JP3479966B2 - Photocurrent monitor circuit and optical receiver - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocurrent monitor circuit for detecting a photocurrent flowing in a photodiode for receiving an optical signal, and an optical receiver including the photocurrent monitor circuit.

[0002]

2. Description of the Related Art Optical receivers are used for optical fiber communications and the like. Such an optical receiver includes an avalanche photodiode (APD) for receiving an optical signal. A bias voltage of 80 V or more is usually applied to the APD.

[0003]

The circuit for detection is an APD.
Since it affects the photocurrent itself, the photocurrent cannot be accurately detected. An object of the present invention is to provide a photocurrent monitor circuit capable of accurately monitoring a photocurrent flowing in a photodiode and an optical receiver including the photocurrent monitor circuit.

[0004]

The photocurrent monitor circuit of the present invention has a photodiode for receiving an optical signal and two parallel lines in which the currents flowing through both are in a proportional relationship. A first current mirror circuit to which one end of is connected, and a second current mirror circuit to which the other line of the first current mirror circuit is connected to one of its parallel lines.
A current mirror circuit and a photocurrent monitor terminal connected to the other of the parallel lines of the second current mirror are provided.

According to this photocurrent monitor circuit, a current proportional to the photocurrent flowing in the photodiode can be detected from the photocurrent monitor terminal through the first and second current mirror circuits, and therefore, for detection. An accurate photocurrent can be monitored without affecting the photocurrent of the photodiode itself by the circuit of.

The first and second current mirror circuits are preferably composed of bipolar transistors whose polarities are opposite to each other. That is, according to this configuration, when bipolar transistors having opposite polarities are connected in series, the directions of current flow can be matched,
The circuit configuration becomes simple.

The photodiode is an avalanche photodiode, and the collector of one of the bipolar transistors forming the first current mirror circuit is the photodiode, and the emitter is a multiplication factor control circuit for providing the emitter with a bias potential having a positive temperature coefficient. Is preferably connected to.

The multiplication factor of the avalanche photodiode has temperature dependency and bias voltage dependency. Here, in the avalanche photodiode, when a potential having a positive temperature coefficient is applied to the bias voltage, the temperature dependence of the multiplication factor can be compensated. The collector potential of the transistor of the first current mirror circuit is uniquely determined from the emitter potential because the base and collector are short-circuited. Therefore, when a multiplication factor control circuit is connected to the emitter and a positive temperature coefficient potential is applied to the emitter, the temperature dependency of the multiplication factor can be compensated.

The multiplication factor control circuit preferably includes a temperature compensation circuit in which a Zener diode having a positive temperature coefficient and a transistor having a negative temperature coefficient of the base-emitter voltage are connected in parallel.

That is, when a Zener diode and a transistor whose temperature coefficients have opposite polarities are connected in parallel, the temperature coefficient of the output potential can be adjusted according to the contribution rate of each element.

The optical receiver of the present invention further comprises a transimpedance amplifier connected to the other end of the photodiode. The photocurrent from the photodiode, on the other hand, is indirectly monitored as described above, whereas the direct photocurrent is voltage converted via the transimpedance amplifier.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical receiver provided with a photocurrent monitor circuit according to the embodiments will be described below by taking an optical module as an example. Note that the same elements or elements having the same function will be denoted by the same reference symbols, without redundant description.

FIG. 1 shows an optical module 1 according to an embodiment.
It is a longitudinal cross-sectional view of 0. A sleeve SV is embedded in the resin material 10a, and an optical fiber OF wrapped in a ferrule 10d is arranged in the sleeve SV. The end surface of the optical fiber OF inside the sleeve SV faces the avalanche photodiode (APD) 1. APD
1 is a lid member SM that seals one end of the opening of the sleeve SV.
The signal light input from the optical fiber OF is received via the spherical lens LS fixed inside the sleeve SV and fixed inside the sleeve SV.

In the present example, the multiplication factor control circuit 40, the current mirror circuit 2, the transimpedance amplifier 3, and the data identification / reproduction / clock extraction circuit 4 are provided on the wiring board 5 and inside the resin material 10a. It is molded into.

More specifically, one end of the APD 1 is electrically connected to the multiplication factor control circuit 40, and the other end thereof is electrically connected to the transimpedance amplifier 3. The bias voltage to APD1 is adjusted by the multiplication factor control circuit 40 and then applied to APD1. When an optical signal from the optical fiber OF is input to the APD 1 in this state, the amount of current flowing changes according to the amount of light of the optical signal. By inputting this current into the transimpedance amplifier 3,
The current / voltage conversion is performed, and the voltage signal corresponding to the optical signal is output.

