WO2011118097A1 - 可視光通信用送信機及び可視光通信システム - Google Patents
可視光通信用送信機及び可視光通信システム Download PDFInfo
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- WO2011118097A1 WO2011118097A1 PCT/JP2010/072522 JP2010072522W WO2011118097A1 WO 2011118097 A1 WO2011118097 A1 WO 2011118097A1 JP 2010072522 W JP2010072522 W JP 2010072522W WO 2011118097 A1 WO2011118097 A1 WO 2011118097A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
- H04B10/114—Indoor or close-range type systems
- H04B10/116—Visible light communication
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
- H04B10/114—Indoor or close-range type systems
Definitions
- the present invention relates to a visible light communication transmitter and a visible light communication system that transmit signals using visible light.
- a white light emitting diode hereinafter referred to as “white LED” including light emission of a phosphor.
- the present invention relates to a visible light communication transmitter and a visible light communication system that are suitable for communication using a wireless communication device.
- White LEDs can be classified mainly into three types according to the light emission method as described in Non-Patent Document 1 below, for example.
- Blue light excitation type white LED It is configured by combining a blue LED and a phosphor that mainly emits yellow light.
- a YAG (yttrium / aluminum / garnet) phosphor is disposed around the blue LED and is housed in one package.
- the surrounding phosphor is excited by the blue light output from the blue LED arranged at the center, and light (mainly yellow) mainly having a complementary color relationship with blue is output from this phosphor.
- pseudo white light can be obtained.
- Advantages of such a blue-light-excited white LED include: a) high energy utilization efficiency and ease of obtaining high luminous intensity compared with other methods, and b) simple construction and low cost production. , Are mentioned.
- the disadvantage is that color rendering is poor. This color rendering property refers to the characteristic of the appearance of the color of an object by illumination, and the closer the color is to natural light, the better the color rendering property.
- An ultraviolet LED is combined with a plurality of phosphors that emit light of three primary colors of R, G, and B (red, green, and blue).
- a phosphor that emits three primary colors of R, G, and B is arranged around an ultraviolet LED, and is housed in one package.
- surrounding phosphors are excited by ultraviolet light output from an ultraviolet LED arranged at the center, and light of three primary colors of R, G, and B is output from these phosphors.
- White light can be obtained by mixing these R, G, and B lights.
- 3-color white LED This is a combination of three types of LEDs, R, G, and B. It has a structure in which three types of LEDs, a red LED, a green LED, and a blue LED, are housed in one package. In this method, white light can be obtained by causing each of the three primary colors to emit light simultaneously.
- the color rendering property is good as in the case of the ultraviolet light excitation type white LED.
- the disadvantage is that since three types of LEDs are mounted in one package, they are more expensive than other methods.
- a conventional optical communication device using a white LED is shown in FIG.
- the white LED 904 when transmission data is supplied to the drive unit 902 of the transmitter 900, a corresponding drive current is output to the white LED 904, and the white LED 904 emits light.
- the white LED 904 blinks using a modulation method such as OOK (On-Off Keying).
- the optical signal output from the white LED 904 is incident on the PD 912 of the receiver 910.
- This optical signal is converted into a current signal by the PD 912, and this current signal is converted into a voltage signal by a transimpedance amplifier (current-voltage conversion amplifier) 914.
- This voltage signal is binarized by a limiting amplifier 918 after desired equalization processing by an equalizer 916, and is output as received data.
- FIG. 13B shows an apparatus configuration in this case, and a blue color filter 922 is arranged on the light incident side of the PD 912 of the receiver 920.
- the blue color filter 922 removes light emitted from the phosphor having a slow response speed in the optical signal. As a result, only the light of the blue LED is incident on the PD 912, thereby enabling faster data transmission than the above configuration. However, even with this method, only a transmission speed of about several tens of Mbps can be obtained.
- the transmission speed is about several Mbps for the same reason as when the blue light excitation type white LED is used.
- the drive voltage of the LED becomes high, the design of the drive circuit becomes difficult.
- the white LED 904 when the above-described three-color light emitting type white LED is used as the white LED 904, there is no phosphor light emitting component as compared with the above method, and wavelength multiplexing is performed such that each LED carries a different signal. Since data transmission is also possible, the speed can be increased (see Patent Document 2 below). However, since several LED is used, cost will become high.
- the transmitter 930 includes a peaking circuit 932.
