JP2009272902A - Light reception circuit, optical beacon having the same, and on-vehicle machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a reception failure associated with reception of high-intensity light even when a photodiode receives the high-intensity light derived from sunlight. <P>SOLUTION: This light reception circuit 16 includes: the photodiode PDi receiving an optical signal for wireless communication to convert the received optical signal to an electric signal; one or more amplifiers 28 and 29 amplifying the output of the photodiode PDi; and a removal circuit 30 removing variation of an output level caused by high-intensity light derived from sunlight from the output of the photodiode PDi or those of the amplifiers 28 and 29. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical receiver circuit that receives an optical signal for wireless communication with a photodiode, an optical beacon in which the optical receiver circuit is applied to road-to-vehicle communication, and an in-vehicle device.

As a traffic information service using a road-to-vehicle communication system, so-called VICS (Vehicle Information and Communication System: registered trademark of Road Traffic Information Communication System Center) using optical beacons, radio beacons or FM multiplex broadcasting has already been developed. ing.
Among these, the optical beacon employs optical communication using near infrared rays as a communication medium, and bidirectional communication with the in-vehicle device is possible. Specifically, uplink information including travel time information between beacons held by the vehicle is transmitted from the in-vehicle device to the optical beacon on the infrastructure side, and conversely, traffic jam information, section travel time information, event regulation information, and lanes Downlink information including notification information and the like is transmitted from the optical beacon to the vehicle-mounted device (see, for example, Patent Document 1).

For this reason, the optical beacon includes a beacon head (projector / receiver) that performs bidirectional communication with an in-vehicle device using an optical signal, and the light-emitting diode (transmitter / receiver) that transmits downlink light. LED) and a photodiode (PD) that receives uplink light from the vehicle-mounted device.
In addition, the beacon head includes a light transmitting unit that inputs a transmission signal from the beacon controller to the light emitting diode to emit downlink light, and a beacon controller that converts the uplink light received by the photodiode into an electric signal. And an optical receiver to be sent to.

JP 2005-268925 A

The optical receiver that receives uplink light is usually composed of a photodiode, an amplifier circuit that amplifies the output signal of the diode, and a comparator connected to the amplifier circuit. This comparator compares the output signal from the amplifier circuit with a threshold value and converts it into a digital signal.
Therefore, if the digital signal output from the comparator is input to a processing processor having a CDR (Clock Data Recovery) function or a CRC (Cyclic Redundancy Check) function, the data signal included in the uplink light can be extracted.

Since the optical receiver of such an optical beacon receives uplink light, which is near-infrared light emitted in the atmosphere for wireless communication, the output voltage of the photodiode is much higher than in other optical communication fields. Has the characteristic of being small.
For example, when the lower limit light quantity specified by the interface standard of the optical beacon is received, the output voltage from the near-infrared photodiode becomes a very small voltage of 10 μV or less, so that normal data is processed in the processing processor. In order to perform demodulation, an amplification factor on the order of 100,000 times is required.

Therefore, for example, as shown in FIG. 9A, an optical receiving unit of an optical beacon employs an amplifier circuit in which a plurality of amplifiers are connected in multiple stages in series. In this case, the weak output voltage from the photodiode is multiplied by each amplifier and amplified to the above order, and this amplified output is input to the comparator.
However, as shown in FIG. 9B, when high-intensity light derived from sunlight (direct sunlight, its reflected light, etc.) is incident on the photodiode simultaneously with the uplink light, the increase in voltage accompanying the high-intensity light causes The signal component may not be demodulated.

That is, for example, the intensity of direct sunlight is about 100,000 lux, and the intensity of reflected sunlight may reach about 80,000 lux when reflected by a highly reflective vehicle or the like. When such high-intensity light enters the photodiode, an abnormal output component y that reaches about 1000 times the signal output component x is rapidly generated as its output voltage.
Then, when the output voltage of the photodiode rapidly increased by the abnormal output component y is amplified by a later amplifier, saturation occurs on the output side of any amplifier, and after this saturation point, the amplifier Until the signal becomes stable again, the uplink optical signal cannot be demodulated.

In addition, for example, high-intensity light (approximately 20,000 lux) due to the reflection of the road surface in the summertime is constantly incident on the photodiode of the beacon head, and this causes the output voltage of the amplifier to steadily reach a high level before saturation. May be.
In this state, if the reflection of the road surface is blocked by the shadow of a dark-colored vehicle or other vehicles passing through, the high output level associated with the reception of high-intensity light decreases rapidly. May not be able to follow the fluctuation of the output level, and the uplink light signal may not be accurately demodulated.
In view of the above-described problems, the present invention provides an optical receiver circuit and the like that can prevent reception failure associated with reception of high-intensity light even when a photodiode receives high-intensity light derived from sunlight. The purpose is to do.

