JP2009010916A - Optical receiver and visible light communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform high-speed and high-quality data transmission by using light in multiple wavelength ranges, which is outputted from multiple light-emitting means different in speeds of response upon optical output. <P>SOLUTION: A data signal to be transmitted is supplied to a modulator 12 of a transmitter 10, and the modulator 12 modulates the output of a blue light-excited white LED 14 and outputs blue LED light and phosphor light. The modulated blue light is made incident on a photoelectric converter 24B through an LED light transmission color filter 22B. Meanwhile, the modulated phosphor light is made incident on another photoelectric converter 24F through a phosphor light transmission color filter 22F. The photoelectric converters 24B, 24F convert the incident light to electrical signals. The converted signals are amplified by amplifiers 26B, 26F; then equalizers 28B, 28F enhances the harmonic component therein, corresponding to the response characteristic of the blue light and to the response characteristic of the phosphor light, and dullness of waveforms is reduced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a data transmission system that transmits a signal using visible light, for example, an optical receiver suitable for communication using a white light emitting diode (hereinafter referred to as a white LED) including light emission of a phosphor. And a visible light communication device.

  In recent years, white LEDs have been actively developed and used in a wide variety of fields such as lighting, on-vehicle lamps, and liquid crystal backlights. 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). That is, the light intensity of the white LED is modulated according to the transmission data, and the light intensity is converted into an electric signal by a photoelectric converter such as a photodiode (Photo Diode: hereinafter referred to as PD) on the receiving side. Realize transmission.

  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) Blue light excitation type white LED: a combination of a blue LED and a phosphor that mainly emits yellow light. A fluorescent material represented by a YAG (yttrium, aluminum, garnet) system is arranged around the 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 a blue-light-excited white LED are: (1) high energy utilization efficiency compared to other methods, easy to obtain high illuminance, and (2) simple construction that can be manufactured at low cost. There are some. 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. 6 (A) 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 driving 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 phosphor 908. Thereby, the phosphor 908 is excited and fluorescence is output. Some blue LEDs have emission characteristics of various wavelengths, but those having a peak wavelength in the range of 440 to 470 nm are used. As the phosphor 908, a phosphor that emits light having a wavelength longer than the peak wavelength of the blue LED 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. FIG. 6B shows the emission spectrum characteristics of the blue light excitation type white LED. A portion surrounded by a dotted line SA is a blue light portion, and a portion surrounded by a dotted line SB is a light emission portion by a phosphor. Thus, light emission by the phosphor exists on the longer wavelength side than the peak wavelength of light emission of the blue LED.

(2) The 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, the disadvantages are: (1) low energy use efficiency compared to the blue light-excited white LED and difficulty in obtaining high illuminance, and (2) high LED driving voltage due to ultraviolet light emission. , Are mentioned.

  (3) Three-color light emitting type white LED: 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 causing each of the three primary colors to emit light simultaneously.

  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, as a disadvantage, since three types of LEDs are mounted in one package, it is expensive compared to other methods.

  Next, the characteristics when the above-described white LEDs of each method are used for data transmission are as follows.

  (1) When a blue light excitation type white LED is used, since the response speed of light output from the phosphor is low, only a transmission speed of about several Mbps can be obtained (see Non-Patent Document 2 below). FIG. 7A shows a transceiver configuration of this method. In the figure, data to be transmitted is input to a modulator 922 of a transmitter 920 and subjected to predetermined modulation, and a modulation signal is supplied to a blue light excitation type white LED 924. As a result, the output light of the blue light excitation type white LED 924 is modulated by a modulation method such as OOK (On-Off Keying) and blinks. The modulated flashing light is input to the photoelectric converter 932 of the receiver 930, converted into an electric signal, amplified by the amplifier 934, and then input to the demodulator 936, where data is demodulated. Here, if the light emission is turned on / off at high speed on the transmission side, the waveform becomes dull due to the slow response speed of the light emitted from the phosphor 908, causing intersymbol interference. Become. That is, as shown in FIG. 7B, the output signal SQ of the photoelectric converter 932 becomes dull with respect to the modulation signal SP of the modulator 922. This becomes an obstruction factor when realizing high-speed transmission using a blue light excitation type white LED.

