Abstract:
An LED module has a controller with a modulator and illumination driver, and first and second LED chains. The first LED chain is connected to the modulator, has a first group of LED cells, and emits a first light under a pulse mode current input from the modulator. The first light has a digital data over a signal carrier. The second LED chain is connected to the illumination driver, has a second group of LED cells, and emits a second light under a constant current input from the illumination driver. There are fewer LED cells in the first group than the second group. The illumination driver is independent from the modulator in controlling emission of the first light. Alternatively, the LED module has a controller, an LED chain connected to the modulator, a first group of LED cells, and a second group of LED cells directly connected to the first group of LED cells. The first group of LED cells operates under a pulse mode current input from the modulator and emits a first light having a digital data over a signal carrier. The second group of LED cells emits a second light under a constant current input from the illumination driver.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation of co-pending application Ser. No. 14/735,572, filed on Jun. 10, 2015, which is a Continuation of application Ser. No. 13/089,946, filed on Apr. 19, 2011, now abandoned, for which priority is claimed under 35 U.S.C. §120, the entire contents of all of which are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates generally to optical communication and array-type light-emitting devices. 
         [0003]    Light emitting diodes (LEDs) are an important class of solid-state devices that convert electric energy to light. They generally comprise an active layer of semiconductor material sandwiched between two oppositely-doped cladding layers. When a bias is applied across the cladding layers, electrons and holes are injected into the active layer where electrons and holes recombine to generate photons, or light. Recent advances in LEDs have resulted in highly efficient light sources that surpass the efficiency of filament-based light sources, providing light with equal or greater brightness in relation to input power. 
         [0004]    Disadvantage of conventional LEDs used for lighting applications is that they cannot generate white light directly from their active layers. Recently, two different ways have been introduced to produce white light from conventional LEDs. One way to produce white light from conventional LEDs is to combine different wavelength of light from different LEDs. For example, white light can be produced by combining the light from red, green and blue LEDs or combining the light from blue and yellow LEDs. The other way to produce white light is using yellow phosphor, polymer or dye to downconvert portion of the light from a blue LED into yellow light. A white LED is seemly produced because it simultaneously emits both blue and yellow light, which combine to provide white light. 
         [0005]    Since white LEDs are developed, LEDs have widely used because of their high durability, longevity, portability, low power consumption, absence of harmful substances such as mercury, and so forth. Often-seen applications of LEDs include white light illumination, indicator lights, vehicle signal and illuminating light, LCD backlight modules, projector light sources, outdoor displays, and so forth. Nevertheless, other applications might use LEDs to replace their light sources. 
       SUMMARY 
       [0006]    Embodiments of the present invention disclose a lighting apparatus capable of simultaneously providing illumination and data transmission to a receiver. The lighting apparatus comprises an LED module and a modulator. The LED module comprises a plurality of LED cells connected as an LED chain having two conductive pads. The light emitted from the LED module is visible. The modulator provides driving current to the LED module to transmit data. 
         [0007]    Embodiments of the present invention disclose an LED module, comprising LEDs and conductive pads. A first group of the LED cells is connected as a first LED chain, driven for illumination. A second group of the LED cells is connected as a second LED chain for data transmission. The conductive pads include a first pair of conductive pads connected to the first LED chain and a second pair of conductive pads connected to the second LED chain. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The invention can be more fully understood by the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0009]      FIG. 1  illustrates a broadcast system; 
           [0010]      FIG. 2  exemplifies light apparatus  12   a;    
           [0011]      FIG. 3  shows the waveform of driving current I IN  that a modem provides to the LED module of  FIG. 2 ; 
           [0012]      FIG. 4  demonstrates a cross section view of LED cells  8   a ( 1 ,  1 ) and  8   a ( 1 ,  2 ), cutting along the dotted line AA′ in  FIG. 2 ; 
           [0013]      FIG. 5  exemplifies another light apparatus; 
           [0014]      FIG. 6  shows the waveform of driving current I IN  and I LIN  that the modulator and the illumination driver of  FIG. 5  provide respectively; 
           [0015]      FIG. 7  exemplifies another light apparatus; 
           [0016]      FIG. 8  demonstrates a cross section view of LED cells  8   c ( 3 ,  1 ) and  8   c ( 3 ,  2 ) in  FIG. 7 , cutting along the dotted line BB′; and 
           [0017]      FIGS. 9-12  exemplify four light apparatuses. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The following embodiments are described in sufficient detail to enable those skilled in the art to make and use the invention. It is to be understood that other embodiments would be evident based on the present disclosure, and that proves or mechanical changes may be made without departing from the scope of the present invention. 