  An optical receiver circuit of the present invention (Claim 1) includes a photodiode that receives an optical signal for wireless communication and converts it into an electrical signal, and one or a plurality of amplifiers that amplify an output signal of the photodiode, And a removal circuit that removes a fluctuation in output level caused by high-intensity light derived from sunlight from the output of the photodiode or the amplifier.

According to the optical receiver circuit of the present invention, the removal circuit removes the fluctuation of the output level caused by the high-intensity light derived from sunlight from the output of the photodiode or the amplifier. Even when the intense light is received, fluctuations in the output level of the amplifier subsequent to the photodiode can be minimized, and the original output level can be quickly restored. For this reason, according to the optical receiver circuit of the present invention, it is possible to prevent reception failures represented by inability to demodulate due to amplifier saturation.
Note that the fluctuation of the output level includes either the following cases (a) or (b) or both cases (Claim 2).
(A) When a constantly low output level suddenly increases due to high-intensity light (b) When a constantly high output level suddenly decreases due to reception of high-intensity light

By the way, as described above, the abnormal output component associated with the reception of high-intensity light derived from sunlight is very large compared to the output component that is originally required (for example, the signal output component). Then, it is difficult to cut such a large abnormal output component.
Therefore, the removal circuit employed in the optical receiver circuit of the present invention includes a detection circuit that detects and outputs an output component generated by the high-intensity light, a pair of input terminals, and a difference between these terminals or amplifies this difference. And a differential output circuit having an output terminal for outputting the signal.

  In this case, if the output of the photodiode or the amplifier is input to one input terminal of the differential output circuit, and the output of the detection circuit is input to the other input terminal, the differential output circuit is connected to the differential output circuit. Or a signal obtained by amplifying the difference is actively output, so that only the necessary output component included in the output of the photodiode or the amplifier can be effectively extracted.

When the active removal circuit using the differential output circuit is employed, the detection circuit is configured by, for example, an analog integrator that is feedback-connected to the output terminal of the differential output circuit and the other input terminal. (Claim 4).
Further, the detection circuit cuts out a required output component from the output of the photodiode or the amplifier to take out an output component generated by the high-intensity light, and the taken out output component is taken as the other input terminal of the differential output circuit It is also possible to configure with a low-pass filter that inputs to (Claim 5).

Further, the detection circuit detects an output component generated by the high-intensity light based on a digital signal obtained by digitally converting the output of the photodiode or the amplifier, and detects the detected output component on the other side of the differential output circuit. It can also be constituted by a digital circuit that inputs to the input terminal.
However, in the case of such a digital circuit, at least an A / D converter, a D / A converter, and a digital processing unit (CPU) capable of wideband data processing capable of recognizing an output component generated by high-intensity light are necessary. In this respect, since the circuit configuration is large, it is preferable to employ the analog integrator or low-pass filter that does not require digital conversion.

The optical receiver circuit of the present invention can be used as an optical receiver of various optical communication devices. For example, the optical receiver circuit is applied to an optical beacon or an in-vehicle device that performs bidirectional road-to-vehicle communication using uplink light and downlink light. It is preferable to do this.
That is, an optical beacon according to the present invention (Claim 7) is an optical beacon that performs road-to-vehicle communication using an optical signal with an in-vehicle device mounted on a vehicle in a communication area set in a predetermined range of a road. An optical receiving circuit that receives the uplink light emitted by the in-vehicle device in the uplink region included in the region, and the optical receiving circuit includes the optical receiving circuit according to the present invention (Claim 1). Features.

In addition, the in-vehicle device of the present invention (Claim 8) is mounted on a vehicle that performs road-to-vehicle communication using an optical signal with a beacon head of an optical beacon installed on a roadside in a communication area set in a predetermined range of a road. And a light receiving circuit that receives the downlink light emitted by the beacon head toward the downlink area included in the communication area. The light receiving circuit includes the light of the present invention described above. It comprises a receiving circuit (claim 1).
Therefore, the optical beacon and the vehicle-mounted device (claims 7 and 8) of the present invention have the same effects as the optical receiver circuit (claim 1) of the present invention.

  As described above, according to the present invention, even when the photodiode receives high-intensity light derived from sunlight, fluctuations in the output level of the amplifier can be minimized, so that reception associated with reception of high-intensity light. Defects can be prevented.

[Overall configuration of road-to-vehicle communication system]
FIG. 1 is a block diagram showing the overall configuration of a road-vehicle communication system using an optical beacon of the present invention.
As shown in FIG. 1, the road-to-vehicle communication system includes an infrastructure-side traffic control system 1 and an in-vehicle device 2 mounted on each vehicle C traveling on a road W.
The traffic control system 1 includes a central device 3 provided in a control room and a large number of optical beacons (optical vehicle detectors) 4 installed at various locations on the road W. The optical beacon 4 performs bidirectional communication with the in-vehicle device 2 by optical communication using near infrared rays as a communication medium. The central device 3 is provided in the traffic control room.

