JP3964766B2 - Liquid crystal display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device that enables high-quality display, and more particularly to a technique for accurately controlling display contrast, brightness, or gamma correction value.
[0002]
[Prior art]
In a television receiver using a CRT, when the average brightness of the screen becomes high, an ABL (automatic brightness limit) circuit is operated to prevent white-out, and the increase in the anode current of the cathode ray tube is controlled.
[0003]
On the other hand, in a liquid crystal television receiver using a liquid crystal display device (hereinafter referred to as “liquid crystal television”), a control technique for displaying a good image has been proposed. FIG. 3 shows an example of a general control circuit used in a liquid crystal display device for a liquid crystal television. The control circuit 100 illustrated in FIG. 3 includes a buffer circuit 102, a sync chip clamp circuit 105, a peak hold circuit 107, and a direct current amplifier circuit 108. The buffer circuit 102 has a transistor Q11 and a resistor R11. The sink chip clamp circuit 105 includes a capacitor C11 and a diode D11. The peak hold circuit 107 includes a diode D12, a capacitor C12, and a resistor R12. The DC amplifier circuit 108 includes an amplifier IC 11 and resistors R13 and R14.
[0004]
The video signal 103 is input to the input terminal of the buffer circuit 102, and the video signal 103 is clamped by the sync peak value 103 a by the sync chip clamp circuit 105. The peak hold circuit 107 detects an average level corresponding to the video signal 103 and is DC-amplified by the DC amplifier circuit 108 to a level suitable for control. The contrast, brightness, etc. of the liquid crystal display device are controlled by the output signal obtained here.
[0005]
[Problems to be solved by the invention]
The above technique is a technique for obtaining an average value of video signals and controlling contrast and brightness in a liquid crystal display device based on the obtained average value. However, when this method is used, a control signal is obtained on the basis of a video signal. For this reason, there is a problem that, for example, it cannot cope with a sudden video change and it is difficult to control with high accuracy.
[0006]
For example, the liquid crystal display device described in Japanese Patent Laid-Open No. 1-42993 and shown in FIG. 4 includes a liquid crystal panel 201, a vertical driver 202 that sequentially selects and scans the lines of the liquid crystal panel 201, an adder 204, and a first polarity inversion. It has a horizontal driver 203 that samples a video signal applied via the circuit 205 and applies the sampled data to the line simultaneously. The resistor R215 is connected between the common electrode of the liquid crystal panel 201 and the ground. A second polarity inversion circuit 207 is connected to the common electrode side end of the resistor R215, and the second polarity inversion circuit 207 is controlled by the same control signal as the first polarity inversion circuit 205.
[0007]
Further, the liquid crystal display device samples and holds the output from the second polarity inversion circuit 207, the low-pass filter 209 that smoothes the output of the sample-hold circuit 208, and the output of the low-pass filter 209 as 1 It has a hold circuit 210 that holds the field period, a comparator 211 that compares the output of the hold circuit 210 with a reference voltage, and a switch 212 that controls application of the output of the comparator 211 to the adder 204.
Automatic luminance control can be performed by detecting the current flowing through the common electrode of the liquid crystal panel 201 based on the voltage appearing at both ends of the resistor R215 and controlling the video signal based on this.
[0008]
However, in the liquid crystal display device shown in FIG. 4, since a resistor R215 for current detection is inserted between the common electrode of the liquid crystal panel 201 and the ground, a potential difference occurs in the common electrode, and this voltage change causes a change in one field. There has been a problem that the brightness of the display device changes.
An object of the present invention is to provide a liquid crystal display device capable of solving the above-described problems and obtaining a high-quality image.
[0009]
[Means for Solving the Problems]
According to one aspect of the present invention, a pair of opposed substrates, a display medium sandwiched between the pair of substrates, a common electrode formed on one of the pair of substrates, and the common electrode A common electrode drive circuit that drives the common electrode, wiring that connects between the common electrode and the common electrode drive circuit, and a detection unit that is inserted on the power supply side of the common electrode drive circuit and detects a current flowing through the common electrode Is provided.
Furthermore, it is preferable to have a control circuit that performs display-related control based on the current detected by the detection unit.
[0010]
When the display device is used, since the current flowing through the common electrode is detected outside the wiring, the detection has little influence on the output of the common electrode driving circuit, and highly accurate detection is possible. In addition, since the detection can be performed with high accuracy, the control of the display device is also improved. Measurement accuracy is improved by measuring the voltage drop value due to the current.
[0011]
The control circuit is input to a control signal input terminal of a drive circuit for driving the display device, and has at least one characteristic selected from the contrast, brightness, color saturation, and gamma correction value of the display device. It should be a circuit to control.
[0012]
According to another aspect of the present invention, a pair of opposed substrates, a liquid crystal sandwiched between the pair of substrates, a common electrode formed on one of the pair of substrates, and the common electrode A common electrode drive circuit that drives the common electrode, wiring that connects between the common electrode and the common electrode drive circuit, and a detection unit that is inserted on the power supply side of the common electrode drive circuit and detects a current flowing through the common electrode And a control circuit that performs control related to display based on the current detected by the detection unit.
