JP2962338B2 - Data output circuit for realizing driving method of liquid crystal display device - 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 device,
In particular, how to drive an active matrix type liquid crystal display
The present invention relates to a data output circuit to be realized .

[0002]

2. Description of the Related Art As is well known, in an active matrix type liquid crystal display device, a plurality of liquid crystal display elements are arranged in a matrix, and a plurality of scanning lines are provided in parallel with each row of the plurality of liquid crystal display elements. A plurality of data signal lines are provided in parallel with each column of the liquid crystal display element, and a switching element is provided at each of the matrix intersections of the plurality of scanning lines and the plurality of data signal lines.

FIG. 4 shows an equivalent circuit diagram of one of the switching elements constituting an active matrix type liquid crystal display device and one of the liquid crystal display elements connected thereto. In this example, an N-channel thin film field effect transistor 21 is used as a switching element,
And a j-th data signal line 23 at a matrix intersection 24. The gate electrode 25 of the N-channel thin film transistor 21 is connected to the i-th scanning line 22.
One of the drain electrode and the source electrode of the N-channel thin film transistor 21 is connected to the j-th column data signal line 23, and the other is connected to the display electrode 26. A liquid crystal display element is connected to the display electrode 26. Here, the liquid crystal display element can be equivalently represented as a liquid crystal capacitor 28 provided between the display electrode 26 and the common electrode 27. One end of a resistor 29 is connected to the common electrode 27.

FIG. 6 shows a voltage waveform diagram of an output data signal output to each of a plurality of data signal lines according to a conventional method of driving an active matrix type liquid crystal display device. Output data signal O output from a data signal line of an arbitrary column
D ′ is the data voltage of the data of the i-th row, the data of the (i + 1) -th row, the data of the (i + 2) -th row,... Sequentially as the scanning lines in the row direction scan line-sequentially. To go. At this time, in the conventional driving method, as shown in FIG. 6, the signal voltage of the output data signal OD 'is temporarily set to 0 V at the time of switching the data voltage of the output data signal OD'. The reason for this is to make it possible to smoothly switch the data voltage, as will be described later in detail.

[0005] The offset voltage shown in FIG.
Is applied to the common electrode 27 side of the liquid crystal capacitor 28 shown in FIG. This offset voltage is, for example, 8V
It is. As is well known, an image displayed by a display device such as a liquid crystal display device is configured by switching a large number of screens at a predetermined cycle (for example, (1/30) second). It is called a frame. In a liquid crystal display device, there are two types of frames called a (+) frame and a (-) frame. As shown in FIG. 6, in the (+) frame, a voltage higher than the offset voltage is applied as the data voltage of the output data signal OD ', and in the (-) frame, the data voltage of the output data signal OD' is lower than the offset voltage. A low voltage is provided. The (+) frame and the (-) frame are alternately switched every time scanning in the row direction is completed. As a result, an AC voltage is applied to the liquid crystal capacitor 28 in FIG.

FIG. 7A shows a conventional data output circuit for realizing the conventional driving method of the active matrix type liquid crystal display device shown in FIG. 6, and FIG. 7B shows a data signal waveform diagram thereof. . The data output circuit is a circuit for supplying an output data signal to each of the plurality of data signal lines.

The conventional data output circuit includes a data input terminal 11 to which an input data signal ID is supplied, a data output terminal 12 to output an output data signal OD ', and an input data signal ID in synchronization with the input data signal ID. A clock input terminal 13 to which an input clock signal ICK having a positive pulse is supplied at a change point of the input data signal, and a voltage corresponding to the maximum value of the input data signal ID or a predetermined voltage which is higher than the voltage. It has a voltage supply terminal 14 and a ground terminal 15 which is a ground potential. In this example, the predetermined voltage supplied to the voltage supply terminal 14 is + 15V.

The conventional data output circuit has a first N-channel MOS transistor 16 ′, a second N-channel MOS transistor 17 ′, and a constant current source 18. In the first N-channel MOS transistor 16 ′, its gate electrode is connected to the data input terminal 11, its drain electrode is connected to the voltage supply terminal 14, and its source electrode is connected to the data output terminal 12. In the second N-channel MOS transistor 17 ′, its gate electrode is connected to the clock input terminal 13, its drain electrode is connected to the data output terminal 12, and its source electrode is connected to the ground terminal 15. Constant current source 1
8 is connected between the data output terminal 12 and the ground terminal 15.

In the conventional data output circuit having such a configuration, considering that the load capacitance 20 which can be connected to the data output terminal 12 is very large, the input data signal I
When D is turned to the negative side, a steep rise can be performed. That is, the input data signal ID
At the time of data switching, the data signal voltage of the output data signal OD 'is temporarily set to the minimum voltage of 0 V in accordance with the input clock signal ICK, and then the level of the data signal voltage to be taken next by the input data signal ID To raise it.

