JP3469787B2 - Liquid crystal display device and power supply circuit for driving the same - Google Patents

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 and a power supply circuit for driving the same.

[0002]

2. Description of the Related Art In a simple matrix type liquid crystal display device, five potential levels (in order of increasing level, an upper selection potential, an upper bias potential, A new driving method using a non-selection potential, a lower bias potential, and a lower selection potential has been proposed. As a power supply circuit used in this new drive system, for example, one disclosed in Japanese Patent Laid-Open No. 9-50007 is known. That is, in this publication,
Even if it is not possible to adjust the contrast of the screen by adjusting the LCD drive voltage, the bias ratio should be adjusted so that the upper and lower bias potentials remain symmetrical with respect to the non-selection potential so that the contrast of the screen can be adjusted. Bias ratio adjusting means for adjusting

[0003]

However, in the power supply circuit disclosed in the above publication, since the adjusting means is composed of a variable resistor incorporated in the resistance division circuit portion, the shading of the screen can be adjusted from an external device. There is a problem that the screen cannot be adjusted by using the signal supplied for the purpose. In addition, if the variable resistor is to be arranged at a location where it can be operated from the outside, there is a problem that noise is likely to occur due to the wiring connected to both ends of the variable resistor and to which a high voltage is applied.

In view of the above points, the present invention provides a liquid crystal display device and a power supply circuit for driving the liquid crystal display device, which are suitable for adjusting a screen using a grayscale signal supplied from an external device for screen adjustment. This is one of the challenges. Another object is to provide a liquid crystal display device and a power supply circuit for driving the liquid crystal display device, in which noise is less likely to be generated from a wiring portion for screen adjustment.

[0005]

According to the present invention, upper and lower selection potentials, a non-selection potential substantially in the middle of the upper and lower selection potentials, an upper bias potential between the upper selection potential and the non-selection potential, and the non-selection potential. A liquid crystal display that operates by receiving a plurality of voltages as a lower bias potential between the potential and the lower selection potential, and a power supply circuit that supplies the voltage of each potential to the liquid crystal display, the power supply circuit In a liquid crystal display device provided with voltage output means for outputting the upper and lower bias potentials so that the upper and lower bias potentials are symmetrical with respect to the non-selection potential, the voltage output means is externally adjusted. A terminal to which a working potential is applied and a resistance division circuit connected to this terminal are provided, and the upper and lower bias potentials are output based on the potential applied to the terminal and divided and output by the resistance division circuit. And it features.

Further, according to the present invention, an upper and lower selection potentials, a non-selection potential substantially in the middle of the upper and lower selection potentials, and an upper bias between the upper selection potential and the non-selection potential are used as driving voltages for the liquid crystal display. A power supply circuit for outputting five potential voltages, a lower bias potential between the non-select potential and the lower select potential, wherein the upper and lower bias potentials maintain symmetry with respect to the non-select potential. In a power supply circuit for driving a liquid crystal, which is provided with voltage output means for outputting the upper and lower bias potentials, the voltage output means is configured to divide the upper and lower sides based on a potential obtained by dividing an adjustment potential given from the outside. It is characterized in that the bias potential of 1 is simultaneously output.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic circuit configuration of a liquid crystal display device according to an embodiment of the present invention. As shown in the figure, the liquid crystal display device 1 includes a liquid crystal panel 2
And a liquid crystal display 4 comprising a driving circuit 3 for driving the same,
The liquid crystal display 4 is provided with a power supply circuit 5 for supplying a plurality of voltages including voltages of five potential levels, and a signal processing circuit 6 for supplying a signal for image formation to the liquid crystal display 4.

The liquid crystal panel 2 is, for example, a simple matrix type liquid crystal panel such as a TN type or STN type liquid crystal panel in which a plurality of common electrodes and segment electrodes, which are arranged to face each other with a liquid crystal layer in between, are crossed in a matrix. Can be used. The drive circuit 3 can be configured to include a common side drive unit 3a that applies a drive voltage to the plurality of common electrodes, and a segment side drive unit 3b that applies a drive voltage to the plurality of segment electrodes. This common side drive unit 3a
On the basis of a signal from the signal processing circuit 6, an upper selection potential VH or a lower selection potential VL described later is applied to a common electrode to be selected in a predetermined cycle, and a non-selection potential VM described later is applied to a common electrode that is not selected. . In addition, the segment side driving unit 3b selectively applies an upper bias potential V0 and a lower bias potential V1 described later to the segment electrodes based on the signal from the signal processing circuit 6.

