JP3212950B2 - Drive power supply for liquid crystal display - Google Patents

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 driving power supply for driving a liquid crystal panel in a matrix liquid crystal display (LCD), and more particularly to a voltage follower (source follower) circuit for obtaining a required supply current. The present invention relates to a liquid crystal display driving power supply device for reducing the number.

[0002]

2. Description of the Related Art Conventionally, this type of driving power supply for liquid crystal display is mainly used for driving a radio selective calling device (pager) or a display panel of a matrix liquid crystal display (LCD) of a portable telephone. In this case, the power supply of the wireless selective calling device and the mobile phone is a built-in rechargeable battery,
Along with further reduction in current consumption, a smaller layout area (small size) is required. In driving such a matrix liquid crystal display, an address pulse is sent to a row electrode,
Further, a display pulse is transmitted to the column electrode. Further, if a voltage of the same polarity is applied to the liquid crystal panel, the liquid crystal is likely to be degraded, so the polarity of the applied voltage is reversed.

FIG. 4 is a timing chart for explaining the voltage polarity applied to the liquid crystal panel. In FIG. 4, a positive polarity voltage is applied in the first frame, and a negative polarity voltage is applied in the next second frame.
Driving in the liquid crystal panel is performed. The applied voltage is a supply voltage V1 and V2, V3, V3 divided by a series-connected resistor element so that the supply voltage V1 is sequentially reduced.
6, V5 and the lowest potential (ground potential) VG. In the first frame, V1 and V1 are output to the COM output to the common (COM) terminal.
A V5 level power supply is used.
SEG output to the terminal) is V4, VG
A level power supply is used. In the second frame, the VG and V2 level power supplies are used for the COM output, and the V
1, V3 level power supply is used.

FIG. 5 is a block diagram showing the configuration of a conventional drive power supply for a liquid crystal display. This liquid crystal display drive power supply device supplies a V1 level power supply (supply voltage) to a resistance element R1,
The voltage is divided by R2, R3, R4, and R5 to generate V2, V3, V4, and V5 level power supplies together with the V1 level power supply. The V2 to V5 level power supplies are used as voltage follower circuits P, N, P, N operating as four current boosters.
And supplies it to the switching circuit so that a necessary supply current can be obtained. In the switching circuit, the V1 to VG level power is switched for each frame, and the V1 or V2 level power / V5 or the VG level power is supplied from the output circuit to the CO.
M outputs 1... N are supplied. In the switching circuit, the V1 to VG level power is switched for each frame, and the V4 or V1 level power / VG or V3 level power is supplied as SEG outputs 1... N from the output circuit.

In this case, only one N-type drive voltage follower circuit and one P-type drive voltage follower circuit operate in each frame, and the other voltage follower circuits do not operate. . That is, an N-type drive voltage follower circuit, P
Two different levels of power are supplied to each of the mold drive voltage follower circuits to supply four levels of power. A conventional example of such a conventional driving power supply for a liquid crystal display is disclosed in Japanese Patent Application Laid-Open No. 4-137991, entitled "Liquid Crystal Display Driving Power Supply Circuit".

FIG. 6 is a block diagram showing a configuration of a main part of such a conventional driving power supply device for a liquid crystal display. This figure 6
In the conventional example shown in (1), the problem that the liquid crystal panel is driven through a switch and the impedance of the switch is reduced to increase the scale of the switch is solved. That is, a voltage follower circuit is provided at the rear of the switch in order to lower the impedance of the drive output, and the size of the switch group is suppressed to reduce the IC chip size. In this case, without changing the number of voltage follower circuits, two unused voltage follower circuits in the four voltage follower circuits are turned off to reduce power consumption.

In this case, although the number of driven voltage follower circuits is always two, for example, four voltage follower circuits are mounted on an IC chip. These two circuits are redundant, and the voltage follower circuit is provided with the entire level power supply, for example, 4
Since it occupies 4.8%, the area occupied on the IC chip becomes relatively large when the arrangement of the phase correction capacitor and the like is included.

In addition to the example of inverting the voltage polarity for each frame, the line inversion driving method for inverting the voltage polarity for each line of the matrix liquid crystal panel, and the AC driving for inverting the voltage polarity each time a plurality of lines are simultaneously driven. There is a similar problem in the inversion method.

[0009]

In such a conventional example, for example, the occupied area on the IC chip becomes large,
There is room for improvement when it is used as a wireless selective calling device or a driving power supply device for liquid crystal display of a mobile phone which requires smaller size, lower power consumption and lower cost.

