Abstract:
A programmable transparent display message center is formed from an array of rows and columns of light emitting diodes (LED&#39;s). A wire connects each row of LED&#39;s. Each column of LED&#39;s is connected to a conductive transparent layer. The transparent layer is electrically isolated from the rows of wires. A voltage drive is associated with each row and with each column. The LED&#39;s, the wires, the conductive transparent layer, and the voltage driver and sequenced controller do not obscure an object located on one side of the display message center to the observer located on the opposite side thereof. Transparency often is achieved when the display obscures less than about 20% of the light emitted from the scene toward the viewer. The message displays to the observer is one or more of alphanumeric characters or graphics.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of application Ser. No. 09/772,050, filed Jan. 29, 2001. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
       [0002]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     The present invention relates generally to displays and more particularly to a transparent display panel. For present purposes, “display” means to project to an observer one or more of alpha numeric characters or graphics.  
         [0004]     There is a need for an attention grabbing message center, which can be placed, for example, in a cooler door or window without significantly obscuring the view of the product inside the cooler. This is especially true when several brands are located within the same cooler. The marketing of the cooler contents demands that the items for sale be visible so that the customer can quickly locate the branded packages, which the manufacturer has otherwise aggressively marketed. On occasion, the store manager would like to display messages on the cooler door to attract the customers to special pricing and/or sale items.  
         [0005]     Traditional prior art Light Emitting Diode (LED) message centers are largely opaque; typically incorporating a fiberglass printed circuit board with copper traces or closely spaced light emitting elements with significant metallic circuit traces. Placed in a cooler door, such traditional LED message centers unacceptably block the view of branded products. Thus, there is a need to create programmable message centers within a generally “transparent” panel.  
         [0006]     Prior art display panels do not provide for visibility of products behind the display. For example, Wei et al. (U.S. Pat. No. 5,684,368) proposes an (organic) LED display which is viewed from one side but there is no claim of providing visibility through the display. Lippmann et al. (U.S. Pat. No. 5,936,603) proposes temperature compensation for a display but again there is no claim of providing visibility through the display. Russ (U.S. Pat. No. 3,899,826) utilizes a conductive glass cover but by design the module does not provide visibility through the display. Curtain (U.S. Pat. No. 5,216,324) includes a phosphor coated viewing surface which precludes visibility through the display. Tang (U.S. Pat. No. 5,276,380), in fact, pursues approaches to get obscuring display elements as close together as practical atop a conductive, transparent faceplate.  
