JP2000292765A - Liquid crystal display - Google Patents

Abstract

(57) [Problem] To provide a liquid crystal display device capable of further reducing power consumption. SOLUTION: A liquid crystal display element having a plurality of pixels arranged in a matrix, and a driving method of selecting two driving voltages determined by a driving method from a plurality of driving voltages and applying the selected driving voltages to the plurality of pixels. And a driving voltage supply unit for supplying each of the driving voltages for driving the pixel to the driving unit, wherein the driving voltage supply unit has an output current flowing in the direction of the driving voltage supply unit. And an output stage circuit only in a direction in which an output current flows into the drive voltage supply means.

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 technique effective when applied to a power supply circuit in a simple matrix type liquid crystal display device.

[0002]

2. Description of the Related Art For example, STN (Super Twisted Nematic) such as an STN liquid crystal display module.
The simple matrix type liquid crystal display device of the type is widely used as a display device of a notebook computer or the like. As a driving method of the simple matrix type liquid crystal display device of the STN mode, a common electrode (or a scanning electrode) is sequentially selected one by one within one frame period, and a driving voltage is applied to each pixel of the liquid crystal during this selection period. A so-called line-sequential driving method for applying is known. As typical examples of the line sequential driving method, an Alt Pleshko driving method (also called smart addressing or HIFAS) and a standard driving method (also called a voltage averaging method) are known. Al
In the tPleshko driving method, a driving voltage (non-selection voltage) applied to an unselected common electrode is set to Vm (for example, 0 V).
(Zero volts)) and the drive voltage (selection voltage) applied to the selected common electrode is Vch (for example, 28 V
-40V) or Vcl (for example, -28V to -4
0V), and the drive voltage applied to the segment electrode (or the data electrode) is varied based on the non-selection voltage (the voltage of Vm). In the standard driving method, the driving voltage (non-selection voltage) applied to the unselected common electrode is V5 (for example, 2 V), and the driving voltage (selection voltage) applied to the selected common electrode is V1 (for example, V1). ,
+30 V) and the drive voltage (non-selection voltage) applied to the unselected common electrode is V6 (for example, 28
V), and a set in which a drive voltage (selection voltage) applied to the selected common electrode is a voltage of V2 (for example, 0 V), is alternately output, and the drive voltage applied to the segment electrode is changed to a non-selected voltage. Select voltage (V5 voltage or V
6).

[0003]