The transimpedance amplifier 3 is connected to the data identification / reproduction / clock extraction circuit 4.
The data identification / reproduction / clock extraction circuit 4 is a circuit for identifying the data included in the output voltage of the transimpedance amplifier 3, reproducing the data, and extracting the clock. The data identification / reproduction / clock extraction circuit 4 includes a main amplifier circuit (not shown). Hereinafter, the circuit configuration of the optical module will be described in detail.

FIG. 2 is a circuit diagram of the optical module. The current mirror circuit 2 is configured by cascading a front stage side current mirror circuit 2F and a rear stage side current mirror circuit 2R. The current mirror circuit is a circuit that operates so that the ratio of currents flowing through both parallel lines including the transistors becomes constant. The current ratio follows Ohm's law and is inversely proportional to the resistance value of each line.
More specifically, the current mirror circuit is a circuit connected in parallel so that the voltage between the base and the emitter becomes equal. Since the current flowing through the transistor depends on this voltage, the current flowing through both transistors is necessarily equal. Further, the respective transistors are arranged close to each other so that the operating environments are the same.

APD1 is used by applying a reverse bias.
To use the positive potential terminal V_APDCurrent mirror from
The voltage drop across the circuit should be sufficient to reverse bias APD1.
It must be small enough to be applied. Current mirror times
The voltage drop of one of the transistors in the path is
It is defined by the source-emitter voltage, which is
Equal to the forward clamp voltage,
Under operating conditions, set to about 0.6-0.7V
Be done. Therefore, the cathode potential of APD1 is V _APD−
(0.6-0.7) V, which is a sufficient reverse direction for APD1
A forward bias voltage will be applied.

The front stage side current mirror circuit 2F is a pnp transistor 2FQ1 having a collector-base short-circuited.
And a pnp transistor 2 having substantially the same characteristics as
It is composed of FQ2. Two transistors 2FQ
The bases of 1 and 2FQ2 are commonly connected, and the emitters of the respective transistors 2FQ1 and 2FQ2 are both connected to the terminal V _APD . It should be noted that resistors 2FR1 and 2FR2 are respectively interposed between these emitters and the terminal V _APD, and both transistors 2FQ1 and 2FQ2 are connected.
Determines the ratio of the current flowing through. The resistor 2FR1,
When the values of 2FR2 are both zero or equal, the current values flowing through the transistors 2FQ1 and 2FQ2 are equal. Below, for simplification, it is assumed that the resistance values of the resistors 2FR1 and 2FR2 are equal.

One of the parallel lines of the pre-stage side current mirror circuit 2F configured in this way is connected to the APD1.
The other is the current mirror circuit 2R on the subsequent stage side via the terminal MT.
It is connected to the. When an optical signal is input to APD1,
APD1 from terminal V _APD via transistor 2FQ1
To the latter-stage side current mirror circuit 2R.

The rear stage side current mirror circuit 2R includes an npn transistor 2RQ1 having a collector-base short-circuited.
And an npn transistor 2 having substantially the same characteristics as
And RQ2. Two transistors 2RQ
The bases of 1 and 2 RQ2 are commonly connected. The collector of one transistor 2RQ1 is connected to the terminal MT, and the collector of the other transistor 2RQ2 is connected to the current monitoring terminal IMT.

Resistors 2RR1 and 2RR2 are respectively interposed between these emitters and the ground,
The ratio of currents flowing through both transistors 2RQ1, RQ2 is determined. If the values of the resistors 2RR1 and 2RR2 are both zero or equal, the transistors 2RQ1 and RQ2
The current values flowing through the two are equal. Below, for simplicity,
It is assumed that the resistors 2RR1 and 2RR2 have the same resistance value.
The emitter of the transistor 2RQ2 is connected to the voltage monitor terminal VMT.

As described above, the same current as the current flowing into the APD 1 flows into the rear stage side current mirror circuit 2R. Also in the latter-stage side current mirror circuit 2R, a current equal to the current flowing into the one transistor 2RQ1 is the other transistor 2RQ2, that is, the transistor 2 to which the current and voltage monitor terminals IMT and VMT are connected.
It flows into RQ2. Therefore, the same current as the current flowing into the APD1 flows into the transistor 2RQ2 with the monitor terminal, so that the respective terminals IMT, VM.
If the current and voltage are monitored at T, the current flowing in the APD 1 or the voltage converted from it can be monitored.

