JP2018046585A - Optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To receive data of an optical signal correctly even if intensity of the optical signal received by a light-receiving element is weak.SOLUTION: In a later stage of a filter receiving a waveform signal generated on the basis of output from a light-receiving element for receiving an optical signal and converting the optical signal into an electric signal, an optical receiver includes a voltage generation circuit which forms reference voltage for defining bias voltage of a filter output waveform, and a variable gain amplifier for amplifying the filter output waveform output from the filter. A control circuit for controlling the reference voltage and gain of the variable gain amplifier on the basis of the output from the variable gain amplifier boosts the bias voltage of the filter output waveform depending on undesired dullness of the output waveform of the variable gain amplifier, and controls the gain of the variable gain amplifier so as to make it smaller than that at present.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical receiver that receives an optical signal by visible light, and relates to a technique that is effective when applied to, for example, an optical communication system that performs data communication by superimposing an optical modulation signal on LED (Light Emitting Diode) illumination light.

  In recent years, visible light communication technology using LED lighting has been developed, and devices that perform data communication by superimposing a light modulation signal on visible light have started to appear. For example, Patent Document 1 describes an optical receiver applicable to visible light communication. According to this, the operation of extracting the frequency component of the electrical signal output from the light receiving element (photodiode) using the band pass filter and demodulating the signal using the A / D converter is performed. The features of the technology described here are “DC component removal processing” and “AGC gain control”. The DC component contained in the output signal of the first stage amplifier is extracted and the first stage amplifier is canceled so as to cancel this DC component. By feeding back the bias current to the input side, the DC component of the electric signal input to the first stage amplifier is removed. By supplying a bias current that cancels the DC component, the DC component of the electric signal input to the first-stage amplifier can be removed, and the amplification factor of the first-stage amplifier can be increased. Thereby, for example, a weak light modulation signal can be received, and the dynamic range of reception of the light modulation signal can be expanded. The adjustment control of the gain of the variable gain amplifier (AGC gain control) is not always performed, but only when the signal preamble is received, so that the adjustment time of the AGC gain is shortened. Yes.

JP 2013-5327 A

  The present inventor has found that there is a possibility that the electrical signal output from the light receiving element (illuminance sensor) may become dull when the reception intensity of the optical signal by the optical receiver is low, that is, when the received optical signal is dark. . For example, the electrical signal output from the light receiving element is passed through a high-pass filter to remove the DC component, and is converted into a signal in which the edge portion of the signal is emphasized, and the amplitude of the converted signal is made constant. Amplified by automatic gain control and matched to the dynamic range of the subsequent A / D converter. The logical value of the A / D converted data is determined using a predetermined determination threshold value, and the determination result data is subjected to predetermined data processing. At this time, if the received optical signal is dark, the signal output from the high-pass filter becomes dull. The cause of this dullness is related to the amount of electric signal current that can be output by the light receiving element and the capacitor capacity of the high-pass filter. When the current amount of the electrical signal output from the light receiving element decreases, it takes time until the capacitor is charged.The rise time of the waveform becomes longer, but the fall time is a discharge time according to the characteristics of the capacitor. It is not related to the strength of the received optical signal. If the discharge is started before the capacitor is fully charged in the operation timing of the high-pass filter, the amplitude of the output waveform of the high-pass filter differs between the upward direction and the downward direction. As a result, it is considered that an error occurs between the high period and the low period of the waveform signal, and it becomes difficult to correctly receive the optical signal. As described above, since the current amount of the electrical signal output from the light receiving element is reduced and the relationship between the charging time and the discharging time in the subsequent stage is not constant, it is difficult to receive the optical signal correctly.

  The above and other problems and novel features will become apparent from the description of the specification and the accompanying drawings.

  An outline of representative ones of the embodiments disclosed in the present application will be briefly described as follows.

  That is, a voltage that forms a reference voltage for defining a bias voltage of a filter output waveform at a subsequent stage of a filter that inputs a waveform signal generated based on an output of a light receiving element that receives an optical signal and converts it into an electrical signal And a variable gain amplifier having a variable gain for amplifying a filter output waveform output from the filter. A control circuit for controlling the reference voltage and the gain of the variable gain amplifier based on the output of the variable gain amplifier is configured to bias a filter output waveform by the reference voltage in response to an undesired blunting of the output waveform of the variable gain amplifier. Control is performed to raise the voltage and make the gain of the variable gain amplifier smaller than the present one.

  The effects obtained by the representative ones of the embodiments disclosed in the present application will be briefly described as follows.

  That is, even if the intensity of the optical signal received by the light receiving element is weak, the data based on the optical signal can be received correctly.

FIG. 1 is a block diagram illustrating an example of an optical receiver. FIG. 2 is a block diagram illustrating an optical transmitter that performs optical communication with an optical receiver. FIG. 3 is an explanatory view illustrating an LED lighting fixture in which an illumination light source is used for optical transmission. FIG. 4 is a circuit diagram illustrating a high-pass filter. FIG. 5 is a circuit diagram illustrating a variable gain amplifier. FIG. 6 is a block diagram illustrating a reference voltage generator. FIG. 7 is a waveform diagram illustrating an electric signal waveform output from the light receiving element and a signal waveform output from the waveform generation circuit and input to the ADC in comparison with a case where the signal is dull and a case where the signal is not blunt. FIG. 8 is a waveform diagram showing a high period and a low period for logical value determination with respect to an ADC input waveform in a case where there is a dullness and a case where there is no dullness. FIG. 9 is an explanatory diagram illustrating the 4PPM system in JEITA CP-1223, which is a communication standard using visible light. FIG. 10 is a waveform diagram exemplarily illustrating the principle of correction for correcting the dullness of the signal waveform as a means for coping with signal dullness. FIG. 11 is a flowchart illustrating an automatic gain control method. FIG. 12 is an explanatory diagram showing a waveform diagram of a waveform signal by automatic gain control and a determination threshold value. FIG. 13 is a waveform diagram illustrating waveform signals when the gain is bright and the gain is increased, and when the gain is dark and the gain is increased. FIG. 14 is a flowchart illustrating the control procedure of the reference voltage VB2 with respect to the dullness of the waveform signal. FIG. 15 is a waveform diagram illustrating another method of automatic gain control for the variable gain amplifier. FIG. 16 is a flowchart illustrating the method of FIG. FIG. 17 is a flow chart illustrating a gain control method for the variable gain amplifier according to the increasing / decreasing tendency of the peak value as still another control flow of the automatic gain control for the variable gain amplifier. FIG. 18 is a waveform diagram showing an example in which the determination threshold value of the high period and the low period is changed according to the dullness of the waveform. FIG. 19 is a flowchart illustrating the determination threshold value changing process by the method of FIG.

