US20120269520A1 - Lighting apparatuses and led modules for both illumation and optical communication - Google Patents

Abstract

Lighting apparatuses and LED modules capable of both illumination and data transmission are disclosed. An exemplifying lighting apparatus has a LED module and a modulator. The LED module comprises a plurality of LED cells connected as a 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.

Description

BACKGROUND
• The present disclosure relates generally to optical communication and array-type light-emitting devices.
• 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.
• 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.
• 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
• 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.
• 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
• The invention can be more fully understood by the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
• FIG. 1 illustrates a broadcast system;
• FIG. 2 exemplifieslight apparatus12a;
• FIG. 3 shows the waveform of driving current I_INthat a modem provides to the LED module ofFIG. 2;
• FIG. 4 demonstrates a cross section view ofLED cells8a(1,1) and8a(1,2), cutting along the dotted line AA′ inFIG. 2;
• FIG. 5 exemplifies another light apparatus;
• FIG. 6 shows the waveform of driving current I_INand I_LINthat the modulator and the illumination driver ofFIG. 5 provide respectively;
• FIG. 7 exemplifies another light apparatus;
• FIG. 8 demonstrates a cross section view ofLED cells8c(3,1) and8c(3,2) inFIG. 7, cutting along the dotted line BB′; and
• FIGS. 9-12 exemplify four light apparatuses.
DETAILED DESCRIPTION
• 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.
• 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.
• 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.
• FIG. 1 illustratesbroadcast system10 withlight apparatuses12aand12baccording to one embodiment of the invention.Light apparatuses12aand12bare powered by AC grid power lines and optionally receive digital data over AC grid power lines by way of power line communication. Each oflight apparatuses12aand12bhas an LED module with at least one LED chip. By modulating the light emitted from the LED chips, each oflight apparatuses12aand12btransmits the digital data over the air toreceiver14aor14b. The modulation should be over a signal carrier with an adequately-high frequency and be imperceptible by a human eye.
• Subject to other factors, the data transmission rate from the AC power lines toreceiver14aor14bis limited by the signal bandwidth that the LED chips inlight apparatuses12aand12bcan support. Input capacitance of each LED chip inlight apparatuses12aand12bcould 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.
• FIG. 2 exemplifieslight apparatus12a. As shown inFIG. 2,light apparatus12ahasmodem16 andLED module19aincludingLED chips8a.Modem16, powered by AC grid power lines, is the combination of a demodulator which retrieves data carried from AC grid power lines, and amodulator17 which provides and modulates driving current I_INtoLED module19ato transmit data over the emitted light.Modulator17 might include a converter converting an AC source current to driving current I_IN. The light emitted from theLED chips8ais 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 ofFIG. 2,LED module19ahas twoLED chips8aconnected in series. For another embodiment, an LED module might have only one LED chip.
• As an example,LED chip8ahasLED cells8a(1,1)˜8a(3,3), arranged as an LED array with3 columns and3 rows. Label WW (N, M) refers to the LED cell located at N^thcolumn and M^throw of LED chip WW.LED cells8a(1,1)˜8a(3,3) are connected in series as an LED chain having two conductive pads IN+ and IN−, which are located at two diagonal corners ofLED cells8a(1,1) and8a(3,3), respectively. The physical orientation for each LED cell in 1^stand 3^rdcolumn is opposite to that of each LED cell in 2^ndcolumn. 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 cells8a(1,1)˜8a(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 ofLED chip8ais the summation of the operation voltages of individual LED cells,LED chip8ais 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.
• 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 K1 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 K1*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 K1 identical LED cells as a whole will be F/K1 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 ofFIG. 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.
• 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 chiip.