On the other hand, the photocurrent output from the APD1 is
The transimpedance amplifier 3 converts it into a corresponding voltage signal. As the transimpedance amplifier 3, an amplifier circuit including a GaAs amplifier 3A and a feedback resistance element 3R connected between its input and output is preferably used.

Here, the current I _APD flowing through the _{APD 1}
The relation with the current I _MTR output from the current monitor terminal IMT provided on the output side of the current mirror circuit 2 will be briefly described. The base current of the transistor (current amplification factor β1) forming the front stage side current mirror circuit 2F is Ib1, the collector current is Ic1, and the base current of the transistor (current amplification factor β2) forming the rear stage side current mirror circuit 2R is Ib2. , Collector current Ic2
And That is, Ic1 and Ic2 satisfy the following relationship. (Equation 1) Ic1 = β1 · Ib1 (Equation 1) (Equation 2) Ic2 = β2 · Ib2 (Equation 2)

First, paying attention to the front stage side current mirror circuit 2F, the current I _APD satisfies the following relationship. (Equation 3)

From the relationships of (Expression 3) and (Expression 1), the collector current Ic1 satisfies the following relationship. (Equation 4) Ic1 = _IAPD / (1 + 2 / β1) (Equation 4)

The monitor current I _MTR in the rear-stage side current mirror circuit 2R satisfies the following relationship, as in the front-stage side current mirror circuit 2F. (Equation 5) I _MTR = Ic1 / (1 + 2 / β2) (Equation 5)

From the relationship of (Equation 4) and (Equation 5), the current I
_{The APD} and the current I _MTR satisfy the following relationship. (Equation 6) I _MTR = I _APD / (1 + 2 / β1) / (1 + 2 / β2) (Equation 6)

That is, the monitor current I _MTR is APD1
_Is proportional to the current I _APD of.

When the resistance values of the resistors included in the current mirror circuit are not equal, the respective resistors 2FR are used.
The resistance values of 1, 2FR2, 2RR1, 2RR2 are r1,
Assuming r2, r3, and r4, (Equation 4) and (Equation 5) are
The following (Equation 7) and (Equation 8) are obtained, respectively. (Equation 7) Ic1 = r1 / r2 · _IAPD / (1+ (1 + r1 / r2) / β1) ··· (Equation 7) I _MTR = r3 / r4 · Ic1 / (1+ (1 + r3 / r4) / Β2) ··· (Equation 8)

Also in this case, the monitor current I
_{The MTR} will be proportional to the current I _APD of APD1.

The use of such a circuit has the advantage that the optical power (current) monitor circuit used in the ordinary optical receiving module operating at 5 V can be used as it is. That is, in this example, it is not necessary to use another special circuit when monitoring the optical input power of the optical receiver using the APD 1, and the circuit configuration is simple.

By the way, the multiplication factor of the APD 1 has temperature dependency and bias voltage dependency. In order for the multiplication factor of APD1 to be substantially constant with respect to temperature change, the bias voltage must be changed so as to compensate for the temperature dependence of the multiplication factor of APD1. Since the potential on the anode side of the _{APD 1} is fixed by the transimpedance amplifier 3, the potential on the cathode side, that is, V _APD may be adjusted so that the temperature dependence is compensated. In order to perform the above compensation, the bias voltage of APD1 needs to have a positive temperature coefficient.

That is, the reason why the bias voltage having a positive temperature coefficient is applied to the APD 1 is that the bias voltage V _B and the amplification factor M satisfy the following relationship. Note that ΔT
Is the temperature difference from the reference temperature, γ is the temperature coefficient of the APD multiplication factor (≈0.6% / ° C.), Vo is the breakdown voltage at the reference temperature, and n is a value determined by the characteristics of the APD and is empirically 0. .106 is adopted. (Equation 9) V _B = Vo · (1 + ΔT · γ) · 10 ^{1 / n · log (1-1 / M)} (Equation 9)

That is, when the multiplication factor M is constant, the APD
The bias voltage V _{B of} 1 changes with a small positive slope with respect to temperature (0.05 to 0.2 (V / ° C.)). Therefore, if the temperature coefficient of the bias voltage V _B is a small positive value, the multiplication factor M becomes constant. Since the bias voltage V _B is a value lower than the terminal potential V _APD by the voltage drop due to the transistor 2FQ1 or this and the resistor 2FR1, ignoring the temperature dependence of this voltage drop,
If the terminal voltage V _APD is set to have a positive temperature coefficient, the temperature coefficient of the bias voltage V _B can be set to a positive value.