As described above, the STN
An STN simple matrix type liquid crystal display device such as a liquid crystal display module is used as a display device of a notebook personal computer or the like, and this notebook personal computer is characterized by being carried and used. Therefore, there is a strong demand for reducing the power consumption of the liquid crystal display device. The present inventors have studied the conventional simple matrix type liquid crystal display device of the STN mode from the viewpoint of reducing power consumption, and as a result, have found the following problems. That is, in a conventional STN simple matrix type liquid crystal display device, a drive voltage applied to a common electrode or a segment electrode (for example, a non-selection voltage (Vm) and a selection voltage (Vch, Vc in the Alt Pleshko driving method)
l) Also, a power supply circuit for supplying non-selection voltages (V5, V6) and selection voltages (V1, V2) of the standard driving method)
It was found that unnecessary current was flowing, thereby consuming extra power. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the related art, and an object of the present invention is to provide a technique capable of further reducing power consumption in a liquid crystal display device. . The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0004]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows. That is, according to the present invention, a liquid crystal display element having a plurality of pixels arranged in a matrix and two driving voltages determined by a driving method are selected from a plurality of driving voltages and applied to the plurality of pixels. Driving means for
A driving voltage supply unit for supplying each of the driving voltages for driving the pixel to the driving unit,
The drive voltage supply means includes an output stage circuit in which only the direction of the output current flows out of the drive voltage supply means, and an output stage circuit in which only the direction of the output current flows into the drive voltage supply means. It is characterized by the following. In addition, the present invention provides a liquid crystal display device having a plurality of pixels arranged in a matrix, and a first column in each pixel row in a row (or column) direction of the plurality of pixels in accordance with a scanning period and a scanning timing.
Scanning electrode driving means for supplying any one of the driving voltage, the third driving voltage, and the fifth driving voltage; and a plurality of pixel columns in a column (or row) direction. Data electrode driving means for supplying any one of the second driving voltage and the fourth driving voltage; and a first driving voltage, a third driving voltage and a fifth driving voltage to the scan electrode driving means. A drive voltage supply unit for supplying a second drive voltage and a fourth drive voltage to the data electrode drive unit, wherein the drive voltage supply unit comprises: An output stage circuit that outputs a second drive voltage has a circuit configuration in which only an output current flows out of the drive voltage supply unit.
The output stage circuit that outputs the fourth power supply circuit has a circuit configuration in which only the direction of the output current flows into the drive voltage supply unit. Further, the present invention provides a liquid crystal display element having a plurality of pixels arranged in a matrix,
A first driving voltage, a first driving voltage,
A scanning electrode driving unit for supplying any one of the second driving voltage, the fifth driving voltage and the sixth driving voltage, and a plurality of pixels arranged in a pixel column in a column (or row) direction. A data electrode driving unit that supplies any one of a first driving voltage, a second driving voltage, a third driving voltage, and a fourth driving voltage according to a scanning period; The first drive voltage, the second drive voltage, the fifth drive voltage, and the sixth drive voltage are supplied to the scan electrode drive unit, and the first drive voltage, the second drive voltage, and the second drive voltage are supplied to the data electrode drive unit.
And a drive voltage supply unit for supplying a third drive voltage, a third drive voltage, and a fourth drive voltage, wherein the drive voltage supply unit outputs the third drive voltage. The stage circuit has a circuit configuration in which only the direction of the output current flows out of the drive voltage supply means,
The output stage circuit that outputs the fourth drive voltage has a circuit configuration in which the direction of the output current flows in the drive voltage supply unit. Further, the present invention provides the first
The output stage circuit that outputs the drive voltage of the second stage has a circuit configuration in which only the direction of the output current flows out of the drive voltage supply unit, and the output stage circuit that outputs the second drive voltage is Is a circuit configuration in which the direction of the reference voltage flows into the drive voltage supply means. Further, according to the present invention, in the output stage circuit in which the direction of the output current flows out of the driving voltage supply means, an operational amplifier, a base is connected to an output terminal of the operational amplifier, and an emitter is one input terminal of the operational amplifier. And an npn-type transistor connected thereto. Further, according to the present invention, the output stage circuit in which the direction of the output current flows into the drive voltage supply means includes an operational amplifier, a base connected to an output terminal of the operational amplifier, and an emitter connected to one input terminal of the operational amplifier. And a pnp-type transistor connected to.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an STN type simple matrix type liquid crystal display module will be described in detail with reference to the drawings. In all the drawings for describing the embodiments, components having the same functions are denoted by the same reference numerals, and repeated description thereof will be omitted. FIG.
1 is a block diagram illustrating a schematic configuration of an STN simple matrix liquid crystal display module (LCM) according to an embodiment of the present invention. In FIG. 1, 101 is a display control device,
102 is a power supply circuit, 103 is a liquid crystal display panel, IC-U
1, IC-U2, IC-U3, and IC-Un are upper drain drivers (segment electrode driving circuits) and IC-L
1, IC-L2, IC-L3, and IC-Ln are lower drain drivers (segment electrode drive circuits), IC-C
1, IC-C2, IC-C3, IC-C4, IC-C5
Denotes a common driver (common electrode drive circuit). The liquid crystal display panel (the liquid crystal display element of the present invention) 103 includes a pair of glass substrates which are arranged to face each other with a liquid crystal interposed therebetween.
On the liquid crystal side of one of the glass substrates, it extends in the X direction,
Further, m common electrodes arranged in the Y direction are formed, and each of the m common electrodes is connected to a corresponding common driver (IC-C1 to Cn). On the liquid crystal side of the other glass substrate, there are formed n segment electrodes extending in the Y direction and juxtaposed in the X direction.
Each of the n divided segment electrodes is divided into two corresponding segment drivers (IC-U1 to Un) or corresponding lower segment drivers (IC-L1 to Ln). ).
The intersection of the plurality of segment electrodes and the plurality of common electrodes constitutes a pixel area, and is formed by the upper segment drivers (IC-U1 to Un) and the lower segment drivers (IC-L1 to Ln). A driving voltage is applied to each of the plurality of segment electrodes and from each of the common drivers (IC-C1 to Cn) to the plurality of common electrodes to drive the pixel.

The display controller 101 supplies display data (Din) to each of the segment drivers (IC-U1 to Un, IC-L1 to Ln) based on display data transferred from the host computer or the like. In addition, the display control device 101 receives a display control signal (clock (CL1,
CL2), frame signal (FLM), AC signal (M)
) And each segment driver (IC-U1 to U-U)
n, IC-L1 to Ln) and each common driver (IC-
A display control signal is transmitted to C1 to Cn to control each segment driver (IC-U1 to Un, IC-L1 to Ln) and each common driver (IC-C1 to Cn). The power supply circuit 102 generates a driving voltage for driving the pixels, and drives each of the segment drivers (IC-U1 to Un, IC-L1 to L-L).
n) and the common drivers (IC-C1 to Cn). Further, the power supply circuit 102 also supplies a power supply voltage for each segment driver (IC-U1 to Un, IC-L1 to Ln) and each common driver (IC-C1 to Cn). Each segment driver (IC-U1 to Un,
IC-L1 to Ln) and each common driver (IC-C1)
To Cn), the display control signal supplied from the display control device 101 includes the clocks (CL1, CL
2), a display control signal other than the AC signal (M) and the frame signal (FLM) is also input, but is omitted in FIG.

