JP4097866B2 - Display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a display device such as a liquid crystal panel provided with a touch panel type input position detection device that detects a touch input position using a pen or the like, and more particularly to a mechanism for removing noise from position information to be detected.
[0002]
[Prior art]
A touch panel type input position detection device (tablet) for detecting a position touched by a pen or the like on a display panel such as a liquid crystal panel (hereinafter referred to as LCD) used in a display device without a portable information terminal or a keyboard Many are equipped with. A combination of the display panel and the input position detection device serves as an input / output device that displays image data and receives external input. FIG. 4 shows a typical configuration example of such an input / output device 51. As shown in the figure, the input position detection device 52 is arranged very closely on a display panel (LCD) 53. The input position detection device 52 is insulated by a display panel 53 and a glass substrate as disclosed in, for example, Japanese Patent Laid-Open No. 6-318137, and a transparent electrode for detecting an X-axis coordinate and a Y-axis are formed on the glass substrate. This is a configuration in which the transparent electrode for axial coordinate detection faces through an insulating spacer.
[0003]
When the input position detection device 52 is pressed with a pen or the like, the transparent electrodes at the pressed positions come into contact with each other. At this time, when a voltage is applied to each transparent electrode, a voltage corresponding to the pressed position is output from each transparent electrode. This voltage is detected as a position detection signal representing the X coordinate and a position detection signal representing the Y coordinate, and is input to the A / D converter 54. The A / D converter 54 samples an analog position detection signal and converts it into a digital signal.
[0004]
[Problems to be solved by the invention]
However, in the conventional display device described above, since the input position detection device 52 is close to the display panel 53 as shown in FIG. 4, the position detection signal of the input position detection device 52 is changed from the drive signal of the display panel 53. There is a problem that the noise B is superimposed and the sample of the position detection signal is likely to be erroneous.
[0005]
For example, when the display panel 53 is an LCD, as shown in FIG. 5, when the LCD drive signal A is supplied to the LCD as an alternating signal of a periodic pulse, the input position detecting device is at the rising and falling timings of the pulse. Noise B is superimposed on the position detection signal 52. The sample of the position detection signal by the A / D converter 54 is started based on the position detection request signal C generated by contact with the input position detection device 52. The sample start timing is determined from the generation timing of the position detection request signal C. Since the time until is determined by the processing time of the microcomputer or the like, it is random as t1 and t2 in FIG.
[0006]
As the A / D converter 54 in the conventional display device, the one provided with the sample hold (S / H) circuit as in the successive approximation conversion method is used, and the S / H acquired in an extremely short sample time is used. A / D conversion is performed on the pulse at an A / D conversion time Tad set within the hold time. Therefore, as shown in the figure, the position detection sample signal S4 whose sample start timing is after the time t1 from the generation timing of the position detection request signal C and whose sampling period coincides with the rising timing of the LCD drive signal A is shown in FIG. The noise B generated at the rising timing is superimposed, and the position information includes a large error. In addition, noise B is present in the position detection sample signal S5 in which the sample start timing is after the time t2 from the generation timing of the position detection request signal C and the sampling period deviates from the rise or fall timing of the LCD drive signal A. Since they are not superimposed, an accurate position detection signal is taken into the A / D converter 54.
[0007]
Therefore, in order to prevent such a large variation in position detection information due to the difference in sample start timing, when T> Tad, samples are taken several times in one data acquisition, and each data is compared. Therefore, it is necessary to perform complicated processing such as determining defective data.
[0008]
On the other hand, if T <Tad, the probability that the sampling period coincides with the noise generation timing increases. Therefore, in the method of comparing sample values several times as described above, the influence of noise B is affected. It cannot be avoided. Therefore, as a countermeasure against noise when the period T is short, a method of stopping the supply of the LCD drive signal A by the LCD drive circuit in advance when detecting position information is employed. However, in this case, since it is necessary to adjust the sample start timing and the LCD drive timing, the control circuit and the processing procedure become complicated.
[0009]
Japanese Patent Laid-Open No. 6-318137 discloses a method for detecting an AC signal and sampling a coordinate detection signal from a tablet in synchronization with a stable portion thereof, so that noise from the LCD is not affected. A method is disclosed. However, this method requires complicated control for adjusting the sample start timing so that the sample period becomes a stable portion of the AC signal.
