JPH09270526A - Avalanche photo diode circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the breakdown or band deterioration of an valance photodiode by providing a bias limiter circuit for limiting the upper and lower limits of the bias voltage of this diode. SOLUTION: The level of a signal detected by a level detector circuit 40 is compared with a preset reference value in a control circuit 50 and inputted to a high voltage generator circuit 60 as an amplified error signal which is limited not so as exceed an upper or lower set values VH and VL of a preset bias voltage. As the result neither over-or under-bias voltage is fed to an avalanche photodiode(APD) 10. The limited amplified error signal controls the high voltage circuit 60 to control the current amplification factor of this diode 10 so that the output of a current-voltage converter-amplifier 20 is held const. despite the input signal level variation. Thus it is possible to prevent the breakdown of the element, band deterioration and waveform deterioration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an avalanche photodiode circuit used in an optical communication device or the like, and more particularly to an avalanche photodiode circuit effective for preventing deterioration of communication quality.

[0002]

2. Description of the Related Art In an avalanche photo diode (APD) used in an optical communication device or the like, its current multiplication factor M can be controlled by a bias voltage. Therefore, generally AP
In the D circuit, the automatic gain control (AG
C) Often constitutes a loop.

FIG. 5 shows an APD using a conventional AGC loop.
The block diagram of a circuit is shown, the avalanche photodiode APD10 which photocurrent-converts an optical signal, the current-voltage conversion amplifier 20 which converts and amplifies a current signal into a voltage signal, the distributor 30 which distributes a part of signal, and the signal level are detected. It is composed of a level detection circuit 40, a control circuit 50 that compares a detection signal with a reference value and differentially amplifies it, and a high voltage generation circuit 60 that supplies a high bias voltage to the APD 10. In FIG.
The optical input signal is converted into a photocurrent signal by the APD 10,
The current signal is converted and amplified by the current-voltage conversion amplifier 20 into a voltage signal, and then input to the distributor 30. An output is obtained from the distributor 30 and a part of the input signal is distributed to the level detection circuit 40. Level detection circuit 40
After the signal level is detected by the control circuit 50, the detected signal level is compared with a preset reference value in the control circuit 50, and the high voltage generation circuit 60 outputs an amplified error signal.
Is input to The error amplified signal controls the high voltage generation circuit 60 which supplies the bias voltage to the APD 10, and the current multiplication factor M of the APD 10 is controlled by this, and the output of the current-voltage conversion amplifier 20 is constant despite the fluctuation of the input optical signal level. Controlled by.

[0004]

However, when controlling the bias voltage of the APD in such a conventional device, if the bias voltage of the APD is too high, the gain bandwidth product (GB product) takes a constant value. When the gain is large, the band becomes narrow and the waveform deteriorates. In addition, there is a problem that the breakdown voltage of the diode may be reached, which may cause the destruction of the APD.

On the other hand, if the bias voltage of the APD is too low, the avalanche effect of the APD is less likely to occur and the band is narrowed, resulting in waveform deterioration. These waveform deteriorations have a problem that the error rate is deteriorated and the communication quality is deteriorated.

In view of the above problems, it is an object of the present invention to provide an avalanche photodiode circuit which is effective in preventing deterioration of communication quality.

[0007]

In order to achieve such an object, in the avalanche photodiode circuit according to the first configuration of the present invention, the upper limit value and the lower limit value of the bias voltage of the APD, or the upper limit value and the lower limit value thereof. A bias limiting circuit for limiting both of the above is provided to limit both the upper limit and the lower limit of the current multiplication factor M of the APD, or both the upper limit and the lower limit.

In the avalanche photodiode circuit according to the second aspect of the present invention, when the upper and lower limits of the current multiplication factor M are intended to be limited by limiting the upper and lower limits of the bias voltage of the APD, In order to prevent the upper limit and the lower limit of the current multiplication factor from being limited by a constant voltage value because the breakdown voltage of the circuit has temperature dependence, and the operating temperature range of the circuit is limited, the first configuration is adopted. In addition, a temperature detector for detecting the temperature of the APD is provided, and the upper and lower limits of the APD bias voltage are corrected according to the temperature.

Further, the correction means is to multiply the temperature detector output by a predetermined coefficient and add it to the preset upper and lower limit values of the APD bias voltage or the output of the bias limiting circuit.

[0010]

DETAILED DESCRIPTION OF THE INVENTION A detailed description will be given below with reference to the drawings. FIG. 1 is a block diagram showing an avalanche photodiode circuit including a bias limiting circuit according to a first embodiment of the present invention. 1 is different from the conventional technique in that a bias limiting circuit 100 is provided between the control circuit 50 and the high voltage generating circuit 60. Hereinafter, the operation will be described.

The optical input signal is converted into a photocurrent signal by the APD 10, the current signal is converted and amplified into a voltage signal by the current-voltage conversion amplifier 20, and then input to the distributor 30. An output is obtained from the distributor 30 and a part of the input signal is distributed to the level detection circuit 40. After the signal level is detected by the level detection circuit 40, the detected signal level is compared with a preset reference value in the control circuit 50 and input to the high voltage generation circuit 60 as an amplified error signal. The error amplification signal is limited by the bias limiting circuit 100 so as not to exceed the upper limit setting value VH and the lower limit setting value VL of the bias voltage set in advance. The limited error amplified signal is A
The high-voltage generating circuit 60 that supplies the bias voltage to the PD 10 is controlled, and the current multiplication factor M of the APD 10 is controlled by this, and the output of the current-voltage conversion amplifier 20 is controlled to be constant despite the fluctuation of the input optical signal level. The bias limiting circuit 100 can be realized by a limiting circuit using an operational amplifier and a diode.