  In addition, in order to solve this point, an LED light transmission color filter that transmits only blue light is provided in front of the photoelectric converter, and the light component with a low response speed output from the phosphor is removed by this color filter. A method has been proposed (see Patent Document 1 below). FIG. 7C shows the configuration of the transmitter / receiver in this case, in which an LED light transmission color filter 952 is arranged on the light incident side of the photoelectric converter 932 of the receiver 950. The LED light transmission color filter 952 removes light emitted from the phosphor having a slow response speed in the optical signal. Thereby, only the light of the blue LED 900 enters the photoelectric converter 932, and as a result, data transmission faster than the above configuration can be performed. However, even with this method, only a transmission speed of about several tens of Mbps can be obtained. In addition, as described in Non-Patent Document 3 below, it is pointed out that the transmission quality of data cannot be maintained due to solid-state variations in light emission characteristics of white LEDs, deterioration with time, and uneven spatial distribution of color temperature.

  (2) When an ultraviolet light excitation type white LED is used, the transmission speed is about several Mbps for the same reason as when the blue light excitation type white LED is used. In addition, since the drive voltage of the LED becomes high, the configuration of the drive circuit becomes difficult.

  (3) When a three-color light emitting type white LED is used, it is possible to transmit data by performing wavelength multiplexing such that each LED carries a different signal without phosphor emission components as compared with the above method, The speed can be increased (see Patent Document 2 below). However, since several LED is used, cost will become high.

  Next, when spatial light transmission is performed by a combination of a diffused light source such as an LED and a photoelectric converter such as a PD, the amount of light received by the PD is inversely proportional to the square of the distance (for example, Non-Patent Documents 4 to 5 below). reference). For this reason, a large dynamic range is required on the receiver side in order to secure a distance range in which information can be transmitted to some extent. For example, in IrDA (Infra-red Data Association) which is an infrared communication standard, a dynamic range of 100 dB or more is required on the receiver side with respect to a transmission distance range of 1 cm to 100 cm (Patent Document 3 to Non-Patent Document 3 below). (See Chapter 2 of Patent Document 6).

  In particular, when performing spatial light transmission using visible light as a data transmission medium as in the present invention, disturbance light such as sunlight and fluorescent lamps is very large. Further, unlike infrared communication, it is difficult to remove optical disturbance light using a visible light cut filter. For this reason, more severe conditions are imposed on the receiver side. In general, to obtain a large dynamic range on the receiver side, an AGC (Auto Gain Control) circuit is used for the amplifier (Chapter 7 of Non-Patent Document 6 below), or multiple amplifiers with different gains are prepared and input. A means for switching the gain of the amplifier in accordance with the signal level is adopted.

Japanese Patent No. 3465017 JP 2002-290335 A JP-A-10-51387 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" 2006 IEICE Basic and Boundary Society Conference “Consideration of luminance degradation of white LEDs” Wednesday Company “Spatial Transmission Optics”, Chapter 6 2005 IEICE Communication Society "Optical analysis of reception characteristics of parallel optical space transmission" Trikeps "Infrared communication technology"

  As described above, the transmission speed can be increased by using a three-color light emitting type white LED. However, since the LED itself is expensive, this method is suitable in terms of cost and versatility. It's hard to say.

  On the other hand, when a blue light excitation type white LED is used, there is no cost inconvenience. As described above, the LED light transmission color filter 952 that blocks the light emission from the phosphor 908 having a slow response speed is used. Data transmission can be performed. However, the cut-off frequency of a general blue LED is about several tens of MHz at most (see Non-Patent Document 2). If OOK modulation is performed at a transmission speed exceeding this frequency, the output optical signal is still shown in FIG. Blurring as shown in (B) occurs and intersymbol interference occurs. For this reason, the upper limit of the data transmission rate is limited, and only a transmission rate of about several tens of Mbps can be obtained. Data transmission quality also deteriorates.

  Furthermore, in the case of data transmission using an ultraviolet light-excited white LED, as in the case of using the blue light-excited white LED, the inconvenience that the transmission speed is slow due to the slow response speed of the phosphor emission cannot be avoided. In addition, there is a disadvantage that the driving voltage of the ultraviolet LED becomes high.

  In addition, a method of increasing the response speed of the light output from the phosphor by improving the phosphor material is also conceivable, but the problem that the desired illuminance cannot be obtained and the cost of the phosphor material itself is increased. Can also occur. From this point of view, it is advantageous if high-speed data transmission can be performed using a general-purpose and inexpensive blue light excitation type white LED.

  On the other hand, it is unavoidable that the circuit configuration becomes complicated by using an AGC circuit or by obtaining a large dynamic range by switching the gain of the amplifier according to the input signal level. In addition, when the distance between the transmitter and the receiver is close and the amount of light incident on the PD is large, a graph SQ is shown in FIG. 7B by a space charge effect (Space Charge Effect, see Non-patent Document 7 below). As described above, a wave tail occurs at the falling edge of the signal waveform, and this may cause intersymbol interference, which may impede securing good transmission quality.

