JP2000077705A - Light receiving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain always the current image magnification of a light- receiving device at a desired current image magnification by a method wherein a potential difference, which is changed according to a temperature change in a photodetector, is generated via a load resistor connected between a first transistor circuit and a second transistor circuit and a bias voltage to respond to the potential difference is generated to feed the bias voltage to the photodetector. SOLUTION: An amplifier 81 is formed of transistors Q1 and Q2 which are used as first transistor circuits, a temperature detection part 82 is formed of a transistor Q3 which is used as a second transistor circuit, and a potential difference ΔVBE which is changed according to a temperature change in a photodetector 42 is generated via a load resistor RE connected between an emitter voltage VE1 of the transistor Q1 of the amplifier 81 and an emitter voltage VE1 of the transistor Q3 of the detection part 82. A bias voltage VB1 to respond to the potential difference ΔVBE is generated to feed the bias voltage VB1 to the photodetector 42. As a result, a light-receiving device can always obtain a desired current image magnification regardless of the temperature change in the photodetector 42.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a light receiving device,
For example, the present invention is suitably applied to a light receiving device that converts an optical signal received in an optical space transmission device into an electric signal and signals the electric signal.

[0002]

2. Description of the Related Art Conventionally, there has been proposed an optical space transmission system for transmitting an information signal between a pair of space optical transmission devices via a light beam. In this space optical transmission system, one space optical transmission device transmits the intensity-modulated light beam by driving the laser diode based on a predetermined information signal to the other space optical transmission device installed at the opposite position. Out. The other optical space transmission device receives the light beam by the light receiving element of the light receiving device and demodulates the output signal to restore the information signal, and thus the information signal is transmitted via the light beam. .

In this light receiving device, a light receiving element composed of an avalanche photodiode (hereinafter referred to as APD) is used. This APD has a current multiplication factor of about 100 times that of a normal photodiode (PD), and has a high current multiplication factor even when a light beam received in optical space transmission over a long distance is weak. Signal components can be sufficiently extracted.

The APD has a predetermined bias voltage (more precisely, a reverse bias voltage of, for example, 200 [V]) in the vicinity of a breakdown voltage (a bias voltage that causes a breakdown).
, A high current multiplication factor can be obtained, but the breakdown voltage has a temperature variation, so that the bias voltage needs to be adjusted according to the temperature condition used.

[0005]

In the light-receiving device having such a configuration, it is necessary to apply an optimum bias voltage to the APD depending on the temperature. Therefore, the temperature in the use environment of the APD is always accurately detected, and the detection result is used. There is a problem that a complicated calculation process for controlling the bias voltage by the microcomputer must be performed based on the calculation.

In this case, it is necessary to provide a temperature sensor for accurately detecting the temperature of the APD in the vicinity of the APD. However, the provision of the temperature sensor avoids an increase in the overall size of the light receiving device. There was a problem that it could not be obtained.

Further, in the light receiving device, even if a temperature sensor is provided in the vicinity of the APD, the temperature sensor does not always detect only the temperature of the APD, but may detect the temperature generated by another circuit. . Therefore, the light receiving device cannot always accurately detect the temperature with the temperature sensor, and therefore cannot apply an optimum bias voltage to the APD, and thus cannot obtain a desired current multiplication factor.

The present invention has been made in view of the above points, and has as its object to propose a light receiving device capable of always obtaining a desired current image magnification regardless of a temperature change.

[0009]

According to the present invention, there is provided a light receiving apparatus for extracting a received signal by converting a received optical signal into an electric signal.
A light-receiving element that is driven by a bias voltage corresponding to temperature and converts a received light signal into an electric signal, and an amplification that generates an output signal by amplifying the electric signal by a first transistor circuit connected to the light-receiving element Means, a first transistor circuit, and a second transistor circuit having a temperature characteristic different from the temperature characteristic of the first transistor circuit, according to a temperature change of the light receiving element via a load resistor connected thereto. A potential difference generating means for generating a changing potential difference and a bias voltage generating means for generating a bias voltage according to the potential difference and supplying the bias voltage to the light receiving element are provided.