- the transmitter 930 includes a peaking circuit 932.
- the present invention pays attention to the above points, and an object thereof is to perform visible light data communication with a sufficient transmission speed while using a blue light excitation type white LED and preventing element destruction. Another object is to perform visible light data communication at a sufficient transmission rate without using a blue color filter on the receiving side.
- a transmitter for visible light communication drives a blue light excitation type white LED based on a drive current signal generated based on transmission data, and transmits a visible light signal to a receiver.
- a transmitter for visible light communication that outputs a rising pulse at the rising edge of the transmission data and adds a falling pulse at the falling edge of the transmission data to generate a multi-tone driving current signal
- a multi-gradation drive unit, wherein the rising pulse and the falling pulse have the same pulse width as the unit interval of the transmission data.
- the drive current value corresponding to the transmission data when no color filter is provided on the receiving side, is 4/5 of the current value of the rising pulse and the falling pulse. It is as follows. According to one aspect of the present invention, the ratio of the falling pulse current value to the rising pulse current value is 1.0 ⁇ 0.2. According to another aspect of the present invention, when a color filter is provided in the receiver, the value of the drive current corresponding to the transmission data is set to 5 with respect to the current values of the rising pulse and the falling pulse. It is characterized as follows.
- One aspect of the visible light communication system of the present invention receives a multi-tone optical signal output from any of the visible light communication transmitters according to an embodiment of the present invention and converts it into an electrical signal, A visible light communication receiver that outputs received data is provided.
- a modulation encoder is provided in a transmitter and a modulation decoder is provided in a receiver, and 8B10B is used as a modulation code to be used.
- One aspect of the visible light communication system of the present invention is provided with a modulation encoder in a transmitter and a modulation decoder in a receiver.
- the modulation code to be used is DC-free and has a coding rate of 2/3 and a minimum run.
- NRZI-modulated data is transmitted and received using an RLL code in which 1 is set.
- the white LED is driven by the multi-tone driving current signal to which the pulse is added at the rising edge and the falling edge of the transmission data, the element destruction is prevented without using the blue color filter.
- the pulse width of the rising pulse and the falling pulse is made equal to the unit interval of the transmission data, the data clock can be used as it is as a clock necessary for generating the multi-grayscale driving signal, and a separately multiplied clock is generated. High-speed transmission can be achieved without adding necessary circuits
- FIG. 1A shows a circuit configuration of the first embodiment.
- transmission data to be transmitted is input to the drive waveform generation unit 110 of the transmitter 100.
- the output side of the drive waveform generator 110 is connected to the blue light excitation type white LED 140 via the multi-tone driver 120.
- the blue light excitation type white LED 140 for example, a blue LED having a peak wavelength range of 440 to 470 nm as shown in FIG. 2 can be used.
- the receiving side is configured in the same manner as the background art described above.
- the optical signal output from the transmitter 100 is incident on the PD 210 of the receiver 200 configured by a general-purpose Si PIN photodiode or the like.
- the electric signal output side of the PD 210 is connected to the input side of a limiting amplifier 216 that performs binarization processing via a transimpedance amplifier 212 that converts a current signal into a voltage signal and an equalizer 214 that performs equalization processing.
- Reception data is output from the output side of the limiting amplifier 216.
- a baseband OOK On-Off-Keying
- a transmission method modulation method
- a transmission rate is 50 to 125 Mbps.
- a circuit including the drive waveform generation unit 110 and the multi-gradation drive unit 120 of the transmitter 100 is used to obtain the transmission data signal shown in FIG.
- the drive current waveform shown in FIG. That is, the signals shown in (C) to (F) of the figure are combined to obtain the drive current having the waveform shown in (B) of the figure.
- FIG. 4G shows clock pulses.
- the drive waveform generation unit 110 is configured by, for example, a digital circuit (not shown) including a PLL that generates a clock synchronized with a transmission data pulse, a rising and falling edge pulse detector, and a D flip-flop.
- it has a function of generating multi-value (four values in this case) gradation waveforms shown in FIGS.
- a data clock may be supplied from the outside like the drive waveform generation unit 130 shown in FIG.
- the multi-tone drive unit 120 is configured by an OR circuit, and synthesizes the signals of FIGS. 3C to 3F output from the drive waveform generation unit 110 (or the drive waveform generation unit 130).
- a function of outputting a drive current having a waveform shown in (B) is provided.