[Configuration of optical beacon]
The optical beacon 4 includes a communication unit 6 that is a communication interface connected to the central apparatus 3 via a communication line 5 such as a telephone line, a beacon controller 7 to which the communication unit 6 is connected, and the beacon controller 7. And a plurality (four in the illustrated example) of beacon heads (projector / receiver) 8 connected to the sensor interface.
Each beacon head 8 accommodates an optical transmitter including a light emitting diode (LED) 10 and an optical receiver 17 including a plurality of photodiodes (PD) 11 in a casing (see FIG. 3).

Among these, the light emitting diode 10 emits downlink light DO (an optical signal constituting downlink information) made of near infrared light to a communication area A described later, and the photodiode 11 is made of near infrared light from the in-vehicle device 2. Uplink light UO (an optical signal constituting uplink information) is received.
The beacon head 8 is provided with a plurality (four in the illustrated example) of photodiodes 11 corresponding to each of the divided areas UA1 to UA4 of the uplink area UA, which will be described later. The optical receiver 17 of the uplink optical UO is configured together with the amplifier circuit 19 that amplifies the output signal (see FIG. 4).

FIG. 2 is a plan view of the optical beacon 4.
As shown in FIG. 2, the optical beacon 4 of the present embodiment is installed on a road W having a plurality of (four in the illustrated example) lanes W1 to W4 in the same direction, and corresponds to each lane W1 to W4. The plurality of beacon heads 8 provided and a single beacon controller 7 serving as a control unit that collectively controls the beacon heads 8.

The beacon controller 7 is composed of a programmable microcomputer including a processing processor 23 (to be described later) and a storage device 24 composed of RAM, ROM, etc. (see FIG. 4), and the storage device 24 executes predetermined functions. A computer program is stored.
When the processor 23 executes the computer program, two-way communication with the central device 3 by the communication unit 6 (FIG. 1) and road-to-vehicle communication with the in-vehicle device 2 by the beacon head 8 are performed. ing.

As shown in FIG. 2, the housing of the beacon controller 7 is installed on a support column 13 erected on the side of the road, and the housing of each beacon head 8 is installed horizontally on the road W side from the support column 13. It is attached to the erection bar 14 and is disposed immediately above each lane W1 to W4 of the road W.
The LED 10 of each beacon head 8 emits near-infrared rays toward the upstream side in the vehicle traveling direction from directly below the lanes W1 to W4, thereby performing road-to-vehicle communication with the in-vehicle device 2. Is set on the upstream side of the head 8.

[About communication area]
FIG. 3 is a side view showing the communication area A of the optical beacon 4.
As shown in FIGS. 2 and 3, the communication area A of the optical beacon 4 is a downlink area (in FIG. 3) in which an in-vehicle head (not shown) that is a light projecting / receiving device of the in-vehicle device 2 can receive the downlink light DO. (Area provided with solid hatching) DA and an uplink area (area provided with broken hatching in FIG. 3) UA in which the beacon head 8 of the optical beacon 4 can receive the uplink light UO from the in-vehicle head. .

The downlink area DA is set in a range indicated by Δdac having apexes at the light emitting / receiving position d of the beacon head 8 and the positions a and c on the road W. Further, the uplink area UA is set in the range indicated by Δdbc with the position d and the positions b and c on the road W as vertices.
Accordingly, the upstream end c of the downlink area DA and the uplink area UA coincide with each other, and the uplink area UA overlaps with the upstream portion (right side portion in FIG. 3) of the downlink area DA in the vehicle traveling direction. Further, the vehicle traveling direction length of the downlink area DA coincides with the same direction length of the entire communication area A.

According to the “near infrared interface standard” of the optical beacon (optical vehicle sensor) 4, the formal area dimensions of the downlink area DA and the uplink area UA are defined. In this rule, in the case of an optical beacon 4 for a general road, the downstream end a of the downlink area DA is located 1.0 to 1.3 m upstream immediately below the beacon head 8 and is downstream of the downlink area DA. The distance from the end a to the downstream end b of the uplink area UA is defined as 2.1 m.
Further, the distance from the downstream end b of the uplink area UA to the upstream end c of the area UA is defined as 1.6 m. Accordingly, the total length of the official communication area A in the vehicle traveling direction (the length between ac) is 3.7 m.

However, in this embodiment, the distance from the downstream end b of the uplink area UA to the upstream end c of the area UA is set longer to the upstream side and the downstream side than the above definition. As a result, the uplink area UA extends in the vehicle traveling direction from the above definition, and the downlink area DA also extends in the vehicle traveling direction from the above definition.
Thus, when the uplink area UA and the downlink area DA are widened, the certainty of transmission / reception of uplink information and downlink information between the in-vehicle device 2 and the optical beacon 4 is increased.

Further, the uplink area UA is composed of divided areas UA1 to UA4 obtained by dividing the area UA in the vehicle traveling direction to such an extent that the traveling position of the vehicle C can be specified. Specifically, the uplink area UA of the present embodiment is divided into four by three boundary lines (boundary portions) BL having a position d as an upper end and positions e1 to e3 on the road W as lower ends. Yes.
The four photodiodes 11 provided in the beacon head 8 use the divided areas UA1 to UA4 of the uplink area UA as reception areas.

