JPH11296144A - Driving circuit of liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a useful technology in which a high quality picture is realized by providing a multi-level picture, the number of driving circuit elements is reduced and the production yield is improved. SOLUTION: The circuit is constituted of switched capacitors SC1, SC2 and SC3 whose one end sides are connected to a reference voltage Vhi of a high voltage side in parallel, a feedback resistor R whose one side is connected to a reference voltage Vlo of a low voltage side and the other side is commonly connected to the capacitors SC1, SC2 and SC3, and MOS switches SW1, SW2 and SW3 which are switch controlled by digital gradation control signals D1, D2 and D3 and supply switched capacitor control signals S1, S2 and S3 to the capacitors SC1, SC2 and SC3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a so-called peripheral circuit integrated type panel in which a liquid crystal display section and a peripheral circuit section are integrated on the same substrate, and displays a light and dark gradation according to a digital input signal. The present invention relates to a driving circuit for a liquid crystal display device.

[0002]

2. Description of the Related Art In general, in a liquid crystal display device in which a predetermined voltage is applied to a liquid crystal sandwiched between two glass substrates, a desired display gradation is obtained by changing the orientation of the liquid crystal, that is, the light transmittance. There are two types: "analog method", which amplifies an analog input signal as it is and uses it for the liquid crystal voltage. In particular, the latter digital system occupies the mainstream of applications requiring high image quality.

[0003] Further, with the recent progress in liquid crystal display device manufacturing technology, a peripheral circuit integrated panel in which a liquid crystal display portion and peripheral circuits including a driving circuit and the like are integrated on the same polysilicon substrate has been put to practical use. I have. FIG. 8 is a schematic configuration diagram of a peripheral circuit integrated type panel, and peripheral circuits such as a digital driver (also referred to as a data driver) 10 and a gate driver 11 are integrally formed around a liquid crystal display panel 12 formed on a substrate 14. Is formed. Reference numeral 13 denotes a control circuit for controlling peripheral circuits.

FIG. 9 shows a configuration diagram of a gradation voltage generation circuit applied to such a display panel. FIG. 9 shows a gray scale voltage generation circuit for generating eight types of gray scale voltages V1 to V8 (types are for convenience). Decoder 21 for activating one of the outputs D1 to D8
And eight switch elements 22 to 29, one of which is turned on by the active output of the decoder 21, and nine resistive elements connected in series between the high-potential power supply Vhi and the low-potential power supply Vlo. 31 to 39, and the potential difference between Vhi-Vlo is divided by nine resistance elements 31 to 39 to generate eight kinds of gradation voltages V1 to V8, and one of them is converted into a digital input signal B1. B3 are selected according to the combination of the logics of .about.B3 and output to the data bus line of the liquid crystal panel (not shown) as the liquid crystal voltage Vout.

That is, the digital driver used in the drive circuit has a number of digital signals corresponding to the number of gray scales of the display panel and a voltage to be applied to the liquid crystal, and decodes the former digital signal to obtain the gray scales. A display signal to be applied to the liquid crystal is selected by generating a selection signal and turning on / off the selection switch. When such a circuit configuration is employed, there is a problem that the number of elements constituting a decoding unit for decoding a digital signal increases as the number of gradations increases.

As a method for solving such a problem, a method of dividing the configuration of a voltage selector section used in a digital driver by resistance, as disclosed in Japanese Patent Application No. 8-125223, is used. Is known to reduce the number of elements. Fig. 1 shows a specific example.
0, shown in FIG. Here, as shown in FIG. 10, the digital driver operates as follows in the display driving of the liquid crystal panel.
During a horizontal scanning period, a latch unit 16 that outputs a digital display signal of a predetermined bit at a predetermined timing at a timing synchronized with a pixel clock, and eight types of floors according to the digital data B1 to B4 output from the latch unit 16. There are provided voltage selectors 15a, 15b,... For selecting one of the adjustment voltages and applying the data to the data bus lines 16a, 16b,.