The present invention solves such a problem in the prior art, and reduces the number of voltage follower circuits (for example, compared with a conventional liquid crystal display driving power supply device using four voltage follower circuits). It is an object of the present invention to provide a drive power supply device for a liquid crystal display, which can reduce current consumption, reduce the mounting area of an IC chip or the like, and reduce the size and cost. .

[0011]

In order to achieve the above object, a liquid crystal display driving power supply according to the present invention supplies a voltage whose polarity is inverted for each frame to a plurality of common terminals and segment terminals of a matrix liquid crystal panel. And a plurality of resistive elements for dividing a supply voltage into four intermediate voltages, and any two of the four intermediate voltages for each frame, line, or plurality of lines. A first switch for selecting and outputting, and a second switch for selecting and outputting, for each frame, line, or a plurality of lines, the other two intermediate voltages not selected by the first switch among the four intermediate voltages, The first switch
Either P-type or N-type bolts connected in series to
Connected in series with a stage follower circuit and the second switch
The voltage switch connected in series to the first switch.
Either P-type or N-type different from the follower circuit type
And a switching circuit for switching the output of each of the two voltage follower circuits to both the common terminal side and the segment terminal side and inputting them.

Further, in the driving power supply device for a liquid crystal display according to the present invention, the switching circuit switches off the first or second switch.
Operation of the voltage follower circuit is stable after switching
Operation stop instruction to stop the switching operation until
The configuration includes a circuit .

Further, in the liquid crystal display drive power supply device according to the present invention, the operation stop instruction circuit may include a frame, a line, or a plurality of lines.
Switching signal of several lines and frame, line or multiple lines
The operation of the voltage follower circuit is stable with the in-switch signal.
Frame, line, or
Is a short pulse generated from the switching delay signal of multiple lines
It is configured to transmit a signal .

The driving power supply for a liquid crystal display according to the present invention as described above.
Location, a plurality of one or the other of the intermediate voltage is selected by the resistance element divided from two intermediate voltage generated by connected in series between a voltage supply terminal and the lowest potential, and one of the other two intermediate voltage Alternatively, the supply voltage and the lowest potential are output as the liquid crystal panel driving power supply together with the intermediate voltage selected for each frame, line, or a plurality of lines. And
The selected intermediate voltage is supplied through two voltage follower circuits for obtaining a required current.

[0015] As a result, when generating a different voltage power supply for performing a liquid crystal panel driven by applying a plurality of common terminals and segment terminals of the matrix liquid crystal panel inverts the voltage polarity frame, line by line or plurality of lines, The number of the voltage follower circuits decreases. For example, the number of voltage follower circuits is halved to two as compared with the conventional liquid crystal display drive power supply device using four voltage follower circuits described in the above-mentioned conventional example. Therefore, current consumption is reduced, and a mounting area of an IC chip or the like is reduced, so that downsizing and cost reduction can be achieved.

Further , in the drive power supply device for liquid crystal display of the present invention, the switching operation of the switching circuit is stopped until the operation of the voltage follower circuit is stabilized, and during this operation stop, the first and second switches are turned off. The switching operation is performed.

[0017] Consequently, when reducing the voltage follower circuit, the frame, for performing drive is applied to the plurality of common terminals and segment terminals of the matrix liquid crystal panel inverts the voltage polarity for each line or plurality of lines Power generation of a plurality of voltages is performed more stably.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a driving device for a liquid crystal display according to the present invention will be described.
An embodiment of a source device will be described in detail with reference to the drawings.
FIG. 1 is a circuit diagram showing a configuration of a liquid crystal display drive power supply device according to an embodiment of the present invention. In this liquid crystal display drive power supply device, the resistance elements R1, R2, R3, R4, and R5 are connected in series, and the non-series connection side (input side) of the resistance element R1 is
The V1 supply voltage is applied, and the other end of the resistance element R5 is connected to the ground as the lowest potential. A connection point A between the resistance elements R1 and R2 and a connection point C between the resistance elements R3 and R4 are connected to respective fixed contacts of the switch SW1 . The movable contact of the switch SW1 is connected to the reference terminal of the P-type drive voltage follower circuit P1. The movable contact of the switch SW1 is switched by the frame signal FRM.

Further , a connection point B between the resistance elements R2 and R3,
The connection point D of the resistance elements R4 and R5 is connected to the switch SW2.
It is connected to each fixed contact . This switch S
The movable contact of W2 is an N-type drive voltage follower circuit N
1 is connected to the reference terminal side. The output terminals of the P-type drive voltage follower circuit P1 and the N-type drive voltage follower circuit N1 are connected to the input terminal of the switching circuit 10. The connection points A, B, C of the resistance elements R1 to R5,
D is a V2, V3, V4, V5 level power supply as an intermediate voltage, the highest supply voltage is a V1 level power supply, and the lowest potential (ground) is a VG level power supply.