The terminal potential V _APD is set by the multiplication factor control circuit 40. The multiplication factor control circuit 40 is a temperature coefficient compensating circuit (temperature compensating circuit) for compensating the temperature coefficient of the potential V _APD corresponding to the output potential with respect to the temperature coefficient of APD1.
40T and a current bypass circuit (hereinafter, referred to as a clip circuit) 40C.

First, the temperature coefficient compensation circuit 40T will be described. Resistor R 'is connected to the power source V _H. The downstream side of the resistor R'is used as the reference potential of the temperature coefficient compensation circuit 40T in the following description.

A resistor group 4 is provided between the reference potential and the ground.
The 0TR3, 40TR4, 40TR5 and the Zener diode 40TD1 are connected in parallel, and the resistor 40TR6 is interposed on the downstream side of the parallel circuit. The resistor 40TR4 is of a split type, and the split point is connected to the base of the transistor 40TQ2. If the voltage drop of the Zener diode 40TD1 is the voltage Vz,
Resistor groups 40TR3 and 40TR connected in parallel to this
The voltage between both ends of 4 and 40TR5 coincides with Vz, and if the division ratio of the resistor is k, the potential difference ΔV at the division point becomes k × Vz as viewed from the reference potential.

A resistor R ', a variable resistor 40TR1, a pnp transistor 40TQ1 whose base and collector are short-circuited, a pnp transistor 40TQ2, and a resistor 40TR2 are sequentially connected between the power source _VH and the ground. Here, when the transistor 40TQ2 is turned on, the current I1 flows from the power supply _VH to the ground.

Bipolar transistors 40TQ1, 40
The base-emitter voltage of TQ2 is fixed to the forward voltage of the pn junction diode and is 0.6V to 0.7V. The base-emitter voltage of the transistor is V _BE . The voltage drop across two transistors connected in series is approximately twice V _BE . Therefore, the variable resistor 40TR1
The potential difference Φ between both ends is given by the following formula. (Equation 10) Φ = ΔV−2V _BE (Equation 10)

The current I1 flowing through the variable resistor 40TR1 is
When the resistance value of the resistor 40TR1 is R1, it is given by the following equation. (Equation 11) I1 = (ΔV−2V _BE ) / R1 (Equation 11)

Once the current value is determined, the potential V2 is given by the following equation. The resistance value of the resistor 40RT2 is R2. (Equation 12) V2 = I1 × R2 (Equation 12)

The variable resistor 40TR1 is connected to the collector of the npn transistor 40TQ3. The output potential V _R of the temperature coefficient compensation circuit 40T, that is, the resistor R ″
The potential V _R of the upper side, the transistor 4 than the potential V2
Since it is lower by V _{BE of} 0TQ3, the output potential V _R is given by the following equation. (Number _{13) V R = V2-V} BE = (I1 × R2) -V BE = ((ΔV-2V BE) / R1) × R2-V BE = ((kVz-2V BE) / R1) × R2- V _BE ... (Formula 13)

In the temperature coefficient compensating circuit 40T, capacitors C'and 40TC1 are appropriately interposed as shown so that high frequency components and noise can be removed.

Here, the temperature coefficient δV _R is given by the following equation. Note that δX represents the temperature coefficient of X. (Number _{14) δV R = (kδVz-} 2δV BE) / R1 · R2 - (kVz-2V BE) / R1 · R2 (δR1 / R1-δR2 / R2) -δV BE ··· ( Formula 14)

[0047] Here, the term δR1 / R1-δR2 / R2 is smaller compared to the other terms, zero and it can be considered, the temperature coefficient .DELTA.V _R is given by the following equation in approximately. (Number _{15) δV R = (kδVz-} 2δV BE) / R1 · R2-δV BE ··· ( Equation 15)

For example, δV _BE = -2 mV / ° C, δVz =
+1.2 mV / ° C, k = 0.8, R1 = 8.7 kΩ, R
When 2 = 200kΩ, δV _R is a small positive value of 0.116V / ℃. This is because a Zener diode having a positive temperature coefficient (V / ° C.) and a transistor having a negative temperature coefficient are connected in parallel and combined. Since the ratio of these contributions is determined by the values of the resistance division ratios k and R1, in this circuit, the temperature coefficient can be freely adjusted by adjusting the values of the division ratios k and R1.
That is, the temperature dependence of the output potential V _R can be adjusted by the temperature coefficient compensation circuit 40T. The temperature coefficient of the Zener diode changes depending on the Zener voltage. In this example, the Zener diode is about 5V
, And such a diode has a positive temperature coefficient.