• FIG. 3 shows the waveform of driving current I_INthatmodem16 could provide toLED module19aofFIG. 2. Driving current I_INsubstantially 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, forcingLED module19ato stop emitting. The high current level (of logic 1) drivesLED module19ato 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 thatLED module19ais 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.
• As an example,FIG. 4 demonstrates a cross section view ofLED cells8a(1,1) and8a(1,2), cutting along the dotted line AA′ inFIG. 2. A similar drawing has been published inFIG. 2 of US Patent Application Publication 2010/0213474, whose entirety is incorporated by reference. As shown inFIG. 4,LED cells8a(1,1) and8a(1,2) are grown on amonolithic substrate60, each having, from bottom to top, n-type contact layer62, n-type cladding layer64,active layer66, p-type cladding layer68, and p-type contact layer70. A wavelength conversion layer72 is optionally formed oncontact layer70 to convert the light emitting from the active layer. Twoelectrodes76 and74 are optionally formed (may be omitted) on n-type contact layer62 and p-type contact layer70, respectively.LED cells8a(1,1) and8a(1,2) are physically separated on monolithic substrate by a trench betweenLED cells8a(1,1) and8a(1,2). Anelectric circuit layer78 provides electric connection between the n-type contact layer62 of8a(1,1) and the p-type contact layer70 of the adjacent LED cell, such as8a(1,2) to forma series connection. Aninsulator layer80 is formed under portion ofelectric circuit layer78 to prevent unwanted short circuits. In one embodiment, each ofLED cells8a(1,1) to8a(3,3) occupies a cell area on themonolithic substrate60 no more than 121 mil². Themonolithic substrate60 has a surface area, for example between 1.21*10²to 1*10⁵mil².
• Two conductive pads IN−, IN+ are provided for electric connection between theLED chip8aand an electric circuit outside the chip through external wires. The two conductive pads IN−, IN+ are respectively formed on themonolithic substrate60 outside the array area forLED cells8a(1,1)˜8a(1,3), and preferably at different corners or borders of theLED chip8a. The conductive pads IN−, IN+ are electrically coupled to theLED cells8a(1,1)˜8a(1,3) via theelectric circuit layer78 as inFIG. 4.
• AsLED cells8a(1,1)˜8a(3,3) are epitaxial grown onmonolithic substrate60 using MOCVD process and other semiconductor process, such as sputtering, lithography, and etching process, the compositions of theactive layers66 therein are substantially the same to emit lights with the same or similar wavelength spectrum. Nevertheless, wavelength conversion layers72 may be different or absent for some LED cells. For example, in one embodiment, allLED cells8a(1,1)˜8a(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 ofLED cells8a(1,1)˜8a(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 ofLED cells8a(1,1)˜8a(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.
• FIG. 5 exemplifieslight apparatus12b.LED module19bis controlled bycontroller11 to provide both illumination and data transmission. Similar withLED chip8aofFIG. 2,LED chip8binLED module19bhas LEDcells8b(1,1)˜8b(3,3), arranged as an LED array on a monolithic substrate.LED chip8bis slightly different withLED chip8a. WhileLED chip8aofFIG. 2 has only one LED chain with one pair of conductive pads IN+ and IN− as inputs,LED chip8bofFIG. 5 has two LEDchains22 and24. The number of LED cells in one LED chain is not restricted and one LED chain might include only one LED cell as exemplified byLED chain24, or more than one LED cell.LED chain22 has a pair of conductive pads LIN+ and IN+/LIN− whileLED chain24 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) ofLED chains24 and the cathode (or the p-type contact layer) ofLED chain22. Conductive pads LIN+, IN−, and IN+/LIN− are provided for electric connection between theLED chip8aand an electric circuit outside the chip through external wires. The conductive pads LIN+, IN−, and IN+/LIN− are respectively formed on themonolithic substrate60 outside the area of the LED cells ofLED chip8b, and preferred at different corners or borders of theLED chip8bas shown inFIG. 5. The conductive pads LIN+, IN−, and IN+/LIN− are electrically coupled to the LED cells via theelectric circuit layer78 as inFIG. 4. For example, pad IN+/LIN− is connected viaelectric circuit layer78 to both a p-type contact layer ofLED chain24 and a n-type contact layer ofLED chain22. The pair of conductive pads LIN+and IN+/LIN− is connected toillumination driver13 ofcontroller11 and the pair of conductive pads IN+/LIN− and IN− is connected to modulator17 ofcontroller11.FIG. 6 shows the waveform of driving current I_INand I_LINrespectively provided bymodulator17 andillumination driver13 ofFIG. 