[0020] The V1, VG-level power supply is connected directly as input to the switching circuit 10. In addition,
The P-type drive voltage follower circuit P1 and the N-type drive voltage follower circuit N1 operate as a current booster (amplification degree = 1) for obtaining a required supply current, and generally use an operational amplifier (op-amp). It is a target.

The V1 level power supply (supply voltage) is connected so as to be input to the switching transistors T1 and T2 of the switching circuit 10. Further, the output terminal of the P-type drive voltage follower circuit P1 is connected to the input terminals of the transistors T3 and T4 of the switching circuit 10. Similarly,
The output terminal of the N-type drive voltage follower circuit N1 is connected to the transistors T5 and T6. The VG level power supply, which is the ground potential, is connected so as to be input to the transistors T7 and T8. Output terminals of the transistors T1, T4, T5, and T7 of the switching circuit 10 are connected to an output circuit (common terminal side) 20. Also, the transistor T
Output terminals of T2, T3, T6, and T8 are connected to an output circuit (segment terminal side) 30.

The output circuit (common terminal side) 20 has up to 2n (not shown). The transistor T9 of the output circuit (common terminal side) 20 is connected to the output of the transistors T1 and T4 of the switching circuit 10. Connected to be input. The transistor T10 of the output circuit (common terminal side) 20 is connected to the transistors T5 and T5 of the switching circuit 10.
It is connected so that the output of T7 is input. Then, the output terminals of the transistors T9 and T10 of the output circuit 20 are commonly connected to output COM1. Note that this output circuit (common terminal side) 2
0.

Furthermore, the output circuit (segment terminal side) 30
The transistor T11 is connected so that the outputs of the transistors T2 and T3 of the switching circuit 10 are input.
The transistor T12 of the output circuit (segment terminal side) 30 is connected so that outputs of the transistors T6 and T8 of the switching circuit 10 are input. Of the transistors T11 and T12 of the output circuit (segment terminal side) 30
The output terminals are commonly connected to output SEG1. Note that the configuration up to the output circuit 3n (not shown) is the same as that of the output circuit (segment terminal side) 30.

The switching circuit 10, the output circuit (common terminal side) 20... 2n and the output circuit (segment terminal side) 3
0 ... 3n may have any configuration as long as they operate in the same manner as described below.

Next, the operation of this embodiment will be described. Here it will be described with reference to FIG. In FIGS. 1 and 4, when a voltage of the same polarity is applied to the liquid crystal, the liquid crystal deteriorates. Therefore, as shown in FIG. 4, a voltage whose polarity is changed for each frame is applied to the liquid crystal panel. First, in the first frame, as shown in FIG. 4, the output circuit (common terminal side) 20 outputs the V1 level power supply during the selection operation, and outputs the V5 level power supply during the non-selection operation. The output circuit (segment terminal side) 30 outputs a V4 level power supply during a non-selection operation and outputs a VG level power supply during a selection operation.

In this case, in the operation of FIG. 1, the transistor T1 is turned on and the transistor T4 is turned off based on the frame signal, and the V1 level power is output to the transistor T9. The switch SW2 has a movable contact connected to the fixed contact at the connection point D with the resistance elements R4 and R5 based on the frame signal. With this connection, the V5 level power is input to the N-type drive voltage follower circuit N1. The V5 level power output from the N-type drive voltage follower circuit N1 is supplied to the transistor T10 of the output circuit (common terminal side) 20 with the transistor T5 turned on and the transistor T7 turned off. In the non- selection operation of the output circuit (common terminal side) 20, the transistor T9 is turned off , and the transistor T10 is turned off.
The output circuit (common terminal side) 20 outputs a V5 level power supply. As a result, the output circuit (common terminal side) 20 outputs the V1 level power during the selection operation and outputs the V5 level power during the non-selection operation.

On the other hand, by connecting the movable contact of the switch SW1 and the fixed contact of the resistive element R3, the connection point of R4 C side, V4
The level power is input to the P-type drive voltage follower circuit P1. The V4 level power output of the P-type drive voltage follower circuit P1 is connected to the transistor T of the switching circuit 10.
3 is turned on, the transistor T2 is turned off, and the transistor T11 of the output circuit (segment terminal side) 30 is turned on.
Is applied to Also, the transistor T8 is turned on,
The transistor T6 is turned off, and the VG level power is applied to the transistor T12.