The voltage selectors 15a and 15b
As shown in FIG. 11 (a), the drains of first to third MOS transistors 41 to 43 having different L / W are connected to VDD, and three-bit digital input signals B1 to B3 are connected to each gate. And each source is connected to VSS via a resistance element 44. Here, W is the channel width of the MOS transistor, L is the channel length, and by setting a predetermined weight to L / W, a function equivalent to the gradation voltage selection circuit shown in FIG. 9 is realized.

As another configuration, as shown in FIG. 11 (b), the weighting of the resistance component is not based on the above-described transistor size L / W, but uniform MOS transistors 51 to 53 are formed and their connection is performed. It is also known that weighting is performed by the number.

[0009]

In the peripheral circuit integrated type panel as described above, a liquid crystal display panel (liquid crystal display) and a digital driver (peripheral circuit) are integrated and mounted on the same substrate. Therefore, there is a problem in manufacturing management that a higher yield is required as compared with the case where both are configured as a single unit.

Further, the number (type) of the gray scale voltages and the scale of the gray scale voltage generating circuit are in a proportional relationship, and in order to realize further multi-gray scale display, the circuit scale is increased and the cost is increased. In order to cause an increase in the yield and a decrease in the yield, there is a demand for a grayscale voltage generation circuit having a small number of components and a simple configuration. In particular, in the above-described conventional voltage selector,
The weighting of the size or the number of connected MOS transistors selects and outputs a predetermined control voltage from the resistance-divided drive voltage, which complicates the manufacturing process and lowers the degree of integration. Had a problem.

In addition, there is a problem that the device characteristics are apt to vary due to the manufacturing process, display gradation is deteriorated, and high quality display is hindered. Therefore, the present invention
Providing a useful technology that can solve the above-described problems and achieve high-quality image quality by contributing to further increase in the number of gradations, reduce the number of elements in a drive circuit, and increase the production yield With the goal.

[0012]

In order to achieve the above object, according to the first aspect of the present invention, a liquid crystal display panel and a peripheral circuit for driving the liquid crystal display panel are integrally formed on polycrystalline silicon. And a digital driver provided in the peripheral circuit for selectively outputting a predetermined display voltage and driving the liquid crystal display panel section at a predetermined number of gradations. In the drive circuit,
The digital driver is provided corresponding to each of at least two reference voltage power supplies, at least one or more switched capacitors connected between the reference voltage power supplies, and each of the switched capacitors. Selection control means for selectively controlling the operation of the switched capacitor based on the gray scale control signal. The reference voltage power supply is provided by the switched capacitor selected based on the gradation control signal. Is divided by a resistor, and the divided voltage is output as the display voltage.

The invention described in claim 2 is the first invention.
3. The high-frequency circuit device according to claim 1, wherein the switched capacitor comprises a first transistor and a second transistor connected in series between the two or more reference power supply voltages, and a connection point between the first and second transistors. , And an output terminal provided at a connection point between the second transistor and the reference voltage power supply. The gate of the first transistor is connected to the gate of the first transistor through the selection control means. A predetermined switched capacitor control signal is directly applied,
An inverted signal of the switched capacitor control signal is applied to a gate of the second transistor.

According to a third aspect of the present invention, in the driving circuit for a liquid crystal display device according to the second aspect, the voltage selector section includes a plurality of the switched capacitors, and the plurality of switched capacitors are provided through the selection control means. The frequency of the switched capacitor control signal applied to each of the plurality of switched capacitors is weighted with each other.

According to a fourth aspect of the present invention, in the driving circuit for a liquid crystal display device according to the third aspect, the frequency of the switched capacitor control signal holds the weighting with each other, and the frequency of the switched capacitor control signal is maintained. Is set variably within one horizontal scanning cycle in the display driving of the above. According to a fifth aspect of the present invention, in the driving circuit of the liquid crystal display device according to the second aspect, the voltage selector section includes a plurality of the switched capacitors, and the capacitive element provided in the switched capacitor. The capacity of
It is characterized by mutual weighting.

