JPH11133919A - Liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display which eliminates any in-plane distribution of flicker and improves the picture quality. SOLUTION: A liquid crystal display is provided with a DC potential automatic adjusting circuit 21 which adjusts a reference voltage Vref outputted by a Vref generation circuit 1 at each source driver IC3 according to the difference between the voltage applied to a drain electrode of TFT(Thin Film Transistor) constituting a pixel and a voltage applied to the opposite electrode, which is arranged opposite to a display electrode connected to the drain electrode across the liquid crystal, so as to feed it to a source driver IC3. In this case, effects of parasitic capacity between the gate and drain electrodes of the TFT on the source drive voltage is eliminated so as to eliminate any dispersion of the flicker in the display part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an active matrix type liquid crystal display device using a thin film transistor (hereinafter, referred to as a TFT), and more particularly to a driving circuit thereof.

[0002]

2. Description of the Related Art FIG. 3 is a schematic diagram showing a conventional liquid crystal display device. In FIG. 3, reference numeral 1 denotes a Vref generating circuit that generates a reference voltage Vref, 2 denotes a source TCP (abbreviation of a tape carrier package), and 3 denotes a source driver IC mounted on the source TCP2. Vref generation circuit 1
N reference voltages generated in (N is usually 7 to 11)
Are supplied in parallel to each source driver IC3. Reference numeral 4 denotes a liquid crystal panel having a TFT at an intersection of a gate line and a source line. A source driver IC 3 supplies a source drive voltage, which is a gray scale voltage, to the source line based on a reference voltage.

FIG. 4 is a diagram showing an equivalent circuit for one pixel of a conventional active matrix type liquid crystal display device. FIG.
, 8 is a gate line, 9 is a source line, and 10 is TF
T and 11 are a parasitic capacitance Cgd between the gate and the drain of the TFT 10, and 12 is a capacitance Clc of a liquid crystal to which a voltage is applied by the TFT 10. The liquid crystal is opposed to a display electrode connected to the drain electrode of the TFT 10 and faces the display electrode. Are sandwiched between the counter electrodes which are arranged in the same manner. 13 is a gate-drain parasitic capacitance Cgd1 when the gate drive voltage is off.
1 is an additional capacitance Cst for reducing the field through voltage ΔVgd. Vg is the gate drive voltage, Vs
Is a source drive voltage, Vd is a drain voltage applied to the drain electrode of the TFT 10, and Vcom is a common voltage applied to the counter electrode.

FIG. 5 is a diagram showing voltage waveforms at various portions of a liquid crystal cell of a conventional liquid crystal display device. In FIG.
14 is the average voltage Vso of the source drive voltage, 15 is the amplitude Vsa of the source drive voltage, 16 is the gate drive voltage Vg, 1
7 is a field-through voltage ΔVg due to the gate-drain parasitic capacitance Cgd when the gate drive voltage Vg16 is off.
d. FIG. 6 is a diagram showing distortion of gate drive voltage waveforms on the left and right sides of a liquid crystal panel of a conventional liquid crystal display device. 6, reference numeral 4 denotes the same liquid crystal panel as in FIG. 3, and reference numeral 18 denotes a gate TCP.
A gate driver IC for transmitting a gate drive voltage Vg, which is a signal for turning on and off the gate of 0 in a horizontal cycle, is mounted. 19 is a gate substrate, which has a plurality of gate TCs
Signal and voltage lines for supplying necessary signals and voltages to the gate driver IC mounted on P18 in parallel are arranged in a bus shape.

