JPH0854468A - Photoreceiver - Google Patents

Abstract

PURPOSE:To reduce the cost and size and to accurately calibrate the sensitivity of a photoreceiver of which sensitivity is calibrated based on a reference light, which receives a light signal with that sensitivity and photoelectrically converts it. CONSTITUTION:The photoreceiver comprises a reference light source 11 for radiating a light signal at a predetermined level, a photoreceiving element 12 which photoelectrically converts the signal, outputs an electric signal and has characteristics varying the efficiency of the conversion and the varying width to the temperature corresponding to the operating point, and an operating point scanning means 13 for scanning a scanning area including the reference point to become a maximum allowable value or less at the distribution of the characteristics at the efficiency and the deviation of the varying range at the operating point. Further, the photoreceiver comprises a level monitoring means 14 for obtaining the ratio to the value of the reference point at the level of the electric signal output from the element in synchronization with the scanning, and a control means 15 for preventing the scanning when the ratio is equal to the ratio of the value at the reference point of the efficiency to a target value previously given for the efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodetector whose sensitivity can be calibrated based on the level of a reference light and which receives an optical signal under the sensitivity to perform photoelectric conversion.

[0002]

2. Description of the Related Art A distance sensor that emits light and determines the relative distance to a target object located at the point where the reflected light is generated based on the correlation with the reflected light of the light is used in various fields such as vehicles. Is being done. Further, in many of such distance sensors, an avalanche photodiode (hereinafter, simply referred to as “APD”) is applied as a light receiving element in order to obtain required distance measuring accuracy and desired high sensitivity. A vessel is installed.

FIG. 10 is a diagram showing a configuration example of a conventional photodetector. In the figure, a first output of a processor (CPU) 80 is connected to a cathode of an APD 83 via a D / A converter (D / A) 81 and a bias control circuit 82,
Its anode is grounded through a resistor 84 and
Connected to the input of amplifier 85. The output of the amplifier 85 is connected to the inputs of the level detecting circuit 86 and the distance measuring circuit 87, and the output of the level detecting circuit 86 is connected to the first input of the processor 80 via the A / D converter 88. The input / output of the distance measuring circuit 87 is connected to the corresponding input / output of the processor 80. The second output of the processor 80 is connected to a drive input of a reference light source 90 via a light source drive circuit 89, and the reference light source 90 is arranged with its emission port facing the light receiving surface of the APD 83.

The operation mode of the photodetector having such a structure is as follows. A calibration mode for calibrating the sensitivity of the APD 83, as will be described later, and photoelectric conversion based on the sensitivity calibrated in the calibration mode to perform a predetermined signal. And a light receiving mode for performing processing (for example, driving the distance measuring circuit 87).

In the calibration mode, the processor 80 drives the reference light source 90 via the light source drive circuit 89, and the reference light source 90 emits the reference light of a constant level. The APD 83 receives such reference light and photoelectrically converts it, and the current signal obtained by the photoelectric conversion is converted into a voltage signal by the resistor 84. The amplifier 85 amplifies such a voltage signal with a predetermined amplification factor and supplies it to the level detection circuit 86, and the level detection circuit 86 performs a predetermined process on the voltage signal thus supplied, so that the reference light described above is obtained. Generates a monitor signal indicating the level of the voltage as a voltage.

On the other hand, as shown in FIG. 11, the APD 83 has a characteristic that the multiplication factor changes according to the bias voltage, and the fluctuation range of the multiplication factor greatly increases or decreases depending on the operating temperature. The processor 80 converts the monitor signal described above into a digital signal via the A / D converter 88, and takes in the signal.
D / A converter 8 based on the value indicated by the digital signal
1 and the bias control circuit 82 to change the bias voltage (operating point) of the APD 83,
The target value control is performed so that the sensitivity of is constant with respect to the characteristics described above. Further, the processor 80 shifts to the light receiving mode when the series of processes in the calibration mode is completed.

In the light receiving mode, the processor 80 stops driving the reference light source 90 via the light source driving circuit 89, and the AP
D83 photoelectrically converts an optical signal provided through an optical system (not shown) to output a current signal. Such a current signal is converted into a voltage signal by the resistor 84 as in the case of the calibration mode described above, further amplified by the amplifier 85, and given to the distance measuring circuit 87. The distance measuring circuit 87 subjects the voltage signal thus provided to distance measuring processing under the control of the processor 80.