According to a sixth aspect of the present invention, in the driving circuit for a liquid crystal display device according to the second, third, fourth, or fifth aspect, the first and second transistors provided in the switched capacitor include: It is a multi-gate transistor. That is, the drive circuit of the liquid crystal display device of the present invention includes two MOS transistors connected in series to the voltage selector of the digital driver;
A switched capacitor composed of a capacitance component (capacitance element) connected to a connection point between the MOS transistors and an inverter for applying an inverted signal of a control signal to one of the MOS transistors. As a method of arbitrarily dividing a voltage supplied from a reference voltage power supply by using a realized resistor and selecting and outputting the voltage as a display voltage, first, a switched capacitor control signal for controlling the operation of the switched capacitor is used. The second feature is that the frequency is weighted. Second, the capacitance component provided in the switched capacitor is weighted.

Therefore, according to the configuration of the present invention, even when the number of gradations is increased to realize a high-quality liquid crystal display, the frequency of the control signal to the switched capacitor or the switched By weighting the capacitive element provided in the capacitor, the desired display voltage can be selected and output with a small number of elements without increasing the number of elements. It is possible to provide a liquid crystal display device which has a high yield and is capable of obtaining a small and high quality image display.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a basic configuration of the present invention will be described with reference to FIGS. FIG. 1 shows a digital driver of eight gradations, in which a 3-bit digital signal is input as a gradation control signal. In FIG. 1, Vhi is a reference voltage on the high voltage side, and Vlo is a reference voltage on the low voltage side.
In between, switched capacitors SC arranged in parallel
1, SC2, SC3 and a common feedback resistance Rf
And are connected in series.

Further, the switched capacitors SC1, SC
2 and SC3 operate in accordance with the digital gradation control signal D.
1, D2, D3, are controlled by switched capacitor control signals S1, S2, S3 applied via MOS switches SW1, SW2, SW3. That is, when the MOS switch SW1 is turned on by the gradation control signal D1, the switched capacitor control signal S
1 is applied to the switched capacitor SC1, the reference voltage Vhi-Vlo is resistance-divided by the resistor R1 and the feedback resistor Rf realized by the switched capacitor SC1, and output as the display voltage Vout.

Similarly, when the MOS switch SW2 is turned on by the gradation control signal D2, the switched capacitor control signal S2 is applied to the switched capacitor SC2, and the resistance R2 and the feedback resistance Rf realized by the switched capacitor SC2 are used. The reference voltage Vhi-Vlo is resistance-divided and output as the display voltage Vout. Further, the MOS switch SW3 is turned on by the gradation control signal D3.
When N, the switched capacitor control signal S3 is applied to the switched capacitor SC3, and the reference voltage Vhi-Vlo is divided by the resistor R3 realized by the switched capacitor SC3 and the feedback resistor Rf, and output as the display voltage Vout. You.

Next, an example of a circuit configuration of the switched capacitor will be described with reference to FIG. As shown in FIG. 2, the switched capacitors SC1, SC2, SC3 are:
MOS transistors Tra and Trb connected in series
A capacitor C provided between a connection point N of these MOS transistors Tra and Trb and a ground potential;
The inverted signal of the switched capacitor control signal applied to the gate of the S transistor
and an inverter to be applied to the gate of rb.

Then, the switched capacitor control signal S
When a predetermined pulse signal is applied, the MOS transistors Tra and Trb perform a complementary switching operation,
As shown in FIG. 3, when the switched capacitor control signal S is at the H level, the MOS transistor Tra is turned on and Tr
b is turned off, and electric charge is accumulated in the capacitor C at the connection point N.

Next, the switched capacitor control signal S
Goes low, the MOS transistor Tra turns off.
F and Trb are turned ON, and the charge stored in the capacitor C is released via the MOS transistor Trb. At this time, the voltage output as the display voltage Vout is MOS
The reference voltage Vhi-Vlo becomes a divided voltage by resistance division of the conduction resistance of the transistor Trb and the feedback resistance Rf connected in series to the switched capacitor.