[0010]

In such a conventional driving method of an active matrix type liquid crystal display device, as shown in FIG. 4, a thin film transistor is used as a switching element constituting the active matrix type liquid crystal display device. When used, there are problems as described below.

FIG. 4 is an equivalent circuit diagram of one element of the i-th row and the j-th column of the active matrix type liquid crystal display device as described above. Here, the problem is that the first parasitic capacitance 26a between the display electrode 26, which is the electrode of the liquid crystal capacitor 28, and the j-th column signal line 23, and the first parasitic capacitance 26a between the common electrode 27 and the j-th column signal line 23. This is the second parasitic capacitance 27a. Due to both of these parasitic capacitances, if the signal voltage of the output data signal OD 'is suddenly dropped at the time of data switching, the display electrode 26 will be capacitively coupled.
Is also lowered. After the liquid crystal capacitor 28 is charged, when the potential of the display electrode 26 decreases to a certain value in the holding state where the thin film transistor 21 is turned off,
The thin film transistor 21 is turned on, a current flows from the display electrode 26 in the direction of the j-th column signal line 23, and the liquid crystal capacitor 28 is discharged. In order to prevent the thin film transistor 21 from being turned on, when the thin film transistor 21 is an N channel, it is necessary to apply a lower potential to the gate electrode 25 of the thin film transistor 21, that is, the i-th scanning line 22.

FIG. 5 shows the results of an experiment conducted by the present inventor on an active matrix type liquid crystal display device having a diagonal of about 9 inches for the above contents. In FIG. 5, the horizontal axis is the voltage value applied at the time of data switching, and the vertical axis is the display electrode 2.
7 shows the gate voltage of the N-channel thin film transistor 21, that is, the cutoff gate voltage, when the leak current flowing from the sixth to the j-th column signal line 23 is so small as to be negligible for the liquid crystal display.

The cutoff gate voltage decreases linearly when the voltage applied during data switching is reduced. In the prior art, as shown in FIG. 6, since the voltage applied at the time of data switching is 0 V, the cutoff gate voltage drops to -3 V or less. The above was confirmed by experiments.

Accordingly, an object of the present invention is to realize a driving method capable of smoothly switching a signal voltage of an output data signal of an active matrix type liquid crystal display device .
To provide a data output circuit .

Another object of the present invention is to realize a driving method that does not degrade the display characteristics of a liquid crystal display element when a thin film transistor constituting a liquid crystal display device is in an off state.
A data output circuit is provided.

[0016]

Means for Solving the Problems Data output according to the present invention
A driving method of a liquid crystal display device realized by a circuit includes a plurality of liquid crystal display elements arranged in a matrix, a plurality of scanning lines provided in parallel with each row of the plurality of liquid crystal display elements, An active matrix liquid crystal display device is provided in which a plurality of data signal lines are provided in parallel with each column of the element, and a switching element is provided at each matrix intersection of the plurality of scanning lines and the plurality of data signal lines. This is the driving method.

[0017] In the driving method of the liquid crystal display device, the again of output switching of the output data signal to each of said plurality of data signal lines in synchronism to sequentially scanning the plurality of scanning lines, the switching time the output signal voltage of the data signal, temporarily pulling on the gel to a voltage above a predetermined voltage corresponding to the maximum values that can take the input data signal.

In the method of driving a liquid crystal display device, when sequentially scanning the plurality of scanning lines, the polarity of the signal voltage of the output data signal applied to each of the plurality of data signal lines is set to an offset voltage. May be inverted for each column of the liquid crystal display device on the basis of.

In the method of driving a liquid crystal display device, when sequentially scanning the plurality of scanning lines, the polarity of a signal voltage of the output data signal applied to each of the plurality of data signal lines is set to: The liquid crystal display device may be inverted every time scanning in the row direction of the liquid crystal display device makes one cycle based on the offset voltage.

In the above method for driving a liquid crystal display device, it is preferable to use an N-channel thin film field effect transistor as the switching element.

A data output circuit according to the present invention is a circuit for supplying the output data signal to each of the plurality of data signal lines in order to realize the above-described method for driving a liquid crystal display device.

According to the present invention, a data input terminal to which the input data signal is supplied, a data output terminal to output the output data signal, and a change point of the input data signal in synchronization with the input data signal. A clock input terminal to which an input clock signal having a positive pulse is supplied; a voltage supply terminal to which the predetermined voltage is supplied; and a ground terminal which is a ground potential, and a gate electrode is connected to the data input terminal. A first P-channel MOS transistor having a drain electrode connected to the ground terminal and a source electrode connected to the data output terminal; a constant current connected between the positive voltage supply terminal and the data output terminal A source; an inverter circuit having an input connected to the clock input terminal;
A second P-channel MOS transistor having a gate electrode connected to the output of the inverter circuit, a drain electrode connected to the data output terminal, and a source electrode connected to the voltage supply terminal. A data output circuit is obtained.