As described above, as a method of driving an STN simple matrix type liquid crystal display module, Alt Pl is used.
There are an esko driving method and a standard driving method. FIG.
FIG. 5 is a diagram for explaining a drive voltage applied to a segment electrode and a drive voltage applied to a common electrode in the lt Pleshko drive method. In this case, the power supply circuit 102 has different Vch, Vsh, Vm,
A drive voltage of Vsl and Vcl is generated, and a drive voltage of Vsh (second drive voltage of the present invention) and a drive voltage of Vsl (fourth drive voltage of the present invention) are applied to each segment driver (IC-
U1 to IC-Ln), and the driving voltage of Vch (first driving voltage of the present invention) and the driving voltage of Vm (third driving of the present invention)
Drive voltage) and Vcl drive voltage (the fifth drive voltage of the present invention) to each common driver (IC-C1 to IC-Cn).
To supply. In addition, a so-called AC drive method is adopted in which each drive voltage applied to the plurality of segment electrodes and the plurality of common electrodes is inverted at a predetermined cycle so that no DC voltage is applied to the liquid crystal. Alt Ples
In the hko driving method, the AC signal (M) is High.
In the case of the level, for example, as shown in FIG. 2, the driving voltage of Vsh supplied from the power supply circuit 102 is applied to each segment electrode of data “1”, and the power supply voltage is applied to each segment electrode of data “0”. A driving voltage of Vsl supplied from the circuit 102 is applied. A drive voltage of Vcl supplied from the power supply circuit 102 is applied to the selected common electrode, and a drive voltage of Vm supplied from the power supply circuit 102 is applied to the non-selected common electrodes. Note that a drive voltage of Vm is applied to the unselected common electrodes regardless of whether the alternating signal (M) is at a high level or a low level. Further, when the AC signal (M) is at the low level, for example, as shown in FIG. 2, the drive voltage of Vsl is applied to each segment electrode of data “1”, and the drive voltage of Vsl is applied to each segment electrode of data “0”. A drive voltage of Vsh is applied. A drive voltage of Vch is applied to the selected common electrode. Each of the segment drivers (IC-
U1 to IC-Ln) select either the Vsh drive voltage or the Vsl drive voltage supplied from the power supply circuit 102 according to the cycle of the display data and the alternating signal (M), and select each segment electrode. Is applied. Each of the common drivers (IC-C1 to IC-Cn) includes a power supply circuit 1 for each scanning line and in accordance with the cycle of the AC signal (M).
Either the driving voltage Vcl, the driving voltage Vm, or the driving voltage Vch supplied from 02 is selected and applied to each common electrode.

FIG. 3 is a block diagram showing a schematic configuration of an example of the power supply circuit 102 shown in FIG. 1 in the Alt Pleshko driving method. The power supply circuit shown in FIG.
The DC / DC converter 201 includes a DC converter 201 and a drive voltage generation circuit 202. The DC / DC converter 201 generates a drive voltage of Vch, a drive voltage of Vcl, and a power supply voltage Vop of an operational amplifier from a power supply voltage of Vcc. Further, the drive voltage generation circuit 201 generates a drive voltage of Vm, a drive voltage of Vsh, and a drive voltage of Vsl from the drive voltage of Vch and the drive voltage of Vcl. In FIG. 3,
Doff is a display off signal, Vctl is a contrast control signal, and this contrast control signal Vct
l may be input to the DC / DC converter 201 in some cases.

FIG. 4 is a diagram for explaining the current flowing through the common electrode and the segment electrode in the Alt Pleshko driving method. In FIG. 1, reference numeral 10 denotes a common electrode, 11 denotes a segment electrode, and CLC denotes a liquid crystal capacitance of a liquid crystal layer at an intersection of the common electrode 10 and the segment electrode 11. FIG. 4 shows a drive voltage of Vch applied to the common electrode 10-3, a drive voltage of Vm applied to the remaining common electrodes (10-1 and 10-2), a drive voltage of Vsh applied to the segment electrode 11-1, and a segment electrode 11-. 2 shows a state in which a drive voltage of Vsl is applied. As is apparent from FIG. 4, the segment electrode 11 to which the driving voltage of Vsl is applied
-2, the current flowing from the common electrode 10 flows,
The current flowing out to the common electrode 10 flows through the segment electrode 11-1 to which the sh drive voltage is applied. A current flows from the common electrode 10-3 to the segment electrode 11-1 between the common electrode 10-3 and the segment electrode 11-1, but the common electrode 10-3 is a selected common electrode. Since this is only one of many common electrodes, the current flowing out to the common electrode 10 flows through the segment electrode 11-1 as a whole.

FIG. 5 is a circuit diagram showing a more specific example of the drive voltage generation circuit 202 shown in FIG. 3 in a conventional example. In the figure, Cs is a capacitance for stabilizing the voltage, and the figure also shows the DC / DC converter 201 for easy understanding. In the circuit shown in FIG. 5, the driving voltage of Vm is V
The driving voltage of Vm is generated by dividing the voltage between the driving voltage of channel ch and the driving voltage of Vcl by the resistors (R1, R2) and the variable resistor Rv. The driving voltage of Vm is generated by an operational amplifier constituting a voltage follower circuit. From OP1, it is supplied to each of the common drivers (IC-C1 to IC-Cn). Vs
The driving voltage of h is obtained by dividing the voltage between the driving voltage of Vch and the driving voltage of Vm by resistors (Rh, Rm), and dividing the divided voltage into an operational amplifier OP constituting an inverting amplifier.
2, and the driving voltage of Vsh is applied to each segment driver (IC-U1 to Un,
IC-L1 to Ln). The drive voltage Vsl is generated by dividing the voltage between the drive voltage Vch and the drive voltage Vm by the resistors (rh, rm), and the drive voltage Vsl forms a voltage follower circuit. The signal is supplied from the operational amplifier OP3 to each of the segment drivers (IC-U1 to Un, IC-L1 to Ln). The contrast control signal (Vctl ′) from the operational amplifier OP4 forming the voltage follower circuit is applied to the inverting input terminal of the operational amplifier OP2 and the non-inverting input terminal of the operational amplifier OP3. According to the magnitude of the voltage value of the contrast control signal (Vctl ′), Vs
The drive voltage of h and the drive voltage of Vch change as shown in FIG. In the operational amplifier OP4, a temperature sensing element TH is inserted into a non-inverting input terminal, and changes the voltage value of the contrast control signal (Vctl ′) according to the temperature of the liquid crystal display panel.