         [0007]     While one could postulate a completely transparent programmable message center, practical conductive/transparent substrates have finite resistances, which preclude the practical fabrication of such a device. Consider a conventional array of LED&#39;s consisting of N rows and M columns, such as depicted in  FIG. 1 . An LED is connected at each “cross point”, as for example an LED,  212 , at the intersection of N=3 and M=2. A complete display matrix consists of N×M such LED&#39;s, one at each crossover point. Utilizing a prior art drive (e.g., a time multiplexed drive such as is disclosed in U.S. Pat. No. 3,899,826) and transparent electrodes, it would appear that a solution to the transparent message center problem has been found. Unfortunately, the finite resistances mentioned above adversely impact this proposed device and render it impractical. Further reducing the glass&#39; coating resistance does not circumvent the problem because the glass begins to become more opaque, i.e., partially silvered, due to the increase in metal content of the coating required to increase its conductivity and reduce its resistivity. Additionally, some transparent conductive coatings such as indium tin oxide are difficult to coat and make uniform as their thickness increases.  
         [0008]     As a practical example of the postulated completely transparent programmable message center, suppose that one wants to construct an array of height 5 cm consisting of 7 rows and 64 columns, and that the column pitch is ⅚ cm (square pixel cells) using indium tin oxide (ITO) sputter coated glass. Practical ITO coated glass has a surface resistivity of more than 2 Ω/square (sq) and the horizontal (Row) traces will, by necessity, be about ⅚ cm high (neglecting the isolating line kerf). Each row would be driven typically for 1/N*100% of the time.  
         [0009]     If the display were called on to simultaneously illuminate all 64 columns and the single average (design) typical surface mount LED current was, say, 10 ma, then each total row conductor current would be 64*N*10 ma=4.48 amp, which must be carried by a conductor having a resistivity of 2 Ω/sq*6/5*5/6=2.0 Ω between each pixel. A single row array as illustrated in  FIG. 2  would have 64 LED&#39;s, illustrated partially by LED&#39;s  214 - 226 , V drive    228 , a current source,  230 , and partial illustrative 2 Ω resistors,  232 - 246 . The current through each LED  214 - 226  would be 0.070 amps. If the array were driven from one end only by current  230 , the conductor voltage drops can be calculated. Such calculated drops are displayed in Table 1 below.  
                                                                               TABLE 1                           Trace Current   Voltage       LED #   (A)   Drop (V)                                1   0.07   0.14       2   0.14   0.28       3   0.21   0.42       4   0.28   0.56       5   0.35   0.7       6   0.42   0.84       7   0.49   0.98       8   0.56   1.12       9   0.63   1.26       10   0.7   1.4       11   0.77   1.54       12   0.84   1.68       13   0.91   1.82       14   0.98   1.96       15   1.05   2.1       16   1.12   2.24       17   1.19   2.38       18   1.26   2.52       19   1.33   2.66       20   1.4   2.8       21   1.47   2.94       22   1.54   3.08       23   1.61   3.22       24   1.68   3.36       25   1.82   3.64       26   1.83   3.64       27   1.89   3.78       28   1.96   3.92       29   2.03   4.06       30   2.1   4.2       31   3.17   4.34       32   2.24   4.48                Driven at Both Ends   73.92 volts            33   2.31   4.62       34   2.38   4.76       35   2.45   4.9       36   2.52   5.04       37   2.59   5.18       38   2.66   5.32       39   2.73   5.46       40   2.8   5.6       41   2.87   5.74       42   2.94   5.88       43   3.01   6.02       44   3.08   6.16       45   3.15   6.3       46   3.22   6.44       47   3.29   6.58       48   3.36   6.72       49   3.43   6.86       50   3.5   7       51   3.57   7.14       52   3.64   7.28       53   3.71   7.42       54   3.78   7.56       55   3.85   7.7       56   3.92   7.84       57   3.99   7.98       58   4.06   8.12       59   4.13   8.26       60   4.2   8.4       61   4.27   8.54       62   4.34   8.68       63   4.41   8.82       64   4.48   8.96                Driven at One End   291.2 volts                      
 
