JPH0968695A - Gray scale voltage generation circuit and liquid crystal display device - Google Patents

Abstract

(57) [Abstract] [Purpose] Increase the resistance value of each division resistor to increase the total resistance value of the series resistance division circuit without increasing the output impedance that causes image quality defects such as color shift and uneven brightness. By increasing the value, reduce the power consumption of the drain drive circuit. A gray scale voltage of a plurality of gray scales to be applied to a liquid crystal layer is generated by dividing a plurality of gray scale reference voltages of a plurality of gray scale reference voltages by a series resistance division circuit, and the multi-story gray scale voltage is generated for each of a plurality of drain signal lines. In the grayscale voltage generation circuit that outputs a predetermined grayscale voltage to each of the plurality of drain signal lines by selecting one of the grayscale voltages of the grayscale level by a plurality of switching elements, A buffer circuit that supplies a predetermined voltage is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device,
In particular, the present invention relates to a technique effectively applied to a resistance division type drain driving circuit using a ladder resistor.

[0002]

2. Description of the Related Art An example of a TFT liquid crystal display device capable of multi-color display, for example, 64-gradation multi-color display is described in Document I below.

I "Low-Power 6-bit
"Column Driver for AMLCDs"
(Published June 1994, SID 94 DIJEST
P. 351-354).

FIG. 5 shows the above-mentioned document. FIG. 3 is a block diagram showing a schematic configuration of the TFT liquid crystal display device described in FIG. 1, in which a liquid crystal display panel (TFT-LCD) is composed of 800 × 600 pixels (800 × 600 × 3 subpixels).

A liquid crystal display panel (TFT-LCD)
A drain drive circuit 602 is disposed on one side of the drain drive circuit 602, and the drain drive circuit 602 is connected to a drain signal line of a thin film transistor (TFT) to supply a voltage for driving a liquid crystal to the thin film transistor (TFT).

Further, a gate drive circuit 603 arranged on the side surface of the liquid crystal display panel (TFT-LCD) is connected to the gate signal line of the thin film transistor (TFT), and a voltage is applied to the gate of the thin film transistor (TFT) for one horizontal operation time. To supply.

The display control device 601 receives display data and a display control signal from a computer (not shown) and drives the drain drive circuit 602 and the gate drive circuit 603 based on this signal.

Here, the display data from the computer body (not shown) is composed of 18 bits, 6 bits for each color.

The drain driving circuit 602 has one gray scale voltage generating circuit, and the gray scale voltage generating circuit has a nine-value gray scale reference voltage (V0-V) inputted from the internal power supply circuit 604.
Based on 8), gradation voltages for 64 gradations are generated.

Further, the drain driving circuit 602 fetches 6 bits of display data for each color for the number of outputs in synchronization with the display data latching clock signal, and further, in accordance with the output timing controlling clock signal, A grayscale voltage corresponding to the display data is selected from the grayscale voltages for 64 grayscales generated by the voltage adjustment voltage generation circuit, and is output to each drain signal line.

Further, in order to prevent the deterioration of the liquid crystal layer which becomes a pixel, the output voltage (voltage applied to the pixel electrode) of the drain drive circuit in the alternating current cycle of the alternating current signal (M) (not shown), and The polarity of the voltage applied to the common electrode is reversed.

FIG. 6 is a circuit diagram showing a schematic structure of a gradation voltage generating circuit of the drain driving circuit 602 in the liquid crystal display device shown in FIG.

As shown in FIG. 6, the grayscale voltage generation circuit 606 of the drain drive circuit 602 in the liquid crystal display device shown in FIG. 5 firstly outputs a nine-value grayscale reference voltage (input from the internal power supply circuit 604). By dividing each gradation reference voltage of V0-V8) into eight by the series resistance dividing circuit 605, a gradation voltage of 8 × 8 = 64 (grayscale) is generated.

Next, the gradation voltage corresponding to the display data is set to 6
Selection circuit 113 composed of 4 × b MOS transistors
And output to the drain signal lines 1 to b.