1. First, an outline of an embodiment disclosed in the present application will be described. Reference numerals in the drawings referred to with parentheses in the outline description of the embodiments merely exemplify what are included in the concept of the components to which the reference numerals are attached.

[1] <Correction of signal waveform dullness>
An optical receiver (10) receives a light signal (102) for receiving an optical signal and converts it into an electrical signal, and inputs an electrical signal output from the light receiving element, filtering and amplifying the first waveform signal (WV1). The first waveform generation circuit (14) for generating the first waveform signal and the second waveform generation circuit (15) for inputting the first waveform signal output from the first waveform generation circuit and generating the second waveform signal by filtering and amplification And a control circuit (12) for performing bias voltage control and automatic gain control for the first waveform generation circuit and the second waveform generation circuit. When the control circuit determines whether the signal waveform of the second waveform signal (WV2) output from the second waveform generation circuit is undesirably blunted, and determines that the signal waveform is undesirably blunted The bias voltage (BV2) in the second waveform generation circuit is controlled to be higher than the current value, and the gain in the second waveform generation circuit is made smaller than the current value.

  According to this, when the intensity of the optical signal received by the light receiving element is weak, the output of the light receiving element and the first waveform signal are dull, and the second waveform signal is dull so that the amplitudes on the positive side and the negative side are different. In response, the control circuit increases the bias voltage of the second waveform generation circuit and then decreases the gain. As a result, the difference in amplitude between the positive polarity side and the negative polarity side of the second waveform signal is alleviated, and the state where the positive and negative bit widths of the second waveform signal deviate from the specified width can be suppressed. Thus, it is possible to reduce the possibility of erroneous determination of the logical value for the second waveform signal. Therefore, even if the intensity of the optical signal received by the light receiving element is weak, data based on the optical signal can be received correctly.

[2] <Determination method of whether the signal waveform is dull>
In item 1, the control circuit is maintained for a predetermined time shorter than the time of the determination slot when the second waveform signal output from the second waveform generation circuit exceeds the logical value determination threshold. If the predetermined waveform is maintained for a predetermined period of time, it is determined that the waveform of the second waveform signal is undesirably dull. If the predetermined period of time is not maintained, the waveform of the second waveform signal is not correct. It is determined that it is not dull as desired (see FIG. 13).

  According to this, it is possible to reduce determination errors compared to the case where it is determined whether or not the second waveform signal is distorted due to the magnitude of the gain by automatic gain control. That is, the electric signal waveform output from the light receiving element tends to become dull as the optical signal becomes darker, and has a characteristic that it is less dull when it is bright and dull when it is dark. Accordingly, it is possible to grasp the tendency of the dullness depending on the output voltage level of the electric signal output from the light receiving element. When it is bright, the output voltage level of the light receiving element is high, and when it is dark, it is low. According to this tendency, it is possible to relate that the dullness is large when the gain by the automatic gain control is large and the dullness is small when the gain is small. However, there are cases where it is necessary to increase the gain by automatic gain control even when it is bright. This is a case where the output of the light receiving element is saturated. In this case, when the output voltage in the high period when the light source is turned on is saturated, the output voltage in the low period when the light is turned off also approaches the saturation voltage when it becomes brighter. The difference of becomes smaller. In such a case, the gain of automatic gain control must be increased. Therefore, it is necessary to determine whether the gain is bright and the gain is increased, or whether the gain is dark and the gain is increased, and this can be distinguished by the above means. This is because the level of the second waveform signal returns to the bias voltage level after a while after exceeding the logical value determination threshold if the amplification factor is large but not dull.

[3] <Control of reference voltage for voltage waveform in second waveform generation circuit>
In item 2, when the control circuit determines that the waveform of the second waveform signal is not undesirably blunted, the bias voltage (BV2) in the second waveform generation circuit is set as the first voltage, and the second When it is determined that the waveform of the waveform signal is undesirably blunted, the bias voltage in the second waveform generation circuit is set to the ratio of the current gain to the maximum gain of the second waveform generation circuit with respect to the first voltage. The second voltage is increased by a voltage corresponding to (see FIG. 14).

  According to this, in view of the fact that the difference in amplitude between the positive polarity side and the negative polarity side of the second waveform signal correlates with the gain of the automatic gain control, the increase in the second voltage with respect to the first voltage is represented as the current amount. It can be determined with a correlation with the gain, and can contribute to optimization of the second voltage when considering reducing the gain of the second waveform signal.

[4] <Gain control of second waveform generation circuit>
In item 1, when the value of the second waveform signal output from the second waveform generation circuit exceeds a predetermined logical value determination threshold value (S1), the control circuit determines a logical value from the determination timing of the logical value. The value of the second waveform signal is acquired after a predetermined time shorter than the determination slot time elapses (S2, S3). Further, the control circuit determines whether or not the acquired value of the second waveform signal exceeds the first threshold value (S4), and if not, initializes the first counter (S6) and exceeds it. If there is, the first counter is incremented by +1 (S5), and if the incremented count value of the first counter exceeds the first value, the gain of the second waveform generation circuit is decreased (S7, S8), Further, it is determined whether or not the value of the acquired second waveform signal exceeds a second threshold value before the first threshold value (S9), and if it exceeds, a second counter is initialized (S11). When the second threshold value is not reached, the second counter is incremented by +1 (S10), and when the count value of the second counter exceeds the second value, the gain control increases the gain of the second waveform generation circuit. (S12, S13) ).

  According to this, it is possible to relatively easily prevent the automatic gain control from becoming sensitive and degrading the convergence of the control.

[5] <Determination method of signal waveform dullness and reference voltage control for voltage waveform in second waveform generation circuit>
In item 4, the control circuit is maintained for a predetermined time shorter than the time of the determination slot when the second waveform signal output from the second waveform generation circuit exceeds the logical value determination threshold. (S21),
If not maintained for the predetermined time, it is determined that the waveform of the second waveform signal is not dulled undesirably, and the bias voltage of the second waveform generation circuit is set as the first voltage (S22). When the predetermined time is maintained, it is determined that the waveform of the second waveform signal is undesirably blunted, and the bias voltage in the second waveform generation circuit is generated with respect to the first voltage. The second voltage is increased by a voltage corresponding to the ratio of the current gain to the maximum gain of the circuit (S23).

  According to this, it is possible to reduce the determination error as to whether or not the second waveform signal is distorted.

[6] <First waveform generation circuit>
In item 1, the first waveform generation circuit receives the electrical signal output from the light receiving element and emphasizes an edge change portion thereof, and a gain for amplifying the output of the high pass filter A variable first variable gain amplifier (104); a low-pass filter (105) that receives the output of the variable gain amplifier to remove high-frequency component noise and outputs the first waveform signal; the high-pass filter; And a first reference voltage generator (108) for generating a reference voltage for defining a first bias voltage of an output signal waveform of the low-pass filter.

  According to this, the first waveform generation circuit can be configured relatively easily.