Next, a second embodiment of the present invention will be described. FIG. 2 is a block diagram showing an avalanche photodiode circuit in which the temperature detector of the APD is further provided in the configuration of the first embodiment and the upper limit value and the lower limit value of the APD bias voltage are corrected by the temperature. As in the first embodiment, when the upper limit and the lower limit of the bias voltage of the APD 10 are limited by the bias limiting circuit 100 to limit the upper limit and the lower limit of the current multiplication factor M, the breakdown voltage of the APD 10 depends on the temperature. Since it has the property, the upper limit and the lower limit of the current multiplication factor M cannot be limited with a constant bias voltage value. As a result, the operating temperature range of the circuit is limited. In order to prevent this, in FIG. 2, a temperature detector 200 for detecting the temperature of the APD 10 is provided in addition to the configuration of the first embodiment. Temperature detector 20 that detects the temperature of the APD 10
0 is the upper limit value V of the APD bias voltage based on the detected temperature
Correct H and the lower limit value VL. Each corrected set value VH
And VL are input to the bias limiting circuit 100, and the error amplification signal from the limiting circuit 50 is limited based on this set value. As a result, the upper limit and the lower limit of the current multiplication factor M can be limited by the bias voltage value corresponding to the temperature change of the APD 10.

FIG. 3 is a block diagram showing another embodiment of the correcting means for the upper limit value and the lower limit value of the bias voltage of the second embodiment. In FIG. 3, the output of the temperature detector 200 is multiplied by a predetermined coefficient by the amplifier 300 and added by the adder 4
Is output to 00. The adder 400 adds the output of the amplifier 300 and the upper limit value VH and the lower limit value VL of the bias voltage of the APD. As a result, the preset upper limit value VH and lower limit value VL are corrected based on the output of the temperature detector 200. The corrected set values VH and VL are input to the bias limiting circuit 100, and the error amplification signal from the limiting circuit 50 is limited based on the set values.

FIG. 4 is a block diagram showing another embodiment of the bias voltage upper limit and lower limit correction means of the second embodiment. In FIG. 4, the output of the temperature detector 200 is multiplied by a predetermined coefficient by the amplifier 300 and added by the adder 5
Is output to 00. The adder 500 adds the output of the amplifier 300 and the error amplification signal limited so as not to exceed the upper limit value VH and the lower limit value VL of the bias voltage preset by the bias limiting circuit 100. As a result, the error amplified signal is corrected based on the output of the temperature detector 200. Each corrected set value VH and V
L is input to the bias limiting circuit 100, and the error amplification signal from the limiting circuit 50 is limited based on this set value.

These correcting means make use of the fact that the breakdown voltage of the APD with respect to temperature is linear. If the output of the temperature detector is not linear, it is necessary to linearize the output. For example, when the output of the temperature detector 200 is not linear like a thermistor, a linearization circuit may be inserted in the subsequent stage of the temperature detector 200 to linearize the output. The linearization circuit for that purpose can be realized by a polygonal line approximation circuit or the like.

[0016]

As described above, according to the avalanche photodiode circuit of the present invention, when the APD bias voltage is controlled, neither excessive nor excessive bias voltage is supplied to the APD, so that breakdown of the element and band deterioration can be prevented. Therefore, it is possible to prevent the deterioration of the error rate. Further, since the upper and lower limits of the current multiplication factor M of the APD can be limited to a constant value without depending on the temperature change, the operating temperature range of the circuit can be expanded.
As described above, the present invention has a remarkable effect of contributing to the prevention of communication quality deterioration.

[Brief description of drawings]

FIG. 1 is a block diagram showing an avalanche photodiode circuit including a bias limiting circuit as a first embodiment of the present invention.

FIG. 2 is a block diagram showing an avalanche photodiode circuit that includes a temperature detector of an APD as a second embodiment of the present invention and corrects an upper limit value and a lower limit value of an APD bias voltage according to the temperature.

FIG. 3 is a block diagram showing a correction unit for correcting an upper limit value and a lower limit value of an APD bias voltage.

FIG. 4 is a block diagram showing another means for correcting the upper limit value and the lower limit value of the APD bias voltage.

FIG. 5 is a block diagram showing a conventional avalanche photodiode circuit.

[Explanation of symbols]

 10 avalanche photodiode (APD) 20 current-voltage conversion amplifier 30 distributor 40 level detection circuit 50 control circuit 60 high voltage generation circuit 100 bias limiting circuit 200 temperature detector 300 amplifier 400 adder 500 adder VH upper limit set value VL bias Voltage lower limit set value

Claims (4)

[Claims] 1. A circuit for detecting a signal level photoelectrically converted by an avalanche photodiode and controlling the bias voltage of the avalanche photodiode by using the signal level. An avalanche photodiode circuit comprising a bias limiting circuit for limiting both values. 2. The avalanche device according to claim 1, further comprising a temperature detector for detecting the temperature of the avalanche photodiode, and means for correcting the upper limit value and the lower limit value of the bias voltage of the avalanche photodiode according to the temperature. Photodiode circuit. 3. The avalanche photodiode according to claim 2, wherein the means for correcting the upper limit value and the lower limit value of the bias voltage of the avalanche photodiode is obtained by multiplying the output of the temperature detector by a predetermined coefficient and setting the value in advance. An avalanche photodiode circuit characterized by adding to the upper and lower limits of 4. The means for correcting the upper limit value and the lower limit value of the bias voltage of the avalanche photodiode according to claim 2, wherein the output of the temperature detector is multiplied by a predetermined coefficient and the value is added to the bias limiting circuit. An avalanche photodiode circuit characterized by: