JP2000315923A - Burst light receiving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of waveform distortion in an outputted signal even when a power level of an inputted light signal is large by turning at least one of two transistors on according to a value of the outputted signal of a transformer impedance amplifier. SOLUTION: When an inputted cussent Iin becomes higher than a second reference current, the outputted voltage Vout of the transformer impedance amplifier 2 exceeds a second reference voltage V2 and the output of a second comparator 4 becomes a high level. In accordance with this, the Q terminal of a second flip-flop circuit 6 changes to a high level as well and a third MOS transistor TR2 becomes an ON state. Thus, the feedback resistor of the transformer impedance amplifier 2 becomes equivalent to the parallel resistor of a first feedback resistor R1, a second feedback resistor R3 and a third feedback resistor R4. Such operation is performed for the initial one bit after the reset signal is inputted in respective R terminals of the first and second flip-flop circuits 5. 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a burst light receiving circuit, and more particularly, to a burst light receiving circuit capable of switching the value of a feedback resistor for a transimpedance amplifier according to an input optical signal.

[0002]

2. Description of the Related Art FIG. 7 shows a conventional PON (Passive).
Optical Network).

In the conventional PON system, optical signals 22a, 22a from subscribers 21a, 21b, 21c are used.
b and 22c are time-division multiplexed and transmitted in the direction of the station 23 (referred to as the "upward direction") in certain fixed cell units.
Since the transmission distances to the subscribers 21a, 21b, 21c are different from each other, the upstream optical signals 22a, 22b,
2c is a burst train 24 having different power levels.

In order to construct an economical PON system, it is necessary to accommodate a wide range of subscribers from near-end to far-end. As a result, the power level difference between the burst signals increases.

Therefore, a burst optical receiver (not shown) installed in the station building 23 is required to have a wide dynamic range.

FIG. 5 shows an example of a burst light receiving circuit installed in the station building 23. The burst light receiving circuit includes a light receiving element 31 for converting a received optical signal into a current, a transimpedance amplifier 32 for converting a current from the light receiving element 31 into a voltage signal, and a feedback connected in parallel to the transimpedance amplifier 32. A resistor R1 and a resistor R2 connected in parallel with the transimpedance amplifier 32;
And a diode RC connected in series to the resistor R2.

In this conventional burst optical receiving circuit, when a large optical signal is input, excess current is released to the diode RC connected in parallel with the feedback resistor R1, thereby overloading the transimpedance amplifier 32. Had been prevented.

[0008]

However, in the conventional burst light receiving circuit, since the high level side of the input signal Iin to the transimpedance amplifier 32 is limited, the input signal Iin is input as shown in FIG. When the power level of the optical signal is large, the output signal Vou
There is a problem that distortion occurs in the waveform of t.

[0009] When an offset current (Ios) exists due to deterioration of the extinction ratio of the input optical signal, the waveform is particularly affected by waveform distortion.

Many burst light receiving circuits have been proposed in addition to the burst light receiving circuit shown in FIG.

For example, Japanese Patent Publication No. Hei 5-48964 discloses that
A burst optical receiving circuit including an amplifier and two feedback impedance elements for the amplifier is proposed.

Japanese Patent Application Laid-Open Nos. H08-331064 and H10-256840 disclose and reproduce the same waveform as an input waveform for logic signal data of an arbitrary pattern including a burst signal regardless of the amplitude. We propose a burst optical receiver circuit that can do this.

However, all of the burst light receiving circuits proposed in these publications have a problem that the waveform of the output signal Vout is distorted similarly to the burst light receiving circuit shown in FIG. ing.

The present invention has been made in view of such a problem in the conventional burst optical receiving circuit. Even when the power level of the input optical signal is large, the output signal has waveform distortion. An object of the present invention is to provide a burst light receiving circuit that does not generate any light.

