JPH024033A - Optical receiver - Google Patents

Abstract

PURPOSE:To improve a minimum receiving sensitivity by giving the output of an automatic gain control circuit to be connected at the output side of an avalanche photodiode and to fix an output voltage to one side of an identifying circuit and adjusting a threshold value given to the other side. CONSTITUTION:When a light input to an avalanche photodiode APD 10 is decreased, a bias voltage is increased so as to increase the amplification factor of the APD 10 by a feedback circuit composed of a peak value detecting circuit 21, an operational amplifier 22 and a DC/DC converter 30 connected to the APD 10. The bias voltage is inputted to the negative terminal of an operational amplifier 50, and to the positive terminal, a reference voltage Vref 1 is given. When the bias voltage is increased, the output of the operational amplifier 50 is decreased, and it is given as a threshold voltage to an identifying circuit 40. Thus, a light input power is decreased, and even when a shot noise is increased, the '1' and '0' of signal data are correctly identified, and the minimum receiving sensitivity is improved.

Description

[Detailed description of the invention] [Summary] Avalanche photodiode (hereinafter referred to as APD)
The purpose of the present invention is to provide an optical receiver that optimizes the discrimination level of "1" and "0" of received data even when the optical input decreases, and improves the minimum reception sensitivity. An APD that converts an input optical signal consisting of “1” and “O” into an electrical signal, and an AP
AP is connected to the output of D to keep the output voltage constant.
An automatic gain control circuit that controls the operating point of D and the output of the automatic gain control circuit are applied to one input terminal, and a predetermined threshold voltage is applied to the other input terminal. In an optical receiver equipped with an identification circuit that discriminates between "1" and "0", an optical receiver is inserted between the threshold voltage input terminal of the identification circuit and the power supply terminal of the 8 PD, and inputs the threshold voltage. It is configured by adding a threshold value adjusting means for changing the value to a predetermined value according to the optical signal power.

[Industrial application field]

The present invention relates to an improvement of an optical receiver using an APD.

At this time, even when the optical input decreases, the received data will be
There is a demand for an optical receiver that optimizes the On discrimination level and improves the minimum receiving sensitivity.

[Conventional technology]

FIG. 4 is a diagram showing an example of a method for identifying signal data.

FIG. 5 is a block diagram of a circuit configuration of a conventional example.

In FIG. 5, when optical signal data consisting of 0" and "I" is input to AI'll l, it is converted into electrical signal data and input to the equalization amplifier circuit 2. The above signal data is equalized. The peak value detection circuit 2-1 in the amplifier circuit 2 is manually operated to detect the peak value of the pulse of the signal data, and the output is input to the operational amplifier 2-2. After comparison, the output voltage of the difference is divided and one side is inputted to the DC/DC converter 3.

In the DC/DC converter 3, so that the amplitude of the output data of the equalization amplifier circuit 2 is constant according to the input voltage,
The multiplication factor is controlled by changing the bias voltage of APD 1.

The other branched output of the above operational amplifier 2-2 is connected to amplifier 2.
-3 to one input terminal of the identification circuit 4, and a threshold voltage is applied to the other input terminal.

Then, as shown in Figure 4, when the input signal data is greater than the threshold voltage, it becomes 1"
When the value is small, it is determined as “0”.

In this way, signal data was identified.

[Problem to be solved by the invention]

However, in the above circuit, the eight PDs generate shot noise only when optical signal data is input, and the APD
The threshold voltage when the multiplication factor is low is “0” of the signal data.
and near the center of "1", but when the optical input decreases and the multiplication factor increases, the shot noise on the "1" side increases, making it difficult to distinguish the "B" signal and causing errors. There was a problem that there was.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical receiver that optimizes the discrimination level between "1" and "0" of received data even when the optical input decreases, and improves the minimum receiving sensitivity.

[Means to solve the problem]

The above problem is solved by the circuit configuration shown in FIG.

That is, in FIG. 1, there is an avalanche photodiode 100 that converts an input optical signal consisting of "1" and "01" into an electrical signal, and an avalanche photodiode 100 that is connected to the output of the avalanche photodiode to keep the output voltage constant. The automatic gain control circuit 200 controls the operating point of the avalanche photodiode as shown in FIG. In an optical receiver equipped with an identification circuit 400 that discriminates between electrical signals "1" and "0",
0 is the threshold voltage input terminal of the identification circuit and the avalanche
This threshold adjusting means is inserted between the photodiode and the power supply terminal, and changes the threshold voltage to a predetermined value according to the input optical signal power.

[Function] In FIG. 1, the avalanche photodiode 100
When the input optical signal power to the avalanche photodiode decreases, the automatic gain control circuit 200 operates to keep the output voltage constant and increases the bias voltage of the avalanche photodiode. By applying this bias voltage to the threshold adjusting means 500, a voltage is output that lowers the threshold voltage input to the identification circuit.

As a result, even if the optical input decreases, the multiplication factor increases, and the shot noise on the "1" side increases, it is still possible to reliably distinguish between "C" and "O" because the threshold voltage is kept low. , it is possible to improve the minimum reception sensitivity.

〔Example〕 FIG. 2 is a circuit configuration block diagram of an embodiment of the present invention.

FIG. 3 is a diagram illustrating the effects of the embodiment.

The same reference numerals indicate the same objects throughout the figures.

In FIG. 2, when the optical input power to APDIO decreases, a feedback loop consisting of a peak value detection circuit 21, an operational amplifier 22, and a DC/DC converter 30 connected to APDIO applies a bias voltage to increase the multiplication factor of APDIO. increases. This bias voltage is applied to the negative input terminal of the operational amplifier 50, and the reference voltage Vref is applied to the positive input terminal. As a result, when the bias voltage increases, the output of the operational amplifier 50 becomes smaller, and this output voltage is applied to the identification circuit 40 as a threshold voltage.

As a result, even when the optical input power decreases and shots and noise increase, the threshold voltage decreases, as shown in Figure 3 (
As shown in bl, it becomes possible to distinguish between signal data "l" and "0".

It is possible to optimize the signal and improve the minimum reception sensitivity.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the principle of the present invention, Fig. 2 is a block diagram of the circuit configuration of an embodiment of the invention, Fig. 3 is a diagram explaining the effects of the embodiment, and Fig. 4 is an example of a signal data identification method. The figure shown in FIG. 5 is a circuit configuration block diagram of a conventional example. In the figure, 500 indicates a threshold value adjusting means. [Effects of the Invention] As explained above, according to the present invention, even when the optical input decreases, it is possible to distinguish between "1" and "0" of received data. Invention n History Threat, J, n Lostepping In Bu'ofu, 7th Garden No. 2
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The figure fits the 1/V, the 7th, the 5th fear, and the Brochus figure.

Claims (1)

[Claims] An avalanche photodiode (100) that converts an input optical signal consisting of "1" and "0" into an electrical signal, and is connected to the output of the avalanche photodiode to keep the output voltage constant. an automatic gain control circuit (200) for controlling the operating point of the avalanche photodiode;
Adding the output of the automatic gain control circuit 1 to one input terminal,
An optical receiver comprising an identification circuit (400) that applies a predetermined threshold voltage to the other input terminal and uses the threshold voltage to discriminate between "1" and "0" of the electrical signal, The threshold voltage input terminal of the identification circuit and the avalanche
1. An optical receiver further comprising a threshold adjusting means (500) inserted between a power supply terminal of a photodiode and changing the threshold voltage to a predetermined value according to the input optical signal power.