As a prior art similar to such a light receiver, for example, there is one disclosed in Japanese Patent Laid-Open No. 57-22944, but its detailed description is omitted here.

[0009]

However, in such a conventional photodetector, the APD 83, which is a photodetector, changes the multiplication factor according to the bias voltage as described above and the operating temperature of the variation width of the multiplication factor. The level of the reference light emitted from the reference light source 90 is accurately stabilized with respect to temperature in order to absorb the increase / decrease according to the above and stably obtain a desired sensitivity, or is given to the light receiving surface of the APD 83 in the light receiving mode. Accurate adjustment of the optical signal level was required.

Therefore, it takes a lot of man-hours to adjust the above-mentioned optical system, and the structure of the light source drive circuit 89 and the like is complicated. An object of the present invention is to provide a photodetector capable of accurately calibrating the sensitivity while achieving cost reduction and size reduction.

[0011]

FIG. 1 is a block diagram showing the principle of the invention described in claim 1. In FIG. The invention according to claim 1 is a reference light source 11 for emitting an optical signal at a constant level,
A light receiving device having a characteristic that the optical signal emitted from the reference light source 11 is photoelectrically converted into an electrical signal and the photoelectric conversion efficiency and the fluctuation range of the efficiency with respect to temperature change according to the operating point. An element 12, a scanning area including a reference point at which the deviations of the efficiency and the fluctuation range with respect to the operating point are below the maximum allowable value under the characteristic distribution, and the operating point scanning means 13 for scanning the scanning area The level monitoring means 14 for obtaining the ratio of the level of the electric signal output by the light receiving element in synchronization with the scanning performed by the point scanning means 13 to the value at the reference point, and the ratio obtained by the level monitoring means 14. Control means 15 for monitoring scanning and blocking the scanning when the ratio is equal to a ratio of a preset target value for the efficiency and a value at the reference point of the efficiency.

FIG. 2 is a block diagram showing the principle of the invention described in claim 2. In the invention according to claim 2, the reference light source 11 that emits an optical signal at a constant level, and the optical signal emitted by the reference light source 11 is optoelectrically converted to output an electric signal, and the optoelectric conversion is performed. Of the light receiving element 12 having a characteristic that the efficiency and the fluctuation range of the efficiency with respect to temperature change in accordance with the operating point, and the standard that the deviation of the efficiency and the fluctuation range at the operating point is less than or equal to the maximum allowable value under the characteristic distribution. A scanning area including points is set, and the operating point scanning means 13 for scanning the scanning area and the level of the electric signal output by the light receiving element are monitored, and the level is multiplied by a coefficient set from the outside to obtain a reference level. When the operating point scanned by the operating point scanning means 13 is the reference point, the ratio of the target value given in advance to the efficiency and the value based on the characteristic of the efficiency is set as a coefficient. Further, when the holding unit 23 that holds the reference level obtained by the level monitoring unit 21 and the operating point scanned by the operating point scanning unit 13 are other than the reference point, the coefficient is set to "1" and the level monitoring is performed. It is characterized in that it comprises a control means 25 for comparing the reference level obtained by the means 21 with the reference level held in the holding means 23, and blocking the scanning when the two match.

FIG. 3 is a block diagram showing the principle of the invention described in claim 3. The invention according to claim 3 is a reference light source 31 for emitting an optical signal at an emission level designated from the outside,
A light receiving device having a characteristic in which the optical signal emitted from the reference light source 31 is photoelectrically converted into an electrical signal, and the efficiency of the photoelectric conversion and the fluctuation range of the efficiency with respect to temperature change according to the operating point. An element 32, an operating point scanning means 33 for scanning a scanning point including a reference point at which deviations of efficiency and fluctuation range of the operating point are equal to or less than the maximum allowable value under the characteristic distribution, and light receiving Level monitoring means 34 for obtaining the level of the electric signal output by the element 32,
When the operating point scanned by the operating point scanning means 33 is the reference point, the emission level is obtained by multiplying the product of the ratio of the target value given in advance to the value based on the characteristic of the efficiency and the steady value of the emission level. And a holding means 35 for holding the level obtained by the level monitoring means 34, and an emission level is set to a steady value when the operating point scanned by the operating point scanning means 33 is other than the reference point. , The level obtained by the level monitoring means 34 and the holding means 35
And a control means 36 for preventing the scanning when the two levels match each other.

