JP2009188813A - Optical receiver and visible light communication equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure superior transmission quality and a wide dynamic range when spatial optical transmission is performed by using a visible optical source, such as a blue photoexcitation type white LED. <P>SOLUTION: When distance between a transmitter and a receiver is short, a perimeter photoelectric conversion unit 12S receives light, which contains many optical yellow factors, from phosphor. The signal level of a signal level detector 22 comes to exceed a predetermined threshold, and a change-over switch 15 is switched to the side of an equalizer 16SY suitable characteristic for optical yellow factors. When the distance between the transmitter and the receiver is long, the perimeter photoelectric conversion unit 12S receives light, which contains optical blue factors, from LED. The signal level of a signal level detector 22 does not exceed the predetermined threshold, so the change-over switch 15 is switched to the side of an equalizer 16SB, which is suitable characteristic for optical blue factors. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a data transmission system that transmits a signal using visible light, and more particularly to an optical receiver and a visible light communication apparatus that are suitable when light having different response speeds such as light emission of a phosphor is included.

  In recent years, in addition to wireless communication using radio waves and infrared rays, attention has been focused on communication using visible light such as indoor lighting fixtures, outdoor advertising lighting, traffic lights, and automobile headlights. Recently, white LEDs (light-emitting diodes) have been actively developed, and they are widely used for lighting, in-vehicle lamps, liquid crystal backlights, and the like. This white LED has a feature that the on / off switching response speed is very fast as compared with a white light source such as a fluorescent lamp. Thus, a visible light communication system has been proposed in which white light from an LED is used as a data transmission medium, and illumination light from the white LED has a data transmission function (see Patent Document 1 below). In other words, data transmission is realized by modulating the emission intensity of the white LED according to the transmission data, and converting the intensity of the light into an electrical signal by a photoelectric converter such as a PD (Photo Diode) on the receiving side. To do.

  By the way, white LED can be mainly classified into three types according to the light emission method as described in Non-Patent Document 1, for example.

  (1) The blue light excitation type white LED is a combination of a blue LED and a phosphor that mainly emits yellow light. This is a structure in which a phosphor such as a YAG (yttrium, aluminum, garnet) system is arranged around a blue LED and is housed in one package. In this method, 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. A pseudo white light is obtained by mixing the yellow fluorescence by the phosphor and the blue light by the blue LED.

  The advantages of such blue light-excited white LEDs are: (a) high energy utilization efficiency compared to other methods, easy to obtain high illuminance, and (b) simple construction that can be manufactured at low cost. There are certain things. On the other hand, 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.

  FIG. 7A shows an example of a blue light excitation type white LED. As shown in the figure, the blue LED 900 is provided on the main surface of the resin case 902. A drive voltage application terminal (not shown) of the blue LED 900 is connected to the extraction electrodes 904 and 906, respectively. When a drive voltage is applied to the extraction electrodes 904 and 906, blue light is output from the blue LED 900, but a part of the blue light enters the yellow phosphor 908. As a result, the yellow phosphor 908 is excited and fluorescence is output. Some blue LEDs 900 have emission characteristics of various wavelengths. For example, those having a peak wavelength in the range of 440 to 470 nm are used. As the yellow phosphor 908, one that emits light having a wavelength longer than the peak wavelength of the blue LED 900 is used. The phosphor particles 908 are arranged in a radial and thick translucent resin so as not to block the light emitted by the blue LED 900. FIG. 7B shows a light emission spectrum (wavelength spectrum) characteristic of a general blue light excitation type white LED. A portion surrounded by a dotted line SA is a blue light portion by the LED, and a portion surrounded by a dotted line SB is a light emission portion by the phosphor. As described above, light emission by the phosphor exists on the longer wavelength side than the peak wavelength of light emission of the blue LED 900.

  (2) An ultraviolet light excitation type white LED is a combination of an ultraviolet LED and a phosphor that emits 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. In this method, 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 is obtained by mixing these R, G, and B lights.

  Some ultraviolet LEDs have emission characteristics of various wavelengths, but those having a peak wavelength in the range of 380 to 410 nm are used. A phosphor that emits light having a wavelength longer than the peak wavelength of the ultraviolet LED is used. A large number of phosphor particles emitting three primary colors of light are arranged in a radial and thick translucent resin so that the light emitted from the ultraviolet LED is sufficiently absorbed and excited.

