JP2616680B2 - Optical receiving circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiving circuit, for example, an optical receiving circuit using an avalanche photodiode as a light receiving element.

[0002]

2. Description of the Related Art Generally, an avalanche photo diode (hereinafter referred to as "APD") is used as a light receiving element in an optical receiving circuit installed in an optical communication system.
The gain control is performed by changing the bias voltage applied to.

FIG. 3 is a block diagram showing an optical receiving circuit using such a conventional APD. In the figure, the input terminal side of the preamplifier circuit 102 is connected to the cathode electrode side of the APD 101. This APD10
In 1, when an optical signal is received, the optical signal is converted into an output current.

In the preamplifier circuit 102, an output voltage of a feedback amplification output 201 having a constant amplification factor is obtained based on the output current sent from the APD. The output terminal side of the preamplifier circuit 102 has an automatic gain control amplifier circuit 1
03 is connected to the input terminal side. The automatic gain control amplification circuit 103 is automatically controlled so that the amplitude of the output voltage that changes in proportion to the light receiving level is output at a constant amplitude.

A circuit section (not shown) and a peak voltage detection circuit 104 are connected to the output terminal side of the automatic gain control amplification circuit 103. This peak voltage detection circuit 1
At 04, the output amplitude of the automatic gain control amplification circuit 103 is repeatedly detected.

On the other hand, a reverse bias circuit 105 is connected to the anode side of the APD 101, and a fixed reverse bias is applied to the APD 101 so that the APD 101 has an optimum multiplication amount of the minimum reception level. In the APD 101, it is necessary to perform temperature compensation because the optimum multiplication amount differs depending on a temperature change. Therefore, APD1 is connected to the input terminal of the reverse bias circuit.
01 is connected to a temperature compensation circuit 106 for compensating the temperature of the APD 101 via a reverse bias control circuit 107 for transmitting a reverse bias control signal. The above-mentioned bias method is based on a so-called fixed bias method.

FIG. 4 is a block diagram showing another example of the conventional optical receiving circuit. Detailed description of the same configuration as the optical receiving circuit shown in FIG. 3 is omitted here. In addition,
The following bias method uses a full automatic gain control (Full-gain control).
AGC) method.

In this optical receiving circuit, the peak voltage detecting circuit 108 has two output terminals. One output terminal is input to the automatic gain control amplifier 103, and the other output terminal is input to the reverse bias control circuit 109. In the reverse bias control circuit 109, the peak voltage detection circuit 108 detects
A control signal for operating the reverse bias control circuit 105 is output based on the peak detection voltage.

FIG. 5 shows the gain (AGC) of the automatic gain control amplifier.
FIG. 4 is a characteristic diagram illustrating a relationship between a gain and a reverse bias applied to the APD 101. In this figure, reference symbol A denotes an automatic gain control amplifier 10 during the operation of the optical receiving circuit shown in FIG.
6 is a characteristic curve showing a relationship between a gain of 2 (AGC gain) and a reverse bias applied to the APD 101. In this characteristic curve, the voltage is the lowest when the VL voltage is on the vertical axis, and the light receiving level is the maximum Prmax.

[0010] Examples of the optical receiving circuit described above are disclosed in JP-A-3-213024 and JP-A-3-188706.
JP, JP-A-3-80230, JP-A-56-1
There is an optical receiving circuit described in Japanese Patent No. 47533 and Japanese Patent Application Laid-Open No. 62-283710.

In the optical receiving circuit described in Japanese Patent Application Laid-Open No. 3-213024, in addition to the configuration of the optical receiving circuit shown in FIG. 4, a bias mode in which a reverse bias of the amplification factor at the minimum light receiving level is maintained. By providing a circuit that switches at the minimum voltage VL, the output of the amplifier system is stabilized regardless of the presence or absence of a transmission signal, and a good reception state can be obtained. Further, in the optical receiving circuit described in Japanese Patent Application Laid-Open No. 3-188706, after obtaining the optimum amplification factor of the APD, further obtaining the optimum amplification factor of the APD therefrom, and outputting a control signal based on the result, APD is set to an optimum amplification factor. On the other hand, in the optical receiving circuit described in Japanese Patent Application Laid-Open No. 3-80230, an optical receiving circuit having good sensitivity and a wide dynamic range can be provided by allowing a received signal to be demodulated linearly. See also
In the optical receiving circuit described in JP-A-6-147533, by adding a load resistance value control circuit, the resistance value of the resistance circuit of the load according to the level signal is changed, so that the fluctuation of the power of the optical reception can be prevented. As a result, the fluctuation of the output of the load resistance can be reduced, and the distortion of the output waveform can be reduced. Further, the optical receiving circuit described in Japanese Patent Application Laid-Open No. 62-283710 realizes complicated nonlinear input / output characteristics and enables high-precision signal processing.

