JPH10170884A - Lcd drive source circuit, and lcd-driving integrated circuit device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to have optimum current consumption for various liquid crystal panels, by providing a switching element between a source division circuit and a power source and providing a capacitor to the output of the source division circuit. SOLUTION: The switch elements SW2, SW3 are connected to between the source division circuit dividing a source voltage, generating plural potential and outputting them and the power source. By turning these switching elements SW2, SW3 on/off, and opening/closing a path of the current flowing through the source division circuit by the source voltage, the current consumption in the source division circuit is suppressed. Further, in an LCD drive source circuit 1, the capacitors C2, C3 are connected to the output of the source division circuit. These capacitors C2, C3 are charged by the output voltage of the source division circuit when the switching elements SW2, SW3 are turned on, and drive an LCD when turned off. By changing charge/discharge periods of these capacitors C2, C3, various liquid crystal panels are driven by the same circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LCD driving power supply circuit, and more particularly to a technique effective when applied to an LCD driving power supply circuit for generating a plurality of liquid crystal driving potentials for driving a liquid crystal panel by a time division driving method.

[0002]

2. Description of the Related Art In an LCD display device, when driving a large number of display pixels or reducing the number of drive circuits, such as in the case of multi-digit display of segment display or dot matrix display for driving many pixels, circuits and display cells In order to reduce the number of connection points,
The time division driving method is effective. In the time-division driving method, a liquid crystal driving potential equal to the number of driving biases is required to form a driving waveform of the liquid crystal, and is supplied by an LCD driving power supply circuit. The method of generating the liquid crystal driving potential is such that a method of dividing the power supply voltage by the impedance of the circuit element is appropriate in terms of the circuit scale, and can be realized by various elements. The method using a resistor is generally referred to as a resistance division method and will be described below. However, a non-linear element can be similarly considered by considering the voltage-current characteristics.

In the resistance division method, a number of resistors corresponding to the number of drive biases are arranged in series between a positive electrode side and a negative electrode side of a power supply voltage, and a terminal voltage of each resistor is extracted to drive a liquid crystal.
If the resistance values of the respective resistors in the series resistance circuit are made equal, a potential obtained by equally dividing the power supply voltage can be taken out as a liquid crystal drive potential, which is suitable for a time-division driving method and is widely used.

Since the load on the liquid crystal panel fluctuates in a complicated manner depending on display data, in order to maintain good display quality of the liquid crystal panel in the time-division driving method, the liquid crystal driving potential is supplied stably regardless of the fluctuation of the load on the liquid crystal panel. (Hereinafter, referred to as an operation margin) is required. Therefore, the division resistance value of the power supply voltage is determined based on a balance between the operation margin and the power consumption. As described above, in the resistance division method, it is desirable that the division resistance value be as high as possible because a steady current consumed by the division resistance flows from the positive electrode side to the negative electrode side of the power supply voltage to increase current consumption. On the other hand, since liquid crystal is a capacitive load, when driving a large number of liquid crystals, the load capacitance becomes large, and when the power supply capacity of the LCD drive power supply circuit is small, the drive waveform of the liquid crystal is distorted, and the LCD drive power supply circuit is distorted. If the impedance of the liquid crystal is high, noise is generated in the driving waveform of the liquid crystal due to the charge / discharge current of the liquid crystal, so that the display quality deteriorates. Therefore, in order to secure an operation margin, it is necessary to lower the resistance value of the split resistor, but this leads to an increase in current consumption. Therefore, it is necessary to determine the resistance value of the split resistor in a compromise between the operation margin and the power consumption. Further, if a voltage follower circuit using an operational amplifier is used for each liquid crystal drive potential, a stable potential can be supplied to the liquid crystal panel while the division resistance is set large. However, since the voltage follower circuit consumes current, the current consumption of the entire device increases, and the mounting area increases due to the additional circuit. The above contents are described in detail in "Explanation of LCD driving method" of "Hitachi LCD Controller / Driver LSI Data Book 8th Edition".

The same can be said for the case where a power supply voltage dividing circuit is constituted by circuit elements other than resistors.

