JPH01291508A - Pre-amplifier for optical communication - Google Patents

Abstract

PURPOSE:To control the output of an amplifier at a constant level and to miniaturize a device by connecting a diode in parallel with a feedback resistor, and connecting the anode of the diode to the connecting point of first and second resistors for biasing a photodetector. CONSTITUTION:The cathode of the diode 6 connected in parallel with the feedback resistor 5 for the amplifier 4 is connected to the connecting point of the resistor 2, the input side of the amplifier 4, and the feedback resistor 5 via a capacitor 7. Simultaneously, it is connected to the ground via a coil 11. Also, the anode of the diode is connected to the connecting point of the output side of the amplifier 4 and the feedback resistor 5 via a capacitor 8. Simultaneously, it is connected to the connecting point of the resistors 2 and 3 via a coil 9. And the more increased an incident optical signal on the photodetector 1, the less a feedback resistance value decided by the feedback resistor 5 and the diode 6 is reduced, which lowers the gain of the amplifier 4. Also, adversely, the more decreased the incident optical signal on the photodetector 1, the more the gain of the amplifier 4 is increased. Therefore, it is possible to keep the output voltage V0 of the amplifier 4 constant.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical communication preamplifier used in an optical receiver in optical communication.

BACKGROUND OF THE INVENTION FIG. 2 shows the configuration of a conventional optical communication preamplifier.

In FIG. 2, when an optical signal enters the light receiving element 1, the optical signal is converted into a current (electrical signal) I proportional to the optical signal.

In optical communication, the resistance value Rto of the resistor 10 is usually set to a value sufficiently larger than the resistance value R6 of the feedback resistor 5,
Since the input impedance of the amplifier 4 is also high, the light receiving element 1
Most of the current Ip from the current Ip flows to the feedback resistor 5.

Therefore, the amplifier 40 input voltage ■ and output voltage ■. Between V+ V-= Ip -Rs -(x
) holds true, and if the gain of amplifier 4 is -A, then V
, -V, ......The relationship (2) holds, so by substituting equation (2) into equation (1) and solving as A>1, we get V, = -1, ・R11 ......(3).

In this way, even in the conventional optical communication preamplifier described above, the output voltage v0 is obtained by multiplying the current Ip obtained by converting the optical signal by the light receiving element 1 by the resistance value R of the feedback resistor 5.

Problems to be Solved by the Invention However, when an optical receiver is configured using the above-mentioned conventional preamplifier for optical communication, the output voltage (1) varies depending on the level of the optical signal incident on the light receiving element 1. As a result, a gain control circuit must be provided at a subsequent stage to control the gain, which poses a problem in that the circuit configuration of the optical receiver becomes complicated and larger.

The present invention solves these conventional problems, and allows a gain control function to be added with a simple configuration.
It is an object of the present invention to provide a preamplifier for optical communication that can be miniaturized.

Means for Solving the Problems In order to achieve the above object, the present invention connects a diode in parallel with the feedback resistor, and connects the anode of this diode to the first. It is connected to the connection point of the second resistor.

Therefore, according to the present invention, when the intensity of the optical signal to the light receiving element is strong, a large current flows from the light receiving element, and the first bias current of the light receiving element connected between the light receiving element and the ground is generated. The potential on the light receiving element side of the second resistor increases,
As the voltage applied to the diode increases, the differential resistance of the diode decreases, and the resistance value determined by the feedback resistance and the differential resistance of the diode decreases, reducing the gain of the amplifier.

Furthermore, when the intensity of the optical signal to the light receiving element is weak, the gain of the amplifier is increased, contrary to when it is strong.

In this way, the output of the amplifier can be controlled to a constant value regardless of the strength of the optical signal to the light receiving element.

Example FIG. 1 shows the configuration of an embodiment of the present invention.

In FIG. 1, reference numeral 1 indicates a light receiving element that converts an incident optical signal into a current (electrical signal) IP, and reference numerals 2 and 3 indicate first and second electrodes for bias, respectively. A second resistor is connected in series between the anode of the light receiving element 1 and the ground. Usually, the relationship is Rt + R->Ra.

Reference numeral 4 indicates an amplifier with a gain of −A, and its input side is connected to the connection point between the anode of the light receiving element 1 and the first resistor 2 .

5 is a feedback resistor connected between the input side and the output side of the amplifier 4, 6 is a diode, and the cathode is connected to the first resistor 2. It is connected to the input side of the amplifier 40 and the connection point with the feedback resistor 5 via the first capacitor 7, and is also connected to the ground via the coil 11, and the anode is connected to the input side of the amplifier 40 and the connection point with the feedback resistor 5.
A second capacitor 8 is connected to the output side of the feedback resistor 5.
and the first. second resistor 2, 3
The coil 9 is connected to the connection point of the coil 9 through the coil 9.

In addition, 1. The second capacitor 7.8 serves to separate the DC potential of the diode 6 and the input/output potential of the amplifier 4.

9 indicates a first coil; 11Fi is connected between the second resistor 2゜3, the anode of the diode 6, and the connection point with the second capacitor 8, and the connection point between the diode 6 and the first capacitor 7 and the ground. is connected between. These coils are for applying a DC bias voltage to the diode 6.

Next, the operation of the above embodiment will be explained.

In the above embodiment, when an optical signal enters the light receiving element 1, the optical signal is converted into a current 2 proportional to the level of the optical signal, and the current IP from the light receiving element 1 is almost the same as the feedback resistor 5.
However, a portion flows to the first and second resistors 2 and 3, so the potential on the light receiving element side of the first resistor 2 is given in proportion to the current, and the voltage applied to the diode 6 is also proportional to the current. 2
given in proportion to.

Therefore, the differential resistance of the diode 6 becomes smaller as the applied voltage increases, so that the current Ip from the light receiving element 1
The larger the optical signal that enters the photodetector 1, the lower the resistance value of the diode 6 becomes. V0 and current I of photodetector 1
The ratio with P becomes smaller.

Conversely, if the optical signal incident on the light receiving element 1 is small,
The ratio between the output voltage V of the amplifier 4 and the current 2 of the light receiving element 1 becomes large.

In this manner, according to the embodiment described above, the feedback resistance value can be changed depending on the intensity of the optical signal to the light receiving element 1, so that the output voltage of the amplifier 4 can be changed. This has the effect of making it possible to maintain a constant value.

Effects of the Invention As is clear from the embodiments described above, the present invention connects a diode in parallel with the feedback resistor, and connects the anode of the diode to the first. Since it is connected to the connection point of the second resistor via the first coil, a gain control function can be added with a simple configuration, and the output of the amplifier can be controlled to a constant value. .

Furthermore, since it is possible to miniaturize, it has the effect that the optical receiver can be miniaturized.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a preamplifier for optical communication according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional preamplifier for optical communication. 1... Light receiving element, 2... First resistor, 3... Second
resistance, 4... amplifier, 5... feedback resistor, 6...
Diode, 9...first coil, 11...second coil. Name of agent: Patent attorney Satoshi Nakao and one other person Figure 1 M 2

Claims (1)

[Claims] A light-receiving element that converts an optical signal into an electrical signal, first and second resistors connected in series between an anode of the light-receiving element and ground, and a connection between the anode of the light-receiving element and the first resistor. an amplifier whose input side is connected to a point, a feedback resistor connected between the input side and the output side of this amplifier, a diode connected in parallel with this, and a connection point between the first and second resistors. and a first coil connected between the anode of the diode and a second coil connected between the cathode of the diode and ground.