         [0019]    In the following description, numerous specific details are given to provide a thorough understanding of the invention. However, it will be apparent that the invention may be practiced without these specific details. In order to avoid obscuring the present invention, some well-known configurations and process steps are not disclosed in detail. 
         [0020]    One embodiment of the invention employs LED cells as a light source to transmit digital information over a free space optical data pathway at the same time when LED cells functions for illumination. Transmission is accomplished by modulating or varying the current flowing through LED cells. 
         [0021]      FIG. 1  illustrates broadcast system  10  with light apparatuses  12   a  and  12   b  according to one embodiment of the invention. Light apparatuses  12   a  and  12   b  are powered by AC grid power lines and optionally receive digital data over AC grid power lines by way of power line communication. Each of light apparatuses  12   a  and  12   b  has an LED module with at least one LED chip. By modulating the light emitted from the LED chips, each of light apparatuses  12   a  and  12   b  transmits the digital data over the air to receiver  14   a  or  14   b.  The modulation should be over a signal carrier with an adequately-high frequency and be imperceptible by a human eye. 
         [0022]    Subject to other factors, the data transmission rate from the AC power lines to receiver  14   a  or  14   b  is limited by the signal bandwidth that the LED chips in light apparatuses  12   a  and  12   b  can support. Input capacitance of each LED chip in light apparatuses  12   a  and  12   b  could strongly affect the bandwidth supported. Hereinafter, input capacitance of an LED chain refers to the capacitance measured from two conductive pads respectively connected to n-type and p-type contact layers of the LED chain, by means of small-signal response. The less input capacitance of an LED chip, the broader bandwidth the LED chip can support. 
         [0023]      FIG. 2  exemplifies light apparatus  12   a.  As shown in  FIG. 2 , light apparatus  12   a  has modem  16  and LED module  19   a  including LED chips  8   a.  Modem  16 , powered by AC grid power lines, is the combination of a demodulator which retrieves data carried from AC grid power lines, and a modulator  17  which provides and modulates driving current I IN  to LED module  19   a  to transmit data over the emitted light. Modulator  17  might include a converter converting an AC source current to driving current I IN . The light emitted from the LED chips  8   a  is a visible light, for example a blue light having a wavelength spectrum around 440˜480 nm, a green light having a wavelength spectrum around 500˜560 nm, a green light having a wavelength spectrum around 500˜560 nm, a red light having a wavelength spectrum around 600˜650 nm, or white light. In the embodiment of  FIG. 2 , LED module  19   a  has two LED chips  8   a  connected in series. For another embodiment, an LED module might have only one LED chip. 
         [0024]    As an example, LED chip  8   a  has LED cells  8   a ( 1 , 1 )˜ 8   a ( 3 , 3 ), arranged as an LED array with 3 columns and 3 rows. Label WW(N, M) refers to the LED cell located at N th  column and M th  row of LED chip WW. LED cells  8   a ( 1 ,  1 )  8   a ( 3 ,  3 ) are connected in series as an LED chain having two conductive pads IN+ and IN−, which are located at two diagonal corners of LED cells  8   a ( 1 ,  1 ) and  8   a ( 3 ,  3 ), respectively. The physical orientation for each LED cell in 1 st  and 3 rd  column is opposite to that of each LED cell in 2 nd  column. If one LED cell in an LED chain is forward biased, all LED cells in the LED chain are forward biased, and vice versa. In one embodiment, LED cells  8   a ( 1 , 1 )˜ 8   a ( 3 , 3 ) are epitaxial grown on a monolithic substrate through MOCVD process and other semiconductor process, such as sputtering, lithography, and etching process, such that the active layers therein are formed at the same time and made of substantially the same material. As the operation voltage of LED chip  8   a  is the summation of the operation voltages of individual LED cells, LED chip  8   a  is sometimes referred as a high-voltage (HV) LED chip. The number of the LED cells of the LED chip is around 3˜80, or preferred 8˜40, depending on the operation voltage to be applied. 