Engineering book "Optical communication device engineering"

  The present invention focuses on the above points, and its purpose is to perform high-speed data transmission using light of a plurality of wavelength bands output from a plurality of light emitting means having different response speeds at the time of light output. is there. Another object is to maintain the quality of data transmission. Yet another object is to obtain a good dynamic range.

  In order to achieve the above object, the optical receiver of the present invention receives data from a plurality of light emitting means having different response speeds depending on the light emitting diode and the phosphor that is excited by the light source of the light emitting diode to transmit data. A plurality of filter means for selectively transmitting light in each of the plurality of wavelength bands from the modulated light in the plurality of wavelength bands in an optical receiver that receives light in the plurality of wavelength bands modulated to perform Is provided.

  One of the main forms is that a plurality of photoelectric conversion means for converting each of light in a plurality of wavelength bands transmitted through the plurality of filter means into an electric signal for each wavelength band, and after conversion by the plurality of photoelectric conversion means A plurality of equalization means for waveform equalizing each of the electrical signals corresponding to the response speed for each wavelength band, an addition means for making the output of the plurality of equalization means one output, and this addition Discriminating means for discriminating the added output of the means.

  One of the other forms is that the plurality of light emitting units are excited by the light source of the light emitting diode having a peak wavelength in the range of 440 to 470 nm and longer than the peak wavelength of the light emitting diode by being excited by the light source of the light emitting diode. It is a blue light excitation type white light emitting means that becomes white light by mixing the light emitted from the phosphor that emits the light.

  Furthermore, in another embodiment, the plurality of light emitting means are excited by a light source of a light emitting diode having a peak wavelength in a range of 380 to 410 nm and emit light having a wavelength longer than the peak wavelength of the light emitting diode. It is an ultraviolet light excitation type white light emitting means for emitting white light from a plurality of kinds of phosphors.

  The invention of another optical receiver was modulated in order to transmit data by receiving outputs from a plurality of light emitting means having different response speeds by a light emitting diode and a phosphor that emits light by being excited by a light source of the light emitting diode. In an optical receiver that receives light of a plurality of wavelength bands, a plurality of filter means that selectively transmit the modulated light of a plurality of wavelength bands, and light that has passed through the plurality of filter means A plurality of photoelectric conversion means for converting each filter means into an electrical signal, an addition means for making the outputs of the plurality of photoelectric conversion means one output, and a discrimination means for discriminating the addition output of the addition means The signal level of the output of one photoelectric conversion means is detected, and when this signal level is below a predetermined threshold, the input of the output of the other photoelectric conversion means is blocked to the adding means. And signal control means for, characterized by comprising a.

  One of the main forms is that the signal control means includes a signal level detection means for detecting the signal level of the output of the one photoelectric conversion means, and the other photoelectric conversion means according to the detection result of the signal level detection means. And switch means for controlling the output of the conversion means. Still another embodiment is characterized in that equalization means for performing waveform equalization corresponding to the response speed at the time of light output by the light emitting means is provided for the output of the photoelectric conversion means.

  Still another embodiment is characterized in that the equalizing means is an adaptive equalizer that adaptively performs waveform equalization.

  The visible light communication device of the present invention uses a white light emitting means including a phosphor as a light emitting means as a light source on the transmission side, and receives light output from the white light emitting means by any one of the light receiving devices described above. It is characterized by that. 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, when receiving light of a plurality of wavelength bands output from a plurality of light emitting means having different response speeds at the time of light output, the light is selectively transmitted by the filter means for each wavelength band. Therefore, it is possible to perform high-speed data transmission with good transmission quality by using an inexpensive and high-speed general-purpose white LED. In addition, according to the present invention, by selecting the light used for transmission according to the incident light level of LED light or phosphor light, the dynamic range of the receiver is expanded, in other words, the distance range of data transmission. Can be expanded. Furthermore, a good transmission quality can be obtained by adding equalization means.

  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. 1 (A) and FIG. FIG. 1A shows a circuit configuration of a main part of the present embodiment. In the figure, from the transmission side, transmission target data is input to the modulator 12 of the transmitter 10. The output side of the modulator 12 is connected to the above-described blue light excitation type white LED 14 which is a white light emitting means. As the modulator 12, an LED driving circuit capable of modulating the output light of the blue light excitation type white LED 14 at high speed can be used.
As the blue light excitation type white LED 14, the apparatus described with reference to FIG. 6A is used. The blue light excitation type white LED 14 uses a blue LED as a light source. Some of these blue LEDs 900 have emission characteristics of various wavelengths, but those having a peak wavelength in the range of 440 to 470 nm are used. As the phosphor 908, a phosphor that emits light longer than the peak wavelength of the blue LED 900 is used. And the fluorescent substance 908 of particle | grains is arrange | positioned so that it may be scattered in transparent resin with radial and thickness so that the light which blue LED may emit may not be interrupted.