[7] <Second waveform generation circuit>
In Item 6, the second waveform generation circuit receives the first waveform signal output from the low-pass filter and emphasizes the edge change portion thereof, and the output of the second high-pass filter A variable gain second variable gain amplifier (107) for amplifying the signal and a second reference for generating a reference voltage for defining a second bias voltage of the output signal waveform of the second high-pass filter and the second variable gain amplifier A voltage generator (109).

  According to this, the second waveform generation circuit can be configured relatively easily.

[8] <Gain control of second waveform generation circuit using average of peak values>
In item 1, when the value of the second waveform signal output from the second waveform generation circuit exceeds the first logical value determination threshold, the control circuit determines the logical value determination from the determination timing of the logical value. The value of the second waveform signal is acquired after a predetermined time shorter than the slot time has elapsed (S33), and the value acquired this time and the latest one or more times of the second acquired in the past in the same manner. An average value with the value of the waveform signal is calculated (S34), and when the average value exceeds the first threshold, the gain of the second waveform generation circuit is lowered (S35, S36), and the average value is If the second threshold value before the first threshold value is not exceeded, the gain of the second waveform generation circuit is increased (S37, S38), and gain control is performed.

  According to this, it is possible to relatively easily prevent the automatic gain control from becoming sensitive and degrading the convergence of the control.

[9] <Gain control of second waveform generation circuit according to increasing / decreasing peak value>
In item 1, when the value of the second waveform signal output from the second waveform generation circuit exceeds a predetermined logical value determination threshold value (S41), the control circuit determines a logical value from the determination timing of the logical value. The value of the second waveform signal is acquired after a certain time shorter than the time of the determination slot elapses (S42, S43), and the value of the acquired second waveform signal is acquired in the same manner as the previous time. The magnitude relationship with the value of the second waveform signal is discriminated (S44). When the value of the second waveform signal tends to increase, the first counter is operated for one step and the count value of the second counter is initialized. (S45, S46) When the value of the second waveform signal tends to decrease, the second counter is operated for one step and the count value of the first counter is initialized (S47, S48). When the count value exceeds the first value, the gain of the second waveform generation circuit is decreased (S49, S50), and when the count value of the second counter exceeds the second value, the gain of the second waveform generation circuit (S51, S52) Gain control is performed.

  According to this, it is possible to relatively easily prevent the automatic gain control from becoming sensitive and degrading the convergence of the control.

[10] <Change logical value judgment threshold>
The optical receiver (10) receives a light signal and converts it into an electrical signal, and generates a waveform signal by filtering and amplifying the electrical signal output from the light receiving element. A control circuit for performing bias voltage control and automatic gain control of the circuit (11) and the waveform generation circuit, and for performing control for determining a logical value of the waveform signal supplied from the waveform generation circuit in a predetermined determination slot unit (12) The control circuit determines whether or not the signal waveform of the waveform signal output from the waveform generation circuit is undesirably blunted (S61), and when not undesirably blunted, is higher than the determination full-scale voltage The first determination criterion on the voltage side is the first threshold voltage, and the second determination criterion on the lower voltage side is the second threshold voltage (S62). The third judgment criterion on the higher voltage side than the judgment full-scale voltage is lower than the first threshold voltage by a voltage obtained by multiplying the current gain of the waveform generation circuit by a predetermined coefficient. The fourth determination criterion on the voltage side lower than the determination full-scale voltage is set to a voltage lower than the third determination criterion voltage by an intermediate voltage between the first threshold voltage and the second threshold voltage. (S63).

  According to this, when the intensity of the optical signal received by the light receiving element is weak, even if the waveform signal is blunted such that the amplitude on the positive polarity side is different from that on the negative polarity side, the control circuit responds to the waveform. Change the signal threshold. The amount of change in the determination threshold depends on the current gain of the waveform generation circuit in view of the fact that the difference in amplitude between the positive polarity side and the negative polarity side of the waveform signal correlates with the gain of automatic gain control in the waveform generation circuit. Since the corresponding voltage is set, it is possible to contribute to suppression of an excessive change of the determination threshold, in other words, optimization of the changed determination threshold.

[11] <Control of gain for waveform generation circuit>
In item 10, when the value of the waveform signal output from the waveform generation circuit exceeds a predetermined logical value determination threshold, the control circuit starts from the determination timing of the logical value based on the time of the determination slot of the logical value determination. The waveform signal value is acquired after a short period of time elapses, and it is determined whether or not the acquired waveform signal value exceeds a first threshold value. If it does not exceed, the first counter is initialized. If it exceeds, the first counter is incremented by +1. If the incremented count value of the first counter exceeds the first value, the waveform generating circuit Reduce gain. Further, it is determined whether or not the acquired value of the waveform signal exceeds a second threshold value before the first threshold value, and if it exceeds, the second counter is initialized and the second threshold value is not reached. In this case, the second counter is incremented by +1, and when the count value of the second counter exceeds the second value, gain control is performed to increase the gain of the waveform generation circuit (see FIG. 11).

  According to this, it is possible to relatively easily prevent the automatic gain control from becoming sensitive and degrading the convergence of the control.

[12] <Correction of signal waveform dullness>
The optical receiver (10) includes a light receiving element (102) that receives an optical signal and converts it into an electrical signal, a filter (106) that inputs a waveform signal generated based on an output of the light receiving element, and the filter A voltage generation circuit (109) for forming a reference voltage for defining a bias voltage of an output waveform output from the output, a variable gain amplifier (107) with variable gain for amplifying the filter output waveform output from the filter, And a control circuit (12) for performing control of the reference voltage and automatic gain control of the variable gain amplifier based on the output of the variable gain amplifier. The control circuit performs control to increase the bias voltage of the filter output waveform by the reference voltage and to make the gain of the variable gain amplifier smaller than the present one in response to an undesired dullness of the output waveform of the variable gain amplifier.

  According to this, even when the waveform signal is weak such that the amplitude on the positive polarity side and the negative polarity side is different when the intensity of the optical signal received by the light receiving element is weak, the control circuit responds accordingly, The gain is reduced after the bias voltage of the waveform generation circuit is boosted. As a result, the difference in amplitude between the positive polarity side and the negative polarity side of the waveform signal is alleviated, and the state where the positive and negative bit widths of the waveform signal deviate from the specified width can be suppressed. It is possible to reduce the possibility of erroneous determination of logical values. Therefore, even if the intensity of the optical signal received by the light receiving element is weak, data based on the optical signal can be received correctly.

[13] <Determination method of whether the signal waveform is dull>
In item 12, the control circuit outputs the output of the filter when the output of the variable gain amplifier exceeds the logical value determination threshold and the state is maintained until a predetermined time shorter than the time of the determination slot elapses. It is determined that the waveform has an undesirable dullness (see FIG. 13).