FIG. 7 shows the gradation reference voltage Vn shown in FIG.
And the gradation reference voltage vn-1 (n = 1 to 8)
6 is a circuit diagram showing a schematic configuration of a series resistance division circuit and a series resistance division circuit which are the grayscale voltage generation circuit 606 corresponding to the grayscale reference voltage. FIG.

As shown in FIG. 7, the conventional series resistance division circuit 605 divides the gradation reference voltages Vn and Vn-1 (n = 1 to 8) input from the internal power supply circuit 604 into eight. Of the dividing resistors 105 to 112, the resistance value of which is R.

On the other hand, as the operating system becomes a graphical user interface and the CPU (central processing unit) becomes faster, it is required that the liquid crystal display device can display more colors or black and white gradations. For example, in order to perform full-color display (16,770,000 colors), it is necessary to generate gradation voltages for 256 gradations of each color.

[0018]

SUMMARY OF THE INVENTION As a result of studying the above prior art, the present inventor has found the following problems.

In the conventional liquid crystal display device, in order to reduce the power consumption of the drain driving circuit, the resistance value of the dividing resistor may be increased to reduce the current flowing through the series resistance dividing circuit.

However, since the output of the drain drive circuit 602 is inverted at the period of the alternating signal (M), the current value for charging and discharging the liquid crystal layer is I, and the output impedance of the drain drive circuit 602 is R. When written as
When the charging / discharging current is flowing, the series resistance divider circuit 60
The selected output voltage level of No. 5 fluctuates within the voltage width determined by V = IR.

For this reason, image quality defects such as color shift and uneven brightness occur on the display screen. Therefore, in the resistance drive type drain drive circuit 602, the resistance values of the division resistors 105 to 112 are increased to make series resistance division. There is a problem that the current flowing through the circuit 605 cannot be reduced and the power consumption of the drain drive circuit cannot be reduced.

An object of the present invention is to increase the resistance value of each division resistor without increasing the output impedance that causes image quality defects such as color shift and uneven brightness, and to increase the total resistance value of the series resistance division circuit. It is to provide a technique capable of reducing the power consumption of the drain drive circuit by increasing the power consumption.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0024]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

(1) A plurality of gradation reference voltages of a plurality of gradation reference voltages are divided by a series resistance dividing circuit to generate a multi-gray scale gradation voltage to be applied to the liquid crystal layer, and a plurality of drain signal lines are provided. In the grayscale voltage generation circuit that outputs a predetermined grayscale voltage to each of a plurality of drain signal lines by selecting one of the grayscale voltages of the multiple grayscales by a plurality of switching elements, A feature is that a buffer circuit that supplies a predetermined voltage to the division circuit is provided.

(2) The buffer circuit comprises a voltage follower circuit.

(3) The drain driving circuit is provided with the gradation voltage generating circuit described in the above (1) or (2).

[0028]

According to the above-mentioned means (1), (2) or (3), for example, 64 gradation display (260,000 color display)
When it is realized by the gradation reference voltage of the value, the series resistance division circuit needs to be divided into eight.

At this time, the maximum value of the output impedance of the drain drive circuit, that is, the output of the division resistance forming the series resistance division circuit farthest from the gradation reference voltage is selected. The resistance value is 4R (R × 4, where R is the resistance value of each divided resistor).
(Divided resistance for each piece)).

At this time, by providing one buffer circuit in the middle of the dividing resistors so that the number of the dividing resistors is four, a current is supplied from the buffer circuit to the output located far from the gradation reference voltage. To be done.

Therefore, the maximum value of the output impedance is the output impedance of the output located farthest from the gradation voltage or the buffer circuit, and the value is 2R.
Becomes

This output impedance has a resistance value of 1/2 of 4R which is the maximum output impedance of the conventional drain drive circuit in which the number of divisions of the series resistance division circuit is eight.

