JPH02203318A - Driving circuit for matrix type liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the contrast of the display device and to reduce electric power consumption by comparing an input signal level and the voltage level of a video signal output section based on the output video signal level in previous scanning and controlling an input signal level. CONSTITUTION:The output voltage VG of a differential amplifier 1 changes cooperatively with the level of the input video signal. The gate of an output transistor (TR) 10 is controlled by the voltage VG and a discharge current i01 flows when the voltage VG is larger than the voltage VOUT of an output line 9. As a result, the voltage VOUT is increased up to the voltage equal to the input voltage VIN of the amplifier 1. On the other hand, a drain current flows in the TR 10 and an output transistor 12 is turned on so that a discharge current i02 flows if the voltage VG is smaller than the voltage VOUT. As a result, the voltage VOUT is lowered until the voltage VOUT equals to the voltage VIN. The contrast of the display device is improved in this way and the electric power consumption is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a drive circuit for a matrix type liquid crystal display device.

(Prior Art) Due to rapid advances in design technology and manufacturing technology in recent years, matrix-type liquid crystal display devices are achieving display quality comparable to that of CRTs. The matrix type liquid crystal display device is
Because it has excellent characteristics such as being thin and lightweight and having low power consumption, it is expected to be used in a wide range of applications, such as the display part of television receivers and display devices for information devices such as personal computers. There is.

FIG. 3 schematically shows an example of a conventional matrix type liquid crystal display device. The matrix type liquid crystal display device shown in FIG. 3 uses T F T as a switching element for driving picture elements.
(Th1n Film TransiStor). In addition to the switching elements, MO
A TFT liquid crystal panel 100 as a 0 display unit that can use an S transistor or the like includes picture elements 103 arranged in a matrix of 0 rows and m columns. In FIG. 3, a plurality of picture elements 103 arranged in a row in the horizontal direction
The horizontal scan lines of the book are constructed. A TPTIO4 is provided near each picture element 103, and the drain electrode of the TFT 104 is connected to the tf! of the picture element 103. It is connected to the. A common counter electrode 105 is arranged between the electrodes of all the picture elements 103. In the TFT liquid crystal panel 100, n scanning electrodes 101 are arranged in parallel. jth scan'': 4f
Ifi 101 is connected to the gate electrode of TFT 104 corresponding to pixel 103 of the j-th horizontal scanning line, and m signal electrodes 102 are arranged in parallel so as to be perpendicular to scanning electrode 101 . The source electrode of the i-th TPT 104 is connected to the pole 102 of the first signal.

The TFT liquid crystal panel 100 includes a gate driver (vertical scanning means) 200 and a source driver (video signal output means) 3
It is driven by a drive circuit including 00. The gate driver 200 and the source driver 300 are the TFT panel 10
0 scanning type 1101 and signal electrode 102, respectively.

The video signal is input to source driver 300.

Control signals such as a scanning pulse input to the gate driver 200 and a sampling clock input to the source driver 300 are provided from a control circuit not shown.

The display operation in the matrix type liquid crystal display device of FIG. 3 will be explained with reference to FIG. 4. The gate driver 200 is
As shown in FIG. 4, the scanning f!
A gate-on signal is sequentially applied to 101. That is, the gate driver 200 scans the horizontal scanning lines in a predetermined order. A time T8 is allocated to scanning one horizontal scanning line.

When the j-th horizontal scanning line is scanned, the TFT 104 connected to the j-th scanning electrode 101 is turned on. The source driver 300 samples the input video signal at a predetermined sampling frequency, and outputs the video signal as a signal ti102 in synchronization with the output of the gate-on signal by the gate driver 200. Therefore, the TFT 104 in the on state
A video signal is written to the picture element 103 via the pixel 103. Picture element 1
The signal written in 03 is the time T until the next write.
, is maintained for a period of .

The write operation by the above-mentioned conventional drive circuit will be explained in more detail. FIG. 5 shows a circuit diagram of an output stage of an example of the source driver 300. The circuit in FIG.
It corresponds to 2.