  According to this, as in the case of item 2, it is possible to reduce determination errors as compared with the case where it is determined whether or not the waveform signal is distorted due to the magnitude of the gain by automatic gain control.

[14] <Control of reference voltage>
In item 12, when the control circuit determines that there is no undesired blunting in the output waveform of the filter, the bias voltage is set to a half of the power supply voltage, and there is an undesired blunting in the filter output waveform. Is determined, the bias voltage is set to a voltage that is higher than the half of the power supply voltage by an amount corresponding to the ratio of the current gain to the maximum gain of the variable gain amplifier (see FIG. 14).

  According to this, in view of the fact that the difference in amplitude between the positive polarity side and the negative polarity side of the waveform signal correlates with the gain of automatic gain control, the bias voltage when there is a dullness with respect to the bias voltage when there is no dullness Can be determined in correlation with the current gain, and can contribute to optimization of the bias voltage when there is a dullness when considering reducing the gain of the waveform signal.

[15] <Automatic gain control of variable gain amplifier>
In item 12, the control circuit determines a logical value for the output of the variable gain amplifier, waits for a certain period of time shorter than the time of the determination slot from the logical value determination timing, and the determined logical value is a logical value. When the determination threshold is exceeded, it is further determined whether or not the output of the variable gain amplifier exceeds the first threshold. If not, the first counter is initialized, and if it exceeds, the first counter is initialized. The counter is incremented by +1. When the incremented count value of the first counter exceeds the first value, the gain of the variable gain amplifier is lowered. It is further determined whether or not the output of the variable gain amplifier exceeds a second threshold value before the first threshold value. If the output value exceeds the second threshold value, the second counter is initialized. The second counter is incremented by +1, and when the count value of the second counter exceeds the second value, gain control is performed to increase the gain of the variable gain amplifier (see FIG. 11).

  According to this, it is possible to relatively easily prevent the automatic gain control from becoming sensitive and degrading the convergence of the control.

[16] <Optical receiver that has an acceleration sensor and receives position information as an optical signal>
The optical receiver (10) receives a light signal and converts it into an electrical signal, and generates a waveform signal by filtering and amplifying the electrical signal output from the light receiving element. A circuit (11), a control circuit (12) for processing a waveform signal supplied from the waveform generation circuit, an acceleration sensor (13), and a power switch (101) for selecting supply of power to the light receiving element And having. The control circuit controls the power switch to be in an ON state only while sensing movement of the optical receiver based on the output of the acceleration sensor in a mode in which position information is received by the optical signal.

  According to this, since the light receiving element is activated only when the received position information needs to be updated, the power consumption when the optical receiver is not moving can be greatly reduced.

2. Details of Embodiments Embodiments will be further described in detail.

<Overall configuration of optical receiver>
FIG. 1 shows an example of an optical receiver. The optical receiver 10 shown in FIG. 1 is provided in the mobile terminal 1 such as a mobile phone or a smartphone, and is used for visible light communication that receives an optical signal from the optical transmitter 20 illustrated in FIG. The In this visible light communication, transmission data to be transmitted on the transmission side is modulated by the modulation circuit 203, and the LED drive circuit 202 drives the LED 201 in accordance with the modulated signal, whereby an optical signal is transmitted. For example, as illustrated in FIG. 3, when the light transmitter 20 is built in a large number of LED luminaires 30 arranged indoors such as an underground shopping center or a department store, the LED 201 is an LED that is the illumination light source.

  The optical receiver 10 receives the optical signal from the LED 201 by the light receiving element 102, converts it into an electrical signal, and demodulates it to recognize it as original data.

  The optical receiver 10 includes, for example, a PIN photodiode or a PN photodiode as the light receiving element 102. The cathode of the light receiving element 102 is provided with a power switch 101 for applying a power supply voltage Vdd. The anode of the light receiving element 102 receives an electric signal output from the light receiving element 102 and generates a waveform signal by filtering and amplification. A control circuit 12 is provided as a circuit that is connected to the waveform generation circuit 11 and processes a waveform signal output from the waveform generation circuit 11. The output of the acceleration sensor 13 is given to the control circuit 12, and the control circuit 12 is connected to a processor unit (not shown) that performs mobile communication processing and application processing built in the mobile terminal 10.

  The waveform generation circuit 11 receives the electrical signal output from the light receiving element 102, generates the first waveform signal WV1 by filtering and amplification, and is output from the first waveform generation circuit 14. A second waveform generation circuit 15 that receives the first waveform signal WV1, generates a second waveform signal WV2 by filtering and amplification, and supplies the second waveform signal WV2 to the control circuit 12 is provided.

  The first waveform generation circuit 14 receives, for example, an electric signal output from the light receiving element 102 and emphasizes an edge change portion, and a variable gain for amplifying the output of the first high pass filter 103. The first variable gain amplifier 104, the low-pass filter 105 that receives the output of the first variable gain amplifier 104, removes high-frequency component noise, and outputs the first waveform signal WV1, the first high-pass filter, the first And a first reference voltage generator 108 for generating a first reference voltage BV1 as a first bias voltage of the output signal waveform of the variable gain amplifier and the low-pass filter.

  The second waveform generation circuit 15 receives, for example, the first waveform signal WV1 output from the low-pass filter 105 and amplifies the output of the second high-pass filter 106 that emphasizes the edge change portion and the second high-pass filter 106. A variable gain second variable gain amplifier 107; a second reference voltage generator 109 that generates a second reference voltage BV2 as a second bias voltage of the output signal waveforms of the second high-pass filter 106 and the second variable gain amplifier 107; Comprising.

  The first high-pass filter 103 is not particularly limited, but can be configured by a CR filter using a capacitor 40 and resistors 41 and 42 as illustrated in FIG. The output of the first high pass filter 103 has a signal level centered on the bias voltage. Here, when the bias voltage is applied, the first reference voltage VB1 is set to ½ of the power supply voltage Vdd.

  Although not particularly illustrated, the second high-pass filter 106 is similarly configured, but the bias voltage is set to the second reference voltage VB2. The high pass filters 103 and 106 may be configured using operational amplifiers.

  The first variable gain amplifier 104 is not particularly limited, but can be configured using a non-inverting amplifier circuit as illustrated in FIG. That is, the input resistor 51 and the feedback resistor 52 of the operational amplifier 50 are variable resistors, and the reference voltage BV1 is input to the inverting input terminal (−) via the input resistor 51, and the signal from the previous stage is input to the non-inverting input terminal (+). Configured as follows. The resistance values of the input resistor 51 and the feedback resistor 52 are determined according to the register values set in the register 53 by the control circuit 12. The output of the first variable gain amplifier 104 causes a signal change of (R1 + R2) / 2 times the input voltage from the non-inverting input terminal (+), and the change is centered on the first reference voltage BV1 which is a bias voltage. Voltage. R1 is the resistance value of the feedback resistor 52, and R2 is the resistance value of the input resistor 51.