         [0025]    In order to provide the function of illumination, an LED chip should have enough number of LED cells emitting at the same time. LED cells connected in parallel could emit light at the same time, but the input capacitance for the LED cells as a whole increases as the number of the LED cells increases. Supposed that there are K 1  identical LED cells connected in parallel and each individual LED cell has input capacitance of F farad, the capacitance of the LED cells as a whole will be K 1 *F farad. As mentioned before, increased input capacitance might reduce the bandwidth and the data transmission rate, such that LED cells connected in parallel are not suitable for data communication. Nevertheless, LED cells connected in series as an LED chain emit at the same time, and the input capacitance for the LED cells as a whole decreases as the number of the LED cells connected in series increases. The input capacitance for K 1  identical LED cells as a whole will be F/K 1  farad if they are connected in series wherein each individual one has input capacitance of F farad. Thus, an LED chain is suitable for both illumination and data transmission. In the embodiment of  FIG. 2 , a driven LED chain has a plurality of LED cells connected in series, the number of the LED cells is around 3˜80, or preferred 8˜40. 
         [0026]    There is another advantage that series connection surpasses parallel connection. Each and every LED in an LED chain of an LED chip will be driven with the same driving current even if there are slight differences between the characteristics of the LED cells in the LED chain. In other words, the LED cells in an LED chain of an LED chip emit power evenly. LED cells connected in parallel acts differently, however. Most of the driving current for the LED cells connected in parallel crowds to the LED cell with the least resistance, such that the LED cell with the least resistance emits higher power in comparison with others, therefore downgrading the reliability of the LED chip. 
         [0027]      FIG. 3  shows the waveform of driving current I IN  that modem  16  could provide to LED module  19   a  of  FIG. 2 . Driving current I IN  substantially switches between a high current level and a low current level back and forth. The low current level (of logic  0 ) is no less than 0 A and could be as low as 0 A, forcing LED module  19   a  to stop emitting. The high current level (of logic  1 ) drives LED module  19   a  to emit visible light. Within a clock cycle time, a rising edge means data “ 1 ” while a falling edge means data “ 0 ”. This kind of encoding scheme is called Manchester coding, a special case of binary phase shift keying. The data transmission rate should exceed the frequency range perceivable by a human eye, such that LED module  19   a  is seen by human eyes to illuminate without flickering and provide constant intensity of light as being driven by average current I BRT , which is the average of the high and low current levels. 
         [0028]    As an example,  FIG. 4  demonstrates a cross section view of LED cells  8   a ( 1 ,  1 ) and  8   a ( 1 ,  2 ), cutting along the dotted line AA′ in  FIG. 2 . A similar drawing has been published in  FIG. 2  of US Patent Application Publication 2010/0213474, whose entirety is incorporated by reference. As shown in  FIG. 4 , LED cells  8   a ( 1 ,  1 ) and  8   a ( 1 ,  2 ) are grown on a monolithic substrate  60 , each having, from bottom to top, n-type contact layer  62 , n-type cladding layer  64 , active layer  66 , p-type cladding layer  68 , and p-type contact layer  70 . A wavelength conversion layer  72  is optionally formed on contact layer  70  to convert the light emitting from the active layer. Two electrodes  76  and  74  are optionally formed (may be omitted) on n-type contact layer  62  and p-type contact layer  70 , respectively. LED cells  8   a ( 1 ,  1 ) and  8   a ( 1 ,  2 ) are physically separated on monolithic substrate by a trench between LED cells  8   a ( 1 ,  1 ) and  8   a ( 1 ,  2 ). An electric circuit layer  78  provides electric connection between the n-type contact layer  62  of  8   a ( 1 , 1 ) and the p-type contact layer  70  of the adjacent LED cell, such as  8   a ( 1 , 2 ) to form a series connection. An insulator layer  80  is formed under portion of electric circuit layer  78  to prevent unwanted short circuits. In one embodiment, each of LED cells  8   a ( 1 ,  1 ) to  8   a ( 3 ,  3 ) occupies a cell area on the monolithic substrate  60  no more than 121 mil 2 . The monolithic substrate  60  has a surface area, for example between 1.21*10 2  to 1*10 5  mil 2 . 
         [0029]    Two conductive pads IN−, IN+ are provided for electric connection between the LED chip  8   a  and an electric circuit outside the chip through external wires. The two conductive pads IN−, IN+ are respectively formed on the monolithic substrate  60  outside the array area for LED cells  8   a ( 1 , 1 )˜ 8   a ( 1 , 3 ), and preferably at different corners or borders of the LED chip  8   a.  The conductive pads IN−, IN+ are electrically coupled to the LED cells  8   a ( 1 , 1 )˜ 8   a ( 1 , 3 ) via the electric circuit layer  78  as in  FIG. 4 . 
