JPS61249094A - Drive circuit for liquid crystal display unit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a drive circuit for a liquid crystal display device that can be used in liquid crystal television receivers and the like.

BACKGROUND OF THE INVENTION In recent years, blurred double-sided LCD televisions have been released. In a liquid crystal television receiver, a switching element of a field effect transistor is provided at a position corresponding to the pixel of a liquid crystal display panel configured in a matrix or spiral shape, and an input signal and a switching signal are applied to this switching element. Connect one electrode of the The opposing electrodes of the liquid crystal are commonly connected to form a common electrode to which a common voltage is applied. Since the liquid crystal panel requires alternating current driving, the polarity of the input signal and common voltage applied to the liquid crystal is reversed for each field.

The conventional liquid crystal display device will be explained below with reference to the drawings.

A specific example of the drive circuit for this device will be explained.

A liquid crystal display device with a matrix is shown in FIG.

In the figure, 1 is a liquid crystal cell, 2 is a storage capacitor,
3 is a field effect transistor, and these three elements constitute one picture element. 4 is an X electrode to which a switching signal is applied, and 5 is a Y electrode to which a video signal is applied.

6 is a common electrode to which a common voltage is applied.

FIG. 3 shows details of a portion constituting one picture element in FIG. 2. In FIG. 3, 1 to 6 are the same as those explained in FIG. 2, and 7, 8.9 are capacitances CGSνCGD gCDs between the respective electrodes of the field effect transistor. Y electrode 5
A video signal whose polarity is inverted every field as shown in 10 in FIG. 4 is applied to the common electrode 6, and a common voltage whose voltage value is inverted every field as shown in 11 in FIG. 4 is applied to the common electrode 6. There is. These switching signals are applied to the X electrode 4 and are applied to both ends of the liquid crystal cell 1 when the field effect transistor 3 is turned on. The switching signal turns on the field effect transistor 3 for IH (63,5 μ5 ec) and turns it off for 1 field (16,7 m5 eC). The storage capacitor 2 retains the charge charged during this on time during the off time. Furthermore, in the next field, the voltage applied to the liquid crystal cell 1 has the opposite polarity, making it possible to drive the liquid crystal panel with alternating current.

Next, FIG. 6 shows a circuit for inverting the video signal and common voltage. In FIG. 6, reference numeral 12 is a VT multiplied signal input terminal that changes high/low level for each field, and the video signal input to this vT multiplied signal video input terminal 13 and v
The polarity and voltage value of the vl and v2 voltages obtained by resistance-dividing cc by resistors R3, R4, and R6 are changed for each field by inverting circuits 14 and 15. That is, the polarity of the video signal is inverted for each field and outputted to the video output terminal 16, and becomes an input signal to the Y electrode 3 in FIG. 3 via the Y driver. In addition, the vl and v2 voltages are output to the common voltage terminal 17 as voltages that change every field,
It is applied to the common electrode 6 in FIG.

Problems to be Solved by the Invention However, the conventional configuration as described above has the following serious problems.

As shown in FIG. 3, there is an interelectrode capacitance CG57 between the electrodes of the field effect transistor 3. CGD3. Since there are C3D9 and the capacitance of the storage capacitor varies in value when manufacturing the panel, the relationship between the video signal applied to the liquid crystal and the common voltage is correct. That is, a reverse voltage is applied to the liquid crystal for each field, making it impossible to perform AC driving.

In view of the above problems, the present invention provides a circuit that can easily adjust the relationship between the video signal and the common voltage to a predetermined relationship.

Means for Solving the Problems In the present invention, the DC level of the video input signal applied to the liquid crystal panel is changed simultaneously by the same amount in the same direction.

Function: With this configuration, the relationship with the common voltage can be adjusted accurately at all times, making it possible to accurately drive the liquid crystal panel with alternating current, thereby improving the performance and extending the life of the liquid crystal panel. FIG. 1 is a circuit diagram showing an embodiment of a driving circuit for a liquid crystal display device according to the present invention. In FIG. 1, 12 is a vT times signal input terminal that changes high/low level for each field, and this V7 signal connects the video signal input to the video input terminal 13 and vcc to resistors R3, R4, R5 ( 7) The polarity and voltage value of the voltage obtained by resistor division are changed by inverting circuits 14 and 15 for each field.

Here, the video signal whose polarity has been inverted by the inversion circuit 14 is taken out by the emitter follower of the transistor Q1, and is connected via a resistor R1 to a current source composed of a transistor Q2 and a variable resistor VR. By changing the current of this current source, the DC level of the video signal can be changed simultaneously by the same amount in the same direction. In other words, the emitter current of transistor Q1 is changed to 1. The emitter current of transistor Q2 is Io, and the current flowing through resistor R2 is calculated. If the voltage at the video output terminal 16 is vo and the emitter voltage of the transistor Q1 is vE, then the current factor of the current source is as follows. By changing , it is possible to simultaneously change the DC level of the video signal whose polarity has been inverted by the same amount in the same direction.

As described above, according to the present invention, the DC level of the video signal whose polarity has been inverted can be changed by the same amount in the same direction at the same time.
The relationship between the common voltage and the video signal can always be adjusted accurately.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a driving circuit of a liquid crystal display device according to an embodiment of the present invention, FIG. 2 is a configuration diagram of the matrix type liquid crystal display device, and FIG. 3 is a circuit diagram of the multi-IJ Fuchs liquid crystal display device. FIG. 4 is a diagram of the voltage waveform applied to the liquid crystal panel, and FIG. 6 is a circuit diagram of a drive circuit of a conventional liquid crystal display device. 12... Pulse input terminal whose polarity is inverted every field, 13... Video signal input terminal, 1
6...Video signal output terminal, 17...Common voltage output terminal. Name of agent: Patent attorney Toshio Nakao and 1 other person12
... 174-rut °° 4 Himoto rate 1st rate 16 ..., gorge output) 1st Figure 77...Common 4 output riko Figure 2 @35! I 5 Figure 4 1 field

Claims (1)

[Claims] A switching element is provided on the liquid crystal panel, a switching signal is applied to the first electrode of the switching element, an input signal is applied to the second electrode of the switching element, and one electrode of the liquid crystal is connected to the third electrode of the switching element. The other electrode serves as a common terminal to which a common voltage is applied, and this common voltage and the input signal are inverted at a constant cycle, and the DC level of the input signal whose polarity has been inverted is simultaneously the same in the same direction. A driving circuit for a liquid crystal display device, characterized in that only the amount is changed.