As shown in FIG . 4, in the selection operation of the output circuit (segment terminal side) 30, the transistor T12 is turned on and the transistor T11 is turned off, so that the VG level power is supplied from the output circuit (segment terminal side) 30. Is output. On the other hand, in the non-selection operation of the output circuit (segment terminal side) 30, the transistor T11 is turned on and the transistor T12 is turned off, and the V4 level power is output from the output circuit (segment terminal side) 30. Thus, from the output circuit (segment terminal side) 30,
A V4 level power supply is output during a non-selection operation, and a VG level power supply is output during a selection operation.

Next, the case of the second frame, as shown in FIG. 4, the output of the output circuit (common terminal side) 20, and outputs a VG level power at the time of selection operation. Also, it outputs the V2 level power supply during the non-selection operation. Further, the output circuit (segment terminal side) 30 outputs a V1 level power supply during the selection operation and outputs a V3 level power supply during the non-selection operation. At this time, in the circuit operation of FIG.
The transistor T7 of 0 is turned on, the transistor T5 is turned off, and the VG level power is applied to the transistor T10.

In the case of the second frame, the movable contact of the switch SW1 is connected to the fixed contact on the connection point A side of the resistance elements R1 and R2. The V2 level power is input to the P-type drive voltage follower circuit P1. The V2 level power output from the P-type drive voltage follower circuit P1 turns on the transistor T4 of the switching circuit 10 and turns on the transistor T4.
1 is turned off and applied to the transistor T9.

As shown in FIG. 4, when the output circuit (common terminal side) 20 is selected, the transistor T10 is turned on and the transistor T9 is turned off. Is output. On the other hand, when the output circuit (common terminal side) 20 is not selected,
The transistor T9 is turned on, the transistor T10 is turned off, and the output circuit (common terminal side) 20 outputs the V2 level power. Thus, the output circuit (common terminal side) 20 outputs the VG level power during the selection operation and outputs the V2 level power during the non-selection operation.

[0032] On the other hand, in the second frame, switch SW2
Is connected to the fixed contact on the connection point B side of the resistance elements R2 and R3, and the V3 level power is input to the N-type drive voltage follower circuit N1. The V3 level power output of the N-type drive voltage follower circuit N1 is
The transistor T6 is turned on, the transistor T8 is turned off, and the voltage is applied to the transistor T12 . In addition, the transistor T2 is turned on, the transistor T 3
Is turned off, and the V1 level power is applied to the transistor T11 of the output circuit (segment terminal side) 30.

As shown in FIG. 4, when the output circuit (segment terminal side) 30 is selected, the transistor T1
1 turns on, the transistor T12 turns off,
The output circuit (segment terminal side) 30 outputs a V1 level power supply. The output circuit (segment terminal side) 3
In the non-selection operation of 0, the transistor T12 is turned on and the transistor T11 is turned off, and the output circuit (segment terminal side) 30 outputs the V3 level power. Thus, the output circuit (segment terminal side) 3
From 0, it outputs V 1 level supply during selection operation, and outputs the V 3-level power supply during non-selection operation.

In this way, every time the frame is switched, the SEG output and the COM output, which are the outputs of the liquid crystal display driving device, are performed as shown in FIG.

FIG . 2 is a circuit diagram showing the configuration of another embodiment, and FIG. 3 is a waveform diagram for explaining the operation of the other embodiment. In this example, a logic circuit 10a for externally inputting a DOFF signal to be described later is added to the switching circuit 10A with respect to the configuration of the embodiment shown in FIG. This configuration is effective when it takes time until the operations of the P-type drive voltage follower circuit P1 and the N-type drive voltage follower circuit N1 are stabilized when the switches SW1 and SW2 are switched.

The DOFF signal is generated from an external frame switching signal FRM shown in FIG. 3A and a frame switching delay signal shown in FIG. 3B obtained by delaying the frame switching signal FRM. 3C, a short pulse signal shown in FIG. 3C is transmitted.

The processing of the AND gate and the inverter of the logic circuit 10a in FIG . 2 causes the DOFF signal to go high at the transition point of the first frame, and this high-level DOFF signal causes the transistors T4 and T6 of the switching circuit 10A to turn on. It turns off, and the transistors T3 and T5 turn off through the inverter. The switches SW1 and SW2 are switched while the DOFF signal is at a high level. When the DOFF signal changes to a low level, the same operation as in the above-described embodiment is performed.

[0038] Similarly, in the second frame, DOFF signal goes high at the change point, D of the high level
The OFF signal, the transistor T of the switching circuit 10 A
4, T6 are turned off, and the transistors T3, T5 are turned off through the inverter. The switches SW1 and SW2 are switched while the DOFF signal is at a high level. When the DOFF signal changes to a low level, the same operation as in the above-described embodiment is performed.