[0015]

In order to achieve the above object, the present invention provides a burst light receiving circuit capable of instantaneously switching a feedback gain to a transimpedance amplifier according to a power level of a burst signal.

More specifically, according to the present invention, in claim 1, a light receiving element for converting a received optical signal into a current, a transimpedance amplifier for converting a current into a voltage signal, and a transimpedance amplifier are connected in parallel. A first feedback resistor, a diode connected in parallel to the transimpedance amplifier, a second feedback resistor connected in parallel to the transimpedance amplifier, and a second feedback resistor connected in series to the second feedback resistor. According to the value of the output signal of the transimpedance amplifier, the second transistor, the third feedback resistor connected in parallel with the transimpedance amplifier, and the third transistor connected in series with the third feedback resistor On / off switching means for turning on at least one of the second and third transistors. Providing paste light receiving circuit.

The on / off switching means may be, for example, a first comparator for comparing an output signal of the transimpedance amplifier with a first reference voltage, and an output of the transimpedance amplifier. A second comparator for comparing the signal with a second reference voltage;
A first control circuit that turns on and off the second transistor according to the output of the first comparator, and a second control circuit that turns on and off the third transistor according to the output of the second comparator, It is possible to construct from.

According to another aspect of the present invention, a light receiving element for converting a received optical signal into a current, a transimpedance amplifier for converting a current into a voltage signal, and a transimpedance amplifier are provided in parallel. A first feedback resistor connected to the transimpedance amplifier, a diode connected in parallel to the transimpedance amplifier, a second feedback resistor connected in parallel to the transimpedance amplifier, and a second feedback resistor connected in series to the second feedback resistor. A second transistor, a third feedback resistor connected in parallel to the transimpedance amplifier, a third transistor connected in series to the third feedback resistor, and a A fourth feedback resistor connected thereto, and a fourth transistor connected in series to the fourth feedback resistor. Providing a burst light receiving circuit and a on-off switching means for turning on at least one of the second to fourth transistors in response to the value of the output signal of the transimpedance amplifier.

The on / off switching means in the burst light receiving circuit includes, for example, a first comparator for comparing the output signal of the transimpedance amplifier with the first reference voltage. A second comparator for comparing the output signal of the transimpedance amplifier with the second reference voltage, a third comparator for comparing the output signal of the transimpedance amplifier with the third reference voltage, and a first comparator. A first control circuit that turns on and off the second transistor according to the output, a second control circuit that turns on and off the third transistor according to the output of the second comparator, and a third comparator And a third control circuit for turning on / off the fourth transistor according to the output.

According to a fifth aspect of the present invention, there is provided a light receiving element for converting a received optical signal into a current, a transimpedance amplifier for converting a current into a voltage signal, and a first , A diode connected in parallel to the transimpedance amplifier, second to Nth feedback resistors (N is a positive integer of 2 or more) respectively connected in parallel to the transimpedance amplifier, And turning on at least one of the second to Nth transistors connected in series to each of the Nth to Nth feedback resistors and the second to Nth transistors according to the value of the output signal of the transimpedance amplifier. And an on / off switching means.

The on / off switching means in the burst light receiving circuit compares the output signal of the transimpedance amplifier with each of the reference voltages, for example, as described in claim 6. Turning on / off the comparator and the corresponding transistor among the second to Nth transistors according to the output of the comparator (N-
1) control circuits.

As the control circuit, for example, a flip-flop circuit can be used.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 is a block diagram of a burst light receiving circuit according to a first embodiment of the present invention.

