Patent Publication Number: US-7912229-B2

Title: Array driving system and method of driving loads

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an array driving system for driving loads arranged like an array such as a speaker array, an LED dot matrix display, or the like, and a method of driving the loads. 
     As the system for driving the loads that are arranged like a one-dimensional or two-dimensional array, there are the speaker array, the LED dot matrix display, and so forth. 
     In the speaker array, for the purpose of the sound directivity control, etc., a number of, e.g., several hundreds of speaker units are arranged on the plane and driven. 
     In such speaker array, since respective speaker units must be driven by different signals, the amplifiers are needed as many as the speaker units and wirings of the twice of number of speaker units are needed between these amplifiers and the speaker units. For example, when 240 speaker units, i.e., vertical 12 columns×lateral 20 rows, are used in total, 240 amplifiers (240 ch) are needed and thus the number of wirings provided between the amplifiers and the speaker units is extremely increased. 
     Therefore, the speaker driving system in which the power supplying function portions are provided to an axis of abscissa and an axis of ordinate of the matrix, in which the speakers are arranged, respectively has been proposed (Patent Literature 1). 
     According to this proposed system, it is feasible to drive the m·n speakers of the m×n matrix by the m+n power supplying function portions. 
     Patent Literature 1 
     JP-A-2001-61196 
     As described above, since the speaker array of the m×n matrix is driven by the m+n power supplying function portions, the number of wirings provided to respective speaker units can be reduced and the number of power amplifiers can be reduced. 
     However, the currents fed from a plurality of speakers belonging to the row flow into each row wiring connected to the ground, and therefore an amount of flowing current is increased. As a result, a potential due to an impedance (ideally this impedance is 0, but actually an infinitesimal impedance is present) of the wiring is generated, and there existed the problem that the good speaker characteristic cannot be obtained. The driving circuits capable of supplying a large current to cause the speakers to suck the current thereinto are needed. 
     The similar situation is generated in the dot matrix display in which a plurality of LEDs are arranged like an array, or the like. In other words, when the LEDs arranged in a matrix fashion are driven, the currents fed to a plurality of LEDs that belong to each row are flown into the row wiring, so that the driving circuits capable of supplying a large current are needed. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to provide an array driving system capable of driving loads arranged like an array with good characteristic and making unnecessary driver circuits that can supply a large current, and a method thereof. 
     It is another object of the present invention to provide a speaker array driving system capable of driving speaker units as the loads arranged like an array with good characteristic and making unnecessary the driver circuits that can supply the large current. 
     In addition, it is still another object of the present invention to provide an LED dot matrix display driving system capable of making unnecessary the driver circuits that can supply the large current when the loads arranged like an array are composed of LEDs. 
     In order to solve the aforesaid object, the invention is characterized by having the following arrangement.
     (1) An array driving system for driving a plurality of loads comprising:
       the plurality of loads arranged like an array; and   a plurality of driving circuits provided to correspond with the plurality of loads, respectively,   wherein one terminals of the plurality of loads are respectively connected to corresponding outputs of the plurality of driving circuits and the other terminals thereof are connected each other, and   wherein driving signals are respectively supplied to the plurality of loads so that a phase of the driving signal supplied to one of the plurality of loads is opposed to that of the driving signal supplied to the adjacent loads.   
       (2) The array driving system according to (1), wherein the other terminals of the plurality of loads connected each other are grounded.   (3) The array driving system according to (1), wherein
       the plurality of loads include a plurality of speaker units,   the plurality of driving circuits include a plurality of amplifiers, and   the plurality of speaker units are connected to the plurality of amplifiers, respectively, such that the adjacent speaker unit have an opposite polarity mutually.   
       (4) The array driving system according to (3), wherein a plurality of inverters are connected to the corresponding amplifiers, respectively, so as to invert phase of input signals supplied to the corresponding amplifiers.   (5) The array driving system according to (1), wherein
       the plurality of loads include a plurality of LEDs;   anodes and cathodes of adjacent LEDs are alternatively connected to a common line,   ones of the plurality of driver circuits are connected between the anodes of the LEDs, cathodes of which are connected to the common line, and a positive power supply, and   the others of the plurality of driver circuits are connected between the cathodes of the LEDs, anodes of which are connected to the common line, and a negative power supply.   