In this embodiment, an example in which the voltage polarity is inverted for each frame has been described. However, the present invention can be applied to a line inversion driving method in which the voltage polarity is inverted for each line of the matrix liquid crystal panel. In this case, a line signal may be supplied to the movable contacts of the switches SW1 and SW2 to perform switching in the same manner as in the frame. Further, the present invention can be applied as it is to an AC drive inversion method in which the voltage polarity is inverted every plural lines of the matrix liquid crystal panel, for example, every ten lines. Also in this case, an AC drive inversion signal is supplied to the movable contacts of the switches SW1 and SW2 to perform switching in the same manner as in the frame. The other embodiments shown in FIGS. 2 and 3 operate similarly by supplying a line signal or an AC drive inversion signal to the logic circuit 10a.

[0040]

As is apparent from the above description, according to the drive power supply for liquid crystal display of the present invention, the voltage is generated by dividing the voltage by a plurality of resistance elements connected in series between the voltage supply terminal and the lowest potential. One or the other of the two intermediate voltages, and one or the other of the other two intermediate voltages are selected for each frame, line, or multiple lines, and together with the intermediate voltages, the supply voltage and the minimum potential are obtained to obtain the required current. As a power supply for driving a liquid crystal panel through two voltage follower circuits.

[0041] As a result, the number of voltage follower circuit is reduced. Further, current consumption is reduced, and a mounting area of an IC chip or the like is reduced, so that downsizing and cost reduction can be achieved.

Further, in the liquid crystal display driving power supply device of the present invention, the switching operation of the switching circuit is stopped until the operation of the voltage follower circuit is stabilized, and the first and second switches are turned off during this operation stop. The switching operation is performed.

[0043] Consequently, in the case of reducing the voltage follower circuit frame, for performing liquid crystal panel driving by inverting the voltage polarity for each line or plural lines is applied to the plurality of common terminals and segment terminals of the matrix liquid crystal panel Power generation of a plurality of voltages is performed more stably.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a liquid crystal display drive power supply device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of another embodiment.

FIG. 3 is a waveform chart for explaining an operation of another embodiment.

FIG. 4 is a timing chart for explaining a voltage polarity applied to a liquid crystal panel in a conventional example.

FIG. 5 is a block diagram showing a configuration of a conventional driving power supply device for liquid crystal display.

FIG. 6 is a block diagram showing a configuration of a main part of a conventional driving power supply circuit for liquid crystal display.

[Explanation of symbols]

 Reference Signs List 10 switching circuit 10a logic circuit COM1, SEG1 output circuit N1 N-type drive voltage follower circuit P1 P-type drive voltage follower circuit R1 to R5 Resistive element SW1, SW2 Switch T1 to T12 Transistor

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoji Takekoshi 403-53, Ichigome, Kosugi-cho, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Within NEC Ic Microcomputer System Co., Ltd. JP-A-9-292599 (JP, A) JP-A-6-324640 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/133 G09G 3/36

Claims (3)

(57) [Claims] 1. A voltage whose polarity is inverted for each frame is
Multiple common terminals and segment
LCD display drive power supply with output circuit
In a device, a plurality of resistive elements for dividing a supply voltage into four intermediate voltages
And any two of the four intermediate voltages are
Or a first switch for selecting and outputting every plural lines
The first switch does not select among the four intermediate voltages.
The other two intermediate voltages into a frame, line or multiple
A second switch for selecting and outputting for each in,Either P-type or N-type connected in series to the first switch
One type of voltage follower circuit, The first switch connected in series to the second switch
Different from the type of voltage follower circuit connected in series to
Either P-type or N-type voltage follower times
Road and  The output of each of the two voltage follower circuits is
Switch to both the common terminal side and segment terminal side
For liquid crystal display, characterized by having a switching circuit for switching
Drive power supply. 2. The switching circuit according to claim 1, further comprising an operation stop instruction circuit for stopping the switching operation from when the first or second switch is switched to when the operation of the voltage follower circuit is stabilized. The drive power supply for a liquid crystal display according to claim 1. 3. The operation stop instruction circuit delays a switching signal of a frame, a line, or a plurality of lines and a switching signal of a frame, a line, or a plurality of lines according to a time until the operation of the voltage follower circuit is stabilized. 3. The driving power supply for a liquid crystal display according to claim 2, wherein a short pulse signal generated from a switching delay signal of a frame, a line, or a plurality of lines is transmitted.