JPH09292596A - Liquid crystal driving power source circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent distortion in a waveform and deterioration in picture quality by voltage dividing between plural source potential and switching an operational amplifier circuit receiving its output voltage and charge driving a liquid crystal display element with the operational amplifier circuit receiving the output voltage and discharge driving the liquid crystal display element at the prescribed timing. SOLUTION: Resistors R potential divide between a plus side power source V0 and a minus side power source VEE, and operational amplifiers OAa, OAb impedance convert the divided voltage to supply liquid crystal element driving power sources (V1, V2a, V2b, V3, V4, Va, V5b). A selector circuit SEL controlled by a timing generation circuit TM switches the operational amplifiers OAa, OAb at the switch timing considering directions of charge/discharge for liquid crystal load capacity related to the voltages V2b, V5b to output the voltages V2b, V5b. Thus, the distortion in the waveform and the deterioration in the picture quality due to the drive power shortage of the power source are prevented even in a display device, etc., with large capacity of liquid crystal material.

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 more particularly to a liquid crystal driving power supply circuit suitable for a medium- or large-sized dot matrix type liquid crystal display device having a large time division number (duty).

[0002]

2. Description of the Related Art Referring to FIG. 6, a conventional liquid crystal drive circuit divides a liquid crystal voltage in the liquid crystal drive circuit by a voltage difference between a plus side power source (for example, + 10V) and a minus side power source (for example, 0V) by an internal resistance. The liquid crystal drive voltage is obtained by directly compressing the voltage and then performing impedance conversion using a voltage follower type operational amplifier.

Such a conventional liquid crystal drive circuit is disclosed in, for example, Japanese Patent Application Laid-Open No. 5-273932. With this conventional circuit configuration, when driving a medium-sized or large-sized liquid crystal display element, the driving capability of each operational amplifier is increased and used.

[0004]

However, the conventional circuit configuration has the following problems.

(1) As the number of liquid crystal display elements increases, the driving capability of the power source is required accordingly, so that it is necessary to increase the driving capability of each operational amplifier, resulting in a large current consumption.

(2) Generally, a liquid crystal element enables display by applying a voltage between a common electrode and a segment electrode, but the common electrode is common when the number of segments, that is, the number of display rows, increases. Therefore, the load capacitance applied to each common (because the liquid crystal element is a capacitive load) becomes large, but as shown in FIG.
Regarding the nth common, the discharge charge from the liquid crystal load is larger than that from the 1st to (n-1) th commons. As a result, considering the driving capability of the nth common, both charging and discharging abilities are There is a problem in that it is necessary to use an operational amplifier that has it, and power consumption cannot be reduced as much as possible.

[0007]

A liquid crystal driving power supply circuit of the present invention includes a resistance voltage dividing circuit having a plurality of resistors for dividing a voltage between a first power supply potential and a second power supply potential, and the resistance dividing circuit. A first operational amplifier circuit that receives the output voltage of the voltage circuit as an input and charges and drives the liquid crystal display element; and a second operational amplifier circuit that receives the output voltage of the resistance voltage divider circuit as an input and discharges and drives the liquid crystal display element; The configuration includes a first switch circuit that switches the first operational amplifier circuit and the second operational amplifier circuit at a predetermined timing, and a timing circuit that controls the first switch circuit.

It is also possible to have a second switch circuit that receives the output voltage of the resistance voltage dividing circuit and switches the supply level voltage of the resistance voltage dividing circuit by the timing circuit.

Furthermore, the liquid crystal driving power supply circuit of the present invention may be arranged such that the first switch circuit and the second switch circuit operate in synchronization with each other by the timing circuit.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings.

Referring to FIG. 1, the liquid crystal driving power supply circuit according to the present embodiment has a plus power supply V0 and a minus power supply VE.
A resistor R for dividing the potential between the two power supplies of E and a power source for driving the liquid crystal element (V1, V2a, V2b, V3, V4, Va, V5b) by impedance conversion of the divided voltages.
The operational amplifiers (OAa, OAb) for supplying 7 levels are provided. Further, regarding the voltages V2b and V5b, the amplifiers OAa and OAb are switched at the switching timing (common n-th waveform edge shown in A and B) in consideration of the charge / discharge direction with respect to the liquid crystal load capacitance as shown in FIG. , V5b respectively output selector circuit SEL
And a timing generation circuit TM for controlling the selector circuit SEL. Correspondence between each reference voltage (V1 to V6) and common is, for example, in the liquid crystal device having the duty number n, the first to (n-1) th commons are voltages V1, V2a and V5.
a, V6 levels are selected, and the nth common is the voltage V
1, V2b, V5b, V6 levels will be selected.

