LCD panel driving device and liquid crystal display device

Abstract

To provide a small and inexpensive LCD panel driving device that uses a capacity partial pressure method which requires a large supply power.SOLUTION: The LCD panel driving device comprises a microcontroller having a plurality of voltage terminals, and a plurality of capacitive elements connected to the plurality of voltage terminals. The microcontroller includes: a switching circuit that switches a connection relationship of the plurality of capacitive elements to generate, at the plurality of terminals of the microcontroller, a power supply voltage and a divided voltage produced by dividing the power supply voltage; and a voltage generation circuit that generates the power supply voltage.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an LCD panel driving device and a liquid crystal display device. [Background technology]

[0002] Conventional liquid crystal display devices, such as those found in home appliances like rice cookers, include an LCD panel and a microcontroller (MCU) for driving the LCD panel. The MCU supplies multiple bias voltages to the LCD panel. The MCU is supplied with, for example, 3V DC power from a battery and 5V DC power generated from AC power. While AC power is being supplied, the MCU operates at 5V. When AC power is not being supplied, the LCD panel is driven by DC power from the battery (battery operation). Conventionally, a resistive voltage divider method has been used to generate the bias voltage supplied to the LCD panel. However, this method has the drawback of reducing the supply current, which degrades the display quality of the LCD panel.

[0003] Another known method for generating bias voltages is a drive device that uses a capacitive voltage division method, which switches the magnitude of the bias voltage by switching the connected capacitive element, and has the advantage of being able to supply more power than a resistive voltage division method. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-253531 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the capacitive voltage division method has the problem that it requires the use of an external regulator or constant voltage generation circuit to generate a large voltage for capacitive voltage division. Installing an external regulator or constant voltage generation circuit in the peripheral circuitry not only hinders the miniaturization of LCD devices, but also makes circuit design, including matching the microcontroller with the peripheral circuitry, more difficult, and keeps product prices high.

[0006] The present invention provides a small and inexpensive LCD panel driver that uses a capacitive voltage division method that requires a large amount of power to be supplied. [Means for solving the problem]

[0007] The LCD panel driving device of the present invention includes a microcontroller having a plurality of voltage output terminals, and a plurality of capacitive elements connected to the plurality of voltage output terminals. The microcontroller includes a switching circuit that switches the connection relationship of the plurality of capacitive elements to generate a power supply voltage and a divided voltage generated by dividing the power supply voltage at a plurality of terminals of the microcontroller, and a voltage generating circuit that generates the power supply voltage. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram illustrating the overall configuration of a liquid crystal display device 1 according to a first embodiment. [Figure 2] 1 is a schematic configuration diagram illustrating a microcontroller 20 and a capacitive element CL according to a first embodiment. [Figure 3] 1 is a schematic configuration diagram illustrating a microcontroller 20 according to a first embodiment. [Figure 4] 2 is a circuit diagram illustrating an example of the configuration of a switching circuit 21. FIG. [Figure 5] 2 is a circuit diagram illustrating an example of the configuration of a voltage generating circuit 22. FIG. [Figure 6] 3 is a schematic diagram illustrating a procedure for generating voltages VL1 to VL3 using a capacitive voltage division method in the liquid crystal display device 1 of the first embodiment. FIG. [Figure 7] 10 is a graph illustrating a procedure for generating voltages VL1 to VL3 using a capacitive voltage division method in the liquid crystal display device 1 according to the first embodiment. [Figure 8] 10 is a graph showing an example of application of generated voltages VL1 to VL3 to segment wirings SEG. [Figure 9] 10 is a graph showing an example of application of the generated voltages VL1 to VL3 to the common wiring COM. [Figure 10] 10 is a schematic diagram showing an example of application of generated voltages VL1 to VL3 to segment wirings SEG and common wirings COM. FIG. [Figure 11] 1 shows a microcontroller 20 and a peripheral circuit 30 according to a comparative example (resistive voltage division method). [Figure 12] 10 is a circuit diagram illustrating the configuration of a voltage generating circuit 22 in a liquid crystal display device 1 according to a second embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. In the accompanying drawings, functionally identical elements may be designated by the same numerals. Note that the accompanying drawings show embodiments and implementation examples according to the principles of the present disclosure, but these are for understanding the present disclosure and are not to be used to interpret the present disclosure in a limiting manner. The descriptions in this specification are merely typical examples and are not intended to limit the scope or application of the present disclosure in any way.

[0010] Although the present embodiment has been described in sufficient detail to enable those skilled in the art to implement the present disclosure, it should be understood that other implementations and forms are possible, and that changes in configuration and structure and substitutions of various elements are possible without departing from the scope and spirit of the technical ideas of the present disclosure. Therefore, the following description should not be interpreted as being limited thereto.