The multiplication factor M of the APD 1 has temperature dependency and bias voltage dependency. As described above, the temperature dependence of the output potential V _R of the temperature coefficient compensating circuit 40T could be adjusted freely, but the bias voltage V _{B of the} APD1 was adjusted.
Passes through the clip circuit 40C and the front-stage side current mirror circuit 2F, so that the output potential V _R is about 2
It is V _BE or a value obtained by lowering it by the sum of the resistance values of the resistor 2FR1 and V _BE .

Therefore, the potential V _B lower than V _R is applied to APD1. Since the temperature characteristic when the potential is lowered does not change much, a voltage having a positive temperature coefficient is applied to the APD1.

Next, the clip circuit 40C will be briefly described. The clip circuit 40C is interposed between the temperature coefficient compensation circuit 40T and the previous stage side current mirror circuit 2F, and is composed of series resistance groups 40CR1 and 40CR2 and an npn transistor 40CQ1 connected in parallel to the series resistance groups 40CR1 and 40CR2. . Series resistance group 40CR1, 40CR
When a very weak current flows through 2, the voltage drop due to this is small, and the base-emitter voltage of the npn transistor 40CQ1 exceeds the forward bias potential (0.6 to 0.7 V) of the pn junction. Therefore, the transistor 40CQ1 is in the off state, and most of the current flows into the front stage side current mirror circuit 2F via the series resistance groups 40CR1 and 40CR2.

On the other hand, series resistance groups 40CR1 and 40CR2
As the amount of current flowing through the resistor increases, the voltage drop across the resistor 40CR2 increases. That is, the npn transistor 4
The base-emitter voltage of 0CQ1 exceeds the threshold value, and the transistor 40CQ1 is turned on to form a low resistance bypass path between the input and output of the clip circuit 40C. As described above, since the clip circuit 40C has a low resistance during operation, it is possible to apply a large bias voltage to the APD1.

When the amount of current flowing through this bypass path further increases, the amount of current flowing through the series resistance groups 40CR1 and 40CR2 relatively decreases.

The above optical module was prototyped and its characteristics were evaluated. The pnp transistor and the npn transistor have a withstand voltage of V _CE (collector-emitter voltage) of 15 V
An element with 0 volt and β of about 80 is used, 10 kΩ for the resistors r1 and r2, and 2.4 kΩ for the resistors r3 and r4.
And + 5V was applied to the APD current monitor terminal IMT. When the APD current I _APD was in the range of 10 to 1000 μA, the proportional relationship shown in the graph of FIG. 3 was obtained.

Incidentally, FIG. 3 shows the current I _APD flowing through the _{APD 1.}
6 is a graph showing the relationship between the monitor current I _MTR and The relationship between the monitor current I _MTR obtained from this graph and the current I _APD of the _{APD 1} is as follows. (Equation 16) I _MTR = 0.948 × I _APD (Equation 16)

It is also possible to take out a voltage output proportional to the photocurrent from the emitter of the transistor 2RQ2.

Although the circuit described above is mounted inside the optical module, some circuits may be arranged outside this. Further, the circuits may be integrated on the same semiconductor chip or the same wiring board. Further, if the circuit conditions are adjusted, a PIN photodiode or the like can be used instead of the APD1. For example, as a semiconductor light receiving element, a PIN photodiode made of InGaAs having a diameter of 50 μm is preferably used. Also, the package is not limited to the resin mold type, but a metal package,
It goes without saying that it is possible to use various things such as plastic packages.

Further, the bias circuit is connected to the cathode side of the APD 1, but it goes without saying that this can also be connected to the anode side by a simple design change.

There are many forms of the current mirror circuit, and it is also possible to adopt another circuit configuration having the same operation as described above. For example, a field effect transistor (FET) can be used instead of the bipolar transistor.

As described above, the photocurrent monitor circuit has the photodiode 1 for receiving an optical signal and two parallel lines in which the currents flowing through the two are in a proportional relationship, and the photodiode is provided in one of these lines. Of the first current mirror circuit 2F to which one end of 1 is connected, and the second current mirror circuit 2R in which one of the parallel lines is connected to the other line of the first current mirror circuit 2F and the second current mirror 2R. And a photocurrent monitoring terminal IMT connected to the other of the parallel lines.