A potential difference corresponding to a temperature change is generated by utilizing a difference in temperature characteristics between the first transistor circuit and the second transistor circuit, and a bias voltage corresponding to the potential difference is generated and supplied to a light receiving element. Accordingly, an optimal bias voltage according to the temperature during use can be supplied to the light receiving element.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

(1) Overall Configuration of Optical Space Transmission System In FIG. 1, reference numeral 1 denotes an optical space transmission system as a whole, and optical space transmission apparatuses 10 and 11 having the same configuration are installed facing each other at a predetermined distance. Have been. The space optical transmission apparatus 10 sends the transmission light beam L1 modulated based on the information signal to the space optical transmission apparatus 11, and the space optical transmission apparatus 11 similarly transmits the transmission light beam L1 modulated based on the information signal. By transmitting L2 to the free-space optical transmission apparatus 10, information signals are mutually transmitted and received via the transmission light beams L1 and L2.

(2) Structure of Optical Space Transmission Apparatus In FIG. 2, in the optical space transmission apparatus 10, a power supply unit 39 converts a current supplied from a power supply (not shown) via a power supply connector 23 into a predetermined voltage. , To each circuit block constituting the space optical transmission apparatus 10.

The holder 40 of the optical space transmission apparatus 10 includes a laser diode 41, a light receiving element (APD) 42, a position detecting element (PSD: Position Sensitive Device) 43, lenses 44 to 47, a filter 49, a prism 50, and a servo mirror 60. And the lens holder 66
By holding the lens 48 via the lens, an optical system integrated as a whole is constituted.

The lens 48 receives the received light beam L 2 arriving from the optical space transmission device 11 with a predetermined plane of polarization, and guides the received light beam L 2 to the prism 50 via the lens 47 and the servo mirror 60.

The servo mirror 60 comprises a mirror 61 which is a plane mirror and an actuator 6 which drives the mirror 61 to rotate.
2 and a skew sensor 63. The mirror 61 is attached to the holder 40 by a mirror support (not shown).
Is rotatably supported. The skew sensor 63 is
The angle information of the mirror 61 is transmitted to the skew sensor angle detector 65.
To a CPU (Central Processing Unit) 36 via

The prism 50 includes a first right-angle prism 50A and a second right-angle prism 50B having the same size, and a third right-angled isosceles prism 50C. The first right-angle prism 50A and the second right-angle prism 50B have the same size. And the right-angled surface of the third right-angled isosceles prism 50C are formed in the same shape.

That is, the prism 50 is formed by bonding the inclined surfaces of the first right-angle prism 50A and the second right-angle prism 50B to the respective right-angle surfaces of the third right-angled isosceles prism 50C. A polarizing beam splitter M1 is formed on the bonding surface between the second right-angle prism 50C and the third right-angle prism 50C.
A beam splitter M2 is formed on the bonding surface between B and the third right-angled isosceles prism 50C.

The polarizing beam splitter M1 reflects the incident light beam at right angles according to the plane of polarization of the light beam. The beam splitter M2 reflects a part of the incident light beam at a right angle, and transmits a part of the incident light beam in a straight line.

The polarizing beam splitter M1 of the prism 50
Guides the received light beam L2 to the beam splitter M2 according to the polarization plane of the received light beam L2. The beam splitter M2 transmits a part of the received light beam L2 to transmit it to the lens 45 as a received light beam L3, and reflects a part of the received light beam L2 to transmit it to the filter 49 as a received light beam L4. I do.

The filter 49 transmits only a predetermined band of the received light beam L4 and sends it out to the position detecting element 43 via the lens 46. The position detection element 43 receives the reception light beam L4 condensed by the lens 46, and has a current level corresponding to the intensity center of gravity of the reception light beam L4 on a light receiving surface (not shown) of the position detection element 43. A position signal S43 is generated and sent to the PSD light receiving circuit 35. The PSD light receiving circuit 35 generates a position signal S35 by subjecting the position signal S43 to current-voltage conversion processing, and sends this to the CPU 36.