The video signal is accumulated in the sampling capacitor C5□2 by inputting the sampling pulse. When writing a video signal to the picture element 103, as shown in FIG.
The signal is brought to a high level, thus transistor 303
The signal electrode 103 is discharged through the zero-order transfer (
TRF) signal is set to high level, and the sampling capacitor Cgs. The signal stored in is transferred to the hold capacitor CH and output to the signal electrode 102 connected to the output line 306 via an output circuit including a differential amplifier 301 and an output transistor 302. Transistor 305 functions as a load. At the same time that the TRF signal is set to high level, the TF corresponding to any of the scanning electrodes 101 is activated by the gate driver 200 described above.
The picture element 103 connected to the TFT 104 in which T104 is turned on and the video signal on the signal electrode 102 is turned on.
will be written to.

(Problems to be Solved by the Invention) In the conventional drive circuit described above, as can be seen from the circuit diagram shown in FIG. Since there was no means for lowering the voltage of the signal electrode 102 when the voltage was low, it was necessary to discharge the signal electrode 102 using the DIS signal prior to writing.

As can be seen from Fig. 6, the presence of the DIS signal indicates that the picture element 1
03, thus reducing the writing time to pixel 103.
This has been an obstacle to improving the charging degree of the liquid crystal display device, and has also become an obstacle to improving the contrast of the liquid crystal display device.

Furthermore, since all the signal electrodes 102 are simultaneously discharged by the DIS signal, a large discharge current flows through the source driver 300 at that time. Furthermore, since discharging by the DIS signal is performed during scanning of each horizontal scanning line, the power consumption of the source driver 300 increases.

The present invention was made in view of the current situation, and
The object is to provide a drive circuit for a matrix type liquid crystal display device that does not require the DIS signal, improves the contrast of the display device, and reduces power consumption.

(Means for Solving the Problems) A drive circuit for a matrix type liquid crystal display device of the present invention is a driving circuit for a matrix type liquid crystal display device having a display unit in which a plurality of picture elements are arranged in a matrix. A drive having a vertical scanning means for scanning the unit for each horizontal scanning line, and a video signal outputting means for outputting a video signal to the display unit via an output section every time the vertical scanning means scans a horizontal scanning line. a circuit, wherein the video signal output means compares an input signal level with a voltage level of the output section of the means based on an output video signal level in a previous scan; If the voltage level is higher than the voltage level, the voltage level is raised to substantially the input signal level; if the input signal level is lower than the voltage level, the voltage level is lowered to substantially the input signal level. An output signal control means is provided, whereby the above object is achieved.

(Example) The invention will now be described with reference to examples.

The drive circuit of this embodiment includes a gate driver and a source driver, similar to the conventional drive circuit shown in FIG. FIG. 1 shows a circuit diagram of the output stage of the source driver. An input line 6 into which a video signal is input is connected to a non-inverting input terminal of a differential amplifier 1 via two gates 7 and 8. There is. The input line 6 has the same circuit as shown in FIG.
A sampling capacitor C□ and a hold capacitor CH are connected. , the output line 13 of the differential amplifier 1 is connected to the gate of the output transistor 2. An output signal is taken out from the source of the output transistor 2 via an output line 9. Output line 9 is connected to the inverting input terminal of differential amplifier 1. Power supply and output line 13 of differential amplifier 10
A transistor 10 is arranged between the two. The gate of transistor 10 is connected to output line 9. Transistor 10 connects the output signal level VQ of differential amplifier 1 and the signal level V on output line 9. This is for comparison with U. An output control transistor 11 is arranged between the power supply and ground. The gate of transistor 11 is connected to the drain of transistor 10. Another output transistor 12 is arranged between the source of the output transistor 2 and ground. The gate of output transistor 12 is connected to the source of transistor 11.

The operation of the circuit shown in FIG. 1 will be explained. As for the video signal, when the sampling pulse is input to the gate 7, the 0th order transfer (TRF) signal stored in the sampling capacitors C and MP is made high level, and the signal stored in the sampling capacitor C30 is held. The signal is transferred to the capacitor CH and is also input to the differential amplifier 1. Since the differential amplifier 1 operates as a non-inverting amplifier, the output voltage v0 of the differential amplifier 1 changes substantially in conjunction with the level of the input video signal.