- FIG. 4 shows an example of the main parts of the drive waveform generation unit 110 and the multi-gradation drive unit 120.
- this main part includes gradation waveform generation circuits 112A to 112D using OP amplifiers, transistors, switches, and resistors, and gradation signals SA to SD shown in FIGS. 3 (C) to (F).
- gradation signals SA to SD shown in FIGS. 3 (C) to (F).
- the pulse heights HA to HD of the gradation signal are set by the voltages VHA to VHD of the plus inputs Vin1 to Vin4 of the OP amplifier.
- the rising and falling timings are set by control signals KWA to KWD applied to the control terminals EN1 to EN4 of the switch.
- the control signal KWA rises at the rising timing of the transmission data in FIG. 3A and falls after a lapse of a certain time corresponding to the pulse width WA. Therefore, the switch is turned on during that period, and the voltage VHA is output as the gradation signal SA.
- multi-gradation signals SB to SD are output from the other gradation waveform generation circuits 112B to 112D, respectively.
- the control signals KWA to KWD can be considered as 4-bit digital signals determined from the logical value of the transmission data.
- the control signal “KWA, KWB, KWC, KWD” is “1, 1, 1, 1” at the timing when the transmission data changes from the logical value L to H (rise timing), and the gradation signal SA from the rise timing. “0, 1, 1, 1” after the elapse of the time corresponding to the pulse width WA of “0, 1, 1, 1”, “0, 0, 0, 1” It becomes “0, 0, 1, 1” after elapse of time corresponding to the pulse width WC of the gradation signal SC from the falling timing.
- the gradation signals SA to SD output from the gradation waveform generation circuits 112A to 112D are added by a wired OR circuit, and the added signal is supplied to the blue light excitation type white LED 140 via the current mirror circuit 114. .
- the pulse width WA of the rising pulse SA generated at the same timing when the transmission data rises has the same pulse width as the unit interval of the transmission data.
- the pulse width WC of the gradation signal SC generated at the same timing when the transmission data falls is the same pulse width as the unit interval of the transmission data.
- the pulse width WB of the data pulse SB is the same as the transmission data.
- the current value HD of the pre-bias current SD is constant regardless of transmission data.
- the sum HA + HB + HC + HD of each pulse is limited by the condition of the rated current value of the LED to be driven or the upper limit of the drive current value of the drive circuit.
- the height HB of the data pulse SB is HB / HA ⁇ 4 / with respect to the height HA of the rising pulse SA and the height HC of the falling pulse SC. 5, HB / HC ⁇ 4/5.
- the multi-gradation driving unit 120 is a circuit capable of current driving on the order of nsec, and can output a bias voltage larger than a forward bias voltage (about 3.6 V) necessary for driving the blue excitation type white LED 140. Composed.
- the blue light excitation type white LED 140 for example, a general-purpose white LED having a rated current of 500 mA (during pulse driving) is used. This white LED is driven under the drive current setting conditions shown in Table 1 below.
- the white LED is driven according to the following conditions.
- Current value of rising pulse SA 82.2 mA
- Current value of data pulse SB 13.9 mA
- Current value of falling pulse SC 88.3 mA
- Pre-bias current value 5.2 mA
- the transmission data shown in FIG. 3A is input to the drive waveform generation unit 110 of the transmitter 100.
- the drive waveform generation unit 110 and the multi-tone drive unit 120 Based on the input transmission data, the drive waveform generation unit 110 and the multi-tone drive unit 120 generate a multi-tone drive signal shown in FIG.
- the generated multi-tone drive signal is supplied to the blue excitation white LED 140, and the blue excitation white LED 140 is driven by the multi-tone drive signal to emit light.
- the optical signal output from the blue excitation type white LED 140 is collected by a lens or the like (not shown) and enters the PD 210 of the receiver 200.
- the incident optical signal is converted into a current signal by the PD 210. This current signal is converted into a voltage signal by the transimpedance amplifier 212.
- the equalizer 214 performs a desired equalization process on the converted voltage signal.
- the equalized voltage signal is binarized by the limiting amplifier 216, and output data is obtained.
- the reception band for the modulated light of the receiver has a sufficient band for the transmission signal, and a receiver having a flat frequency characteristic within the band necessary for reception is used.
- the present inventors conducted data transmission / reception experiments using a visible light communication system prototyped for this example.