The CPU 36 calculates the focal position of the received light beam L4 on the light receiving surface of the position detecting element 43 based on the position signal S35, and determines a predetermined focus reference point and the received light beam L4.
By controlling the servo mirror 60 so that the focal position of the optical fiber 4 coincides with the focal position of the optical fiber 4, the optical axis of the reception light beam L2 and the transmission light beam L1 that enters and exits the free-space optical transmission device 10 is adjusted to match.

That is, the CPU 36 calculates a position difference between the focus position of the received light beam L4 on the light receiving surface of the position detection element 43 and a predetermined focus reference point based on the voltage level of the position signal S35, and according to the position difference. Drive signal S64
To the actuator drive unit 64. The actuator driving unit 64 drives the actuator 62 according to the driving signal S64 to rotate the mirror 61,
The rotation of the mirror 61 causes the focal position of the reception light beam L4 to coincide with the focus reference point.

On the other hand, the APD 42 generates an output signal S42 by performing light-to-current conversion on the received light beam L3 condensed by the lens 45, and outputs the output signal S42 to the A as a light receiving device.
The light is transmitted to the PD light receiving device 34. The APD light receiving device 34
The output signal S <b> 42 is subjected to current-voltage conversion to generate an output signal S <b> 34, which is sent to the demodulation unit 33.

The demodulation section 33 generates an information signal S33 by demodulating the output signal S34, and outputs this to the outside via the output connector 22. Thereby, the optical space transfer apparatus 10 receives the received light beam L2 from the optical space transfer apparatus 11.
And recovers the information signal based on the received light beam L2.

In the optical space transfer apparatus 10, the modulation section 31 generates a modulation signal S31 by modulating a carrier of a predetermined frequency based on an information signal S1 supplied from the outside via the input connector 21. It is sent to the laser diode drive circuit 32.

The laser diode drive circuit 32 converts the modulation signal S31 into a drive current S3 by performing voltage-to-current conversion.
2 is generated and sent to the laser diode 41.
The laser diode 41 converts the driving current S32 from current to light, thereby transmitting the transmission light beam L having a predetermined polarization plane.
1 is sent to the lens 44.

At this time, the CPU 36 generates a control signal S36 based on the light amount control information supplied from the outside and supplies the control signal S36 to the laser diode drive circuit 32 so as to control the output of the transmission light beam L1. It has been done.

The lens 44 converts the transmission light beam L1 into parallel light and sends it to the polarization beam splitter M1 of the prism 50. The polarization beam splitter M1 reflects the transmission light beam L1 according to the polarization plane of the transmission light beam L1 and sends it to the servo mirror 60.

The servo mirror 60 reflects the transmission light beam L 1 and guides it to the lens 47. Lens 47 and lens 48
Converts the transmission light beam L <b> 1 into substantially linear parallel light having a predetermined light beam diameter, and sends this light to the optical space transmission device 11.

(3) Configuration of APD light receiving device As shown in FIG. 3, the APD light receiving device 34 includes an amplifier section 81 as amplifying means, a temperature detecting section 82 as a potential difference generating means, and a current mirror section as a bias voltage generating means. 83, a load resistor RB, a variable power supply VP, and an APD 42 as a light receiving element are integrally formed as a whole.

The amplifier section 81 is formed by transistors Q1 and Q2 as a first transistor circuit, and supplies an output signal S42 obtained by performing light-to-current conversion of the received light beam L3 by the APD 42 to the base of the transistor Q1. I do.

The transistor Q1 has a collector connected to the power supply line V _CC1 via the load resistor RL1, and
It is connected to the base of transistor Q2. The transistor Q1 has an emitter grounded via a load resistor RE1.

The transistor Q2 has a collector connected to the power supply line V _CC1 , an emitter grounded via the load resistor RE2, and a negative feedback loop from the emitter to the base of the transistor Q1 via the resistor R1. I have.

Therefore, when the output signal S42 is supplied to the base of the transistor Q1, the amplifier 81 is amplified by the transistors Q1 and Q2 at a predetermined amplification rate and outputs the output signal S34 from the emitter of the transistor Q2.