  As an advantage of such an ultraviolet light excitation type white LED, the color rendering property described above is good. On the other hand, there are disadvantages: (a) low energy use efficiency compared to the blue light excitation type white LED, and high illuminance is difficult to obtain; (b) high LED driving voltage due to ultraviolet light emission. , Are mentioned.

  (3) The three-color light emitting white LED is a combination of R, G, and B LEDs. 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 simultaneously emitting light of the three primary colors. As an advantage of such a three-color light emitting type white LED, a color rendering property is good as in the case of the ultraviolet light excitation type white LED. On the other hand, there are disadvantages: (a) Three types of LEDs are mounted in one package, which is expensive compared to other methods, and (b) Different LEDs are driven independently. Therefore, the drive circuit becomes complicated.

  The most popular white LED currently on the market is the blue light-excited white LED (1) described above. If a circuit or the like is configured using the blue light-excited white LED, the cost is reduced. This is advantageous and advantageous.

  FIG. 8A shows one mode of a data transmission system using the white LED as described above. The example in the figure is a peer-to-peer data transmission mode in which transceivers are arranged to face each other in one-to-one, and assumes a case where there is one white LED as a transmission source, that is, a single light source. In the figure, data terminals 920A and 920B such as notebook computers are connected to transceivers 922A and 922B, respectively. The transceivers 922A and 922B include transmitters 930A and 930B and receivers 940A and 940B, respectively. The light output from the transmitter 930A is received by the receiver 940B, and the light output from the transmitter 930B is received by the receiver 940A.

  FIG. 8B shows an example of the transmitters 930A and 930B. Data to be transmitted is input to the modulator 932 and subjected to predetermined modulation processing, and the modulation signal is converted into a blue light excitation type white LED 934. To be supplied. Thereby, the output light of the blue light excitation type white LED 934 is modulated by a modulation method such as OOK (On-Off Keying), and blinks. FIG. 8C illustrates an example of the receivers 940A and 940B. The received optical signal is converted into an electric signal (current) by the photoelectric converter 942. The converted electric signal is converted into a voltage signal and amplified by an amplifier 944. The amplified signal is corrected by the equalizer 946 for the frequency dependence of the transfer function of the previous system, and a band sufficient for transmission is secured. When the modulation method is OOK, processing for emphasizing and compensating mainly for the high frequency is performed. After the equalization processing by the equalizer 946, the identification reproduction circuit (demodulator) 948 performs identification reproduction processing. That is, the logical value 0/1 is determined for the equalizer output, and the transmission source data is reproduced.

  By the way, the blue light excitation type white LED generally has concentric color unevenness composed of blue and yellow in the radiation pattern (see Non-Patent Document 1 below). FIG. 9 (A) shows this state, and the light output from the blue light-excited white LEDs 934 of the transmitters 930A and 930B spreads radially as the distance increases. As shown in (B) and (C), respectively. This is because the emission pattern of the blue LED 900 and the emission pattern of the yellow phosphor 908 are different. In a commercially available blue light-excited white LED, the blue color is strong near the center and the yellow color is strong at the periphery. Often distributed. Therefore, the light indicated by the dotted lines in FIGS. 7B and 7C is incident on the light receiving surfaces of the photoelectric converters 942 of the receivers 940A and 940B. As shown in (D) and (E), the light color distribution varies depending on the light receiving position. More specifically, at the position PA where the distance between the transmitter and the receiver is relatively short, the center of the light receiving surface is blue and yellow is distributed around it, and contains a relatively large amount of yellow components that are emitted from the yellow phosphor 908. On the other hand, at the position PB where the distance between the transmitter and the receiver is relatively long, the entire light receiving surface has a substantially blue distribution, and contains a large amount of blue component that is the amount of light emitted from the blue LED 900. It should be noted that the distance at which such a relationship is obtained differs depending on the radiation angle and the distribution of color unevenness, and thus cannot be generally described.