[0013]
The common electrode driving circuit includes a transistor in which the wiring and one first output terminal (emitter terminal) thereof are connected to the final output stage, and the detection unit includes the first output terminal of the transistor. It is preferable to include a circuit for measuring a voltage of a resistor connected to a second output terminal (collector terminal) different from the first output terminal.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
A method of directly detecting the current flowing through the common electrode and performing display control based on the detected current is suitable from the balance of the entire screen. The inventor considered not to provide a current detection unit between the drive signal output terminal of the common electrode drive circuit and the common electrode, but to direct the detection unit outside the current detection unit. In particular, it is preferable to provide a detection unit in the vicinity of the drive signal output end.
[0015]
In this way, the current flowing through the common electrode can be detected at a position close to the common electrode drive circuit without affecting the drive capability of the common electrode drive circuit, and the liquid crystal display device (liquid crystal panel) Can be accurately controlled.
[0016]
Based on the above consideration, a liquid crystal display device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a functional block diagram of a liquid crystal display device according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a main part of FIG. As shown in FIG. 1, a liquid crystal display device A according to an embodiment of the present invention includes a liquid crystal panel 1, a control circuit 3, a common electrode drive circuit 5, and a current detection circuit 7.
[0017]
The liquid crystal panel 1 is an active matrix type liquid crystal panel, for example, and includes two opposing substrates and liquid crystal sandwiched between the substrates. On one (first substrate) side of the two substrates, there are a large number of pixel electrodes that are partitioned for each pixel and arranged in a matrix, and TFTs (thin film transistors) that are provided for each pixel electrode and switch the pixel electrodes ), A plurality of scanning lines and signal lines connected to the gate terminal and the source terminal of the TFT and extending in the row direction and the column direction, a scanning line driving circuit for driving the scanning lines, and a signal line for driving the signal lines And a drive circuit. On the other (second substrate) side of the two substrates, a common electrode 1b is formed on almost the entire surface of the substrate. A desired pixel electrode is selected by a scanning line and a signal line, and the orientation of the liquid crystal is changed by switching the voltage between the pixel electrode and the common electrode 1b. Display (when a color filter is used) can be performed.
[0018]
A common electrode driving circuit 5 for driving the common electrode 1b is also formed on the first substrate side. The current detection circuit 7 includes a current detection unit 11 having a current detection function and an IV conversion function for converting the detected current into a voltage, and a voltage signal output from the current detection unit 11. And an amplifier unit 15 for amplification.
[0019]
As shown in FIG. 1, in the liquid crystal display device A according to the present embodiment, the current detection circuit 7 is not in the wiring between the common electrode driving circuit 5 and the common electrode 1b, but is driven by the common electrode rather than the wiring. The circuit 5 is provided outside the circuit. Here, a current flowing through the common electrode 1b is detected, and based on this, a first control signal relating to what control is to be performed by the control circuit 3 is output. An output signal from the current detection circuit 7 is input to a control circuit (microcomputer, hereinafter referred to as “microcomputer”) 3. The control circuit 3 outputs various control signals, for example, outputs a second control signal (drive signal) to the liquid crystal drive circuit 1a of the liquid crystal panel 1. In response to the second control signal, the liquid crystal driving circuit 1 a drives the liquid crystal panel 1.
[0020]
As shown in FIG. 2, the common electrode drive circuit 5 includes, for example, an npn-type bipolar transistor Q1 and a reverse-conduction-type pnp-type bipolar transistor Q2. The emitter terminal of the npn-type bipolar transistor Q1 and the emitter terminal of the pnp-type bipolar transistor Q2 are commonly connected, and the base terminals of both are commonly connected via a resistor. The collector terminal of the npn-type bipolar transistor Q1 is connected to the power supply voltage VCC via the first resistor R1, and the collector terminal of the pnp-type bipolar transistor Q2 is connected to VEB via the resistor.
[0021]
With these configurations, a complementary circuit is formed. The complementary circuit can supply current to the common electrode 1b or absorb current so that the common electrode 1b of the liquid crystal panel 1 is held at a constant voltage. That is, a predetermined bias is applied to the common electrode 1b by a complementary circuit.
[0022]
A first resistor R1 is provided closer to the power supply voltage VCC than the collector terminal of the npn bipolar transistor Q1. The first resistor R1 has a collector current substantially equal to the emitter current flowing through the common electrode 1b (actually depending on the current gain of the transistor, but if the current gain is large, the difference between the emitter current and the collector current is very small. ) Flows. The voltage drop for the collector current is held by the diode D1 and the capacitor C1. In this way, the value of the current flowing through the common electrode 1b is converted to a voltage value, and based on the changed voltage value, a control voltage suitable for control is set by the capacitor C2, resistors R6, R3, R4 and the amplifier IC7. . The resistor R7 is provided to give hysteresis to the control voltage.