[0010]
The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to easily avoid the influence of noise caused by a display panel drive signal and accurately perform position detection by an input position detection device. It is to provide a display device.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problem, the display device of the present invention is a display device including an input position detection device that detects an input position due to external contact on a display panel that is driven using a periodic pulse as a drive signal. Sample means for performing sampling by integrating the position detection signal output from the input position detection device, and the sample start timing of the sampling means is made to coincide with the timing at which the drive signal becomes a predetermined phase. It is said.
[0012]
According to the above invention, the sample means for performing sampling by integrating the position detection signal output from the input position detection device is provided. Examples of the sampling means include an integration type A / D converter and an integration circuit provided in the preceding stage of the non-integration type A / D converter. Thereby, since the ratio of the noise superimposed on the position detection signal from the drive signal of the display panel to the integrated value can be reduced, it is possible to avoid the influence of the noise on the signal obtained by the sample.
[0013]
Further, the sampling start timing of the sampling means is made to coincide with the timing at which the drive signal of the display panel has a predetermined phase. In order to match the timing in this way, the operation of the sampling means may be controlled by a signal obtained by, for example, dividing a clock signal used when generating a display panel drive signal. As a result, the sample period for the phase of the drive signal is fixed between the samples, so that variations in the amount of noise superimposed from the drive signal can be easily suppressed. In addition, since sampling by integration is performed, variation in the amount of noise superimposed on each sample can be suppressed even if the sample start timing is made to coincide with any phase timing of the drive signal.
[0014]
As a result, it is possible to provide a display device that can easily avoid the influence of noise due to the drive signal of the display panel and can accurately perform position detection by the input position detection device.
[0015]
Furthermore, in order to solve the above problems, the display device of the present invention is characterized in that the sample start timing is synchronized with a timing at which the level of the drive signal is inverted.
[0016]
According to the above invention, the sample start timing is synchronized with the timing at which the level of the drive signal of the display panel is inverted, that is, the timing at which noise from the drive signal is generated. Therefore, it is possible to obtain a signal synchronized with the drive signal by dividing the clock signal that is the generation source of the drive signal, and to start sampling using the timing at which the level of the signal is inverted. Become.
[0017]
Further, in order to solve the above-described problem, the display device of the present invention is provided when a certain level time from when the level of the drive signal is inverted to when the level is inverted is longer than the integration time in the sample means. The sampling start timing is determined so that the integration is performed within the fixed level time.
[0018]
According to the above invention, when the constant level time of the drive signal is longer than the integration time, the integration is performed within the constant level time, that is, within a period in which noise from the drive signal does not occur. Therefore, no noise is superimposed on the integral value, and a more accurate sample can be performed.
[0019]
Further, in order to solve the above problems, the display device of the present invention is characterized in that the integration time in the sample means is an integral multiple of the period of the drive signal.
[0020]
According to the above invention, the integration time is an integral multiple of the period of the drive signal. Therefore, for example, even when the period of the drive signal is shorter than the minimum necessary integration time and the amount of noise superimposed on the signal obtained by the sample increases, the ratio of noise to the integration amount is reduced. The influence can be avoided. This also eliminates the need for complicated control such as stopping the supply of drive signals in advance at the start of sampling.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the display device of the present invention will be described with reference to FIGS. 1 to 3 as follows.
[0022]
FIG. 2 shows a configuration of the display device 1 according to the present embodiment. The display device 1 includes an input / output unit 2 including a display panel 2a and an input position detection device 2b, a display panel drive circuit 3, an input position detection device drive circuit 4, an A / D conversion circuit 5a, and an A / D conversion control circuit 5b. A / D conversion unit 5 comprising: a signal generation unit 6 comprising a clock oscillation circuit 6a and frequency dividing circuits 6b, 6c, 6d, and an arithmetic / control unit 7.
[0023]
In the input / output unit 2, the display panel 2a is composed of, for example, an LCD, and the input position detection device 2b is a tablet similar to that described above, which is provided closely and integrally on the display panel 2a. When an operation start event such as contact with a pen occurs, the input position detection device 2b outputs a position detection request signal C to the calculation / control unit 7 described later. The display panel drive circuit 3 is a circuit for driving the display panel 2a, generates a necessary operation signal such as an alternating signal as the LCD drive signal A, and supplies it to the display panel 2a. The input position detection device drive circuit 4 generates a necessary control signal such as a voltage to be applied to the transparent electrode of the input position detection device 2b. When the input position detection device 2b is driven by the input position detection device drive circuit 4, a position detection signal is output from the input position detection device 2b toward the A / D conversion circuit 5a.