That is, when the maximum value of the output impedance is set to the same value as that of the conventional gradation voltage generating circuit of 64 gradations, the resistance value of each division resistor can be set to twice the conventional resistance value, so that the series resistance can be set in series. The total resistance value of the resistance division circuit is twice as large as that of the conventional one, and the power consumption consumed in the division resistance portion of the gradation voltage generation circuit can be reduced to half.

As described above, by inserting a buffer circuit for each predetermined number of dividing resistors of the series resistance dividing circuit, a current can be supplied from this buffer circuit, so that a gradation reference voltage is newly added. It is possible to reduce the output impedance of the grayscale voltage generation circuit.

Therefore, it is possible to reduce the power consumption of the gradation voltage generating circuit by increasing the resistance value of each dividing resistor and increasing the total resistance value of the series resistance dividing circuit.

Therefore, by using the gradation voltage generating circuit in the liquid crystal display device, a liquid crystal display device with low power consumption can be provided.

[0037]

Embodiments in which the present invention is applied to a TFT liquid crystal display device will be described below in detail with reference to the drawings.

In all the drawings for explaining the embodiments, parts having the same function are designated by the same reference numerals, and the repeated description thereof will be omitted.

Since the structure of the TFT liquid crystal display device to which the present invention is applied is the same as that of the conventional TFT liquid crystal display device shown in FIG. 6, the description thereof will be omitted.

(Embodiment 1) FIG. 1 shows a schematic circuit configuration of a series resistance division circuit and a selection circuit which are gradation voltage generation circuits for one gradation reference voltage of a drain drive circuit according to Embodiment 1 of the present invention. It is a circuit diagram, 101 is a series resistance division circuit, 1
Reference numeral 02 is a well-known voltage follower circuit (buffer circuit) by an operational amplifier, 103 to 112 are resistors, 113 is a selection circuit, and 114 is a MOS transistor (switching element).
It is.

In FIG. 1, the series resistance division circuit 101 is similar to the gradation voltage generation circuit 606 shown in FIG.
A grayscale voltage for 64 grayscales is obtained by equally dividing each grayscale reference voltage of the nine-value grayscale reference voltage (V0-V8) input from the internal power supply circuit 604 into 8 equal parts by resistors 105 to 112 having the same resistance value. (8 gradation reference voltage × 8 divisions = 64 gradations) is generated.

At this time, the resistors 103 and 104 connected in series have the same resistance value, the resistor 103 is the gradation reference voltage Vn−1, and the resistor 104 is the gradation reference voltage Vn (n = 1.
~ 8).

On the other hand, the reference voltage of the voltage follower circuit 102 by the operational amplifier is a voltage divided by the resistors 103 and 104, that is, the gradation reference voltage Vn-.
1 and the gradation reference voltage Vn (n = 1 to 8), which is an intermediate voltage (Vn4), and the output of the voltage follower circuit 102 is divided by the connection point of the resistors 108 and 109, that is, the resistors 105 to 112. It is connected to a position that is an intermediate voltage of the voltage to be compressed.

Voltage follower circuit 1 with operational amplifier
A well-known non-inverting amplifier 02 having a voltage gain of 1 is widely used as an impedance converter or a buffer.

The selection circuit 113 has a gradation voltage (Vn0-V).
n8, where n = 1 to 8) and the output terminals 1 to b of the drain drive circuit (where b is a natural number of 1 or more) are controlled by controlling a MOS transistor 114, which is shown in the drawing. The grayscale voltage corresponding to the display data latched by the data latch is output to the output terminal of any drain drive circuit.

Next, referring to FIG. 1, the operation of the series resistance division circuit for one gradation reference voltage of the drain drive circuit of the first embodiment will be described. The output impedance of the series resistance division circuit 101 of the present embodiment, that is, The output impedance of the drain drive circuit is highest when the grayscale voltages Vn2 and Vn are the intermediate points of the resistors that divide the grayscale reference voltage.
6 (n = 1 to 8) is selected, and the output impedance at this time is 2R, which is the resistance value of two dividing resistors 105 to 112.

