JPH11127122A - Optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent each receiver section from being deteriorated due to an increased current of an avalanche photodiode(APD) caused when there is an input of a non-modulation light or no-input of a signal light. SOLUTION: A preamplifier 2 amplifies a current output from the APD 1 into a voltage signal, and a variable gain amplifier 3 adjusts gain to keep an output signal amplitude constant. The variable gain amplifier 3 controls a high voltage generating circuit 7, when a prescribed output signal amplitude is not obtained when the gain reaches a prescribed value and outputs a control voltage to adjust a multiplication factor of the APD 1 to be constant to a control circuit 6. Furthermore, when a timing extract circuit 5 outputs an adequately high voltage, when a clock frequency component is detected from the output or a control voltage whose voltage is less than a breakdown voltage of the APD 1 when the component is not detected to the control circuit 6. The control circuit 6 controls the high voltage generating circuit 7 with a lower voltage, in both the control voltages to prevent an overvoltage from being applied to the APD 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver using, for example, an avalanche photodiode as a light receiving element used for optical communication, and more particularly to an optical receiver capable of preventing deterioration of characteristics.

[0002]

2. Description of the Related Art Conventionally, an avalanche diode (hereinafter, also referred to as "APD") or the like capable of changing a multiplication factor by an applied voltage has been used as a light receiving element for converting an optical signal into an electric signal. An optical receiver having a preamplifier for converting a current into a voltage and a variable gain amplifier for amplifying an output of the preamplifier to a certain amplitude is used.

Usually, such an optical receiver keeps the voltage applied to the APD constant, when the output signal amplitude of the variable gain amplifier can be kept at a predetermined value by controlling the gain of the variable gain amplifier. If the output amplitude of the variable gain amplifier does not reach a predetermined value even when the gain of the variable gain amplifier is maximized by controlling the gain, the multiplication factor of the APD is controlled by adjusting the voltage applied to the APD. Then, the output signal amplitude of the variable gain amplifier is set to a predetermined value.

FIG. 7 is a block diagram showing such an optical receiver. The input signal light is converted into a current by the APD 1 and input to the preamplifier 2. The preamplifier 2 converts the input current into a voltage and outputs the voltage to the variable gain amplifier 3. The variable gain amplifier 3 amplifies the input voltage signal having a controlled gain to a predetermined amplitude to obtain a timing extraction circuit 5.
Is output to the identification circuit 4.

If the output amplitude does not reach a predetermined amplitude even when the gain of the variable gain amplifier 3 is maximized, the variable gain amplifier 3 controls the control circuit of the high voltage generating circuit 7 which applies a voltage to the APD 1. 31 to output a control signal to the APD 1
The gain applied to the APD 1 is controlled so that the output amplitude of the variable gain amplifier 3 becomes a predetermined value by adjusting the voltage applied to the APD 1. In response to a signal input from the variable gain amplifier 3, the timing extraction circuit 5 reproduces a clock,
Retiming of the signal by the reproduced clock from the timing extraction circuit 5 to identify the signal and output data.

Another conventional optical receiver for controlling the multiplication factor of an APD is disclosed in, for example, JP-A-3-13641.
No. 9 is known. In this optical receiver, a circuit for detecting an average current flowing through the APD is provided between the APD and a high voltage generating circuit that applies a voltage to the APD.
The output voltage of the high voltage generation circuit is controlled by the current flowing through the PD.

FIG. 8 is a block diagram showing an example of the optical receiver. An average current flowing through the APD 1 is detected by an average current detection circuit 42, and this detection signal is input to a high voltage generation circuit 43 via a control circuit 44. High voltage generation circuit 43
Adjusts the voltage applied to the APD 1 according to the detection signal.
The multiplication factor of PD1 is controlled. In this way, the output signal from the controlled APD 1 is amplified to a predetermined value by the preamplifier 2 and the variable gain amplifier 41, and then output to the identification circuit 4 and the timing extraction circuit 5. The identification circuit 4
The signal is retimed and identified by the clock recovered by the timing extraction circuit 5, and the data is output.

