Patent Application
20060103639
1. Field of the Invention
The present invention relates to a display device to show a desired video or information by driving a display panel section and more particularly to the display device capable of preventing noise caused by components exhibiting a piezoelectric effect and by driving the display panel section and of realizing silent operations and removal of unpleasant audible noise.
The present application claims priority of Japanese Patent Application No. 2004-332500 filed on Nov. 16, 2004, which is hereby incorporated by reference.
2. Description of the Related Art
In recent years, as a display device to be employed for televisions, monitor displays, or a like is becoming large in size, maximum power required for driving a display panel section used in the display device is increasing. The required power differs depending on a display pattern, and a difference in the required power among display patterns is becoming large. In the case of components exhibiting a piezoelectric effect such as a capacitor used in a driving circuit of the display device, since the difference in the required power appears as a voltage ripple, the larger the ripple amount becomes, the larger the vibration amount becomes and, therefore, if its vibration period is within a range of an audio frequency, the possibility that the vibration is recognized as audible noise, increases.
For an explanation thereof, electrical configurations and operational examples of a conventional display device will be described below.
Next, operations of the conventional display device are explained. In a display device in which, the lower the luminance is, the smaller the driving load is and the higher the luminance is, the larger the driving load is; it is here assumed that a driving horizontal frequency is 65 kHz.
First, if each line is driven according to a display pattern in which a white and a black produced by a change in luminance appear repeatedly in each line, a load variation frequency is obtained in every one line so that the pattern is displayed in order of “white, black, white, black, . . . ” and, therefore, ripples as shown in
Conventional technology to suppress noise occurring in a display device is disclosed in Japanese Patent Application Laid-open No. 2000-349360 (Patent reference 1) in which a connecting conductor is connected to a connecting portion of a piezoelectric transformer with an vibration-absorbing section interposed between the connecting conductor and connecting portion of the piezoelectric transformer in order to prevent occurrence of audible noise of the connecting conductor caused by an vibration frequency of the piezoelectric transformer used in a liquid crystal display panel section or a like.
Another conventional technology is disclosed in Japanese Patent Application Laid-open No. 2004-086147 (Patent reference 2) in which, in order to reduce a low-frequency sound occurring from a surface of a liquid crystal display panel section caused by a piezoelectric phenomenon of a liquid crystal, based on the assumption that the low-frequency sound occurs when one of a bipolar voltage of a facing electrode increases in one vertical period, by reversing the polarity of a driving signal of the facing electrode in every one horizontal period (line) and, when a period of one polarity is longer than that of another polarity in one vertical period, by reversing the polarity occurring in the longer period on arbitrary timing, an effective bipolar voltage of the facing electrode is made equal in one vertical period.
Still another conventional technology is disclosed in Japanese Patent Application Laid-open No. Hei11-133424 (Patent reference 3) in which, in order to reduce audible noise occurring in an EL (Electroluminescence) light-emitting element, in the EL light-emitting element made up of a front electrode (electrode mounted on a side of a liquid crystal panel) and a rear electrode with an EL layer being sandwiched between the both electrodes, a solid-fill shaped copper foil is formed on a facing surface of a printed board placed on a side of the rear electrode with an electrical insulating layer interposed between the rear electrode and printed board and, by connecting the formed copper foil to the front electrode, an alternating voltage being in phase with that of the front electrode is applied.
However, the conventional technologies have problems. As a display device is becoming larger in size, an amount of load variation occurring at time of driving a display panel section increases and, as a result, a possibility increases that noise produced by components exhibiting a piezoelectric effect employed in the display device becomes a problem. That is, in recent years, due to the widespread use of flat devices, large-sized flat display devices are being used in very silent environments such as an art museum, hospital, or a like, where silent operations and removal of unpleasant audible noise are required on all conditions. When a large-sized display device is introduced in such environments, there is a fear that a display device that produces noise occurring in components exhibiting a piezoelectric effect becomes unfit for use therein.