The drive voltage generation circuit 202 shown in FIG. 5 has the following problems. (1) As described above, since the current flowing out to the common electrode 10 flows through the segment electrode 11-1 to which the driving voltage of Vsh is applied, the operational amplifier OP2 originally has only the function of supplying the current. It should just be. That is, as shown in FIG. 8, when the voltage of the load circuit (capacitance Cs) is lower than the drive voltage of Vsh, the operational amplifier OP2 uses the capacitor Cs to bring the voltage of the capacitor Cs closer to the drive voltage of Vsh.
, And charges the capacitor Cs (period (a) shown in FIG. 8). However, in general, the output stage circuit of the operational amplifier has a push-pull configuration of a pnp transistor and an npn transistor as shown in FIG. Therefore, if the voltage of the capacitor Cs fluctuates and the voltage of the capacitor Cs is higher than the drive voltage of Vsh, the operational amplifier OP2 outputs the current Ish from the capacitor Cs in order to bring the voltage of the capacitor Cs closer to the drive voltage of Vsh. Inhale,
The capacitor Cs is discharged (period (b) shown in FIG. 8). FIG.
As described above, the current flowing out to the common electrode 10 flows through the segment electrode 11-1 to which the driving voltage of Vsh is applied. Therefore, when the voltage of the capacitor Cs is higher than the driving voltage of Vsh, the capacitance Cs Without discharging the capacitor Cs
Voltage naturally approaches the drive voltage of Vsh,
Discharge current (sink current) during period (b) shown in FIG.
Is a useless current and consumes extra power. (2) Since the current flowing from the common electrode 10 flows through the segment electrode 11-2 to which the drive voltage of Vsl is applied, the operational amplifier OP3 only has to have a function of sinking the current. . That is, as shown in FIG. 9, when the voltage of the load circuit (capacitance Cs) is higher than the driving voltage of Vsl, the operational amplifier OP3 changes the current Isl from the capacitance Cs to bring the voltage of the capacitance Cs closer to the driving voltage of Vsl. To discharge the capacitance Cs (period (b) shown in FIG. 9). However, if the voltage of the capacitor Cs fluctuates and the voltage of the capacitor Cs is lower than the drive voltage of Vsl, the operational amplifier OP3 supplies the current Isl to the capacitor Cs in order to bring the voltage of the capacitor Cs closer to the drive voltage of Vsl. Then, the capacitor Cs is charged (period (a) shown in FIG. 9). As described with reference to FIG. 4, a current flowing from the common electrode 10 flows through the segment electrode 11-2 to which the driving voltage of Vsl is applied, and thus the voltage of the capacitor Cs is reduced to Vsl.
If the driving voltage is lower than the driving voltage of the capacitor Cs, the voltage of the capacitor Cs naturally approaches the driving voltage of Vsl even if the capacitor Cs is not charged. Therefore, the charging current in the period (a) shown in FIG. Current, and extra power is consumed. (3) Segment electrode 1 to which drive voltage Vsh is applied
The outflow current flowing in 1-1 and the inflow current flowing in the segment electrode 11-2 to which the driving voltage of Vsl is applied vary depending on the screen size, operating frequency, liquid crystal material, display pattern, and the like of the liquid crystal display panel. From several mA to 33
About 0 mA is required, and an operational amplifier capable of flowing such a large amount of current is required. However, an operational amplifier capable of flowing a large output current generally requires a large amount of current to flow internally during operation. (4) In the same operational amplifier, since the current that can flow from the operational amplifier and the current that flows into the operational amplifier are not the same, it is difficult to select the operational amplifier.