  On the other hand, although depending on the driving method, the light emission by the blue LED (blue component) in the output light of the blue light excitation type white LED has a frequency response of about several tens of MHz, whereas the light emission by the phosphor (mainly Yellow) is at most several MHz, and it is known that the response time of the phosphor light is slower than that of the LED light (see Non-Patent Document 2 below). Thus, the light output from the blue light excitation type white LED is a combination of light having different time response characteristics, and the light distribution of the light source has the color unevenness as described above. For this reason, the time response characteristic of the received signal waveform may differ depending on the light receiving position, and the signal waveform on the receiving side changes depending on the distance between transmission and reception. Specifically, when the distance between transmission and reception is short, light containing a large amount of light emitted from a phosphor with a slow response speed is received, so the response speed of the output waveform is slow. On the contrary, when the distance between transmission and reception is long, light containing a large amount of light emitted from the LED having a high response speed is received, so that the response speed of the output waveform is increased.

  FIG. 10 shows an example of the signal waveform as described above. FIG. 4A shows the original signal waveform input to the white LED. On the other hand, the blue LED outputs light having a waveform indicated by a solid line in FIG. 5B, and the phosphor outputs light having a waveform indicated by a broken line in FIG. On the other hand, the received light waveform when the distance between transmission and reception is relatively long is as shown in FIG. 10C, whereas the received light waveform when the distance between transmission and reception is relatively close is as shown in FIG. . Comparing the two, it can be seen that the waveform (D), which is affected by the light from the phosphor, is duller and the response speed is slower than the case (C).

  As shown in FIG. 8, in a general receiver configuration, there are many cases where an equalizer exists, but when the phenomenon shown in FIG. 10 occurs, an appropriate equalizer condition depends on the distance between transmission and reception. It will be different. That is, even if appropriate equalization can be performed at a certain distance between transmission and reception, proper equalization cannot be performed at other distances between transmission and reception, for example, signal reception quality represented by a bit error rate is The possibility of getting worse comes out.

  In general, not only when a white LED is used, but when spatial light transmission is performed in a combination of a diffused light source such as an LED and a light receiving element such as a PD, the amount of light received by the light receiving element is the square of the distance. It is inversely proportional (see, for example, Non-Patent Document 3 to Non-Patent Document 4 below). For this reason, in order to secure a certain transmission distance range, a large dynamic range is required on the receiver side.

  Furthermore, when the transmitter side and the receiver side are close to each other and the amount of light incident on the light receiving element is large, the space charge effect (see Non-Patent Document 5 below) causes the FIG. ), A wave tail occurs at the falling edge of the received pulse waveform, which may cause intersymbol interference and prevent good transmission quality from being ensured.

As described above, when using a blue light excitation type white LED,
a, fluctuation of equalization condition due to change in light distribution of blue LED and phosphor depending on receiver position,
b, variation in the amount of received light depending on the distance between transmission and reception,
c, space charge effect when the distance between transmission and reception is short,
May affect the signal quality.
Japanese Patent No. 3465017 CMC Publishing, “Application and Future Prospect of White LED Lighting System Technology” IEICE Technical Report ICD2005-44, Vol.105, No.184, 25-30p, "Prototype LED Driver for Visible Light Communication and Evaluation of Response Performance of Visible Light LED" Wednesday Company, “Spatial Transmission Optics”, Chapter 6 2005 IEICE, Communications Society Conference, "Optical analysis of reception characteristics of parallel optical space transmission system" Optical books, "Optical communication device engineering", Chapter 6

  The present invention focuses on the above points, and when performing spatial light transmission using a visible light source, an optical receiver capable of obtaining good transmission quality and ensuring a wide dynamic range, and An object is to provide a visible light communication device.

  In order to achieve the above object, an optical receiver of the present invention includes a light emitter that outputs light in a first wavelength region, and light in a second wavelength region that is excited by the light output therefrom and has a different response speed. An optical receiver for receiving an optical signal output from a light emitting means including a phosphor to output, a plurality of photoelectric conversion means arranged corresponding to the distribution of the optical signal output from the light emitting means, A plurality of units are provided selectively for at least one of the plurality of photoelectric conversion units, and the waveform of the electrical signal converted by the photoelectric conversion unit is equalized according to the response speed of the light receiving wavelength band. Switching means for switching the plurality of equalization means so as to correspond to the wavelength band of light incident on the photoelectric conversion means according to the distance between the optical transmitter provided with the light emitting means and the optical receiver, It is provided with.

  According to one of the main embodiments, the plurality of photoelectric conversion units receive a central photoelectric conversion unit that receives light at a central portion of the output light of the light emitting unit, and light around the central portion. A peripheral photoelectric conversion unit, and an equalization unit of the peripheral photoelectric conversion unit is switched by the switching unit.