In an LCD display device, when an LCD drive power supply circuit is incorporated in a large-scale integrated circuit (LSI), mounting of circuit elements for dividing the power supply voltage is omitted, which is advantageous in terms of mounting and cost. . On the other hand, since the power supply capacity of the LCD drive power supply circuit is fixed because the circuit element is fixed, there is a point to be considered in circuit design. LCD
If the power supply capacity of the driving power supply circuit is smaller than that of the liquid crystal panel, some external circuit is required. For example, there is a method of using a voltage follower circuit using an operational amplifier. Connect. Alternatively, in the case of the resistance division method, an external resistance is added between the terminals for outputting the liquid crystal driving potential to reduce the combined impedance with the division resistance inside the LSI, thereby enhancing the power supply capacity of the LCD driving power supply circuit. In either case, an additional circuit is required, and the advantage of incorporating the power supply dividing element in the LSI cannot be used. When the power supply capacity of the LCD drive power supply circuit is larger than that of the liquid crystal panel, an excessive current is consumed by the internal power supply dividing element compared to the drive current of the liquid crystal. Therefore, when an LSI incorporating a power supply dividing element is used for an LCD display device, there are disadvantages in terms of current consumption and mounting in combination with a liquid crystal panel.

[0007]

As described above, in the prior art, the opposing effects of ensuring an operation margin by low impedance and suppressing current consumption by high impedance are caused by the equivalent impedance of the power supply dividing element in the LCD drive power supply circuit. There were two tasks to do. Further mounting surface
When a power supply dividing element is built in an LSI from the viewpoint of cost effectiveness, there is a problem that it is difficult to optimally design current consumption for various types of liquid crystal panels.

Therefore, in the present invention, an LCD driving power supply circuit and an LCD driving circuit capable of securing an operation margin and suppressing current consumption, and enabling an LSI having a built-in power dividing element to supply optimum current consumption for various liquid crystal panels. To realize an integrated circuit device.

[0009]

In an LCD drive power supply circuit according to the present invention, a switching element is connected between a power supply and a power supply division circuit that divides a power supply voltage to generate and output a plurality of potentials. Turn on this switching element
By turning off the power supply voltage to open and close the path of the current flowing to the power supply division circuit, the current consumed by the power supply division circuit can be suppressed. Further, in the LCD drive power supply circuit according to the present invention, a capacitor is connected to the output of the power supply division circuit. This capacitor is charged by the output voltage of the power supply division circuit when the switching element is on. When the switching element is off, the LCD is driven using the charged capacitor as a power supply. Further, by controlling the ON / OFF of the switching element and changing the charge / discharge period of the capacitor, it becomes possible to drive various types of liquid crystal panels with the same circuit.

An LCD driving integrated circuit device (for example, an LCD controller, a driver or a microcomputer) capable of driving various kinds of liquid crystal panels with low power consumption by incorporating all or a part of the LCD driving power supply circuit according to the present invention. Is realized.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) As an embodiment of the present invention, a block diagram of an LCD display device having three common terminals and 30 segment terminals and incorporating a resistor for dividing a power supply voltage for driving a liquid crystal in an LSI is shown in FIG. Shown in In the figure, 1 is an LCD drive power supply circuit, 2 is a common driver, 3 is a segment driver, 4 is a charge / discharge clock generation circuit, 5 is a charge / discharge time register, 6 is a CPU (Central Processing Unit), and 7 is a ROM (Read). Only Memory), 8 is an LCD control circuit, 9
Denotes a liquid crystal panel. Reference numerals 1 to 8 denote a built-in circuit of the LSI, which performs display on an external liquid crystal panel 9. A power supply for driving the liquid crystal is connected to the Vcc terminal.
The liquid crystal driving potential is generated by dividing cc, and each potential is set to V1, V
2. Output to V3 line. The potentials of V1, V2, and V3 pass through common terminals COM1 to COM3 and segment terminals SEG1 to SEG via a common driver and a segment driver.
Output to the EG 30 to drive the liquid crystal panel. At this time, the driving waveform of the liquid crystal output from each terminal follows the control signals output from the LCD control circuit to the common driver and the segment driver. The supply / non-supply of the liquid crystal drive potential in the LCD drive power supply circuit is controlled by a charge / discharge clock signal CKc output from a charge / discharge clock generation circuit.
CKc is a binary logic level “High” level or “L”.
It has a potential of “low” level, and the “High” level means supply of the liquid crystal driving potential, and the “Low” level means no supply.

The control of supply / non-supply of the liquid crystal drive potential is performed by CK
c This corresponds to signal control, and is performed as follows. "Hi" of CKc
A program for setting the counter values corresponding to the lengths of the "gh" level period and the "Low" level period in the charge / discharge register is written in the ROM. The charge / discharge clock generation circuit reads the counter value set in the charge / discharge time register and generates a CKc signal, and the charge / discharge time register is a counter for each level period of CKc. It has the following relationship with the CKc signal.