According to this photocurrent monitor circuit, a current proportional to the photocurrent flowing in the photodiode 1 can be detected from the photocurrent monitor terminal IMT via the first and second current mirror circuits 2F and 2R. Therefore, the photocurrent can be accurately monitored without the detection circuit affecting the photocurrent of the photodiode itself.

First and second current mirror circuits 2F, 2
R is composed of bipolar transistors whose polarities are opposite to each other, and these are connected in series, so that the directions of current flow can be made coincident, and the circuit configuration becomes simple.

The photodiode 1 is an avalanche photodiode, and the first current mirror circuit 2F
Of one of the bipolar transistors 2FQ1 is connected to the photodiode 1, and the emitter of the bipolar transistor 2FQ1 is connected to the multiplication factor control circuit 40 which gives the potential of the positive temperature coefficient (V / ° C.) to the emitter.

The multiplication factor of the avalanche photodiode 1 has temperature dependency and bias voltage dependency. Here, in the avalanche photodiode 1, when a potential having a positive temperature coefficient is applied to the bias voltage, the temperature dependence of the multiplication factor can be compensated. The collector potential of the transistor 2FQ1 of the first current mirror circuit 2F that provides the bias voltage of the avalanche photodiode 1 is uniquely determined from the emitter potential. Therefore, when the multiplication factor control circuit 40 is connected to this emitter and a positive temperature coefficient potential is applied to this emitter, the temperature dependency of the multiplication factor can be compensated.

The multiplication factor control circuit 40 has a positive temperature coefficient (V
The temperature coefficient (V / ° C) on the output side of the zener diode 40TD1 having a temperature coefficient (V / ° C.) And the transistor 40TQ1 (40TQ2) having a negative temperature coefficient (V / ° C) between the base and the emitter are positive. And a temperature compensation circuit 40T connected in parallel with the temperature compensation circuit 40T. The output of the temperature compensation circuit 40T is connected to the emitter.

That is, the zener diode 40TD1 and the transistor 40TQ1 (4
0TQ2) is connected in parallel, the temperature coefficient of the output potential V _R can be adjusted according to the contribution rate of each element, and a suitable multiplication factor setting of the avalanche photodiode 1 can be performed.

Further, the optical receiver has a transimpedance amplifier 3 connected to the other end of the photodiode 1.
Further, the transimpedance amplifier 3 outputs optical signal information. On the other hand, the photocurrent from the photodiode 1 is indirectly monitored as described above, but the direct photocurrent can be output as the information of the optical signal by being voltage-converted via the transimpedance amplifier 3. it can.

[0068]

According to the present invention, the photocurrent can be accurately monitored without the detection circuit affecting the photocurrent of the photodiode itself.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an optical module 10 according to an embodiment.

FIG. 2 is a circuit diagram of an optical module.

[FIG. 3] Current I _APD flowing through APD1 and monitor current I _MTR
A graph showing the relationship with.

[Explanation of symbols]

1 ... Photodiode, 2F ... 1st current mirror circuit, 2R ... 2nd current mirror circuit, IMT ... Photocurrent monitor terminal.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-10-13164 (JP, A) JP-A-9-130158 (JP, A) JP-A-6-350351 (JP, A) JP-A-2- 165709 (JP, A) JP-A-2-151089 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03F 3/08 H03F 1/30

Claims (3)

(57) [Claims] 1. An avalanche photodiode for receiving an optical signal
The avalanche has two parallel lines in which an ion and a current flowing through the two are in a proportional relationship.
A first current mirror circuit to which one end of the photodiode is connected; a second current mirror circuit to which one of parallel lines of the first current mirror circuit is connected to the other line of the first current mirror circuit; And a photocurrent monitor terminal connected to the other of the parallel lines, wherein the first and second current mirror circuits have polarities with respect to each other.
Comprising opposite bipolar transistors, the first
One of the bipolar transistors forming the current mirror circuit
The collector of the transistor is the avalanche photodiode.
In addition, the emitter applies a positive temperature coefficient bias potential to the emitter.
A photocurrent monitor circuit, which is connected to a multiplication factor control circuit that supplies the data to the computer. 2. The multiplication factor control circuit includes a temperature compensation circuit in which a Zener diode having a positive temperature coefficient and a transistor having a negative temperature coefficient of the base-emitter voltage are connected in parallel. The photocurrent monitor circuit according to claim 1 . 3. An optical receiver, further comprising a transimpedance amplifier connected to the other end of the photodiode according to claim 1.