         [0010]     Thus, a total drive voltage,  228 , (V drive ) of more than 290 volts would be required. This amount of voltage could be decreased to about 74 volts by driving the display from both ends. In either case, however, the design would be very complex and impractical in that both the row drive voltage and the cathode sink current for each column would have to be dynamically varied as the display pattern changes.  
         [0011]     This high voltage problem does not appear in the art because the (opaque/printed board) trace resistances either are small enough (i.e., short enough) to ignore or they can be compensated for using very small fixed series resistances.  
       BRIEF SUMMARY OF THE INVENTION  
       [0012]     A programmable transparent display message center is formed from an array of rows and columns of light emitting diodes (LED&#39;s). A wire connects each row of LED&#39;s. Each column of LED&#39;s is connected to a conductive transparent layer. The transparent layer is electrically isolated from the rows of wires. A voltage drive is associated with each row and with each column. The LED&#39;s, the wires, the conductive transparent layer, and the voltage driver and sequenced controller do not obscure an object located on one side of the display message center to the observer located on the opposite side thereof. The message displays to the observer is one or more of alphanumeric characters or graphics in any language.  
         [0013]     For present purposes, a display message center is “transparent” to a viewer if it uses transparent components and/or components that are of such a size that the viewer would not be hindered in viewing objects (a “scene”) behind the display message center. A message display center is transparent for present purposes if only a portion of the display center is transparent and another section of the display center is not transparent. The inventive display is transparent in both directions. Said another way, the display is two-way transparent. That is, a viewer can see through the display to view objects disposed on the opposite side of the display regardless of which side of the display the viewer is located. The inventive display can be driven to display messages viewable by a viewer regardless of which side of the display the viewer is located.  
         [0014]     Transparency, then, often is achieved when less than about 20% of the display is obscured, i.e., one can see through about 80% or more of the display. To achieve this end, the display&#39;s components must be capable of driving the display and either be formed of transparent material or be of sufficiently diminutive size so as to allow a viewer to view objects disposed on the opposite side of the display from the viewer.  
         [0015]     One advantage of the present invention is an innovative display that can be viewed by a viewer located on one side of the display, while concomitantly permitting the viewer to clearly view the scene located on the opposite side of the display. Another advantage is that the inventive display can be made rather large, for example, to serve as a walk-in cooler door. A further advantage is the ability of the display to project a bright, unexpected message to grab the attention of a purchaser. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     For a fuller understanding of the nature and advantages of the present invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:  
         [0017]      FIG. 1  is a conventional array of LED&#39;s consisting of N rows and M columns showing an LED at one cross over point;  
         [0018]      FIG. 2  is a representation of a prior art array of 64 LED&#39;s for calculating the voltage required to drive, V drive , the array;  
         [0019]      FIG. 3  is an illustrative embodiment of the programmable transparent message display center;  
         [0020]      FIG. 4  depicts a single column land associated with 7 rows in order to illustrate both the Anode Drive Level Changes embodiment of constructing a programmable transparent message display center and the Constant Anode Drive Level with ON Time Consumption embodiment of constructing a programmable transparent message display center;  
         [0021]      FIG. 5  represents the drive and logic signals to illuminate rows  1 ,  4 , and  6  for the Anode Drive Level Changes embodiment of  FIG. 4 ;  
         [0022]      FIG. 6  represents the drive and logic signals to illuminate rows  1 ,  4 , and  6  for the Constant Anode Drive Level with ON Time Consumption embodiment;  
         [0023]      FIG. 7  is a programmable transparent message display center embodiment constructed in accordance with the invention; and  
         [0024]      FIG. 8  is another programmable transparent message display center embodiment constructed in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     With respect to driving the display, the invention is based on a hybrid solution to the voltage problem outlined above. To that end, each row conductor of the LED array consists of a thin diameter, low resistance wire (e.g., copper, silver). Using good conductors for the row traces, which must simultaneously drive many columns means that the end to end row voltage drop can be made small, e.g., 4.48 A*0.1 Ω=0.448 V for a 64*5/6=53 cm long display using #30 gauge copper wire.  
         [0026]     With respect to the columns, integrated circuit column drivers and control circuitry cannot be distributed along the display as is typical in the prior art (printed circuit design), as the transparency of the display would be unacceptably compromised and reduced. If simple connections to conductive traces leading from the display ends to the columns were made, voltage problems again would be faced. For example, a multiplexed 0.07 amp cathode column current through a 5/32″ wide trace of 2 Ω per square ITO glass would have a voltage drop of about 0.9 V/cm or about 24 V to get to the center of the example display. Again, driving circuitry would need to be necessarily complex if the current is to be balanced in all pixels in all columns.  