  On the other hand, the reception side includes a circuit for LED light output from the blue LED of the blue light excitation type white LED 14 and a circuit for fluorescence output from the phosphor. First, the LED light circuit will be described. On the light incident side, a photoelectric converter 24B as a photoelectric conversion means is provided via an LED light transmission color filter 22B as a filter means. The output side of the photoelectric converter 24B is connected to an equalizer or an adaptive equalizer 28B via an amplifier 26B. On the other hand, for the phosphor light circuit, a photoelectric converter 24F is provided on the light incident side via a phosphor light transmitting color filter 22F. The output side of the photoelectric converter 24F is connected to the equalizer 28F via the amplifier 26F.

  Among the above portions, the LED light transmission color filter 22B is a color filter that selectively transmits blue light emitted by the blue LED 900 (see FIG. 6A) in the blue light excitation type white LED 14. On the other hand, the phosphor light transmitting color filter 22F is a color filter that selectively transmits light emitted from the phosphor 908 in the blue light excitation type white LED 14. The photoelectric converters 24B and 24F are photodetectors that convert input light into electric signals, and the converted electric signals are amplified by the amplifiers 26B and 26F, respectively. The equalizers 28B and 28F emphasize the high frequency of the amplified signal and equalize the waveform.

  The output sides of the equalizers 28B and 28F are connected to the input side of the adder 30 which is addition means, and the output side of the adder 30 is connected to the discriminator 34 of the demodulator 32 which is discrimination means. Yes. The equalized signals are added by an adder 30 and further discriminated into a binary signal by a discriminator 34.

  Next, the operation of the present embodiment configured as described above will be described. The data signal to be transmitted is supplied to the modulator 12 of the transmitter 10, and the light output of the blue light excitation type white LED 14 is modulated by the modulator 12 by, for example, the OOK method. As described above, the blue light excitation type white LED 14 has the configuration shown in FIG. 6A. When the output light of the blue LED 900 is modulated, the output light of the phosphor 908 is also modulated.

  The modulated blue LED light and phosphor light are incident on the receiver 20. On the receiver 20 side, of the incident light, blue light output from the blue LED 900 (see dotted line SA in FIG. 6B) passes through the LED light transmission color filter 22B and enters the photoelectric converter 24B. On the other hand, the phosphor light output from the phosphor 908 (see the dotted line SB in FIG. 6B) passes through the phosphor light transmitting color filter 22F and enters the photoelectric converter 24F. In the photoelectric converters 24B and 24F, incident light is converted into electric signals. The converted signals are amplified by the amplifiers 26B and 26F, respectively.

  FIG. 2 shows signal waveforms of each part. FIG. 3A shows a data signal waveform on the transmission side. In contrast, the converted signal waveform of the blue light by the photoelectric converter 24B is as shown by the dotted line graph SB1 in FIG. On the other hand, the converted signal waveform of the phosphor light by the photoelectric converter 24F is as shown by a dashed-dotted line graph SF1 in FIG. When both are compared, the graph SF1 has a dull waveform with respect to the graph SB1. This is because the response speed of the light output from the phosphor 908 is slow as described above.

  Therefore, in this embodiment, waveform equalization is performed by the equalizers 28B and 28F. The equalizers 28B and 28F have their frequency characteristics adjusted with respect to the blue light response characteristic or the phosphor light response characteristic, respectively, and emphasize harmonic components. For this reason, the graphs SB1 and SF1 in FIG. 5B become like the graphs SB2 and SF2 shown in FIG. 5C, and the waveform dullness is reduced. The equalized signals are added by the adder 30 and then input to the discriminator 34 of the demodulator 32 for binarization. Since the dullness of the waveform is improved, the binarization process can be performed satisfactorily. For this reason, high-speed data transmission is possible.

  In the case of a method that does not separate blue light and phosphor light as in the background art described above, equalization processing is performed in a state in which light having different time response characteristics is added. For this reason, there is an inconvenience that the circuit configuration of an equalizer for performing equalization optimal for high-speed data transmission is complicated and adjustment is difficult. On the other hand, according to the present embodiment, an equalizer may be configured for each of blue light and phosphor light, which is simple and practical.