In the temperature detecting section 82, the base of a transistor Q3 as a second transistor circuit is connected to a power supply line V _CC1 via a resistor R2, grounded via a resistor R3, and the collector is a current mirror section 83. Of the transistor Q4. Note that a capacitor C1 is connected to the base of the transistor Q3, thereby removing noise and, even when an excessive current flows when the power is turned on, allowing the excessive current to escape to the capacitor C1 and cause the excessive current to flow to the base. I try not to.

The emitter of the transistor Q3 is connected to the emitter of the transistor Q1 via the load resistor RE. At this time, the temperature characteristic dV of the transistor Q3
_BE3 / dT is generally given by

[0038]

(Equation 1)

Given by

On the other hand, since the output of the transistor Q2 is negatively fed back to the base of the transistor Q1, the transistor Q1 has the emitter voltage V
_E1 is

[0041]

(Equation 2)

Is represented by

Here, the base current of the transistor Q1 is negligibly small, and the transistors Q1 and Q2 are transistors of the same performance, so that the base-emitter voltage V _BE1 and the base-emitter voltage V
_Since it is considered that this is almost the same as _BE2 , the emitter voltage V _{E1 in the} expression (2) is given by the following expression:

[0044]

(Equation 3)

When this is modified, the emitter voltage V _E1 is given by the following equation:

[0046]

(Equation 4)

Becomes

Here, the resistance value R _L1 of the load resistance RL1 = 30
0 [Ω] and the resistance value R _E1 of the load resistor RE1 = 47 [Ω], the emitter voltage V _{E1 in the} equation (4) is calculated by the following equation.

[0049]

(Equation 5)

Is represented by

At this time, the emitter voltage V _{E1 in} equation (5) is
Regardless of the term is the temperature characteristic of the V _CC1, also believed that the transistor by Q1 and Q3 are transistors of the same performance, the base and emitter voltage V _BE1 and the base and emitter voltage V _BE3 is approximately the same Therefore, if attention is paid only to the term V _BE1, the emitter voltage V _E1 is given by the following equation.

[0052]

(Equation 6)

Is represented by Therefore, the temperature characteristic dV _BE1 / dT of the transistor Q1 is given by the following equation.

[0054]

(Equation 7)

Is as follows.

This is due to the temperature characteristic dV of the transistor Q1.
_BE1 / dT is the temperature characteristic dV _BE3 /
It represents that only 27 [%] extent as compared with dT, this number is determined by the resistance value of the resistance value R _L1 and the load resistor RE1 of the load resistor RL1.

Therefore, the potential difference ΔV _BE between the emitter voltage V _E1 of the transistor Q1 and the emitter voltage V _E3 of the transistor Q3 is given by the following equation.

[0058]

(Equation 8)

Is represented by

The potential difference ΔV _{BE in the} equation (8) is a value that changes in accordance with the temperature.
A collector current I _C3 according to V _BE flows. That is, the collector current I _C3 changes according to the temperature change.

The current mirror unit 83 includes a transistor Q
4 has a base connected to the power supply line V _CC1 , an emitter connected to the collector of the transistor Q3, and a collector connected to the collector of the transistor Q5.

The transistor Q5 has a base commonly connected to the transistor Q6, a collector connected to the base, and an emitter connected to the power supply line V _CC2 via the resistor R4. The transistor Q6 has an emitter connected to the power supply line V _CC2 via a resistor R5, a collector connected to a load resistor RB set to a predetermined resistance value, and a variable power supply VP based on a predetermined voltage value, AP
D42 is connected to the cathode.

As a result, in the current mirror section 83, the collector current I _C3 of the transistor Q3 flows also to the collector of the transistor Q6. Actually, the current mirror unit 83 has the resistance value of the resistor R5 set to 1 / X times smaller than the resistance value of the resistor R4 (in this case, R5 = R4 / 1.68), so that the collector current I _C3 is X times larger. Of the collector current I _C6 flows.