  Although not shown, the second variable gain amplifier 107 receives the second reference voltage VB2 as a bias voltage, and is configured in the same manner as the first variable gain amplifier 104. Both the first variable gain amplifier 104 and the second variable gain amplifier 107 determine the gain according to the set value of the register 53. GD1 is gain control data set in the register 53 of the first variable gain amplifier 104, and GD2 is gain control data set in the register 53 of the second variable gain amplifier 107.

  Although not particularly limited, the first reference voltage generator 108 is generated using a digital-analog converter (DAC) 64 that converts a digital signal into an analog signal as illustrated in FIG. The power of the DAC 64 is a ground voltage GND supplied through the buffer amplifier 63 and a power supply voltage supplied through the buffer amplifier 62 by dividing the power supply voltage Vdd by the resistors 60 and 61. The output voltage of the DAC 64 is determined according to the register value set in the register 65 by the control circuit 12. The output voltage of the DAC 64 is adjusted (trimmed) by the negative feedback amplifier 66, thereby generating a first reference voltage VB1 that is used as a bias voltage. Although not shown, the second reference voltage generator 109 is similarly configured. Although not particularly limited, here, both the first reference voltage generator 108 and the first reference voltage generator 109 determine the first reference voltage BV1 and the second reference voltage BV2 according to the set value of the register 65. However, the first reference voltage generator 108 is set to a predetermined register value in the power-on reset process, and the second reference voltage generator 109 is set to have a dull waveform in the optical communication reception waveform after the power-on reset process. It will be set variably according to. VD1 is voltage control data set in the register 65 of the first reference voltage generator 108, and VD2 is voltage control data set in the register 65 of the second reference voltage generator 109.

  For example, as illustrated in FIG. 1, the control circuit 12 includes a signal control unit 120, a power supply control unit 121, a demodulation unit 122, and an analog-digital converter (ADC) that converts an analog signal into a digital signal. The signal control unit 120 and the demodulation unit 122 are each realized by dedicated hardware, or configured by a CPU that performs program processing, a program memory that holds a program executed by the CPU, and a RAM that is used as a work area of the CPU. Is possible.

  The ADC 123 converts the waveform signal WV2 into digital data, and supplies the converted data to the signal control unit 120 and the demodulation unit 122. Although not shown in particular, when both the demodulating unit 122 and the signal control unit 120 compare the digital data of the waveform signal WV2 with the determination threshold value and need the determination result of the high period or the low period, either one is required. It is sufficient to pass the result of determination in (1) to the other.

  The demodulator 122 determines the logical value of the waveform signal WV2 based on the data supplied from the ADC 123 and reproduces the optical communication signal.

  The signal control unit 120 performs automatic gain control on the variable gain amplifiers 104 and 107 by generating gain control data GD1 and GD2. In addition, the signal control unit 120 performs bias voltage control on the filters 103, 105, and 106 and the variable gain amplifiers 104 and 107 by generating voltage control data VD1 and VD2. In particular, the bias voltage control and the automatic gain control by the control circuit 120 take into account the case where the electrical signal output from the light receiving element 102 is dull when the optical signal received by the light receiving element 102 is dark. Hereinafter, the contents will be described in detail in consideration thereof.

<Signal dullness when the light signal is dark>
FIG. 7 illustrates the electric signal waveform output from the light receiving element and the signal waveform output from the waveform generation circuit and input to the ADC in comparison with the case where the signal is dull. The cause of the dull output waveform of the light receiving element when the optical signal is dark is related to the amount of electric signal current that can be output from the light receiving element 102 and the capacitance of the capacitor 40 of the first high-pass filter 103 (see FIG. 4). In the dark, the amount of current that can be output from the light receiving element 102 is reduced, and the time until the capacitor 40 is charged is increased. Therefore, the rise time of the electric signal is increased. On the other hand, since the fall is determined by the discharge time of the capacitor 40, it does not relate to the brightness of the reception environment. Furthermore, if the discharge starts before the capacitor 40 is fully charged, the amplitude of the output waveform of the first high-pass filter 103 differs between positive polarity (upward convex) and negative polarity (downward convex). become. Such a difference appears as a dullness in the output waveform from the waveform generation circuit 11, that is, the input waveform of the ADC 123.

  In FIG. 8, the high period and the low period for the logical value determination for the input waveform of the ADC 123 are compared with and without the dullness. For example, as a method for determining the high period and the low period of the electric signal, there is a method of measuring a difference between when the signal voltage exceeds the threshold A and when the signal voltage falls below the threshold B. If the positive side is different from the lower side (negative side with respect to the center), the correct period cannot be measured. As shown in FIG. 8, when the waveform is dull, the high period is short and the low period is long. The determination of the thresholds A and B and the measurement of the high period and the low period are performed by the demodulator 122 based on the conversion result of the ADC 123.

  As a standard for communication using visible light, for example, there is EITA CP-1223 (visible light beacon system). As illustrated in FIG. 9, a fixed time defined as a symbol time is set to 4 slots by the 4PPM system. In this example, a pulse of one slot time is allowed in one symbol time, and optical communication is performed using 2-bit information assigned according to the slot in which the pulse exists. If the signal waveform is dull as described above, an error may occur in the measurement time of the high period and the low period in the demodulator 122 with respect to the slot time (104 μs) defined in the standard.

<Correction of signal waveform dullness>
As a means for dealing with signal dullness, signal waveform dullness is corrected. FIG. 10 illustrates the principle of correction. The control circuit 120 determines whether or not the signal waveform of the waveform signal WV2 output from the second waveform generation circuit 15 is undesirably blunted. Control is performed such that the reference voltage VB2 of the second high-pass filter 106 and the second variable gain amplifier 107 in the generation circuit 15 is made higher than the present, and the gain of the second variable gain amplifier 107 in the second waveform generation circuit 15 is made smaller than the present. Do. By making the reference voltage VB2 higher than the current value, the positive polarity amplitude and the negative polarity amplitude are made substantially the same, and then the gain is made smaller than the current value so that the signal waveform falls within the dynamic range of the ADC 123. Become. As a result, as in the case where the waveform is not blunt, the high period and the low period can be correctly recognized. Even if the optical signal becomes dark and the output signal of the light receiving element 102 becomes blunt, the received signal in the demodulator 122 is received. This makes it difficult to make an error in the determination. Such control is performed by the signal control unit 120 based on the conversion data from the ADC 123. In FIG. 10, Ht means a correct high period, Lt means a correct low period, Hf means an erroneous high period, and Lf means an erroneous low period.

<Automatic gain control>
The correction of the dullness of the signal waveform is performed as necessary while automatic gain control is being performed on the first variable gain amplifier 104 and the second variable gain amplifier 107. First, a control method of automatic gain control will be described.