Since this output impedance has a resistance value half that of the output impedance 4R of the conventional drain drive circuit shown in FIG. 5, for example, the resistor 10 of the first embodiment is used.
Even when each resistance value of 5 to 112 is doubled to 2R, the output impedance of the drain drive circuit of this embodiment is 2 ×.
At 2R = 4R, the same value as that of the conventional drain drive circuit is set.

On the other hand, the series resistance division circuit 101 at this time
Since the total resistance of each is set to twice the resistance value of the conventional resistance, the total resistance is twice that of the conventional series resistance division circuit.

Therefore, since the power consumed by the series resistance division circuit 101 can be reduced to 1/2, the power consumed by the grayscale voltage generation circuit of the drain drive circuit can be reduced to 1/2. it can.

As described above, according to the first embodiment, the gradation reference voltage Vn and the gradation reference voltage Vn-1 (n = 1).
8 to 8) of the dividing resistors 105 to 112, for example, the output of the voltage follower circuit 102 by the operational amplifier is connected between the dividing resistors 108 and 109 corresponding to the middle, while the voltage is divided into Follower circuit 102
Of the reference potential of the gray scale reference voltage Vn and the gray scale reference voltage Vn-1
The output impedance of the grayscale voltage Vn0 that maximizes the output impedance in the conventional series resistance division circuit 101 by setting the potential divided by the resistors 103 and 104 having the same resistance value provided between (4
Since R) can be supplied with current from the voltage follower circuit 102, it can be reduced to almost zero.

The maximum value of the output impedance at this time is when the gray scale reference voltage Vn, the gray scale reference voltage Vn-1 or the gray scale voltage in the middle of the voltage follower circuit 102 is output. 1 is Vn2 and Vn6, and the output impedance at this time is two dividing resistors, that is, 2R, which is half the output impedance of the conventional series resistance dividing circuit 101.

Therefore, it becomes possible to set the resistance value of the dividing resistors 105 to 112 to 2R so that the output impedance becomes 4R which is the same as the conventional one, and the dividing resistors 105 to 1
Each resistance value of 12 can be set to 2R which is twice as large as the conventional one.

The output impedance at this time is 4R, which is the same as that of the conventional drain drive circuit, but since the resistance value of the series resistance division circuit 101 that constantly consumes power is doubled, the drain drive circuit Power consumption of conventional 1
It can be reduced to / 2.

Therefore, by using the drain driving circuit in a liquid crystal display device, a liquid crystal display device with low power consumption can be provided.

(Embodiment 2) FIG. 2 is a circuit diagram showing a schematic configuration of a series resistance division circuit and a selection circuit which are gradation voltage generation circuits for one gradation reference voltage of a drain drive circuit of Embodiment 2 of the present invention. It is a diagram, and particularly shows a grayscale voltage generation circuit that generates a voltage for 128 grayscales.

In FIG. 2, reference numerals 201 to 203 denote voltage follower circuits 1 to 3 and 204 to 223 which are operational amplifiers.
Indicates resistance, and in particular, 208 to 223 indicate division resistors.

Voltage follower circuit 1 with operational amplifier
3 to 201 (203 to 203) are well-known non-inverting amplifiers having a voltage gain of 1 and are widely used as impedance converters and buffers.

The resistors 204 to 207 all have the same resistance value, and the resistors 204 to 207 calculate the potential difference Vn (n-1) between the gradation reference voltage Vn and the gradation reference voltage Vn-1 by the voltage follower circuit 1. Is a voltage dividing resistor for dividing the gradation voltages Vn4, Vn8, and Vn12 at the positions where 3 to 201 (201 to 203) are inserted.

The dividing resistors 208 to 223 have a potential difference Vn (n-1) between the gradation reference voltage Vn and the gradation reference voltage Vn-1.
16 gradation voltages Vn0 to Vn16 (where V
n0 = V (n-1) 16), which is a resistor for voltage division, and the resistance value of each dividing resistor is R.

