JP2001066568A - LCD module bias circuit - Google Patents

Abstract

(57) [Problem] To reduce the total current consumption related to the bias drive of a liquid crystal module with a simple configuration. SOLUTION: A voltage between voltages V1 to V6 is divided by resistors R11 to R15 connected in series to generate voltages V2 to V5, and a sufficient drive current is obtained using a current buffer by operational amplifiers OP11 to OP14. Between V1 and V2, V2
Capacitors C11, C12, C13 and C14 are provided between −V3, between V4 and V5, and between V5 and V6, respectively. Operational amplifier OP1 for supplying voltages V2 and V3
1 and OP12 are the power supply potential VB and the ground potential G
The power supply operates with the second power supply connected to the ND as the power supply,
OP13 and OP1 that supply V5 and V5
4 operates using a voltage between the power supply potential VEE of the first power supply and the power supply potential VB of the second power supply as a power supply.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving technique for a liquid crystal module using a liquid crystal display device, and more particularly, to a bias circuit for a liquid crystal module suitable for a multi-level bias of the liquid crystal module.

[0002]

2. Description of the Related Art For example, STN (Supertwisted Nemati)
c) liquid crystal display device (Liquid Crystal Display ~ below,
A liquid crystal module using an “LCD” is driven using a plurality of different voltages. For example, when driving is performed using six levels of drive voltages, the six levels of drive voltages are sequentially applied to the voltages V1, V2, V3, V4, V5 from the lower voltage side.
And V6, the voltage V1 is the common potential, that is, the ground (earth) potential GND, and the voltage V6 is the maximum value VEE of the power supply voltage. An example of a driving method of the liquid crystal module using these six levels will be briefly described.

A selection voltage V6 or V1 is applied to the scanning electrodes of the liquid crystal module one row at a time, and a non-selection voltage V2 or V5 is applied during other periods. On / off information of each dot of the selected row is sequentially applied to the signal electrodes of the liquid crystal module. That is, while the voltage applied to the selected row is at the voltage V6, the voltage V1 is applied to the on-dot signal electrodes of the selected row, and the voltage V3 is applied to the off-dot signal electrodes. Then, while the voltage applied to the selected row is at the voltage V1, the voltage V6 is applied to the on-dot signal electrodes of the selected row, and the voltage V4 is applied to the off-dot signal electrodes. The voltage applied to the liquid crystal of each dot is a difference voltage between the scanning voltage and the signal voltage. A dot having a high effective difference voltage is turned on, and a dot having a low effective difference voltage is turned off. In this way, the liquid crystal module is driven in an alternating manner to prevent the deterioration of the liquid crystal. V6-V5 = V5-V4 = V3-
There is a relationship of V2 = V2-V1. Generally, 1/20
In the case of 0 duty (duty is the ratio between the selection period of one row and the selection period, that is, one frame period), V6−V5 is about 1.7V, and V6−V1 (LCD operating voltage) is about 22V.
About V.

FIG. 3 shows an example of a conventional configuration of a 6-level bias generation circuit for generating a 6-level bias voltage for driving such a liquid crystal module. Power supply potential VEE and ground potential (common potential)
GND is supplied, and these power supply voltage VEE and ground potential GND are derived as voltages V6 and V1, respectively. A resistor R in which a voltage between the voltages V1 and V6 is connected in series
1, R2, R3, R4 and R5 to divide V2, V
3. Generate voltages corresponding to V4 and V5. Basically, resistance R1 = R2 = R4 = R5, and several kΩ ~
It is assumed to be several tens kΩ. The resistance of the resistor R3 is set to several tens kΩ to several hundred kΩ when the duty is 1/200. In such a voltage divider circuit using a simple series resistor, a sufficient current for driving the liquid crystal module cannot be obtained. Therefore, the divided voltage is made a sufficient drive current by using a current buffer. As a current buffer, operational amplifiers (operational amplifiers) OP1, OP2, OP3, and OP4 are usually used as voltage followers as shown in the figure.

The operational amplifiers OP1, OP2, OP3 and OP4 output voltages V2, V3, V4 and V5 via resistors R6, R7, R8 and R9, respectively.
The resistors R6 to R9 limit the output currents of the operational amplifiers OP1 to OP4, stabilize the operation, and
This is provided to reduce power consumption in OP4, and is set to, for example, several Ω to several tens of Ω. Further, the voltage V1-V
2, between the output terminals of the voltage V2-V3, between the output terminals of the voltage V4-
Between the output terminals of V5 and between the output terminals of voltages V5-V6,
Several μF capacitors C1, C2, C3 and C
4 is provided to suppress the fluctuation of the voltages V2 to V5.