       (6) A method of driving a plurality of loads which are arranged like an array, the method comprising the steps of:
       respectively supplying driving signals to the plurality of loads so that a phase of the driving signal supplied to one of the plurality of loads is opposed to that of the driving signal supplied to the adjacent loads.   
       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a configurative example of a speaker array driving system as a first embodiment of an array driving system of the present invention. 
         FIGS. 2A and 2B  are block diagrams showing a configurative example of an LED array driving system as a second embodiment of the array driving system of the present invention, wherein  FIG. 1A  is a view showing an overall configuration, and  FIG. 2B  is a view explaining connections between LED driving drivers and LEDs. 
         FIGS. 3A and 3B  are views explaining an operation of the embodiment shown in  FIGS. 2A and 2B . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  is a block diagram showing a configuration of a speaker array driving system according to a first embodiment of the present invention. 
     In this  FIG. 1 , reference sign SP 1  to SPn (n is an integer of 2 or more) denote n speaker units arranged like a one-dimensional or two-dimensional array, and reference sign A 1  to An denote n power amplifiers provided to correspond to the speaker units SP 1  to SPn respectively and supply driving signals to corresponding speaker units SP 1  to SPn. One terminal of the speaker units SP 1  to SPn are connected to corresponding outputs of the power amplifiers A 1  to An, while the other terminals are connected commonly and grounded. Reference sign I 2 , I 4 , . . . , In denote inverters provided on the input side of the power amplifiers A 2 , A 4 , . . . , An. The driving signals being output from the power amplifiers A 2 , A 4 , . . . , An, to which the inverter is provided respectively, to the corresponding speaker units are set in an opposite phase to the driving signals being output from remaining power amplifiers A 1 , A 3 , . . . , An−1, to which the inverter is not provided respectively. 
     Where, assume that the speaker units (SP 1  and SP 2 , SP 3  and SP 4 , . . . , SP 2   k −1 and SP 2   k , . . . , SPn−1 and SPn) to which adjacent suffices are affixed are arrange in physically adjacent positions in the array. 
     More particularly, in the present invention, the speaker units arranged in the physically adjacent positions are constructed such that the driving signals having an opposite phase mutually are supplied to them. Then, in order to set final acoustic outputs in the same phase, the adjacent speaker units are connected in such a manner that their polarities are in opposite phase mutually. That is, as shown in  FIG. 1 , plus-side terminals of the speaker units SP 1 , SP 3 , . . . SPn−1 to which the inverters are not connected are connected to the outputs of the corresponding power amplifiers A 1 , A 3 , . . . An−1 respectively, while minus-side terminals thereof are connected commonly. In contrast, minus-side terminals of the speaker units SP 2 , SP 4 , . . . , SPn to which the inverters are connected are connected to the outputs of the corresponding power amplifiers A 2 , A 4 , . . . , An respectively, while plus-side terminals thereof are connected commonly. Accordingly, phases of the acoustic signals being output from the speaker units that are driven by the driving signal in the opposite phase respectively are set equal to phases of the acoustic signals being output from other speaker units. 
     As well known, in case the directivity control to aim at an acoustic lens effect is carried out by the speaker array, the sound waves are concentrated upon a desired point in the space by applying the driving signals, to which a predetermined delay is given respectively, to a number of speaker units SP 1  to SPn. In this case, since the speaker units located in the adjacent positions in the speaker array are physically positioned in close vicinity to each other, phase differences between these driving signals are small and thus a correlation between the driving signals becomes very high. 
