JP2001221989A - Power source circuit for liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power source circuit for driving liquid crystal whose cost is lowered and whose power consumption is reduced. SOLUTION: This circuit is a power source circuit for a liquid crystal display device in which the power source voltage of the logic part of a driver IC for drive is used as an input voltage and it is boosted in a charge pump circuit and the boosted voltage is supplied as the selection voltage of the high potential side of a common driver via a liquid crystal driving voltage adjusting circuit ad the input voltage is negatively doubtingly lowered in a charge pump circuit and it is supplied as the selection voltage of the low voltage-side of the common driver and the non-selection voltage of the common driver is the high voltage-side voltage of the power source voltage of the logic part of the driver IC and, also, it is the center voltage between the selection voltage of the high potential side and the selection voltage of the low potential side of the common driver and a voltage that the power source voltage of the logic part of the driver IC is doublingly boosted in a charge pump circuit is used as the power source voltage of operational amplifiers and a voltage that the selection voltage of the common driver is divided by resistors is supplied as liquid crystal driving voltages of segment drivers for driving liquid crystal via the operational amplifiers connected as voltage followers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power supply circuit for driving a liquid crystal of a simple matrix liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been widely used in applications ranging from small and medium-sized portable information terminals and notebook computers to large monitors. Above all, in a portable information terminal or the like, a reflection type liquid crystal display device which performs display by reflecting external incident light has been receiving attention.

According to this reflective liquid crystal display device, the backlight is not used, and the power of the illuminating portion is reduced as compared with the conventional transmissive liquid crystal display device. On the other hand, the power consumption of the liquid crystal panel itself is the same as that of the conventional transmissive liquid crystal display device, and in that respect, low power consumption has not yet been achieved. Therefore, technology development has been conducted to reduce the power consumption of the liquid crystal panel itself. Is desired. FIG. 4 shows a configuration of a power supply circuit for driving a liquid crystal used in a simple matrix type liquid crystal display device.

A power supply voltage VEE-VSS is used as an input voltage, and a liquid crystal drive voltage adjusting circuit including a transistor TR10, a volume VR10, and a voltage dividing resistor R10 is provided. The power supply voltage VEE-VSS is usually about 20 to 50 V, and the input voltage is adjusted by a liquid crystal drive voltage adjustment circuit to output VH which is a high-potential side selection voltage of a common driver for driving the liquid crystal. .

The liquid crystal drive voltage adjusting circuit has a resistor R1.
1 to R14, the divided voltages are connected in series, and the divided voltages are connected via voltage-follower connected operational amplifiers OP11 to OP14 to the liquid crystal driving voltages VS1, VS2 of the liquid crystal driving segment driver and the common driver. Is output as the non-selection voltage VM.

As the low-potential-side selection voltage V L of the common driver for driving the liquid crystal, the low-potential-side voltage VSS of the input power supply is used.

Therefore, the liquid crystal driving voltage is V
H, VS1, VM, VS2, and VL.
These voltages are applied to the liquid crystal panel through the driver IC for driving the liquid crystal.

Incidentally, VH-VM = VM-VL, VS1
There is a relation of -VM = VM-VS2, and depending on the threshold voltage and duty of the liquid crystal, VH-VM is generally 20V.
５０50V, and VS1−VM is about 1V to 2V.

Further, in such a liquid crystal drive power supply circuit, the high-potential-side voltage VEE of the input power supply is connected to the positive-side power supply terminals of the operational amplifiers OP1 to OP4, and the low-potential-side voltage VSS of the input power supply is connected. And each operational amplifier OP1 to OP
The negative side power terminal of P4 is connected.

[0010]

However, in the conventional power supply circuit for driving a liquid crystal as described above, the three liquid crystal driving voltages VS1, VM and VS2 are applied to the operational amplifiers OP11 to OP11.
13, a high voltage of about 20 V to 50 V is used for the power supply of the operational amplifier.
The steady current flowing from EE to VSS through the operational amplifier steadily increases the power consumption of this operational amplifier, which increases the power consumption of the power supply circuit for driving the liquid crystal, and further complicates the circuit configuration. As a result, when the power supply circuit for driving the liquid crystal is formed into an IC, there is a problem that the chip size increases and the cost increases. The present invention has been completed in view of the above, and an object of the present invention is to provide a liquid crystal driving power supply circuit having a simple circuit configuration and achieving low cost and low power consumption.