Next, the operation of the series resistance dividing circuit for one gradation reference voltage of the second embodiment will be described with reference to FIG. 2, and the output impedance of the series resistance dividing circuit 101 of the present embodiment will be described.
That is, the output impedance of the drain drive circuit is highest at the midpoint of the dividing resistors that divide the reference voltages, but the grayscale voltage Vn of the series resistor dividing circuit 101 is higher.
4, voltage follower circuits 1 to 3 for Vn8 and Vn12
Since (201 to 203) are connected, they serve as a current supply source.

Therefore, the output impedance of the series resistance division circuit 101 is highest in the gradation voltage Vn2.
The output impedance at this time is Vn6, Vn10, and Vn14, and the output impedance at this time is 2R because there are two dividing resistors.
It is.

This output impedance is 1 / the output impedance 4R of the conventional drain drive circuit shown in FIG.
2 is a resistance value of, for example, the division resistance 2 of the second embodiment.
Even when each resistance value of 08 to 223 is doubled to 2R, the output impedance of the drain drive circuit of the present embodiment is 2 × 2R = 4R, which is the same value as the conventional drain drive circuit.

At this time, the total resistance of the series resistance dividing circuit 101 is 2R × 16 × 8 = 4 × R × 64 = 256R, and the output impedance of the drain drive circuit remains 4R as in the conventional case, and the total resistance is 4R. Since it can be set to double, the power consumption of the drain drive circuit can be significantly reduced.

As described above, according to the second embodiment, the voltage dividing followers 201 to 2 by the operational amplifier are provided for the four dividing resistors of the series resistance dividing circuit 101.
By inserting one 03, a current can be supplied from the voltage follower circuits 201 to 203 to the resistance of the series resistance division circuit 101, so that the output impedance of the drain drive circuit can be reduced.

As a result, the power consumption can be reduced while maintaining the same output impedance as that of the conventional drain drive circuit or a small output impedance, and, for example, among the adjacent drain drive elements, the output voltage of all the specific elements is the same. When the output voltage of a small number of outputs of the elements adjacent to this element has the same output voltage as that of the element, the voltage value when all the one drain driving elements output the same output voltage and Output impedance (output drive capability) when a small number of outputs select the voltage value
The difference in the output voltage makes a slight difference, and it is possible to prevent the result from appearing as brightness unevenness on the display screen.

Therefore, by using the gradation voltage generating circuit of the second embodiment, a liquid crystal display device with high image quality and low power consumption can be constructed.

(Embodiment 3) FIG. 3 is a circuit diagram showing a schematic configuration of a series resistance division circuit and a selection circuit which is a gradation voltage generating circuit for one gradation reference voltage of a drain drive circuit according to Embodiment 3 of the present invention. FIG. 4 is a diagram showing the relationship between the voltage applied to the liquid crystal layer and the transmittance.

As shown in FIG. 4, generally, the relationship between the voltage applied to the liquid crystal layer and the transmittance is not linear, and the transmittance with respect to the voltage applied to the liquid crystal layer is different at high and low transmittances. The change is small, and the change in the transmittance is large in the middle of the change.

Therefore, for example, in a liquid crystal display device capable of multi-color display of 64 gradations, in order to linearly display 64 gradations, the gradation reference voltage applied to the gradation voltage generating circuit of the drain drive circuit is used. The values are not evenly spaced, and the difference is small near the halftone and must be large at other points.

Therefore, in the gradation voltage generating circuit of the drain driving circuit, the resistance value of each of the dividing resistors 105 to 112 shown in FIG. 7 is R, and the total number of dividing resistors is 8R. When a gradation reference voltage that is not evenly spaced as described above is applied to the used gradation voltage generation circuit, a direct current (DC) current flows between the gradation reference voltages,
Power consumption increases.