As described above, the intermediate voltages, that is, the voltages V2 to V5 are usually buffered by the current buffers using the operational amplifiers OP1 to OP4, except for a small one which consumes less power. A sufficient drive current is obtained.

[0007]

In the conventional six-level bias circuit as shown in FIG.
The current consumed from D to VEE is a sum of the inflow and outflow currents of the voltages V1 to V6 and the bias currents of the operational amplifiers OP1 to OP4 forming the current buffer.

In the conventional six-level bias circuit shown in FIG. 3, each of operational amplifiers OP1 to OP
P4 is the potential GND to VEE of the original power supply, that is, the voltage V1-
Since they are connected in parallel between V6, current loops of the inflow and outflow currents of the voltages V1 to V6 also exist in parallel, and the current consumption cannot be reduced as it is. FIG. 3 shows, as examples of the current loop, a current loop a1 relating to the outflow current of the voltage V3 and a current loop a2 relating to the inflow current of the voltage V4.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a liquid crystal module bias circuit capable of reducing the total current consumption for bias driving of a liquid crystal module with a simple configuration. And Still another object of the present invention is to provide a bias circuit for a liquid crystal module capable of reducing a loss with a simple configuration and biasing the liquid crystal module more efficiently.

[0010]

In order to achieve the above object, a bias circuit for a liquid crystal module according to a first aspect of the present invention divides a power supply voltage by a plurality of resistors connected in series, and A first power supply that generates the power supply voltage corresponding to the highest potential among the bias voltages in a bias circuit of the liquid crystal module that outputs a potential of each connection point as a bias voltage together with a potential at both ends of the series resistor; A second power supply for generating a power supply voltage of an intermediate potential between the highest potential of the bias voltages and a lowest potential corresponding to a common potential of the bias voltages; It operates as a power supply between a corresponding intermediate voltage output and a common voltage corresponding to the lowest potential, and outputs a potential at a connection point of the series resistor as a bias voltage. One or more low-potential-side current buffer circuits, and operate as a power supply between a high-voltage output corresponding to the highest potential of the first power supply and an intermediate voltage output corresponding to the intermediate potential of the second power supply. And one or more high-potential-side current buffer circuits that output the potential of the connection point of the series resistor as a bias voltage.

[0011] A bias circuit of a liquid crystal module according to a first aspect of the present invention includes a first power supply and a second power supply which are separated by a potential near a middle between a high voltage side and a low voltage side of a plurality of bias voltages. The one or more low-potential-side current buffer circuits that operate using the second power supply as a power supply and output the potential at the connection point on the low-potential side of the series resistor as a bias voltage while being used while being stacked and connected substantially in series. A connection point on the high-potential side of the series resistor by one or more high-potential-side current buffer circuits operating between the high-voltage side output of the first power supply and the high-voltage side output of the second power supply; Is output as a bias voltage. In the bias circuit of this liquid crystal module, the power supply of the current buffer circuit is divided into the first and second power supplies, and these are stacked and connected in series, so that the total consumption current can be reduced by utilizing and canceling the input / output current. Can be reduced.

In a bias circuit for a liquid crystal module according to a second aspect of the present invention, a power supply voltage is divided by a plurality of serially connected resistors, and the potential at each connection point of the series resistors is calculated by:
A first power supply for generating the power supply voltage corresponding to the highest potential among the bias voltages; and a first power supply for generating the power supply voltage corresponding to the highest potential among the bias voltages. A second power supply for generating a power supply voltage of an intermediate potential between the highest potential and the lowest potential corresponding to the common potential among the bias voltages, an intermediate voltage output corresponding to the intermediate potential of the second power supply, One or more low-potential-side current buffer circuits that operate between a common voltage corresponding to the lowest potential as a power supply and output a potential at a connection point of the series resistor as a bias voltage; A DC / DC converter for transmission power control, one end of which is connected to the intermediate voltage output corresponding to a potential; and a high voltage corresponding to the highest potential of the first power supply. Operating as a power supply between a voltage output and the other end of the DC / DC converter connected to an intermediate voltage output corresponding to the intermediate potential of the second power supply, and a potential at a connection point of the series resistor. And at least one high-potential-side current buffer circuit that outputs the same as a bias voltage.