[0014]

In the light receiver according to the invention described in claim 1,
The light receiving element 12 photoelectrically converts an optical signal of a constant level emitted from the reference light source 11 into an electric signal. Further, the deviation between the photoelectric conversion efficiency of the light receiving element 12 and the fluctuation range of the efficiency with respect to temperature has a different value depending on the distribution of the characteristics of the light receiving element. The operating point scanning unit 13 sets a scanning area including a reference point at which the deviation of the operating point of the light receiving element 12 is equal to or less than the maximum allowable value under the above-described characteristic distribution, and scans the scanning area. Under such scanning, the level monitoring means 14 monitors the level of the above-mentioned electric signal to obtain a ratio with the value at the reference point, and the control means 15 monitors the ratio and the light-receiving element 12 performs the light- The above-described scanning is stopped when the ratio of the target value given in advance for the efficiency of electrical conversion and the value at the reference point of the efficiency are matched.

That is, within the range of variations in the characteristics of the light-receiving element 12, the efficiency of the target value is set relative to the level of the electric signal at the reference point at which the above-mentioned deviation is below the maximum allowable value. Since the operating point is set at the point where the light source is obtained, the level of the light emitted from the reference light source can be stabilized accurately with respect to temperature, and the accuracy can be improved without accurately adjusting the level of the optical signal incident on the light receiving element. The sensitivity is often calibrated.

In the light receiver according to the second aspect of the present invention, the light receiving element 12 optically-electrically converts an optical signal of a constant level emitted from the reference light source 11 and outputs an electrical signal. Further, the deviation between the photoelectric conversion efficiency of the light receiving element 12 and the fluctuation range of the efficiency with respect to temperature has a different value depending on the distribution of the characteristics of the light receiving element. The operating point scanning means 13 sets a scanning area including a reference point at which the deviation is equal to or less than the maximum allowable value under the distribution of the above-described characteristics, and scans the operating area of the light receiving element 12. .

When the operating point becomes the reference point in response to the scanning as described above, the holding control means 23 sets the ratio of the above-mentioned target value of efficiency and the value obtained based on the characteristic of the efficiency as a coefficient and sets the level. The monitoring means 21 obtains a reference level by multiplying the level of the electric signal output by the light receiving element 12 by its coefficient. Further, the holding means 23 holds the reference level. Further, when the operating point becomes other than the reference point in response to such scanning, the control means 25 sets the coefficient to "1", and the level monitoring means 21 sets the level of the electric signal output by the light receiving element 12. The coefficient is multiplied to obtain the reference level. Further, the control means 25 compares such a reference level with the reference level held by the holding means 23, and when they match each other, scanning of the operating point with respect to the light receiving element 12 is blocked.

That is, within the range of variations in the characteristics of the light receiving element 12, the efficiency of the target value is set relative to the level of the electric signal at the reference point at which the above-mentioned deviation is below the maximum allowable value. Since the operating point is set at the point where the light source is obtained, the level of the light emitted from the reference light source can be stabilized accurately with respect to temperature, and the accuracy can be improved without accurately adjusting the level of the optical signal incident on the light receiving element. The sensitivity is often calibrated.

In the light receiver according to the third aspect of the invention, the light receiving element 32 photoelectrically converts the optical signal emitted from the reference light source 31 into an electric signal and outputs the electric signal. Further, the deviation between the photoelectric conversion efficiency of the light receiving element 32 and the fluctuation range of the efficiency with respect to temperature has a different value depending on the distribution of the characteristics of the light receiving element. The operating point scanning means 33 sets a scanning area including a reference point at which the deviation of the operating point of the light receiving element 32 is equal to or less than the maximum allowable value under the above-described distribution of characteristics, and scans the scanning area. .

When the operating point becomes the reference point in response to scanning in this way, the holding control means 35 causes the reference light source 3 to hold the ratio of the above-described efficiency target value to the value obtained based on the efficiency characteristic.
1. The emission level is set to the product of the emission level of the optical signal emitted from 1 and the steady value, and at that time, the level monitoring means 3
Hold the level determined by 4. Further, when the operating point becomes other than the reference point in response to such scanning, the control means 36 sets the level of the optical signal emitted by the reference light source to the above-mentioned steady value, and the level monitoring means 3
Reference numeral 4 obtains the level of the electric signal output from the light receiving element 32 in accordance with the optical signal having such a steady value level. Further, the control means 36 controls such level and holding means 35.
If the two levels are compared with each other by comparing the level held at, the scanning of the operating point with respect to the light receiving element 32 is blocked.