That is, the in-vehicle device 2 of the vehicle C repeatedly transmits the uplink light UO of the same data signal from the in-vehicle head while passing through the uplink area UA, and any one of the repeatedly transmitted uplink light UOs. In order to receive one of them, four photodiodes 11 corresponding to the divided areas U1 to UA4 are provided.
For example, as shown by a solid line in FIG. 3, when the in-vehicle head of the in-vehicle device 2 transmits the uplink light UO in the divided area UA1 located on the most upstream side, the photodiode 11 corresponding to the divided area UA1 is up. The link light UO is received.

[Circuit configuration of optical receiver circuit]
FIG. 4 is a block diagram showing an example of the circuit configuration of the optical receiver circuit according to the present invention.
In the following, the photodiode 11 corresponding to the uppermost divided area UA1 is defined as PD1, and the photodiodes 11 corresponding to the second, third, and fourth divided areas UA2 to UA4 from the upstream side are respectively defined as PD1. Defined as PD2, PD3 and PD4.

As shown in FIG. 4, the optical receiver circuit 16 of the present embodiment includes the optical receiver 17 housed in the housing of the beacon head 8 corresponding to each lane W1 to W4, and the housing of the beacon controller 7. And a digital processing unit 18 housed in the storage. The light receiving unit 17 of each beacon head 8 and the digital processing unit 18 of the beacon controller 7 are connected to each other by a transmission cable.
The optical receiver 17 includes a plurality of the photodiodes 11 (PD1 to PD4) corresponding to the divided areas UA1 to UA4, a plurality of amplifier circuits 19 connected to the respective diodes 11, and And an analog adder 20 connected to the rear stage side.

The optical receiver 17 includes a comparator 21 connected to the subsequent stage side of the analog adder 20 and a plurality of detection circuits 22 connected to the subsequent stage side of each amplifier circuit 19.
On the other hand, the digital processing unit 18 performs the digital signal processing on the input signal from the optical receiving unit 17, and the storage device 24 that stores the processing program executed by the processing processor 23. And an A / D converter 25.

Each amplifier circuit 19 of the optical receiver 17 includes an amplifying element 28 made of an n-type MOSFET, a plurality of operational amplifiers 29 that further amplify the output voltage of the element 28, and the like. Amplification can be performed on the order of 100,000 times.
The output signal of each amplifier circuit 19 is input to the analog adder 20 at the subsequent stage and superimposed on one analog addition signal S1. Therefore, each amplifier circuit 19 and the subsequent analog adder 20 connected to PD1 to PD4 function as an adder that amplifies the output signal of each photodiode 11 and adds it to one added signal S1.

FIG. 5A shows an example of a circuit configuration of the analog adder 20, and here, an adder using an operational amplifier (operational amplifier) 26 is illustrated.
The analog adder 20 shown in FIG. 5A outputs an output voltage Vout calculated by the following equation, where V1 to V4 are input voltages from the amplifier circuits 19 corresponding to PD1 to PD4.
Vout = − (V1 / R1 +... + V4 / R4) · Rf

Therefore, in this case, if all the resistance values R1 to R4 are set to the same value Rc, the value obtained by adding all the input voltages V1 to V4 as the output voltage Vout of the analog addition signal S1 is further amplified by (Rf / Rc) times. The obtained value is obtained.
In the case of the analog adder 20 using the operational amplifier 26, it is necessary that the open loop gain of the operational amplifier 26 is sufficiently large and the output impedance of the previous stage is sufficiently small.

Returning to FIG. 4, the comparator 21 subsequent to the analog adder 20 generates the digital signal S2 by comparing the analog addition signal S1 with a predetermined threshold (for example, 0 volts). For example, an inverting comparison circuit using an operational amplifier. It consists of The digital signal S2 generated by the comparator 21 is transmitted to the processing processor 23 of the digital processing unit 18.
The output side of each amplifier circuit 19 is branched and connected to the detection circuit 22. The detection circuit 22 is composed of, for example, a diode detection circuit shown in FIG. 5B, and outputs an envelope voltage Vout obtained by smoothing the input voltage Vin input from the amplifier circuit 19.

The output side of each detection circuit 22 is connected to the A / D converter 25 of the digital processing unit 18, and this converter 25 converts the envelope voltage Vout into a digital value.
For this reason, the output voltage of each amplifier circuit 42 is envelope-detected by the detection circuit 22 at the subsequent stage, further converted into a digital signal by the A / D converter 25 at the subsequent stage, and the processing processor 23 of the digital processing unit 18. Sent to.

[Processing content of the digital processing unit]
The processing processor 23 of the digital processing unit 18 has a CDR function and a CRC function, and converts the analog addition signal S1 into a transmission signal (electric signal) generated by the in-vehicle device 2 from the digital signal S2 digitized by the comparator 21. In synchronization, a data signal (including a communication control signal) included in the transmission signal is extracted.
As described above, the processing processor 23 has a function as a data acquisition unit that acquires the data signal included in the optical signal based on the analog addition signal S1.