Therefore, by controlling the resistance value realized by the switched capacitor, it is possible to arbitrarily set the display voltage determined by the resistance division of the reference voltage,
In addition, by providing a plurality of such switched capacitors, it is possible to select and output a display voltage corresponding to a desired gradation display (the number of gradations). By the way, a resistor Rs generally realized by a switched capacitor has a frequency fs of a switched capacitor control signal S, a capacitance element Cs
If the capacitance value of is represented by cs, it is expressed as follows.

Rs = 1 / (cs × fs) (1) Therefore, in the voltage selector unit shown in FIG. 1, outputting a display voltage corresponding to eight gradations is realized by a switched capacitor. Resistances R1 and R
If R2 and R3 are set, the resistors R1, R2 and R3 should be set (weighted) so as to satisfy the following condition.

R1 <R2 (2) R1 + R2 <R3 Based on the above, according to the present invention, the frequency of the switched capacitor control signal S or the predetermined value of the capacitance element C provided in the switched capacitor By performing the weighting, for example, the above-described condition can be set to the resistance value realized by the switched capacitor according to the gradation control signal (digital signal), and the display voltage corresponding to the desired number of gradations can be set. Can be generated and output.

(Embodiment) Next, a first embodiment of a drive circuit of a liquid crystal display device according to the present invention will be described with reference to FIGS. This embodiment is different from the circuit configuration shown in FIG. 1 in that, as shown in FIG.
1, SC2 and SC3 to control the operation and realize the resistor R
A predetermined weighting is applied to the frequencies f1, f2, f3 of the switched capacitor control signals S1, S2, S3 for selecting 1, R2, R3, and the resistance Rs shown in the equation (1) is set stepwise. Features.

For example, when generating a display voltage of eight gradations, the switched capacitors SC1, SC2, SC3
Since the resistors R1, R2, and R3 realized by the formula (1) need to satisfy the condition of the above equation (2), each frequency f of the switched capacitor control signals S1, S2, and S3
1, f2 and f3 are weighted so as to satisfy the following conditions.

F1> f2 (3) f3 <f1 × f2 / (f1 + f2) In FIG. 4, the frequencies f1, f2, and f3 are weighted as follows so as to satisfy such a condition. ing.

F2 = f1 / 2 (4) f3 = f1 / 4 Therefore, by appropriately weighting the frequencies f1, f2, and f3 in this way, the switched capacitor S
Resistance values R1, R realized by C1, SC2, SC3
2, R3 can be set to different resistance values, and the gradation control signal D1, D2 can be set by resistance division with the feedback resistance R.
A display voltage Vout corresponding to D2 and D3 is generated and output.

Here, the switched capacitor control signal S
Since 1, S2, and S3 can be supplied from outside the voltage selector section (drive circuit), the switch is set by appropriately setting the weights of the frequencies f1, f2, and f3 so as to realize a desired number of gradations. Capacitor SC1, SC
2. Since the resistance values R1, R2, and R3 realized by SC3 can be arbitrarily weighted, the elements of the voltage selector section including the switched capacitors SC1, SC2, and SC3 are configured to have a uniform size. Thus, it is possible to suppress manufacturing variations among elements and to improve the degree of integration on a substrate.

Next, a second embodiment of the driving circuit of the liquid crystal display device according to the present invention will be described with reference to FIG.
In the present embodiment, as shown in FIG. 5, the switched capacitors SC1, SC2, SC
3, the capacitance values c1, c2, and c3 of the capacitance elements C1, C2, and C3 provided in each of the capacitors 3 are weighted in a predetermined manner, and the resistance Rs shown in the equation (1) is set stepwise. .

More specifically, as shown in FIG. 5, MOS transistors TR1a, Tr1b, inverter INV1,
Switched capacitor SC composed of capacitive element C1
1 and a switched capacitor SC1
OS transistors TR2a, Tr2b, inverter IN
V2, a switched capacitor SC2 composed of a capacitive element C2, and MOS transistors TR3a, Tr3b,
The inverter INV3 and the switched capacitor SC3 composed of the capacitive element C3 form the reference voltage Vhi on the high voltage side.
And one end are connected in parallel between the reference voltage Vlo on the constant voltage side.