         [0027]     In order to inventionally solve this problem, reference is made to  FIG. 3 , which depicts one embodiment of a display panel. Anode (time multiplexed) voltages, V 1  through V 7 , are applied to row wires,  21  through  27 , respectively. Wires  21 - 27  lie atop a conducting, transparent sheet,  30 , but are insulated (gapped from) sheet  30 .  
         [0028]     For illustrative purposes only and not by way of limitation, only 3 columns and 2 LED&#39;s are shown in  FIG. 4 . Lines,  45 - 48 , are (laser) cut lines in the conductive surface of sheet  30 , which produce isolated conductive lands,  55 - 57 , in conductive sheet  30 . A cut line,  60 , isolates lands  55 - 57  at the top and a second cut line,  61 , isolates lands or bars  55 - 57  at the bottom. Individual (surface mount) LED&#39;s, as represented as  70  and  71 , are connected so that the anode is connected to a wire, such as wire  22  for LED  70 , and the cathode is connected to the conductive coating of land  55 .  
         [0029]     A wire,  80 , provides a high current path for all LED cathodes and is connected to the sources of column driver FETs (field effect transistors),  85  through  87 , whose gates are driven via isolated conductive paths,  95  through  97 , respectively. Conductive paths  95 - 97  are formed by cutting the conductive layer of sheet  30  and are driven by data (logic) signals, represented as D 5  through D 7 , respectively.  
         [0030]     The areas of sheet  30  identified by numeral  90  in each cathode drive bar lands  55  through  57  provide a minimum protective series resistance for each LED. Area  90 , then, may be made narrow to increase this series resistance, such as, for example, as depicted by dashed lines  91 .  
         [0031]     The column resistance for the representative LED  70  also includes the conductive column resistance identified by numeral  92 . Thus, diode  70  will receive less current than LED  71 , because LED  70  is located a greater distance (i.e., resistance) from cut line  61 . To balance the display row currents, the ON time for voltage source V 1  can be made longer than the ON time for voltage source V 2 , etc. This scheme will be described in more detail below in connection with the “Constant Anode Drive level with ON time compensation” embodiment. Alternatively (and with additional complexity), the anode (row wire) voltages may differ for each row as will be described in more detail below in connection with the “Anode Drive Level Changes” embodiment.  
         [0032]     Column drive transistors  85 - 87  also are very small surface mount devices and all isolating cuts within conductive sheet  30  are quite thin (e.g., about 0.1 mm wide) and nearly invisible. The result is a nearly transparent, attention grabbing display, which does not obscure the product behind it.  
         [0033]     The controlling voltage signal levels and timings to accommodate the conductive coating resistance are described for example by Wei et al. in U.S. Pat. No. 5,684,386 and Lippmann, et al. in U.S. Pat. No. 5,936,603 and Norman in U.S. Pat. No. 5,719,589, the disclosures of which are hereby incorporated by reference.  
         [0034]     Neither Wei nor Lippmann nor Norman disclose a display panel which is designed so that it can be seen through or mention this novel application.  
         [0000]     Anode Drive Level Changes  
         [0035]     As stated above, the resistivity of practical glass coatings (e.g., ITO, pyrolytic tin oxide) lies in the range of about 10 to 100 Ω/square (dimensionless). This means that a 0.25″ wide (column) conductor strip (land) has a resistance of between about 40 and 400 Ω/linear inch. Referring to  FIG. 4 , a single column land,  100 , is seen to be connected to 7 LED&#39;s, LED 1 -LED 7 . In a complete message center there may be, say between about 40 and 64 such column lands. The anode of each LED is connected to the (negligible resistance) wires,  101 - 107 , respectively. The cathodes of each LED is bonded to the (resistive) coating in column land  100 , which is switched to a common (wire connected) ground,  111 , by an N channel FET,  110 . The controlling gate signal for FET  110  is identified by numeral V 8 .  
         [0036]     The resistivity of column land  100  is illustrated schematically in  FIG. 4  by a series of 6 segment additive resistances identified by numerals  120 - 125 , and an additional protective, connective resistance,  126 , leading to a switching column driver,  110 , whose ON resistance can be ignored.  
         [0037]     By way of example, assume that the resistivity of column land  100  is 30 Ω/square and that its width is 0.25″. Also assume that the spacing between anode wires  101 - 107  also is 0.25″, thus producing 0.25″/side square pixel spacing in the resultant display.  
         [0038]     The Anode Drive Level Changes embodiment, then, utilizes multiplexed anode (row) drive signals, V 1 -V 8  (N=1 to 8), which can be sequenced with equal ON times for each row and higher levels on signal V 1  than for signal V 2 , which is higher than signal V 3 , etc.  
         [0039]     For the assumed values, the resistance of resistances  120 - 125  equals 30 Ω/square*0.25″/0.25″=30 Ω each. Now, supposed that resistance  126  results from a 2.0″ length of column land  100 . This means that resistance  126  equals 30 Ω/square*2.0″/0.25″=240 Ω. Equal ON times, thus, require a peak row current equal to 7 resistances*0.010 amps=0.70 amps. This means that Vx (x=1-7)=0.070 amps*(240 Ω+30 Ω/square*(7−N)) volts. Thus, the voltage for each Vx is as follows: 
 