Next, the setting of the resistor R on the circuit will be described. First, the resistor R basically simply divides the voltage between the power sources V0 to VEE, and a resistor with a large constant is selected to reduce the current value. . The resistor R'is an operational amplifier (OA
a or a constant substantially equal to the impedance of OAb) is selected to make the overall balance uniform.

The resistor R "is a resistor that determines the value of the current flowing in the low current circuit in each operational amplifier, and a large resistor of several hundreds KΩ is selected in order to reduce the overall current consumption.

Regarding the pulse widths ts and th shown in FIG. 2, considering the response times of the segment and common outputs,
By setting the time to about several tens of μs, it takes a sufficient time so that the display is not affected by the timing shift.

Next, a second embodiment of the present invention will be described with reference to FIGS.

With reference to FIG. 4, in this embodiment, a resistor R'for adjusting the first power supply potential V0 to the level voltage V1.
And a selector circuit SEL2 for switching between two output voltages of the resistance divider circuit
The configuration is the same as that of the first embodiment, and the same components are designated by the same reference numerals.

The timing circuit TM of this embodiment has an output 0 for driving the selector circuit SEL1 as shown in FIG.
1 and the output 02 for driving the selector circuit SEL2 are output in synchronization with each other to output the liquid crystal display drive voltage (V1 to V
6) outputs the waveforms shown in FIG. 5 by switching the selector circuits SEL1 and SEL2, respectively.

The second embodiment of the present invention has a circuit configuration for adjusting the voltage V0, that is, the positive power supply potential V0.
Is supplied from the inside or the outside as the high-voltage power supply VDD, it is not necessary to perform impedance conversion using the operational amplifier circuit OAa. Therefore, the operational amplifier circuit OAa of the output level V1 becomes unnecessary. Further, the operational amplifier OAa for inputting the output level V2a and the operational amplifier OAa for inputting the level V4 are not selected at the same time and can be shared, and the operational amplifier OAb for inputting the output level V5 and the output level are input. The operational amplifier OAb can also be shared. Therefore, three operational amplifier circuits can be eliminated from the first embodiment to obtain the same effect, and further lower power consumption can be achieved.

[0019]

As described above, according to the present invention, even in a display device having a large capacity of liquid crystal material or a liquid crystal display element of a large panel, it is possible to prevent waveform distortion and deterioration of image quality due to insufficient driving capability of a power supply. And the effect of reducing the power consumption of the liquid crystal driving semiconductor element having the power supply circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of a liquid crystal driving power supply circuit of the present invention.

FIG. 2 is an output timing waveform of the timing circuit shown in FIG.

3 is a circuit diagram of the operational amplifier circuit shown in FIG.

FIG. 4 is a circuit diagram according to a second embodiment of the present invention.

5 is an output waveform of the timing circuit shown in FIG.

FIG. 6 is a circuit diagram of a conventional liquid crystal driving power supply circuit.

FIG. 7 is a timing chart showing voltages V1 to V6 of FIG. 6 and common and segment waveforms when driving a liquid crystal.

[Explanation of symbols]

 V1 to V6 Liquid crystal drive voltage V0 Positive power supply VEE Negative power supply OAa, b Operational amplifier R Bleeder resistance R'Auxiliary resistance R "Bias resistance TM Timing generation circuit SEL selector circuit VDD High-voltage power supply

Claims (3)

[Claims] 1. A resistance voltage dividing circuit having a plurality of resistors for dividing a voltage between a first power source potential and a second power source potential, and a liquid crystal display element charged with an output voltage of the resistance voltage dividing circuit as an input. A first operational amplifier circuit for driving, a second operational amplifier circuit for receiving the output voltage of the resistance voltage dividing circuit as an input and driving the liquid crystal display element for discharge, the first operational amplifier circuit and the second operational amplifier circuit. A liquid crystal driving power supply circuit comprising: a first switch circuit that switches at a predetermined timing; and a timing circuit that controls the first switch circuit. 2. The liquid crystal driving device according to claim 1, further comprising a second switch circuit that receives the output voltage of the resistance voltage dividing circuit and switches the supply level voltage of the resistance voltage dividing circuit by the timing circuit. Power supply circuit. 3. The liquid crystal drive power supply circuit according to claim 2, wherein the first switch circuit and the second switch circuit operate in synchronization with each other by the timing circuit.