[0011] [First embodiment] A liquid crystal display device 1 according to a first embodiment will be described with reference to Fig. 1. The liquid crystal display device 1 comprises an LCD panel 10, a microcontroller (microcomputer) 20, and a peripheral circuit 30.

[0012] As will be described later, the LCD panel 10 is configured such that segments are arranged at the intersections of segment wiring SEG and common wiring COM, and the voltage applied to each segment is appropriately controlled to switch the segments on or off.

[0013] The microcontroller 20 is a control unit that controls the voltages of the segment lines and common lines to control the LCD panel 10. The peripheral circuit 30 includes a power supply circuit and the like for executing control in the microcontroller 20. The peripheral circuit 30 is supplied with DC power (about 5 V) generated from AC power to generate various voltages necessary for the operation of the microcontroller 20, and when AC power is not supplied, is supplied with a battery (for example, about 3 V) not shown to generate various necessary voltages.

[0014] An example of the detailed configuration of the microcontroller 20 and the peripheral circuit 30 will be further described with reference to Figure 2. The microcontroller 20 is configured to include a plurality of voltage terminals (e.g., voltage terminals T0 to T6) in addition to signal input / output terminals (not shown). A plurality of capacitance elements CL constituting part of the peripheral circuit 30 are connected to the microcontroller 20 via voltage terminals T1 to T5 and supply voltages necessary for the operation of the LCD panel 10. Furthermore, a power supply voltage VDD (e.g., 5V) is supplied to the voltage terminal T0, while a ground potential VSS is supplied to the voltage terminal T6. In the example shown, the plurality of capacitance elements CL include three capacitance elements (capacitors) CL1 to CL3 (first capacitance elements) and one switching capacitance element C12.

[0015] One end of each of the capacitive elements CL1 to CL3 is connected to the voltage terminals T1 to T3, and the other end is grounded. The switching capacitive element C12 is connected between the voltage terminals T4 and T5. By switching the connection relationship between the capacitive element C12 and the capacitive elements CL1 to CL3, voltages VL1, VL2, and VL3 (for example, 1V, 2V, and 3V) are generated at the voltage terminals T1 to T3, respectively, by the capacitive voltage division method. The voltages VL1, VL2, and VL3 are, for example, in the relationship VL1 < VL2 < VL3, and are supplied to the segment wiring SEG and the common wiring COM as appropriate.

[0016] As shown in FIG. 3, the microcontroller 20 includes a switching circuit 21 and a voltage generation circuit 22 inside. The switching circuit 21 is composed of transistors or the like in the microcontroller 20, and switches the connection relationship of the capacitive element CL to generate the above-described voltages VL1 to VL3 at the voltage terminals T1 to T3. The voltage generation circuit 22 generates the above-described voltage VL3 and supplies it to the capacitive element CL.

[0017] An example of the configuration of the switching circuit 21 will be described with reference to FIG. 4. As an example, the switching circuit 21 is configured by connecting a plurality of switching elements SW (in the illustrated example, six switching elements SW1 to SW6) between the voltage terminals T1 to T6. The switching element SW1 is connected between the voltage terminals T3 and T4. The switching element SW2 is connected between the voltage terminals T2 and T5. The switching element SW3 is connected between the voltage terminals T2 and T4. The switching element SW4 is connected between the voltage terminals T1 and T5. The switching element SW5 is connected between the voltage terminals T1 and T4. The switching element SW6 is connected between the voltage terminals T5 and T6.

[0018] Switching elements SW1 and SW2 are simultaneously brought into a conductive state (ON) in the first stage described below (while the other switching elements are in a non-conductive state (OFF)). Switching elements SW3 and SW4 are simultaneously brought into a conductive state (ON) in the second stage described below (while the other switching elements are in a non-conductive state (OFF)). Switching elements SW5 and SW6 are simultaneously brought into a conductive state (ON) in the third stage described below (while the other switching elements are in a non-conductive state (OFF)). Capacitive voltage division using the capacitive voltage division method is performed by such switching operations.

[0019] 5 shows an example of the configuration of the voltage generating circuit 22. The voltage generating circuit 22 includes a reference voltage source 221, a trimming unit 222, a differential amplifier 223, and a negative feedback circuit 224, for example.

[0020] The reference voltage source 221 is, for example, a circuit that generates a constant reference voltage VB, and a bandgap reference circuit, for example, can be used. The trimming unit 222 is configured, for example, by connecting variable resistors 2221 and 2222 in series between the output terminal of the reference voltage source 221 and a ground terminal, and outputs a trimming voltage Vtr from the connection node of the variable resistors 2221 and 2222. The trimming voltage Vtr changes by appropriately adjusting the resistance values ​​of the variable resistor elements 2221 and 2222.