  In another mode, the equalization means includes a first equalizer that performs waveform equalization corresponding to light of a light emitter that outputs light in the first wavelength range, and the second wavelength. And a second equalizer that performs waveform equalization corresponding to the light of the phosphor that outputs the light in the region.

  In still another embodiment, the switching means switches to the second equalizer when the transmitter and the receiver are close to each other, and when the transmitter and the receiver are far from each other, Switching to the first equalizer is characterized. Alternatively, the switching means is configured not to use the signal output of the central photoelectric conversion unit when the transmitter and the receiver are close to each other. Further, the switching means includes signal level detection means for detecting a signal level before identification reproduction in the optical receiver, signal waveform state detection means for detecting a signal waveform state before identification reproduction in the optical receiver, and the optical It is one of error detection means for detecting an error after identification reproduction in the receiver.

  Still another embodiment is characterized in that the light emitting means is a blue light excitation type white LED, and a light emitting body that outputs light in the first wavelength band is a blue LED.

  A visible light communication apparatus according to the present invention includes any one of the optical receivers described above and an optical transmitter including the light emitting means. The above and other objects, features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

  According to the present invention, the photoelectric conversion means of the optical receiver is constituted by a plurality of photoelectric conversion units, and the equalization processing for the converted signal is switched according to the distance between the optical transmitter and the optical receiver; Therefore, good transmission quality can be obtained. In addition, when the optical transmitter and the optical receiver enter in close proximity, the output of the photoelectric conversion unit is selected, so that a wide dynamic range can be ensured.

  Hereinafter, the best mode for carrying out the present invention will be described in detail based on examples.

  First, Embodiment 1 of the present invention will be described with reference to FIG. FIG. 1 shows a light receiving surface of a photoelectric converter 10 on the receiver side in this embodiment, and a central photoelectric conversion unit 12C having a circular light receiving surface located at the center and an annular light receiving surface surrounding the periphery thereof. The peripheral photoelectric conversion unit 12S having a surface is configured. Among these, the electrical signal output side of the central photoelectric conversion unit 12C is connected to the input side of the equalizer 16C via the amplifier 14C. On the other hand, the electrical signal output side of the peripheral photoelectric conversion unit 12S is connected to the input side of the changeover switch 15 via the amplifier 14S. The two switch output sides of the changeover switch 15 are connected to the input sides of the equalizers 16SB and 16SY. The output sides of the equalizers 16C, 16SB, and 16SY are connected to the addition input side of the adder 18, respectively. The addition output side of the adder 18 is connected to the input side of the identification reproduction circuit 20 and the signal level detector 22, respectively. The detection output side of the signal level detector 22 is connected to the control side of the changeover switch 15.

  Among the above units, the amplifiers 14C and 14S are for converting the current signals supplied from the photoelectric conversion units 12C and 12S into voltage signals and amplifying them. The changeover switch 15 is for distributing the output signal of the amplifier 14S to the equalizers 16SB and 16SY according to the detection result by the signal level detector 22. The equalizers 16 </ b> C and 16 </ b> SB have characteristics set so that appropriate equalization processing can be performed on a light signal including a large amount of light emitted from the blue LED in the output light of the blue light excitation type white LED. ing. On the other hand, the equalizer 16SY has a characteristic set so that an appropriate equalization process can be performed on a signal of light that includes a large amount of light emitted from the phosphor among the output light of the blue light excitation type white LED. ing. The signal level detector 22 has a function of detecting the magnitude of the amplitude level of the input signal and outputting the result as a control signal for switching, for example, RSSI (Received Signal Strength Indicator) using a log amplifier. And peak bottom detectors are used.

The changeover switch 15 performs the following changeover operation depending on whether the magnitude of the output signal level of the signal level detector 22 exceeds a predetermined threshold value set in advance.
a, If the predetermined threshold value is not exceeded, the amount of incident light is small, that is, the distance between transmission and reception is long, so switching to the equalizer 16SB side by the control signal of the signal level detector 22 is performed.
b. When the predetermined threshold value is exceeded, the amount of incident light is large, that is, the distance between transmission and reception is short, so that the signal is switched to the equalizer 16SY side by the control signal of the signal level detector 22.