5. The operation ofmodulator17 is not detailed here for brevity since it has been done in the paragraphs regarding withFIGS. 2 and 3. It is comprehensive thatLED chain24 driven bymodulator17 transmits data via the light it emits.Illumination driver13 ofFIG. 5 provides driving current I_LINtoLED chain22. Driving current I_LINis almost a constant and conveys no data as shown inFIG. 6, such thatLED chain22 only acts as a lighting source for illumination. Accordingly,LED chip8bhas two LEDchains22 and24 whereLED chain22 is only for illumination andLED chain24 is for data transmission. In one embodiment,LED chip8bis formed on a monolithic substrate, each ofLED cells8b(1,1) to8b(3,3) occupies a cell area on a monolithic substrate no more than 121 mil², and the number of LED cells inLED chain24 is smaller than that inLED chain22. In another embodiment, the area of one of the LED cell(s) inLED chain24 for data transmission is smaller than that inLED chain22 for illumination. In one embodiment, the area of one of the LED cell (s) for data transmission is preferred no more than 121 mil², and the area of one of the LED cells for illumination is preferred no more than 400 mil².
• In one embodiment,LED chains22 and24 emit light of different colors. For example, LED cells inchain22 comprises white LED cells andLED cell8b(3,3) inchain24 is a blue LED cell.
• FIG. 7 exemplifieslight apparatus12c. Similar withLED chip8bofFIG. 5,LED chip8cofFIG. 7 has two LEDchains26 and28.LED chain26 is only for illumination, driven via a pair of conductive pads LIN+ and LIN−/IN− byillumination driver13.LED chain28 is for data transmission, driven via a pair of conductive pads IN+ and LIN−/IN− bymodulator17. The conductive pad LIN−/IN− is electrically connected to both two n-type contact layers ofLED chains26 and28. In one embodiment,LED chip8cis formed on a monolithic substrate.FIG. 8 demonstrates a cross section view ofLED cells8c(3,1) and8c(3,2) inFIG. 7, cutting along the dotted line BB′. As shown inFIG. 8, even though they are located in the same column,LED cell8c(3,1), which belongs toLED chain26, has a cell orientation opposite toLED cell8c(3,2), which belongs toLED chain28.
• 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 exemplifylight apparatuses12dand12e. InFIG. 9,LED chip8dhas LEDchain30 only for illumination andLED chain32 for data transmission. Conductive pads LIN+ and LIN− forLED chain30 are independent to conductive pads IN+ and IN− forLED chain32, whileLED cell8d(3,1) has the same cell orientation withLED cell8d(3,2).LED chains30 and32 are electrically insulated on the monolithic substrate. InFIG. 10,LED chip8ehas LEDchain34 only for illumination andLED chain36 for data transmission, whileLED cell8e(3,1) has a cell orientation opposite toLED cell8e(3,2).
• FIG. 11 exemplifieslight apparatus12f. It is unnecessary that LED cells in an LED module are all monolithically formed as an array on a monolithic substrate. InFIG. 11,LED module19fhas individual LED chips8f1 to8fn, where n is an integer. LED chips8f1 to8fn 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 chips8f1 to8fn are all white LED chips. In another embodiment, LED chips8f1 to8fn consist of red, green and blue LED chips.LED module19fhas two conductive terminals TIN+ and TIN−, through whichmodulator17 provides driving current I_INto LED cells8f1 to8fn to transmit data.
• FIG. 12 exemplifieslight apparatus12g. Similar withFIG. 11,LED module19gofFIG. 12 has LED chips8g1 to8gn, where n is an integer. LED chips8g1 to8g5 are grouped and connected asLED chain38, driven byillumination driver13 and functioning only for illumination. LED chips8g6 to8gn are grouped and connected asLED chain40, driven bymodulator17 for data transmission. The light fromLED chain38 might be the same with or different to that fromLED chain40. LED chips8g1 to8g5 ofLED chain38 or LED chips8g6 to8gn ofLED chain40 comprise at least one selected from blue LED, green LED, red LED, and white LED chips. For example, LED chips8g1 to8g5 ofLED chain38 consist of green and red LED chips and LED chips8g6 to8gn consist of only blue LED chips. In one embodiment,LED chain38 provides visible light, andLED chain40 provides invisible light. In view of noise immunity, it is preferable that the wavelength spectrum of the light fromLED chain40 has a peak that is not affected by the intensity of the light fromLED chain38.
• 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.
• 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.