[0024]
In the A / D conversion unit 5, the A / D conversion circuit 5a includes an integration type A / D converter used for A / D conversion such as a ΔΣ conversion method, a double integration method, and a feedback pulse width modulation method. Become. Alternatively, as shown in FIG. 3, as the A / D conversion circuit 5a, a non-integration type A / D converter 12, and an input integration circuit 11 including a voltage follower circuit 13, a switch 14, and a capacitor 15 in the preceding stage, May be combined. In the latter case, the switch 14 is controlled so as to connect the voltage follower circuit 13 and the capacitor 15 during integration and to connect the capacitor 15 and the A / D converter 12 during A / D conversion. The A / D conversion control circuit 5b is a circuit that generates a control signal necessary for driving the A / D conversion circuit 5a.
[0025]
In the signal generator 6, the clock oscillation circuit 6 a is a circuit that generates the base clock CK of the display device 1, and the frequency dividing circuits 6 b, 6 c, and 6 d divide the base clock CK, respectively, and display panel drive circuit 3 The operation clock CK1 for generating the output signal, the operation clock CK2 for generating the output signal of the input position detector driving circuit 4, and the operation clock CK3 of the A / D conversion circuit 5a are generated. The operation clock CK3 is a count clock for A / D conversion operation. Since each of the frequency dividing circuits 6b, 6c, and 6d divides the clock generated by the same oscillation circuit, the level inversion timing of the operation clocks CK1, CK2, and CK3 is the level inversion of the operation clock having the highest frequency (for example, CK1). It matches the timing. Thus, since the operation clock CK3 of the A / D conversion circuit 5a and the operation clock CK1 of the display panel drive circuit 3 are in phase, the integration time period in the A / D conversion is set to the LCD drive signal of the display panel 2a. While synchronizing with A, it can be selected to match the period.
[0026]
The arithmetic / control unit 7 performs a series of operation control such as ON / OFF for the display panel driving circuit 3, the input position detection device driving circuit 4, and the A / D conversion control circuit 5b, and the A / D conversion circuit 5a. The input position information is calculated using the A / D output from. In particular, when a position detection request signal C is input from the input position detection device 2b, a signal for instructing drive start is output to the input position detection device drive circuit 4 and the A / D conversion control circuit 5b.
[0027]
Next, the operation of the display device 1 having the above configuration will be described with reference to the timing chart of FIG. First, the case where the period T of the LCD drive signal A is longer than the integration time Ts of the A / D conversion circuit 5a will be described. In the present embodiment, the integration time Ts indicates the sample time. When an input is performed on the input position detection device 2b with a pen or the like, a position detection request signal C is output from the input position detection device 2b to the calculation / control unit 7. As a result, the input position detection device drive circuit 4 outputs a control signal to the input position detection device 2b based on the operation clock CK2 from the frequency dividing circuit 6b under the control of the calculation / control unit 7. The input position detection device 2b outputs an analog voltage corresponding to the X coordinate or Y coordinate of the input position to the A / D conversion circuit 5a as a position detection signal.
[0028]
Also, the A / D conversion control circuit 5b starts operation control of the A / D conversion circuit 5a under the control of the arithmetic / control unit 7, and the A / D conversion circuit 5a is based on the operation clock CK3 from the frequency dividing circuit 6d. To start sampling the position detection signal. The position detection signal that is the target of sampling at the integration time Ts is the position detection sample signal S1 shown in FIG. The time required from the output of the position detection request signal C to the start of sampling is the time t1 until the sample start signal rises.
[0029]
Here, the operation clock CK3 and the operation clock CK1 output from the frequency dividing circuit 6b are generated by dividing the same base clock CK from the clock oscillation circuit 6a. As described above, since the operation clock CK3 of the A / D conversion circuit 5a and the operation clock CK1 of the display panel drive circuit 3 are in phase, the sample start timing can be synchronized with the LCD drive signal A.