  Next, the operation of the first embodiment configured as described above will be described. As described above, the radiation pattern of the light distribution of the blue light excitation type white LED 30 on the transmitter side is influenced by concentric blue and yellow color unevenness. First, as shown in FIG. 1 (B), when the distance between the transmitter and the receiver is short, the light distribution as shown in FIG. 9 (B) is obtained, and the peripheral photoelectric conversion unit 12S has yellow light from the phosphor. Receives light containing many components. The central photoelectric conversion unit 12C receives light containing a lot of blue light components from the LED. On the other hand, since the photoelectric conversion units 12C and 12S are close to the transmitter, the detection signal level of the signal level detector 22 exceeds a predetermined threshold. For this reason, the changeover switch 15 is switched to the equalizer 16SY side by the control signal of the signal level detector 22.

  Accordingly, the output of the central photoelectric conversion unit 12C having a large blue component is equalized by the equalizer 16C after being amplified by the amplifier 14C and supplied to the adder 18, and the output of the peripheral photoelectric conversion unit 12S having a large yellow component is After amplification by the amplifier 14S, the signal is equalized by the equalizer 16SY and supplied to the adder 18. The adder 18 adds these input signals, and the identification / reproduction circuit 20 performs data identification / reproduction processing based on the added signal.

  On the other hand, as shown in FIG. 1C, when the distance between the transmitter and the receiver is long, the light distribution as shown in FIG. 9C is obtained, and the peripheral photoelectric conversion unit 12S also has the central photoelectric conversion unit 12C. Similarly, light containing a large amount of blue light component from the LED is received. On the other hand, since the photoelectric conversion units 12C and 12S are far from the transmitter, the detection signal level of the signal level detector 22 does not exceed a predetermined threshold. For this reason, the changeover switch 15 is switched to the equalizer 16SB side by the control signal of the signal level detector 22.

  Therefore, the output of the central photoelectric conversion unit 12C having a large blue component is amplified by the amplifier 14C, equalized by the equalizer 16C, and supplied to the adder 18. The output of the peripheral photoelectric conversion unit 12S is output by the amplifier 14S. After amplification, the signal is equalized by the equalizer 16SB and supplied to the adder 18. The adder 18 adds these input signals, and the identification / reproduction circuit 20 performs data identification / reproduction processing based on the added signal.

Thus, according to the present embodiment, the distance between the transceivers is determined based on the signal level,
a, When the distance is short, an equalization process suitable for the yellow light component is performed on the output of the peripheral photoelectric conversion unit 12S.
b. On the contrary, when the distance is long, the same equalization processing as that of the central photoelectric conversion unit 12C is performed on the output of the peripheral photoelectric conversion unit 12S.

  That is, by switching the equalization characteristic for the signal of the peripheral photoelectric conversion unit 12S according to the distance between transmission and reception, it is possible to always maintain the optimum equalization state for the received light signal and maintain good transmission quality. In addition, the blue light excitation type white LED is advantageous in terms of cost because it is general-purpose and inexpensive.

  Next, Embodiment 2 of the present invention will be described with reference to FIGS. In addition, the same code | symbol shall be used for the component which is the same as that of Example 1 mentioned above, or respond | corresponds. In the present embodiment, as shown in FIG. 2, a signal waveform state detector 40 is connected instead of the signal level detector 22 of the first embodiment. As the signal waveform state detector 40, for example, a waveform blunt detector, a circuit for detecting frequency response characteristics by FFT (Fast Fourie Transform), or the like is used.

  FIG. 11A shows an example of a waveform dullness detector, and the addition signals from the adder 18 are compared with the comparison voltages Vref1 and Vref2 (where Vref1 ≠ Vref2) by the comparators 42 and 44, respectively. The The comparison result is supplied to the XOR circuit 46 and XOR (eXclusive OR) calculation is performed, and the low frequency component of the calculation result is output from the low pass filter (LPF) 48 as a waveform dullness detection signal.

  When there is no dullness in the waveform, the relationship between the input signal and the comparison voltages Vref1 and Vref2 is as shown in FIG. For this reason, the outputs of the comparators 42 and 44 are as shown in (B-2) and (B-3) of FIG. Therefore, the output of the XOR circuit 46 becomes almost zero as shown in FIG. 4B-4, and the output of the LPF 48 becomes almost zero. On the other hand, when the waveform is dull, the relationship between the input signal and the comparison voltages Vref1 and Vref2 is as shown in FIG. For this reason, the outputs of the comparators 42 and 44 are as shown in (C-2) and (C-3), respectively, and they do not match. Accordingly, the output of the XOR circuit 46 is as shown in FIG. 5C-4, and the LPF 48 outputs a signal corresponding to the waveform dullness.

