JPH0352424A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To operate an optical input monitor normally in a required reception level area by configuring the subject circuit in such a manner that a comparator is inserted between a bias supply circuit and a photodetector, and the output of the bias supply circuit is added on the photodetector as it is when it exceeds a second reference value set in advance, and no output is issued when it is less than a second reference value. CONSTITUTION:The circuit is configured in such a manner that the comparator 900 is provided between the bias supply circuit 800 and the photodetector 100, and the output of the bias supply circuit 800 is inputted, and when input exceeds the second reference value set in advance, the input is outputted as it is, and is added on the photodetector 100, and when it is less than the second reference value, it is not outputted. Therefore, one kind of control voltage can correspond to the constant gain of an AGC amplifier 300. In such a manner, it is possible to operate the optical input monitor normally in the required reception level area.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to an automatic gain control circuit used in a reception circuit of an optical submarine repeater, etc., and provides an automatic gain control circuit that operates normally in a reception level region where optical input monitoring is required. A light-receiving element that receives an optical signal and converts it into an electrical signal; an amplifier that inputs the output of the light-receiving element and amplifies the output signal level to a constant level according to an output control signal of a switch;
A switch that branches the output of the amplifier and inputs it, adds the output to the amplifier when the input value is larger than a preset reference value, and adds the output to the bias supply circuit when it is smaller than the reference value, and between the switch and the light receiving element. In an automatic gain control circuit for an optical receiver, the circuit is connected to a bias supply circuit that inputs the output of the switch and outputs a bias for driving the light receiving element, and is inserted between the bias supply circuit and the light receiving element, A comparator is provided that inputs the output of the bias supply circuit, and when the input is larger than a preset second reference value, outputs the input as is and adds it to the light receiving element, and does not output when it is smaller than the second reference value. Configure.

[Industrial application field]

The present invention is an automatic gain control system used in receiving circuits such as optical submarine repeaters. This invention relates to an improvement of an IJ control circuit (hereinafter referred to as an AGC circuit).

In the AGC circuit described above, optical input is monitored in order to detect the occurrence of a failure in the transmission line, circuit, etc. at an early stage.

At this time, there is a need for an AGC circuit that operates normally in the reception level range where optical input monitoring is required. [Prior art] Figure 3 shows an example of a DC/DC converter (hereinafter referred to as DC/DC converter).
CONV) is a human/output characteristic diagram.

Figure 4 shows an example of an avalanche photodiode (A
FIG.

FIG. 5 is a block diagram showing the structure of a conventional AGC circuit.

Figure 6 shows a conventional AGC amplifier (hereinafter referred to as A) for optical input.
FIG. 2 is a diagram showing the characteristics of a GC amplifier (referred to as a GC amplifier) and the APD bias voltage characteristics.

In FIG. 5, when a digital optical signal, for example, is input to the APD 1, it is converted into an electrical signal and output. This output is input to the AGC amplifier 3 via the preamplifier 2, and is amplified and outputted so that the output voltage of the AGC amplifier 3 is constant according to a control signal of the output of the contact 7 of the switch, which will be described later. This output is a discriminator (hereinafter referred to as DIS) 4
In addition, the digital signal is output after being distinguished between "l" and "o".

The above output is divided, for example, at a ratio of 9:1, and the 1/10 output predetermined portion is added to the average value circuit 5 to obtain the average value of the digital output. The output of the average value circuit 5 is connected to an operational amplifier (
(hereinafter referred to as operational amplifier) 6. A predetermined reference voltage Vref is applied to the other input terminal of the operational amplifier 6. The operational amplifier 6 compares the input from the average value circuit 5 and the reference voltage Vref.

Then, the output of the operational amplifier 6 is applied to the contact 7 of the switch, but when the output of the average value circuit 5 is higher than the reference voltage Vref in the operational amplifier 6, the contact 7 of the switch is switched to the side of the GC amplifier 3, and the average value circuit 5 output is AGC
This signal can be applied to the amplifier 3 as a control signal. or,
When the output of the average value circuit 5 is smaller than the reference voltage V ref, the switch contact 7 is switched to the DC/DC CONV8 side, and the output of the average value circuit 5 is set to the DC/DC CONV side.
8.

AGC amplifier 3 has gain characteristics as shown in Figure 6. ＾When the optical input to PD 1 is above a certain value So (corresponding to the M quasi-voltage Vref), the above-mentioned operational amplifier 6
By applying the output to the AGC amplifier 3 via the switch contact 7, the gain decreases as the optical input increases,
A constant voltage is output from the AGC amplifier 3.

Also, when the optical input to the APD l is below a certain value S0, the output of the operational amplifier 6 is changed to DC via the contact 7 of the switch.
/DC Added to CONVB. DC/DC CON
As shown in Figure 3, V8 has the characteristic that the output voltage increases as the absolute value of the input negative voltage increases, so as the optical input decreases, the negative input voltage to DC/DC CONV8 increases and the DC The output voltage of /DC CONν8 also increases. This output is added to APD l and APD
The bias voltage of APD 1 is increased, and as a result, the multiplication factor M of APD 1 is also increased, and the electrical signal output of ^pot is increased,
Make the output of AGC amplifier 3 constant. In this way A
The output of the GC circuit is kept constant.

