JPS6249679A - Optical signal receiving circuit - Google Patents

Abstract

PURPOSE:To prevent the deterioration of the maximum light-receiving level by a method wherein a diode is brought in a conductive state when the level of photo input is made larger, a current is applied to a light-receiving element from the diode, and the degree of voltage drop on the first resistor is reduced. CONSTITUTION:When the input level of an optical signal is small, a diode 14 is in the state of interruption due to the low degree of voltage drop when the level of an optical signal is small. When the level of optical input is large, the degree of voltage drop on the resistor 11 is increased, the diode 14 is turned into the state of conduction, and a current is applied to a light-receiving element 2 through the diode 14. Accordingly, sufficient voltage can be applied to the element 2, and the deterioration of the maximum light-receiving level can also be prevented.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an optical receiving circuit.

[Prior art]

As shown in FIG. 3, a conventional optical receiving circuit has an anode connected to the earth, for example, and receives an optical signal 1, converts it into an electrical signal, and outputs it to a cathode. A light-receiving element 2 such as an avalanche photodiode or a PIN photodiode, a resistor 4 provided between the cathode and the power supply 3, and a capacitor 5 that passes the alternating current component of the electric signal generated at the connection point between the resistor and the cathode. , and a preamplifier circuit 6 that amplifies and outputs the extracted AC signal component.

[Problem that the invention seeks to solve]

In the conventional optical receiving circuit described above, the resistor 4 is approximately 100 Ω in order to improve the minimum light receiving level. Therefore, when the level of the received optical signal 1 increases, as the output current of the light receiving element 2 increases, sufficient voltage is no longer applied to the light receiving element 2 due to the voltage drop caused by the resistor 4, and the maximum light receiving It had the disadvantage of degrading the level. The present invention therefore seeks to overcome the above-mentioned drawbacks.

[Means for solving problems]

The optical receiving circuit of the present invention includes a light receiving element that receives an optical signal and converts it into an electrical signal, a resistor, and a first electric signal connected in series. It is characterized in that it consists of two resistors arranged at , and further, a second power supply having a lower stain pressure than the first power supply is connected to the connection part of the two resistors via a diode. This is an optical receiving circuit.

〔Example〕

Next, the present invention will be explained in detail.

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. In the figure, a photoelectric element 2. Capacitor 5. The arrangement of the preamplifier circuit 6 is the same as that of the conventional circuit shown in FIG. The difference from the conventional circuit is that the resistor 4 in FIG. 3 is divided into a first resistor 11 and a second resistor 12 arranged in series.
Also, a first power source 13 whose power source is connected to the first resistor 11
The second power supply 15 is connected to the connection point between the first resistor 11 and the second resistor 12 via a diode 14, and has a lower voltage than the first power supply. .

In the above configuration, when the input level of the optical signal 1 is small, the voltage drop across the first resistor 11 is small, so the diode 14 is in a cutoff state, but when the optical input level is high, the first resistor 11 is cut off. When the voltage drop across the resistor 11 increases and the diode 14 becomes conductive, current to the light receiving element 2 is supplied through the diode 14.

Therefore, a sufficient voltage is applied to the light receiving element 2.

Deterioration of the maximum light reception level can be prevented.

FIG. 2 is a block diagram of a second embodiment in which the output of the light receiving element is taken out from the anode. In FIG. 2, the arrangement of photoelectric elements, diodes, and resistors is upside down from that in FIG. 1, but the same reference numerals as in FIG. 1 are used because the elements themselves have not changed. However, since the positive and negative outputs of the power sources are reversed, the first power source is 13a and the second power source is 15a. In this case as well, as in the case of FIG. 1, when the optical input level is small, the diode 14 is in the cutoff state, but when the optical input level becomes too low, the voltage drop across the first resistor 11 becomes large. ,
When the diode 14 is not in a conductive state, the current from the light receiving element 2 is caused to flow through the diode 14. The result is exactly the same as the case shown in FIG.

〔Effect of the invention〕

As explained above, the present invention makes the diode conductive when the optical input level increases, and supplies current to the photodetector from the diode, thereby reducing the voltage drop across the first resistor. Even when the light input level is high, sufficient voltage can be applied to the light receiving element, which has the effect of preventing deterioration of the maximum light receiving level.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an optical receiving circuit according to an embodiment of the present invention.
Figure 2 is a block diagram of the $saving system in Figure 2, and Figure 3 is a block diagram of a conventional optical receiver circuit. Explanation of symbols: 1 is an optical signal, 2 is a light receiving element, 5 is a capacitor, 6 is a preamplifier circuit, 11 is a first resistor, 12 is a second resistor, 13 is a first power supply. 14 is a diode, and 15 is a second power source. Figure 1 to 42 Figure 3

Claims (1)

[Claims] 1. A light-receiving element that receives an optical signal and converts it into an electrical signal, a resistor, and a first power source are arranged in series, and a connection portion between the light-receiving element and the resistor is provided with the In an optical receiving circuit which is connected to a means for taking out and amplifying an electric signal via a capacitor, the resistor is composed of two resistors arranged in series, and further, at a connection part of the two resistors, An optical receiving circuit characterized in that a second power source having a lower voltage than the first power source is connected via a diode.