  Next, the operation of the present embodiment will be described. First, when the distance between the transceivers is short, the yellow component light from the phosphor enters the peripheral photoelectric conversion unit 12S. For this reason, as shown in FIG. 7C, the output signal waveform of the adder 18 becomes dull. When this is detected by the signal waveform state detector 40, as shown in FIG. 2A, the changeover switch 15 is switched to the equalizer 16SY side, and the yellow light component with respect to the output of the peripheral photoelectric conversion unit 12S. The characteristic equalization processing is performed.

  Conversely, when the distance between the transmitter and the receiver is long, the blue component light of the LED enters the peripheral photoelectric conversion unit 12S as well as the central photoelectric conversion unit 12C. For this reason, the waveform dullness is not detected by the signal waveform state detector 40, the changeover switch 15 is switched to the equalizer 16SB side, and the characteristics suitable for the blue light component with respect to the output of the peripheral photoelectric conversion unit 12S, etc. Processing is performed. According to the second embodiment, the same effect as the first embodiment can be obtained.

    Next, Embodiment 3 of the present invention will be described with reference to FIG. In this embodiment, as shown in FIG. 3, an error detector 50 is connected to the output side of the identification reproduction circuit 20 instead of the signal level detector 22 of the first embodiment. Examples of the error detector 50 include a circuit that performs error detection using a parity check, a circuit that detects an error rate using a training signal, and an error detection circuit that uses an ARQ (Automatic Repeat Request) signal from the receiving side. used.

  The operation of the present embodiment will be described. When the distance between the transmitter and the receiver is short, the yellow component light from the phosphor enters the peripheral photoelectric conversion unit 12S, and the response speed of the output signal waveform becomes slow. For this reason, an error occurs in the reproduction result of the identification reproduction circuit 20. When this is detected by the error detector 50, the changeover switch 15 is switched to the equalizer 16SY side, and an equalization process suitable for the yellow light component is performed on the output of the peripheral photoelectric conversion unit 12S.

  Conversely, when the distance between the transmitter and the receiver is long, the blue component light of the LED enters the peripheral photoelectric conversion unit 12S as well as the central photoelectric conversion unit 12C. For this reason, error detection by the error detector 50 is also not performed, and the changeover switch 15 is switched to the equalizer 16SB side, and equalization processing of characteristics suitable for the blue light component with respect to the output of the peripheral photoelectric conversion unit 12S Is done. According to the third embodiment, the same effect as that of the first embodiment can be obtained.

  Next, Embodiment 4 of the present invention will be described with reference to FIGS. In this embodiment, the state in which the transmitter / receiver is further approached in the first embodiment described above is detected, and control for reducing the influence of the space electrification effect and the like is performed. FIG. 4 shows the configuration of this embodiment, and an open / close switch 60 is provided between the amplifier 14C and the equalizer 16C shown in FIG. Further, the signal level detector 62 detects the level of the output signal of the adder 18, and detects whether the transmitter / receiver distance is close to or far from the case of the first embodiment. The function to perform.

Next, the operation of this embodiment will be described with reference to FIG. First, when the distance between the transmitter and the receiver is short, the selector switch 15 is switched to the equalizer 16SY side as shown in FIG. Further, the open / close switch 60 is closed. Therefore, it becomes the same as FIG. Next, when the distance between the transceivers is long, the changeover switch 15 is switched to the equalizer 16SB side as shown in FIG. Further, the open / close switch 60 is closed (on). Therefore, it is the same as FIG. Next, when the distance between the transceivers is close, the output signal level of the adder 18 becomes higher than in the case of FIG. When this is detected by the signal level detector 62, the changeover switch 15 is switched to the equalizer 16SY side as in the first embodiment, and the open / close switch 60 is opened (FIG. 5A). )reference). Table 1 below summarizes the relationship between the distance between the transmitter and the receiver, switching of the changeover switch 15, and opening / closing of the open / close switch 60.