[0008]

In the example of the general optical receiver described with reference to FIG. 7, when continuous light (unmodulated light) is input to the receiver, the amplitude of the signal output from the variable gain amplifier is reduced. Since it cannot be obtained, the light receiving element such as the APD is controlled so as to increase the multiplication factor, and an excessive photocurrent flows to the light receiving element. As a result, the light receiving element and the preamplifier may be deteriorated. Further, when no signal light is input, the amplitude output from the variable gain amplifier becomes small, so that an excessive voltage (VB) that causes a breakdown is applied to the light receiving element. When a breakdown voltage is applied to the light receiving element, an excessive current (dark current) is generated, so that the light receiving element and the preamplifier may be similarly deteriorated.

In the example of the optical receiver described with reference to FIG.
Since a high voltage needs to be applied to the light receiving element, a special component that can withstand the high voltage needs to be used to detect the current of the light receiving element. Also, when the signal light is no input,
The current flowing through the light receiving element is the operating voltage of the light receiving element (see FIG. 2, V
B)), the control becomes very difficult.

(Object of the Invention) It is an object of the present invention to provide a receiving device which can receive a signal by increasing the current of a light receiving element such as an avalanche photodiode even when continuous light (unmodulated light) is input or when signal light is not input. An object of the present invention is to provide an optical receiver having a simple configuration capable of preventing deterioration of each part of the device.

[0011]

An optical receiver according to the present invention uses a light receiving element having a variable photoelectric conversion efficiency as a light receiving element for converting an optical signal into an electric signal, and amplifies an output signal of the light receiving element to obtain a gain. In the optical receiver including an amplifier for adjusting the output to make the output signal amplitude constant, when the gain of the amplifier becomes a predetermined value or more, the voltage applied to the light receiving element is controlled to increase the gain of the light receiving element. Means for controlling the amplitude of the signal output from the amplifier to be constant, and controlling the voltage applied to the light receiving element to not exceed a predetermined voltage when a specific frequency component is not detected from the output of the amplifier. Means for limiting

Specifically, an avalanche photodiode for converting an optical signal to an electric signal, a preamplifier for converting an output signal of the avalanche photodiode to a voltage,
An amplifier that amplifies the output of the preamplifier and adjusts the gain to maintain the signal amplitude of the output constant, when the gain of the amplifier becomes a predetermined value or more, the avalanche photodiode Means for controlling the applied voltage to adjust the multiplication factor of the avalanche photodiode so as to control the signal amplitude output from the amplifier to be constant, and avalanche when the specific frequency component is not detected from the output of the amplifier. Means for restricting the voltage applied to the photodiode so that a predetermined voltage lower than the breakdown voltage becomes an upper limit.

In the optical receiver, the predetermined voltage lower than a breakdown voltage of an avalanche photodiode is a temperature-compensated voltage, and the specific frequency component is a clock component or a signal format of a transmission speed of a reception signal. At the frame frequency component.

(Operation) The state of the signal light to the optical receiver is determined based on the presence or absence of a clock frequency component extracted from the output of the gain control amplifier of the optical receiver and a specific frequency component in the transmission signal. It is possible to prevent an excessive bias voltage from being applied to a light receiving element when no signal light or signal light is not input, and to prevent deterioration of characteristics of a light receiving element such as an avalanche photodiode and an amplifier.

[0015]

FIG. 1 is a block diagram showing a first embodiment of the present invention using an avalanche photodiode as a light receiving element of an optical receiver.

In the present embodiment, a high voltage generating circuit 7 for generating a bias voltage for an avalanche photodiode APD1, an avalanche photodiode 1 for receiving signal light, a preamplifier 2 for receiving a current output thereof,
In an optical receiver including a variable gain amplifier 3 having an output of the preamplifier 2 as an input, a control circuit 6 for controlling a high voltage generating circuit 7 is provided, and the control circuit 6 includes a control output from the variable gain amplifier 3 and It has a configuration in which control is performed by a control output from the timing extraction circuit 6.

The input signal light is converted by the APD 1 into a current signal. The current signal converted by the APD 1 is converted by the preamplifier 2 into a voltage proportional to the photocurrent output from the APD 1 and output to the variable gain amplifier 3.

In the variable gain amplifier 3, when the signal amplitude of the output signal can be maintained at a predetermined value by the gain control, the automatic gain control operation in the variable gain amplifier is performed to keep the output signal amplitude constant. At this time, gain control is performed so that the voltage applied to the APD 1 is kept constant.
If the output signal amplitude does not reach the predetermined value even when the gain of the variable gain amplifier 3 becomes sufficiently large or maximum, the AP
The voltage applied to D1 is adjusted to control the multiplication factor of APD1 so that the signal amplitude of the output of variable gain amplifier 3 is controlled to a predetermined value. The signal amplified by the variable gain amplifier 3 is output to the timing extraction circuit 5 and the identification circuit 4, respectively.