  FIG. 11 illustrates an automatic gain control method. The ADC 13 sequentially converts the input waveform signal WV2 from an analog signal to a digital signal to obtain A / D conversion data. The demodulator 122 compares the A / D conversion data with the thresholds A and B in FIG. 12, measures the high period and the low period, and performs decoding according to the 4PPM system. The signal control unit 120 performs automatic gain control and bias control by comparing the A / D conversion data with, for example, the threshold values A, C, and D in FIG.

  The signal control unit 120 determines whether or not the A / D conversion data exceeds the threshold A (S1), and enters the automatic gain control flow when it exceeds. First, after 10 μs elapses after exceeding the threshold A (S2), A / D conversion data is acquired (S3), and it is determined whether or not this exceeds the threshold D (S4). If it has exceeded, the overcounter (over) is incremented by +1 (S5), and if not, the overcounter (over) is initialized to 0 (S6). It is determined whether or not the value of the overcounter (over) exceeds the number of times A (S7), and the gain is reduced only when it exceeds (S8). Next, it is determined whether or not the A / D conversion data acquired in step 3 is smaller than a threshold value C (S9). If it is smaller, the undercounter (under) is incremented by +1 (S10). If it is not smaller, the undercounter (under) is initialized to 0 (S11). It is determined whether the value of the under counter (under) exceeds the number of times B (S12), and the gain is increased only when it exceeds (S13). By this control, automatic gain control is performed so that the peak of the waveform signal WV2 is between the threshold value C and the threshold value D. Such gain control is performed by the signal control unit 120, and is given to the variable gain amplifiers 104 and 107 by the control signals GD1 and GD2. Note that 10 μs waiting for the passage in step S2 exemplifies the time taken to reach the waveform peak from the threshold A.

  Here, since the state where the amplitude on the positive polarity side and the amplitude on the negative polarity side are made equal around the bias voltage is considered as the normal waveform signal WV2, only the positive polarity side is viewed. According to the automatic gain control, the automatic gain control can be performed so that the peak point of the waveform converges between the threshold value C and the threshold value D. In particular, since the gains of the variable gain amplifiers 104 and 107 are changed when the peak point of the waveform continuously exceeds the threshold value D several times, or when the peak point of the waveform falls below the threshold value C several times in succession, the gain is sensitively increased. It can be relatively easily suppressed that the convergence of the control is deteriorated due to the change. Also, since the gain control processing flow is entered only when the waveform signal exceeds the threshold A, current consumption when the threshold A is not exceeded can be suppressed. Step S1 can be used as a subroutine or interrupt generation determination condition, and processing after satisfying the condition can be realized as subroutine processing or interrupt processing.

  In the description of the automatic gain control, the case where the threshold value A is exceeded has been described. However, the present invention does not prevent the same processing even when the value of the waveform signal falls below the threshold value B. If processing is performed while paying attention to both thresholds A and B, the accuracy of gain control increases, but power consumption increases. As described with reference to FIG. 7, when considering that the amplitude of the input waveform of the ADC 123 when the waveform is not blunted converges symmetrically around the center, pay attention to only one threshold A side on the positive positive side. Even if automatic gain control is performed, it is considered that there is substantially no problem.

<Determination method of whether the signal waveform is dull>
When the signal waveform is blunt, how much the reference voltage VB2 should be raised depends on how blunt the output signal of the light receiving element 102 is. Since it has a characteristic that it is difficult to dull when it is bright and is duller when it is dark, if it is determined by the output voltage level of the light reception block 102 whether or not there is a dullness, the output voltage level of the light receiving element 102 is high when it is bright, Since it becomes low when it is dark, the reference voltage VB2 is controlled in accordance with the gain of the second variable gain amplifier 107. However, the gain of the variable gain amplifier 107 may need to be increased even when it is bright. This is a case where the output of the light receiving element 102 is saturated. In other words, when the output voltage in the high period is saturated, the output voltage in the low period approaches the saturation voltage as the brightness further increases, so the difference between the output voltage in the high period and the output voltage in the low period becomes small. In such a case, the output voltage of the high pass filter 103 becomes small and the gain of the variable gain amplifier 107 needs to be increased. Therefore, is it bright and increasing the gain (whether the gain of the variable gain amplifier 107 is increased due to the output saturation of the light receiving element 102) or is it dark and increasing the gain (the output signal of the light receiving element 102)? It is necessary to determine whether the gain of the variable gain amplifier 107 is increased due to dullness, and the reference voltage BV2 needs to be increased only when it is dark.

  The waveforms of the waveform WV2 when the gain is bright and the gain is increased and when the gain is dark and the gain is increased are different as illustrated in FIG. By paying attention to this difference, when the signal level after 50 μs after exceeding the threshold A exceeds a predetermined voltage, it is determined that it is dark, that is, the waveform of the light receiving element 102 is dull, and is lower. In this case, it can be determined that the waveform is bright, that is, the waveform of the light receiving element 102 is not dull. The time of 50 μs is a value that is exemplarily determined to distinguish between a bright case and a dark case in consideration of the relationship with the slot time (104 μs) shown in FIG. 9 as an example, and is particularly limited. is not.

<Control of reference voltage VB2 with respect to signal waveform dullness>
FIG. 14 illustrates a control procedure of the reference voltage VB2 with respect to the dullness of the waveform signal WV2. If the signal control unit 120 determines that the waveform of the second waveform signal WV2 is not undesirably dull (S21), the signal control unit 120 sets the second reference voltage BV2 that is a bias voltage in the second waveform generation circuit to the first voltage, for example, The voltage is half the power supply voltage Vdd (S22). When it is determined that the waveform of the second waveform signal WV2 is undesirably blunted, the second reference voltage BV2 that is the bias voltage in the second waveform generation circuit is set to the second voltage with respect to the first voltage (Vdd / 2). The second voltage is increased by a voltage corresponding to the ratio of the current gain to the maximum gain of the variable gain amplifier 107 (S23). For example, if the current gain for the maximum gain 256 of the second variable gain amplifier 107 is n and α is a suitable coefficient, the second voltage is
Second voltage = Vdd × {128+ (n × α)} / 256,
As described above, the voltage is increased by a voltage corresponding to the ratio of the current gain to the maximum gain of the second variable gain amplifier 107 with the first voltage (Vdd / 2) as a reference. The control of the second voltage with respect to the second reference voltage BV2 is performed by the signal control unit 120 based on the control signal VD2.

  According to the control of the reference voltage VB2, in view of the fact that the degree of amplitude difference between the positive polarity side and the negative polarity side of the second waveform signal WV2 correlates with the gain of the automatic gain control for the variable gain amplifier 107, the first The amount of increase in the second voltage relative to the voltage can be determined in correlation with the current gain, and when considering reducing the gain of the second waveform signal WV2, it can contribute to optimization of the second voltage. .