The processing processor 23 also has a function as a position specifying unit that specifies the traveling position of the vehicle C in the uplink area UA depending on which of the plurality of photodiodes PD1 to PD4 receives the uplink light UO. is doing.
That is, the processing processor 23 detects the reception level of PD1 to PD4 from the digital signal of the A / D converter 25, and compares this reception level with a predetermined threshold value, so that which of the photodiodes PD1 to PD4 is selected. Determines whether the uplink light UO is actually received.

That is, the processing processor 23 specifies in which divided areas UA1 to UA4 the uplink light UO is received by the vehicle C (onboard unit 2) traveling in the uplink area UA.
Therefore, if the optical beacon 4 of this embodiment is used, the optical beacon 4 on the infrastructure side determines the traveling position of the vehicle C (onboard unit 2) that has emitted the uplink light UO in the uplink area UA. It can be determined with an accuracy equal to or less than the length of the UA1 to UA4 in the vehicle traveling direction.

Further, the processing processor 23 of the digital processing unit 18 executes a computer program stored in the storage device 24 to control the light receiving unit 17 and the light transmitting unit of the beacon head 8, and Car-to-vehicle communication.
That is, the processing processor 23 has a function as a communication control unit for causing the beacon head 8 to perform road-to-vehicle communication with the in-vehicle device 2.

And in performing this road-to-vehicle communication, the processing processor 23 includes the information on the vehicle position specified by itself in the downlink light DO transmitted after downlink switching, and receives this downlink light DO. The in-vehicle device 2 can recognize the traveling position of the own vehicle C.
In this case, as shown in FIG. 3, the distance Li (i = 1 to 1) from the reference position Pi of the divided area UAi (i = 1 to 4) to the predetermined position P0 (for example, the position of the stop line 50) downstream thereof. Information regarding 4) may be included in the downlink optical DO.

[Circuit Configuration of Amplifier Circuit (First Embodiment)]
FIG. 6 is a circuit diagram showing an internal configuration of the amplifier circuit 19 according to the first embodiment.
In FIG. 6, the analog adder 20 (see FIG. 4) is not shown in order to illustrate the output waveforms of the post-stage amplifier 29 and the comparator 21. This is the same in the case of FIG. 7 relating to the amplifier circuit 19 of the second embodiment described later and FIG. 8 relating to the third embodiment.

  As shown in FIG. 6, each amplifier circuit 19 according to the first embodiment includes a preamplifier 28 composed of an amplifier element such as an n-type MOSFET connected to each of the photodiodes PDi (i = 1 to 4), A post-stage amplifier 29 composed of an operational amplifier or the like that further amplifies the output voltage of the pre-stage amplifier 28, a removal circuit 30 provided between these amplifiers 28 and 29 for removing output level fluctuations due to high intensity light, and a post-stage And a trap circuit 31 provided at a subsequent stage of the amplifier 29.

The removal circuit 30 of the present embodiment uses the pre-stage amplifier 28 to change the output level (for example, the abnormal output component y in FIG. 9) due to the reception of high-intensity light derived from sunlight such as direct sunlight or its reflected light. Specifically, the differential output circuit 32 interposed between the front-stage amplifier 28 and the rear-stage amplifier 29, and the non-operation of the operational amplifier 34 that constitutes the differential output circuit 32 are used. It is composed of an inverting input terminal and an analog operation integration circuit (analog integrator) 33 connected in a feedback manner to the output terminal.
The differential output circuit 32 includes an operational amplifier 34, an input-side resistor 35, and a feedback resistor 36. The input-side resistor 35 is connected to the output terminal of the preamplifier 28 and the inverting input terminal of the operational amplifier 34. ing.

The feedback resistor 36 is connected to the output terminal of the operational amplifier 34 and its inverting input terminal, whereby negative feedback is applied to the operational amplifier 34 by a resistor. In the example shown in FIG. 6, the resistance value R of the input-side resistor 35 and the feedback resistor 36 are the same value, and the differential output circuit 32 has no amplification function.
For this reason, the differential output circuit 32 shown in FIG. 6 has a difference calculation function that outputs the difference between the pair of input terminals without amplification.

In other words, the input voltage to one input terminal of the differential amplifier circuit 32 (output voltage of the preamplifier 28) is V _A, and the input voltage to the other input terminal (input voltage to the non-inverting input terminal of the operational amplifier 34). It was a V _B, and the output voltage of the differential amplifier circuit 32 (output voltage of the operational amplifier 34) and V _C, the relationship of V _C = V _B -V _a is adapted to hold. However, in the differential output circuit 32 shown in FIG. 6, an amplification function can be provided by making the resistance value of the feedback resistor 36 larger than the resistance value of the input resistor 35.
On the other hand, the analog integrator 33 is composed of an operational amplifier 37, an input side resistor 38, and a feedback capacitor 39. The input side resistor 38 is an inversion of the output terminal of the differential output circuit 32 and the operational amplifier 34. Connected to the input terminal.