FIG. 10 is a circuit diagram showing a more specific example of the drive voltage generation circuit 202 shown in FIG. 3 in the present embodiment. In the figure, Cs is a capacitance for stabilizing the voltage, and the figure also shows the DC / DC converter 201 for easy understanding. This embodiment is different from the driving voltage generation circuit 202 shown in FIG. 5 in the following points. In this embodiment, instead of the operational amplifier OP2 shown in FIG. 5, an operational amplifier OP'2, a base is connected to the output terminal of the operational amplifier OP'2, and an emitter is connected to the inverting input of the operational amplifier OP'2 via a resistor Rf. An npn transistor TR1 connected to the terminal is used. The operational amplifier O shown in FIG.
Instead of P3, an operational amplifier OP'3 and a pnp transistor TR2 whose base is connected to the output terminal of the operational amplifier OP'3 and whose emitter is connected to the inverting input terminal of the operational amplifier OP'3 are used. According to the present embodiment, the following effects can be obtained. (1) In the present embodiment, as shown in FIG. 11, when the voltage of the load circuit (capacitance Cs) is lower than the drive voltage of Vsh, npn is used to make the voltage of capacitor Cs close to the drive voltage of Vsh. The type transistor TR1 allows the current Ish to flow through the capacitor Cs to charge the capacitor Cs (period (a) shown in FIG. 11). However, if the voltage of the capacitor Cs fluctuates and the voltage of the capacitor Cs is higher than the drive voltage of Vsh, the npn transistor TR1 is turned off (period (B) shown in FIG. 11). Therefore, no useless current flows as described with reference to FIG. 8 and no extra power is consumed. (2) In addition, as shown in FIG.
When the driving voltage is higher than the driving voltage of sl, the voltage of the capacitor Cs is set to V
The pnp transistor TR2 sinks the current Isl from the capacitor Cs and makes the capacitor C
s is discharged (period (b) shown in FIG. 12). However, if the voltage of the capacitor Cs fluctuates and the voltage of the capacitor Cs is lower than the drive voltage of Vsl, the pnp transistor TR2 is turned off (period (a) in FIG. 12). Therefore, no useless current flows as described with reference to FIG. 9 and no extra power is consumed. (Period (a)). (3) Since the operational amplifiers (OP'2, OP'3) need only flow the base current of the transistors (TR1, TR2), the operational amplifiers (OP'2, OP'3) may have small output currents. Therefore, the operational amplifier (OP'2,
The current flowing inside during the operation of OP'3) also becomes small. (4) Considering the screen size of the liquid crystal display panel, the operating frequency, the liquid crystal material, the display pattern, and the like, the transistors (TR1, TR2) through which the necessary current can flow are selected, so that the operational amplifiers (OP'2, OP ') In 3), only one type having a small output current can be used. Further, the transistors (TR1 and TR2) through which necessary current can flow can be selected in consideration of the screen size of the liquid crystal display panel, the operating frequency, the liquid crystal material, the display pattern, and the like. The power supply circuit can be standardized (or shared) regardless of the frequency and the liquid crystal material.

FIG. 13 is a diagram for explaining the drive voltage applied to the segment electrode and the drive voltage applied to the common electrode in the standard driving method. In this case,
The power supply circuit 102 generates different driving voltages V1 to V6, and converts the driving voltages of V1, V2, V3 and V4 into segment drivers (IC-U1 to Un, IC-L1). To Ln), and the driving voltage V1, the driving voltage V2, the driving voltage V5, and the driving voltage V6 are supplied to each common driver (IC-C1 to IC-C1).
Cn). In this standard driving method, when the alternating signal (M) is at the High level, for example, as shown in FIG. 13, each segment electrode of the display data “1” is driven by V1 supplied from the power supply circuit 102. The voltage is
The power supply circuit 1 is connected to each segment electrode of the display data “0”.
02 is supplied with the driving voltage V3. The driving voltage of V2 supplied from the power supply circuit 102 is applied to the selected common electrode, and the driving voltage V2 is applied to the unselected common electrodes.
A drive voltage of V6 supplied from the power supply circuit 102 is applied. Further, when the AC signal (M) is at the low level, for example, as shown in FIG. 13, the drive voltage of V2 supplied from the power supply circuit 102 is applied to each segment electrode of the display data “1”. A drive voltage of V4 supplied from the power supply circuit 102 is applied to each segment electrode of data “0”. The V1 drive voltage supplied from the power supply circuit 102 is applied to the selected common electrode, and the V5 drive voltage supplied from the power supply circuit 102 is applied to the non-selected common electrodes. Each of the segment drivers (I
C-U1 to IC-Ln) correspond to the driving data of V1, the driving voltage of V2, the driving voltage of V3, or the driving of V4 supplied from the power supply circuit 102 in accordance with the cycle of the display data and the alternating signal (M). One of the voltages is selected and applied to each segment electrode. Each of the common drivers (IC-C1-
IC-Cn) is for each scan line and for the AC signal (M)
, The drive voltage V1 supplied from the power supply circuit 102, the drive voltage V2, the drive voltage V5 or the drive voltage V5.
6 is selected and applied to each common electrode.

FIG. 14 is a block diagram showing a schematic configuration of an example of the power supply circuit 102 shown in FIG. 1 in the standard driving method. The power supply circuit shown in FIG. 14 includes a DC / DC converter 211 and a drive voltage generation circuit 212.
/ DC converter 211 converts Vcc power supply voltage to Vcc
1 and a drive voltage of V2. Also,
The drive voltage generation circuit 212 generates drive voltages V3 to V6 from the drive voltage V1 and the drive voltage V2.
In FIG. 14, the DC / DC converter 211
Also generates the power supply voltage Vop of the operational amplifier.
In the figure, illustration is omitted. Further, in FIG.
off is a display off signal, Vctl is a contrast control signal, and in the circuit configuration shown in FIG.
1 is input. In this standard driving method, as shown in FIG. 14, the outflow current flowing out to the common electrode flows through the segment electrode to which the driving voltage of V4 is applied and the segment electrode to which the driving voltage of V1 is applied. The inflow current flowing from the common electrode 10 flows through the segment electrode to which the driving voltage V3 is applied and the segment electrode to which the driving voltage V2 is applied. The direction of this current is
Since it can be easily understood from the voltage waveform shown in FIG. 13, the illustration is omitted.