A bias circuit for a liquid crystal module according to a second aspect of the present invention is a DC / DC converter for controlling transmitted power between a high-voltage power supply output of a second power supply and a high-potential current buffer circuit. Insert In the bias circuit of this liquid crystal module, the power supply voltage supplied to the high-potential-side current buffer circuit is minimized, and a DC / DC converter is inserted into the remaining voltage difference to form a current loop without loss. Power loss can be reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings, taking a six-level bias generation circuit for generating a six-level bias voltage for driving a liquid crystal module as an example.

In a bias voltage system for driving a liquid crystal module such as an STN type, the low voltage side voltage groups V1 to V3 and the high voltage side voltage groups V6 to V4 are symmetrical in terms of voltage. Groups V1 to V3 and high voltage side voltage groups V4 to V
6 is large. Further, the low voltage side voltage group V1
V3 to V3 and the power supply output currents of the high voltage side voltage groups V6 to V4 have opposite polarities and substantially equal absolute values. Further, the magnitudes of the bias currents of the respective current buffers including the operational amplifiers OP11 to OP14 are substantially equal.

Focusing on the above, the first embodiment of the present invention shown in FIG.
The bias circuit of the liquid crystal module according to the embodiment
The current buffer including the operational amplifiers OP11 to OP14 is divided into two current buffer groups on the high potential side and the low potential side by a bias voltage, and the potential VEE− is divided via the intermediate potential VB.
The power supply of each current buffer group is connected in series between GND.

Referring to FIG. 1, a description will be given of a bias circuit of the liquid crystal module according to the first embodiment of the present invention.
FIG. 1 schematically shows a configuration of a bias circuit of a liquid crystal module.

The bias circuit of the liquid crystal module shown in FIG. 1 has a first power supply having a power supply potential VEE supplied from a power supply device 11, and a ground potential (common potential) GND.
Are supplied, and these power supply potential VEE and ground potential GND are derived as voltage V6 and voltage V1, respectively. Further, the power supply device 12 outputs a second potential having an intermediate potential between the power supply potential VEE and the ground potential GND, that is, an intermediate potential VB corresponding to an intermediate potential between the voltage V6 and the voltage V1.
Power is supplied.

Between the power supply potential VEE and the ground potential GND, resistors R11, R12, R13, R14 and R
15 are connected in series, and the power supply potential VEE and the ground potential G
A voltage between ND and ND, that is, a voltage between voltages V1 and V6 is divided by resistors R11, R12, R13, R14 and R15 to generate voltages corresponding to V2, V3, V4 and V5. Resistors R11, R12, R14 and R15
Is, for example, resistance R11 = R12 = R14 = R15, and is several kΩ to several tens kΩ. The resistance R13 is １ ／
In the case of 00 duty, it is several tens kΩ to several hundred kΩ. Resistors R11, R12, R13, R14 and R15
A current buffer is connected to each connection point in order to obtain a sufficient drive current with the divided voltage. As the current buffer, operational amplifiers OP11, OP12, OP13 and OP
14 are used.

Operational amplifiers OP11, OP12, OP13
And OP14 are respectively connected to resistors R16, R17, R1
Voltages V2, V3, V4 and V5 are output via 8 and R19. The resistors R16 to R19 are connected to an operational amplifier O
It is provided in order to stabilize the operation by limiting the output current of P11 to OP14 and to reduce the power consumption in the operational amplifiers OP11 to OP14, for example, several Ω to several tens Ω. Further, between the output terminals of the voltages V1 and V2, the voltage V
Between the output terminals of 2-V3, the output terminals of voltages V4-V5, and between the output terminals of voltages V5-V6, capacitors C11, C12, C13 and C14 of several μF are provided, respectively.
Variations in the voltages V2 to V5 are suppressed.

The low-potential-side operational amplifiers OP11 and OP12 for supplying the bias voltages V2 and V3 operate between the intermediate potential VB and the ground potential GND, that is, using the second power supply as a power supply, and operate on the bias voltages V4 and V5.
-Side operational amplifiers OP13 and OP1 for supplying
4 operates between the power supply potential VEE and the intermediate potential VB, that is, between the high voltage output of the first power supply and the intermediate voltage output of the second power supply.

That is, the bias circuit of the liquid crystal module according to the first embodiment includes a low potential side operational amplifier OP.
11 and OP12 as one current buffer group, operational amplifiers OP13 and OP14 on the high potential side as the other current buffer group, and these current buffer groups as intermediate voltage V
The circuit configuration is stacked via B.

The bias circuit of the liquid crystal module according to the first embodiment operates as follows.