In the conventional liquid crystal display device thus configured, the TFT 10 shown in FIG. 4 is turned on and off by a gate drive voltage inputted to the gate line 8, and when the TFT 10 is turned on, a source drive voltage which is a gray scale voltage is applied from the source line 9. Liquid crystal capacitance Clc
12 and the additional capacity Cst13. However, TF
Since the gate-drain parasitic capacitance Cgd11 exists between the gate electrode and the drain electrode of T10, a voltage shift occurs by the field-through voltage ΔVgd17 when the gate drive voltage Vg16 falls, as shown in FIG. This field-through voltage ΔVgd17 is expressed by (1)
It is expressed like a formula. ΔVgd = Cgd · Vg / (Cgd + Clc + Cst) (1) Therefore, between the voltage applied to the source line and the voltage actually applied to the drain side, that is, the liquid crystal, this field-through voltage ΔVgd17 minutes Of the common voltage, which is the potential of the common electrode, the source drive voltage is previously set to the field through voltage ΔVgd17
The voltage needs to be increased.

The field through voltage ΔVgd17
Varies with the gate-drain parasitic capacitance Cgd11 as can be seen from the equation (1). The gate-drain parasitic capacitance Cgd11 is a value that changes according to the rise / fall time of the gate drive voltage. When the rise / fall time of the gate drive voltage is short, the gate-drain parasitic capacitance Cgd11 is large,
Therefore, the field through voltage ΔVgd17 increases, but when the rise / fall time of the gate drive voltage is long, the gate-drain parasitic capacitance Cgd11 is small, and the field through voltage ΔVgd17 is also small. Since the normal gate drive voltage is input from the left end of the screen, as shown in FIG. 6, the rise / fall time of the left end gate drive voltage is short and the rise / fall time of the right end gate drive voltage is long. Therefore, since the field through voltage ΔVgd17 differs between the left area and the right area of the screen, the optimum common voltage value for making the flicker invisible differs between the left and right areas in one screen. This is what is usually called the in-plane distribution of flicker. This in-plane distribution becomes more apparent as the size of the liquid crystal display screen increases.

[0007]

Since the conventional active matrix type liquid crystal display device is configured as described above, the optimum common voltage is shifted between the left and right sides of the screen, and the flicker is caused by adjusting only the common voltage. Was difficult to completely hide.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to provide a liquid crystal display device capable of eliminating flicker in-plane distribution and improving image quality.

[0009]

In a liquid crystal display device according to the present invention, a plurality of scanning lines and a plurality of signal lines are arranged in a matrix at intersections, and a first electrode is connected to a scanning electrode by a second electrode. A display unit having a switching element in which a third electrode is connected to a display electrode to a signal line, a first drive circuit connected to a scanning line and supplying a first voltage to the switching element, A reference voltage generation circuit that outputs a voltage, a plurality of second drive circuits that are connected to the signal line and supply a second voltage to the switching elements, and are provided for each of the second drive circuits, Adjust the reference voltage output from the reference voltage generation circuit according to the effect of the parasitic capacitance between one electrode and the third electrode on the voltage applied to the third electrode, and supply it to the second drive circuit A second adjustment circuit. Dynamic circuit, a second voltage based on the adjusted reference voltage and supplies to the switching element.

A switching element is disposed at the intersection of a plurality of scanning lines and a plurality of signal lines, a first electrode being connected to the scanning line and a second electrode being connected to the signal line, respectively, A display section in which pixels each having a display electrode connected to the three electrodes and a counter electrode disposed so as to face the display electrode and sandwich the liquid crystal are connected to a matrix, and a switching section is connected to a scanning line. A first driving circuit that supplies a first voltage to the element, a reference voltage generating circuit that outputs a plurality of reference voltages, and a plurality of second voltages that are connected to the signal line and supply a second voltage to the switching element. A drive circuit, and a reference voltage provided for each of the second drive circuits and output by a reference voltage generation circuit in accordance with a voltage applied to a third electrode of the pixel switching element and a voltage applied to the counter electrode. Adjust the An adjustment circuit for supplying the drive circuit, the second driving circuit, a second voltage based on the adjusted reference voltage and supplies to the switching element.