The feedback capacitor 39 is connected to the output terminal of the operational amplifier 37 and its inverting input terminal, whereby negative feedback by the capacitor is applied to the operational amplifier 37.
The output terminal of the operational amplifier 37 constituting the analog integrator 33 is connected to the non-inverting input terminal of the operational amplifier 34 constituting the differential output circuit 32. Further, the RC time constant of the analog integrator 33 is such that a high-frequency component which is a necessary output component (a signal output component included in the uplink light UO) is smoothed, and a low-frequency component accompanying reception of high-intensity light. Is set to be integrated.

For this reason, the output voltage V _B of the analog integrator 33 substantially follows the behavior of the low-frequency component if the low-frequency component is included in the output voltage V _C of the differential output circuit 32, but the differential output The high frequency component included in the output voltage V _C of the circuit 32 is not followed.
Therefore, as shown in the time chart at the bottom of FIG. 6, even if the output voltage V _A of the front-stage amplifier 28 changes greatly because the photodiode PDi receives high-intensity light, the analog integrator 33 changes to the low-frequency component. The tracked output voltage V _B is output.

Then, the differential output circuit 32 outputs the difference V _C (= V _B −V _A ), whereby only the signal output component included in the output voltage V _A of the pre-stage amplifier 28 is output.
Thus, the removal circuit 30 of the present embodiment removes the low-frequency component V _B associated with the reception of high-intensity light derived from sunlight such as direct sunlight and its reflected light from the output voltage V _A of the pre-amplifier 28, and outputting the difference V _C after its removal in the subsequent stage.

However, since the analog integrator 33 requires a certain amount of follow-up time for a sudden rise of the low frequency component, the actual difference V _C is somewhat disturbed as shown in the waveform of V _C in FIG. 40 is produced.
The trap circuit 31 filters a sneak component from the downlink light DO emitted from the light emitting diode 10 included in the output voltage of the post-stage amplifier 29, and signals in the frequency bands of 500 kHz and 1 MHz used for the downlink. It is comprised by the band pass filter which cuts.

[Effect of the optical receiver circuit of this embodiment]
As described above, according to the optical receiver circuit 16 of the present embodiment, the removal circuit 30 that removes the fluctuation of the output level caused by the high-intensity light derived from sunlight from the output of the preamplifier 28 is provided. Even if the diode PDi (i = 1 to 4) receives high-intensity light derived from sunlight at the same time as the uplink light UO, the post-stage amplifier 29 does not reach the saturation level, and the demodulation accompanying the saturation of the post-stage amplifier 29 It is possible to prevent reception failure such as inability.

Further, according to the optical receiver circuit 16 of the present embodiment, not only when the output level of the post-amplifier 29 suddenly increases from a low state to a high state, but also when the output level rapidly decreases from a high state to a low state. That variation can be eliminated.
That is, for example, high-intensity light of about 20,000 lux is constantly incident on the photodiode PDi of the beacon head 8 due to the reflection of the road surface in summer, so that the output voltage of the amplifiers 28 and 29 saturates before the saturation. However, in this case, even if the shadow of a dark-colored vehicle or other vehicle passes and the reflection of the road surface is interrupted, the high output level steadily decreases rapidly. Thus, it is possible to prevent a demodulation failure caused by a rapid decrease in the output level.

Further, according to the optical receiver circuit 16 of the present embodiment, the analog adder 20 of the optical receiver 17 adds the output signal of each photodiode PDi (i = 1 to 4) to one analog addition signal S1, Since the processing processor 23 of the digital processing unit 18 reproduces the data signal based on the digital signal S2 generated by the comparator 21 from the analog addition signal S1, the processing signal 23 is selected from a plurality of digital signals generated for each photodiode PDi. There is no need to implement complicated logic for selecting a correct signal in the digital processing unit 18.
For this reason, the optical receiver circuit 16 can be mounted more easily, and the manufacturing cost of the circuit 16 can be reduced.

Further, according to the optical receiving circuit 16 of the present embodiment, there is an advantage that the optical beacon 4 capable of road-to-vehicle communication at a speed higher than usual can be realized.
That is, since the photodiode generally has an impedance of a capacitor component (capacitance), the larger the light receiving region, the larger the time constant, and the characteristic is that the rise time and fall time of the output signal (electric signal) are dull.

  In this regard, in the optical receiving circuit 16 of the present embodiment, when receiving the optical signal (uplink light UO) emitted from the vehicle-mounted device 2 in the uplink area UA, the divided areas UA1 to UA4 are divided into areas UA1 to UA4. Correspondingly, it is divided into a plurality of PDi (i = 1 to 4). For this reason, the response time of the output signal (electric signal) with respect to the optical signal is shortened as compared with the case of using one photodiode having a light receiving area that follows the entire uplink area UA.