Then, each of the switched capacitors SC1,
Capacitance elements C1, C2, C3 provided in SC2, SC3
Are the capacitance values c1, c2, c3 so that the resistances R1, R2, R3 realized by the switched capacitors SC1, SC2, SC3 satisfy the condition of the above-mentioned equation (2).
Are weighted so as to satisfy the following condition. c1> c2 (5) c3 <c1 × c2 / (c1 + c2) Therefore, by appropriately weighting the capacitance values c1, c2, and c3 in this manner, the switched capacitor S
Resistance values R1, R realized by C1, SC2, SC3
2, R3 can be set to different resistance values, and the gradation control signal D1, D2 can be set by resistance division with the feedback resistance R.
A display voltage Vout corresponding to D2 and D3 is generated and output.

Here, by appropriately setting the capacitance values c1, c2, c3 of the capacitance elements C1, C2, C3, the resistance values R1, R2, R3 realized by the switched capacitors SC1, SC2, SC3 are weighted. It is possible,
In addition, since only one type of the switched capacitor control signal S is required, the display voltage Vout for realizing a desired number of gradations can be generated and output by a simple control method.

Next, a third embodiment of the driving circuit of the liquid crystal display device according to the present invention will be described with reference to FIG.
This embodiment is different from the first embodiment described above in that the weighted switched capacitor control signals S1, S2,
As shown in FIG. 6, each frequency was switched and set (variable) within one horizontal scanning period (1H) of the liquid crystal display while maintaining the mutual ratio of the frequencies f1, f2 and f3 of S3 constant. It is characterized by.

More specifically, of the period (one horizontal scanning period) in which a display voltage is applied for each horizontal scanning line of the liquid crystal panel by a line sequential driving method known as a liquid crystal display driving method, one of the periods is applied to the liquid crystal display element. In the writing period in which the charging of the switch capacitor is performed, the switched capacitor control signals S1, S2, S
3, the frequencies f1 and f2, which are substantially the same as those shown in FIG.
f3 is set.

In the holding period for holding the charge state of the liquid crystal display element after the writing period, the switched capacitor control signals S1, S2, and S3 have the frequencies f1 ', f2', and f3 ', which are slower than the writing period. Is set.
Here, the frequencies f1, f2, f in the writing period
3, and the frequencies f1 ', f2', f in the holding period
3 'is frequency-weighted so that the relationship of the above-described equation (3) is maintained.

Therefore, after the writing to the liquid crystal display element is completed, the switched capacitors SC1, SC2, SC2
3 controls the switched capacitor control signal S
Since the frequencies f1, f2, and f3 of S1, S2, and S3 are switched so as to be slower (smaller) while maintaining the mutual ratio, they are realized by the switched capacitors SC1, SC2, and SC3 according to the above equation (1). Resistance R1,
R2 and R3 increase, the flowing current value (current value of the through current) is suppressed, and the power consumption can be reduced.

Next, a fourth embodiment of the driving circuit of the liquid crystal display device according to the present invention will be described with reference to FIG.
In this embodiment, the switched capacitors SC1, SC2, S
As shown in FIG. 7, a multi-gate transistor is applied as the MOS transistors Tra and Trb forming C3.

More specifically, as shown in FIG. 7, MOS transistors having a plurality of gate electrodes (two in the figure) are connected to the MOs of the switched capacitors SC1, SC2 and SC3.
This is applied to the S transistor, that is, the switch unit. In general, a multi-gate transistor can suppress a through current in an OFF state to an extremely small level. Therefore, such a transistor is called a switched capacitor SC1,
By applying to SC2 and SC3, O
Since the FF current is suppressed, a through current in the switch portion is reduced, and power consumption can be reduced. It is needless to say that the same effect can be obtained even with a configuration in which a plurality of MOS transistors are connected instead of the multi-gate transistor.