That is, within the range of variations in the characteristics of the light-receiving element 32, the efficiency of the target value is relative to the level of the electric signal at the reference point at which the above-mentioned deviation is less than the maximum allowable value. Since the operating point is set at the point where the light source is obtained, the level of the light emitted from the reference light source can be stabilized accurately with respect to temperature, and the accuracy can be improved without accurately adjusting the level of the optical signal incident on the light receiving element. The sensitivity is often calibrated.

[0022]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 4 is a diagram showing an embodiment corresponding to the invention described in claim 1.

In the figure, parts having the same functions and configurations as those of the conventional example shown in FIG. 10 are designated by the same reference numerals, and the description thereof will be omitted here. This embodiment and FIG.
The difference from the conventional example shown in FIG. 0 is that a processor 40 is provided in place of the processor 80.

Regarding the correspondence relationship between this embodiment and the block diagram shown in FIG. 1, the light source drive circuit 89 and the reference light source 90 correspond to the reference light source 11, the APD 83 corresponds to the light receiving element 12, and the processor 40, The D / A converter 81 and the bias control circuit 82 correspond to the operating point scanning means 13, and include a resistor 84, an amplifier 85, a level detection circuit 86, and A.
The / D converter 88 and the processor 40 correspond to the level monitoring means 14, and the processor 40 corresponds to the control means 15.

FIG. 5 is an operation flowchart of this embodiment. The operation of this embodiment will be described below with reference to FIGS. The feature of the present invention resides in the operation procedure of the program executed by the processor 40 in the present embodiment. In addition,
Of these calculation procedures, those relating to the light receiving mode are the same as those in the conventional example, and therefore the description thereof will be omitted below.

In the calibration mode, the processor 40 causes the AP
Regarding D83, the reference value of the bias voltage (for example, 5 V in the characteristic shown in FIG. 11) in which the multiplication factor becomes “1” and the variation width of the multiplication factor according to the temperature becomes the maximum allowable value or less. A bias voltage, which is given in advance and has a reference value, is set via the D / A converter 81 and the bias control circuit 82 (FIG. 5 (1)). Further, the processor 40 drives the reference light source 90 via the light source drive circuit 89 (FIG. 5 (2)),
The reference light source 90 emits a certain level of reference light.
The APD 83 receives such reference light and photoelectrically converts it.
The current signal obtained by the optical conversion is converted into a voltage signal by the resistor 84. The amplifier 85 amplifies such a voltage signal by a predetermined amplification factor and supplies it to the level detection circuit 86. The level detection circuit 86 performs the same processing as the conventional example on the voltage signal thus supplied, A reference monitor signal indicating the above-mentioned level by voltage is generated (FIG. 5 (3)).

The processor 40 converts the above-mentioned reference monitor signal into a digital signal via the A / D converter 88 and fetches it, and the amplitude value A _S of the digital signal is multiplied by the APD 83 to be set in the light receiving mode. It is multiplied by (= μ ₀ ) and held in the main memory (FIG. 5 (4)).

Further, the processor 40 sets a scanning area in the plus direction starting from the above-mentioned reference value for the bias voltage of the APD 83, and through the D / A converter 81 and the bias control circuit 82 as described above. The scanning area is scanned (FIG. 5 (5)).

During the scanning of such bias voltage, the processor 40 synchronizes the amplitude value a _S of the monitor signal at each bias voltage value with the resistor 84, the amplifier 85 and the level detection circuit 86 in synchronization with the scanning. Measured through (Fig. 5
(6)), and the magnitude relationship between the amplitude value a _S and the value (= μ ₀ · A _S ) held in the main memory as described above is monitored.
Further, the processor 40 may a
Upon recognizing that the condition represented by the equation _S = μ ₀ · A _S is satisfied (FIG. 5 (7)), the above scanning is immediately stopped to hold the bias voltage at that time, and at the same time, the light source is The driving of the reference light source 90 is stopped via the drive circuit 89 (FIG. 5 (8)) to shift to the light receiving mode.

That is, as shown in FIG. 11, the APD8
3, the reference monitor signal level is accurately obtained by setting the bias voltage at a point where the value of the multiplication factor is known within a region in which the variation width of the multiplication factor with respect to temperature and the characteristic variation between elements are small, Further, the bias voltage is scanned up to a point where desired sensitivity is obtained with reference to such a level.