<Process to correct signal waveform dullness>
When the signal control circuit 120 detects the dullness of the signal waveform WV2 by the method described based on FIG. 13 or the like, the voltage level of the signal waveform WV2 is increased by increasing the second threshold voltage VB2 by the method described in step S22 of FIG. Is lifted (see FIG. 10). When the signal waveform WV2 is raised by this, the gain is reduced by the automatic gain control so that the peak value of the waveform converges between the threshold value C and the threshold value D illustrated in FIG. 10, and as a result, illustrated in FIG. As a result, the waveform signal WV2 in which the distortion is corrected is obtained. However, when the process of decreasing the gain after increasing the threshold voltage is performed by the automatic gain control of FIG. 11, it is necessary to satisfy the condition of step S7, and therefore the response of the process of reducing the gain may be delayed. There is. In order to avoid such a possibility, when the threshold voltage VB2 is manipulated as described above, step S8 for lowering the gain may be executed immediately after the operation of the threshold voltage VB2.

  By correcting the dullness of the signal waveform as described above, the difference in amplitude between the positive polarity side and the negative polarity side of the second waveform signal WV2 can be alleviated, and the positive and negative bit widths of the second waveform signal WV2 can be reduced. Can be prevented from deviating from the specified width, and the possibility of erroneous determination of the logical value for the second waveform signal WV2 can be reduced. Therefore, the optical receiver 10 can correctly receive data based on the optical signal even if the intensity of the optical signal received by the light receiving element 102 is weak. For example, what can be received only up to 36 lux as an experimental result can be received up to 26 lux by correcting the waveform. In other words, reception is possible even at a brightness reduced by 27% from 36 lux.

<Gain control of variable gain amplifier using average peak value>
FIG. 15 illustrates another automatic gain control method for the variable gain amplifiers 104 and 107 as a waveform diagram, and FIG. 16 illustrates this method as a control flow by the signal control unit.

  The signal control unit 120 determines whether or not the A / D conversion data exceeds the threshold A (S31), and enters the automatic gain control flow when it exceeds. First, for example, after 10 μs has passed since the threshold A was exceeded (S32), A / D conversion data is acquired (S33). For example, as shown in FIG. The average value of the acquired data is calculated (S34). Next, it is determined whether or not the average value exceeds the threshold D (S35), and if it exceeds, the gain of the second variable gain amplifier 107 is decreased (S36). Further, it is determined whether or not the average value has reached the threshold value C (S37), and if not, the gain of the second variable gain amplifier 107 is increased (S38).

  By this control, automatic gain control is performed so that the peak of the waveform signal WV2 is between the threshold value C and the threshold value D. Such gain control is performed by the signal control unit 120, and is given to the variable gain amplifiers 104 and 107 by the control signals GD1 and GD2. Also with this method, it is possible to relatively easily prevent the automatic gain control from becoming too sensitive and degrading the convergence of the control as described above.

<Gain control of variable gain amplifier according to increasing / decreasing peak value>
FIG. 17 illustrates still another control flow of automatic gain control for the variable gain amplifiers 104 and 107.

The signal control unit 120 determines whether or not the A / D conversion data exceeds the threshold A (S41), and enters the automatic gain control flow when it exceeds. First, after 10 μs elapses after the threshold A is exceeded (S42), A / D conversion data is acquired (S43),
The magnitude relationship between the A / D conversion data (current waveform peak value) acquired this time and the A / D conversion data (previous waveform peak value) acquired similarly to the previous time is determined (S44), and the waveform peak value of the waveform signal is determined. Is increasing, the first counter (up) is counted by one step (S45) and the count value of the second counter (down) is initialized (S46). When the value of the waveform signal tends to decrease, the second counter (down) is counted by one step (S47) and the count value of the first counter (up) is initialized (S48). When the count value of the first counter (up) exceeds the number of times A as the first value, the gains of the variable gain amplifiers 104 and 107 are lowered (S49, S50), and the count value of the second counter (down) is the first value. When the number of times B as a binary value is exceeded, gain control is performed to increase the gain of the variable gain amplifiers 104 and 107 (S51, S52). When the count value of the first counter (up) exceeds A, the peak value of the waveform signal WV2 that continuously increases corresponds to the state that exceeds the threshold value D in FIG. Further, the state where the count value of the second counter (down) exceeds B corresponds to the state where the peak value of the waveform signal WV2 continuously decreasing is lower than the threshold value C in FIG.

  By this control, automatic gain control is performed so that the peak of the waveform signal WV2 is between the threshold value C and the threshold value D. Such gain control is performed by the signal control unit 120, and is given to the variable gain amplifiers 104 and 107 by the control signals GD1 and GD2. Also with this method, it is possible to relatively easily prevent the automatic gain control from becoming too sensitive and degrading the convergence of the control as described above.

<Correction by changing the threshold value of the logical value for waveform dullness>
It is not limited to correcting the waveform signal for signal dullness when the optical signal is dark, and the high period and low period determination thresholds performed by the signal control unit 120 or the demodulation unit 122 are changed according to the waveform dullness. It is possible to cope with this problem, and a countermeasure method based on this will be described based on the waveform diagram of FIG. 18 and the control flow of FIG.

  For example, when the signal control unit 120 controls the determination threshold, as illustrated in FIG. 18, when the waveform signal WV2 is not blunt, the determination is performed to determine the low period and the high period of the waveform signal WV2. The determination threshold value on the higher voltage side with respect to the full scale voltage Vdd is the threshold value A, and the determination threshold value on the lower voltage side is the threshold value B. When the waveform signal WV2 becomes dull, the threshold A is changed to A 'and the threshold B is changed to B' so that the same low period and high period as when the waveform signal WV2 is not dull are obtained.

  For the determination threshold value setting, as illustrated in the flowchart of FIG. 19, first, it is determined whether the waveform signal WV2 is blunt (S61). For the determination, the method described in FIG. 13 may be used.

  If it is not dull, assuming that the determination full-scale voltage is Vdd, the center is Vdd × 0.5, the threshold A that is the determination criterion on the high voltage side is vdd × 0.75, and the threshold B that is the determination criterion on the low voltage side Is set to Vdd × 0.25 (S62).

When it is dull, the threshold A ′, which is a determination criterion on the higher voltage side with respect to the determination full-scale voltage Vdd, is set to the voltage obtained by multiplying the current gain of the wave second variable gain amplifier 107 by a predetermined coefficient β. The voltage is lower than the threshold A (S62). Further, the threshold value B ′, which is a determination criterion on the lower voltage side with respect to the determination full-scale voltage Vdd, is lower than the threshold value A ′ by an intermediate voltage (Vdd × 0.5) between the threshold value A and the threshold value B. Voltage. (S62). The center voltage (center ′) at this time is the average voltage of the threshold voltages A ′ and B ′. (S62). Each formula is
Threshold A ′ = Vdd × 0.75−gain of variable gain amplifier 107 × β,
Center '= (Threshold A' + Threshold B ') / 2,
Threshold B ′ = threshold A′−Vdd × 0.5,
It is.