- the bit rate was measured under the drive setting conditions shown in Table 1 with four transmission speeds of 50 Mbps, 75 Mbps, 100 Mbps, and 125 Mbps.
- the transmission data was PRBS2 7 ⁇ 1 and the number of transmission data was 10 10 bits.
- the measurement results are shown in Table 2 below.
- At least the ratio of the data pulse current value HB to the rising pulse current value HA (HB / HA) and the ratio of the data pulse current value HB to the falling pulse current value HC (HB / HC) should be 4/5 or less.
- transmission at 50 Mbps can be performed satisfactorily.
- the ratio of the data pulse current value HB to the rising pulse current value HA (HB / HA) and the rising value are different even when the data transmission is 75 Mbps or more, although the optimum value of the driving condition itself is different.
- the ratio of the data pulse current value HB to the falling pulse current value HC (HB / HC) needs to be 4/5 or less.
- the ratio of the falling pulse current value HC to the rising pulse current value HA is preferably set to 1.0 ⁇ 0.2.
- FIG. 5 shows the result of observing an eye pattern during 50 Mbps transmission under the driving conditions of “Setting 7” and “Setting 11”.
- a good eye pattern is obtained under the error-free “Setting 7” driving condition (see FIG. 7A), but the bit error rate deteriorates to 8.0 ⁇ 10 ⁇ 3.
- FIG. 5B It was observed that intersymbol interference occurred under the driving condition of “Setting 11” (see FIG. 5B). Thus, it can be seen that intersymbol interference is a cause of deterioration of the bit error rate.
- the second embodiment differs from the first embodiment described above in that a color filter is added and the LED drive current condition.
- FIG. 6 shows a circuit configuration of the second embodiment.
- the configuration on the transmission side is the same as that of the first embodiment including the white LED, but the driving conditions of the LED are different.
- the color filter 208 having the transmittance characteristics shown in FIG. 7 is provided on the receiving side before the PD 210 in the first embodiment.
- the optical signal output from the transmitter 100 is incident on the PD 210 after most of the light emitted from the phosphor is filtered by the color filter 208.
- the processing after the transimpedance amplifier 212 is the same as in the first embodiment.
- the transmission method (modulation method) in this embodiment is “OOK” similar to that in the first embodiment, and the transmission speed is 50 to 125 Mbps.
- the gradation signals generated by the drive waveform generator 110 and the multi-gradation driver 120 are the same as those in the first embodiment in both the number of gradations and the pulse width, but in this embodiment, 50 Mbps or more.
- the height HB of the data pulse SB is set to HB / HA ⁇ 5 and HB / HC ⁇ 5 with respect to the height HA of the rising pulse SA and the height HC of the falling pulse SC. Has been. By setting in this way, intersymbol interference can be suppressed and the bit error rate can be lowered.
- blue light excitation type white LED 140 for example, a general-purpose white LED having a rated current of 500 mA (during pulse driving) is used. This is driven under the drive current setting conditions shown in Table 3 below.
- the white LED is driven according to the following conditions.
- Current value of rising pulse SA 45.6 mA
- Current value of data pulse SB 42.7 mA
- Falling pulse SC current value 67.0 mA
- Pre-bias current value 5.2 mA
- transmission data as shown in FIG. 3A is input to the drive waveform generation unit 110 of the transmitter 100.
- the drive waveform generation unit 110 and the multi-tone drive unit 120 Based on the input transmission data, the drive waveform generation unit 110 and the multi-tone drive unit 120 generate a multi-tone drive signal shown in FIG.
- the generated multi-tone drive signal is supplied to the blue excitation white LED 140, and the blue excitation white LED 140 is driven by the multi-tone drive signal to emit light.
- the optical signal output from the blue excitation type white LED 140 enters the color filter 208 of the receiver 200.
- the reception band for the modulated light of the receiver has a sufficient band for the transmission signal, and a receiver having a flat frequency characteristic within the band necessary for reception is used.
- the present inventors conducted data transmission / reception experiments using a visible light communication system prototyped for this example.
- the transmission speed was set to four types of 50 Mbps, 75 Mbps, 100 Mbps, and 125 Mbps, and the bit error rate was measured under each drive setting condition shown in Table 3 above.
- the transmission data was PRBS2 7 ⁇ 1 and the number of transmission data was 10 10 bits. The measurement results are shown in Table 4 below.