Tc = Cc × Tck Tdc = Cdc × Tck Here, Tc is the “High” level period of CKc, Tdc is the “Low” level period of CKc, and Cc is “Hi” of CKc.
gh ”level period, Cdc is also“ Lo ”
The w "level period counter value, Cc and Cdc are set in the charge / discharge time register. Tck is the time of one cycle of the basic clock.
After outputting the "High" level to Kc, the basic clock is counted Cc times and CKc is set to "Low" level. From this point, the basic clock is counted Cdc times and then CKc again.
Are set to the “High” level. Therefore, the supply / non-supply of the liquid crystal drive potential is controlled by R
This can be performed by software using a program written in the OM.

FIG. 2 shows a circuit configuration of the LCD drive power supply circuit. In the figure, R1, R2 and R3 are division resistors,
Assuming that the resistance value is R1 = R2 = R3, the liquid crystal driving potentials V1, V2, and V3 that divide the Vcc into three equals are generated together with the Vcc connected to the inside of the circuit. MOS transistor P
1. The CMOS switches SW2 and SW3 control the supply and non-supply of the liquid crystal drive potential and simultaneously control the inflow and cutoff of the current _ILCD flowing from Vcc into the circuit. P1, SW2
SW3 operates according to CKc and its inverted signal. V
Capacitors C2 and C3 connected to lines V2 and V3 have a function of driving the liquid crystal when the liquid crystal driving potential is not supplied. According to this circuit, by controlling the potential of CKc, I
It is possible to control the supply and non-supply of the liquid crystal driving potential to the _LCD control and V2, V3 line.

The specific operation of this embodiment will be described below with reference to the timing chart of FIG. The figure shows the case of 1/3 bias, 1/3 duty, and A type waveform.
OM1, COM2, COM3 and any segment terminal waveform SEGn are the same as those of the prior art. As described above, the supply of the liquid crystal drive potential from the LCD drive power supply circuit can be controlled by CKc. Here CKc
波形 of one frame during the charging period Tc, 2
/ 3 is defined as a discharge period Tdc. In the period Tc, CKc becomes “H”.
P1, SW2, S in FIG.
W3 is turned on. Therefore, liquid crystal drive potentials V2 and V3 are supplied from the LCD drive power supply circuit, and the liquid crystal is driven through a common driver and a segment driver together with V1.
The charge / discharge of electric charge is performed so as to be × 2/3, Vcc × １ ／. During the period Tdc, CKc is at the “Low” level, and P1, SW2, and SW3 in FIG. 2 are turned off. During this period, the liquid crystal driving potential except V1 is not supplied from Vcc, and the supply source of the liquid crystal driving potential is the capacitors C2 and C3. That is, the liquid crystal during the discharging period Tdc is driven by using the charge charged in each capacitor during the charging period Tc. The driving waveform of the liquid crystal changes in a complicated manner depending on the data to be displayed. However, since the charge is transferred between a capacitor as a charge supply source and a capacitive load of the liquid crystal, V2,
The potential of V3 fluctuates toward averaging over time. In FIG. 3, the maximum values of these fluctuation amounts are Vd2 and Vd3, respectively. In order to maintain good display quality of the liquid crystal, Vd2 and Vd3 must be kept as small as possible, and this can be achieved by appropriately setting Tc and Tdc for the liquid crystal panel. The period Tdc is followed by the period Tc again,
Liquid crystal display is performed by repeating these two periods periodically.

Next, the current consumption will be described. All the currents for driving the liquid crystal are supplied from a liquid crystal driving power supply Vcc, and this current is shown as I _LCD in FIG. The I _LCD is composed of a current consumed for driving the liquid crystal and a current flowing to the ground potential via the dividing resistor. The change of I _LCD is followed by the timing chart of FIG. At the beginning of the period Tc, the charging and discharging of the capacitors C2 and C3 and the driving of the liquid crystal overlap, so that the peak current Ip flows. Eventually, the current value decreases and approaches the steady value Is. The value of Is is constantly equal to the value of the current flowing through the divided resistor, and Is = Vcc / (R1 + R2 + R3). In the period Tdc, since the MOS transistor P1 is turned off, only the current consumed for driving the liquid crystal via the V1 line is obtained. As is apparent from the above, in this example, the LCD
The current that is constantly consumed in the drive power supply circuit is reduced, which is effective for reducing the current consumption in the LCD display device.