  According to this, when the intensity of the optical signal received by the light receiving element 102 is weak, the control circuit 12 responds to the waveform signal WV2 even if the waveform signal WV2 is blunted such that the positive side and the negative side have different amplitudes. Thus, the determination threshold value of the waveform signal WV2 is changed. In view of the fact that the difference in amplitude between the positive polarity side and the negative polarity side of the waveform signal WV2 correlates with the gain of automatic gain control in the second variable gain amplifier 107, the amount of change in the determination threshold is changed. Therefore, it is possible to contribute to the suppression of an excessive change of the determination threshold value, in other words, the optimization of the changed determination threshold value.

  The method of correcting the waveform signal and the method of changing the determination threshold are difficult. The method for changing the determination threshold depends on how much the determination threshold is changed. If a suitable degree of change was obtained, it was possible to obtain an experimental result that what can be received only up to 36 lux can be received up to 16 lux. It seems that many experiments are required to obtain such a suitable degree of change. Even when the waveform signal is corrected, it is necessary to optimize the increase in the bias voltage (threshold voltage) and the gain reduction range of the variable gain amplifier, but the adjustment target is the bias voltage (threshold voltage) and the variable gain amplifier. Since both are gains, the adjustment cost is increased, and it is considered that optimization is relatively easy.

<Optical receiver that has an acceleration sensor and receives position information as an optical signal>
As illustrated in FIG. 1, the optical receiver 10 includes an acceleration sensor 13 and a power switch 101 that selects supply of power to the light receiving element 102. The control circuit 12 controls the power switch 101 to be in an on state only while sensing the movement of the optical receiver 10 based on the output of the acceleration sensor 13 in the mode of receiving position information as an optical signal. For example, as described with reference to FIG. 3, the optical transmitter 20 built in a large number of LED lighting fixtures 30 arranged indoors such as an underground shopping center or a department store outputs position information on the location of the lighting fixture 30. The position information includes information such as latitude, longitude, and the number of floors (height) of the building. It becomes possible to grasp the current position in an indoor environment where GPS (Global Positioning System) cannot be used. At this time, since the optical signal can be received by the light receiving element 102 only when it is moving, the light receiving element 102 is activated only when the received position information needs to be updated. Power consumption when 10 is not moving can be greatly reduced.

  Even when position information is received as an optical signal in accordance with the setting of the mode register, it is naturally possible to select an operation mode in which the power switch is turned on regardless of the detection state of the acceleration sensor.

  It goes without saying that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.

  For example, the optical receiver is not limited to the case where the optical receiver is applied to the portable terminal 1, and can be widely applied to loads such as other electronic devices and vehicles.

  The specific configuration of the waveform generation circuit 11 is not limited to the example of FIG. 1 and can be changed as appropriate. For example, the output of the light receiving element may be received by a high pass filter, the output may be variable gain amplified, the amplified output may be received by a low pass filter, and the output may be amplified by a variable gain amplifier to generate a waveform signal. In that case, it is necessary to manipulate the bias voltage of the low-pass filter. Various other functional modifications are possible.

DESCRIPTION OF SYMBOLS 10 Optical receiver 1 Portable terminal 11 Waveform generation circuit 12 Control circuit 13 Acceleration sensor 14 1st waveform generation circuit 15 2nd waveform generation circuit WV1 1st waveform signal WV2 2nd waveform signal 20 Optical transmitter 30 LED lighting fixture 40 Capacity | capacitance 41 42 resistance 50 operational amplifier 51 input resistance 52 feedback resistance 53 register 53
60, 61 Resistor 62 Buffer amplifier 63 Buffer amplifier 64 Digital-analog converter (DAC)
65 register 66 negative feedback amplifier 101 power switch 102 light receiving element 103 first high pass filter 104 first variable gain amplifier 105 low pass filter 106 second high pass filter 107 second variable gain amplifier 108 first reference voltage generator 109 second reference voltage generation BV1 first reference voltage BV2 second reference voltage 120 signal control unit 121 power supply control unit 122 demodulation unit GD1, GD2 gain control data 201 LED
202 LED drive circuit 203 Modulation circuit

Claims (3)

A light receiving element that receives an optical signal and converts it into an electrical signal;
A waveform generation circuit that inputs an electrical signal output from the light receiving element and generates a waveform signal by filtering and amplification; and
A control circuit that performs bias voltage control and automatic gain control of the waveform generation circuit, and performs control for determining a logical value of a waveform signal supplied from the waveform generation circuit in a predetermined determination slot unit,
The control circuit determines whether the signal waveform of the waveform signal output from the waveform generation circuit is undesirably blunted, and when not undesirably blunted, the control circuit has a higher voltage side than the determination full-scale voltage. The first criterion is the first threshold voltage, the second criterion on the lower voltage side is the second threshold voltage,
The third judgment criterion on the higher voltage side than the judgment full-scale voltage is lower than the first threshold voltage by a voltage obtained by multiplying the current gain of the waveform generation circuit by a predetermined coefficient. The fourth determination criterion on the voltage side lower than the determination full-scale voltage is set to a voltage lower than the third determination criterion voltage by an intermediate voltage between the first threshold voltage and the second threshold voltage. , Optical receiver. 2. The control circuit according to claim 1, wherein when the value of the waveform signal output from the waveform generation circuit exceeds a predetermined logical value determination threshold value, the control circuit determines the time of the determination slot for the logical value determination from the determination timing of the logical value. Waits for a certain period of time to elapse to obtain the value of the waveform signal,
It is determined whether or not the acquired value of the waveform signal exceeds a first threshold value. If not, the first counter is initialized, and if it exceeds, the first counter is incremented by +1 and incremented. When the count value of the first counter exceeds the first value, the gain of the waveform generation circuit is reduced,
Further, it is determined whether or not the acquired value of the waveform signal exceeds a second threshold value before the first threshold value, and if it exceeds, the second counter is initialized and the second threshold value is not reached. In this case, the second counter is incremented by +1, and when the count value of the second counter exceeds the second value, gain control is performed to increase the gain of the waveform generation circuit. A light receiving element that receives an optical signal and converts it into an electrical signal;
A waveform generation circuit that inputs an electrical signal output from the light receiving element and generates a waveform signal by filtering and amplification; and
A control circuit for processing a waveform signal supplied from the waveform generation circuit;
An acceleration sensor;
An optical receiver having a power switch for selecting supply of power to the light receiving element,
The control circuit controls the power switch to be on only while sensing movement of the optical receiver based on the output of the acceleration sensor in a mode in which position information is received by the optical signal. .

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