Therefore, the multiplication factor of the APD 83 is accurately set by suppressing variations in the characteristics of the APD and errors due to temperature. FIG. 6 is a diagram showing a first embodiment corresponding to the invention described in claim 2.

In the figure, parts having the same functions and configurations as those shown in FIG. 4 are designated by the same reference numerals, and the description thereof will be omitted here. The difference between the present embodiment and the embodiment shown in FIG. 4 is that a processor 50 is provided instead of the processor 40, and a resistor 51 connected in parallel is used.
And a switch 52 is placed in series with a resistor 84, the control input of which is connected to the third output of the processor 50.

Regarding the correspondence between this embodiment and the block diagram shown in FIG. 2, the light source drive circuit 89 and the reference light source 90 correspond to the reference light source 11, the APD 83 corresponds to the light receiving element 12, the processor 50, The D / A converter 81 and the bias control circuit 82 correspond to the operating point scanning means 13, and the resistors 84 and 51, the switch 52, the amplifier 85, the level detection circuit 86, the A / D converter 88 and the processor 50 monitor the level. Corresponding to the means 21, the processor 50 corresponds to the holding means 23 and the control means 25.

FIG. 7 is an operation flowchart of this embodiment. The operation of this embodiment will be described below with reference to FIGS. 6 and 7. In the calibration mode, the processor 50 sets the contact of the switch 52 to open (FIG. 7 (1)). Further, the processor 50 causes the APD 83 to have a reference value of the bias voltage (for example, 5 in the characteristic shown in FIG. 11) in which the multiplication factor becomes “1” and the variation width of the multiplication factor according to the temperature becomes the maximum allowable value or less. Voltage is applied in advance, and the bias voltage of the reference value is set via the D / A converter 81 and the bias control circuit 82 (FIG. 7 (2)). Further, the processor 50 is similar to the embodiment shown in FIG.
0 (FIG. 7 (3)), and the reference light source 90 emits reference light of a constant level. The APD 83 receives and photoelectrically converts such reference light, and the current signal obtained by the photoelectric conversion is converted into a voltage signal by the resistors 84 and 51. The amplifier 85 amplifies such a voltage signal by a predetermined amplification factor and supplies it to the level detection circuit 86. The level detection circuit 86 performs the same processing as the conventional example on the voltage signal thus supplied, A reference monitor signal indicating the above-mentioned level by a voltage is generated.

The processor 50 converts the above-mentioned reference monitor signal into a digital signal via the A / D converter 88 and fetches it (FIG. 7 (4)), and holds the value A _{S of the} digital signal in the main memory. (Fig. 7 (5)).

Further, the processor 50 sets only the resistor 84 as the load resistance of the APD 83 by closing the contact of the switch 52 (FIG. 7 (6)), and starts the reference value described above for the bias voltage of the APD 83. Then, the scanning area in the plus direction is set, and the scanning area is scanned through the D / A converter 81 and the bias control circuit 82 (FIG. 7 (7)).

During the scanning of such a bias voltage, the amplifier 85 and the level detection circuit 86 continue the same operation and generate a monitor signal. The processor 50 is A /
A digital signal corresponding to the monitor signal is taken in through the D converter 88, and its value b _S is measured (FIG. 7 (8)),
Moreover, the magnitude relationship between the value b _S and the value (= A _S ) held in the main memory as described above is monitored.

Further, the processor 50 recognizes that the condition expressed by the equation b _S = A _S is satisfied under such monitoring (FIG. 7).
(9)), and immediately stop the above-mentioned scanning to hold the bias voltage at that time, and stop the driving of the reference light source 90 by the light source drive circuit 89 (FIG. 7 (10)) to enter the light receiving mode. Transition.

By the way, the amplitude v of the voltage signal applied to the output of the amplifier 85 in response to the scanning of the bias voltage, the multiplication factor μ of the APD 83 which changes in accordance with the bias voltage, and the load resistance of the APD. V between value R
The relational expression of ∝μR holds. Further, the amplitudes v ₁ and v ₂ of the voltage signal at the starting point and the other points of the above-described scanning area based on the above relational expression are the resistance value R ₁ of the resistor 51 and the resistance value R ₂ of the resistor 84. On the other hand, it is represented by a relational expression of v ₁ ∝ 1 · (R ₁ + R ₂ ) v ₂ ∝μR ₂ . Furthermore, these amplitudes v ₁ , v
₂ is the value A _S held in the main memory as described above, because the characteristics of the amplifier 85, the level detection circuit 86 and the A / D converter 88 are constant over the entire scanning range described above.
And the amplitude value b _S , the relational expression of v ₁ ∝A _S v ₂ ∝b _S holds.