In the case where a dividing resistor is built in an LSI, it is difficult to supply an optimum current to various types of liquid crystal panels by the conventional technique. However, according to the present embodiment, this problem can be solved. . As described above, the charge / discharge period Tc,
Since the power supply capacity of the LCD drive power supply circuit can be adjusted by Tdc, the resistance value of the built-in divided resistor can be set low. In this case, the power supply capacity of the LCD drive power supply circuit is large, so that a large liquid crystal panel can be driven. When driving a small liquid crystal panel, the charging period Tc is set short, and the discharging period Tc is set.
By setting dc to be long, the power supply capacity of the LCD drive power supply circuit is reduced. In this way, it is possible to drive various types of liquid crystal panels with optimal current values.

As described above, according to this embodiment, it is possible to secure the operation margin and suppress the current consumption in the LCD drive power supply circuit, and the LSI incorporating the power supply dividing element can optimize various types of liquid crystal panels with optimum current values. Can be driven.

(Embodiment 2) In the LCD display device of Embodiment 1, when driving a large or a large number of liquid crystals,
It is necessary to increase the capacitance value of the capacitor built in the drive power supply circuit. That is, the increase in the capacitive load of the liquid crystal increases the amount of charge carried by the capacitor when the liquid crystal driving power is not supplied from the liquid crystal driving power supply. However, increasing the capacitance value of the capacitor increases the circuit area of the LSI, which is not preferable. As a solution, there is a method of externally attaching a capacitor, and since it is an external component, an appropriate capacitance value can be selected according to the liquid crystal panel.

The present invention enables the external connection of a capacitor in the LCD display device shown in the first embodiment. An embodiment is shown in FIG. 10 in the figure corresponds to the LCD drive power supply circuit 1 in the block diagram of the first embodiment (FIG. 1), and the other configuration is the same as that of the first embodiment. As shown in FIG. 4, capacitors C2 and C3 are terminals V for outputting a liquid crystal driving potential.
2, externally connected to V3. Since the operation of the circuit is the same as that of the first embodiment, the current consumption can be optimally set by appropriately setting the capacitance value of the external capacitor in addition to the setting of the charge / discharge period.

Also, in the LCD drive power supply circuit having a built-in capacitor as shown in FIG. 2, by providing a terminal for an external capacitor and adding a capacitor as in this example, the combined capacitance with the built-in capacitor can be obtained. Thus, the same effect as in the present embodiment can be obtained.

As described above, according to the present embodiment, the capacitance value of the capacitor of the LCD drive power supply circuit can be set arbitrarily, and it is possible to drive various types of liquid crystal panels with optimal current values.

Embodiment 3 As described in Embodiment 2, in order to drive a large or a large number of liquid crystals, it is necessary to increase the capacitance value of the capacitor. Therefore, it is not preferable from the viewpoint of mounting. In addition, it is necessary to set the charging period Tc to be long.
The current consumed constantly during the period c increases, and there is a problem in the current consumption. Therefore, the capacitance value of the capacitor has a certain limit and cannot be increased without limit. In order to drive a large number of liquid crystals under this condition, the liquid crystal driving potential must be maintained by frequently providing a capacitor charging period Tc. Moreover, since the charging period Tc is required to be short in terms of current consumption, it is necessary to charge and discharge a large-capacity capacitor in a short time. That is, it is necessary to increase the power supply capacity of the LCD drive power supply circuit. In the LCD driving power supply circuit according to the second embodiment, the power supply capacity is enhanced by using an external circuit.

An embodiment is shown in FIG. 11, reference numeral 11 denotes an LCD drive power supply circuit 1 in the block diagram of the first embodiment (FIG. 1).
The other configuration is the same as that of the first embodiment. FIG.
, The capacitors C2 and C3 are externally attached,
As described in the second embodiment, it is also possible to configure with a built-in only or a combined built-in and external capacitor. As shown in FIG.
R1, VR2, and VR3 are provided, and an external dividing resistor R11,
R12 and R13 are connected. At this time, R11, R12, and R13 have the action of lowering the combined impedance by making their resistance values lower than the built-in split resistors R1, R2, and R3, respectively.
The power supply capacity of the LCD drive power supply circuit can be increased. Since the operation of the circuit is the same as that of the first and second embodiments, an external circuit for strengthening the power supply capacity of the LCD drive power supply circuit is provided in addition to the setting of the charging / discharging period and the setting of the capacitor value. Even when driving a large number of liquid crystals, the current consumption can be set optimally.

In addition, if the LCD drive power supply circuit of the present embodiment has a circuit configuration in which the built-in divided resistance is eliminated, the divided resistance value can be set arbitrarily by an external resistor, and the circuit area of the LSI can be reduced. Can be reduced.