It should be noted that the output of the contact 7 of the switch to the AGC amplifier 3 is boosted up and the optical input to the APD 1 is monitored in order to prepare for failures in the transmission path, circuits, etc.

[Problem to be solved by the invention]

However, in the circuit configuration described above, as shown in FIG. ) has constant or decreasing characteristics. For this reason, as shown in FIG. 6, when the optical input decreases, the bias voltage of APD 1 increases, but the dark current also increases, which amplifies noise in AGC amplifier 3. The gain of the AGC amplifier 3 in the part a) is reduced by a certain value.

As a result, as shown in FIG. 6, there are two types of control voltages for a constant gain of the AGC amplifier 3, resulting in the problem that the optical input monitor does not function properly.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an automatic gain control circuit that operates normally in a reception level range where an optical input monitor is required.

[Means to solve the problem]

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

That is, in FIG. 1, there is a light receiving element 100 that receives an optical signal and converts it into an electrical signal, and an amplifier that receives the output of the light receiving element and amplifies it so that the output signal level is constant according to the output control signal of the switch 700. 300, a switch 700 which branches the output of the amplifier and inputs it, adds the output to the amplifier when the input value is greater than a preset reference value, and adds the output to the bias supply circuit 800 when the input value is smaller than the reference value; and a bias supply circuit 800 connected between the light receiving element and the light receiving element, and inputting the output of the switch and outputting a bias for driving the light receiving element, 900 is a bias supply circuit; Provided between the light receiving elements,
A comparator that inputs the output of the bias supply circuit, and when the input is larger than a preset second reference value, outputs the input as is and adds it to the light receiving element, and does not output when it is smaller than the second reference value. be.

[For production]

In FIG. 1, a voltage corresponding to SI shown in FIG. 6 is set as the second reference value applied to the comparator 900. Then, the output of the bias supply circuit 800 is input to the comparator 900, and when the input is larger than a preset second reference value, the input is output as is and applied to the light receiving element 100. Further, when the input is smaller than the second reference value, no output is made.

As a result, the part (a) shown in Figure 6 is removed and the eight GCs are removed.
One type of control voltage now corresponds to a constant gain of the amplifier 3, and the optical input monitor can be operated normally in a required reception level range.

〔Example〕

Figure 2 is a block diagram showing the structure of the GC circuit according to the embodiment of the present invention. The same reference numerals indicate the same objects throughout the figures.

Figure 2 shows APD 1 and DC/DC CONV.
A voltage corresponding to S1 shown in FIG. 6 is set as the reference voltage Vref, which is applied to one input terminal of the comparator 9 provided between B and B. The other input terminal of the comparator 9 has a DC/D
Add the output of C CONV 8. And DC/D
The input voltage from C CONV8 is the reference voltage V ref
When it is greater than 1, the input from DC/DC CONV8 is output as is and added to APD1. On the other hand, D.C.
/DC The input voltage from CONV8 is the reference voltage Vref
, the comparator 9 outputs nothing.

As a result, the part (a) shown in FIG. 6 is removed, and the optical input monitor can be operated normally in the required reception level range.

〔Effect of the invention〕

As described above, according to the present invention, the optical input monitor can be operated normally in a necessary reception level range.

4

[Brief explanation of drawings]

Fig. 1 is a principle diagram of the present invention, Fig. 2 is a block diagram showing the configuration of an AGC circuit according to an embodiment of the present invention, Fig. 3 is an input/output characteristic diagram of an example of DC/DC CONV, and Fig. 4 is FIG. 5 is a block diagram showing the configuration of a conventional AGC circuit. FIG. 6 is a diagram showing AGC amplifier characteristics and APD bias voltage characteristics for optical input in a conventional example. In the figure, 900 is a comparator. shows. *Block diagram of the invention No. 1 Figure ACrC of the embodiment of the invention Figure 3

Claims (1)

[Claims] A light receiving element (10
0) and the output of the light receiving element, and turn the switch (70
An amplifier (300) that amplifies the output signal level to a constant level according to the output control signal of 0), and the output of the amplifier is branched and inputted, and when the input value is larger than a preset reference value, the output is output. In addition to the amplifier, a switch (
700), connected between the switch and the light receiving element,
In an automatic gain control circuit for an optical receiver, the circuit includes a bias supply circuit (800) that inputs the output of the switch and outputs a bias for driving the light receiving element, wherein: between the bias supply circuit and the light receiving element; is inserted, inputs the output of the bias supply circuit, and when the input is larger than a preset second reference value, outputs the input as is and adds it to the light receiving element, and when smaller than the second reference value, outputs. An automatic gain control circuit characterized in that a comparator (900) is provided.