FIG. 15 is a circuit diagram showing a more specific example of the drive voltage generation circuit 212 shown in FIG. 14 in the conventional example. In the figure, Cs is a capacitance for stabilizing the voltage, and the figure also shows a DC / DC converter 211 for easy understanding. Drive voltage generation circuit 212 shown in FIG.
Calculates the voltage between the driving voltage of V1 and the driving voltage of V2,
Voltage is divided by the resistors (R11 to R14) to generate drive voltages V3 to V6. The driving voltage of V3 and the driving voltage of V4 are connected to an operational amplifier (OP) constituting a voltage follower circuit.
12, OP13), each segment driver (IC-
U1 to Un, IC-L1 to Ln). The driving voltage V5 and the driving voltage V6 are supplied from the operational amplifiers (OP11, OP14) constituting the voltage follower circuit to the common drivers (IC-C1 to IC-Cn). The drive voltage generation circuit 212 shown in FIG. 15 has the following problems. (1) As described above, the current flowing out to the common electrode 10 flows through the segment electrode to which the drive voltage of V4 is applied. That is, when the voltage of the load circuit (capacitance Cs) is lower than the driving voltage of V4, the operational amplifier OP14 supplies a current to the capacitance Cs and charges the capacitance Cs in order to bring the voltage of the capacitance Cs closer to the driving voltage of V4. . However, if the voltage of the capacitor Cs fluctuates and the voltage of the capacitor Cs is higher than the drive voltage of V4, in order to bring the voltage of the capacitor Cs closer to the drive voltage of V4, the operational amplifier OP14
s, and discharges the capacitance Cs. This discharge current (suck current) is a useless current as described with reference to FIG. 8, and consumes extra power. (2) In addition, a current flowing from the common electrode flows through the segment electrode to which the drive voltage of V3 is applied. That is,
When the voltage of the capacitor Cs is higher than the drive voltage of V3, the operational amplifier OP13 sinks the current from the capacitor Cs to make the voltage of the capacitor Cs close to the drive voltage of V4,
discharge s. However, if the voltage of the capacitor Cs fluctuates and the voltage of the capacitor Cs is lower than the drive voltage of V3, the operational amplifier OP13 supplies a current to the capacitor Cs in order to bring the voltage of the capacitor Cs closer to the drive voltage of V3. , The capacitor Cs is charged. This charging current is a useless current as described with reference to FIG. 9, and extra power is consumed. (3) The outflow current flowing through the segment electrode to which the V4 drive voltage is applied and the inflow current flowing through the segment electrode to which the V3 drive voltage is applied are determined by the screen size, operating frequency, liquid crystal material, and display of the liquid crystal display panel. Although it varies depending on the pattern and the like, about several mA to about 330 mA is required, and an operational amplifier capable of flowing such a large amount of current is required. In general, however, an operational amplifier capable of flowing a large output current also has a large internal current flowing during operation. (4) In the same operational amplifier, since the current that can flow from the operational amplifier and the current that flows into the operational amplifier are not the same, it is difficult to select the operational amplifier.

FIG. 16 shows an embodiment of the present invention.
FIG. 4 is a circuit diagram showing a more specific example of the drive voltage generation circuit 212 shown in FIG. In the figure, Cs is a capacitance for stabilizing the voltage, and the figure also shows a DC / DC converter 211 for easy understanding. This embodiment is different from the one shown in FIG.
Is different from the drive voltage generation circuit 212 shown in FIG. In the present embodiment, the DC / DC converter 211 does not generate the driving voltage V1 and the driving voltage V2,
The converter 211 generates a drive voltage of V′1 and a drive voltage of V′2. The drive voltage generation circuit 212 converts the voltage between the drive voltage of V′1 and the drive voltage of V′2 into a resistor (R
21 to R27) to generate driving voltages V1 to V6. The drive voltage of V1 is the operational amplifier OP'11
The base is connected to the output terminal of the operational amplifier OP'11 and the emitter is connected to the inverting input terminal of the operational amplifier OP'11.
-C1 to IC-Cn) and each segment driver (IC
-U1 to Un, IC-L1 to Ln). The base of the drive voltage V2 is connected to an operational amplifier OP'16 and an output terminal of the operational amplifier OP'16.
Each common driver (IC-C1 to IC-C1) has a voltage follower circuit including a pnp transistor (TR16) whose emitter is connected to the inverting input terminal of the operational amplifier OP'16.
IC-Cn) and each segment driver (IC-U1-
Un, IC-L1 to Ln). FIG.
In place of the operational amplifier OP13 shown in FIG.
13 and a pnp transistor (TR13) whose base is connected to the output terminal of the operational amplifier OP'13 and whose emitter is connected to the inverting input terminal of the operational amplifier OP'13.
Use Further, instead of the operational amplifier OP14 shown in FIG.
Npn whose base is connected to the output terminal of P'14 and whose emitter is connected to the inverting input terminal of operational amplifier OP'14
A type transistor (TR14) is used.