  Next, a second embodiment of the present invention will be described. 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 this embodiment, as the equalizers 28B and 28F of the first embodiment, adaptive equalizers that adaptively equalize the waveform of the amplified signal are used. Although the equalizer of the above embodiment has a fixed coefficient (that is, the characteristic is fixed), the adaptive equalizer of the present embodiment has a variable coefficient, and the characteristic changes according to the input waveform. When such an adaptive equalizer is used, a good data transmission quality is always obtained with respect to a change in output light characteristics due to solid-state variations in the light emission characteristics of the blue light-excited white LED 14 and deterioration with time (see Non-Patent Document 3). Can be maintained. In particular, an adaptive equalizer is suitable because phosphors are more likely to deteriorate than LEDs. Moreover, it is said that the blue light excitation type white LED 14 has a color nonuniformity with respect to the light emission direction (refer the said nonpatent literature 1). Specifically, in the spatial distribution of light, the center portion changes so that the blue color is strong and the yellow color is strong toward the outside. Even in such a case, according to the present embodiment, good data transmission quality can always be maintained regardless of the positional relationship (specifically, the incident angle of light) between the blue light excitation type white LED 14 and the receiver 20. It becomes possible.

  Next, Embodiment 3 of the present invention will be described with reference to FIG. As shown in the figure, in the present embodiment, the transmitter 40 is provided with an ultraviolet light excitation type white LED 44 which is a white light emitting means, and the output light is modulated by the modulator 12 at high speed. Yes. On the other hand, on the receiver 50 side, a blue fluorescent transmission color filter 52B, a red fluorescent transmission color filter 52R, and a green fluorescent transmission color filter 52G are provided as filter means. Among these, the blue fluorescent transmission color filter 52B is a filter that selectively transmits light emitted from the blue light emitting phosphor among the white light output from the ultraviolet light excitation type white LED 44. Similarly, the red fluorescent transmission color filter 52R is a filter that selectively transmits light emitted from the red light-emitting phosphor out of white light output from the ultraviolet light excitation type white LED 44. The green fluorescent transmission color filter 52G is a filter that selectively transmits light emitted from the green light emitting phosphor out of white light output from the ultraviolet light excitation type white LED 44.

  Photoelectric converters 54B, 54R, and 54G, which are photoelectric conversion means, are provided on the light output sides of these filters 52B, 52R, and 52G, respectively, and electric signals converted by these are supplied to amplifiers 56B, 56R, and 56G. And are supplied to equalizers (or adaptive equalizers) 58B, 58R and 58G which are equalization means. The outputs of the equalizers 58B, 58R and 58G are added by an adder 60 which is an adding means, and further discriminated by a discriminator 64 of a demodulator 62 as a discriminating means.

In the present embodiment, since the ultraviolet light excitation type white LED 44 is used, the blue, red, and green lights constituting the white light are all phosphor light. Therefore, these phosphor lights are extracted by the color filters 52B, 52R, and 52G, respectively, and the photoelectric conversion, amplification, and equalization processes are performed as in the above-described embodiment. Also in the present embodiment, the equalizers 58B, 58B, and 58G have their frequency characteristics adjusted with respect to the response characteristics of the blue, red, and green phosphor lights, respectively, and the waveform becomes blunt by emphasizing harmonic components. Is improved. For this reason, the binarization processing can be performed satisfactorily as in the above-described embodiment, and high-speed data transmission is possible.
In addition, the ultraviolet light excitation type white LED 44 of the light emitting means is excited by a light source of a light emitting diode having a peak wavelength in a range of 380 to 410 nm, and emits light having a wavelength longer than the peak wavelength of the light emitting diode. These emit three primary colors of blue, red, and green from a plurality of types of phosphors, and white light is emitted by their photosynthesis.

  Next, Embodiment 4 of the present invention will be described with reference to FIG. The present embodiment is an embodiment aimed at expanding the dynamic range. The output side of the amplifier 26 </ b> B in the circuit on the blue LED light side of the receiver 100 is connected to one input side of the adder 30 that is addition means and the input side of the signal level detector 102. On the other hand, the output side of the amplifier 26F in the phosphor side circuit is connected to the input side of the analog switch 104 of the switch means, and the output side of the analog switch 104 is connected to the other input side of the adder 30. ing. The detection output side of the signal level detector 102 described above is connected to the control terminal of the analog switch 104, and the analog switch 104 is turned on / off according to the detection result of the signal level detector 102. ing. Thus, the signal level detector and the analog switch constitute a signal control means. The output side of the adder 30 is the same as that in the first embodiment.

  Among these, the signal level detector 102 detects the magnitude of the amplitude level of the input signal and outputs the result. For example, RSSI (Received Signal Strength Indicator) using a log amplifier or peak bottom detection. A vessel is used. A predetermined threshold value is set in advance in the signal level detector 102. When the input signal level does not exceed this threshold value, the analog switch 104 is controlled to “ON” by the control signal, and the threshold value is input. When the signal level exceeds, the analog switch 104 is controlled to be “OFF”.