[0012]

Among these optical receiving circuits, in the optical receiving circuit employing the fixed bias system shown in FIG. 3, the amplification factor is set at the minimum light receiving level. Saturation of the preamplifier circuit 102 is accelerated, and the maximum light receiving level is reduced due to waveform distortion due to the saturation of the preamplifier circuit 102, the light receiving level of the receiver is reduced, and the dynamic range of the light receiving level of the receiver may not be obtained. was there.

Further, as shown in FIG.
Optical receiver circuit adopting the system
In the light receiving circuit and the like described in the publication, the light receiving level is low, and in the state where the reverse bias is controlled and the gain is controlled by the amplification factor, the speed of responding to the high-speed change of the light receiving level becomes slow. When the light reception level changes at a high speed, the reception signal may be erroneously received.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to increase the dynamic range by increasing the range of the light receiving level, and to improve the resistance to fluctuations in the light receiving level by increasing the response speed.

[0015]

In order to achieve the above object, according to the present invention, there is provided an amplifying means for converting an optical signal into an electric signal and then amplifying the electric signal, wherein the amplifying means converts the electric signal into an electric signal. The gain control means keeps the output amplitude constant in accordance with the change in the amplitude of the output signal of the amplifying means, and an amplitude signal for controlling the amplitude signal output from the gain control means. A peak detection circuit for detecting and outputting the amplitude detection signal to gain control means, wherein the amplification is performed by controlling a reverse bias voltage of the light receiving element in response to a change in the light receiving level of the optical signal. A hysteresis circuit for outputting a hysteresis signal for switching the rate, and a reverse bias control signal for controlling a reverse bias voltage based on the hysteresis signal output from the hysteresis circuit. A bias control circuit comprises a reverse biasing circuit for applying a reverse bias voltage to the light receiving element by the reverse bias control signal output from the reverse bias control circuit.

According to the second aspect of the present invention, the amplifying means includes a light receiving element for converting an optical signal into an electric signal, and a preamplifier circuit for converting an electric signal obtained by the light receiving element into a voltage.

According to the third aspect of the present invention, the reverse bias control circuit operates in response to an output from the temperature compensation circuit for correcting the temperature of the light receiving element to a temperature corresponding to an expected value of the temperature fluctuation.

According to the fourth aspect of the invention, the output of the hysteresis circuit is set such that the hysteresis width corresponding to the light receiving level of the light receiving element is larger than the fluctuation width of the light receiving level.

According to the present invention, the reverse bias voltage of the light receiving element is switched by the first and second reverse bias voltages.

[0020]

According to the first aspect, in the hysteresis circuit shown in FIG. 1, the range of the light receiving level of the light receiving element is controlled in accordance with the change in the light receiving level of the optical signal by controlling the reverse bias voltage of the light receiving element. To switch the amplification factor. The reverse bias control circuit outputs a control signal for controlling the reverse bias voltage based on the hysteresis signal output from the hysteresis circuit. The reverse bias applying circuit applies a reverse bias voltage to the light receiving element according to a control signal output from the reverse bias control circuit. This allows
Along with widening the dynamic range,
By increasing the response speed, it is possible to improve the resistance to fluctuations in the light receiving level.

According to the second aspect, the amplifying means converts the optical signal into an electric signal by the light receiving element, and converts the electric signal obtained by the light receiving element into a voltage by the preamplifier circuit.

According to the third aspect, the reverse bias control circuit operates in response to an output from the temperature compensating circuit for correcting the temperature of the light receiving element to a temperature corresponding to an expected value of the temperature fluctuation.

According to the fourth aspect, the output of the hysteresis circuit is set such that the hysteresis width corresponding to the light receiving level of the light receiving element is set to be larger than the fluctuation width of the light receiving level. The circuit can be prevented from operating.

According to the fifth aspect, by switching the reverse bias voltage of the light receiving element between the first and second reverse bias voltages, a wider dynamic range can be obtained.