Therefore, the collector current I _C6 and the load resistance R
A potential determined by the voltage value determined by B and the voltage value of the variable power supply VP is generated at the point A. At this time, the potential generated at the point A is set as the bias voltage VB1 and the AP
D42.

By the way, in the APD light receiving device 34,
A microcomputer 84 for controlling the voltage value of the variable power supply VP is provided. Thereby, the APD light receiving device 34
For example, when a light beam having a high optical power such as sunlight is incident on the APD 42, the APD 42 is normally thermally destroyed even with the optimum bias voltage VB1.
In such a case, by lowering the voltage value of the variable power supply VP based on the control of the microcomputer 84, A
The PD 42 is protected from thermal destruction.

When a simulation is performed in such an APD light receiving device 34 when the actual use temperature is 25 ° C., as shown in FIG. 4, the base-emitter voltage V _BE3 of the transistor Q3 is 455. [mV], and the base-emitter voltage V _{BE1 of} the transistor Q1 is 36
9 [mV]. In this case, the voltage across the load resistor RE, that is, the potential difference ΔV _{BE (25)} is 86 [mV]. At this time, if the resistance value of the load resistor RE is 620 [Ω], the collector current I
_C3 is 138 [μA].

This collector current I _C3 is multiplied by 1.68 (X = 1.68) by the current mirror unit 83.
As a result, a collector current I _C6 of 232 [μA] flows through the collector of the transistor Q6. Where the load resistance R
The resistance value of B is 200K [Ω] and the voltage value of the variable power supply VP is 1
00 [V], the voltage V _RB (4
6.4 [V]) and 100 [V] of the variable power supply VP are added.
The potential [V] is generated at the point A, and this can be supplied to the APD 42 as the bias voltage VB1.

That is, as shown in FIG.
In order to obtain a desired current multiplication factor (M = 100) when the temperature is 5 [° C.], a bias voltage of about 146 [V] is required. It turns out that it has been obtained.

Similarly, when a simulation is performed in the case where the operating temperature is 75 ° C. in the APD light receiving device 34, as shown in FIG. 5, the voltage V _BE3 between the base and the emitter of the transistor Q3 is 551 [mV]. ], And the voltage V _BE1 between the base and the emitter of the transistor Q1 is 399.5 [mV]
Becomes In this case, the voltage across the load resistor RE, that is, the potential difference ΔV _{BE (75)} is 151.5 [mV]. At this time, if the resistance value of the load resistor RE is 620 [Ω], the collector current I _C3
Is 243 [μA].

This collector current I _C3 is multiplied by 1.68 (X = 1.68) by the current mirror unit 83.
As a result, a collector current I _C6 of 407 [μA] flows through the collector of the transistor Q6. Again, the resistance value of the load resistor RB is 200K [Ω] and the voltage value of the variable power supply VP is
If the voltage is the same at 100 [V], the voltage V across the load resistor RB
_RB (81.4 [V]) and 100 [V] of variable power supply VP were added
A potential of 181.4 [V] is generated at the point A, and this can be supplied to the APD 42 as the bias voltage VB1.

That is, as shown in FIG.
In order to obtain a desired current multiplication factor (M = 100) when the temperature is 5 [° C], a bias voltage of about 181 [V] is required. It turns out that it has been obtained.

When the operating temperature is 75 ° C., the potential difference ΔV _{BE (75)} is 151.5 [mV], and the operating temperature is 2
The potential difference ΔV _{BE (25)} when the temperature is 5 ° C. is 86 [mV] and the difference voltage ΔV _RE is 65.5 [mV]. However, in the transistors Q 1 and Q 3 having the same performance, the amount of current flowing Changes, the emitter voltage also changes accordingly.

Therefore, the difference voltage ΔV _RE includes a voltage value V _BE 'corresponding to a current change (243 [μA] / 138 [μA]) corresponding to a temperature change.
Will be included. Therefore, the operating temperature is 75 [°
C], assuming that a collector current I _C3 of 138 [μA] flows as in the case of 25 ° C., the increased voltage value V _BE ′ at that time is expressed by the following equation.