  Next, the operation of the present embodiment configured as described above will be described. The operation on the transmitter 10 side is the same as that of the first embodiment described above, and blue LED light and phosphor light after modulation based on the data signal are incident on the receiver 100. During the operation on the receiver 100 side, the operations up to the amplification signal output by the amplifiers 26B and 26F are the same as those in the first embodiment.

  The signal relating to the blue LED light output from the amplifier 26B is input to the signal level detector 102. Here, when the signal level detector 102 determines that the signal level of the blue LED light exceeds a predetermined threshold value, the analog switch 104 is controlled to be “OFF”. Therefore, only the signal related to the blue LED light from the amplifier 26 </ b> B is supplied to the adder 30, and this is supplied to the demodulator 32. On the other hand, when the signal level detector 102 determines that the signal level of the blue LED light does not exceed the predetermined threshold, the analog switch 104 is controlled to be “ON”. For this reason, the adder 30 is supplied with the signal relating to the blue LED light from the amplifier 26B and the signal relating to the phosphor light from the amplifier 26F, and these are added and supplied to the demodulator 32.

  For example, when the distance between the transmitter 10 and the receiver 100 is close and the amount of blue LED light incident on the receiver 100 is large, only the blue LED light signal is input to the demodulator 32. In this case, it is possible to sufficiently transmit information using only the blue LED light. Since phosphor light is not used, waveform dullness caused by the phosphor light and influence caused by the space charge effect are reduced. On the contrary, when the distance between the transmitter 10 and the receiver 100 is long and the amount of blue LED light incident on the receiver 100 is small, the signals of the blue LED light and the phosphor light are added and the demodulator 32 is added. Is demodulated by effectively using not only blue LED light but also phosphor light.

  Thus, according to the present embodiment, by selecting the light used for transmission according to the incident light level of the blue LED light, the dynamic range of the receiver is expanded, in other words, the distance of data transmission. The range can be expanded.

  Next, the second signal control means will be described as Embodiment 5 of the present invention with reference to FIG. As shown in the figure, in this embodiment, as compared with the above-described fourth embodiment, switch means of a PGA (Programmable Gain Amplifier) 112 instead of the amplifier 26F and the analog switch 104 on the phosphor light side of the receiver 110. Are connected, and the control signal of the signal level detector 102 described above is input to the control input side of the PGA 112. The PGA 112 has a function capable of adjusting the gain of signal amplification according to the detection result of the signal level detector 102. That is, when the signal level detector 102 determines that the input signal level does not exceed the threshold value, the control signal controls the gain of the PGA 112 to a predetermined value, and conversely, when the input signal level is determined to exceed the threshold value. Is configured such that the gain of the PGA 112 is controlled to “0”. According to the present embodiment, the operations of the amplifier 26F and the analog switch 104 in the fourth embodiment are performed by the PGA 112.

  Next, Embodiment 6 of the present invention will be described with reference to FIG. The present embodiment is a combination of the first embodiment shown in FIG. 1A and the fourth embodiment shown in FIG. That is, the output side of the amplifier 26B, which is a circuit on the blue LED light side of the receiver 120, is connected to the input side of the equalizer 28B and the input side of the signal level detector 102, respectively. On the other hand, the output side of the amplifier 26F, which is a phosphor side circuit, is connected to the input side of the analog switch 104, and the output side of the analog switch 104 is connected to the input side of the equalizer 28F. . The output sides of the equalizers 28B and 28F are connected to the input side of the adder 30, respectively. The output side of the adder 30 is the same as that in the first embodiment.

  The operation of the present embodiment is a combination of the first embodiment and the fourth embodiment described above. That is, when the signal level detector 102 determines that the signal level of the blue LED light exceeds a predetermined threshold, the analog switch 104 is controlled to be “OFF”. Therefore, only the signal output from the amplifier 26B is subjected to waveform equalization processing by the equalizer 28B and supplied to the adder 30. On the other hand, when the signal level detector 102 determines that the signal level of the blue LED light does not exceed the predetermined threshold, the analog switch 104 is controlled to be “ON”. Therefore, the signals output from the amplifiers 26B and 28B are subjected to waveform equalization processing by the equalizers 28B and 28F, respectively, and are added by the adder 30.

  According to the present embodiment, the effect of the waveform equalization processing of the first embodiment and the effect of signal selection of the fourth embodiment can be obtained. That is, not only can the transmission quality be improved during high-speed transmission, but also the dynamic range can be expanded. If adaptive equalizers are used as the equalizers 28B and 28F, the combination of the second embodiment and the fourth embodiment is obtained.