The voltage ■ is the voltage V of the output line 9. If U, the voltage V. The gate of output transistor 10 is controlled by , and charging current to+ flows.

As a result, the voltage V0. Y is raised until it becomes equal to the input voltage VIN of the differential amplifier 1. At this time, transistors 10, 11 and 12 are off.

On the other hand, the voltage V is the voltage V. , if it is smaller than T, then
A drain current flows through the transistor 10, and the output control transistor 11 is controlled by the drain voltage of the transistor 10.
The gate of transistor 11 is controlled, and a drain current flows through transistor 11. Therefore, the output transistor 12 is turned on, and the free current io2 flows. As a result, the voltage v08. is lowered until it becomes equal to the voltage v1.

In this way, the drive circuit of this embodiment eliminates the need for discharging the signal electrodes using the DIS signal, which was conventionally required. As shown in FIG. 2, if the drive circuit of this embodiment is used, - the time T allocated for scanning the horizontal scanning line
, can all be used for writing to picture elements. Therefore, the charge level of the picture element is increased compared to the conventional method,
The contrast of the display device is improved. Moreover, the current associated with the above-mentioned discharge is eliminated, and the required currents are the input voltage V1H and the output voltage V. Since it is only for filling the difference with U7, the power consumption of the display device including the drive circuit is greatly reduced.

(Effects of the Invention) According to the present invention, a drive circuit for a matrix type liquid crystal display device is provided, which can improve the contrast of the display device and reduce power consumption.

In the field of matrix-type liquid crystal display devices, it is thought that larger display screens and higher definition will be pursued in the future. Along with this, the writing time for picture elements will have to be further shortened.Furthermore, as the screen becomes larger, the source capacitance and gate capacitance within the display panel will increase, increasing the signal delay time. Taking these into account, it is thought that the conditions for writing to picture elements will become increasingly strict.The present invention is extremely effective in such situations.

As the resolution of screens increases, the number of signal extraction terminals increases, so high-density packaging technology is considered to be necessary. COG is seen as a promising technology for high-density packaging, but
The reduction in power consumption achieved by the present invention is also very effective in realizing high-density packaging using COG.

,...'s t=day FIG. 1 is a circuit diagram of the output stage of a source driver in an embodiment of the present invention, FIG. 2 is a timing chart for explaining the operation of the embodiment, and FIG. 3 is a timing chart for explaining the operation of the embodiment. A diagram schematically showing an example of a conventional matrix type liquid crystal display device, FIG. 4 is a timing chart of a gate-on signal in the matrix type liquid crystal display device, and FIG. 5 is a drive diagram for the conventional matrix type liquid crystal display device. A circuit diagram of an output stage of an example of a source driver in the circuit, and FIG. 6 is a timing chart for explaining the operation of the drive circuit having the source driver of FIG. 5.

DESCRIPTION OF SYMBOLS 1... Differential amplifier, 2.12... Output transistor, 6... Input line, 9... Output line, 10... Comparison transistor, 11... Output control transistor, 10
0...TFT liquid crystal panel, 101...Scanning tf! ,
102...Signal electrode, 103...Picture element, 104...
・TPT, 200... Gate driver, 300...
source driver.

Figure 3 that's all

Claims (1)

[Scope of Claims] 1. Vertical scanning means for scanning the display unit for each horizontal scanning line, for a matrix type liquid crystal display device having a display unit in which a plurality of picture elements are arranged in a matrix; A drive circuit comprising a video signal output means for outputting a video signal to the display unit via an output section every time a horizontal scanning line is scanned by the scanning means, the video signal output means having an input signal level and a predetermined level. a comparison means for comparing the voltage level of the output section of the means based on the output video signal level in the scanning of the input signal; and if the input signal level is higher than the voltage level, the voltage level is substantially lowered to Raise the signal level to
A driving circuit for a matrix type liquid crystal display device, comprising output signal control means for reducing the voltage level substantially to the input signal level if the input signal level is lower than the voltage level.