V1=29.4 volts 
 
V2=27.3 volts 
 
V3=25.2 volts 
 
V4=23.1 volts 
 
V5=21.0 volts 
 
V6=18.9 volts 
 
V7=16.8 volts. 
 
         [0040]      FIG. 5  represents the drive and logic signals to illuminate rows  1 ,  4 , and  6 . Note should be taken that the scan time shown as T10 must be less than 1/30 sec to avoid the appearance of display flicker to the human eye.  
         [0000]     Constant Anode Drive Level with ON Time Compensation  
         [0041]     Using the same physical resistances as in the Anode Drive Level Changes embodiment above, V7 is 16.8 volts and is applied for T7 seconds. Thus, the following times can be calculated:  
             T7   =     1.0   *   T7                 T6   =     1.125   *   T7                 T5   =     1.250   *   T7                 T4   =     1.375   *   T7                 T3   =     1.500   *   T7                 T2   =     1.635   *   T7                 T1   =       1.750   9.625     *   T7               
 
 The total time for all rows to be multiplexed in this example, then, is 9.625*Timax (flicker)=9.625*1/30 sec (persistence of vision). Thus, T7 should be less than 3.5 msec. 
 
         [0042]      FIG. 6  represents the drive and logic signals to illuminate rows  1 ,  4 , and  6  using on time compensation. Note should be taken that the period of the logic signals must match the (differing) row pulse widths.  
         [0043]     A section of a transparent display message center constructed in accordance with the precepts of the present invention is illustrated in  FIG. 7 . In particular thin (e.g., #28) copper wire rows,  200  and  202 , along with laser cut lines,  204 - 208 , which form column land conductors,  210  and  212 , which are formed from ITO coated glass (e.g., 1 micron thickness ITO layer). Again, the actual display constructed consisted of 7 rows and 64 columns, with only a section of this display being illustrated in  FIG. 7 . Associated mesas,  214 - 220 , are laser cut in the ITO to isolate such mesas within their respective columns. A conductive epoxy, identified by numerals  222 - 228 , attaches row wire  200  or  202  to their respective mesas. Surface mount LEDS (e.g., LNJ208R8ARA LED manufactured by Panasonic of Japan),  230 - 236 , are attached to each mesa  214 - 220  at one end and to their respective columns at the other end. Voltage drives associated with each wire  200  and  202  are not shown, but are provided. A laser cut line,  238 , terminates the length of column lands  210  and  212 . The terminal resistance, which can be varied by physical design, of each column land  210 ,  212 , is shown generally by numeral  240 . FET&#39;s,  242  and  244 , are associated respectively with column lands  210  and  212 . The source (S), gate (G), and drain (D) are connected in conventional fashion. A ground wire,  246 , is electrically coupled to the ITO coated glass by conductive epoxy, such as identified by numerals  248  and  250 . Logic to FET&#39;s  242  and  244  are represented as V1 Logic and V2 Logic. The size of each pixel is 0.25″ (ignoring kerf).  
         [0000]     Component Selection for the Inventive Display  
         [0044]     Considering now the transparency of the display message center manufactured as shown partially, for example, in  FIG. 7 , the areas of opacity may, for example, come from the FET&#39;s (e.g.,  244  and it&#39;s affixing conductive adhesive spots) and associated LED&#39;s (e.g.,  232  and  234  and their affixing conductive adhesive spots), and the row wire conductors (e.g.,  200 ,  202 ). By selecting appropriate components, the display can achieve a transparency of about 80% or greater. For example, the inventive display may utilize widely dispersed, surface mount LED&#39;s having dimensions of, for example, about 0.8 mm×1.6 mm. LED&#39;s of this size are available in an industry standard package, known as the “0603” package. 7 rows and 64 columns for a total of 448 LEDs are placed on a square matrix pitch of 6 mm. With this configuration, the apparent opacity of the LED&#39;s is the area of the LED divided by the area of the matrix or (0.8*1.6)/(6.0*6.0)=3.55%.  
         [0045]     The attachment of the FETs and LEDs to the conductive transparent surface and to the row conductors requires opaque conductive adhesive spots or “dots”. Generally, the area of the two dots are less than the area of the LED device itself, thereby producing an additional 3.55% obscurity in the assembled display.  
         [0046]     Lastly, the opacity of the row conductors, such as at  200  and  202  in  FIG. 7 , must be considered. If conductors of width X are placed upon a matrix display with square spacing between elements of Y, the apparent opacity due to the conductors is approximately (X*Y)/(Y*Y)=X/Y. Table 2, below, based on Reference Data for Engineers Seventh Edition Howard Sams &amp; Co Edited by E. C. Jordan, illustrates the apparent opacity resulting when standard thickness copper platings, for example, are etched away leaving a conductor that will carry the required 4.5 A current without fusing at 30 deg. C. for a display with 64 columns of LED elements spaced 6 mm (240 mil inches) apart.  
                                     TABLE 2                       Thickness   Width   Resulting       (mil inches)   (mil inches)   Obscurity (%)                                1.0   60   25       2.0   30   12.5       3.0   20   8.3       4.0   15   6.25                  
 