[0025]

Next, an optical receiving circuit according to the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing one embodiment of the optical receiving circuit of the present invention.

In FIG. 1, the input terminal side of the preamplifier circuit 2 is connected to the cathode electrode side of the APD 1.
In the APD 1, the received light is converted into an electric signal and input to the preamplifier circuit 2. This preamplifier circuit 2 includes an amplifier 2a and a feedback resistor 2b. In the preamplifier circuit 2, when a current flows to the input side of the amplifier 2a, the current is amplified by the amplifier 2a via the feedback resistor 2b until it is amplified to a predetermined voltage.

The output terminal of the preamplifier circuit 2 is connected to the input terminal of the automatic gain control amplifier 3. The automatic gain control amplifier 3 is automatically controlled so that the amplitude of a signal (voltage) that changes in proportion to the light receiving level is output with a constant amplitude. A circuit section (not shown) and a peak voltage detection circuit 4 are connected to the output terminal side of the automatic gain control amplification circuit 3. In this peak voltage detection circuit 4,
The peak voltage output from the automatic gain control amplifier circuit 3 is repeatedly detected.

The input terminal side of the hysteresis circuit 8 is connected to the peak voltage detection circuit 4, and the output terminal side of the hysteresis circuit 7 is connected to the input terminal side of the reverse bias control circuit 7. The hysteresis circuit 8 outputs a hysteresis signal based on the peak detection voltage of the peak voltage detection circuit 4. The output of the hysteresis circuit 8 has a preset hysteresis characteristic, for example,
These are two output signals.

On the other hand, a reverse bias circuit 5 is connected to the anode electrode side of the APD 1, and a fixed reverse bias is applied to the APD 1 so that the APD 1 has an optimum multiplication amount of the minimum reception level. The reverse bias circuit 5 operates in response to a control signal output from the reverse bias control circuit 7.

In the APD 1, it is necessary to perform temperature compensation because the optimum multiplication amount differs depending on the temperature change. Therefore, a temperature compensating circuit 6 for compensating the temperature of the APD 1 is connected to an input terminal of the reverse bias circuit 5 via a reverse bias control circuit 7 for transmitting a reverse bias control signal to the APD 1. The temperature compensation circuit 6 outputs a temperature compensation signal.

In the temperature compensating circuit 6, the temperature compensating signal is input to the reverse bias control circuit 7, the reverse bias control signal is output from the reverse bias control circuit 7, and the reverse bias circuit 5 is operated by the reverse bias control signal. Thus, temperature compensation corresponding to the predicted temperature characteristic of the reverse bias of the APD 1 can be performed.

Next, the operation of the embodiment of the present invention will be described with reference to FIG.
A description will be given based on FIG. FIG. 2 is a diagram showing a correlation between the light receiving level with respect to the AGC gain and the light receiving level with respect to the reverse bias applied to the APD 1.

In FIG. 1, when an optical signal is received by the APD 1, the APD 1 converts the optical signal into an electric signal, and then, based on the output voltage amplified by the preamplifier circuit 2, controls the automatic gain control amplifier 3. Performs automatic gain control.

In the peak voltage detecting circuit 4, the peak voltage is detected by the peak voltage detecting circuit 4 in response to the gain control output repeatedly input from the automatic gain control amplifier 3.
The hysteresis circuit 8 selects and outputs a preset hysteresis curve based on the voltage output from the peak voltage detection circuit 4.

On the other hand, in the reverse bias control circuit 7, the temperature compensation circuit 6 can be operated based on a curve having a hysteresis characteristic selected by the hysteresis circuit 8.
At this time, in the reverse bias control circuit 7, the reverse bias voltage applied to the APD 1 is controlled by two reverse bias voltage values having hysteresis characteristics.
Is input to At this time, the reverse bias voltage applied to the anode electrode of the APD 1 becomes a fixed bias within the range of AB or CD in FIG. 2, and the response speed of the optical receiving circuit increases because the bias of the APD 1 does not respond.

At this time, the reverse bias voltage of the APD 1 is set to, for example, the range A of the first bias voltage VH shown in FIG.
B, and light is received in the range CD of the second bias voltage VL, but the temperature is compensated by the output from the temperature compensating circuit 6 in the range X, Y of the reverse bias voltage including the dotted line portion sandwiching the solid line. , The level fluctuation tolerance of the optical reception signal received from the receiver.