The timing extracting circuit 5 regenerates a clock corresponding to the signal transmission speed from the input signal, and the discriminating circuit 4 retiming the signal from the variable gain amplifier 3 by the clock from the timing extracting circuit 5. And identify.

Further, in the present embodiment, when a clock corresponding to a transmission rate can be extracted from an input signal, the timing extraction circuit 5 outputs a high control voltage V1 to the control circuit 6, and When the clock cannot be extracted, the control circuit 6 outputs a low control voltage V2 (<V1) to the control circuit 6. Here, the high control voltage V1 is
The low control voltage V2 is a voltage that is equal to or higher than the breakdown voltage of the APD1, and is a voltage that is equal to or lower than the breakdown voltage of the APD1, or a voltage that enables proper operation near the breakdown voltage.

The control circuit 6 selects the lower one of the control voltage input from the variable gain amplifier 3 and the control voltage input from the timing extraction circuit 5, and outputs the selected control voltage to the high voltage generation circuit 7. That is, when the timing extraction circuit 5 outputs the control voltage V1, the variable gain amplifier 3
When the timing extraction circuit 5 outputs the control voltage V2, the control voltage V2 is output when the timing extraction circuit 5 outputs the control voltage V2.

FIG. 2 is a characteristic diagram showing the relationship between the input control voltage Vc and the output voltage Vo of the high voltage generation circuit 7. The high voltage generation circuit 7 supplies the APD 1 with an output voltage Vo corresponding to the control voltage Vc from the control circuit 6 according to the characteristics shown in FIG. Here, VB (VB ') represents the breakdown voltage of APD1.

Therefore, when the optical receiver receives the signal light in the normal intensity range, the variable gain amplifier performs the normal gain control operation as described above, and the timing extraction circuit 5 normally operates the clock. Reproduction and the identification circuit 4 outputs demodulated data by the clock.

On the other hand, when continuous light (non-modulated light) is input to the light receiving element or when there is no input, the variable gain amplifier 3 cannot output a desired signal amplitude. The control voltage output to the control circuit 6 rises excessively.

At this time, the clock cannot be reproduced in the timing extraction circuit 5 because a signal having a predetermined amplitude is not input, and therefore, the low control voltage V2 shown in FIG. Is done.

As a result, since the control circuit 6 selects the low control voltage V2 input from the timing extraction circuit 5 and outputs it to the high voltage generation circuit 7, the corresponding low bias voltage is output from the high voltage generation circuit 7. The APD 1 is output, and a voltage equal to or lower than the breakdown voltage is applied to the APD 1, thereby preventing an excessive current from flowing through the APD 1.

In this way, when continuous light (non-modulated light) is input to the light receiving element or when there is no input,
Deterioration of characteristics of the light receiving element, the amplifier, and the like due to application of an excessive voltage for increasing the multiplication factor of the light receiving element is prevented.

FIG. 3 is a diagram showing a second embodiment of the present invention. The second embodiment will be described with reference to the characteristic diagram of the APD shown in FIG.

In the optical receiver according to the present embodiment, the low control voltage V2 output from the timing extraction circuit 5 is set to a value near the breakdown voltage of the APD. And a temperature compensation circuit 11 for the control voltage V2.

In general, the APD is A as shown in FIG.
The breakdown voltage VB changes depending on the ambient temperature of the PD. Therefore, it becomes difficult to set or control the bias voltage of the APD 1 due to a change in the ambient temperature.

In this embodiment, the timing extraction circuit 5
The temperature compensating circuit 11 performs temperature compensation so as to increase or decrease according to the rise or fall of the temperature, and outputs the control voltage V2 to the control circuit 6. By performing such temperature compensation, the APD 1 based on the output of the high voltage
Can always be set to a favorable state with respect to temperature fluctuations. In this way, when the optical receiver returns to the normal signal light from the input state of the continuous light (unmodulated light) or the non-input state, the optical receiver can be immediately restored to the proper operation state.

FIG. 5 is a diagram showing a third embodiment of the present invention. This embodiment is an example in which the signal light input to the receiver is an STM-N signal. The signal output from the variable gain amplifier 3 has a bright line spectrum at 8 kHz, which is the frame frequency of the STM-N signal.