According to the present embodiment, the following effects can be obtained. (1) In the present embodiment, when the voltage of the capacitor Cs is lower than the drive voltage of V4, the npn-type transistor TR1 is used to make the voltage of the capacitor Cs close to the drive voltage of V4.
4 supplies a current to the capacitor Cs and charges the capacitor Cs. However, if the voltage of the capacitor Cs fluctuates and the voltage of the capacitor Cs is higher than the drive voltage of V4, the npn transistor TR14 is turned off. Therefore, no useless current flows as described with reference to FIG. 8 and no extra power is consumed. (2) When the voltage of the capacitor Cs is higher than the drive voltage of V3, the pnp transistor TR13 sinks the current from the capacitor Cs and discharges the capacitor Cs in order to make the voltage of the capacitor Cs close to the drive voltage of V3. I do. However,
If the voltage of the capacitor Cs fluctuates and the voltage of the capacitor Cs becomes V3
Is lower than the driving voltage of the pnp transistor T
R13 is turned off. Therefore, no useless current flows as described with reference to FIG. 9 and no extra power is consumed. (3) When the voltage of the capacitor Cs is lower than the drive voltage of V1, the npn transistor TR11 causes a current to flow through the capacitor Cs to charge the capacitor Cs in order to make the voltage of the capacitor Cs close to the drive voltage of V1. I do. However, suppose,
When the voltage of the capacitor Cs fluctuates and the voltage of the capacitor Cs is higher than the drive voltage of V1, the npn-type transistor TR11
Turns off. Therefore, no useless current flows as described with reference to FIG. 8 and no extra power is consumed. (4) When the voltage of the capacitor Cs is higher than the drive voltage of V2, the pnp transistor TR16 sinks current from the capacitor Cs and discharges the capacitor Cs in order to make the voltage of the capacitor Cs close to the drive voltage of V2. I do. However,
If the voltage of the capacitor Cs fluctuates and the voltage of the capacitor Cs becomes V2
Is lower than the driving voltage of the pnp transistor T
R16 is turned off. Therefore, no useless current flows as described with reference to FIG. 9 and no extra power is consumed. (5) Operational amplifiers (OP'11, OP'13, OP'1
4, OP'16) are transistors (TR11, TR1)
3, TR14, TR16), the operational amplifiers (OP'11, OP'13, OP ')
14, OP'16) may have a small output current. Therefore, the operational amplifiers (OP'11, OP'13, OP '
14, OP'16) also reduces the current flowing inside during operation. (6) Transistors (TR11, TR13, TR14, T) through which necessary current can flow in consideration of the screen size of the liquid crystal display panel, operating frequency, liquid crystal material, display pattern, and the like.
R16), the operational amplifier (OP'1)
1, OP'13, OP'14, OP'16) can use only one type having a small output current. Also,
LCD screen size, operating frequency, LCD material,
In addition, transistors (TR11, TR13, TR14, TR1) through which necessary current can flow in consideration of display patterns and the like.
Since it is sufficient to select item 6), the power supply circuit can be standardized (or shared) regardless of the screen size, operating frequency, and liquid crystal material of the liquid crystal display panel.

The drive voltage generation circuit 21 shown in FIG.
2, the operational amplifiers (OP'11, OP'13, O
P'14, OP'16) can be omitted.
Further, in the drive voltage generation circuit 212 shown in FIG.
The operational amplifiers (OP'11, OP'16) and the transistors (TR11, TR16) can be omitted. In that case, the DC / DC converter 211 generates a drive voltage of V1 and a drive voltage of V2, and the drive voltage generation circuit 212 outputs the drive voltage of V1 and the drive voltage of V2 as shown in FIG. The voltage between the resistors (R11-R11)
R14) may be used to generate the driving voltages V3 to V6. Further, in the present embodiment, an embodiment in which the present invention is applied to an STN mode liquid crystal display module employing a line sequential driving method has been mainly described, but the present invention is not limited to this. The present invention is also applicable to an STN type liquid crystal display module employing an active driving method for selecting a line or a TFT type liquid crystal display module. As described above, the invention made by the inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and can be variously modified without departing from the gist of the invention. Of course, it is.

[0019]

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows. According to the present invention, useless current does not flow through the drive voltage supply means and no extra power is consumed, so that power consumption can be further reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an STN simple matrix type liquid crystal display module (LCM) according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a driving voltage applied to a segment electrode and a driving voltage applied to a common electrode in the Alt Pleshko driving method.

FIG. 3 shows the Alt Pleshko driving method.
FIG. 3 is a block diagram illustrating a schematic configuration of an example of a power supply circuit illustrated in FIG.

FIG. 4 is a diagram for explaining a current flowing through a common electrode and a segment electrode in the Alt Pleshko driving method.

5 is a circuit diagram showing a specific example of a drive voltage generation circuit 202 shown in FIG. 3 in a conventional example.

FIG. 6 shows a contrast control signal (Vct) shown in FIG.
It is a schematic diagram which shows the change of the drive voltage of Vsh and the drive voltage of Vch by l ').

FIG. 7 is a diagram showing a circuit configuration of an output stage of a general operational amplifier.

8 is a diagram for explaining an operation of the operational amplifier OP2 shown in FIG.

9 is a diagram for explaining an operation of the operational amplifier OP3 shown in FIG.

FIG. 10 is a circuit diagram showing a more specific example of the drive voltage generation circuit shown in FIG. 3 in the embodiment of the present invention.

FIG. 11 is a diagram illustrating an operation of the transistor TP1 shown in FIG.

12 is a diagram illustrating an operation of the transistor TP2 illustrated in FIG.

FIG. 13 is a diagram for explaining a driving voltage applied to a segment electrode and a driving voltage applied to a common electrode in a standard driving method.

14 is a block diagram illustrating a schematic configuration of an example of a power supply circuit illustrated in FIG. 1 in a standard driving method.

FIG. 15 is a circuit diagram showing a specific example of the drive voltage generation circuit shown in FIG. 14 in a conventional example.

