JP3235893B2 - Drive circuit for liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit suitable for an XY matrix type liquid crystal display device, particularly a COG type liquid crystal display device.

[0002]

2. Description of the Related Art A liquid crystal display device has the characteristics that it can be driven at a low voltage and has low power consumption, and is widely used in various applications as a display device replacing a CRT. As the driving method, an active matrix method in which a switching element is provided for each pixel,
There is an XY matrix method in which a liquid crystal cell in which an X-axis electrode group and a Y-axis electrode group are superimposed is driven in a time-division manner, but the latter is advantageous in that the manufacturing yield is good and the manufacturing process is relatively simple. The method is becoming mainstream.

In such an XY matrix type liquid crystal display device, it is necessary to increase the number of electrodes in order to enlarge the screen and increase the amount of display information, and accordingly, the bias voltage applied to each electrode must be increased. The display quality is likely to deteriorate due to the fluctuation. In order to solve this problem, various proposals have been made to improve the bias power supply section for obtaining a predetermined drive voltage by dividing the power supply voltage by a resistor, and to stabilize the output voltage (for example, Japanese Patent Application Laid-Open No. 61-1986). -159694,
See JP-A-61-162028).

[0004]

However, in the case of a COG type liquid crystal display device in which a driving semiconductor element such as an IC is directly mounted on a substrate constituting a liquid crystal cell, it is necessary to arrange fine wiring on the substrate. When the size of the liquid crystal display device is increased, the resistance of these wirings is inevitably increased to a level that cannot be ignored. Therefore, it is difficult to supply the voltage Vop necessary for obtaining the highest contrast ratio to the driving semiconductor element due to the voltage drop due to the resistance of the wiring, and to stabilize the voltage on the power supply side as proposed in the above-mentioned publication. However, there arises a problem that good display quality cannot be ensured only by the conversion. As a countermeasure against this, it is conceivable to set the output voltage on the power supply to a higher value in consideration of the voltage drop. It is very difficult to keep the driving voltage constant.

The present invention has been made in view of this point, and has been made to stabilize the driving voltage of the driving semiconductor element with a relatively simple circuit configuration.

[0006]

According to the present invention, an X-axis electrode group and a Y-axis electrode group are formed by two substrates.
An XY matrix type liquid crystal cell is formed by superimposing the axis electrode group, a plurality of driving semiconductor elements are arranged on the substrate along the outer periphery of the liquid crystal cell, and are formed on the substrate on the outer periphery of the liquid crystal cell by routing. A liquid crystal display device configured to drive a liquid crystal cell in a time-division manner by supplying a bias voltage generated by a bias power supply unit through the input wiring to the driving semiconductor element. And a feedback circuit connected to the input wiring in the vicinity of the other and connected to the inverting input terminal of the operational amplifier of the bias power supply section.

[0007]

The voltage actually applied to the driving semiconductor element is fed back to the operational amplifier of the bias power supply section by the feedback circuit, so that a stable driving voltage is always supplied to the driving semiconductor element by removing the influence of the wiring resistance. And good display quality can be obtained.

[0008]

Next, one embodiment shown in the drawings will be described. In FIG. 1, reference numeral 1 denotes a COG liquid crystal display device, and 2 and 3
Is a substrate constituting the liquid crystal display device 1, 4 and 5 are driving semiconductor elements (for example, ICs) mounted on the substrate 3, the element 4 is used as a signal driver, and the element 5 is used as a scanning driver. Things. Reference numeral 6 denotes an input wiring for a bias voltage formed on the substrate 3, reference numeral 7 denotes a feedback wiring similarly formed on the substrate 3, and reference numeral 8 denotes a flexible printed circuit board for connection.

Reference numeral 11 denotes a well-known bias power supply for generating six levels of bias voltages; 12, a divided resistance circuit in which a plurality of resistors are connected in series to divide the power supply voltage; 13, an operational amplifier; Is a connector cable having an output wiring 14a of the operational amplifier 13 and a feedback wiring 14b to the operational amplifier 13.
4b is connected to the input wiring 6 and the return wiring 7 of the liquid crystal display device 1 via the flexible printed circuit board 8, respectively. Reference numeral 15 denotes a feedback circuit formed by the feedback wiring 7 and the feedback wiring 14b.
And the inverting input terminal 13a of the operational amplifier 13
Are connected to each other. R ₁ indicates the entire equivalent resistance of the output wiring 14 a and the input wiring 6, and R ₂ indicates the entire resistance of the feedback wiring 14 b and the feedback wiring 7, that is, the equivalent resistance of the feedback circuit 15.

Although FIG. 1 shows only one input wiring of the signal-side bias voltage, the others are omitted to avoid complicating the drawing and making it difficult to understand. Actually, the same wiring is performed for all the other bias potentials of the driving semiconductor elements 4.

[0011] This embodiment is constructed as described above, even if the resistance component R ₁ to the wiring, divided parts of the potential and resistance division circuit 12 for taking out a feedback voltage input wirings 6 by feedback by the feedback circuit 15 The potentials at the points can be equalized. For this reason, the bias voltage supplied from the input wiring 6 to the driving semiconductor element 4 is kept constant, and a stable voltage at which the highest contrast is obtained is supplied irrespective of a change in display pattern or a change in temperature, thereby improving display quality. It is possible to keep it in a good state.

[0012]

As is apparent from the above embodiments, the present invention relates to a driving circuit for driving an XY matrix type liquid crystal display device in a time-division manner, in which a voltage of an input wiring of a bias voltage to a driving semiconductor element is reduced. A feedback circuit is provided for feeding back to the inverting input terminal of the operational amplifier of the bias power supply unit. Therefore, even if the input wiring is formed by arranging fine wiring on the substrate and the input wiring is long to such an extent that the resistance of the wiring cannot be ignored, as in the case of a COG type liquid crystal display device, for example, the feedback The potential of the input wiring for extracting the voltage and the potential of the divided resistance end of the power supply circuit are kept equal, and a stable bias voltage can be applied to the driving semiconductor element. The display quality of the liquid crystal display device can be improved. In addition, this makes it possible to supply a voltage very close to the optimum bias voltage obtained by the theoretical formula to the driving semiconductor element, which is advantageous in designing a liquid crystal display device.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 4, 5 Driving semiconductor element 6 Input wiring 7 Feedback wiring 11 Bias power supply 13 Operational amplifier 13a Inverting input terminal 14b Feedback wiring 15 Feedback circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/133 520 G02F 1/1345 G09G 3/36

Claims (1)

(57) [Claims] An X-axis electrode group and a Y-axis electrode group are overlapped by two substrates to form an XY matrix type liquid crystal cell, and a plurality of driving semiconductor elements are provided on the substrate along the outer periphery of the liquid crystal cell. The liquid crystal cell is driven in a time-division manner by supplying a bias voltage generated by a bias power supply unit to the driving semiconductor element via an input wiring formed on a substrate on the outer periphery of the liquid crystal cell. In the liquid crystal display device configured as described above, a feedback circuit having one end connected to the input wiring near the driving semiconductor element and the other end connected to the inverting input terminal of the operational amplifier of the bias power supply unit is provided. A driving circuit for a liquid crystal display device, comprising: