JPH10308636A - Optical signal receiving circuit - Google Patents

Abstract

(57) [Summary] [Problem] Even when a high-level optical signal is input, A
Provided is an optical signal receiving circuit that can limit a current flowing through a PD. SOLUTION: An average optical input level represented by a DC component of an electric signal from an APD 3 is separated by a DC separating unit 19, and when the average optical input level is higher than a predetermined level, the average optical input level is determined according to the average optical input level. , Transistor 23
Adjustment is made so that the bias voltage from the drive circuit 13 is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical signal receiving circuit used in an optical communication system or the like.

[0002]

2. Description of the Related Art Conventionally, an optical signal receiving circuit 101 shown in FIG. 2 is known as an optical signal receiving circuit. The optical signal receiving circuit 101 converts an APD (A
(valanche Photo Diode) 103
, A preamplifier 105 for current-to-voltage conversion of the current from the APD 103, and an AGC (Autom
atic gain control) circuit 107,
Main amplifier 1 for amplifying the output voltage from AGC circuit 107
09, a control voltage generator 111 for outputting a voltage to the AGC circuit 107, a drive circuit 113 for supplying a voltage to the APD 103, and a drive circuit adjustment circuit 115 for adjusting the output voltage level of the drive circuit 113.

In order to operate the APD 103, an AP
It is necessary to apply a voltage in a direction opposite to the current generated in D103, and this voltage is called a reverse bias voltage (hereinafter, simply referred to as a bias voltage). In general, PD (Potio
In de), the output current becomes constant even when the bias voltage is changed, but in the APD 103, when the bias voltage is changed, the output current also changes.

FIG. 3 is a schematic diagram showing a light receiving level in the APD 103. As shown in FIG. In the figure, for example,
The light receiving level increases as the level (b) approaches the level (a), while the light receiving level decreases as the level approaches the level (c) from the level (b). The level (b) is
This is a predetermined level predetermined as an electrical specification.

Next, the operation of the optical signal receiving circuit 101 will be described. The APD 103 receives an optical signal,
This optical signal is photoelectrically converted into a current. Further, this current is subjected to current-voltage conversion by the preamplifier 105. Next, when the amplitude level of the optical signal is equal to or higher than a predetermined level, for example, as shown in level (b) to level (c) shown in FIG. Is controlled by controlling the gain of the AGC circuit 107 so that the output level of the optical signal receiving circuit 101 becomes constant.

However, for example, level (b) shown in FIG.
When the amplitude level of the optical signal is lower than the predetermined level as in the level (c), the control cannot be performed by adjusting the gain of the AGC circuit 107. Therefore, utilizing the fact that the current multiplication factor of the photoelectric conversion of the APD 103 is adjusted by the supply voltage of the drive circuit 113, the output voltage of the drive circuit 113 is changed by the drive circuit adjustment circuit 115, and the current output from the APD 103 is changed. Is increased so that the output level of the optical signal receiving circuit 101 becomes constant.

[0007]

However, in the conventional optical signal receiving circuit 101, if an excessively high level optical signal is input to the APD 103, the driving circuit 11
3 is controlled to supply a constant voltage,
An excessive current flows through D103, and APD10
3 causes deterioration.

[0008] The present invention has been made in view of the above,
An object of the present invention is to provide an optical signal receiving circuit capable of limiting a current flowing through a light receiving element even when a high-level optical signal is input.

[0009]

According to the first aspect of the present invention,
In order to solve the above problems, a light receiving element that converts an optical signal into an electric signal, an amplifier that amplifies the electric signal and outputs an electric output, and a voltage supply unit that supplies a bias voltage for driving the light receiving element are provided. In the optical signal receiving circuit configured, the voltage supply means adjusts to increase the bias voltage of the light receiving element according to the magnitude of the electric output,
The gist of the present invention is to include a bias voltage adjusting unit that adjusts the bias voltage of the light receiving element so as to decrease according to the magnitude of the DC component of the electric signal from the light receiving element.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of an optical signal receiving circuit 1 used in an optical communication system or the like according to an embodiment of the present invention.

As shown in FIG. 1, this optical signal receiving circuit 1
Is an APD (Av) that converts the current into a current corresponding to the intensity of the optical signal.
Alanche Photo Diode) 3 and AP
A preamplifier 5 for current-to-voltage conversion of the current from D3;
AGC (Automatic GainCo) that automatically adjusts the gain according to the change in the amplitude level of the input signal.
ntrol) circuit 7, a main amplifier 9 for amplifying an output voltage from the AGC circuit 7, a control voltage generator 11 for outputting a control voltage to the AGC circuit 7, a driving circuit 13 for supplying a bias voltage to the APD 3, and a driving circuit. It comprises a drive circuit adjustment circuit 15 for adjusting the output voltage level of the circuit 13, and a protection circuit 17 for protecting the drive circuit 13 from lowering the bias voltage for an optical signal input of a certain level or more.