Therefore, in the present embodiment, the resistor 51 is set to a _{value such} that μ ₀ = (R ₁ + R ₂ ) / R ₂ holds for the multiplication factor μ ₀ to be set in the APD 83 in the light receiving mode. By setting the resistance value R ₁ and the resistance value R ₂ of the resistor 84 respectively, the bias voltage at the time when the scanning is stopped is reliably set to the point where the multiplication factor μ ₀ is obtained as described above. .

Further, such scanning stop control is performed by the AP
Among the characteristics of D83, the value of the multiplication factor is known, and since it is performed with reference to one point in the region where the variation width of the multiplication factor with respect to temperature and the variation in the characteristics between elements are small, the AP
The multiplication factor of D83 is set accurately.

Further, in the present embodiment, the gain in the section from the APD 83 to the input terminal of the level detection circuit 86 is switched at the starting point and the other points in the scanning of the bias voltage, but the dynamic ledge of such section is switched. 4 has a large value adaptable to the multiplication factor of the APD 83 in the light receiving mode, the embodiment shown in FIG. 4 may be applied.

FIG. 8 is a diagram showing a second embodiment corresponding to the invention described in claim 2. In FIG. In the figure, parts having the same functions and configurations as those shown in FIG. 6 are designated by the same reference numerals, and the description thereof will be omitted here.

The difference between the present embodiment and the embodiment shown in FIG. 6 is that the resistor 84 is directly grounded without the resistor 51 and the switch 52, and the amplifier 61 is provided in place of the amplifier 85. The processor 5 is connected to the control input of the amplifier 61.
The second output of 0 is at the connected point.

In the present embodiment, the gain in the section from the APD 83 to the input of the level detection circuit 86 is the gain of the amplifier 61 which is a predetermined value corresponding to the above-mentioned bias reference value and a multiplication factor μ _{0 of} that value. It is set to one value by switching under the control of the processor 50.

In the embodiment shown in FIG. 6, such gain switching is performed by connecting and disconnecting both ends of the resistor 51 arranged in series with the APD 83 via the switch 52. The operation of each of the other parts in the example is exactly the same, so the description thereof is omitted here.

Therefore, in this embodiment, the multiplication factor of the APD 83 is set accurately with the same manner as in the embodiment shown in FIG. In addition, since the variation of the operating point of the APD 83, which is caused by the connection and disconnection of the contact of the switch 52 in the embodiment shown in FIG. 6, is suppressed, the scan control of the bias voltage is simplified and made efficient, and the calibration mode Can be completed promptly. In the embodiment shown in FIGS. 6 and 8, A
The resistance value of the resistor connected in series to the PD 83 and the gain of the amplifier 61 arranged in the subsequent stage are variable, but the present invention is not limited to such a configuration, and for example, the level detection circuit 86 or A The input / output characteristics of the / D conversion means 88 may be changed, or the multiplier applied to the multiplication may be changed so that the processor 40 (50) performs the multiplication based on software.

FIG. 9 is a diagram showing an embodiment corresponding to the invention described in claim 3. In FIG. In the figure, those having the same functions and configurations as those shown in FIG. 8 are designated by the same reference numerals, and the description thereof will be omitted here.

The difference between the present embodiment and the embodiment shown in FIG. 8 is that a light source drive circuit 71 having a control input is provided in place of the light source drive circuit 89, and the control input has a second input of the processor 50. Is connected, and an amplifier 85 is provided in place of the amplifier 61.

Regarding the correspondence between this embodiment and the block diagram shown in FIG. 3, the light source drive circuit 71 and the reference light source 90 correspond to the reference light source 31, the APD 83 corresponds to the light receiving element 32, and the processor 50, The D / A converter 81 and the bias control circuit 82 correspond to the operating point scanning means 33, and include a resistor 84, an amplifier 85, a level detection circuit 86, and A.
The / D converter 88 and the processor 50 correspond to the level monitoring means 34, and the processor 50 corresponds to the holding means 35 and the control means 36.

The operation of this embodiment will be described below. In the present embodiment, the gain from the APD 83 to the input of the level detection circuit 86 is set constant via the resistor 84 and the amplifier 85, and the gain switching performed in the embodiments shown in FIGS. 6 and 8 is replaced. Then, the drive level of the reference light source 90 is switched via the light source drive circuit 71 under the control of the processor 50.