[0023]

Next, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a voltage waveform diagram of an output data signal showing a driving method of an active matrix type liquid crystal display device according to a first embodiment of the present invention.

Also in this embodiment, as shown in FIG. 4, the thin film transistor 21 used in the liquid crystal display device is an N-channel type, and the liquid crystal display device is driven by sequentially scanning the scanning lines in the row direction. It is assumed that a thin film transistor in a row direction is turned on, and an output data signal is supplied from a data signal line in a column direction accordingly.

The output data signal OD output from the data signal line of an arbitrary column is composed of data of the i-th row, data of the (i + 1) -th row, data of the (i + 2) -th row,. The data voltage is switched one after another in accordance with the line-sequential scanning. At this time, in the driving method of the present embodiment, as shown in FIG. 1, at the time of switching the data voltage of the output data signal OD, the signal voltage of the output data signal OD is once set to the maximum value that the input data signal ID can take. , Or a predetermined voltage higher than the voltage, and thereafter, the input data signal ID of the corresponding row is output.

The specific numbers are as follows. It is assumed that the signal voltage of the input data signal ID has an amplitude of ± 4 V with an offset voltage of 8 V. That is, the range of the voltage that the input data signal ID can take is +2
V to + 12V. At this time, the predetermined voltage applied at the time of switching the signal voltage of the output data signal OD may be set to + 15V which is equal to or higher than + 12V.

FIG. 2A shows a data output circuit of the present invention which realizes the driving method of the active matrix type liquid crystal display device according to the first embodiment shown in FIG. 1, and FIG.
The data signal waveform diagram is shown in FIG. The data output circuit is a circuit for supplying an output data signal to each of the plurality of data signal lines.

The data output circuit of the present invention is a circuit in which the polarity of the circuit of FIG. 7A described in the prior art is inverted as it is, and the MOSFET is replaced by an N-channel to a P-channel.

More specifically, the data output circuit of the present invention has a first P-channel MOS transistor 16, a second P-channel MOS transistor 17, a constant current source 18, and an inverter circuit 19. In the first P-channel MOS transistor 16, its gate electrode is connected to the data input terminal 11, its drain electrode is connected to the ground terminal 15, and its source electrode is connected to the data output terminal 12, respectively. The input of the inverter circuit 19 is connected to the clock input terminal 13. In the second P-channel MOS transistor 17, its gate electrode is connected to the output of the inverter circuit 19, its drain electrode is connected to the data output terminal 12, and its source electrode is connected to the voltage supply terminal 14, respectively. Constant current source 18
Is connected between the voltage supply terminal 14 and the data output terminal 12.

(Embodiment 2) FIG. 3 is a voltage waveform diagram of an output data signal showing a driving method of an active matrix type liquid crystal display device according to a second embodiment of the present invention. In the second embodiment, the i-th scanning line, the (i + 1) -th scanning line, the (i +
2) This is a case where the present invention is applied to a driving method in which the polarity of the data voltage of the output data signal ODa is inverted for each row in which the scanning lines are sequentially scanned. In other words, the (+) frame and the (-) frame are alternately switched for each row. In this embodiment, as in the first embodiment, at the time of switching the data voltage of the output data signal ODa, the signal voltage of the output data signal ODa is temporarily raised to +15 V, and thereafter, the corresponding row is changed. An input data signal is output.

[0032]

As described above, according to the present invention,
By temporarily raising the output data signal to a predetermined voltage equal to or greater than the voltage corresponding to the maximum possible value of the input data signal at the time of the switching, a relatively simple signal output circuit enables a smooth operation. There is an effect that the signal can be switched. Further, when this method is applied to a liquid crystal display device having a thin film transistor as a switching element, there is an advantage that the display characteristics of the liquid crystal display element are not deteriorated when the thin film transistor is off.

[Brief description of the drawings]

FIG. 1 is a voltage waveform diagram of an output data signal for explaining a driving method of an active matrix liquid crystal display device according to a first embodiment of the present invention.

FIGS. 2A and 2B show a data output circuit of the present invention for realizing the driving method of the active matrix type liquid crystal display device according to the first embodiment shown in FIG. 1, FIG. 2A being a circuit diagram thereof, and FIG. It is a signal waveform diagram.

FIG. 3 is a voltage waveform diagram of an output data signal for explaining a driving method of an active matrix liquid crystal display device according to a second embodiment of the present invention.

FIG. 4 is an equivalent circuit diagram of one of the switching elements constituting the active matrix type liquid crystal display device and one of the liquid crystal display elements connected thereto.

FIG. 5 is a diagram showing a relationship between a voltage value applied at the time of data switching and a cutoff gate voltage of a thin film transistor.