  Next, Embodiment 7 of the present invention will be described with reference to FIG. As shown in the figure, in this embodiment, compared to the above-described Embodiment 6, a PGA 112 is connected instead of the amplifier 26F and the analog switch 104 on the phosphor light side of the receiver 130. The control signal of the signal level detector 102 described above is input to the control input side. It can be considered that the first embodiment in FIG. 1A and the fifth embodiment in FIG. 3B are combined, and the operation of the amplifier 26F and the analog switch 104 in the sixth embodiment is performed by the PGA 112. Also in the present embodiment, adaptive equalizers may be used as the equalizers 28B and 28F.

  Next, Embodiment 7 of the present invention will be described with reference to FIG. As shown in the figure, the signal level detector 142 of the receiver 140 is connected to the output side of the amplifier 26F on the phosphor light side. That is, in Example 4 of FIG. 3A described above, the signal level of the blue LED light of the amplifier 26B is detected, but in this example, the signal level of the phosphor light of the amplifier 26F is detected to detect the analog switch 104. Is controlled. According to this embodiment, when the signal level detector 142 determines that the signal level of the phosphor light has exceeded a predetermined threshold, the analog switch 104 is controlled to be “OFF”. Therefore, only the signal related to the blue LED light from the amplifier 26 </ b> B is supplied to the adder 30, and this is supplied to the demodulator 32. On the other hand, when the signal level detector 142 determines that the signal level of the phosphor light does not exceed the predetermined threshold, the analog switch 104 is controlled to be “ON”. For this reason, the adder 30 is supplied with the signal relating to the blue LED light from the amplifier 26B and the signal relating to the phosphor light from the amplifier 26F, and these are added and supplied to the demodulator 32.

  Next, Embodiment 8 of the present invention will be described with reference to FIG. The present embodiment is a combination of the first embodiment shown in FIG. 1 (A) and the eighth embodiment shown in FIG. 5 (A). That is, the output side of the amplifier 26B on the blue LED light side of the receiver 150 is connected to the input side of the equalizer 28B. On the other hand, the output side of the amplifier 26F on the phosphor side is connected to the input side of the analog switch 104 and the signal level detector 142, and the output side of the analog switch 104 is connected to the input side of the equalizer 28F. It is connected. The output sides of these equalizers 28B and 28F are connected to the addition input side of the adder 30, respectively. The output side of the adder 30 is the same as that in the first embodiment.

  The operation of the present embodiment is a combination of the first embodiment and the eighth embodiment described above. That is, when the signal level detector 142 determines that the signal level of the phosphor light has exceeded a predetermined threshold, the analog switch 104 is controlled to “OFF”. For this reason, only the signal relating to the blue LED light from the amplifier 26B is equalized by the equalizer 28B, supplied to the adder 30, and further supplied to the demodulator 32. On the other hand, when the signal level detector 142 determines that the signal level of the phosphor light does not exceed the predetermined threshold, the analog switch 104 is controlled to be “ON”. Therefore, the output signals of the amplifiers 26B and 26F are equalized by the equalizers 28B and 28F and supplied to the adder 30. Then, the added signal is supplied to the demodulator 32. Also in the present embodiment, adaptive equalizers may be used as the equalizers 28B and 28F.

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) In the above embodiment, the phosphor 908 excited by the light of the blue LED 900, which is a blue light excitation type white LED, emits yellow light having a complementary color relationship. There is also an LED including, and such an LED is also included in the “blue light excitation type white LED”.
(2) As the above-described equalizer or adaptive equalizer, either an analog type or a digital type may be used.
(3) The color filter and the photoelectric converter may be integrated to form a color sensor or a light receiving element. Since the light receiving element has a wavelength band of light to be subjected to photoelectric conversion, setting this to a desired value can also serve as a color filter.

  According to the present invention, since signal processing is performed by extracting light in a plurality of wavelength bands from modulated light including phosphor light, high-speed data transmission is possible. For this reason, it is suitable for visible light communication using white LED, especially blue light excitation type white LED.

It is a circuit block diagram which shows the main structures of the Example of this invention. (A) is a block diagram of the first and second embodiments, and (B) is a block diagram of the third embodiment. 3 is a graph showing signal waveforms of main parts in the first embodiment. (A) shows the data signal waveform, (B) shows the signal waveform before equalization, and (C) shows the signal waveform after equalization. (A) is a block diagram of the fourth embodiment, and (B) is a block diagram of the fifth embodiment. (A) is a block diagram of the sixth embodiment, and (B) is a block diagram of the seventh embodiment. (A) is a block diagram of the eighth embodiment, and (B) is a block diagram of the ninth embodiment. (A) is a figure which shows an example of a structure of blue light excitation type | mold white LED, (B) is a graph which shows the emission spectrum characteristic. (A) is a circuit block diagram showing an example of the prior art, (B) is a graph showing an example of a signal waveform, and (C) is a circuit block diagram showing another example of the prior art.

