JP2000049717A - Optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cancel an offset, even if the negative offset occurs in the output of a preamplifier by feeding back the output of an offset detection circuit to a phototransistor through an offset suppression circuit. SOLUTION: Optical burst signals transmitted from respective subscribers are made incident on a photodiode 1, and the optical burst signals are converted into electric current. The output current inputted to a preamplifier 2 is converted into voltage and amplified. The amplified voltage is outputted to a post-stage circuit and a differential amplifier 3. An offset detection circuit 4 detects the offset quantity generated in the output of the preamplifier 2 from the differential output of the amplifier 3. An offset suppression circuit 5 feeds back an output equivalent to an offset detected in the offset detection circuit 4 to the input part of the preamplifier 2. As a result, even if the offset generated in the output of the preamplifier 2 is negative, it can be canceled automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiver used for an optical subscriber system and the like.

[0002]

2. Description of the Related Art Conventionally, wired communication has been mainly telecommunication using copper wires. However, due to an increase in transmission capacity and quality problems with respect to noise, etc., optical communication, that is, using an optical fiber cable, for example, PDS (Passive Doub
le Star) The optical subscriber system is spreading.

FIG. 5 shows a configuration example of an optical subscriber system.
FIG. 6 shows a configuration example of a transmission frame in the optical subscriber system. As shown in these figures, a plurality of subscribers # 1
The distance from # 4 to the station is different. Therefore, the signal level received at the station, that is, the amplitude (magnitude) of the optical burst signal is different. In order to receive an optical burst signal and correctly identify and reproduce the signal, the optical burst receiving module corresponding to the burst signal in the station needs to be configured by DC coupling.

FIG. 7 shows a conventional circuit block diagram of such an optical burst receiving module (see Japanese Patent Application Laid-Open No. 5-227104). In this conventional example, the PIN incident light is detected by a photodetector such as a photodiode. This light detection signal is subjected to voltage conversion and amplification by a preamplifier. The output of the preamplifier detects an offset with an offset detector via an average detector and a peak detector.

On the other hand, a constant current circuit is connected in series to the photodetector. The value of the current flowing through the constant current circuit is controlled by the output of the offset detector. This cancels out the positive offset in the input current signal to the preamplifier.

[0006]

However, in the conventional DC-coupled optical receiving module circuit configuration, if a negative offset occurs in the output of the preamplifier, it is not possible to correct (relieve) a defect due to a circuit failure. There was a problem. The reason is that the internal circuit elements that constitute the preamplifier,
This is because, for example, a negative offset may occur in the output due to variations in the IC and the like. However, there is no function to cancel this.

Accordingly, an object of the present invention is to provide an optical receiver capable of solving the problem in the case where a negative offset occurs in the output of the preamplifier due to a variation in the internal circuit and improving the productivity and quality. It is in.

[0008]

In order to solve the above-mentioned problems, an optical receiving apparatus according to the present invention has the following characteristic configuration.

(1) An optical receiving apparatus configured to detect an optical burst of an optical subscriber system by a photodiode, amplify the optical burst by a preamplifier, and then feed it back via an offset detection circuit. An optical receiving device that outputs an output to the phototransistor via an offset suppression circuit.

(2) The optical receiver according to (1), wherein the offset suppression circuit controls a current flowing from the photodiode to the preamplifier.

(3) The optical receiver according to (1), wherein the offset suppression circuit controls a current flowing from the photodiode to the preamplifier or a threshold value of the preamplifier.

(4) The preamplifier includes an amplifier for generating a differential output, and operates the peak value detection circuit and the average value detection circuit of the pre-offset detection circuit based on the differential output of the amplifier. The optical receiver according to (2) or (3).

(5) The optical receiver according to (4), wherein the offset suppression circuit includes an operational amplifier that receives outputs of the average value detection circuit and the peak value detection circuit of the offset detection circuit.

(6) The optical receiver according to (2) or (3), wherein the preamplifier has an input stage of an inverting operational amplifier and a post-amplifier for outputting a differential signal.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of an optical receiver according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a preferred embodiment of the optical receiver according to the present invention. This optical receiver includes a photodiode (PD) 1, a preamplifier (Preamp).
IC) 2, a differential amplifier 3, an offset detection circuit 4, and an offset suppression circuit 5.