[0030]
Thus, at the sample start timing that coincides with the rise timing of the LCD drive signal A, the noise B from the LCD drive signal A is superimposed on the position detection sample signal S1, and the fall timing of the LCD drive signal A during the sample period. Is included, the noise B is also superimposed at this timing. However, since the target of A / D conversion is the value of integration by the A / D conversion circuit 5a, the change in the input signal of the A / D conversion circuit 5a is averaged within the integration time Ts. Therefore, the ratio of the noise B to the integrated value becomes small, and the influence of the noise B on the signal obtained by the sample can be avoided.
[0031]
In the above example, the sample start timing is made to coincide with the rise timing of the LCD drive signal A, but may be made to coincide with the fall timing of the LCD drive signal A. As described above, the control for making the sample start timing coincide with the timing at which the level of the LCD drive signal A is inverted is easy because the operation clock CK3 from the frequency dividing circuit 6d can be directly used.
[0032]
Furthermore, each sample start timing may be made to coincide with the timing at which the LCD drive signal A has a predetermined phase, including the level inversion timing of the LCD drive signal A. As a result, the sample period for the phase of the LCD drive signal A is fixed between the samples. Accordingly, it is possible to save the time and effort of performing the calculation processing by performing a plurality of samples as in the prior art, and it is possible to easily suppress the variation in the amount of noise superimposed from the LCD drive signal A. Further, since sampling by integration is performed, even if the sample start timing is made to coincide with any phase timing of the LCD drive signal A, variation in the amount of noise superimposed on each sample can be suppressed.
[0033]
Further, as shown in FIG. 1, when the constant level time Tc of the LCD drive signal A (“Low” level time in this figure but “High” level time may be sufficient) is longer than the integration time Ts, Like the position detection sample signal S2, the sample start timing may be shifted from the level inversion timing of the LCD drive signal A by a predetermined time Td, and integration may be performed within the constant level time Tc. In this case, since the sample is performed within a period in which the noise B from the LCD drive signal A is not generated, no noise is superimposed on the integral value, and a more accurate sample can be performed.
[0034]
Next, a case where the period T of the LCD drive signal A is shorter than the integration time Ts will be described. Although the integration time Ts is required to some extent in order to convert the sample value into an accurate digital signal, the period T of the LCD drive signal A may be shorter than the minimum integration time Ts. In this case, sampling is started based on the position detection request signal C. However, since the period T of the LCD drive signal A is shorter than the integration time Ts, the level inversion of the LCD drive signal A is performed three or more times during the sample period. It will be. Accordingly, since the ratio of the amount of noise mixed in the integrated value from the LCD drive signal A becomes larger than that in the case of T> Ts, in order to avoid this, the sample start timing is set like the position detection sample signal S3 shown in FIG. In synchronization with the rising timing of the LCD drive signal A, the integration time Ts is set to an integral multiple of the period T of the LCD drive signal A.
[0035]
By setting the integration time Ts in this way, the average ΔV per period of the total noise superimposed on the position detection sample signal S3 through the n period (n is an integer) of the LCD drive signal A is calculated as follows. If the amount of noise to be superimposed at ΔV1, ΔV2,.
ΔV = (ΔV1 + ΔV2 +... + ΔVn) / n
It becomes. Since the sample start timing is synchronized with the rise timing of the LCD drive signal A, the same number of noise pulses are superimposed on each sample, and ΔV becomes substantially the same amount. ΔV is an offset value with respect to the integral value of each sample. However, since the same value is only an offset value for each sample with respect to an actual position detection signal, there is no problem. In addition, setting the integration time Ts to be long leads to a reduction in variation of the integration value in each sample.
[0036]
Note that the sample start timing may be synchronized with the falling timing of the LCD drive signal A, and the control clock CK3 from the frequency dividing circuit 6d can be directly used for the control synchronized with the level inversion timing of the LCD drive signal A. So easy. Furthermore, each sample start timing may be made to coincide with the timing at which the LCD drive signal A has a predetermined phase, including the level inversion timing of the LCD drive signal A. As long as this relationship is maintained, ΔV can be made substantially the same between the samples.