Explanation of symbols

10: Transmitter 12: Modulator 14: Blue light excitation type white LED
20: Receiver 22B: LED light transmission color filter 22F: Phosphor light transmission color filter 24B: Photoelectric converter 24B, 24F: Photoelectric converter 26B, 26F: Amplifiers 28B, 28F: Equalizer 30: Adder 32: Demodulation 34: Discriminator 40: Transmitter 44: Ultraviolet light excitation type white LED
50: Receiver 52B: Blue fluorescent transmission color filter 52G: Green fluorescent transmission color filter 52R: Red fluorescent transmission color filter 54B, 54R, 54G: Photoelectric converters 56B, 56R, 56G: Amplifiers 58B, 58R, 58G: Equalizer 60: Adder 62: Demodulator 64: Discriminator 100: Receiver 102: Signal level detector 104: Analog switch 110: Receiver 112: PGA
120, 130, 140: Receiver 142: Signal level detector 150: Receiver 900: Blue LED
902: Resin case 904, 906: Extraction electrode 908: Phosphor 920: Transmitter 922: Modulator 924: Blue light excitation type white LED
930: Receiver 932: Photoelectric converter 934: Amplifier 936: Demodulator 950: Receiver 952: LED light transmission color filter

Claims (9)

Receiving outputs from a plurality of light emitting means having different response speeds by a light emitting diode and a phosphor that emits light by being excited by a light source of the light emitting diode, receives light in a plurality of wavelength bands modulated to perform data transmission In the optical receiver,
An optical receiver comprising a plurality of filter means for selectively transmitting light in each of the plurality of wavelength bands from the modulated light in the plurality of wavelength bands. A plurality of photoelectric conversion means for converting each of the light in the plurality of wavelength bands transmitted through the plurality of filter means into an electrical signal for each wavelength band;
A plurality of equalization means for equalizing each waveform of the electrical signals converted by the plurality of photoelectric conversion means corresponding to the response speed for each wavelength band;
Adding means for converting the outputs of the plurality of equalizing means into one addition output;
Discrimination means for discriminating the addition output of the addition means;
The optical receiver according to claim 1, further comprising:   The plurality of light emitting means includes light from a light emitting diode having a peak wavelength in a range of 440 to 470 nm and a phosphor that is excited by a light source of the light emitting diode and emits light having a wavelength longer than the peak wavelength of the light emitting diode. 3. The optical receiving device according to claim 1, wherein the light receiving device is a blue light excitation type white light emitting means that generates white light by mixing color with emitted light.   The plurality of light emitting means emit white light from a plurality of types of phosphors that emit light having a wavelength longer than the peak wavelength of the light emitting diode when excited by a light source of a light emitting diode having a peak wavelength in a range of 380 to 410 nm. The optical receiver according to claim 1, wherein the optical receiver is an ultraviolet light excitation type white light emitting means. Receiving outputs from a plurality of light emitting means having different response speeds by a light emitting diode and a phosphor that emits light by being excited by a light source of the light emitting diode, receives light in a plurality of wavelength bands modulated to perform data transmission In the optical receiver,
A plurality of filter means for selectively transmitting the modulated light in a plurality of wavelength bands;
A plurality of photoelectric conversion means for converting the light transmitted through the plurality of filter means into electrical signals for each of the plurality of filter means;
Adding means for making the outputs of the plurality of photoelectric conversion means into one added output;
Discrimination means for discriminating the addition output of the addition means;
A signal control means for detecting the signal level of the output of one photoelectric conversion means and shutting off the input of the output of the other photoelectric conversion means to the addition means when the signal level is equal to or lower than a predetermined threshold;
An optical receiver characterized by comprising: The signal control means;
Signal level detection means for detecting the signal level of the output of the one photoelectric conversion means;
In accordance with the detection result of the signal level detection means, switch means for controlling the output of the other photoelectric conversion means,
The optical receiver according to claim 5, comprising:   A plurality of equalization means for waveform equalizing each of the outputs of the plurality of photoelectric conversion means corresponding to the response speed at the time of light output by the light emitting means is provided in the subsequent stage of the plurality of photoelectric conversion means, respectively. The optical receiver according to claim 5 or 6, characterized in that:   8. The optical receiver according to claim 2, wherein the equalizing means is an adaptive equalizer that adaptively performs waveform equalization.   A white light emitting means including a phosphor as a light emitting means is used as a light source on the transmission side, and the light output from the white light emitting means is received by the light receiving device according to claim 1. Visible light communication device.

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