 Thicker platings are possible, but would be difficult to reliably etch with such small width to thickness ratios. Any platings of necessity would be electroless, as the plating must be electrically isolated from the conductive glass surface. 
 
         [0047]     Preferably, the row conductors consist of small  30  gauge wire, which has a diameter of 10 mil inches and a fusing current of over 10 amperes. Using this thin wire, the resulting obscurity would be about 4.1%.  
         [0048]     Considering these elements together, the total obscurity caused by the foregoing components will be the sum of the obscurities of the LEDs, their associated dots, and the row conductors. Thus, the total obscurity would be 3.55%+4.1%%+3.55%=11.2%. This means that the transparency of the display is approximately 88%. Thus, while the LED&#39;s, conductive adhesive spots, and row conductors represent opaque areas, these should not objectionably interfere with the otherwise transparent display message center manufactured as shown in  FIG. 7 .  
         [0049]     Another advantage of the transparent display message center is that it is programmable. Because the display is two-way transparent, the message center may be programmed to display a message viewable from either side of the display. For example, when driven in one direction, the message may be displayed to a viewer observing the front or exterior side of a cooler door. When driven in the opposite direction, the message may be displayed to be a viewer observing the back or interior side of a cooler door, e.g., when viewer has opened the cooler door to examine or remove a product.  
         [0050]      FIG. 8  shows a second and preferred embodiment of a section of a transparent display message center constructed in accordance with the precepts of the present invention. The construction of the column and rows in this second embodiment is the same as the construction described in connection with  FIG. 7 . Here, however, column drives for each column consist of a sinking driver,  291 , controlled by a control shift register/latch data,  292 , located in a thin, opaque block,  290 , at one edge of the otherwise nearly transparent display. Similar column drivers are associated with each column. Although opaque block  290  detracts somewhat from the otherwise nearly transparent display, block  290  can be positioned over a cooler shelf edge and, thereby still not obscure the produce on display in the cooler. The LED message still appears “magically” in a nearly clear area and the point of purchase attention is gleaned.  
         [0051]     While the invention has been described with reference to a preferred embodiment, those skilled in the art will understand that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. In this application all units are in the English system and all amounts and percentages are by weight, unless otherwise expressly indicated. Also, all citations referred herein are expressly incorporated herein by reference.