Claims (20)

1. A lighting apparatus capable of simultaneously providing illumination and data transmission to a receiver, comprising:

an LED module capable of emitting visible light, comprising a plurality of LED cells connected as an LED chain having two conductive pads;

a modulator providing driving current to the LED module to transmit data through the LED module.

2. The lighting apparatus ofclaim 1, wherein the LED cells are of the same color.

3. The lighting apparatus ofclaim 1, wherein a first group of the LED cells is capable of emitting a first color and a second group of the LED cells is capable of emitting a second color different from the first one.

4. The lighting apparatus ofclaim 1, wherein the LED module is a single chip, and the LED cells are arranged as an LED array on a monolithic substrate of the single chip.

5. The lighting apparatus ofclaim 1, wherein the LED cells are series connected.

6. The lighting apparatus ofclaim 1, wherein the number of the LED cells is around 3˜80.

7. The lighting apparatus ofclaim 1, wherein an area of one of the LED cells is not more than 121 mil².

8. The lighting apparatus ofclaim 1, wherein an area of the monolithic substrate is between 1.21*10²to 1*10⁵mil².

9. The lighting apparatus ofclaim 1, wherein the modulator is of a modem coupled to and powered by grid power lines and receives the data from the grid power lines.

10. An LED cell module, comprising:

a substrate;

LED cells monolithically formed on the substrate, wherein a first group of the LED cells is connected as a first LED chain, driven for illumination, and a second group of the LED cells is connected as a second LED chain for data transmission;

a first pair of conductive pads connected to the first LED chain and a second pair of conductive pads different from the first conductive pads, connected to the second LED chain.

11. The LED module ofclaim 10, wherein the first pair of conductive pads and the second pair of conductive pads share a common conductive pad.

12. The LED module ofclaim 11, wherein the common conductive pad is coupled connected to a first-type contact layer of the first LED chain, and to a second-type contact layer of the second LED chain, the first-type and the second-type contact layers comprises different conductivities selected from the group consisting of p-type and n-type.

13. The LED module ofclaim 11, wherein the common conductive pad is coupled to a first-type contact layer of the first LED chain and to a first-type contact layer of the second LED chain, and the first-type is p-type or n-type.

14. The LED module ofclaim 10, wherein one LED cell of the second LED chain occupies a cell area no more than 121 mil².

15. The LED module ofclaim 10, wherein at least one LED cell of the first LED chain is capable of emitting a first color, at least one LED cell of the second LED chain is capable of emitting a second color, and the first color is different from the second color.

16. The LED module ofclaim 10, wherein all LED cells of the first LED chain are capable of emitting a first color, all LED cells of the second LED chain are capable of emitting a second color, and the first color is different from the second color.

17. The LED module ofclaim 10, wherein the first LED chain comprises a first LED cell, the second LED chain comprises a second LED cell, and at least one of the first and the second LED cell comprises a wavelength conversion layer.

18. The LED module ofclaim 17, wherein at least one first LED cell of the first LED chain and at least one second LED cell of the second LED chain are located in a column of the LED array, and the orientation of the at least one first LED cell is different from that of the at least one second LED cell.

19. The LED module ofclaim 10, wherein the number of the LED cells in the second LED chain is smaller than that in the first LED chain.

20. The LED module ofclaim 10, wherein the substrate has an area between 1.21*10²to 1*10⁵mil².

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