That is, the level of the reference light is set to a predetermined value in correspondence with the reference value of the bias voltage described above, and the level of the reference light is reduced to one of the multiplication factor μ ₀ instead of decreasing the gain described above. Set to the value of. Further, since the other parts operate in the same manner as the embodiment shown in FIG. 8, the description of the operation is omitted here.

Therefore, in this embodiment, the multiplication factor of the APD 83 is set accurately with the same manner as in the embodiment shown in FIG. Further, since the above-mentioned switching is surely performed without changing the operating point of the APD 83, the scanning control of the bias voltage is simplified and made efficient, and the calibration mode is quickly completed.

In each of the above embodiments, the APD 83
However, the present invention is not limited to such a configuration, and may be subjected to any modulation processing as long as the level of the reference light can be measured reliably.

Further, in each of the embodiments described above, the APD 83 is provided at different timings for the light to be actually received and the reference light.
However, the present invention is not limited to such a configuration. For example, for these lights, separation processing based on the difference in wavelength and the modulation method applied to both is performed with the level detection circuit 86 and the distance measurement. If it can be surely done by the circuit 87, they may be given at the same time.

Further, in each of the above-mentioned embodiments, it is assumed that the optical signal corresponding to the signal to be processed by the distance measuring circuit 87 is subjected to predetermined modulation based on the sine wave signal or the pulse signal. However, the present invention is not limited to such a modulation method, and may be an analog amplitude modulation method, an angle modulation method, a digital modulation method for realizing a predetermined signal arrangement, a modulation method for spreading on the frequency axis, or any other modulation method. You may apply.

Further, in each of the above-mentioned embodiments, the APD 83 is applied as the light receiving element, but the present invention is not limited to the light receiving device using such an APD, and the opto-electric conversion is performed according to the operating point. If the light receiving element has a characteristic in which the efficiency of changes and the fluctuation range of the efficiency changes with temperature,
For example, it can be applied to a photoreceiver using any photodetector such as a photomultiplier tube.

Further, in each of the above-described embodiments, the bias voltage whose multiplication factor is "1" is applied to the APD 83 in order to obtain the reference monitor signal, but the present invention uses such a multiplication factor value. The multiplication factor is not limited, and if the multiplication factor is known based on the photoelectric conversion characteristics obtained in advance and the fluctuation range of the multiplication factor with respect to temperature is equal to or less than the allowable maximum value, the multiplication factor has any value. However, the bias voltage does not necessarily have to be applied to obtain the multiplication factor.

Furthermore, in each of the above-described embodiments, the APD 83 is used in addition to the measurement and comparison relating to the level of the reference light.
The operating point setting and switching of the processor 40 (50)
Is performed under the control of the software executed by
The present invention is not limited to the configuration using such a processor, and may be configured using dedicated hardware, and these hardware may perform processing in either the analog domain or the digital domain.

Further, in each of the above-mentioned embodiments, the distance measurement is performed by the processor 50 by the distance measuring circuit 87 performing a predetermined process on the optical signal received through the APD 83. In this way, the device or system is not limited to the configuration in which the existing processor is shared, and a dedicated processor may be mounted if necessary.

Further, in each of the embodiments described above, the operating point at which the desired multiplication factor of the APD is obtained by the processor 40 (50) stopping the scanning of the bias voltage is set. However, the configuration is not limited to this, and for example, a configuration may be employed in which a transparent latch is provided at the output end of the D / A converter 81 and latching is performed instead of stopping scanning.

[0062]

As described above, in the invention described in claims 1 to 3, within the range of the characteristic variation of the light receiving element, the efficiency and the deviation of the fluctuation range of the efficiency with respect to temperature are equal to or less than the maximum allowable value. The operating point is set at a point where the efficiency of the target value is relatively obtained with reference to the level of the electric signal at the reference point.

That is, the level of the light emitted from the reference light source is accurately stabilized with respect to temperature, and the sensitivity is calibrated with high accuracy without accurately adjusting the level of the optical signal incident on the light receiving element.

Therefore, in the equipment to which the present invention is applied, desired sensitivity can be surely obtained while simplifying the scale and configuration of the circuit, and the performance can be improved while reducing the cost and the size.

[Brief description of drawings]

FIG. 1 is a principle block diagram of the invention according to claim 1.