Therefore, as the number of divisions of PDi is increased, the signal processing can be performed at high speed, and the optical beacon 4 can perform high-speed communication of Mbps order.
On the other hand, when the light receiving area of the photodiode is small, the signal magnitude (S / N ratio) with respect to the noise level also becomes small, but a plurality of PDi (i) as in the optical receiving circuit 16 of the present embodiment. If the output signals corresponding to = 1 to 4) are added, it is possible to obtain an S / N ratio equivalent to that of one photodiode obtained by adding up the light receiving areas.

[Circuit Configuration of Amplifier Circuit (Second Embodiment)]
FIG. 7 is a circuit diagram showing an internal configuration of the amplifier circuit 19 according to the second embodiment.
The amplifier circuit 19 (FIG. 7) of the second embodiment is different from the amplifier circuit 19 (FIG. 6) of the first embodiment in that a detection circuit for an output component generated by high-intensity light replaces the analog integrator 33. The low-pass filter 42 is used.

The low-pass filter 42 includes an RC filter including a grounding capacitor 43 and a resistor 44 connected thereto, and one end of the resistor 44 is connected to the output terminal of the pre-stage amplifier 28.
The RC time constant of the filter 42 allows a low-frequency component accompanying the reception of high-intensity light included in the output of the preamplifier 28 to pass therethrough, but a high-frequency component that is a necessary output component (signal output included in the uplink light UO). The component) is set not to pass.

The output terminal of the low-pass filter 42 is connected to the input terminal of an inverting circuit 45 using an operational amplifier as an inverting amplifier with a magnification of 1. A voltage follower may be used instead of the inverting circuit 45.
For this reason, as shown in the time chart of the lower stage of FIG. 7, even if the output voltage V _A of the front-stage amplifier 28 changes greatly because the photodiode PDi receives high-intensity light, the inversion circuit 45 in the rear stage of the low-pass filter 42 Output voltage B following the change of the low frequency component is output.

The output terminal of the inverting circuit 45 is connected to the non-inverting input terminal of the operational amplifier 34 constituting the differential amplifier circuit 32. For this reason, the differential output circuit 32 outputs the difference V _C (= V _B −V _A ), whereby only the signal output component included in the output voltage V _A of the pre-stage amplifier 28 is output.
As described above, the removal circuit 30 of the second embodiment also removes the low-frequency component V _B accompanying the reception of high-intensity light derived from sunlight, such as direct sunlight and its reflected light, from the output voltage V _{A of the} preamplifier 28. and has a function of outputting the difference V _C after its removal in the subsequent stage.

[Circuit Configuration of Amplifier Circuit (Third Embodiment)]
FIG. 8 is a circuit diagram showing an internal configuration of the amplifier circuit 19 according to the third embodiment.
The amplifier circuit 19 (FIG. 8) according to the third embodiment is different from the amplifier circuit 19 (FIG. 6) according to the first embodiment in that the analog integrator 33 is used as a detection circuit for an output component generated by high-intensity light. In addition, a digital circuit 46 that detects an output component generated by high-intensity light based on a digital signal obtained by digitally converting the output of the pre-stage amplifier 28 and inputs the detected output component to the input terminal of the differential output circuit 32 is employed. There is in point.

That is, the digital circuit 46 includes an A / D converter 47 that digitally converts the output of the pre-stage amplifier 28, a digital processing unit (CPU) 48 connected to the subsequent stage of the converter 47, and a subsequent stage of the digital processing unit 48. The D / A converter 49 is connected, and the output terminal of the D / A converter 49 is connected to the non-inverting input terminal of the operational amplifier 34 constituting the differential output circuit 32.
Further, the digital processing unit 48 calculates the value of the low frequency component in real time based on the digital signal from the A / D converter 47, and the calculation result is converted into an analog signal by the D / A converter 49, and the operational amplifier 34. Is input to the non-inverting input terminal.

Therefore, the differential output circuit 32 outputs the difference V _C (= V _B −V _A ), and thereby only the signal output component included in the output voltage V _A of the pre-stage amplifier 28 is output.
Thus, the removal circuit 30 of the third embodiment also removes the low-frequency component V _B accompanying the reception of high-intensity light derived from sunlight, such as direct sunlight and its reflected light, from the output voltage V _{A of the} preamplifier 28. and has a function of outputting the difference V _C after its removal in the subsequent stage.

[Other variations]
The present invention is not limited to the above embodiment.
For example, in the above embodiment, since the amplifier circuit 19 includes two amplifiers 28 and 29, the removal circuit 30 is disposed between the front-stage amplifier 28 and the rear-stage amplifier 29. Further, it may be arranged between the photodiode PDi and the pre-stage amplifier 28, or may be arranged after the post-stage amplifier 29. Further, the amplifier circuit 19 may include three or more amplifiers or only one amplifier.