         [0030]    As LED cells  8   a ( 1 , 1 )˜ 8   a ( 3 , 3 ) are epitaxial grown on monolithic substrate  60  using MOCVD process and other semiconductor process, such as sputtering, lithography, and etching process, the compositions of the active layers  66  therein are substantially the same to emit lights with the same or similar wavelength spectrum. Nevertheless, wavelength conversion layers  72  may be different or absent for some LED cells. For example, in one embodiment, all LED cells  8   a ( 1 , 1 )˜ 8   a ( 3 , 3 ) are white LED cells each having an active layer emitting blue light and a wavelength conversion layer downconverting the blue light into yellow light. In another embodiment, some of LED cells  8   a ( 1 , 1 )˜ 8   a ( 3 , 3 ) are white LED cells each having a wavelength conversion layer downconverting the blue light into yellow light, and others are blue LED cells having a wavelength conversion layer downconverting the blue light into red light. In another embodiment, some of LED cells  8   a ( 1 , 1 )˜ 8   a ( 3 , 3 ) are white LED cells each having a wavelength conversion layer and others are blue LED cells having no wavelength conversion layer. In one embodiment, the wavelength conversion layer is formed a layered structure bonded to the contact layer through a glue bonding layer under chip process for the foregoing embodiments. In another embodiment, the wavelength conversion layer is formed by encapsulating the LED chip by an encapsulating material containing a wavelength conversion material under packaging process. 
         [0031]      FIG. 5  exemplifies light apparatus  12   b.  LED module  19   b  is controlled by controller  11  to provide both illumination and data transmission. Similar with LED chip  8   a  of  FIG. 2 , LED chip  8   b  in LED module  19   b  has LED cells  8   b ( 1 , 1 )˜ 8   b ( 3 , 3 ), arranged as an LED array on a monolithic substrate. LED chip  8   b  is slightly different with LED chip  8   a.  While LED chip  8   a  of  FIG. 2  has only one LED chain with one pair of conductive pads IN+ and IN− as inputs, LED chip  8   b  of  FIG. 5  has two LED chains  22  and  24 . The number of LED cells in one LED chain is not restricted and one LED chain might include only one LED cell as exemplified by LED chain  24 , or more than one LED cell. LED chain  22  has a pair of conductive pads LIN+ and IN+/LIN− while LED chain  24  has a pair of conductive pads IN+/LIN− and IN−. It can be found conductive pad IN+/LIN− is a common conductive pad connected to both the anode (or the n-type contact layer) of LED chains  24  and the cathode (or the p-type contact layer) of LED chain  22 . Conductive pads LIN+, IN−, and IN+/LIN− are provided for electric connection between the LED chip  8   a  and an electric circuit outside the chip through external wires. The conductive pads LIN+, IN−, and IN+/LIN− are respectively formed on the monolithic substrate  60  outside the area of the LED cells of LED chip  8   b,  and preferred at different corners or borders of the LED chip  8   b  as shown in  FIG. 5 . The conductive pads LIN+, IN−, and IN+/LIN− are electrically coupled to the LED cells via the electric circuit layer  78  as in  FIG. 4 . For example, pad IN+/LIN− is connected via electric circuit layer  78  to both a p-type contact layer of LED chain  24  and a n-type contact layer of LED chain  22 . The pair of conductive pads LIN+ and IN+/LIN− is connected to illumination driver  13  of controller  11  and the pair of conductive pads IN+/LIN− and IN− is connected to modulator  17  of controller  11 .  FIG. 6  shows the waveform of driving current I IN  and I LIN  respectively provided by modulator  17  and illumination driver  13  of  FIG. 5 . The operation of modulator  17  is not detailed here for brevity since it has been done in the paragraphs regarding with  FIGS. 2 and 3 . It is comprehensive that LED chain  24  driven by modulator  17  transmits data via the light it emits. Illumination driver  13  of  FIG. 5  provides driving current I LIN  to LED chain  22 . Driving current L LIN  is almost a constant and conveys no data as shown in  FIG. 6 , such that LED chain  22  only acts as a lighting source for illumination. Accordingly, LED chip  8   b  has two LED chains  22  and  24  where LED chain  22  is only for illumination and LED chain  24  is for data transmission. In one embodiment, LED chip  8   b  is formed on a monolithic substrate, each of LED cells  8   b ( 1 ,  1 ) to  8   b ( 3 ,  3 ) occupies a cell area on a monolithic substrate no more than 121 mil 2 , and the number of LED cells in LED chain  24  is smaller than that in LED chain  22 . In another embodiment, the area of one of the LED cell(s) in LED chain  24  for data transmission is smaller than that in LED chain  22  for illumination. In one embodiment, the area of one of the LED cell(s) for data transmission is preferred no more than 121 mil 2 , and the area of one of the LED cells for illumination is preferred no more than 400 mil 2 . 