- the transmission speed When the transmission speed is set to 50 Mbps, it is error free under the conditions from “Setting 2” to “Setting 11”, and it is recognized that data can be transmitted without any problem.
- the ratio HB / HA of the data pulse current value HB to the rising pulse current value HA is 5.27
- the ratio HB / HC of the data pulse current value HB to the falling pulse current value HC is 4.21.
- the respective ratios are values of 5 or less.
- the ratio HB / HA of the data pulse current value HB to the rising pulse current value HA and the ratio HB / HC of the data pulse current value HB to the falling pulse current value HC are 5 or less, transmission of 50 Mbps is possible. It can be done well.
- the ratio of the data pulse current value HB to the rising pulse current value HA and the falling pulse current HB / HA and the optimum value of the driving condition itself are different even at the time of data transmission of 75 Mbps or more.
- the ratio HB / HC of the data pulse current value HB to the value HC needs to be 5 or less.
- FIG. 8 shows the result of observing the eye pattern during 50 Mbps transmission under the driving conditions of “Setting 8” and “Setting 12”.
- the bit error rate deteriorates to 6.3 ⁇ 10 ⁇ 7.
- intersymbol interference occurred as shown in FIG.
- FIG. 8 shows the result of observing the eye pattern during 50 Mbps transmission under the driving conditions of “Setting 8” and “Setting 12”.
- a modulation encoder and a decoder are added to the first and second embodiments, respectively.
- FIG. 9 shows a circuit configuration of the third embodiment.
- the modulation encoder 108 and the decoder 218 are added to the circuit configuration of the first embodiment shown in FIG.
- 8B10B for example, see Patent Document 4
- 17PP for example, see Patent Document 5
- the reasons for using these codes are 1) DC-free codes, so that clock recovery on the receiving side is easy, and unnecessary flickering that can cause problems when using visible light as a carrier is suppressed.
- the DC component can be removed on the receiving circuit, the influence of unmodulated disturbance light (sunlight) can be suppressed.
- 17PP is classified as a (1,7) RLL code (Run Length Limited code).
- the RLL code is “0” that falls between “1” and “1” in the code sequence before NRZI modulation when NRZI (NonReturn to Zero Inverted) modulation in which the transmission rectangular wave is inverted by bit 1 is assumed.
- the minimum number (minimum run) and / or maximum value (maximum run) of the number is limited.
- the RLL code is expressed as “(d, k) RLL” where d is the minimum run and k is the maximum run.
- the coding rate of 17PP (represented by m / n, where m is the data bit length before encoding and n is the data bit length after encoding) is 2/3.
- FIG. 10 shows an eye pattern of the output of the equalizer 214 when the data transmission rate is 100 Mbps and 8B10B and 17PP are used as modulation codes.
- the eye pattern of 8B10B in FIG. 9A is obtained using the driving condition of “Setting 4” in Table 1.
- FIG. 11 shows a circuit configuration of the fourth embodiment.
- the modulation encoder 108 and the decoder 218 are added to the circuit configuration of the second embodiment.
- FIG. 12 shows an eye pattern of the output of the equalizer 214 when the data transmission rate is 100 Mbps and 8B10B and 17PP are used as modulation codes.
- the eye pattern of 8B10B in FIG. 8A is obtained using the driving condition of “Setting 6” in Table 3.
- the eye pattern of 17PP in FIG. It was obtained using the following drive conditions. Regardless of which modulation code is used, a good eye pattern is obtained and error-free transmission is realized. Needless to say, the drive conditions as shown in the second embodiment are satisfied when the error is free.
- 17PP is used as an example of a modulation code to be used.
- a code other than 17PP may be used if it is DC-free and is a (1, x) RLL code.
- the same effect as the third and fourth embodiments can be expected. Therefore, the effect of the present invention is not limited to the case where 17PP is used as the modulation code.
- the pulse height can be adjusted digitally and easily, and an overcurrent exceeding the rated current of the white LED can be detected, such as a peaking circuit with an analog configuration. There is no fear that the element will be destroyed by flowing.
- the pulse widths WA and WC of the rising pulse SA and the falling pulse SC are set to the same width as the unit interval.
- the clock may be the same frequency as the transmission data clock.
- the transmitter for visible light communication is easy to mount and has an advantage in cost.
- the first embodiment and the third embodiment since no blue color filter is used on the receiving side, the number of parts can be reduced, which is advantageous in terms of cost.