  Next, the reason why the opening / closing switch 60 on the central photoelectric conversion unit 12C side is opened when the transmitter / receiver approaches is as follows. In the state where the transceiver is closest, the amount of incident light near the center of the light receiving surface of the photoelectric converter 10 becomes extremely large. For this reason, the above-mentioned space charge effect, output signal level decrease and band decrease due to insufficient reverse bias voltage occur, and the transmission quality of the output signal from the central photoelectric conversion unit 12C deteriorates. On the other hand, the incident light amount to the peripheral photoelectric conversion unit 12S is a sufficient light amount for reproducing data, but the ratio of the yellow component from the phosphor is relatively larger than the blue component. Therefore, in the state where the transmitter / receiver is closest, the output of the central photoelectric conversion unit 12C is not used, and the output signal of the peripheral photoelectric conversion unit 12S is converted into yellow light containing a large amount of light emitted from the phosphor. On the other hand, an equalizer 16SY that performs appropriate equalization is used. By doing so, the transmission quality is not deteriorated even when the transmitter and the receiver are close to each other, and the dynamic range can be expanded.

  Next, Embodiment 5 of the present invention will be described with reference to FIG. The embodiment of FIG. 6A is obtained by applying the embodiment 2 of FIG. 2 to the embodiment 4 of FIG. 4 described above, and has a configuration in which a signal waveform state detector 70 is connected instead of the signal level detector 62. It has become. In this example, the signal waveform state detector 70 determines whether or not the transceiver is close. The embodiment of FIG. 6B is obtained by applying the embodiment 3 of FIG. 3 to the embodiment 4 of FIG. 4 described above, and has a configuration in which an error detector 80 is connected instead of the signal level detector 62. ing. In this example, the error detector 80 determines whether the transceiver is in close proximity.

In addition, 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. For example, the following are also included.
(1) The configurations of the transmitter and the receiver shown in the above embodiment are merely examples, and a known circuit technique may be applied. For example, a circuit such as a filter, an amplifier, and a timing extraction unit in terms of 3R functions (Reshaping, Regeneration, Retiming) may be added on the receiver side (for example, “Optical Communication Optics (1)” No. (See Chapter 3).
(2) In the blue light excitation type white LED shown in the above embodiment, the phosphor excited by the light of the blue LED emits yellow light having a complementary color relationship, but the white light containing the red component in the phosphor emission component There are also LEDs, which are also included in the “blue light excitation type white LED” of the present invention.
(3) The case where the output light of the blue light-excited white LED is modulated by a modulation method such as OOK (On-Off Keying) and flashes has been shown as an example. ), PPM (Pulse Position Modulation), QAM (Quadrature Amplitude Modulation), and the like.
(4) In the above-described embodiment, the photoelectric converter on the receiver side is constituted by the central photoelectric conversion unit and the peripheral photoelectric conversion unit, but this does not prevent the provision of a plurality of photoelectric conversion units. Further, in the above-described embodiment, the case where the yellow light is distributed in a substantially concentric manner around the blue light is shown. However, even in the case of an ellipse or the like, the shape of the photoelectric conversion unit is changed to the light distribution shape. By making it correspond, this invention is applicable. Further, in the above-described embodiment, the peripheral photoelectric conversion unit having the annular light receiving surface is provided so as to surround the periphery of the central photoelectric conversion unit having the circular light receiving surface. However, other shapes such as the central photoelectric conversion unit and the peripheral photoelectric conversion unit are provided. It does not preclude various shapes and arrangements, such as a rectangular conversion unit and the peripheral photoelectric conversion units arranged on the left and right or top and bottom of the central photoelectric conversion unit.
(5) In the above embodiment, the characteristics of the equalizer are switched with respect to the output of the photoelectric converter by the methods of signal level detection, signal waveform state detection, and error detection. However, these are also examples, and other methods are used. It does not prevent application.
(6) Although the said Example mainly demonstrated the case where this invention was applied with respect to blue light excitation type | mold white LED, when using other white LED, Furthermore, it applies when using visible light sources other than LED. It does not prevent it.

According to the present invention, it is possible to provide an optical receiver and a visible light communication device that can be used for a visible light source such as a blue light-excited white LED and that can ensure good transmission quality and a wide dynamic range. This is suitable for spatial light transmission in which the systems are arranged in a one-to-one relationship.