The adjustment circuit adjusts the reference voltage according to the difference between the voltage applied to the third electrode of the switching element of the pixel and the voltage applied to the counter electrode.
Further, the adjustment circuit includes a first circuit for detecting a difference between a voltage applied to the third electrode of the switching element of the pixel and a voltage applied to the counter electrode, and an output of the first circuit as a reference voltage. And a second circuit for superimposing the second circuit. Further, the reference voltage is adjusted so that the average of the voltage applied to the third electrode of the switching element of the pixel is equal to the average of the voltage applied to the counter electrode.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a schematic configuration diagram showing a liquid crystal display device according to an embodiment of the present invention. FIG.
, 1 to 4 are the same as those of the conventional apparatus in FIG. 3, and the description thereof is omitted. Reference numeral 21 denotes D for automatically adjusting the potential of the reference voltage Vref output from the Vref generation circuit 1.
The C potential automatic adjustment circuit is provided for each source driver IC3 and outputs the adjusted reference voltage Vref to the source driver IC3. FIG. 2 is a detailed diagram showing a DC potential automatic adjustment circuit of the liquid crystal display device according to the embodiment of the present invention. In FIG. 2, reference numeral 22 denotes an error amplifier for detecting a potential difference between the common voltage Vcom and the drain voltage Vd, and reference numeral 23 denotes D for superimposing the output of the error amplifier 22 on the reference voltage Vref.
This is a C voltage superposition circuit.

In the liquid crystal display device configured as described above, the N reference voltages Vref generated by the Vref generation circuit 1 are applied to each source driver IC as shown in FIG.
The signals are supplied in parallel to the DC potential automatic adjustment circuits 21 provided for each of the three circuits. In addition, the DC potential automatic adjustment circuit 21 receives a common voltage Vcom and a drain voltage Vd of an arbitrary TFC 10 within a source drive voltage supply range of the source TCP2 to which the output of the DC potential automatic adjustment circuit 21 is supplied. Supplied through source TCP2. D
In the C potential automatic adjustment circuit 21, the voltage difference between the common voltage Vcom and the drain voltage Vd is referred to as an error amplifier 22.
, And the output is input to the DC voltage superimposing circuit 23 and superimposed on the reference voltage Vref for output.

The reference voltage Vref output from each DC potential automatic adjustment circuit 21 is input to each source driver IC 3, and is internally stored in the source driver IC 3.
The image is divided into four gradations and the like and output to the liquid crystal panel 4. Therefore, the DC on the counter electrode side (common electrode) across the liquid crystal
The DC potential on the signal input electrode side (drain electrode) is adjusted to be always the same as the DC potential on the counter electrode side (common electrode) based on the potential. In addition, the screen is divided in the area of the source TCP2, and adjusted to the optimum DC potential in each area.

[0015]

Since the present invention is configured as described above, it has the following effects. The reference voltage is set according to the effect of the parasitic capacitance between the first electrode connected to the scanning line of the switching element and the third electrode connected to the display electrode on the voltage applied to the third electrode. Since the adjusting circuit for adjusting the reference voltage output from the generating circuit for each second driving circuit and supplying the adjusted voltage to the second driving circuit is provided, the second driving circuit switches the adjusted second voltage to the switching element. And a display free from the influence of the parasitic capacitance between the first electrode and the third electrode can be obtained, and variations in flicker in the display unit can be eliminated.

The reference voltage output from the reference voltage generation circuit is adjusted for each second drive circuit according to the voltage applied to the third electrode of the switching element of the pixel and the voltage applied to the counter electrode. And an adjustment circuit for supplying to the second drive circuit, eliminating the influence of the parasitic capacitance between the first electrode and the third electrode of the switching element on the voltage applied to the third electrode, and displaying It is possible to eliminate flicker variation in the department. Further, the adjustment circuit adjusts the reference voltage according to the difference between the voltage applied to the third electrode of the switching element of the pixel and the voltage applied to the counter electrode, so that the reference voltage can be surely adjusted. it can.