- the third embodiment and the fourth embodiment by using a DC-free modulation code, a) Unnecessary flickering that may cause a problem when using visible light as a carrier can be suppressed. b) Since the DC component can be removed on the receiving circuit, the influence of unmodulated ambient light (sunlight) can be suppressed. (5) Since a general-purpose multi-tone drive LD driver IC used in an optical media system can be used, the system can be configured at low cost.
- this invention is not limited to the Example mentioned above, A various change can be added in the range which does not deviate from the summary of this invention.
- the following are also included.
- a blue light excitation type white LED 140 a type in which a phosphor excited by light of a blue LED emits yellow light having a complementary color relationship is common, but recently, in order to improve color rendering properties.
- an LED in which a light emitting component from a phosphor contains a red component or the like. Such an LED is also included in the “blue light excitation type white LED” of the present invention.
- the circuit configurations of the drive waveform generation unit 110 and the multi-gradation drive unit 120 shown in the above embodiment are merely examples, and various known circuit configurations that exhibit the same operation are possible.
- visible light data communication with a sufficient transmission speed can be performed using a blue light excitation type white LED, which is suitable for high-speed visible light communication.
- transmitter 108 modulation encoder 110: drive waveform generation units 112A to 112D: gradation waveform generation circuit 114: current mirror circuit 120: multi-gradation drive unit 130: drive waveform generation unit 140: blue light excitation type white LED 200: Receiver 208: Color filter 210: PD 212: Transimpedance amplifier 214: Equalizer 216: Limiting amplifier 218: Decoder 900: Transmitter 902: Drive unit 904: White LED 910: Receiver 912: PD 914: transimpedance amplifier 916: equalizer 918: limiting amplifier 920: receiver 922: blue color filter 930: transmitter 932: peaking circuit
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Abstract
Description
青色LEDと、主に黄色を発光する蛍光体を組み合わせて構成される。青色LEDの周囲にたとえばYAG(イットリウム・アルミニウム・ガーネット)系の蛍光体を配置し、一つのパッケージに納めた構造となっている。この方式では、中心に配置された青色LEDから出力された青色光によって周囲の蛍光体が励起され、この蛍光体から主に青色と補色関係のある光(主に黄色)が出力される。この蛍光体からの黄色蛍光と、前記青色LEDからの青色光とを混色することで、擬似的に白色光が得られる。
紫外LEDと、R,G,B(赤,緑,青)の3原色をそれぞれ発光する複数の蛍光体を組み合わせて構成される。紫外光LEDの周囲にR,G,Bの3原色を発光する蛍光体をそれぞれ配置し、一つのパッケージに納めた構造となっている。この方式では、中心に配置された紫外光LEDから出力された紫外光によって周囲の蛍光体が励起され、これらの蛍光体からR,G,Bの3原色の光がそれぞれ出力される。これらのR,G,Bの光を混色することで白色光が得られる。