Next, the operation of the optical signal receiving circuit 1 will be described. Upon detecting the optical signal, the APD 3 photoelectrically converts the optical signal into a current corresponding to the intensity of the optical signal. In addition, this current
The current-voltage conversion is performed by the preamplifier 5. Next, the output voltage of the preamplifier 5 is amplified by the AGC circuit 7 and the main amplifier 9 to a predetermined amplitude level.

Here, when the amplitude level of the optical signal is lower than the predetermined level, the bias voltage of the drive circuit 13 is changed by the drive circuit adjustment circuit 15 to increase the current output from the APD 3 and The output level of the signal receiving circuit 1 is adjusted to be constant. At this time, A
The output voltage of the control voltage generator 11 for driving the GC circuit 7 is constant.

When the amplitude level of the optical signal is equal to or higher than a predetermined level, the gain of the AGC circuit 7 is controlled by the feedback control constituted by the control voltage generator 11, and the output of the optical signal receiving circuit 1 is controlled. The level is controlled to be constant. At this time, the bias voltage of the drive circuit 13 is constant.

Furthermore, in order to perform stable reception even when an optical signal of an excessive level is input, the protection circuit 17 controls the driving circuit 13 for an optical signal of a certain level or more.
Protection so that the voltage of the

The protection circuit 17 includes a DC separation unit 19,
It has an amplifier circuit 21 and a transistor 23. The DC separation unit 19 includes a capacitor, a coil, and the like.
From the electric signal from the DC signal.
The amplification circuit 21 amplifies the DC voltage from the DC separation unit 19. The transistor 23 has a base connected to the output terminal of the amplifier circuit 21, a collector connected to the output terminal of the drive circuit adjustment circuit 15, and an emitter connected to the ground level.

First, the DC separator 19 separates the DC voltage of the electric signal. The signal level of the separated DC component corresponds to the average optical input level, and is input to the amplifier circuit 21. The average optical input level input to the amplifier circuit 21 is amplified and output to the base of the transistor 23. When an average light input level equal to or higher than a predetermined level is input to the base of the transistor 23, a current flows between the collector and the emitter according to the average light input level.
As a result, the output voltage from the drive circuit adjustment circuit 15 to the drive circuit 13 decreases, and the drive circuit 13 reduces the bias voltage of the APD 3 and reduces the current flowing through the APD 3.

As described above, when the average light input level from the APD 3 exceeds a predetermined level, the protection circuit 17
Reduces the bias voltage of the drive circuit 13 so that the APD 3 can be used even when a very high-level optical signal is input.
By limiting the current flowing through the APD 3, deterioration of the APD 3 and the like can be prevented. Further, the protection circuit 17 is connected to the APD3
, It is possible to protect by the characteristic of the APD 3 alone without being affected by the performance change of the amplifier or the like due to the temperature change or the like.

In this embodiment, the case where the APD is used as the light receiving element has been described. However, the present invention is not limited to such a case, and the same applies to the case where a PIN photodiode or the like is used. By limiting the current flowing through the element, deterioration of the light receiving element can be prevented.

In this embodiment, the AGC circuit is used, but in the present invention, the AGC circuit is not necessarily used.
The C circuit is not essential, and the present invention can be applied to a light receiving circuit in which the AGC circuit is omitted.

[0021]

According to the first aspect of the present invention, the average light input level represented by the DC component of the electric signal from the light receiving element is separated, and when the average light input level is higher than a predetermined level, By adjusting the bias voltage from the voltage supply means to decrease according to the average light input level,
Even when a high-level optical signal is input to the light receiving element, the current flowing through the light receiving element can be limited.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram of a conventional optical signal receiving circuit 101.

FIG. 3 is a schematic diagram of a light receiving level in an APD 103 of a conventional optical signal receiving circuit 101.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical signal receiving circuit 3 APD 7 AGC circuit 13 Drive circuit 15 Drive circuit adjustment circuit 17 Protection circuit 19 DC separation part 21 Amplification circuit 23 Transistor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04B 10/04 10/06 10/08

Claims (1)

[Claims] A light-receiving element that converts an optical signal into an electric signal; an amplifier that amplifies the electric signal and outputs an electric output;
An optical signal receiving circuit configured to supply a bias voltage for driving a light receiving element, wherein the voltage supplying means increases a bias voltage of the light receiving element according to a magnitude of an electric output. And a bias voltage adjusting means for adjusting the bias voltage of the light receiving element so as to decrease in accordance with the magnitude of the DC component of the electric signal from the light receiving element. circuit.