Further, the adjustment circuit includes a first circuit for detecting a difference between a voltage applied to the third electrode of the switching element of the pixel and a voltage applied to the counter electrode, and an output of the first circuit. Is superimposed on the reference voltage, so that the adjusted reference voltage can be reliably obtained. Further, since the reference voltage is adjusted such that the average of the voltage applied to the third electrode of the switching element of the pixel is equal to the average of the voltage applied to the counter electrode, the reference voltage can be adjusted to an optimum value.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a detailed diagram showing a DC potential automatic adjustment circuit of the liquid crystal display device according to the embodiment of the present invention.

FIG. 3 is a schematic configuration diagram showing a conventional liquid crystal display device.

FIG. 4 is a diagram showing an equivalent circuit for one pixel of a conventional liquid crystal display device.

FIG. 5 is a diagram showing voltage waveforms at various portions of a liquid crystal cell of a conventional liquid crystal display device.

FIG. 6 is a diagram showing distortion of gate drive voltage waveforms on the left and right sides of a liquid crystal panel of a conventional liquid crystal display device.

[Explanation of symbols]

1 Vref generation circuit, 2 source TCP, 3 source driver IC, 4 liquid crystal panel, 8 gate lines,
9 source line, 10 TFT, 11 gate-drain parasitic capacitance Cgd, 12 liquid crystal capacitance Clc,
18 gate TCP, 21 DC potential automatic adjustment circuit,
22 error amplifier, 23 DC voltage superposition circuit.

Claims (5)

[Claims] 1. A plurality of scanning lines and a plurality of signal lines are arranged in a matrix at intersections, with a first electrode serving as the scanning line, a second electrode serving as the signal line, and a third electrode serving as a display electrode. A display unit having a switching element connected thereto, a first drive circuit connected to the scanning line and supplying a first voltage to the switching element, a reference voltage generating circuit outputting a plurality of reference voltages, and the signal line A plurality of second drive circuits connected to and supplying a second voltage to the switching element, provided for each of the second drive circuits, between the first electrode and the third electrode of the switching element. An adjustment circuit that adjusts a reference voltage output from the reference voltage generation circuit in accordance with an influence of a parasitic capacitance on a voltage applied to a third electrode and supplies the reference voltage to a second drive circuit, and The drive circuit is A liquid crystal display device, wherein a second voltage is supplied to a switching element based on a pressure. A switching element having a first electrode connected to the scanning line and a second electrode connected to the signal line, wherein the switching element is disposed at an intersection of the plurality of scanning lines and the plurality of signal lines; A display section in which pixels each having a display electrode connected to the third electrode and a counter electrode disposed so as to oppose the display electrode with the liquid crystal interposed therebetween is connected to the scanning line and is connected to the scanning line. A first drive circuit that supplies a first voltage to the switching element, a reference voltage generation circuit that outputs a plurality of reference voltages, and a plurality of supply circuits that are connected to the signal line and supply a second voltage to the switching element. A second drive circuit, provided for each second drive circuit,
The reference voltage output from the reference voltage generation circuit is adjusted according to the voltage applied to the third electrode of the switching element of the pixel and the voltage applied to the counter electrode and supplied to the second drive circuit. A liquid crystal display device comprising an adjustment circuit, wherein the second drive circuit supplies a second voltage to the switching element based on the adjusted reference voltage. 3. The adjustment circuit according to claim 2, wherein the adjustment circuit adjusts the reference voltage according to a difference between a voltage applied to the third electrode of the switching element of the pixel and a voltage applied to the counter electrode. The liquid crystal display device as described in the above. 4. An adjustment circuit comprising: a first circuit for detecting a difference between a voltage applied to a third electrode of a switching element of a pixel and a voltage applied to a counter electrode; and an output of the first circuit. 4. The liquid crystal display device according to claim 2, further comprising a second circuit that superimposes a reference voltage on the reference voltage. 5. The reference voltage is adjusted such that the average of the voltage applied to the third electrode of the switching element of the pixel is equal to the average of the voltage applied to the counter electrode. The liquid crystal display device according to claim 2.