Moreover, the piezoelectric transformer disclosed in the Patent reference 1 is so configured as to vibrate a vibration plate using a driving signal on a primary side and to take a voltage on a secondary side induced by the vibration and, therefore, the noise occurring in the piezoelectric transformer is different from that occurring due to load variations caused by a display pattern which is to be overcome by the present invention. Also, in the technology disclosed in the Patent reference 2, it is presumed that the low-frequency sound produced from the surface of the liquid crystal panel occurs when one of the bipolar voltage of a facing electrode in one vertical period increases and, therefore, the produced low-frequency sound is different from the noise occurring due to load variations caused by a display pattern. Similarly, the audible noise occurring in the EL light-emitting element disclosed in the Patent reference 3 is a noise produced by an alternating voltage to be applied to the front and rear electrodes to make the EL layer emit light and, therefore, the noise is different from that occurring due to load variations caused by a display pattern in the present invention. That is, the conventional technologies described above cannot prevent noise occurring in components exhibiting a piezoelectric effect due to load variation caused by a display pattern.
In view of the above, it is an object of the present invention to provide a display device which is capable of, at time of driving display panel section, preventing occurrence of audible noise from components exhibiting a piezoelectric effect due to a variation period of load variations caused by a display pattern and of achieving silent operations and removal of unpleasant audible noise.
According to a first aspect of the present invention, there is provided a display device including:
a display panel section having a plurality of scanning lines;
a driver to drive the display panel section for every scanning line;
at least one piezoelectric component exhibiting a piezoelectric effect;
a detecting unit to detect, predict or estimate directly or indirectly a variation period and timing of occurrence of a first load variation causing occurrence of audible noise from the at least one piezoelectric component; and
a driver controlling unit to output a control signal to the driver, the control signal used to permute order of driving the plurality of the scanning lines for another order of driving the plurality of the scanning lines which gives a variation period of a second load variation that prevents occurrence of audible noise caused by the at least one piezoelectric component, according to the detected, the predicted or the estimated variation period of the first load variation.
In the foregoing, a preferable mode is one wherein the detecting unit totalizes input display data for every the scanning line, and detects, predicts or estimates directly or indirectly the variation period and the timing of occurrence of the first load variation, based on a variation amount and the variation period of the total value of the input display data for every the scanning line.
Also, a preferable mode is one wherein the detecting unit detects the audible noise caused by the at least one piezoelectric component, and detects, predicts or estimates directly or indirectly the variation period and the timing of occurrence of the first load variation, based on the detected audible noise.
Also, a preferable mode is one wherein the detecting unit measures an amount of load variation and a variation period, and detects, predicts or estimates directly or indirectly the variation period and the timing of occurrence of the first load variation, based on the measured amount of the load variation and the measured variation period.
Also, a preferable mode is one wherein the detecting unit detects binary luminance values as the input display data for every the scanning line.
Also, a preferable mode is one wherein the detecting unit detects a display pattern made up of binary luminance values, the variation period of the first load variation represented by the display pattern made up of binary luminance values.
Also, a preferable mode is one wherein the detecting unit detects an individual line number of a scanning line associated with the input display data, the timing of occurrence of the first load variation represented by the detected line number.
Also, a preferable mode is one wherein the detecting unit detects or calculates a count of the scanning lines, the variation period of the first load variation represented by the detected or calculated count of the scanning lines.
Also, a preferable mode is one wherein the driver controlling unit calculates the count of the scanning lines based on the variation period of the first load variation detected, predicts or estimates directly or indirectly by the detecting unit.
Also, a preferable mode is one wherein the driver controlling unit has a table storing, in advance, driving order patterns for permuting the scanning lines, corresponding to the variation period of the first load variation.
In addition, a preferable mode is one wherein the driver controlling unit searches the table based on the detected, the predicted or the estimated variation period of the first load variation, and as a result of the search, permutes order of driving the plurality of the scanning lines for another order of driving the plurality of the scanning lines which provides the variation period of the second load variation that prevents occurrence of audible noise caused by the at least one piezoelectric component.
Another preferable mode is one wherein the driver has a shift register being able to shift driving order of the scanning lines forward or backward, and wherein the driver controlling unit outputs a first control signal to perform masking of an output of display data according to order of driving the scanning lines and a second control signal to indicate to shift driving order of the scanning lines forward or backward.
Still another preferable mode is one wherein the driver controlling unit permutes order of driving the scanning lines according to order of driving the scanning lines by using a memory section capable of storing the input display data for the plurality of the scanning lines.