In the conventional grayscale voltage generation circuit shown in FIG. 7, for example, between the grayscale reference voltages V0-V1, V1-
The gradation reference voltage differences between V2, V6 and V7, and V7 and V8 are the gradation reference voltages V2 and V3, V3 and V4, and V4.
Double the gradation reference voltage difference between V5 and V5-V6, and the dividing resistors 105 to 112 of the series resistance dividing circuit 101.
The resistance value R of R is set to R = 12.5Ω (8 × R = 100Ω).

As a result, the current value flowing between the gradation reference voltages V6 and V7 of the series resistance division circuit 101 and between the gradation reference voltages V1 and V2 is:
While it is 10 mA (1.0 V / 100Ω = 10 mA), the gradation reference voltage V5 of the series resistance division circuit 101 is
The current value flowing between V6 and the grayscale reference voltages V2 and V3 is 5 mA (0.5 V / 100Ω = 5).
mA).

Therefore, current flows in and out from the application terminal of the gradation reference voltage V6 and the application terminal of the gradation reference voltage V2 of the series resistance division circuit 101 in which the gradation reference voltage difference is discontinuous, and the power consumption is reduced. Will increase.

When the number of drain signal lines outputting the same gray scale voltage in one drain drive circuit increases,
The voltage fluctuation of the gradation voltage of the gradation reference voltage generation circuit becomes large, and in particular, in the halftone display part where the change in the transmittance of the liquid crystal layer with respect to the applied voltage is large, uneven brightness (brightness difference) occurs on the display screen. To do.

In order to solve this problem, in the grayscale voltage generation circuit of the third embodiment, the input grayscale reference voltage is set as shown in FIG.
As shown in, the gradation reference voltage values are
The voltage difference is set to be small near the halftone and large in other cases.

That is, the gradation reference voltage Vn of the nine-value gradation reference voltage (V0-V8) supplied to the gradation voltage generation circuit.
And the grayscale reference voltage Vn-1 (n = 1 to 8) is V.
If the sum of the resistance values of the series resistance division circuit 101 for one gradation reference voltage is expressed as Rn, it is represented by n (n-1), and in the gradation voltage generation circuit of the third embodiment, R8: R7: R6. : R
5: R4: R3: R2: R1 = V87: V76: V6
5: V54: V43: V32: V21: V10.

The current flowing through the series resistance division circuit 101 is
Since a constant current value (Vn (n-1) / Rn = from a constant current value) is obtained, in the grayscale voltage generation circuit of the third embodiment, the maximum grayscale reference voltage and the minimum grayscale reference voltage are equal to each other. The applied gradation reference voltage (V0 and V
The current value from other than the application terminal of 8) becomes almost “0”, and the power consumption of the drain drive circuit can be reduced.

Furthermore, in the series resistance division circuit 101 of the third embodiment, as shown in FIG.
The dividing resistor 30 which is the middle of the dividing resistors 301 to 308
By inserting the voltage follower circuit 102 by an operational amplifier between the voltage divider circuit 4 and the dividing resistor 305, a voltage (current for charging and discharging the liquid crystal layer) applied to the liquid crystal layer is supplied from this voltage follower circuit 102. Therefore, the dividing resistors 301 to 301 can be used without increasing the output impedance.
08 can have a large resistance value.

For example, as shown in the first embodiment, the current value can be further reduced by setting each resistance value to a large value.

Therefore, by using the gray scale voltage generation circuit of the third embodiment, a low power consumption liquid crystal display device can be constructed.

Further, when the number of drain signal lines that output the same gray scale voltage in one drain drive circuit increases, the voltage fluctuation range of the gray scale voltage of the gray scale reference voltage generating circuit can be reduced, In particular, it is possible to prevent uneven brightness (brightness difference) on the display screen that occurs in the halftone display portion where the change in the transmittance of the liquid crystal layer with respect to the applied voltage is large.

In the gradation voltage generating circuit of the third embodiment, the resistance value between the gradation reference voltage applying terminals of the series resistance division circuit 101 is set as a resistance value which is completely proportional to the potential difference between the gradation reference voltages. However, even if they are not in perfect proportion,
It goes without saying that it has a similar effect.