An optical burst signal transmitted from each subscriber in the optical subscriber system enters the photodiode 1. The photodiode 1 converts an optical burst signal into light / electricity (current). This output current is input to the preamplifier 2. The preamplifier 2 performs current / voltage conversion for amplification. The amplified output is output to a subsequent circuit (not shown) and the differential amplifier 3. The offset detection circuit 4 detects an offset amount generated from the differential output of the amplifier 3 to the output of the preamplifier 2. In the offset suppression circuit 5, an output corresponding to the offset detected by the offset detection circuit 4 is fed back to the input section of the preamplifier 2. This automatically cancels not only when the offset generated in the output of the preamplifier 2 is positive but also when it is negative.

Next, a specific circuit diagram of the optical receiver according to the present invention will be described with reference to FIG. In this optical receiver, the optical burst signal received by the photodiode 1 is differentially output to a subsequent circuit and an amplifier 3 via a preamplifier 2. The preamplifier 2 includes a preamplifier 6, a resistor 7 connected between its input and output terminals, and an output stage amplifier 8 which is a single-ended / differential conversion amplifier.

The differential output signal from the preamplifier 2 is amplified by the amplifier 3. One (non-inverted) output is supplied to the average value detection circuit 9 of the offset detection circuit 4, and the other (inverted) output is supplied to It is input to a peak value detection circuit (PD) 10. The output of the offset detection circuit 4 is
Is input to The offset suppression circuit 5 includes an operational amplifier 11 having a pair of input terminals to which outputs of the average value detection circuit 9 and the peak value detection circuit 10 of the offset detection circuit 4 are inputted, an input resistor 13 for amplifying the output, and It has an inverting amplifier 15 having a feedback resistor 14, a pair of transistors 16 and 17 connected in series with resistors 18 and 19, and a resistor 12 for inputting the output of the operational amplifier 11 to the base of the transistor 16. The output of the inverting amplifier 17 is supplied to the base of the transistor 17. The photodiode 1 is connected to a common connection point between the transistor 16 and the resistor 19.

Next, the operation of the optical receiver of FIG. 2 will be described with reference to the time chart of FIG. The optical burst signal transmitted from each subscriber is first subjected to optical-electrical (current) conversion by the photodiode 1. This current signal is subjected to current-voltage in the preamplifier 6, amplified in the output stage amplifier 8, and input to the subsequent circuit and the amplifier 3.

The output of the amplifier 3 is input to an offset detection circuit 4 composed of an average value detection circuit 9 and a peak value detection circuit 10. The average value detection circuit 9 outputs the positive-phase (non-inverted) and negative-phase (inverted) outputs 23 (a) and 23 of the amplifier 3.
The average value 24 of (b) is detected. Further, the peak value detection circuit 10 calculates the peak value 2 of the inverted-phase output 23 (b) of the amplifier 3.
5 is detected. The average value 24 and the peak value 25 are compared and amplified by the operational amplifier 11, and the
Is fed back to the preamplifier 2. Here, it is assumed that the peak value holding time of the peak value detection circuit 10 is sufficiently longer than one burst period of the optical burst signal.

When a positive offset occurs in the output of the preamplifier 2, the output of the operational amplifier 11 becomes a positive DC voltage and the transistor 16 conducts through the resistor 12 to flow the output current. Since the value of the current flowing into the preamplifier 2 is reduced, the output of the preamplifier 2 is reduced, and the above-described offset is cancelled. At this time, the positive DC voltage input to the inverting amplifier 15 via the resistor 13 reduces the base voltage of the transistor 17 and
Is kept off.

On the other hand, an operation when a negative offset occurs in the output of the preamplifier 2 will be described. The output of the operational amplifier 11 becomes a negative DC voltage, turning on the transistor 17,
The transistor 16 is turned off. As a result, the current flowing into the preamplifier 2 is increased, and the offset of the preamplifier 2 is canceled.

Next, another embodiment of the optical receiver of the present invention will be described in detail with reference to FIG. This optical receiver is shown in FIG.
Since the optical receiving device is similar to the optical receiving device described above, the main differences will be mainly described. The preamplifier 2 'for converting the output current of the photodiode 1' into a voltage is an amplifier 6 'having a feedback resistor 7'.
2 in that the output stage amplifier 8 '
In addition to inputting the output of the amplifier 6 'to its negative input terminal, the input of the amplifier 20' having a feedback resistor 21 'for amplifying a feedback signal described later is input to its positive input terminal.