The burst light receiving circuit according to the present embodiment comprises:
A light receiving element 1 for converting a received optical signal into a current Iin, a transimpedance amplifier 2 for converting the current Iin into a voltage signal, a first feedback resistor R1 connected in parallel to the transimpedance amplifier 2, and a transimpedance amplifier 2, a diode RC connected in series with the resistor R2, a second feedback resistor R3 connected in parallel with the transimpedance amplifier 2, and a second resistor R3 connected through a drain-source terminal. A second MOS transistor TR1 connected in series to the second feedback resistor R3 ("second" according to the number of the "second" feedback resistor)
MOS transistor. There is no first MOS transistor. ), A third feedback resistor R4 connected in parallel to the transimpedance amplifier 2, a third MOS transistor TR2 connected in series to the third feedback resistor R4 via a drain / source terminal, On / off switching means for turning on only the second MOS transistor TR1 or both the second MOS transistor TR1 and the third MOS transistor TR2 in accordance with the value of the output signal of the transimpedance amplifier 2;
It has.

The cathode terminal of the diode RC is common to the output terminal of the transimpedance amplifier 2.

Further, the on / off switching means includes a first comparator 3 for inputting an output signal Vout of the transimpedance amplifier 2 at a positive-phase input terminal and for inputting a first reference voltage V1 at a negative-phase input terminal. A second comparator 4 that inputs an output signal Vout of the transimpedance amplifier 2 at a positive-phase input terminal and inputs a second reference voltage V2 at a negative-phase input terminal;
A first flip-flop circuit 5 that turns on and off the second transistor TR1 according to the output of the first comparator 3, and a third transistor TR2 that turns on and off according to the output of the second comparator 4. And a second flip-flop circuit 6.

The outputs of the first and second comparators 3 and 4 are connected to the first and second flip-flop circuits 5 and 6 by the C
Input to each terminal. First and second flip
The D terminals of the flop circuits 5 and 6 are both pulled up to a high level.

The Q terminal of the first flip-flop circuit 5 is connected to the gate terminal of the second transistor TR1, and the Q terminal of the second flip-flop circuit 6 is connected to the gate terminal of the third transistor TR2. It is connected.

A reset signal is externally input to each of the R terminals of the first and second flip-flop circuits 5 and 6. When the reset signal is input, the first and second flip-flop circuits 5, 6 are initialized.

The operation of the burst light receiving circuit according to this embodiment having the above configuration will be described below.

In FIG. 1, the second transistor TR1
The third transistor TR2 is turned off in the initial state. Therefore, the feedback resistance of the transimpedance amplifier 2 in the initial state is equal to the first feedback resistance R1 when the input current Iin is small. When the input current Iin increases and the diode RC becomes conductive, the feedback resistance of the transimpedance amplifier 2 becomes equal to the resistance R2.

FIG. 2 shows the input / output characteristics of the transimpedance amplifier 2 in the initial state, that is, the relationship between the input current (Iin) and the output voltage (Vout). The output voltage Vf corresponding to the input current If indicates the forward voltage of the diode RC, and when Iin ≧ If, the diode RC
Indicates that it is conducting.

When a burst optical signal is input, the input current Iin
Is higher than the first reference current I1, the output voltage Vout of the transimpedance amplifier 2 exceeds the first reference voltage V1, and the output of the first comparator 3 goes high.

Accordingly, the Q terminal of the first flip-flop circuit 5 also changes to the high level, and the second MOS transistor TR connected at the Q terminal and the gate terminal.
1 is turned on. Second MOS transistor TR1
Is turned on, the feedback resistance of the transimpedance amplifier 2 becomes equivalent to the parallel resistance of the first feedback resistance R1 and the second feedback resistance R3.

Further, when the input current Iin becomes higher than the second reference current I2, the output voltage Vout of the transimpedance amplifier 2 exceeds the second reference voltage V2, so that the output of the second comparator 4 becomes high level. Become.

Accordingly, the Q terminal of the second flip-flop circuit 6 also changes to the high level, and the third MOS transistor TR connected at the Q terminal and the gate terminal.
2 is ON. Third MOS transistor TR2
Is turned on, the feedback resistance of the transimpedance amplifier 2 becomes equivalent to the parallel resistance of the first feedback resistance R1, the second feedback resistance R3, and the third feedback resistance R4.