With the above configuration, when the load variations that vary depending on a display pattern of display data to be input are large and when a load variation frequency is within an audio frequency range, displaying free from occurrence of audible noise in all load variations depending on a display pattern can be achieved by permuting order of driving lines to cause a frequency of piezoelectric vibration to be outside of an audio frequency range so as to prevent audible noise occurring due to a piezoelectric effect exhibited by components such as a capacitor.
With another configuration, prevention of audible noise caused by components exhibiting a piezoelectric effect can be achieved by exercising control of frequency components in the audible noise phenomenon by permuting order of driving lines without taking a measure to reduce a load of each pixel that may affect an image quality and without using components exhibiting no piezoelectric effect that may present a problem in terms of a mounting area and/or costs.
With still another configuration, a memory section mounted to sort input display data according to a method of driving a display panel section or a frame memory mounted to improve a display characteristic such as a moving-image characteristic can be also used as a memory section to change a driving scanning line, which can reduce costs further.
The above and other objects, advantages, and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:
Best modes of carrying out the present invention will be described in further detail using various embodiments with reference to the accompanying drawings.
In a display device of the present invention, a purpose of preventing noise caused by components exhibiting a piezoelectric effect and realizing silent operations and removal of unpleasant audible noise is achieved, when a driving load variation that varies depending on a display pattern periodically for every several lines has a component of an audio frequency, by estimating or detecting audible noise occurring in the components exhibiting a piezoelectric effect such as a capacitor or a like and by permuting the order of the driving lines. That is, when an amount of variation in driving load is large and its variation frequency is within an audio frequency range, by permuting order of driving lines to make the variation frequency be outside of the audio frequency range, occurrence of audible noise is avoided. Since the variation frequency differs depending on a pattern of display data, a plurality of patterns to be used for making the variation frequency be outside of the audio frequency range is prepared and selection is made out of the patterns according to a thing that represents the detected, predicted or estimated variation frequency. The number of a start line is detected as a thing that represents timing for permuting order of driving lines at time of detecting a variation period or the timing is determined based on the number of the line to be driven or a like by considering a difference in driving timing. Moreover, though the audio frequency is 20 kHz to 20 Hz, order changing patterns are prepared in a range where occurrence of audible noise in circuit components or a like is anticipated.
To judge whether order of driving lines should be permuted, following three methods are available.
(1) Judgement is made from an amount of variation in values obtained by totalizing input display data for every line and from a frequency of the variation.
(2) Judgement is made from a result from detection of actual noise using a sensor.
(3) Judgement is made from an amount of variation in loads detected from voltage ripples or a like and from a frequency of the variation.
Moreover, permuting of driving order is made for every frame since noise is recognized only when same display patterns appear during several frames. Also, a display pattern displayed during a present frame is very analogous to that displayed during a subsequent frame and, therefore, permuting of driving order that has been judged during the present frame is made also during the subsequent frame. The permuting of driving order is made by using a memory section to store data of the number of lines for each line, a line driving IC (Integrated Circuit) (gate driver) that can be shifted in both directions and have a function of controlling an output, and a controlling circuit (driver controlling section) to control the memory section and line driving IC (control of shifting direction, clock, and output enable signal (VOE)). Capacity being able to store, at least, data of the maximum number of lines corresponding to prepared display patterns to be used for permuting the order of the driving lines is required as capacity of the memory section.
A first embodiment of the present invention will be described. The first embodiment is carried out according to a method (1) described above.