[0023]
As described above, the output signal from the current detection circuit 7 is input to an AD converter of a microcomputer provided in the control circuit 3, for example, and the microcomputer performs contrast, brightness, color saturation, gamma correction value, etc. of the liquid crystal panel 1. Various control signals for controlling each of these are output.
[0024]
In the liquid crystal panel 1, the transmittance of the liquid crystal layer is determined by the sum of the potential of the common electrode and the signal level. The current flowing through the liquid crystal panel 1 is the sum of the currents flowing through all the pixels because the common electrode is common to all the pixels. Therefore, the liquid crystal display has the best accuracy when it is controlled based on the current flowing through the common electrode. Further, the current flowing through the common electrode may be considered as a value representative of the display balance of the entire display screen, and the most suitable control is possible.
[0025]
As described above, according to the liquid crystal display device according to the embodiment of the present invention, it is possible to obtain a highly accurate average image level that is not easily affected by a sudden change in the video signal. Accordingly, the accuracy of video control is improved, and the display quality can be improved.
[0026]
As mentioned above, although demonstrated along this Embodiment, it cannot be overemphasized that this invention is not limited to these examples, and various deformation | transformation are possible. The liquid crystal display device according to this embodiment can be applied to various electronic devices using a liquid crystal display device including a liquid crystal television and a notebook personal computer.
[0027]
【The invention's effect】
When the liquid crystal display device of the present invention is used, it is difficult to be affected by a sudden change in the video signal, and an accurate average image level can be obtained. Accordingly, the accuracy of video control is improved, and the display quality can be improved.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing a schematic configuration of a liquid crystal display device according to an embodiment of the present invention.
FIG. 2 is a circuit diagram centering on a current detection circuit which is a main part of a liquid crystal display device according to an embodiment of the present invention;
FIG. 3 is an example of a general control circuit used in a liquid crystal display device.
FIG. 4 is another example of a liquid crystal display device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS A ... Liquid crystal display device, 1a ... Liquid crystal drive circuit, 1b ... Common electrode, 3 ... Control circuit, 5 ... Common electrode drive circuit, 7 ... Current detection circuit, 11 ... Current detection part, 15 ... Amplifier part, R1 ... 1st 25, an integration circuit, Q1, a first transistor, Q2, a second transistor, Vto, an output terminal, L, a wiring, VCC, a power source.

Claims (4)

A pair of opposed substrates;
A display medium sandwiched between the pair of substrates;
A common electrode formed on one of the pair of substrates;
A common electrode driving circuit for driving the common electrode;
Wiring connecting between the common electrode and the common electrode drive circuit;
A detection unit that is provided on a power supply side of the common electrode driving circuit and detects a current flowing through the common electrode ;
A control circuit that performs display-related control based on the current detected by the detection unit,
The common electrode driving circuit includes a transistor having the wiring and one of the first output terminals connected to the final output stage,
The display unit includes a circuit that measures a voltage of a resistor connected to a second output terminal different from the first output terminal of the transistor. The control circuit is input to a control signal input terminal of a drive circuit that drives the display device, or a control signal input terminal of a signal processing circuit for a video signal input to the display device,
The display device according to claim 1 , wherein the display device is a circuit that controls at least one characteristic selected from a contrast, brightness, color saturation, and a gamma correction value of the display device. A pair of substrates disposed opposite to each other; a liquid crystal sandwiched between the pair of substrates; a common electrode formed on one of the pair of substrates; a common electrode driving circuit that drives the common electrode; A liquid crystal display device comprising: a wiring connecting between a common electrode and the common electrode driving circuit; and a detection unit that is inserted on a power supply side of the common electrode driving circuit and detects a current flowing through the common electrode,
Furthermore, it has a control circuit for controlling a display based on the detected current in the detection unit,
The common electrode driving circuit includes a transistor having the wiring and one of the first output terminals connected to the final output stage,
The liquid crystal display device , wherein the detection unit includes a circuit that measures a voltage of a resistor connected to a second output terminal different from the first output terminal of the transistor . A pair of substrates disposed opposite to each other; a liquid crystal sandwiched between the pair of substrates; a common electrode formed on one of the pair of substrates; a common electrode driving circuit that drives the common electrode; A control circuit for controlling a liquid crystal display device having a common electrode and a wiring connecting between the common electrode drive circuit,
Furthermore, it possesses a detector for detecting a current flowing through the common electrode is inserted in the power supply side of the common electrode driving circuit, and a control unit for controlling a display based on the detected current in the detection unit ,
The common electrode driving circuit includes a transistor having the wiring and one of the first output terminals connected to the final output stage,
The detection unit is a control circuit including a circuit for measuring a voltage of a resistor connected to a second output terminal different from the first output terminal of the transistor .

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