The above operation is performed in the first bit after the reset signal is input to each of the R terminals of the first and second flip-flop circuits 5 and 6.

FIG. 3 is a time chart corresponding to each input level of the burst optical signal.

(A) is a transimpedance amplifier 2
5 shows a signal waveform of the input current (Iin) of FIG. (B) shows the signal waveform of the output voltage (Vout) of the transimpedance amplifier 2. (C) shows the waveform of the reset signal.
(D) and (e) show ON / OFF states of the gate potentials of the second MOS transistor TR1 and the third MOS transistor TR2, respectively. (F) shows the value of the total feedback resistance (Rf) of the transimpedance amplifier 2. In FIG. 3, the symbol “//” indicates a parallel resistance.

As shown in the signal waveform of the output voltage Vout of the transimpedance amplifier 2 shown in (b), the input level is detected in the first bit, and the optimum level is immediately determined according to the detected input level. The feedback resistor is set.

As a result, a waveform without distortion is output for the second and subsequent bits.

When the processing of one burst optical signal is completed, a reset signal is externally input to each of the R terminals of the first and second flip-flop circuits 5 and 6, and the feedback resistor is set to an initial state.

With the burst light receiving circuit according to the present embodiment, the following effects can be obtained.

The first effect is that an output waveform with little distortion can be obtained in a wide dynamic range. The reason is that the burst light receiving circuit according to the present embodiment has a configuration in which the amplifier gain, that is, the feedback resistance, can be set to an arbitrary value according to the level of the input power.
This is because linear amplification can be performed in the entire range of the input level.

In particular, in a DC coupling circuit which is frequently used in a burst optical receiving circuit, when an optical signal having an input offset is input, it is easily affected by waveform distortion due to saturation, so this first effect is extremely significant. It is.

The second effect is that it is possible to respond instantaneously within one bit. The reason is 1
This is because the input level is detected at the rising edge of the bit and the switching to the optimum feedback resistance is immediately performed.

Particularly, in the burst light receiving circuit, an instantaneous response is essential, so the second effect is significant.

A third effect is that even when burst optical signals having different input power levels are alternately input, they can be normally received. The reason is that there is a configuration in which a burst signal receiving circuit is initialized every burst cycle by a reset signal.

(Second Embodiment) FIG. 4 is a block diagram of a burst light receiving circuit according to a second embodiment of the present invention.

The burst light receiving circuit according to the present embodiment
A light receiving element 1 for converting a received optical signal into a current Iin, a transimpedance amplifier 2 for converting the current Iin into a voltage signal, a first feedback resistor R1 connected in parallel to the transimpedance amplifier 2, and a transimpedance amplifier 2, a diode RC connected in series with the resistor R2, a second feedback resistor R3 connected in parallel with the transimpedance amplifier 2, and a second resistor R3 connected through a drain-source terminal. A second MOS transistor TR1 connected in series to the second feedback resistor R3, a third feedback resistor R4 connected in parallel to the transimpedance amplifier 2, and a third feedback transistor via the drain-source terminal. The third MOS transistor TR2 connected in series to the resistor R4 and the transimpedance amplifier 2 A fourth feedback resistor R5 connected in parallel, a fourth MOS transistor TR3 connected in series to the fourth feedback resistor R5 via a drain / source terminal, and an output signal of the transimpedance amplifier 2. Depending on the value, only the second MOS transistor TR1, only the second MOS transistor TR1 and the third MOS transistor TR2, or the second MOS transistor TR1 and the third MOS transistor TR2 and the fourth MOS transistor TR1 On / off switching means for turning on all of the transistors TR3.

The cathode terminal of the diode RC is common to the output terminal of the transimpedance amplifier 2.

