JPH0813016B2 - Optical receiver circuit - Google Patents

Description

The present invention relates to an optical receiving circuit used in an optical communication device.

[Conventional technology]

 An example of a conventional light receiving circuit will be described with reference to FIG.

In the figure, the optical signal is an avalanche photodiode.
The light-to-electricity is converted into photocurrent by 21. This photocurrent is current-voltage converted by the preamplifier circuit 22. Then, this signal is amplified to a predetermined band and amplitude by the variable gain amplifier circuit 23, the equalizer 24 and the main amplifier circuit 25. Here, the average light receiving level of the optical signal input to the optical receiving circuit generally changes depending on the distance of the electric transmission path and therefore fluctuates. The peak detection circuit 26, the AGC circuit 27 and the DC / DC
The feedback control configured by the DC converter 28 controls the electric gain of the variable gain amplifier circuit 23 and the current multiplication factor of the avalanche photodiode 21. 29
Is an output terminal from which the reception equalized waveform output is obtained from the main amplification circuit 25.

[Problems to be Solved by the Invention]

The photocurrent input to the preamplifier circuit of this conventional optical receiver circuit is of the order of several hundreds nA at the minimum light receiving level. Also, if the transmission distance is extremely short, an excessive received light level will be input to the avalanche photodiode, and the photocurrent will be several
Increase to near mA order.

In such a case, the conventional optical receiver circuit described above has a problem that the preamplifier circuit is saturated and the output thereof causes waveform distortion, so that a normal reception equalized waveform cannot be obtained.

[Means for solving the problem]

The optical receiving circuit of the present invention, an avalanche photodiode for converting light into an electric signal, a preamplifier circuit for current-voltage converting the photocurrent of the avalanche photodiode, and a bias voltage for the avalanche photodiode. In a light receiving circuit having a bias supply circuit for supplying, the bias voltage supplied to the avalanche photodiode is divided and input to a voltage comparator for comparison with a predetermined reference voltage for detecting an excessive light reception level. , The output of this voltage comparator operates a current bypass circuit provided between the avalanche photodiode and the preamplifier circuit to bypass a part of the photocurrent input to the preamplifier circuit. It is the one.

[Work]

In the present invention, by operating the bypass circuit with the photocurrent input to the preamplifier circuit in the region where the average light receiving level becomes excessive, the output waveform distortion of the preamplifier circuit is suppressed and the maximum light receiving level is improved. .

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

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

In FIG. 1, 1 is an avalanche photodiode for converting into an electric signal of light, 2 is a preamplifier circuit for converting the photocurrent of the avalanche photodiode 1 into current-voltage, and 3 is this preamplifier circuit 2. Of the variable gain amplifier circuit 4 connected to the output side of the equalizer 5, 4 is an equalizer having the output of the variable gain amplifier circuit 3 as an input, 5 is a main amplifier circuit having the output of the equalizer 4 as an input, and 6 is the main amplifier circuit. A peak detection circuit having the output of the main amplification circuit 5 as an input, 7 is an AGC circuit having the output of the peak detection circuit 6 as an input, and the output of the AGC circuit 7 is guided to the variable gain amplification circuit 3 and DC / DC. It is configured to be introduced into the converter 8.

The DC / DC converter 8 constitutes a bias supply circuit that supplies a bias voltage to the avalanche photodiode 1.

Reference numeral 9 is a voltage comparator that divides a part of the bias voltage of the avalanche photodiode 1 and compares it with a reference voltage, and reference numeral 10 is a current bypass circuit controlled by the output of the voltage comparator 9.

Then, the bias voltage supplied to the avalanche photodiode 1 is divided and input to the voltage comparator 9 for comparison with a predetermined reference voltage, and the output of the voltage comparator 9 causes the avalanche photodiode 1 and the preamplification. The current bypass circuit 10 provided between the circuits 2 is operated to bypass a part of the photocurrent input to the preamplifier circuit 2. Reference numeral 11 is an output terminal from which the reception equalized waveform output is obtained from the main amplifier circuit 5.

FIG. 2 is an explanatory diagram showing the voltage input to the voltage comparator 9 in FIG.

Next, the operation of the embodiment shown in FIG. 1 will be described with reference to FIG.

The optical signal is converted into a photocurrent by the avalanche photodiode 1. This photocurrent is a current − by the preamplifier circuit 2.
The voltage is converted. Here, when an optical signal of an excessive light receiving level is input to the avalanche photodiode 1, the input current of the preamplifier circuit 2 increases up to several mA, and the preamplifier circuit 2 is completely saturated. The output waveform becomes abnormal. Generally, the maximum allowable input current of this type of preamplifier circuit is about several hundred μA. Therefore, it is necessary to suppress the saturation of the preamplifier circuit 2 in order to perform normal reception even at such an excessive light reception level.

For this reason, in the present invention, a part of the photocurrent input to the preamplification circuit 2 is bypassed by the current bypass circuit 10,
It prevents the preamplifier circuit 2 from being saturated.

The current bypass circuit 10 is controlled by the output of the voltage comparator 9 so as to operate only in a region where the light receiving level is excessively high. That is, a part of the bias voltage of the avalanche photodiode 1 is used as the input of the voltage comparator 9, and the light receiving level increases as shown in FIG.
When the input voltage of the voltage comparator 9 exceeds a predetermined reference voltage, the output of the voltage comparator 9 changes and the current bypass circuit 10 is operated. In addition, the received light level is low and the voltage comparator 9
If the input of is less than the reference voltage, the voltage comparator 10 does not operate.

〔The invention's effect〕

As described above, according to the present invention, the photocurrent input to the preamplifier circuit is bypassed by the current bypass circuit in the region where the average received light level is excessive. Therefore, the output waveform distortion of the preamplifier circuit is suppressed. It has an effect that the maximum light receiving level can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the optical receiving circuit according to the present invention, FIG. 2 is an explanatory diagram showing the voltage input to the voltage comparator in FIG. 1, and FIG. 3 is a conventional optical receiving circuit. It is a block diagram which shows an example. 1 ... Avalanche photodiode, 2 ... Preamplifier circuit, 8 ... DC / DC converter, 9 ... Voltage comparator, 10
...... Current bypass circuit.

Claims (1)

[Claims] 1. An avalanche photodiode for converting light into an electric signal, a preamplifier circuit for converting a photocurrent of the avalanche photodiode into a current-voltage, and a bias for supplying a bias voltage to the avalanche photodiode. In a light receiving circuit having a supply circuit, the bias voltage supplied to the avalanche photodiode is divided and input to a voltage comparator for comparison with a predetermined reference voltage for detecting an excessive light reception level, and this voltage is input. The current bypass circuit provided between the avalanche photodiode and the preamplifier circuit is operated by the output of the comparator, and a part of the photocurrent input to the preamplifier circuit is bypassed. Optical receiver circuit characterized by.