     In the configuration shown in  FIG. 1 , an input signal from an input terminal S 1  is amplified by the power amplifier A 1 , then input into a plus-side terminal of the speaker unit SP 1 , and then flown into the ground via a minus-side terminal of the unit SP 1  (in the case the input signal is positive), so that the speaker unit SP 1  is driven. An input signal from an input terminal S 2  is supplied to the power amplifier A 2  via the inverter I 2 . In this case, since the power amplifier A 2  is set in the opposite phase, a current flows from the ground along a plus-side terminal of the speaker unit SP 2 , a minus-side terminal of the unit SP 2 , and the power amplifier A 2 . At this time, since a correlation between the input signal of the terminal S 1  and the input signal of the terminal S 2  is high, most of the current flows as indicated by a broken line in  FIG. 1  and only a current equivalent to a difference between the input signal of the terminal S 1  and the input signal of the terminal S 2  flows into the ground. This is similarly true of the connections between the terminals S 3  and S 4 , S 5  and S 6 , . . . , Sn−1 and Sn. After all, the current flowing into the ground is given as a total sum of the differences between the driving signals in the adjacent speaker units and is very small. As a result, a ground potential generated by wiring impedances becomes small and thus the good characteristic can be expected. 
     As described above, since it can be expected that the current flowing into the ground becomes very small, the problem in no means arises particularly even though a line to which terminals of the speaker units SP 1  to SPn, which are not connected to the power amplifiers, are connected commonly (common line) is not connected to the ground, as indicated by a broken line in  FIG. 1 . Therefore, it is possible that a common line to which the other terminals of a plurality of speaker units are connected commonly should not be connected to the ground. In this case, the wirings provided between the power amplifiers and the speaker units can be reduced to the number (n) corresponding to the number of the speaker units, and thus the number of wirings can be reduced much more. 
     As described above, according to the array driving system of the present invention, the driving signals can be supplied to respective speaker units via one wiring, and the earth wire can be used in common to all speaker units. Therefore, only (n+1) wirings are required of n speaker units, and the number of wirings can be reduced. 
     In case the common line to which respective speaker units are connected commonly is not connected to the ground, only one wiring is required every speaker unit. 
     In addition, since the adjacent speaker units are driven by the driving signals having the opposite phase, the current flowing through the earth wire to which respective speaker units are connected commonly can be reduced very small and degradation of the characteristic due to the earth potential that is generated by the wiring impedance can be prevented. 
     In this case, if a plurality of speaker units are fixed to a baffle to put a metal plate therebetween, it can be implemented simply to connect the other terminals of respective speaker units commonly. 
     In the above, explanation is made where n is the even number. In the case that n is large (e.g., several hundreds), the effect can be expected sufficiently if n is the odd number. 
     In the embodiment explained up to now, a plurality of speaker units in the speaker array are driven. The array driving system of the present invention can be applied to the case that the LEDs are driven in the LED display panel. 
     Another embodiment of the present invention to drive the LEDs in the LED display panel will be explained hereinafter. Here, suppose that the LEDs are arranged in m rows and n columns. 
       FIG. 2A  is a block diagram showing a pertinent configuration of an LED array driving system in this embodiment of the present invention. In this  FIG. 2A , reference numeral  11  is an A/D converter for converting the input video signal such as the NTSC signal, or the like into frame data in the form of n×m pixels, and numeral  12  denotes a frame memory for storing the frame data supplied from the A/D converter  11 . Reference numeral  13  denotes a clock generator circuit for generating a read clock in a period of (1/30×1/(m×n)) when 30 frames of the image are displayed every second. Reference numeral  14  denotes a read control circuit for generating a read address of the frame memory  12  in response to the read clock from the clock generator circuit  13 . The read address used to read the pixel data is generated sequentially from the read control circuit  14  in such a way that first the data is read sequentially from the upper leftmost pixel toward pixels on the right side and then the data is read from the leftmost pixel in the next row when the data reading comes up to the rightmost pixel in this row. Accordingly, image data of corresponding pixels are read from the frame memory  12 , and supplied to corresponding driver circuits of LED elements in an LED driving driver  15 . 
     The driver circuits for supplying the driving current in correspondence to m×n LEDs arranged in an LED display panel  16  respectively are provided to the LED driving driver  15 . Each driver circuit has a memory element for storing the image data read from the frame memory  12  corresponding to the pixel, and a driving circuit for supplying the current corresponding to a value of the image data to the corresponding LED. In this case, the color display is employed, the frame memory is provided every color of RGB, and the m×n LEDs are provided to each color respectively. 