Further, the on / off switching means includes a first comparator 3 for inputting an output signal Vout of the transimpedance amplifier 2 at a positive-phase input terminal and for inputting a first reference voltage V1 at a negative-phase input terminal. A second comparator 4 that inputs an output signal Vout of the transimpedance amplifier 2 at a positive-phase input terminal and inputs a second reference voltage V2 at a negative-phase input terminal;
Transimpedance amplifier 2 at the positive-phase input terminal
The second comparator 7 receives the output signal Vout of the second comparator 7 and inputs the third reference voltage V3 at the negative-phase input terminal.
And a first flip-flop circuit 5 for turning on / off the second transistor TR1 according to the output of the first comparator 3, and turning on / off the third transistor TR2 according to the output of the second comparator 4. It comprises a second flip-flop circuit 6 for turning off, and a third flip-flop circuit 8 for turning on / off the fourth transistor TR3 according to the output of the third comparator 7.

The outputs of the first to third comparators 3, 4, and 7 are connected to the first to third flip-flop circuits 5,
The signals are input to C terminals 6 and 8, respectively. The D terminals of the first to third flip-flop circuits 5, 6, and 8 are all pulled up to a high level.

The Q terminal of the first flip-flop circuit 5 is connected to the gate terminal of the second transistor TR1,
The Q terminal of the second flip-flop circuit 6 is connected to the gate terminal of the third transistor TR2, and the Q terminal of the third flip-flop circuit 8 is connected to the fourth transistor TR2.
3 is connected to the gate terminal.

A reset signal is externally input to each of the R terminals of the first to third flip-flop circuits 5, 6, and 8. When the reset signal is input, the first to third flip-flop circuits 5, 6, and 8 are initialized.

The operation of the burst light receiving circuit according to this embodiment having the above configuration will be described below.

In FIG. 4, the second transistor TR
The first, third and fourth transistors TR2 and TR3 are OFF in the initial state.
Therefore, the feedback resistance of the transimpedance amplifier 2 in the initial state is equal to the first feedback resistance R1 when the input current Iin is small. When the input current Iin increases and the diode RC becomes conductive, the feedback resistance of the transimpedance amplifier 2 becomes equal to the resistance R2.

When a burst optical signal is input, the input current Iin
Is higher than the first reference current I1, the output voltage Vout of the transimpedance amplifier 2 exceeds the first reference voltage V1, and the output of the first comparator 3 goes high.

Accordingly, the Q terminal of the first flip-flop circuit 5 also changes to a high level, and the second MOS transistor TR connected at the Q terminal and the gate terminal.
1 is turned on. Second MOS transistor TR1
Is turned on, the feedback resistance of the transimpedance amplifier 2 becomes equivalent to the parallel resistance of the first feedback resistance R1 and the second feedback resistance R3.

Further, when the input current Iin becomes higher than the second reference current I2, the output voltage Vout of the transimpedance amplifier 2 exceeds the second reference voltage V2, so that the output of the second comparator 4 becomes high level. Become.

Accordingly, the Q terminal of the second flip-flop circuit 6 also changes to the high level, and the third MOS transistor TR connected at the Q terminal and the gate terminal.
2 is ON. Third MOS transistor TR2
Is turned on, the feedback resistance of the transimpedance amplifier 2 becomes equivalent to the parallel resistance of the first feedback resistance R1, the second feedback resistance R3, and the third feedback resistance R4.

Further, when the input current Iin becomes higher than the third reference current I3, the output voltage Vout of the transimpedance amplifier 2 exceeds the third reference voltage V3, so that the output of the third comparator 7 becomes high level. Become.

As a result, the Q terminal of the third flip-flop circuit 8 also changes to high level, and the fourth MOS transistor TR connected at the Q terminal and the gate terminal.
3 is turned on. Fourth MOS transistor TR3
Is turned on, the feedback resistance of the transimpedance amplifier 2 becomes four of the first feedback resistance R1, the second feedback resistance R3, the third feedback resistance R4, and the fourth feedback resistance R5.
It is equivalent to the parallel resistance of the feedback resistors.