R,G,Bの3種類のLEDを組み合わせたものである。赤色LED,緑色LED,青色LEDの3種類のLEDを一つのパッケージに収めた構造となっている。この方式は、3原色であるそれぞれのLEDを同時に発光させることで、白色光が得られる。
詳述すると、駆動波形生成部110は、例えば、送信データパルスに同期したクロックを生成するPLL,立ち上がり及び立下りのエッジパルス検出器,Dフリップフロップによるデジタル回路(図示せず)によって構成されており、図3(A)の送信データに基づいて、同図(C)~(F)に示す多値(ここでは4値)の階調波形を生成する機能を備えている。
(1)立ち上がりパルスSAの電流値:82.2mA
(2)データパルスSBの電流値:13.9mA
(3)立ち下がりパルスSCの電流値:88.3mA
(4)プリバイアス電流値:5.2mA
(1)立ち上がりパルスSAの電流値:45.6mA
(2)データパルスSBの電流値:42.7mA
(3)立ち下がりパルスSCの電流値:67.0mA
(4)プリバイアス電流値:5.2mA
(1) 白色LEDを多階調駆動するので、パルス高さなどをデジタル的に良好かつ簡便に調整することができ、アナログ構成によるピーキング回路のように白色LEDの定格電流を超えた過電流が流れて素子が破壊される恐れがない。
(2) 多階調駆動を行う場合、駆動パルス幅の最小分解能が小さいほど最適な波形が得られやすいが、その分、データクロックの(ユニットインターバル÷駆動最小パルス幅)倍のクロックが必要となる。これに対し、本発明の各実施例によれば、立ち上がりパルスSA及び立ち下がりパルスSCのパルス幅WA,WCをユニットインターバルと同じ幅にしているため、多階調駆動電流波形の生成に使用するクロックが送信データクロックと同じ周波数でよい。このため、本発明の様々な実施形態に係る可視光通信用送信機は、実装が容易で、コスト面で優位である。
(3) 第一の実施例と第三の実施例によれば、受信側で青色カラーフィルタを使用しないため、部品点数を減らすことができ、コスト面で優位である。
(4) 第三の実施例と第四の実施例によれば、DCフリーの変調符号を使用することにより、
a)キャリアに可視光を用いた際に問題となりうる不要なチラツキを抑制することができる。
b)受信回路上で直流成分を除去できるため、変調されていない外乱光(太陽光)などの影響を抑制することができる。
(5) 光メディアシステムに使用されている汎用の多階調駆動型LDドライバICを使用することができるため、システムを安価に構成することが可能となる。
(1) 青色光励起型白色LED140としては、青色LEDの光により励起された蛍光体が、補色関係にある黄色の光を発光するタイプが一般的であるが、最近では、演色性を改善するために、蛍光体からの発光成分に赤色成分その他を含んでいるLEDがある。このようなLEDも、本発明の「青色光励起型白色LED」に含まれる。
(2) 前記実施例で示した駆動波形生成部110及び多階調駆動部120の回路構成は一例であり、同様の作用を奏する公知の各種の回路構成が可能である。
108:変調符号器
110:駆動波形生成部
112A~112D:階調波形生成回路
114:カレントミラー回路
120:多階調駆動部
130:駆動波形生成部
140:青色光励起型白色LED
200:受信機
208:カラーフィルタ
210:PD
212:トランスインピーダンスアンプ
214:イコライザ
216:リミッティングアンプ
218:復号器
900:送信機
902:駆動部
904:白色LED
910:受信機
912:PD
914:トランスインピーダンスアンプ
916:イコライザ
918:リミッティングアンプ
920:受信機
922:青色カラーフィルタ
930:送信機
932:ピーキング回路
Claims (8)
- 送信データに基づいて生成された駆動電流信号に基づいて駆動される青色光励起型白色LEDからの可視光信号を受信機に対して出力する可視光通信用送信機であって、前記送信データの立ち上がり時に立ち上がりパルスを付加するとともに、前記送信データの立ち下がり時に立ち下がりパルスを付加して、多階調の駆動電流信号を生成する多階調駆動手段を備えており、前記立ち上がりパルス及び立ち下がりパルスのパルス幅を、前記送信データのユニットインターバルと等しくしたことを特徴とする可視光通信用送信機。
- 前記送信データに対応する駆動電流の値を、前記立ち上がりパルス及び立ち下がりパルスの電流の値に対して、4/5以下としたことを特徴とする請求項1記載の可視光通信用送信機。
- 前記立ち上がりパルス電流値に対する立ち下がりパルスの電流値の比率を、1.0±0.2としたことを特徴とする請求項2記載の可視光通信用送信機。
- 請求項1~3のいずれか一項に記載の可視光通信用送信機と、該可視光通信用送信機から出力された多階調の可視光信号を受光して電気信号に変換し、受信データを出力する可視光通信用受信機と、を備えたことを特徴とする可視光通信システム。
- 前記可視光通信用受信機において、カラーフィルタを介して可視光信号を受信するとともに、前記送信データに対応する駆動電流の値を、前記立ち上がりパルス及び立ち下がりパルスの電流の値に対して、5以下としたことを特徴とする請求項4記載の可視光通信システム。
- 変調符号器を前記可視光通信用送信機に設けるとともに、前記変調符号器で変調された変調符号を復号する変調復号器を前記可視光通信用受信機に設けたことを特徴とする請求項4又は5記載の可視光通信システム。
- 使用する変調符号として8B10Bを用いたことを特徴とする請求項6記載の可視光通信システム。
- 使用する変調符号として、DCフリーであり、かつ、符号化率2/3、最小ランを1としたRLL符号を用い、NRZI変調されたデータを送受信することを特徴とする請求項6記載の可視光通信システム。
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JP2011205223A (ja) | 2011-10-13 |
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