108A of the switch circuit 108, the movable contact 108B of the switch circuit 108 is connected to the fixed contact 110A of the switch circuit 110, and the movable contact 110B of the switch circuit 110 is connected to the non-contact of the differential amplifier 112. It is connected to the inverting terminal. A capacitor 116 is inserted between the switch circuit 108 and the switch circuit 110, and one side of the capacitor 116 is grounded. The switch circuit 108 receives the signal input to the sample hold circuit 27 of FIG. While the switching operation is performed at d, the switch circuit 110 is configured to perform the switching operation by the signal in which the polarity of the signal d is inverted by the inverter 118.

Here, the inverting terminal of the differential amplifier 112 is
It is short-circuited with its own output terminal (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 three resistors 12
The voltage control unit 14 in which 0, 122, and 124 are connected in series
0 (controlled so that V _A = V _C ) is connected,
Further, from the output terminal of the differential amplifier 114, V _A = V _C
The output voltage V ₀ controlled so that
The signal is input to the brightness adjusting signal input terminal 102A of No. 2, and the loop formed in the 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 causing “whiteout”. As a result, an easily viewable image can be easily obtained. 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 are A ₁ <A ₂ <A.
₃ is satisfied, the symbol V _H is the hold potential,
The symbol W indicates each "whiteout" area.

As described above, in this embodiment, the value V of the signal output from the sample hold circuit 27 is used.
_A is generated by the white hold reference voltage generation circuit 15
By comparing with the value V _C of the output reference voltage,
A feedback clamp is applied to the output signal Y of the signal processing circuit 23. Therefore, even when the surrounding environment is bright, the contrast of the image is automatically adjusted so that the brightness is automatically set to the optimum state while avoiding the “whitening”. As a result of being controlled, the black level can be raised and an easy-to-see screen can be obtained.

The present invention is not limited to the above-described embodiments, and various other configurations can be adopted 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. By doing so, a feedback clamp is applied to the output signal of the signal processing circuit, so when the surrounding environment is bright, the brightness of the video signal is automatically adjusted to the best state while avoiding "whiteout". As a result of the controlled contrast, the black level is raised and there is the benefit that a clear screen can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram in 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 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 indicating illuminance when “whiteout” does not occur.

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

FIG. 12 is an explanatory diagram showing a video signal when “whiteout” occurs.

FIG. 13 is an explanatory diagram showing a video signal when “whiteout” becomes more severe.

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 when “whiteout” occurs.

[Explanation of symbols]

1, 3, 5, 7 Input terminals 11 Average value detection circuit 13 White reference pulse insertion pedestal clamp circuit 15 White reference pulse generation circuit 17 Switch circuit 19 Black expansion auto pedestal circuit 21 LCD controller 23 Liquid crystal display drive signal processing circuit 25 Control amplifier 27 Sample and hold circuit 29 Liquid crystal drive buffer 29 31 LCD (liquid crystal display device) 33 White hold reference voltage generation circuit

Claims (1)

[Claims] 1. A white reference pulse insertion circuit in which a white reference pulse is inserted in a front porch portion of a luminance signal with reference to a pedestal of a video signal, and desired signal processing for an output signal of the white reference pulse insertion circuit. A signal processing circuit for performing the above, a sample hold circuit for sampling and holding the white reference pulse with respect to an output signal of the signal processing circuit, and a white hold reference voltage generating circuit for generating and outputting a white hold reference voltage. , And the value of the signal output from the sample and hold circuit is
A feedback signal is applied to the output signal of the signal processing circuit by being compared with the value of the reference voltage output from the white hold reference voltage generation circuit, and the drive signal processing of the liquid crystal display device is performed. circuit.