FIG. 16 is a circuit diagram showing a more specific example of the drive voltage generation circuit shown in FIG. 14 in the embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Common electrode, 11 ... Segment electrode, 101 ... Display control device, 102 ... Power supply circuit, 103 ... Liquid crystal display panel, 201, 211 ... DC / DC converter, 202,
212 ... Drive voltage generation circuit, IC-U1, IC-U2
IC-U3, IC-Un... Upper drain driver (segment electrode drive circuit), IC-L1, IC-L2, I
C-L3, IC-Ln: Lower drain driver (segment electrode drive circuit), IC-C1, IC-C2, IC
-C3, IC-C4, IC-C5: common driver (common electrode drive circuit), R, r: resistor, OP: operational amplifier, TR: transistor, Cs: capacitor, CLC: liquid crystal capacitor, TH: thermosensitive element.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09G 3/36 G09G 3/36 (72) Inventor Yasuaki Kondo 3681 Hayano, Mobara City, Chiba Prefecture Hitachi Device Engineering Co., Ltd. F term (reference) 2H093 NA10 NA33 NA43 NC03 NC05 NC07 NC09 NC11 ND03 ND39 NF13 5C006 AC02 BB12 BB14 BC03 BC11 BF25 BF31 BF42 BF43 FA47 5C080 AA10 BB05 DD26 FF03 FF10 FF12 JJ02 JJ03 JJ04

Claims (8)

[Claims] A liquid crystal display element having a plurality of pixels arranged in a matrix; and a plurality of driving voltages determined by a driving method.
A liquid crystal display device comprising: a driving unit that selects one driving voltage and applies the driving voltage to the plurality of pixels; and a driving voltage supply unit that supplies each driving voltage for driving the pixel to the driving unit. The voltage supply means includes an output stage circuit in which only the direction of the output current flows out of the drive voltage supply means, and an output stage circuit in which only the direction of the output current flows into the drive voltage supply means. Characteristic liquid crystal display device. 2. A liquid crystal display element having a plurality of pixels arranged in a matrix, and a first column in each pixel column in a row (or column) direction of the plurality of pixels according to a scanning period and a scanning timing. Drive voltage,
Scanning electrode driving means for supplying any one of a third driving voltage and a fifth driving voltage; and a second column in a column (or row) direction of the plurality of pixels,
Drive voltage or any one of the fourth drive voltages
A first drive voltage, a third drive voltage, and a fifth drive voltage to the scan electrode drive means, and a second drive voltage to the scan electrode drive means, and a second drive voltage to the data electrode drive means. A liquid crystal display device comprising: a drive voltage supply unit that supplies a drive voltage and a fourth drive voltage, wherein the drive voltage supply unit includes: an output stage circuit that outputs the second drive voltage; Is a circuit configuration only in the direction flowing out of the drive voltage supply means.
A liquid crystal display device, wherein the output stage circuit for outputting the power supply circuit has a circuit configuration in which only the direction of the output current flows into the drive voltage supply means. 3. A liquid crystal display element having a plurality of pixels arranged in a matrix, and a first column in each pixel column in a row (or column) direction of the plurality of pixels in accordance with a scanning period and a scanning timing. Drive voltage,
Scanning electrode driving means for supplying any one of a second driving voltage, a fifth driving voltage and a sixth driving voltage; and a plurality of pixels arranged in a pixel column in a column (or row) direction. , The first drive voltage, the second drive voltage, the third drive voltage,
Drive voltage or any one of the fourth drive voltages
A first drive voltage, a second drive voltage, a fifth drive voltage, and a sixth drive voltage to the scan electrode drive means; A liquid crystal display device having a driving voltage supply unit for supplying a first driving voltage, a second driving voltage, a third driving voltage, and a fourth driving voltage to the liquid crystal display device. The output stage circuit for outputting the third drive voltage has a circuit configuration in which only the direction of the output current flows out of the drive voltage supply means, and the output stage circuit for outputting the fourth drive voltage Has a circuit configuration in which the direction of the output current flows into the drive voltage supply means. 4. An output stage circuit for outputting the first drive voltage has a circuit configuration in which only the direction of an output current flows out of the drive voltage supply means, and the output stage circuit outputs the second drive voltage. 4. The liquid crystal display device according to claim 3, wherein the output stage circuit has a circuit configuration in which the direction of the output current flows in the drive voltage supply unit. 5. The output stage circuit in which the direction of the output current flows out of the drive voltage supply means is constituted by an npn-type transistor. 3. The liquid crystal display device according to 1. 6. An output stage circuit in which the direction of the output current flows out of the drive voltage supply means, includes an operational amplifier, a base connected to an output terminal of the operational amplifier, and an emitter connected to one input terminal of the operational amplifier. Np to be connected
The liquid crystal display device according to any one of claims 1 to 4, wherein the liquid crystal display device is configured by an n-type transistor. 7. The output stage circuit in which the direction of the output current flows into the drive voltage supply means is formed of a pnp transistor. 3. The liquid crystal display device according to 1. 8. An output stage circuit in which the direction of the output current flows into the drive voltage supply means, an operational amplifier, a base connected to an output terminal of the operational amplifier, and an emitter connected to one input terminal of the operational amplifier. Pn connected
The liquid crystal display device according to any one of claims 1 to 4, wherein the liquid crystal display device is configured by a p-type transistor.