[0021] The differential amplifier 223 differentially amplifies the trimming voltage Vtr and the feedback voltage from the negative feedback circuit 224, and outputs the output voltage VL3. As an example, the negative feedback circuit 224 includes resistor elements 2241 and 2242 connected in series between the output terminal of the differential amplifier 223 and the ground terminal, and outputs the voltage of the connection node between the resistor elements to the differential amplifier 223 as a feedback voltage.

[0022] The procedure for generating voltages VL1 to VL3 by the microcontroller 20 using the capacitive voltage division method will be described with reference to Fig. 6. The microcontroller 20 of the liquid crystal display device 1 shown in Figs. 1 to 5 generates voltages VL1 to VL3 by using the capacitive voltage division method by repeatedly executing three stages (first stage 1 to third stage).

[0023] In the first stage, switching elements SW1 and SW2 are turned on and the other switching elements SW3 to SW6 are turned off, so that the capacitive element C12 is connected between the voltage terminals T3 and T2, as shown in FIG. 6 (1st Stage).

[0024] In the second stage, switching elements SW3 and SW4 are turned on, and the other switching elements SW1, SW2, SW5, and SW6 are turned off, so that the capacitance element C12 is connected between the voltage terminals T1 and T2, as shown in Figure 6 (2nd Stage).

[0025] In the third stage, switching elements SW5 and SW6 are turned on and the other switching elements SW1 to SW4 are turned off, thereby connecting the capacitive element C12 between the voltage terminals T1 and T6 as shown in Fig. 6 (3rd Stage). Thereafter, the first to third stages are repeated as appropriate, and the voltages VL1 to VL3 at the voltage terminals T1 to T3 rise to desired voltages as shown in Fig. 7.

[0026] 8, 9, and 10, the voltages VL1 to VL3 generated in this manner are applied to, for example, the segment wirings SEG0 to SEG2 and the common wirings COM0 to COM2 as shown in Figures 8 and 9. The voltages applied to the segment wirings SEG0 to SEG2 and the common wirings COM0 to COM2 are changed stepwise between the voltages VSS to VL3 while being changed every moment in a time-division manner, thereby controlling the lighting / extinguishing of the segments at their intersections.

[0027] 11 shows, as a comparative example of the first embodiment, a microcontroller 20 that divides the power supply voltage VDD using a resistive voltage division method to supply voltages VL1, VL2, and VL3. In this method, one end of resistor elements R1 to R3 is connected to voltage terminals T1 to T3, respectively, and the resistor elements R1 to R3 are connected in series. The power supply voltage VDD is resistively divided by the resistor elements R1 to R3, generating voltages VL1 to VL3, which are supplied from the voltage terminals T1 to T3.

[0028] However, with the resistive voltage divider method, for example, if three 100kΩ resistor elements are used, and the power supply voltage VDD is 3V, the supply current will be 3V ÷ 300kΩ = 10uA. In the case of voltage VL2, current is supplied from both the top and bottom, so the supply current will be 20μA. While 20μA may seem sufficient for a small LCD panel, it is insufficient for a large LCD panel, and a deterioration in display quality will be unavoidable.

[0029] As explained in Figure 6, the capacitive voltage division method can supply sufficient current by repeating multiple stages. As in the example above, if there are three bias voltages, VL1 to VL3, and the bias clock is 2 kHz, voltage VL1 is generated at one-third of that frequency, or 0.67 kHz. If voltage VL1 is 1 V, the supply current is 0.67 kHz x 1 μF x 1 V = 0.67 mA. In other words, the supply current can be increased 30 times compared to the resistive voltage division method. This large supply current, combined with a bias clock frequency that significantly exceeds the frame frequency, gives the capacitive voltage division method the advantage of improving the display quality of LCD panels.

[0030] However, capacitive voltage division poses a problem in supplying the voltages that form the basis of voltage division. For example, in the case of resistive voltage division, for example, if a power supply voltage VDD of 5V is used to generate voltages VL3=3V, VL2=2V, and VL1=1V, the power supply voltage VDD=5V can be first reduced to VL3=3V by an additional resistive element, and then voltage VL3 can be resistively divided to generate voltages VL2=2V and VL1=1V (voltages VL1 to VL3 can be generated using only resistive elements). However, when generating voltages VL3=3V, VL2=2V, and VL1=1V using capacitive voltage division, voltage VL3=3V must be directly supplied to voltage terminal T3 in the configuration shown in Figure 5. Therefore, conventional LCD devices using capacitive voltage division require a separate, external constant-voltage circuit using an LDO regulator or Zener diode in the peripheral circuitry to generate voltage VL3. Providing such an external regulator or the like hinders the miniaturization of the liquid crystal display device, and also complicates the design between the external regulator and the microcontroller, which causes problems such as product prices remaining high.