In the present embodiment, the frequency component for extracting this frequency component from the signal output from the variable gain
It has a band-pass filter 22 of kHz and a detector 23 for detecting the output of the band-pass filter 22.

The detector 23 outputs a control voltage V1 as shown in FIG. 2 to the control circuit 6 when the frequency component of 8 kHz can be detected, and outputs a control voltage V2 as shown in FIG. Is output to the control circuit 6.

Also in the present embodiment, it is possible to control the output voltage of the high-voltage generating circuit 7 depending on whether or not a signal of normal amplitude is output from the variable gain amplifier 3.
It is possible to prevent an excessive current from flowing through PD1.

FIG. 6 is a diagram showing a fourth embodiment of the present invention. This embodiment has a configuration in which the temperature compensation circuit 11 is provided between the detector 23 and the control circuit 6.

The low control voltage V output from the detector 23
2 is set close to the breakdown voltage of the APD, and the control voltage output from the detector 23 for the control voltage is adjusted by the temperature compensating circuit 11 in accordance with the temperature fluctuation and output to the control circuit 6. This makes it possible to stabilize the bias state of the APD against temperature fluctuation.

[0038]

As described above, the optical receiver according to the present invention has a bias voltage applied to the light receiving element even when continuous light is input to the light receiving element such as an APD or when there is no input. Can be controlled to be lower than the breakdown voltage of the light receiving element, so that deterioration of the light receiving element and deterioration of the preamplifier can be prevented.

Further, in the optical receiver of the present invention, when continuous light is input to the light receiving element or when there is no input, the bias voltage applied to the light receiving element is slightly lower than the breakdown voltage of the light receiving element. Since the bias voltage is set and temperature compensation is performed on the bias voltage at that time, an optimal bias voltage can be supplied, and the bias voltage can be easily controlled.

[0040]

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a control voltage and an output voltage of a high voltage generation circuit.

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

FIG. 4 is a diagram showing the relationship between the voltage and current of the APD when no light is input.

FIG. 5 is a block diagram showing a third embodiment of the present invention.

FIG. 6 is a block diagram showing a fourth embodiment of the present invention.

FIG. 7 is a block diagram showing a first conventional example.

FIG. 8 is a block diagram showing a second conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 avalanche photodiode (APD) 2 preamplifier 3 variable gain amplifier 4 identification circuit 5 timing extraction circuit 6 control circuit 7 high voltage generation circuit 11 temperature compensation circuit 21 variable gain amplifier 22 bandpass filter 23 detector 31 control circuit 41 variable gain Amplifier 42 Average current detection circuit 43 High voltage generation circuit 44 Control circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H03F 3/08 H03G 3/30

Claims (5)

[Claims] 1. A light-receiving element having a variable photoelectric conversion efficiency is used as a light-receiving element for converting an optical signal into an electric signal, and the output signal of the light-receiving element is amplified and the gain is adjusted to keep the output signal amplitude constant. In an optical receiver having an amplifier that performs, when the gain of the amplifier becomes a predetermined value or more, the signal amplitude output from the amplifier by controlling the voltage applied to the light receiving element to adjust the gain of the light receiving element. Means for controlling so as to be constant, and means for restricting a voltage applied to the light receiving element so as not to exceed a predetermined voltage when a specific frequency component is not detected from the output of the amplifier. Optical receiver. 2. An avalanche photodiode for converting an optical signal into an electric signal, a preamplifier for converting an output signal of the avalanche photodiode into a voltage, and an output of the preamplifier by amplifying an output and adjusting a gain. In an optical receiver including an amplifier that maintains a constant signal amplitude, when the gain of the amplifier is equal to or more than a predetermined value, by controlling the voltage applied to the avalanche photodiode and adjusting the gain of the avalanche photodiode, Means for controlling the signal amplitude output by the amplifier to be constant, and a predetermined voltage lower than the breakdown voltage as a voltage applied to the avalanche photodiode when a specific frequency component is not detected from the output of the amplifier is an upper limit. Means for restricting the optical receiver as described above. 3. The optical receiver according to claim 2, wherein the predetermined voltage lower than a breakdown voltage of the avalanche photodiode is a temperature compensated voltage. 4. The apparatus according to claim 2, wherein the specific frequency component is a clock component of a transmission speed of a received signal.
Or the optical receiver according to 3. 5. The optical receiver according to claim 2, wherein the specific frequency component is a frame frequency component of a received signal.