[0011]

According to the present invention, a power supply circuit for driving a liquid crystal uses a power supply voltage of a logic portion of a driver IC for driving a liquid crystal panel as an input voltage and boosts the input voltage by a charge pump circuit. By supplying the selection voltage on the high potential side of the common driver for driving the liquid crystal through the liquid crystal drive voltage adjustment circuit, the selection voltage on the high potential side of the common driver is stepped down by approximately -2 times by the charge pump circuit. Supplies the selection voltage on the low potential side of the common driver for driving the liquid crystal. The non-selection voltage of the common driver is the voltage on the high voltage side of the power supply voltage of the logic portion of the driver IC, and the high potential of the common driver is supplied. This is approximately the center potential between the selection voltage on the common side and the selection voltage on the low potential side of the common driver. The voltage obtained by boosting the voltage almost twice by the step-up circuit is used as the power supply voltage of the operational amplifier, and the voltage obtained by dividing the selection voltage of the common driver by a resistance so as to have a predetermined bias ratio is supplied to the liquid crystal through a voltage follower-connected operational amplifier. The liquid crystal device is characterized in that it is configured to be supplied as a liquid crystal driving voltage of a driving segment driver.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to FIGS. FIG. 1 shows a power supply circuit for driving a liquid crystal according to the present invention, and FIG.
FIG. 3 is a basic configuration diagram of a charge pump type 8 × booster circuit used in the liquid crystal drive power supply circuit of the present invention. FIG. 3 is a basic configuration diagram of a charge pump type × 2 booster circuit used in the liquid crystal drive power supply circuit of the present invention. It is.

As shown in FIG. 1, a liquid crystal driving driver I
It is a single power supply input with the logic power supply voltage VDD-VSS of C as the input voltage. This input voltage is about 2 to 5 V. Hereinafter, a case where the input voltage VDD-VEE is 3.3 V will be described.

First, the input voltage is boosted by eight times the input voltage by the charge pump type booster circuit CHP1, thereby obtaining the high potential voltage VB (about 2
6.4V). Next, in order to adjust the high potential voltage VB to the optimum driving voltage of the liquid crystal panel, the transistor T is adjusted.
A liquid crystal drive voltage adjusting circuit including R0, volume VR0, and voltage dividing resistor R0 is provided, and VH which is a selection voltage on the high potential side of the common driver of the liquid crystal drive voltage is generated through the liquid crystal drive voltage adjusting circuit. Thereafter, this VH is stepped down by a factor of -2 by the charge pump type step-down circuit CHP2 to generate VL which is a low-potential side selection voltage of the common driver of the liquid crystal drive voltage.

Next, the logic power supply voltage VDD is boosted twice by the charge pump type step-down circuit CHP3,
The power supply voltage of the operational amplifier OP1 for supplying the liquid crystal drive voltage on the high potential side of the segment driver is generated. Then, so that the liquid crystal drive voltage has the optimum bias ratio,
The voltage dividing resistors R1 and R2 are inserted between VH and VDD, and the voltage divided by the resistors R1 and R2 is applied to the liquid crystal drive via an operational amplifier OP1 connected in a voltage follower connection. A voltage VS1, which is a liquid crystal driving voltage on the high potential side of the segment driver for the LCD, is generated.

Next, voltage dividing resistors R3 and R3 are connected between VSS and VL.
4 (R1 = R4, R2 = R3), and the voltage divided by this resistor becomes the liquid crystal driving voltage on the low potential side of the liquid crystal driving segment driver via the operational amplifier OP2 connected in a voltage follower connection. A voltage VS2 is generated.

The logic power supply voltage VDD-VSS is used as the power supply of the operational amplifier OP2, and the input voltage VDD is used as the non-selection voltage VM of the common driver. As described above, in the present invention, low cost and low power consumption can be achieved with a simple circuit configuration. For example, when the input voltage VDD-VEE is 3.3 V, the liquid crystal panel with a duty of 1/240 is set to (R1 +
When driving with the setting of R2) / R2 = 15, VH = 2
4.3V, VL = -17.7V, VS1 = 4.7V, VS2
= -1.9V and VM = 3.3V, an optimum image can be obtained, and the power consumption of the 3.8 "QVGA color liquid crystal panel is about 18 mW, which is lower than that of the conventional liquid crystal driving power supply circuit. (Basic configuration of charge pump circuit) Next, the charge pump circuit will be described in detail with reference to Fig. 2 and Fig. 3. According to the charge pump circuit shown in Fig. 2, a switch using a MOS transistor or the like is used. S1 to S8, transfer capacity (C1, C3, C5, C
7), and storage capacitors (C2, C4, C6, C8). The switch S1 and the switch S2, the switch S3 and the switch S4, the switch S5 and the switch S6, the switch S7 and the switch S8 operate in conjunction with each other, and are configured to always fall in the same direction on the circuit diagram.

Hereinafter, the operation of the charge pump circuit of eightfold boosting will be described.

First, in a state where the input voltage Vin is being input, the switches S1 and S2 are tilted downward as shown in the figure, so that a charge corresponding to the input voltage Vin is charged to C1.

Next, when the switches S1 and S2 are tilted upward, the charge charged in C1 is distributed and transferred to C2.

By repeating the switching operation in which the switches S1 and S2 are alternately turned up and down in the figure, Vin is applied between both terminals of C2 (between nodes b and c).
And a voltage approximately equal to
Between them, a voltage approximately twice as high as Vin is generated.

Next, when the switches S3 and S4 are tilted downward as shown in the figure, C3 is charged with a charge corresponding to the voltage 2 × Vin between the nodes a and c.