FIG. 6 is a voltage waveform diagram of an output data signal for describing a driving method of a conventional active matrix liquid crystal display device.

7A and 7B show a conventional data output circuit for realizing the driving method of the conventional active matrix type liquid crystal display device shown in FIG. 6, in which FIG. 7A is a circuit diagram, and FIG. 7B is a data signal waveform diagram. .

[Explanation of symbols]

 Reference Signs List 11 data input terminal 12 data output terminal 13 clock input terminal 14 voltage supply terminal 15 ground terminal 16 first P-channel MOS transistor 17 second P-channel MOS transistor 18 constant current source 19 inverter circuit 20 load capacitance 21 N-channel thin film transistor 22 i row scanning line 23 j column data signal line 24 matrix intersection 25 gate electrode 26 display electrode 26a first parasitic capacitance 27 common electrode 27a second parasitic capacitance 28 liquid crystal capacitance 29 resistance

Claims (2)

(57) [Claims] A plurality of liquid crystal display elements are arranged in a matrix.
A plurality of liquid crystal display elements arranged in parallel with each row of the plurality of liquid crystal display elements.
Are provided, and each column of the plurality of liquid crystal display elements is provided with
A plurality of data signal lines are provided in parallel, and the plurality of data signal lines are provided.
Each matrix intersection between a scanning line and the plurality of data signal lines
Active matrix with switching element at point
Output to realize the method of driving the liquid crystal display device
A circuit for sequentially scanning the plurality of scanning lines.
Switch output data signal to each of several data signal lines
When outputting, the output data signal at the time of the switching is output.
Signal voltage to the maximum possible value of the input data signal.
The voltage is temporarily raised to a predetermined voltage equal to or higher than the corresponding voltage, and the plurality of scanning lines are sequentially scanned when sequentially scanning the plurality of scanning lines.
Output data signal applied to each of the data signal lines of
The polarity of the signal voltage of the above with reference to the offset voltage
The liquid crystal display device is inverted for each column, and the switching element is an N-channel thin film electric field.
In order to realize the driving method of the liquid crystal display device using the effect transistor, a data output circuit for supplying the output data signal to each of the plurality of data signal lines is provided.
There are a data input terminal to which the input data signal is supplied, the output data output terminal for outputting the data signal, the input clock signal in synchronization with the input data signal with a positive pulse at the change point of the input data signals Is provided, a voltage supply terminal to which the predetermined voltage is supplied, and a ground terminal that is a ground potential, a gate electrode is connected to the data input terminal, and a drain electrode is the ground terminal. A first P-channel MOS transistor having a source electrode connected to the data output terminal; a constant current source connected between the voltage supply terminal and the data output terminal; An inverter circuit connected to the terminal; a gate electrode connected to the output of the inverter circuit; and a drain electrode connected to the data output terminal. And a second P-channel MOS transistor having a source electrode connected to the voltage supply terminal. 2. A plurality of liquid crystal display elements are arranged in a matrix.
A plurality of liquid crystal display elements arranged in parallel with each row of the plurality of liquid crystal display elements.
Are provided, and each column of the plurality of liquid crystal display elements is provided with
A plurality of data signal lines are provided in parallel, and the plurality of data signal lines are provided.
Each matrix intersection between a scanning line and the plurality of data signal lines
Active matrix with switching element at point
Data to realize a method of driving a liquid crystal display
An output circuit for sequentially scanning the plurality of scanning lines.
Switch output data signal to each of several data signal lines
When outputting, the output data signal at the time of the switching is output.
Signal voltage to the maximum possible value of the input data signal.
The voltage is temporarily raised to a predetermined voltage equal to or higher than the corresponding voltage, and the plurality of scanning lines are sequentially scanned when sequentially scanning the plurality of scanning lines.
Output data signal applied to each of the data signal lines of
The polarity of the signal voltage of the above with reference to the offset voltage
Each time the scanning in the row direction of the liquid crystal display device makes one round, it is inverted, and an N-channel thin film electric field
In order to realize the driving method of the liquid crystal display device using the effect transistor, a data output circuit for supplying the output data signal to each of the plurality of data signal lines is provided.
There are a data input terminal to which the input data signal is supplied, the output data output terminal for outputting the data signal, the input clock signal in synchronization with the input data signal with a positive pulse at the change point of the input data signals Is provided, a voltage supply terminal to which the predetermined voltage is supplied, and a ground terminal that is a ground potential, a gate electrode is connected to the data input terminal, and a drain electrode is the ground terminal. A first P-channel MOS transistor having a source electrode connected to the data output terminal; a constant current source connected between the voltage supply terminal and the data output terminal; An inverter circuit connected to the terminal; a gate electrode connected to the output of the inverter circuit; and a drain electrode connected to the data output terminal. And a second P-channel MOS transistor having a source electrode connected to the voltage supply terminal.