The offset suppression circuit 5 'outputs the output of the operational amplifier 11' to the transistor 1 'via the resistor 12'.
6 'and input to the transistor 1 via an inverting amplifier 15' including a resistor 13 'and a feedback resistor 14'.
Input to the base of 7 '. The collector of the transistor 17 is connected to a positive power supply via a resistor 22 and to the input terminal of an amplifier 20 ', and the emitter is grounded via a resistor 19'.

The operation of the optical receiver shown in FIG. 3 will be described. The amplifiers 6 'and 20' have the same amplification factor by making the feedback resistors 7 'and 21' equal. In this manner, the detection output of the photodiode 1 and the feedback signal via the transistor 17 'are amplified at the same amplification factor, and the output stage amplifier 8' obtains a differential output of the difference signal. The average voltage 24 and the peak voltage 25 of this output are obtained by the average value detection circuit 9 'and the peak detection circuit 10' of the offset detection circuit 4 'via the differential amplifier 3'.

When a positive offset occurs in the output of the preamplifier 2 ', the output of the operational amplifier 11 becomes a positive DC voltage and turns on the transistor 16 via the resistor 12'. Thereby, the amount of current flowing from the photodiode 1 'to the preamplifier 6' is adjusted, and the preamplifier 2 '
Cancel the offset that occurs in the output of At this time, the inverting amplifier 1 connected via the resistor 13 '
Since the output of 5 'is a negative voltage, transistor 17' remains off.

On the other hand, when a positive offset occurs in the output of the preamplifier 2 ', the output of the operational amplifier 11' becomes a negative voltage. Therefore, the output of the inverting amplifier 15 'connected via the resistor 13' becomes a positive voltage, and the transistor 17 'conducts. This adjusts the voltage level of amplifier 20 'to cancel the offset that occurs at the output of preamplifier 2'. At this time, since the output of the resistor 12 'is a negative voltage, the transistor 16' remains off.

The preferred embodiment of the optical receiver according to the present invention has been described with reference to the accompanying drawings. However, it should be understood that the present invention should not be limited to only such specific embodiments, but that various modifications can be made in accordance with specific applications.

[0030]

As can be understood from the above description, according to the optical receiving apparatus of the present invention, even when a negative offset occurs in the output of the preamplifier due to the variation of the IC circuit in the preamplifier, It has a function to cancel the offset automatically. Therefore, in the burst optical receiving module, it is possible to remedy an IC failure when a negative offset occurs in the output of the preamplifier, and the yield of the entire optical receiving device (module) as well as the preamplifier can be reduced. This has a practically remarkable effect of being improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a preferred embodiment of an optical receiver according to the present invention.

FIG. 2 is a circuit diagram of a specific example of the optical receiver in FIG. 1;

FIG. 3 is a circuit diagram of a modification of the optical receiver in FIG. 2;

FIG. 4 is a timing chart for explaining the operation of the optical receiver of FIGS. 2 and 3;

FIG. 5 is a block diagram illustrating a configuration example of a general optical subscriber system.

6 is a diagram illustrating a configuration example of a transmission frame of the optical subscriber system of FIG. 5;

FIG. 7 is a circuit diagram showing partial blocks of a conventional optical receiver.

[Explanation of symbols]

 1, 1 'photodiode 2, 2' preamplifier 4, 4 'offset detection circuit 5, 5' offset suppression circuit 6, 6 'preamplifier 8, 8' output stage amplifier 9, 9 'average value detection circuit 10 , 10 'peak value detection circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H03F 3/08

Claims (6)

[Claims] An optical receiving apparatus comprising: an optical subscriber unit, wherein an optical burst is detected by a photodiode, amplified by a preamplifier, and then fed back via an offset detection circuit; Is fed back to the phototransistor via an offset suppression circuit. 2. The optical receiver according to claim 1, wherein said offset suppression circuit controls a current flowing from said photodiode to said preamplifier. 3. The optical receiver according to claim 1, wherein the offset suppression circuit controls a current flowing from the photodiode to the preamplifier or a threshold of the preamplifier. 4. The preamplifier includes an amplifier for generating a differential output, and operates a peak value detection circuit and an average value detection circuit of a pre-offset detection circuit based on the differential output of the amplifier. The optical receiving device according to claim 2 or 3, wherein 5. The optical receiver according to claim 4, wherein the offset suppression circuit includes an operational amplifier that receives outputs of the average value detection circuit and the peak value detection circuit of the offset detection circuit as inputs. apparatus. 6. The optical receiver according to claim 2, wherein the preamplifier includes an input stage of an inverting operational amplifier and a post-stage amplifier that outputs a differential signal.