[0074]

(Equation 9)

The voltage value V _BE 'at this time is 17.1
[mV]. Incidentally, since the temperature characteristics of the transistors Q1 and Q3 are different, strictly, the collector current I _C3 does not become constant with respect to the temperature change.

At this time, the accurate difference voltage ΔV _RE ′ including the increased voltage value V _BE ′ is given by the following equation:

[0077]

(Equation 10)

And the differential voltage ΔV _RE ′ at that time
Is 82.6 [mV], and when this is converted per 1 [° C.], the potential difference ΔV _BE ′ becomes

[0079]

[Equation 11]

As a result, 1.66 [mV / C °] is obtained.

Here, the temperature characteristic dV _BE3 / dT of the transistor Q3 composed of the NPN transistor used in this simulation model is -2.22 [mV / C °] in this case.
This potential difference ΔV _BE ′ (= 1.66 [mV / C °]) is about 73% of the temperature characteristic dV _BE3 / dT of the transistor Q3.
Thus, it is proved that the simulation result is correct by agreeing with the equation (8).

(4) Operation and Effect In the above configuration, the APD light receiving device 34 has the emitter voltage V _E1 of the transistor Q1 and the emitter voltage V 3 of the transistor Q3 of the negative feedback amplifier circuit in which the transistors Q1 and Q2 are connected in two stages. _A load resistance RE is provided between _E3 and _E3 to generate a predetermined potential difference ΔV _BE according to the temperature characteristic of the transistor, and the resistance value of the load resistance RB and the voltage value of the variable power supply VP are set according to the potential difference ΔV _BE. The potential difference Δ generated in response to a temperature change.
Based on V _BE , an optimum bias voltage VB1 corresponding to the operating temperature of the APD 42 is generated.

That is, the APD light receiving device 34
2, it is possible to supply the APD 42 with the optimum bias voltage VB1 that can always obtain a desired current multiplication factor regardless of the temperature change.

According to the above configuration, the APD light receiving device 34
Generates a potential difference corresponding to a temperature change by utilizing a difference in temperature characteristics between the amplifier unit 81 and the temperature detection unit 82, and generates a bias voltage VB1 corresponding to the potential difference, thereby providing an optimum voltage corresponding to a temperature during use. Bias voltage VB1
Is supplied to the APD 42 to always obtain a desired current image magnification.

The APD light receiving device 34 adjusts the resistance value of the load resistor RE provided between the emitter of the transistor Q1 and the emitter of the transistor Q2.
The bias voltage VB1 can be adjusted, and thus an optimum bias voltage VB1 suitable for transistors having different performance and temperature characteristics can be generated.

In the APD light receiving device 34, the cathode of the APD 42 is directly connected to the base of the transistor Q1.
By adopting a current driving method in which a change in the light beam received by the PD 42 is supplied to the base of the transistor Q1 and driven as an output signal S42 obtained by converting the change in the light beam into a change in current,
The change in the temperature of the APD 42 is determined by the transistor Q1 and the load resistance R.
E and the potential difference ΔV _BE obtained through the transistor Q3
Can be detected accurately.

Further, since the APD light receiving device 34 employs the current driving method, even when an excessive light beam enters the APD 42, the emitter voltage V _{E1 of the} transistor Q1 increases based on the current amount of the output signal S42. As a result, the potential difference ΔV _BE generated between the transistor Q3 and the emitter voltage V _E3 is reduced, so that the bias voltage VB1 is automatically reduced, so that the APD 42 can be protected automatically.

Further, the APD light receiving device 34 is provided with the capacitor C1 at the base of the transistor Q3,
Even if an excessive current flows when the power is turned on, the excessive current can be prevented from flowing to the capacitor C1 and directly supplied to the base, and thus the APD 42 can be protected from being destroyed.

Further, the APD light receiving device 34 includes an APD 42
And the transistor Q1 and the transistor Q3 are integrally formed, it is possible to always generate the optimum bias voltage VB1 according to the change of the operating temperature of the APD 42,
Thus, a desired current multiplication factor can be obtained with respect to a temperature change.