The above operation is performed in the first bit after the reset signal is input to each of the R terminals of the first to third flip-flop circuits 5, 6, and 8.

Also in the burst light receiving circuit according to the present embodiment, the input level is detected in the first bit, as in the case described with reference to FIG. 3 in the first embodiment. The optimum feedback resistor is immediately set according to the input level.

As a result, in the second and subsequent bits, a waveform without distortion is output.

When the processing of one burst optical signal is completed, the first to third flip-flop circuits 5, 6, 8
A reset signal is externally input to each of the R terminals, and the feedback resistor is set to an initial state.

With the burst light receiving circuit according to the present embodiment, the same effects as those of the burst light receiving circuit according to the first embodiment can be obtained.

In particular, the burst light receiving circuit according to the present embodiment is different from the burst light receiving circuit according to the first embodiment in that the third comparator 7, the third flip-flop circuit 8, and the fourth By additionally providing the feedback resistor R5 and the fourth MOS transistor TR3, the total feedback resistance for the transimpedance amplifier 2 can be switched to four values. Therefore, compared with the burst light receiving circuit according to the first embodiment in which the feedback resistance is switched to three values, the receiving dynamic range can be further expanded.

Anyone having ordinary knowledge in the technical field of the present invention can use the burst light receiving circuit according to the first embodiment shown in FIG. 1 and the burst light receiving circuit according to the second embodiment shown in FIG. The number of feedback resistors can be set to any number so that it can be easily inferred from each configuration of the receiving circuit.

That is, in the burst light receiving circuit according to the present invention, if N is a positive integer of 2 or more, in addition to the first feedback resistor R1, the second feedback resistor R2 and the N-th feedback resistor RN (N-1) feedback resistors can be set.

In this case, corresponding to the (N-1) feedback resistors from the second feedback resistor R2 to the Nth feedback resistor RN, the (N-1) MOS transistors from the second to the Nth are provided. A transistor, second to N-th (N-1) comparators, and second to N-th (N-1) flip-flop circuits are additionally provided.

As described above, by setting the number of feedback resistors to an arbitrary number N, the transimpedance amplifier 2
Can be switched to the N value, and the range of the receiving dynamic range can be adjusted.

The above-described first embodiment is a case where N = 3, and the second embodiment is a case where N = 4.

[0075]

As described above, according to the burst light receiving circuit of the present invention, the feedback resistance can be switched to an arbitrary value in accordance with the level of the input power. It is possible to get in the range.

Further, according to the burst light receiving circuit of the present invention, since the input level is detected at the rising edge of the first bit and immediately switched to the optimum feedback resistance, switching of the feedback resistance value is performed. Can be instantaneously performed within one bit.

[Brief description of the drawings]

FIG. 1 is a block diagram of a burst light receiving circuit according to a first embodiment of the present invention.

FIG. 2 is a graph showing a relationship between an input current (Iin) and an output voltage (Vout) of a transimpedance amplifier in an initial state.

FIG. 3 is a time chart corresponding to each input level of a burst optical signal.

FIG. 4 is a block diagram of a burst light receiving circuit according to a second embodiment of the present invention.

FIG. 5 is a block diagram of a conventional burst light receiving circuit.

FIG. 6 is a graph showing a relationship between an input current (Iin) and an output voltage (Vout) of a transimpedance amplifier in a conventional burst light receiving circuit.

FIG. 7 shows a conventional PON (Passive Optical).
1 is a system block diagram illustrating an example of (Network).