1 is a circuit block diagram illustrating a main configuration of a photoelectric converter and an optical transmission system of Example 1. FIG. (A) is a figure which shows the structure of the light-receiving surface of a photoelectric converter, (B) and (C) are the circuit block diagrams of Example 1. FIG. FIG. 6 is a circuit block diagram illustrating a main configuration of a second embodiment. FIG. 10 is a circuit block diagram illustrating a main configuration of Example 3. FIG. 10 is a circuit block diagram illustrating a main configuration of a fourth embodiment. FIG. 10 is a circuit block diagram illustrating a main configuration of a fourth embodiment. FIG. 10 is a circuit block diagram illustrating a main configuration of a fifth embodiment. (A) is a diagram showing an example of the configuration of a blue light-excited white LED, (B) is a graph showing its emission spectrum characteristics, and (C) is a graph showing an example of signal waveform dullness due to the space charge effect of the signal waveform. is there. It is a block diagram which shows an example of the data transmission system which uses white LED. It is a figure which shows the mode of the light distribution of blue light excitation type | mold white LED. It is a graph which shows an example of the signal waveform of the receiving side by the distance of the distance of a transmitter / receiver. (A) is a block diagram showing an example of a waveform dullness detector, (B) is a time chart showing an operation when there is no waveform dullness, and (C) is a time chart showing an operation when there is a waveform dullness.

Explanation of symbols

10: photoelectric converter 12C: central photoelectric converter 12S: peripheral photoelectric converters 14C, 14S: amplifier 15: changeover switch 16C, 16SB, 16SY: equalizer 18: adder 20: identification reproduction circuit 22: signal level detector 30: Blue light excitation type white LED
40: Signal waveform state detector 42, 44: Comparator 46: XOR circuit 48: Low pass filter 50: Error detector 60: Open / close switch 62: Signal level detector 70: Signal waveform state detector 80: Error detector 900: Blue LED
902: Resin case 904, 906: Extraction electrode 908: Yellow phosphor (phosphor particle)
920A, 920B: Data terminals 922A, 922B: Transceivers 930A, 930B: Transmitter 932: Modulator 934: Blue light excitation type white LED
940A, 940B: receiver 942: photoelectric converter 944: amplifier 946: equalizer 948: identification reproduction circuit (demodulator)

Claims (8)

Light output from a light emitting means including a light emitting body that outputs light in the first wavelength region and a phosphor that is excited by the light output from the light source and outputs light in the second wavelength region having a different response speed. An optical receiver for receiving a signal,
A plurality of photoelectric conversion means arranged corresponding to the distribution of the optical signal output from the light emitting means;
A plurality of units are provided selectively for at least one of the plurality of photoelectric conversion units, and the waveform of the electrical signal converted by the photoelectric conversion unit is equalized according to the response speed of the light receiving wavelength band. Means of
Switching means for switching the plurality of equalization means so as to correspond to a wavelength band of light incident on the photoelectric conversion means according to a distance between the optical transmitter provided with the light emitting means and the optical receiver;
An optical receiver comprising: The plurality of photoelectric conversion units include a central photoelectric conversion unit that receives light of a central portion of output light of the light emitting unit, and a peripheral photoelectric conversion unit that receives light around the central portion,
2. The optical receiver according to claim 1, wherein the equalizing means of the peripheral photoelectric conversion unit is switched by the switching means.   The equalization means includes a first equalizer that performs waveform equalization corresponding to light of a light emitter that outputs light in the first wavelength region, and a phosphor that outputs light in the second wavelength region. The optical receiver according to claim 2, further comprising: a second equalizer that performs waveform equalization corresponding to the light.   The switching means switches to the second equalizer when the transmitter and the receiver are close to each other, and switches to the first equalizer when the transmitter and the receiver are far from each other. The optical receiver according to claim 3.   5. The switch according to claim 2, wherein the switching unit does not use a signal output of a central photoelectric conversion unit when the transmitter and the receiver are close to each other. 6. Optical receiver. The switching means is
Signal level detecting means for detecting a signal level before identification reproduction in the optical receiver;
Signal waveform state detecting means for detecting a signal waveform state before identification reproduction in the optical receiver;
Error detection means for detecting an error after identification reproduction in the optical receiver;
The optical receiver according to claim 1, wherein the optical receiver is any one of the following.   7. The optical receiver according to claim 1, wherein the light emitting means is a blue light excitation type white LED, and a light emitting body that outputs light in the first wavelength range is a blue LED. .   A visible light communication apparatus comprising: the optical receiver according to claim 1; and an optical transmitter including the light emitting unit.

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