FIG. 2 is a principle block diagram of the invention described in claim 2.

FIG. 3 is a principle block diagram of the invention according to claim 3;

FIG. 4 is a diagram showing an embodiment corresponding to the invention described in claim 1.

FIG. 5 is an operation flowchart of the present embodiment.

FIG. 6 is a diagram showing a first embodiment corresponding to the invention described in claim 2;

FIG. 7 is an operation flowchart of the present embodiment.

FIG. 8 is a diagram showing a second embodiment corresponding to the invention described in claim 2.

FIG. 9 is a diagram showing an embodiment corresponding to the invention according to claim 3;

FIG. 10 is a diagram showing a configuration example of a conventional light receiver.

FIG. 11 is a diagram showing an example of characteristics of an APD.

[Explanation of symbols]

 11, 31, 90 Reference light source 12, 32 Light receiving element 13, 33 Operating point scanning means 14, 21, 34 Level monitoring means 15, 25, 36 Control means 23, 35 Holding means 40, 50, 80 Processor (CPU) 51, 84 resistor 52 switch 61,85 amplifier 71,89 light source drive circuit 81 D / A converter (D / A) 82 bias control circuit 83 avalanche photodiode 86 level detection circuit 87 distance measuring circuit 88 A / D converter ( A / D)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location G01S 7/48 Z 9108-2F

Claims (3)

[Claims] 1. A reference light source that emits an optical signal at a constant level, an optical signal that is optically-electrically converted from the optical signal emitted by the reference light source, and outputs an electrical signal. A light receiving element having a characteristic that the fluctuation range of the efficiency changes according to the operating point, and a reference point at which the deviation of the efficiency and the fluctuation range of the operating point is equal to or less than a maximum allowable value under the distribution of the characteristics. A scanning area including the scanning point is set, and an operating point scanning means for scanning the scanning area, and a level of the electric signal output by the light receiving element in synchronization with the scanning performed by the operating point scanning means, the reference point at that level And a level monitoring means for obtaining a ratio with the value in the above, and the ratio obtained by the level monitoring means is monitored, and the ratio is set to a target value given in advance for the efficiency and the reference point of the efficiency. Light receiver, characterized in that a control means for inhibiting said scanning when equal to the ratio of the that value. 2. A reference light source that emits an optical signal at a constant level, and an optical signal that is photo-electrically converted from the optical signal emitted by the reference light source to output an electrical signal. A light receiving element having a characteristic that the fluctuation range of the efficiency changes according to the operating point, and a reference point at which the deviation of the efficiency and the fluctuation range of the operating point is equal to or less than a maximum allowable value under the distribution of the characteristics. A scanning area including the scanning area is set, the operating point scanning means for scanning the scanning area, and the level of the electric signal output by the light receiving element are monitored, and the level is multiplied by a coefficient set from the outside to obtain a reference level. When the operating point scanned by the operating point scanning means is the reference point, the ratio of the target value given in advance to the efficiency and the value based on the characteristic of the efficiency is used as the coefficient. And a holding unit that holds the reference level determined by the level monitoring unit, and the operating point scanned by the operating point scanning unit is other than the reference point, the coefficient is set to "1". In addition to setting, the control means compares the reference level obtained by the level monitoring means with the reference level held by the holding means, and prevents the scanning when the two match. Receiver to be. 3. A reference light source that emits an optical signal at an emission level designated from the outside, an optical signal that is optically-electrically converted from the optical signal emitted by the reference light source, and an electrical signal is output. A light-receiving element having a characteristic that the efficiency and the fluctuation range of the efficiency with respect to temperature change according to the operating point, and the deviation of the efficiency and the fluctuation range at the operating point is equal to or less than the maximum allowable value under the distribution of the characteristics. A scanning area including the reference point is set, an operating point scanning means for scanning the scanning area, a level monitoring means for obtaining a level of an electric signal output by the light receiving element, and an operation for scanning by the operating point scanning means When the point is the reference point, the emission level is set to the product of the ratio between the target value given in advance for the efficiency and the value based on the characteristic of the efficiency and the steady value of the emission level. Together, holding means for holding the level obtained by the level monitoring means, when the operating point scanned by the operating point scanning means is other than the reference point, while setting the emission level to the steady value, A light receiving device comprising: a control unit that compares the level obtained by the level monitoring unit with the level held by the holding unit, and blocks the scanning when the two match.