The load variation detecting section 5 employs a method for estimating an amount of load variation and its variation period from input display data. That is, a sum total of pixel data is calculated on each line of input display data to obtain an amount of load occurring on every driving line. Each pixel data represents a luminance value of each color out of RGB (Red, Green, and Blue) colors and, therefore, a sum total of the pixel data for every line is a total value of luminance for every line, which is a value representing a load of a line. When the value obtained by the above calculation exceeds a predetermined high load value that may cause noise, counting of the number of lines is started. The counting of the number of lines is continued after the calculated load value, being not higher than the predetermined high load value, is detected more than once until the calculated load value, being not lower than the predetermined high load value, is again detected and the number of lines obtained by the counting is used as a value representing a variation period. Next, judgement is made as to whether the value obtained by the counting is within a predetermined range (the number of lines being within an audio frequency range) or, if the counted value is within the range, another judgement is made as to whether the value obtained by the counting occupies the variation period during a frame, the same display occurs and for more than a specified period of time and, if so, the driver controlling section 6 receives an instruction so that, when display is made during a subsequent frame, driving order is switched in a manner to correspond to a load variation period or display pattern. The instruction contains the number of the line from which counting is started which represents timing of permuting of driving order, and the number of lines that represents a load variation period or a display pattern, and the judgement may be made at every time of the above judgement or at every time when the judgement for one frame is terminated. The driver controlling section 6 accumulates the instruction in order to permute the order of driving lines during a subsequent frame. If the load variation detecting section 5 instructs a display pattern, the display pattern is indicated by an arrangement of luminance values obtained by converting a calculated load value of each line, based on a threshold value, into binary values with a white level and a black level. Moreover, it is presumed that the number of a line has been added to input display data.
Next, permuting of the driving order to be made by the driver controlling section 6 is explained. In the display in which, the lower luminance, the smaller the driving load and the higher the luminance, the larger the driving load, when a driving horizontal frequency is 65 kHz and in the case of use of a display pattern in which a white and a black appear repeatedly for every two lines, a case where periodic load variation appears for every four lines is described. When each line is driven by a white/black horizontal band display method, a pattern of “white, white, black, black, white, white, black, black, . . . ” is displayed and, therefore, a load varies for every two lines and, as a result, such a ripple as shown in
Similarly, as shown in
In the above example, an instruction for permuting the order of driving lines is provided by using the number of a start line and display pattern, however, the instruction for permuting the order of driving lines can be provided by using the number of the start line and load variation period, that is, the number of lines representing the load variation period. To do this, by storing, in advance, driving order patterns corresponding to the number of lines representing all load variation periods in a form of a table and by searching the table for the driving order pattern corresponding to the number of lines detected by the load variation detecting section 5, the order of driving lines is permuted.
Capacity of the memory section 4 required for permuting of order of driving lines differs depending on a driving order pattern to be permuted and is provided in a manner to satisfy the maximum condition necessary for a pattern to be prepared. Specifically, the memory section 4 has to store display data for a succeeding line while the order of driving the specified number of lines “a” is being permuted and, therefore, the capacity capable of storing the number of lines “a+1” of display data is required. Moreover, it is assumed that the number of a line is added to input display data and the number of the line is sequentially stored in an empty memory for a line. The driver controlling section 6 searches for a plurality of lines of data stored in the memory section 4 by using the number of the line to be driven to read the data. At this time point, judgement is first made as to whether the number of a line of data to be read is the number of a start line to which an instruction for permuting the order is provided and, if the number of the line is a number of the start line, a display pattern that represents a variation period or order changing pattern corresponding to the number of lines is obtained by searching the table and, according to the obtained order pattern, the number of the line following the number of the start line are changed.
Next, control signals output from the driver controlling section 6 to each driver and used to realize permuting of the described driving order are explained.
When order of driving lines is permuted, as shown in
The case where lines are driven in an ordinary driving order as shown in
In the embodiment, a type of feedback control is not exercised in which a variation period of load variations is detected from an actual noise or a voltage ripple to permute order of driving lines, but a type of feed-forward control is exercised in which a variation period of load variations causing nose is detected from input display data to permute order of driving lines. As a result, there is no fear of occurrence of a control hunting phenomenon caused by a deviation in time occurring when order of driving lines in a subsequent frame is permuted according to a result from detection during a present frame. Despite the deviation in time occurring when order of driving lines is permuted in a subsequent frame according to a result from detection during a present frame, since a video or image being displayed during a present frame is very analogous to that displayed during a subsequent frame and since noise is recognized only when the same display patterns appear over a time period of several frames, a high effect of suppressing noise caused by components exhibiting a piezoelectric effect can be achieved. This method of reducing noise has an advantage that adoption of the method is not required in which a load on each pixel that may affect an image quality is reduced by exercising control of frequency components causing audible noise and that there is no need for using components exhibiting no piezoelectric effect which present a problem in terms of an mounting area and/or costs.