Among the above-mentioned current buffer groups, the voltage V3 and the voltage V4 have a particularly large current ratio with respect to the total current, and the current flowing out of the voltage V3 is dominant.
In No. 4, the flowing current is dominant. Therefore, as in the current loop b shown in FIG. 1, the current flowing from the voltage V4 flows out of the voltage V3 via the intermediate potential VB by the second power supply. Therefore, the second power supply does not consume much current as the power supply of the current buffer due to the effect of diverting the current to cancel the consumption current. On the other hand, conventionally, the power supply currents are individually consumed by the voltages V3 and V4 as in the current loops a1 and a2 shown in FIG.

The current as a power supply for each current buffer is equal to the operational amplifiers O of the upper two current buffers.
The bias currents of P13 and OP14 flow as the bias currents of the operational amplifiers OP11 and OP12 of the lower two current buffer groups via the intermediate potential VB from the second power supply, and are consumed again. That is, in contrast to the conventional configuration, four operational amplifiers OP1 to OP4 each constituting a current buffer are connected in parallel to a common power supply as shown in FIG. 3 to consume a bias current for four operational amplifiers. 1, the bias current for two operational amplifiers is sufficient as described above.

When the configuration shown in FIG. 1 according to this embodiment is used, a stabilized separate power source is required as the second power source as compared with the conventional configuration shown in FIG. The power consumed by the power supply is very small, being only the difference between the upper block and the lower block described above.

As described above, all the operational amplifiers OP1 to OP4, which are current buffer elements, are compared with the conventional circuit of FIG. 3 in which only the single power supply is connected in parallel to the embodiment of the present invention shown in FIG. Then, the operational amplifiers OP11 to OP
14 is divided into two parts, low-potential-side operational amplifiers OP11 and OP12 and high-potential-side operational amplifiers OP13 and OP14, which are connected in series so that current can be effectively used. Therefore, it is possible to greatly reduce the total current consumption.

In an experiment with an actual load, it was confirmed that the configuration according to this embodiment can greatly reduce the power consumption current of the operational amplifiers OP11 to OP14 of the current buffer as compared with the related art. In other words, the power consumption current of the operational amplifiers OP11 to OP14 of the current buffer is 1 /
It was confirmed that it was reduced to 2.5.

Next, a description will be given of a bias circuit of a liquid crystal module according to a second embodiment of the present invention.

As described above, assuming that the six-level output voltages in the bias circuit of the liquid crystal module are V1 to V6, the magnitude relation between the voltages V1 to V6 is V1 <V2 <V3.
<V4 <V5 <V6, and in particular, the voltage difference between the voltage V3 and the voltage V4 is set to be larger than other voltage differences.
For this reason, it can be divided into blocks V1 to V3 on the side closer to the ground potential GND and voltages V4 to V6 on the side closer to the highest power supply potential VEE.

As described above, conventionally, voltages V2 to V
The power supply of the operational amplifiers (OP1 to OP4 in FIG. 3) used for buffering the output current of No. 5 is connected to the potential VEE-GND.
And a single voltage between the two. On the other hand, in the first embodiment, the power supply of the low-potential-side operational amplifiers OP11 and OP12 close to the ground potential GND is changed to the high-potential-side operational amplifier OP13 as shown in FIG. Further, the current consumption is reduced by supplying at an intermediate power supply voltage VB lower than the maximum power supply potential VEE supplied to the OP14 and OP14.

However, even in the case of FIG. 1, the operational amplifier OP of the block closer to the power supply potential VEE on the higher potential side is used.
13 and OP14 are supplied between the potentials VEE-VB, and the operational amplifiers O and O14 are provided in a current loop having a large voltage difference from the power supply potential VEE to the ground potential GND.
P13 and OP14 are operated, and the current consumption of this portion remains large.

Therefore, the bias circuit of the liquid crystal module according to the second embodiment of the present invention is configured as schematically shown in FIG. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals.

That is, the liquid crystal module according to the second embodiment differs from that of FIG. 1 in that between the low potential side power supply terminals of the operational amplifiers OP13 and OP14 forming the high potential side current buffer group and the intermediate potential VB. , A DC / DC converter (DC / DC converter) DD is inserted.
An operational amplifier O is provided on the input side of the DC / DC converter DD.
The power supply terminals on the low potential side of P13 and OP14 are commonly connected, and the output side of the DC / DC converter DD is connected to the intermediate potential VB which is the high potential side of the second power supply. In addition,
The DC / DC converter DD is connected to a ground potential G as shown in FIG.
Connected to ND. The control method of the DC / DC converter DD controls the transmission power so that the voltage between the input voltages VB and VA is stabilized.