       FIG. 2B  is a view showing a fashion of connections between the LED driving driver  15  and the LEDs contained in the LED display panel  16 . As shown in  FIG. 2B , in the LED array driving system of the present invention, adjacent LEDs are driven by different polarities. In more detail, an LED ( 16 - 11 ) in the first row and the first column and a driver circuit  15 - 11  for driving the LED, an LED ( 16 - 13 ) in the first row and the third column and a driver  15 - 13  for driving the LED, . . . are connected in series between a positive power supply voltage (+5 V) and the ground, while an LED ( 16 - 12 ) in the first row and the second column and a driver  15 - 12  for driving the LED, an LED ( 16 - 14 ) in the first row and the fourth column and a driver  15 - 14  for driving the LED, . . . are connected in series between the ground and a negative power supply voltage (−5 V). 
     In this manner, in the present invention, the LEDs ( 15 - 11 ), ( 15 - 13 ), . . . in the odd columns are driven by the currents that have a magnitude in response to the corresponding image data D ( 1 , 1 ), D( 1 , 3 ), . . . respectively and flow from the plus power supply to the ground, while the LEDs in the even columns are driven by the currents that have a magnitude in response to the corresponding image data respectively and flow from the ground to the minus power supply. Namely, the LED array driving system of the present invention is constructed such that adjacent LEDs are driven by the opposite polarities. 
     An operation of the LED array driving system of the present invention constructed in this manner will be explained with reference to  FIGS. 3A and 3B  hereunder. 
     Normally, in the image data, the pixel value is not independent of the neighboring pixel and has the similar value in most cases. When the image is represented by the gray scale, the density gradient is often present in the natural image, and adjacent pixel values have the almost same value.  FIG. 3A  shows an example in which one pixel is represented by 8 bits (=256 levels). In this example, the case where a level Dt 1  (i,j)=127 of the pixel (i, j) and a level Dt 1  (i,j+1)=126 of the adjacent pixel (i, j+1) are given at a time t 1 , and then a level Dt 2  (i,j)=126 and a level Dt 2  (i,j+1)=126 are given at a next time t 2  is shown. 
       FIG. 3B  is a view showing absolute values of an LED driving current supplied from the driver circuit corresponding to the pixel (i, j) and an LED driving current supplied from the driver circuit corresponding to the pixel (i,j+1). 
     In this example shown in  FIG. 3B , a difference in the driving current between the adjacent pixels in a period t 1  is a current corresponding to the pixel level  1 , and this difference is eliminated in a period t 2 . Here, a displacement Δt=1/(30×m×n) second is generated in a start time of t 2 , based on a difference in times at which the pixel data are read by the read control circuit  14 . But such influence is negligible. 
     In this manner, absolute values of the driving currents of the LEDs corresponding to the adjacent pixels are almost identical, but directions of the currents are in the opposite direction. It is possible to say that the same is true of all sets of the adjacent LEDs. In the end, it is appreciated that the current flowing through the line (common line), which connects cathodes and anodes of the LEDs in  FIG. 2  commonly and is connected to the ground, can be very reduced. 
     In this case, since this current is very small, this common line is kept not to be connected to the ground. 
     The case where the circuit that has the memory element and can be driven at a duty of 100% is employed as the driver circuit is explained herein. The present invention is not limited to this case, and can be applied similarly to the case where the driver circuit for driving the LEDs by the PWM (pulse width modulation) system is used. 
     As described above, according to the array driving system of the present invention, since one terminals of a plurality of loads are connected commonly and adjacent loads are driven mutually in opposite phase, the current flowing through the commonly-connected portions can be very reduced and thus deterioration of the characteristic due to the common impedance can be prevented. 
     According to the array driving system for driving the speaker array of the present invention, above deterioration of the characteristic due to the common impedance can be prevented and the number of wirings for connecting the amplifiers and the speaker units can be reduced. 
     In addition, according to the array driving system for driving the LED matrix of the present invention, since adjacent LEDs can be driven mutually in opposite phase, the current flowing through the earth wire can be reduced.