  Further, in the above embodiment, the case of the so-called PD division type optical beacon 4 in which the photodiode 11 is divided into a plurality of parts is illustrated, but the present invention is also applied to a normal optical beacon in which the photodiode 11 is not divided. Can be adopted.

Furthermore, the optical receiver circuit of the present invention can be mounted not only on the optical beacon 4 but also on the vehicle-mounted device 2 (see FIG. 3). That is, the vehicle-mounted device 2 that performs road-to-vehicle communication with the optical beacon 4 requires an optical receiving circuit that receives the downlink light DO that is emitted toward the downlink area UA by the light emitting diode 10 of the beacon head 8. You may decide to apply this invention to the optical receiver circuit of the vehicle equipment 2.
The optical receiver circuit of the present invention can be employed not only in the optical beacon 4 and the in-vehicle device 2 but also in other wireless communication devices that perform optical communication.

It is a block diagram which shows the whole structure of a road-vehicle communication system. It is a top view of an optical beacon. It is a side view which shows the communication area | region of an optical beacon. It is a block diagram which shows the circuit structure of an optical receiver circuit. (A) is a circuit diagram of an analog adder, and (b) is a circuit diagram of a detection circuit. 1 is a circuit diagram showing an internal configuration of an amplifier circuit according to a first embodiment. It is a circuit diagram which shows the internal structure of the amplifier circuit which concerns on 2nd Embodiment. It is a circuit diagram which shows the internal structure of the amplifier circuit which concerns on 3rd Embodiment. It is a figure which shows schematically the circuit structure of the conventional optical receiving part in an optical beacon, (a) shows circuit operation in normal time, (b) shows circuit operation in case high intensity light injects.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 Vehicle equipment 4 Optical beacon 7 Beacon controller 8 Beacon head 10 Light emitting diode 11 Photodiode 16 Optical receiving circuit 17 Optical receiving part 18 Digital processing part 19 Amplifying circuit 28 Previous stage amplifier 29 Rear stage amplifier 30 Removal circuit 32 Differential output circuit 33 Analog Integrator (detection circuit)
42 Low-pass filter (detection circuit)
46 Digital circuit (detection circuit)
C Vehicle A Communication area UA Uplink area DA Downlink area UO Uplink light DO Downlink light

Claims (8)

A photodiode that receives an optical signal for wireless communication and converts it into an electrical signal;
One or more amplifiers for amplifying the output of the photodiode;
A removal circuit for removing fluctuations in the output level caused by high-intensity light derived from sunlight from the output of the photodiode or the amplifier;
An optical receiver circuit comprising: The optical receiving circuit according to claim 1, wherein the fluctuation of the output level includes one of the following cases (a) and (b) or both cases.
(A) When a constantly low output level suddenly increases due to high-intensity light (b) When a constantly high output level suddenly decreases due to reception of high-intensity light The removal circuit includes a detection circuit that detects and outputs an output component generated by the high-intensity light, and a difference having a pair of input terminals and an output terminal that outputs a difference between the terminals or a signal obtained by amplifying the difference. Dynamic output circuit,
The optical receiver circuit according to claim 1, wherein an output of the photodiode or the amplifier is input to one input terminal of the differential output circuit, and an output of the detection circuit is input to the other input terminal.   4. The optical receiver circuit according to claim 3, wherein the detection circuit includes an analog integrator that is feedback-connected to an output terminal of the differential output circuit and the other input terminal. 5.   The detection circuit cuts out a required output component from the output of the photodiode or the amplifier to extract an output component generated by the high-intensity light, and inputs the extracted output component to the other input terminal of the differential output circuit The optical receiver circuit according to claim 3, comprising a low-pass filter.   The detection circuit detects an output component generated by the high-intensity light based on a digital signal obtained by digitally converting the output of the photodiode or the amplifier, and detects the detected output component on the other input terminal of the differential output circuit 4. The optical receiver circuit according to claim 3, further comprising a digital circuit that inputs to the optical circuit. In a communication area set in a predetermined range of a road, an optical beacon that performs road-to-vehicle communication with an in-vehicle device mounted on a vehicle and an optical signal,
An optical receiving circuit that receives the uplink light emitted by the in-vehicle device in the uplink region included in the communication region;
The optical receiver circuit receives the uplink light and converts it into an electrical signal, one or more amplifiers that amplify the output of the photodiode, and an output generated by high-intensity light derived from sunlight An optical beacon comprising: a removal circuit for removing level fluctuations from the output of the photodiode or the amplifier. In a communication area set in a predetermined range of a road, an in-vehicle device mounted on a vehicle that performs road-to-vehicle communication using an optical signal with a beacon head of an optical beacon installed on a road side,
An optical receiving circuit that receives downlink light emitted by the beacon head toward a downlink area included in the communication area;
A photodiode that receives the downlink light and converts it into an electrical signal, one or a plurality of amplifiers that amplify the output of the photodiode, and an output generated by high-intensity light derived from sunlight An in-vehicle device comprising: a removal circuit for removing level fluctuation from the output of the photodiode or the amplifier.

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