Subsequently, when the switches S3 and S4 are tilted upward, the charge charged in C3 is distributed and transferred to C4. By repeating the switching operation in which the switches S3 and S4 are alternately turned up and down in the figure in this manner, 2 × is placed between both terminals of C4 (between nodes cd).
A voltage substantially equal to Vin is maintained. Therefore, node a
A voltage approximately four times Vin is generated between -d.

When the switches S5 and S6 are tilted downward as shown in the figure, C5 is charged with a charge corresponding to the voltage 4 × Vin between the nodes a and d. Next, when the switches S5 and S6 are tilted upward, the charge charged in C5 is distributed and transferred to C6. By repeating the switching operation in which the switches S5 and S6 are alternately turned up and down in this manner, a connection between both terminals of C6 (node d−
During (e), a voltage substantially equal to 4 × Vin is held. Therefore, a voltage approximately eight times Vin is generated between the nodes ae.

Thus, a voltage obtained by boosting the input voltage Vin by eight times is output as the output voltage Vout by the charge pump circuit as shown in FIG. Next, another charge pump circuit will be described with reference to FIG. FIG. 9 shows the operation of the charge pump circuit of -2 step-down.

First, when the input voltage Vin is being input, the switches S7 and S8 are tilted downward as shown in the figure, so that a charge corresponding to the input voltage Vin is charged to C7.

Next, when the switches S7 and S8 are tilted upward, the electric charge charged in C7 is distributed and transferred to C8. By repeating the switching operation in which the switches S7 and S8 are alternately turned up and down in this manner,
A voltage substantially equal to Vin is held between both terminals of C8 (between nodes g and h), and as a result, V is applied between nodes f and h.
A voltage approximately twice as large as in is generated. Therefore, according to the charge pump circuit of FIG. 3, a voltage obtained by stepping down the input voltage Vin by -2 times is output as the output voltage Vout.

[0028]

As described above, according to the power supply circuit for driving a liquid crystal of the present invention, the power supply voltage of the logic section of the driver IC for driving the liquid crystal panel is used as the input voltage, and this input voltage is used by the charge pump circuit. By increasing the voltage, the high-potential-side selection voltage of the common driver for driving the liquid crystal is supplied through the liquid-crystal drive voltage adjustment circuit, and the high-potential-side selection voltage of the common driver is reduced by approximately -2 times by the charge pump circuit. Thus, the selection voltage on the low potential side of the common driver for driving the liquid crystal is supplied, and the non-selection voltage of the common driver is the voltage on the high voltage side of the power supply voltage of the logic part of the driver IC, and the high potential of the common driver This is approximately the center potential between the selection voltage on the side and the selection voltage on the low potential side of the common driver. Is used as the power supply voltage of the operational amplifier, and the voltage obtained by dividing the selection voltage of the common driver by a resistance so as to have a predetermined bias ratio is supplied to the liquid crystal drive via the operational amplifier connected with a voltage follower. In other words, the high-voltage side power supply is formed by a charge pump circuit with high conversion efficiency, and the operational amplifier is used only for a part of the low-voltage side power supply. As a result, a simple circuit configuration can be achieved, thereby achieving low cost and low power consumption.

[Brief description of the drawings]

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

FIG. 2 is a basic configuration diagram of a charge pump type 8 × booster circuit used for a liquid crystal drive power supply circuit of the present invention.

FIG. 3 is a diagram showing a basic configuration of a charge pump type-2 × step-down circuit used in a power supply circuit for driving a liquid crystal according to the present invention.

FIG. 4 is a diagram showing a conventional liquid crystal driving power supply circuit.

[Explanation of symbols]

 CHP1 Charge pump type booster circuit VB High potential voltage TR0 Transistor TR0 Volume TR0 Divider resistance VH, VL Selection voltage CHP2 Charge pump type step-down circuit VDD Logic power supply voltage CHP3 Charge pump type step-down circuit OP1, 2 Operational amplifiers R1, R2, R3, R4 voltage divider resistor

Claims (1)

[Claims] 1. A high-potential side of a common driver for driving a liquid crystal by using a power supply voltage of a logic part of a driver IC for driving a liquid crystal panel as an input voltage and boosting the input voltage by a charge pump circuit. The selection voltage is supplied through a liquid crystal drive voltage adjustment circuit, and the selection voltage on the high potential side of the common driver is stepped down by approximately -2 times by the charge pump circuit, so that the selection voltage on the low potential side of the liquid crystal drive common driver is reduced. And the non-selection voltage of the common driver is a voltage on the high voltage side of the power supply voltage of the logic portion of the driver IC, and the selection voltage on the high potential side of the common driver and the selection voltage on the low potential side of the common driver. And a voltage obtained by boosting the power supply voltage of the logic portion of the driver IC almost twice by the charge pump circuit to the operational amplifier. It is used as a source voltage, and a voltage obtained by dividing a selection voltage of a common driver by a resistance so as to have a predetermined bias ratio is supplied as a liquid crystal drive voltage of a segment driver for driving a liquid crystal through an operational amplifier connected with a voltage follower. A power supply circuit for a liquid crystal display device, comprising: