JPH05114887A - Light receiving device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a waveform at the stage of amplification by detecting the intensity of an input signal and controlling the light current to be inputted to the stage of amplification. CONSTITUTION:The optical signal is converted into light current by a light receiving element 1. A capacitor 2 sends the only signal components to a front amplifier 8 through a variable attenuator 3. Light current 7 of a signal component passing the capacitor 2 is attenuated by the variable attenuator 3 consisting of, for example, a field effect transistor. The light current detection circuit 5 detects the average value of the signal component out from the light current flowing through resistance 4. A control voltage generation circuit 6 compares the voltage detected in the light current detection circuit 5 with the reference voltage, and generates the voltage controlling the attenuation amount of the light current 7 in the variable attenuator 3. The light current 1 which is attenuated in the variable attenuator 3 is amplified by the front amplifier 8. Accordingly, the light current 7 to be inputted to the front amplifier 8 can be reduced, and the gain saturation in the front amplifier 8 can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver for converting an optical signal into an electric signal, and more particularly to controlling photocurrent.

[0002]

2. Description of the Related Art An optical receiver for converting an optical signal into an electric signal has conventionally been constructed as shown in FIG. The operation will be described below with reference to the drawings. An optical signal received by the light receiving element 1 is converted into a photocurrent 7 and amplified by a preamplifier 8. The photocurrent amplified by the preamplifier 8 is amplified by the variable gain amplifier 10 into a photocurrent having a constant output amplitude. In order to obtain this photocurrent with a constant output amplitude, the gain of the variable gain amplifier 10 is controlled. This control is performed by the control voltage generated by the control voltage generation circuit 12 after the output level of the variable gain amplifier 10 is detected by the detection circuit 11.

[0003]

Generally, in an optical receiver,
In order to prevent the deterioration of the receiving performance due to the fluctuation of the input power of the optical signal received by the light receiving element, the output level at the output stage is detected and the variable gain amplifier is controlled by the circuit configuration of FIG. 3 to make the output amplitude constant. .. However, the conventional optical receiver has a problem that when the input power of the optical signal received by the light receiving element is large, gain saturation occurs in the preamplifier, and the waveform deterioration that occurs cannot be recovered by the variable gain amplifier in the subsequent stage. Was.

The present invention aims to prevent gain saturation in the preamplifier.

[0005]

To achieve this object, an optical receiver according to the present invention comprises a light receiving element for converting an optical signal into a photocurrent, and a variable attenuator for attenuating the photocurrent of the light receiving element. A configuration having a photocurrent detection circuit that detects an average photocurrent of the light receiving element and a control voltage generation circuit that is connected to the photocurrent detection circuit and that controls the variable attenuator, or a variable gain instead of the variable attenuator. It has a configuration including a pre-value amplifier.

[0006]

The optical receiver of the present invention has the above-described structure and detects the photocurrent flowing through the light receiving element and controls the photocurrent input to the preamplifier to prevent gain saturation in the preamplifier. To do.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical receiver according to a first embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the light receiving element 1 converts the received optical signal into a photocurrent. The capacitor 2 transmits only the signal component to the preamplifier 8 via the variable attenuator 3. The photocurrent 7, which is a signal component that has passed through the capacitor 2, is attenuated by a variable attenuator 3 such as a field effect transistor. The photocurrent detection circuit 5 detects the average value of the signal component from the photocurrent flowing through the resistor 4. If the mark ratio of the digital signal is known, the detected average photocurrent is the photocurrent as shown in FIG. It is proportional to the amplitude of the current 7. From this relationship, the amplitude of the photocurrent 7 can be controlled by detecting the average photocurrent. The control voltage generation circuit 6 compares the voltage detected by the photocurrent detection circuit 5 with the reference voltage, and the variable attenuator 3
A voltage that controls the amount of attenuation of the photocurrent 7 is generated. The photocurrent 7 attenuated by the variable attenuator 3 is amplified by the preamplifier 8.

When the optical power incident on the light receiving element 1 is large, the photocurrent flowing through the resistor 4 increases. From this photocurrent, the photocurrent detection circuit 5 detects the average photocurrent, and the control voltage generation circuit 6 generates a control voltage that increases the amount of attenuation in the variable attenuator 3. By increasing the amount of attenuation, the photocurrent 7 input to the preamplifier 8 can be reduced, and the gain saturation in the preamplifier 8 can be prevented.

FIG. 2 shows a second embodiment of the present invention. Hereinafter, elements having the same operations as those of the elements constituting the first embodiment are designated by the same reference numerals and the description thereof will be omitted. Figure 2
As shown in, the functions of the light receiving element 1, the capacitor 2, the photocurrent detection circuit 5, and the control voltage generation circuit 6 are the same as those in the first embodiment. Instead of amplifying the output signal, which is obtained by attenuating the photocurrent with the variable attenuator, with the preamplifier 8, in the second embodiment, a variable gain preamplifier 9 such as a dual gate field effect transistor is provided. The control voltage generated by the control voltage generation circuit 6 controls the gain of the variable gain preamplifier 9. As a result, the functions of the preamplifier 8 and the variable attenuator 3 in the first embodiment are controlled by the variable gain preamplifier 9
The number of circuit components can be reduced as compared with the first embodiment.

When the optical power incident on the light receiving element 1 is large, the photocurrent flowing through the resistor 4 increases. From this photocurrent, the photocurrent detection circuit 5 detects the average photocurrent, and the control voltage generation circuit 6 generates a control voltage that reduces the gain in the variable gain preamplifier 9. By reducing the gain of the variable gain preamplifier 9, it is possible to prevent gain saturation there.

[0011]

As described above, the optical receiver of the present invention is effective in preventing waveform deterioration in the amplification stage by detecting the magnitude of the input signal and controlling the photocurrent input to the amplification stage. It is something.

[Brief description of drawings]

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

FIG. 2 is a block diagram of an optical receiver of the second embodiment.

FIG. 3 is a block diagram of a conventional optical receiver.

FIG. 4 is an explanatory diagram showing the relationship between photocurrent and average photocurrent.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photodetector 2 Capacitor 3 Variable attenuator 4 Resistor 5 Photocurrent detection circuit 6 Control voltage generation circuit 7 Photocurrent 8 Preamplifier 9 Variable gain preamplifier

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuyuki Fujito 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A light receiving element for converting an optical signal into a photocurrent, a variable attenuator for attenuating the photocurrent of the light receiving element, a photocurrent detection circuit for detecting an average photocurrent of the light receiving element, and the photocurrent. An optical receiver having a control voltage generation circuit connected to a detection circuit and controlling the variable attenuator. 2. The optical receiver according to claim 1, further comprising a variable gain preamplifier that amplifies a photocurrent instead of the variable attenuator.