The second embodiment is achieved by using a method (2) described above. Electrical configurations of a display device (liquid crystal display device) according to the second embodiment are described by referring to
First, configurations of the load variation detecting section 5 of the second embodiment are explained. The load variation detecting section 5 is configured to receive a signal output from a sensor section 8 to detect actual audible noise. An acoustic sensor with, for example, a small-sized microphone or a like or vibration sensor can be also employed in the sensor section 8. The vibration sensor is so configured that vibration is detected, based on a relative movement between a permanent magnet supported, in a manner to absorb mechanical impact, via an elastic member such as a spring-mass system, elastic resin, or a like and a conductor that moves together with a vibrating portion, by an induced current or eddy current flowing through a conductor. Sensitivity of the sensor section 8 is calibrated in advance based on a frequency characteristic and amplification of an amplifier or a like so as to detect a vibration with a level of being recognized as audible noise. The sensor section 8 is placed in the vicinity of components exhibiting a piezoelectric effect. The load variation detecting section 5 measures a frequency or period of the audible noise detected by the sensor section 8 and outputs an instruction for permuting order of driving lines to a driver controlling section 6 one by one or collectively. The instruction for permuting order of driving lines is associated, by the load variation detecting section 5 or driver controlling section 6, with a start line representing timing with which the order of driving lines is permuted. An example of a method for measuring a frequency or period of audible noise includes a method in which the frequency or period is calculated by counting a clock pulse occurring between peaks of the audible noise. By measuring a pulse having the same period as a line period or the number of input display data, instead of a clock pulse, the number of lines representing the load variation period can be obtained.
Configurations in which an instruction for permuting the order of the driving lines is associated with a start line by the load variation detecting section 5 are determined by considering a timing difference based on the number obtained by subtracting the number of lines accumulated by a memory section 4 from the numbers of the lines indicated in input display data. Here, if a value of an original number is negative, the number of a final number is used as a start line number and, therefore, a number obtained by adding the number of the end line to the negative value is used. Moreover, configurations in which the instruction is associated with a start line by the driver controlling section 6 are determined by the method in which the load variation detecting section 5 outputs an instruction for permuting the order of the driving lines to the driver controlling section 6 one by one every time a period of audible noise is detected and the driver controlling section 6 traces the number of lines in reverse order from the number of the line having been driven. The number of lines, though being able to be obtained by counting on the load variation detecting section 5 side, also can be calculated by dividing the period of the audible noise by a line period and, therefore, the number of lines may be calculated by doing division on the load variation detecting section 5 side or on the driver controlling section 6 side.
Next, functions of the driver controlling section 6 being different from those provided in the first embodiment are described. A display device according to the first embodiment is so configured that the number of the start line for which order of driving lines is to be permuted, display pattern, or the number of lines are received as an instruction for permuting order of driving lines and are held until a subsequent frame starts during which the order of driving lines is permuted. A display device according to the second embodiment is so configured that the number of a start line for which the order of the driving lines is to be permuted and a variation period or the number of lines are received and are held until a subsequent frame starts during which the order of driving lines is to be permuted or that a variation period, the number of lines and timing of detecting the variation period and the number of lines are received, and the number of the start line for which the order of driving lines is to be permuted is associated with the variation period and the number of lines based on the timing and the associated state is held until a subsequent frame starts during which the order of driving lines is permuted.
In the second embodiment, a type of feedback control is exercised in which a load variation period is detected from an actual noise to permute order of driving lines and, therefore, there is a concern of occurrence of a hunting phenomenon caused by a deviation in time occurring when the order of driving lines is to be permuted during a subsequent frame according to a result from the detection during a present frame. That is, if, by using a result from the detection of the audible noise at time of displaying during one frame 1, order of driving lines during a subsequent frame 2 is permuted, the occurrence of the audible noise can be avoided during the subsequent frame 2. Therefore, since no audible noise is detected at time of displaying during the frame 2, at the time of displaying during a frame 3 subsequent to the frame 2, the order of driving lines is not permuted. However, a state occurring during the frame 3 is very analogous to that occurring during the frame 2 and there is, therefore, a high possibility that a display pattern exists in which load variations causing audible noise readily to occur during the frame 3 as in the case of the frame 2. Despite this state, order of driving lines is not permuted during the frame 3 and, therefore, a possibility exists that the audible noise is produced at time of displaying during the frame 3. Thus, if noise is detected at time of displaying during the frame 3, order of driving lines is permuted in the subsequent frame 4, as a result, causing a control hunting phenomenon. This means that the effect of preventing the occurrence of the audible noise is reduced by half.