The problem with the configuration according to the first embodiment as shown in FIG. 1 is that the low-potential side power supply terminals of the operational amplifiers OP13 and OP14, that is, the voltage at the point VA shown in FIG. This is because the voltage difference between the intermediate potential VB and the intermediate potential VB is large, and power loss occurs due to the current flowing through the voltage difference.

Therefore, as in the bias circuit of the liquid crystal module according to the second embodiment shown in FIG.
A DC / DC converter DD is inserted between the points B and VA, and the bias current c flowing into this portion is controlled so as to be connected without causing a power loss to efficiently drive the operational amplifiers OP13 and OP14. I was able to do it.

As described above, the operational amplifier O on the high potential side
In a bias circuit of a liquid crystal module in which P13 and OP14 are driven by a voltage higher than the originally required power supply voltage, the power supply voltage supplied to the operational amplifiers OP13 and OP14 is minimized, and a control method is applied to the remaining voltage difference. By inserting the devised DC / DC converter DD, a current loop is formed without loss. By doing so, unnecessary power loss in the bias circuit of the liquid crystal module can be eliminated.

In the above description, a resistor is provided on the output side of each operational amplifier, and a capacitor is interposed between the output voltages of the high potential group and the low potential group. Capacitors and the like can be further inserted or omitted as necessary on the circuit. In the above description, the case where a 6-level bias voltage is generated has been described. However, the present invention is not limited to the 6-level bias voltage, and a circuit for supplying a contrasting high-potential voltage group and a low-potential voltage group is provided. Then, it can be applied to any object.

[0039]

As described above, according to the present invention, it is possible to provide a bias circuit for a liquid crystal module capable of reducing the total current consumption for bias driving of the liquid crystal module with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a circuit diagram schematically showing a configuration of a bias circuit of a liquid crystal module according to a first embodiment of the present invention.

FIG. 2 is a circuit configuration diagram schematically showing a configuration of a bias circuit of a liquid crystal module according to a second embodiment of the present invention.

FIG. 3 is a circuit configuration diagram schematically illustrating an example of a configuration of a bias circuit of a conventional liquid crystal module.

[Explanation of symbols]

R11 to R19: resistor, OP11 to OP14: operational amplifier (operational amplifier), C11 to C14: capacitor
DD: DC / DC converter (DC / DC converter), VEE: Power supply potential, VB: Intermediate potential, GND: Ground potential

Claims (2)

[Claims] 1. A bias circuit of a liquid crystal module for dividing a power supply voltage by a plurality of serially connected resistors and outputting a potential at each connection point of the series resistors as a bias voltage together with a potential at both ends of the series resistor. A first power supply that generates the power supply voltage corresponding to the highest potential of the bias voltages; and a first power supply that generates the power supply voltage corresponding to a highest potential of the bias voltages and a lowest potential corresponding to a common potential of the bias voltages. A second power supply for generating a power supply voltage of an intermediate potential; an intermediate voltage output of the second power supply corresponding to the intermediate potential; and a common voltage corresponding to the lowest potential, operating as a power supply, and At least one low-potential-side current buffer circuit that outputs a potential at a connection point of a resistor as a bias voltage; a high-voltage output corresponding to the highest potential of the first power supply; And at least one high-potential-side current buffer circuit that operates as a power supply between an intermediate voltage output corresponding to the intermediate potential of the power supply and outputs a potential at a connection point of the series resistor as a bias voltage. A bias circuit for a liquid crystal module. 2. A bias circuit for a liquid crystal module, which divides a power supply voltage by a plurality of serially connected resistors and outputs a potential at each connection point of the series resistors together with a potential at both ends of the series resistor as a bias voltage. A first power supply that generates the power supply voltage corresponding to the highest potential of the bias voltages; and a first power supply that generates the power supply voltage corresponding to a highest potential of the bias voltages and a lowest potential corresponding to a common potential of the bias voltages. A second power supply for generating a power supply voltage of an intermediate potential; an intermediate voltage output of the second power supply corresponding to the intermediate potential; and a common voltage corresponding to the lowest potential, operating as a power supply, and One or more low-potential-side current buffer circuits that output a potential at a connection point of a resistor as a bias voltage; and one of the intermediate voltage outputs corresponding to the intermediate potential of the second power supply. A DC / DC converter for transmission power control having an end connected thereto; a high voltage output corresponding to the highest potential of the first power supply; and an intermediate voltage output corresponding to the intermediate potential of the second power supply. One or more high-potential-side current buffer circuits that operate using the voltage between the other end of the DC / DC converter as a power supply and output the potential of the connection point of the series resistor as a bias voltage. A bias circuit for a liquid crystal module.