The power supply circuit 5 is constructed as shown in FIG. 2, and includes a DC power supply 7 having terminals P1 and P2 for giving the maximum and minimum potential levels of the five potential levels. The terminal P1 is connected to the drive circuit 3 in order to supply the upper selection potential VH (about 40 V) for selectively scanning the common electrode of the display unit 4. The terminal P2 is an indicator 4
Lower selection potential VL (-for selectively scanning the common electrode of
It is connected to the drive circuit 3 in order to supply (about 35V). The DC power supply 7 is a DC power supply voltage VDD (3.3) supplied from an external device connected to the liquid crystal display device 1.
Voltage converter for converting V) into a voltage, for example, three-output type DC
It can be configured by the / DC converter 8. D
The C / DC converter 8 is also configured to output the driving power supply voltage VLCD of an operational amplifier or the like from the terminal VLCD. When the DC / DC converter 8 is not used, the upper / lower selection potentials VH and VL can be directly supplied to the terminals P1 and P2 from an external device.

A series circuit of resistors R1 and R2 is connected between the terminals P1 and P2 of the DC power supply 7. Resistors R1 and R2
Is set to have substantially the same resistance value in order to obtain an approximately intermediate potential between the upper and lower selection potentials VH and VL, and the potential at the connection point P3 is taken out as the non-selection potential VM via the operational amplifier OP1 connected in the voltage follower. Be done. This non-selection potential VM is set to a potential of 2.5V.

In the power supply circuit 5, of the five potential levels, the remaining two potential levels located between the upper and lower selection potentials VH and VL and the non-selection potential VM are externally supplied with a control signal VCON. A variable bias voltage output means is provided for changing and outputting in a vertically symmetrical manner with respect to the non-selection potential VM as a reference.

This variable bias voltage output means includes a resistor R
An operational amplifier OP2 in which a terminal P4 to which a signal VCON for image density adjustment is externally applied is directly or voltage follower-connected to a resistor division circuit 9 in which 3 and R4 are connected in series.
And the potential at the division point P5 of the resistance division circuit 9 is output as the lower bias potential V1 through the operational amplifier OP3 connected in the voltage follower, while the non-selection potential VM is selected.
An inverting amplifier 10 is connected between the terminals P3 and P5 so as to obtain an upper bias potential V0 that keeps symmetry with respect to.

A signal V given from an external device to the terminal P4
The potential level of CON is 1.8 when adjusting the screen density.
It fluctuates in the range of 0.8 to 2.8 V centering on the DC voltage of V. The resistors R3 and R4 are set so that their ratio falls within the range of about 1: 1 to 3: 2. Therefore, the lower bias potential V1 fluctuates in the range of about 0.3 to 1.4 V with reference to around 0.8 V by the signal VCON given from the external device.

In the inverting amplifier 10, the lower bias potential V1 (division point P5) is based on the non-selection potential VM (connection point P3).
Is input to output the inverted output as the upper bias potential V0, the operational amplifier OP4 and the feedback resistors R5 and R5.
6 are connected and configured. That is, the resistors R5 and R6
Is connected between the output terminal of the operational amplifier OP4 and the division point P5 of the resistance dividing circuit 9, and the connection point of the resistors R5 and R6 is connected to the inverting input terminal of the operational amplifier OP4 to form the resistance R1.
The connection point P3 of R2 is connected to the non-inverting input terminal of the operational amplifier OP4. Here, the resistance values of the resistors R5 and R6 are set to the same value and the amplification factor of the inverting amplifier 10 is set to -1 so that the upper and lower bias potentials V0 and V1 vary with symmetry with respect to the non-selection potential VM. is doing. Therefore, when the lower bias potential V1 is 1V, the upper bias potential V0 becomes 4V, and when the lower bias potential V1 is changed to 0.5V, the upper bias potential V0 is changed to 4.5V in conjunction with it. . The change of the upper and lower bias potentials V0 and V1 is performed independently of the upper and lower selection voltages VH and VL.