(5) Other Embodiments In the above-described embodiment, a case has been described in which the APD 42 is used as the light receiving element that receives the reception light beam L3. However, the present invention is not limited to this. As long as the bias voltage VB1 supplied according to the temperature needs to be changed, various other light receiving elements such as a photodiode may be used.

In the above-described embodiment, the voltage generated between the emitter voltage V _E1 of the transistor Q1 and the emitter voltage V _E3 of the transistor Q3 in the negative feedback amplifier circuit in which the transistors Q1 and Q2 are connected in two stages. Although the description has been given of the case where the potential difference ΔV _BE is detected as a difference in temperature change, the present invention is not limited to this. The transistor Q 1 and the transistor Q 3 having different temperature characteristics from the beginning use the emitter voltage V _E1 and the emitter voltage V _E1. The potential difference ΔV _BE generated with the voltage V _E3 may be detected as a difference in temperature change. In this case, the APD light receiving device 34 uses a transistor Q1 having an amplification factor enough to amplify a weak output signal S42.

Furthermore, in the above-described embodiment, a case has been described where the collector current I _C6 that is 1.68 times the collector current I _C3 is generated by the current mirror unit 83, but the present invention is not limited to this, and the load is not limited to this. The current mirror unit 83 may generate a collector current I _C6 that is one time the collector current I _C3 according to the settings of the resistance value of the resistor RE, the load resistance RB, and the voltage value of the variable power supply VP.

[0093]

As described above, according to the present invention, a potential difference corresponding to a temperature change is generated by utilizing a difference in temperature characteristics between the first transistor circuit and the second transistor circuit, and the potential difference corresponding to the potential difference is generated. By generating a bias voltage and supplying it to the light receiving element, an optimum bias voltage according to the temperature at the time of use can be supplied to the light receiving element, and thus a desired current image magnification can always be obtained regardless of a temperature change. A light receiving device can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an overall configuration of an optical space transmission system.

FIG. 2 is a block diagram illustrating a configuration of a free-space optical transmission device.

FIG. 3 is a circuit diagram showing a configuration of an APD light receiving device according to the present invention.

FIG. 4 is a circuit diagram for explaining a simulation result at 25 ° C.

FIG. 5 is a circuit diagram for explaining a simulation result at 75 °.

FIG. 6 is a characteristic curve diagram showing a temperature characteristic of the APD.

[Description of Signs] 1 ... space optical transmission system, 10, 11 ... space optical transmission device, 34 ... APD light receiving device, 81 ... amplifier section, 8
2... Temperature detector 83... Current mirror 84.
... microcomputer.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 10/04 10/06

Claims (6)

[Claims] 1. A light receiving device for extracting a received signal by converting a received optical signal into an electric signal, comprising: a light receiving element driven by a bias voltage corresponding to a temperature and converting the received optical signal into the electric signal. Amplifying means for generating an output signal by amplifying the electric signal by a first transistor circuit connected to the light receiving element; the first transistor circuit; and the temperature characteristics of the first transistor circuit. Potential difference generating means for generating a potential difference that changes according to a temperature change of the light receiving element via a load resistor connected between the second transistor circuit having different temperature characteristics, and a predetermined potential corresponding to the potential difference And a bias voltage generating means for generating a bias voltage and supplying the bias voltage to the light receiving element. 2. The light receiving device according to claim 1, wherein said potential difference generating means adjusts said potential difference by arbitrarily setting a resistance value of said load resistor. 3. The light receiving device according to claim 1, wherein said light receiving element is an avalanche photodiode. 4. The light receiving device according to claim 1, wherein a bypass capacitor is connected to a base of the second transistor circuit. 5. A current mirror circuit for generating said output current in said second transistor circuit in response to said potential difference, said bias voltage generation means generating said output current in response to said potential difference, 2. A voltage generating circuit for generating the bias voltage.
3. The light receiving device according to claim 1. 6. The voltage generating circuit according to claim 5, wherein said voltage generating circuit is a variable voltage control circuit for changing a voltage value of said output voltage in accordance with an output level of an optical signal received by said light receiving element. Light receiving device.