In each of the above embodiments, the case where the present invention is applied to the liquid crystal display device has been described. However, the present invention is not limited to this, and the present invention can be applied to all liquid crystal display devices such as liquid crystal display modules. Needless to say.

Further, in each of the above-described embodiments, the insertion position of the voltage follower circuit by the operational amplifier is described as a case where one voltage follower circuit is inserted for four resistors of the series resistance dividing circuit. Of course, the present invention is not limited to this, and it is needless to say that the series resistance dividing circuit can insert one voltage follower circuit into two or more resistors.

However, the power consumption of the drain driving circuit is reduced by reducing the output impedance by inserting the voltage follower circuit, and the power consumption is increased by the resistance for setting the voltage follower circuit and the reference voltage of the voltage follower circuit. Considering the factors, it is desirable to insert one voltage follower circuit for every 4 to 8 series resistors.

As described above, the invention made by the present inventor is
Although the present invention has been specifically described based on the above-mentioned embodiments, the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the scope of the invention.

[0087]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.

(1) Since the resistance value of each division resistor can be increased and the total resistance value of the series resistance division circuit can be increased without increasing the output impedance, the power consumption of the drain drive circuit can be reduced. .

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a schematic circuit configuration of a series resistance division circuit and a selection circuit which are gradation voltage generation circuits for one gradation reference voltage of a drain drive circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a schematic circuit configuration of a series resistance division circuit and a selection circuit which are gradation voltage generation circuits for one gradation reference voltage of a drain drive circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a schematic circuit configuration of a series resistance division circuit and a selection circuit which are gradation voltage generation circuits for one gradation reference voltage of a drain drive circuit according to a third embodiment of the present invention.

FIG. 4 is a graph showing the relationship between the voltage applied to the liquid crystal layer and the transmittance.

FIG. 5 is a block diagram showing a schematic configuration of a conventional TFT liquid crystal display device.

6 is a circuit diagram showing a schematic configuration of a grayscale voltage generation circuit of a drain drive circuit in the liquid crystal display device shown in FIG.

7 is a circuit diagram showing a schematic configuration of a series resistance division circuit and a selection circuit for one gradation reference voltage of the gradation voltage generation circuit shown in FIG.

[Explanation of symbols]

101, 605 ... Series resistance division circuit, 102, 2011-
203 ... voltage follower circuit with operational amplifier, 10
3 to 112 ... Resistor, 113 ... Selection circuit, 114 ... MOS
Transistors, 204-207 ... Voltage dividing resistors, 208-2
23 ... Dividing resistor, 601 ... Display control device, 602 ... Drain drive circuit, 603 ... Gate drive circuit, 604 ... Internal power supply circuit, 606 ... Gradient voltage generation circuit, TFT-LCD
... Liquid crystal display panel, TFT ... Thin film transistor.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasuyuki Mishima 3300 Hayano, Mobara-shi, Chiba Hitachi, Ltd. Electronic Device Division

Claims (3)

[Claims] 1. A multi-gradation gray scale voltage to be applied to a liquid crystal layer is generated by dividing the gray scale reference voltages of a plurality of gray scale reference voltages by a series resistance division circuit, and the plurality of gray scale reference voltages are generated for each of a plurality of drain signal lines. In the grayscale voltage generation circuit for outputting a predetermined grayscale voltage to each of the plurality of drain signal lines by selecting one of the grayscale voltages of multiple grayscales by a plurality of switching elements, the series resistance division A gradation voltage generation circuit, characterized in that a buffer circuit for supplying a predetermined voltage to the circuit is provided. 2. The grayscale voltage generation circuit according to claim 1, wherein the buffer circuit is a voltage follower circuit. 3. A liquid crystal display device, wherein a drain driving circuit comprises the grayscale voltage generating circuit according to claim 1 or 2.