In the above-described embodiment, only the case where the display voltage of eight gradations is generated and output has been described. However, it goes without saying that the present invention is not limited to this. Further, in the above-described embodiment, a resistance element having an individual configuration is shown as the feedback resistor R. However, the present invention is not limited to this, and the feedback resistor R may have a configuration equivalent to that of another switched capacitor. It goes without saying that the configuration may be good.

[0043]

As described above, according to the drive circuit for a liquid crystal display device according to the present invention, a small-sized and high-quality display can be obtained with a high yield by a digital driver used for driving a peripheral circuit integrated panel. A driving circuit can be provided.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a liquid crystal display device according to the present invention.

FIG. 2 is a diagram illustrating a circuit configuration example of a switched capacitor applied to the present invention.

FIG. 3 is a waveform chart showing an operation of the switched capacitor.

FIG. 4 is a waveform chart showing a first embodiment of the drive circuit of the liquid crystal display device according to the present invention.

FIG. 5 is a circuit diagram showing a second embodiment of the drive circuit of the liquid crystal display device according to the present invention.

FIG. 6 is a waveform chart showing a third embodiment of the driving circuit of the liquid crystal display device according to the present invention.

FIG. 7 is a plan view of a transistor showing a fourth embodiment of the driving circuit of the liquid crystal display device according to the present invention.

FIG. 8 is a schematic configuration diagram of a peripheral circuit integrated type panel.

FIG. 9 is a schematic configuration diagram showing a grayscale voltage generation circuit according to the related art.

FIG. 10 is a schematic configuration diagram of a digital driver.

FIG. 11 is a diagram illustrating a circuit configuration example of a voltage selector unit.

[Explanation of symbols]

SC1, SC2, SC3 Switched capacitor S1, S2, S3 Switched capacitor control signal D1, D2, D3 Gradation control signal R Feedback resistor TRa, TRb MOS transistor Vout Display voltage

Claims (6)

[Claims] 1. A liquid crystal display panel on polycrystalline silicon,
A peripheral circuit for driving and driving the liquid crystal display panel is integrally formed, and a predetermined display voltage is selectively output by a digital driver provided in the peripheral circuit, and the liquid crystal display panel is driven to a predetermined floor. In a driving circuit of a liquid crystal display device integrated with a peripheral circuit, the digital driver comprises: at least two reference voltage power supplies; at least one switched capacitor connected between the reference voltage power supplies; And a selection control means provided corresponding to each of the switched capacitors and selectively controlling the operation of the switched capacitor based on the grayscale control signal. The voltage supplied from the reference voltage power supply is divided by the resistor by the switched capacitor selected based on the tone control signal. Driving circuit of a liquid crystal display device and outputs the pressure of the display voltage. 2. The switched capacitor is connected to a first transistor and a second transistor connected in series between the two or more reference power supply voltages, and to a connection point of the first and second transistors. A capacitance element, and an output terminal provided at a connection point between the second transistor and the reference voltage power supply. A gate of the first transistor is connected to the gate of the first transistor through the selection control unit. 2. The driving method for a liquid crystal display device according to claim 1, wherein the switched capacitor control signal is directly applied, and an inverted signal of the switched capacitor control signal is applied to a gate of the second transistor. circuit. 3. The voltage selector section includes a plurality of the switched capacitors, and sets a frequency of the switched capacitor control signal applied to each of the plurality of switched capacitors via the selection control means. 3. A driving circuit for a liquid crystal display device according to claim 2, wherein the driving circuits are weighted with each other. 4. The frequency of the switched capacitor control signal is variably set within one horizontal scanning cycle in display driving of the liquid crystal display panel while holding the weights with each other. Item 4. A driving circuit for a liquid crystal display device according to item 3. 5. The voltage selector section includes a plurality of the switched capacitors, and the capacitances of the capacitive elements provided in the switched capacitors are mutually weighted. Drive circuit for liquid crystal display device. 6. The switch according to claim 2, wherein said first and second transistors provided on said switched capacitor are multi-gate transistors.
The driving circuit of the liquid crystal display device according to the above.