As described above, according to this embodiment, the power supply capacity of the LCD drive power supply circuit can be adjusted by an external circuit, and it is possible to drive various types of liquid crystal panels with optimal current values. (Embodiment 4) In the first to third embodiments, a resistor is used as an element for dividing a power supply voltage for driving a liquid crystal. However, other circuit elements can be used. Can be simplified. FIG. 6 shows a circuit using a MOS transistor as a power supply dividing element. 12 corresponds to the LCD drive power supply circuit 1 in the block diagram of the first embodiment (FIG. 1), and the other configuration is the same as that of the first embodiment. In FIG. 6, P11, P12 and N12, N
13 turn on when CKc is at "High" level, divide the Vcc voltage by the resistance value of each MOS transistor at the time of on operation, generate a liquid crystal driving potential, charge and discharge capacitors C2 and C3, and charge and discharge the liquid crystal. Drive. When CKc goes to a "Low" level, the operation is turned off, and the supply of potential except V1 from Vcc is stopped. The above operation is the same as that of the LCD drive power supply circuits of the first to third embodiments, and the entire LCD display device operates in exactly the same manner. On the other hand, since the MOS transistor has a role of dividing the power supply voltage and also controls the supply / non-supply of the potential from Vcc, the number of elements constituting the circuit is reduced.

As described above, according to this embodiment, an element having a switching characteristic is used as an element for dividing the power supply voltage for driving the liquid crystal, thereby simplifying the circuit configuration of the LCD drive power supply circuit and reducing the circuit area of the LSI. I can do it.

[0028]

The effects obtained by the invention disclosed by the present application will be briefly described as follows. LC
In the D display device, by controlling the generation of the liquid crystal drive potential by software, it is possible to secure an operation margin and suppress current consumption, and to drive the liquid crystal panel with an optimal current value over various types of liquid crystal panels.

[Brief description of the drawings]

FIG. 1 shows a configuration of an embodiment of the present invention, and is a block diagram of an LCD display device.

FIG. 2 shows an embodiment of the present invention and shows a configuration example of an LCD drive power supply circuit.

FIG. 3 shows changes in the potential of each terminal for explaining the operation of the LCD drive power supply circuit according to one embodiment of the present invention.

FIG. 4 shows a second embodiment of the present invention and shows a configuration example of an LCD drive power supply circuit.

FIG. 5 shows a third embodiment of the present invention and shows a configuration example of an LCD drive power supply circuit.

FIG. 6 shows a fourth embodiment of the present invention, and shows a configuration example of an LCD drive power supply circuit.

[Explanation of symbols]

1, 10 to 12 LCD drive power supply circuit, 2 common driver, 3 segment driver, 4 charge / discharge clock generation circuit, 5 charge / discharge time register, 6 CPU (Centra)
l Processing Unit, 7… ROM (Read Only Memor)
y), 8: LCD control circuit, 9: Liquid crystal panel.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroyuki Kida 3-1-1, Sachimachi, Hitachi-shi, Ibaraki Pref. Hitachi, Ltd. Hitachi Plant (72) Inventor Ken Sugai 3-1-1, Sachimachi, Hitachi-shi, Ibaraki No. 1 Inside Hitachi, Ltd. Hitachi Plant (72) Inventor Katsunori Koike 3-2-1 Komachi, Hitachi City, Ibaraki Prefecture Inside Hitachi Engineering Co., Ltd. (72) Inventor Masahiko Numata Bentencho, Hitachi City, Ibaraki Prefecture 3-10-2 Hitachi Haramachi Electronics Co., Ltd.

Claims (7)

[Claims] A power supply dividing circuit for dividing a power supply voltage to generate and output a plurality of potentials; a switching element connected between the power supply dividing circuit and a power supply; And a capacitor to be driven. 2. The LCD according to claim 1, wherein said power supply dividing circuit divides a power supply voltage by a resistor.
Drive power supply circuit. 3. The LCD drive power supply circuit according to claim 2, wherein a plurality of potentials generated by said power supply division circuit are output via switch means. 4. The power supply dividing circuit according to claim 1,
An LCD drive power supply circuit, wherein a power supply voltage is divided by an OS transistor. 5. A power supply dividing circuit for generating a plurality of potentials by dividing a power supply voltage and outputting the plurality of potentials, and a switching element connected between the power supply dividing circuit and a power supply. An integrated circuit device for driving an LCD, wherein a capacitor is connected to an output of the dividing circuit. 6. The LCD driving integrated circuit device according to claim 5, wherein said capacitor is externally connected. 7. The LCD driving integrated circuit device according to claim 5, wherein said power supply dividing circuit divides a power supply voltage by a resistor, and another resistor is externally connected to said resistor.