         [0032]    In one embodiment, LED chains  22  and  24  emit light of different colors. For example, LED cells in chain  22  comprises white LED cells and LED cell  8   b ( 3 , 3 ) in chain  24  is a blue LED cell. 
         [0033]      FIG. 7  exemplifies light apparatus  12   c.  Similar with LED chip  8   b  of  FIG. 5 , LED chip  8   c  of  FIG. 7  has two LED chains  26  and  28 . LED chain  26  is only for illumination, driven via a pair of conductive pads LIN+ and LIN−/IN− by illumination driver  13 . LED chain  28  is for data transmission, driven via a pair of conductive pads IN+ and LIN−/IN− by modulator  17 . The conductive pad LIN−/IN− is electrically connected to both two n-type contact layers of LED chains  26  and  28 . In one embodiment, LED chip  8   c  is formed on a monolithic substrate.  FIG. 8  demonstrates a cross section view of LED cells  8   c ( 3 ,  1 ) and  8   c ( 3 ,  2 ) in  FIG. 7 , cutting along the dotted line BB′. As shown in  FIG. 8 , even though they are located in the same column, LED cell  8   c ( 3 ,  1 ), which belongs to LED chain  26 , has a cell orientation opposite to LED cell  8   c ( 3 ,  2 ), which belongs to LED chain  28 . 
         [0034]    It is unnecessary that the LED chain only for illumination must shares a common conductive pad with the LED chain for data transmission.  FIGS. 9 and 10  exemplify light apparatuses  12   d  and  12   e.  In  FIG. 9 , LED chip  8   d  has LED chain  30  only for illumination and LED chain  32  for data transmission. Conductive pads LIN+ and LIN− for LED chain  30  are independent to conductive pads IN+ and IN− for LED chain  32 , while LED cell  8   d ( 3 ,  1 ) has the same cell orientation with LED cell  8   d ( 3 ,  2 ). LED chains  30  and  32  are electrically insulated on the monolithic substrate. In  FIG. 10 , LED chip  8   e  has LED chain  34  only for illumination and LED chain  36  for data transmission, while LED cell  8   e ( 3 ,  1 ) has a cell orientation opposite to LED cell  8   e ( 3 ,  2 ). 
         [0035]      FIG. 11  exemplifies light apparatus  12   f.  It is unnecessary that LED cells in an LED module are all monolithically formed as an array on a monolithic substrate. In  FIG. 11 , LED module  19   f  has individual LED chips  8   f   1  to  8   fn,  where n is an integer. LED chips  8   f   1  to  8   fn  could be formed on different substrates individually and together packaged on a submount, where the data transmitting speed would be lower compared with the LED module as disclosed in the foregoing embodiments using a monolithically-formed LED cell array on a single chip. In one embodiment, LED chips  8   f   1  to  8   fn  are all white LED chips. In another embodiment, LED chips  8   f   1  to  8   fn  consist of red, green and blue LED chips. LED module  19   f  has two conductive terminals TIN+ and TIN−, through which modulator  17  provides driving current I IN  to LED cells  8   f   1  to  8   fn  to transmit data. 
         [0036]      FIG. 12  exemplifies light apparatus  12   g.  Similar with  FIG. 11 , LED module  19   g  of  FIG. 12  has LED chips  8   g   1  to  8   gn,  where n is an integer. LED chips  8   g   1  to  8   g   5  are grouped and connected as LED chain  38 , driven by illumination driver  13  and functioning only for illumination. LED chips  8   g   6  to  8   gn  are grouped and connected as LED chain  40 , driven by modulator  17  for data transmission. The light from LED chain  38  might be the same with or different to that from LED chain  40 . LED chips  8   g   1  to  8   g   5  of LED chain  38  or LED chips  8   g   6  to  8   g n of LED chain  40  comprise at least one selected from blue LED, green LED, red LED, and white LED chips. For example, LED chips  8   g   1  to  8   g   5  of LED chain  38  consist of green and red LED chips and LED chips  8   g   6  to  8   gn  consist of only blue LED chips. In one embodiment, LED chain  38  provides visible light, and LED chain  40  provides invisible light. In view of noise immunity, it is preferable that the wavelength spectrum of the light from LED chain  40  has a peak that is not affected by the intensity of the light from LED chain  38 . 
         [0037]    All the previously-mentioned LED chains that function, partially or fully, for illumination provide visible light. Nevertheless, the previously-mentioned LED chains that function only for data transmission could provide visible or invisible light. 
         [0038]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.