[0031] In contrast, the liquid crystal display device 1 of the first embodiment includes a voltage generation circuit 22 for generating a voltage VL3 inside the microcontroller 20. The voltage generation circuit 22 can be configured inside the microcontroller 20 by a reference voltage source formed by transistors inside the microcontroller 20, a resistor, and an operational amplifier. The voltage generation circuit 22 can supply a voltage VL3 (e.g., 3 V) based on a power supply voltage VDD (e.g., 5 V) supplied to the microcontroller 20. This voltage VL3 is capacitively divided by capacitors CL1 to CL3 and C12, and voltages VL2 (e.g., 2 V) and VL1 (e.g., 1 V) can be generated.

[0032] As described above, according to the liquid crystal display device 1 of the first embodiment, the capacitive voltage division method allows a larger supply current to flow, thereby improving the display quality of the LCD panel 10, and also eliminates the need for an additional voltage generation circuit in the peripheral circuit 30, making the device smaller and less expensive.

[0033] [Second embodiment] Next, a liquid crystal display device 1 according to a second embodiment will be described with reference to FIG. 12. The overall configuration of this liquid crystal display device 1 and the basic configuration of the microcontroller 20 are the same as those of the first embodiment (FIGS. 1 to 4), so duplicated descriptions will be omitted. However, in the second embodiment, the configuration of the voltage generating circuit 22 is partially different from that of the first embodiment (FIG. 5). The voltage generating circuit 22 of this second embodiment will be described with reference to FIG. 12. The same parts as those in the first embodiment are given the same reference numerals as those in FIG. 5, so duplicated descriptions will be omitted.

[0034] In the voltage generating circuit 22 of the second embodiment, the resistive elements constituting the negative feedback circuit 224 are variable resistive elements 2243 and 2244. By finely adjusting the resistance values ​​of the variable resistive elements 2243 and 2244, the gain of the amplifier circuit including the OP amplifier 223 can be changed, thereby finely adjusting the value of the voltage VL3. By finely adjusting the voltage VL3, the contrast of the LCD panel 10 can be changed. In other words, the negative feedback circuit 224 functions as a contrast adjustment unit for the LCD panel 10.

[0035] In this way, the liquid crystal display device 1 of the second embodiment can achieve the same effects as the liquid crystal display device 1 of the first embodiment. In addition, the liquid crystal display device 1 of the second embodiment can adjust the contrast of the LCD panel 10 by adjusting the resistance values ​​of the variable resistance elements 2243 and 2244 in the negative feedback circuit 224 serving as a contrast adjustment unit.

[0036] [others] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0037] 1...Liquid crystal display device 10...LCD panel 20...Microcontroller (MCU) 21...Switching circuit 22...Voltage generation circuit 30...Peripheral circuit 221...Reference voltage source 222...Trimming section 223...Differential amplifier 224, 224A...Negative feedback circuit SEG...Segment wiring COM...Common wiring T0~T6...Voltage terminals CL1 to CL3: Capacitor elements C12: Switching capacitance element SW1 to SW6: Switching elements

Claims

1. An LCD panel driver for driving an LCD panel, comprising: a microcontroller having a plurality of voltage terminals; a plurality of capacitance elements connected to the plurality of voltage terminals; Equipped with The microcontroller a switching circuit that switches a connection relationship of the plurality of capacitance elements to generate a power supply voltage and a divided voltage that is generated by dividing the power supply voltage at the plurality of voltage terminals of the microcontroller; a voltage generating circuit that generates the power supply voltage; An LCD panel driving device comprising:

2. The voltage generating circuit a reference voltage source that generates a reference voltage; a trimming unit that generates a trimmed voltage by trimming the reference voltage; a regulator that amplifies the trimming voltage and outputs it as the power supply voltage; 2. The LCD panel driver of claim 1, comprising:

3. 3. The LCD panel driver according to claim 2, wherein the regulator further comprises an adjustment section for adjusting an amplification factor.

4. The plurality of capacitive elements include a first capacitance element connected between the plurality of voltage terminals and a ground terminal; a second capacitive element configured to be sequentially connected between two of the plurality of voltage terminals by the switching circuit; and 2. The LCD panel driver of claim 1, comprising:

5. An LCD panel; an LCD panel driver that drives the LCD panel; A liquid crystal display device comprising: The LCD panel driver includes: a microcontroller having a plurality of voltage terminals; a plurality of capacitance elements connected to the plurality of voltage terminals; Equipped with The microcontroller a switching circuit that switches the connection relationship of the plurality of capacitance elements to generate a power supply voltage and a divided voltage that is generated by dividing the power supply voltage at a plurality of terminals of the microcontroller; a voltage generating circuit that generates the power supply voltage; A liquid crystal display device comprising:

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