To solve this problem, the driver controlling section 6 of the second embodiment, when receiving an instruction for permuting order of driving lines from the load variation detecting section 5, permutes the order of driving lines at time of displaying from a subsequent frame over a period of time of a plurality of frames so that the same order patterns are displayed. If an instruction for permuting order of driving lines is provided by the load variation detecting section 5 during this period of time, no effect of suppressing the audible noise by permuting order of driving lines is expected and, therefore, permuting of order of driving lines during a subsequent frame is stopped and, if an instruction for permuting order of driving lines is provided by the load variation detecting section 5 thereafter, the order of driving lines is again permuted during a plurality of frames by using the same order pattern. This enables prevention of the control hunting phenomenon as described above. Thus, the same effect obtained in the first embodiment can be achieved also in the second embodiment.
Next, the third embodiment will be explained which is realized according to a method (3) described above. Electrical configurations of a display device are similar to those adopted in the second embodiment. Electrical configurations of the display device according to the third embodiment are described by referring to
First, configurations of the load variation detecting section 5 of the third embodiment are explained. The load variation detecting section 5 has a sensor section 8 to detect an amplitude of a voltage ripple and a frequency. An amplification circuit coupled to a capacitor that interrupts a direct current and detects only alternating current components can be connected to a resistor used to detect a load voltage in the sensor section 8. The load variation detecting section 5 measures an amplitude of the load variation based on the power ripple detected by the sensor section 8 and a variation period and judges, if the load variation has peak values greater than a specified magnitude and a period between the peak values is found to be within an audio frequency range, that audible noise occurs from components exhibiting a piezoelectric effect and outputs an instruction for permuting order of driving lines to a driver controlling section 6 one by one or collectively at time of termination of displaying during one frame and in response to a request from the driver controlling section 6. The instruction for permuting the order of the driving lines is associated with a start line to be used when the order of the driving lines is permuted. Configurations in which the detected variation period is associated with a start line representing timing of permuting the order of the driving lines and in which the number of lines are detected or calculated are the same as those in the second embodiment.
In the third embodiment as in the case of the second embodiment, a type of feedback control is exercised in which a load variation period is detected from an actual audible noise to permute order of driving lines and, therefore, there is a possibility of occurrence of the control hunting phenomenon caused by a deviation in time occurring when the order of the driving lines is to be permuted during a subsequent frame according to a result from the detection during a present frame.
To prevent the effect of avoiding occurrence of audible noise from being reduced to one-half, the driver controlling section 6 of the third embodiment, when receiving an instruction for permuting order of driving lines from the load variation detecting section 5, permutes the order of the driving lines at time of displaying during a subsequent frame over a plurality of frames so that the same order patterns are displayed. If an instruction for permuting the order of the driving lines is provided by the load variation detecting section 5 during this period of time, no effect of suppressing audible noise by permuting the order of the driving lines is expected and, therefore, permuting of the order of the driving lines at time of displaying during a subsequent frame is stopped and, when an instruction for permuting the order of the driving lines is provided by the load variation detecting section 5 thereafter, the order of the driving lines is again permuted during a plurality of frames by using the same order pattern. This enables prevention of the hunting phenomenon described above. Thus, the same effect obtained in the first embodiment can be also achieved in the third embodiment.
It is apparent that the present invention is not limited to the above embodiments but may be changed and modified without departing from the scope and the spirit of the invention. For example, in the above embodiments, a liquid crystal display panel section is described as an example of a display device. However, the present invention can be applied to a display device using other display panel section such as a plasma display panel section, an organic electro-luminescent display panel section, or a like.
The present invention can be suitably employed for a large-sized flat-type display device to be used in a pavilion such as an art museum, museum, or a like and in a place where silence is required such as a hospital or a like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-332500 | Nov 2004 | JP | national |