[0037]
As described above, according to the display device 1 of the present embodiment, sampling is performed by integrating the position detection signal output from the input position detection device 2b, and the sample start timing is determined by the LCD drive signal A. The timing is matched with a predetermined phase. Therefore, it is possible to easily avoid the influence of noise caused by the LCD drive signal A and accurately perform position detection by the input position detection device 2b.
[0038]
Further, by setting the integration time Ts to an integral multiple of the period T of the LCD drive signal A, the period of the LCD drive signal A becomes shorter than the minimum necessary integration time, and noise is superimposed on the signal obtained by the sample. Even when the amount increases, the influence of the noise can be avoided by reducing the proportion of noise in the integrated amount. This also eliminates the need for complicated control such as stopping the supply of the LCD drive signal A in advance when starting the sample.
[0039]
In this embodiment mode, an example in which the present invention is applied to a display device using an LCD has been described. However, the present invention is not limited to this, and is generated from a driving signal of a display panel such as a plasma display panel or a fluorescent display tube, particularly a pulse signal The present invention is applied to all display devices in which the periodic noise to be an error of A / D conversion at the time of position detection.
[0040]
【The invention's effect】
As described above, the display device of the present invention has the sample means for sampling by integrating the position detection signal output from the input position detection device, and the drive signal is set to the sample start timing of the sample means. It is the structure made to correspond to the timing used as this phase.
[0041]
Therefore, since the ratio of the noise superimposed on the position detection signal from the drive signal of the display panel to the integral value can be reduced, the influence of the noise on the signal obtained by the sample can be avoided. In addition, the sample start timing may be made to coincide with the timing of any phase of the drive signal, and the sampling period relative to the phase of the drive signal is fixed between the samples, so that the noise superimposed from the drive signal Can be easily suppressed.
[0042]
As a result, it is possible to provide a display device that can easily avoid the influence of noise due to the drive signal of the display panel and can accurately perform position detection by the input position detection device.
[0043]
Furthermore, as described above, the display device of the present invention is configured to synchronize the sample start timing with the timing at which the level of the drive signal is inverted.
[0044]
Therefore, it is possible to obtain a signal synchronized with the drive signal by dividing the clock signal that is the generation source of the drive signal, and to start sampling using the timing at which the level of the signal is inverted, so that the control is easy. Has the effect of becoming.
[0045]
Further, as described above, the display device of the present invention can integrate when the level of the drive signal is inverted until the next level inversion is longer than the integration time in the sample means. The sample start timing is determined so as to be performed within the certain level time.
[0046]
Therefore, when the constant level time of the drive signal is longer than the integration time, the integration is performed within a period in which noise from the drive signal does not occur. Therefore, no noise is superimposed on the integrated value, and an effect is obtained that a more accurate sample can be performed.
[0047]
Furthermore, as described above, the display device of the present invention has a configuration in which the integration time in the sample means is an integral multiple of the cycle of the drive signal.
[0048]
Therefore, for example, even if the period of the drive signal is shorter than the minimum required integration time and the amount of noise superimposed on the signal obtained by the sample increases, the ratio of noise to the integration amount is reduced. The effect that the influence can be avoided. This also has the effect of eliminating the need for complicated control such as stopping the supply of the drive signal in advance when starting the sample.
[Brief description of the drawings]
FIG. 1 is a timing chart illustrating a sample operation of a display device according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating a configuration of a display device according to an embodiment of the present invention.
3 is a circuit diagram showing an example of an A / D conversion circuit used in the display device of FIG. 2;
FIG. 4 is an explanatory diagram showing a part of the configuration of a conventional display device.
FIG. 5 is a timing chart illustrating a sample operation of the display device of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Display apparatus 2a Display panel 2b Input position detection apparatus 5a A / D conversion circuit (sample means)
11 Input integration circuit (sample means)
A LCD drive signal (drive signal)
B Noise T Period Tc Constant level time Ts Integration time

Claims (2)

In a display device equipped with an input position detection device for detecting an input position by contact from the outside on a display panel driven with a periodic pulse as a drive signal,
Sample means for performing sampling by integrating the position detection signal output from the input position detection device, and matching the sample start timing of the sample means with the timing at which the drive signal becomes a predetermined phase ,
A display device characterized in that the integration time in the sample means is an integral multiple of the period of the drive signal .   The display device according to claim 1, wherein the sample start timing is synchronized with a timing at which a level of the drive signal is inverted.

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