It should be noted that the resistor R3 which constitutes the resistance division circuit 10
In addition to the resistor R10, the thermistor R7 and the resistor R8 are provided as necessary to compensate for variations in liquid crystal characteristics due to temperature.
It is also possible to include a parallel circuit of. Further, the resistor R3 may include a variable resistor R9 (adjustable only during the assembling work), if necessary, in order to enhance the adjusting workability during the assembling work.

Since the liquid crystal display device 1 constitutes the power supply circuit 5 as described above, the signal VCON applied from the outside to the terminal P4 is maintained while the voltage between the terminals P1 and P2 of the DC power supply 7 is kept constant. The upper and lower bias potentials V0 and V1 can be easily changed only by changing the potential level.
As described above, by changing the upper and lower bias potentials V0 and V1 applied to the segment side drive unit 3b while keeping the upper and lower selection potentials VH and VL and the non-selection potential VM applied to the common side drive unit 3a constant. The screen density of the liquid crystal panel 2 can be adjusted while changing the bias ratio for driving the liquid crystal.

Particularly, as the variable bias voltage output means for changing the upper and lower bias potentials V0 and V1 symmetrically with respect to the non-selection potential VM, the potential of the resistor division circuit 9 and its division point P5 is set to the non-selection potential VM. Since the configuration includes the inverting amplifier 10 that inverts with reference to
Problems of the conventional method in which a variable resistor is placed between R2 and R2,
That is, it is possible to solve problems such as the need to dispose the variable resistor at a position where it can be operated from the outside and the point that noise easily occurs due to the wiring to the variable resistor.

[0019]

As described above, according to the present invention, it is possible to provide a liquid crystal display device suitable for adjusting a screen using a signal supplied from an external device and a power supply circuit for driving the liquid crystal display device. Further, it is possible to provide a liquid crystal display device having a structure in which noise is less likely to be generated from the screen adjustment wiring portion and a power supply circuit for driving the liquid crystal display device.

[Brief description of drawings]

FIG. 1 is a circuit block diagram according to an embodiment of a liquid crystal display device of the present invention.

FIG. 2 is a circuit diagram of a power supply circuit portion of the embodiment.

[Explanation of symbols]

2 LCD panel 3 drive circuit 4 liquid crystal display 5 power supply circuit 7 DC power supply 8 DC / DC converter 9 resistance division circuit 10 Inverting amplifier

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02F 1/133 G09G 3/18 G09G 3/36

Claims (2)

(57) [Claims] 1. An upper and lower selection potentials, a non-selection potential substantially in the middle of the upper and lower selection potentials, an upper bias potential between the upper selection potential and the non-selection potential, and a non-selection potential and the lower selection potential. A liquid crystal display that operates by being supplied with a plurality of voltages as a lower bias potential, and a power supply circuit that supplies a voltage of each potential to the liquid crystal display. In a liquid crystal display device provided with voltage output means for outputting the upper and lower bias potentials so as to maintain symmetry with respect to the non-selection potential, the voltage output means includes a terminal to which an adjustment potential is applied from the outside, A liquid crystal display device comprising: a resistance division circuit connected to the terminal, and outputting the upper and lower bias potentials based on a potential applied to the terminal and divided and output by the resistance division circuit. 2. An upper and lower selection potentials, a non-selection potential approximately in the middle of the upper and lower selection potentials, an upper bias potential between the upper selection potential and the non-selection potential, as a driving voltage of the liquid crystal display,
A power supply circuit for outputting a voltage of five potentials of a lower bias potential between the non-selection potential and the lower selection potential, wherein the upper and lower bias potentials are symmetrical with respect to the non-selection potential. In a power supply circuit for driving a liquid crystal, which is provided with voltage output means for outputting upper and lower bias potentials, the voltage output means is configured to divide the upper and lower bias potentials based on a potential obtained by dividing an adjustment potential supplied from the outside. A power supply circuit for driving a liquid crystal, which is configured to output potentials simultaneously.