[Explanation of symbols]

 Reference Signs List 1 light receiving element 2 transimpedance amplifier 3 first comparator 4 second comparator 7 third comparator 5 first flip-flop circuit 6 second flip-flop circuit 8 third flip-flop circuit R1 first Feedback resistor R2 Resistance RC diode R3 Second feedback resistor R4 Third feedback resistor R5 Fourth feedback resistor TR1 Second MOS transistor TR2 Third MOS transistor TR3 Fourth MOS transistor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 10/26 10/14 10/04 10/06 F term (Reference) 5J090 AA01 AA56 CA21 CA32 FA18 GN01 GN06 HA10 HA19 HA25 HA39 HA44 HN07 HN15 KA17 KA27 KA36 SA13 TA02 TA06 5J092 AA01 AA56 CA21 CA32 FA18 HA10 HA19 HA25 HA39 HA44 KA17 KA27 KA36 SA13 TA02 TA06 UL01 5J100 JA01 KA05 LA00 LA09 LA10 QA01 QA04 SA02 5K002

Claims (7)

[Claims] A light receiving element that converts a received optical signal into a current; a transimpedance amplifier that converts the current into a voltage signal; a first feedback resistor connected in parallel with the transimpedance amplifier; A diode connected in parallel to the impedance amplifier; a second feedback resistor connected in parallel to the transimpedance amplifier; a second transistor connected in series to the second feedback resistor; A third feedback resistor connected in parallel to the impedance amplifier; a third transistor connected in series to the third feedback resistor; and the second transistor according to a value of an output signal of the transimpedance amplifier. Or on / off switching means for turning on at least one of the third transistors. Burst light receiving circuit. 2. An on / off switching unit comprising: a first comparator that compares an output signal of the transimpedance amplifier with a first reference voltage; and an output signal of the transimpedance amplifier and a second reference voltage. A first control circuit that turns on and off the second transistor according to an output of the first comparator, and a third control circuit that turns on and off the second transistor according to an output of the second comparator. The burst light receiving circuit according to claim 1, comprising: a second control circuit for turning on / off the transistor. A light-receiving element that converts a received optical signal into a current; a transimpedance amplifier that converts the current into a voltage signal; a first feedback resistor connected in parallel with the transimpedance amplifier; A diode connected in parallel to the impedance amplifier; a second feedback resistor connected in parallel to the transimpedance amplifier; a second transistor connected in series to the second feedback resistor; A third feedback resistor connected in parallel to the impedance amplifier, a third transistor connected in series to the third feedback resistor, and a fourth transistor connected in parallel to the transimpedance amplifier. A feedback resistor; a fourth transistor connected in series with the fourth feedback resistor; Burst optical reception circuit and a on-off switching means for turning on at least one of said second to fourth transistors in response to the value of the output signal of the transimpedance amplifier. 4. An on / off switching unit comprising: a first comparator for comparing an output signal of the transimpedance amplifier with a first reference voltage; and an output signal of the transimpedance amplifier and a second reference voltage. A second comparator that compares the output signal of the transimpedance amplifier with a third reference voltage, and turns on the second transistor according to the output of the first comparator. A first control circuit for turning off, a second control circuit for turning on and off the third transistor in accordance with an output of the second comparator, and a fourth control circuit in accordance with an output of the third comparator The burst light receiving circuit according to claim 3, comprising: a third control circuit for turning on / off the transistor. 5. A light receiving element for converting a received optical signal into a current, a transimpedance amplifier for converting the current into a voltage signal, a first feedback resistor connected in parallel to the transimpedance amplifier, and the transformer A diode connected in parallel to the impedance amplifier; second to N-th feedback resistors (N is a positive integer of 2 or more) respectively connected in parallel to the transimpedance amplifier; And turning on at least one of the second to Nth transistors in accordance with the value of the output signal of the transimpedance amplifier and the second to Nth transistors connected in series to each of the feedback resistors. A burst light receiving circuit comprising: on / off switching means. 6. The on / off switching means includes: (N-1) comparators for comparing an output signal of the transimpedance amplifier with each reference voltage; and the second to the second in accordance with an output of the comparator. 6. The burst light receiving circuit according to claim 5, comprising: (N-1) control circuits for turning on / off corresponding transistors among the N transistors. 7. The burst light receiving circuit according to claim 1, wherein the control circuit is a flip-flop circuit.