As described above, in the present optical receiving circuit, two values of the reverse bias voltage can be used as compared with the optical receiving circuit of the fixed bias system, so that the light receiving level range is widened and the dynamic range is widened. In addition to the above, the fixed bias is applied in the range of the reverse bias in the range AB or CD, so that the response speed is fast and the tolerance to the level fluctuation can be improved.

The output of the hysteresis circuit 8 has a hysteresis width H shown in FIG. 2 corresponding to the light receiving level of the light receiving element 1 and is set to be larger than the fluctuation width of the light receiving level. The bias control circuit 7 can be prevented from operating. Further, the reverse bias voltage of the light receiving element 1 is the first and second reverse bias voltages V
By switching between H and VL, the dynamic range can be made wider.

In the embodiment described above,
The case where the control is performed assuming that the output of the hysteresis circuit 8 has two values has been described.
It is needless to say that the number is not limited thereto, and may be two or more as long as the gist of the present invention is not deviated.

[0040]

As described above, in the optical receiving circuit according to any one of the first to fifth aspects, the dynamic range can be widened, and the response speed can be increased to improve the resistance to fluctuations in the light receiving level. be able to.

In particular, according to the second aspect of the present invention, an amplified voltage can be obtained quickly. According to the third aspect of the present invention, it is possible to widen the light receiving dynamic range as compared with a conventional optical receiving circuit using a fixed bias system. Further, according to the fourth aspect of the present invention, the reverse bias control circuit does not operate with respect to the fluctuation width of the light receiving level, so that the fluctuation tolerance of the light receiving level can be increased. According to the fifth aspect of the present invention, the dynamic range can be made wider.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of an optical receiving circuit according to the present invention.

FIG. 2 is a characteristic diagram for explaining the operation of one embodiment of the present invention.

FIG. 3 is a block diagram showing another embodiment of the present invention.

FIG. 4 is a block diagram illustrating an example of a conventional optical receiving circuit.

FIG. 5 is a characteristic diagram for explaining an operation of an example of a conventional optical receiving circuit.

[Explanation of symbols]

 Reference Signs List 1 APD 2 Preamplifier circuit 3 Automatic gain control amplifier 4 Peak voltage detection circuit 5 Reverse bias circuit 6 Temperature compensation circuit 7 Reverse bias control circuit 8 Hysteresis circuit 50 APD output current 51 Preamplification output 52 AGC control output 53 Peak voltage detection Output 54 Hysteresis output 55 Temperature compensation output

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H04L 25/03

Claims (5)

(57) [Claims] Amplifying means for converting an optical signal into an electric signal and then amplifying the electrical signal; and an output corresponding to a change in the amplitude of an output signal of the amplifying means which increases and decreases in proportion to a level change of the optical signal. Gain control means for keeping the amplitude constant; and a peak detection circuit for detecting an amplitude signal for controlling an amplitude signal output from the gain control means and outputting the amplitude detection signal to the gain control means. A hysteresis circuit that controls a reverse bias voltage applied to the light receiving element to switch an amplification factor and outputs a history signal in response to a change in a light receiving level of the optical signal; and a history signal output from the hysteresis circuit. A reverse bias control circuit for outputting a reverse bias control signal for controlling a reverse bias voltage by using a reverse bias control signal output from the reverse bias control circuit. Optical receiving circuit characterized by comprising a reverse bias applying circuit that applies a reverse bias voltage to the light receiving element. 2. The optical receiving circuit according to claim 1, wherein said amplifying means comprises a light receiving element for converting an optical signal into an electric signal, and a preamplifier circuit for converting an electric signal obtained by said light receiving element into a voltage. . 3. The light according to claim 1, wherein the reverse bias control circuit operates in response to an output from a temperature compensation circuit for correcting the temperature of the light receiving element to a temperature corresponding to an expected value of the temperature variation. Receiver circuit. 4. The light according to claim 1, wherein the output of the hysteresis circuit has a hysteresis width corresponding to a light receiving level of the light receiving element set to be larger than a fluctuation width of the light receiving level. Receiver circuit. 5. The method according to claim 1, wherein the reverse bias voltage of the light receiving element is a first voltage.
5. The optical receiving circuit according to claim 1, wherein switching is performed by using a second reverse bias voltage.