JP5132543B2 - Optical receiver - Google Patents

Description

  The present invention relates to an optical receiver that receives an optical burst signal transmitted from a subscriber side apparatus in a PON (Passive Optical Networks) system in which burst signals of different transmission rates are mixed by time division multiplexing.

  Conventionally, in an access network that transmits multimedia services to homes, a point-to-multipoint access optical communication system called a PON system is widely used as a method for realizing a public network using optical fibers. .

  The PON system consists of ONU (Optical Network Unit), which is a plurality of subscriber terminal devices connected via optical star couplers, which are multiple branching units, and one OLT (Optical Line Terminal), which is a station side device. It can be configured to share most of the optical fiber and OLT as the transmission path for multiple ONUs, so it can be expected to reduce the operating cost associated with network construction, and power can be supplied to the optical star coupler, which is a passive component. In recent years, it has been actively introduced as a trump card for realizing a broadband network because it has the advantage of being highly reliable because it is unnecessary and easy to install outdoors.

  For example, in a GE-PON (Gigabit Ethernet (registered trademark) -Passive Optical Network) system with a transmission rate of 1.25 Gbit / s, which is standardized by IEEE (Institute of Electrical and Electronics Engineers, Inc.) 802.3ah, A broadcast communication system using an optical wavelength band of 1480 to 1500 nm is adopted for downstream communication from the OLT to the ONU, and each ONU extracts only the data addressed to its own station in the assigned time slot. On the other hand, for upstream communication from each ONU to the OLT, the optical wavelength 1260-1360nm band is used, and the time division multiplex communication system that controls the transmission timing so that the data of each ONU does not collide is adopted. .

  In IEEE802.3av, standardization activities are being carried out for standardization of 10G-EPON (10 Gigabit-Ethernet (registered trademark) Passive Optical Network) system with a transmission speed of 10.3 Gbit / s. Although currently in the draft stage, 10G-EPON uses a broadcast communication system that uses the optical wavelength band 1574 to 1580 nm for downstream communication from the OLT to the ONU. Only the data for the slot's own station is taken out. On the other hand, in the upstream communication from each ONU to the OLT, the optical wavelength band of 1260 to 1280 nm is used, and the time division multiplex communication system is adopted as described above.

  In introducing the 10G-EPON system, the GE-PON system and the 10G-EPON system can be integrated into the same optical fiber network by effectively utilizing the existing infrastructure such as the optical fiber network already installed for the GE-PON system. IEEE802.3av discusses measures to reduce system operation costs by mixing systems. This system has a system configuration in which a burst signal of 1.25 Gbit / s and a burst signal of 10.3 Gbit / s are time-division multiplexed because the upstream optical wavelengths from each ONU to the OLT overlap. Therefore, it is desired to realize an OLT including an optical receiver that can receive burst signals having different transmission rates.

  Further, since each ONU and the optical star coupler are connected at different distances for each subscriber, the optical signal reception level in the upstream direction from each ONU to the OLT is different for each received packet. Therefore, the optical receiver is required to have a wide dynamic range characteristic that stably reproduces burst signals having different received light levels. Therefore, the optical receiver is provided with an AGC (Automatic Gain Control) circuit that changes the conversion gain according to the received light level, and an ATC (Automatic Threshold Control) circuit that generates a threshold voltage for identification reproduction. Is common.

  The AGC circuit has a time constant from when the burst signal is received until the conversion gain is stably converged. Further, the ATC circuit has a time constant from when the burst signal is received until the threshold voltage stably converges. That is, the optical receiver takes a desired time until the data is stably reproduced after receiving the burst signal. This time is standardized as “Receiver Settling Time” in IEEE802.3ah and IEEE802.3av. The standard value is 400 ns for IEEE802.3ah, which is the standard for the GE-PON system, and 800 ns (draft) for IEEE802.3av, which is the standard for the 10G-EPON system.

  Each burst signal is composed of an overhead area and a data area having a length equal to or longer than the Receiver Settling Time. In order to improve the throughput of the entire system, it is desirable that this overhead area is short. Here, in the AGC circuit and ATC circuit that operate based on the average value detection result of the received signal, the same code continuous time included in the code string of the received signal and the time constant until the conversion gain or threshold voltage converges stably Are in a trade-off relationship. For example, when the same code continuous time in each burst signal is long, it is necessary to lengthen the time constant in order to suppress fluctuation of the average value detection result when the same code continues. On the other hand, when the same sign continuous time is short, the time constant may be shortened because it does not significantly affect the fluctuation of the average value detection result.

  In addition, in the GE-PON system, code conversion called “8B / 10B” is performed in order to prevent a continuous code from continuing, and the converted code string has the same code sequence of up to 5 bits, That is, there is a continuous time of the same sign of 4 ns. On the other hand, code conversion called “64B / 66B” is performed in the 10G-EPON system, and the converted code string has a maximum of 66 bits of the same code, that is, 6.4 ns of the same code continuous time. . In this way, since the maximum same-code continuous time to be considered is different in each system, the optimal time constants of AGC and ATC are also different.

  Various systems have been proposed for optical receivers. For example, the optical receiver disclosed in Patent Document 1 below includes a bit rate determination circuit that determines the transmission speed of a received signal. Based on the result, a system is disclosed in which an optimum receiving sensitivity is obtained in accordance with the transmission speed by feedback controlling the gain and band of the preamplifier circuit.

  In addition, the optical receiver disclosed in Patent Document 2 below includes a transmission rate detection / control circuit that determines the transmission rate of the received signal, as described above, and configures a preamplifier based on the detected transmission rate. Discloses a method for obtaining an optimum reception sensitivity according to a transmission speed by controlling a resistance value of a variable resistor and a band value of a variable equalization filter connected in series to an output of a preamplifier. Yes.

WO2005 / 078969 JP 2007-005875 A

  However, in the optical receiver shown in Patent Document 1 or Patent Document 2 described above, an optimum reception sensitivity can be obtained according to the transmission speed for a continuous signal, but a burst signal for a burst signal. There is no disclosure or suggestion regarding the AGC technology and time constant and the ATC technology and time constant corresponding to. In other words, when these optical receivers are applied as upstream optical receivers in a PON system, the dynamic range in which burst signals with different received light levels can be stably reproduced is narrow, and the overhead area is longer than necessary. There was a problem that the throughput of the entire system may be reduced.

  The present invention has been made in view of the above, and in a PON system in which burst signals of different transmission rates are mixed by time division multiplexing, optimum reception sensitivity is obtained according to the transmission rate, and packets of different light reception levels are obtained. It is an object of the present invention to provide an optical receiver that has a wide dynamic range characteristic that stably reproduces light, and that can achieve high throughput characteristics by combining high-speed response and same-code continuity tolerance.

In order to solve the above-described problems and achieve the object, an optical receiver according to the present invention is an optical receiver that receives optical burst signals transmitted from a plurality of subscriber-side devices via an optical transmission path. A light receiving element that converts the received optical burst signal into a current signal; a preamplifier that converts the current signal into a first voltage signal and performs gain control based on a transmission speed of the optical burst signal;
A first detection circuit that changes its own time constant based on the transmission speed, detects an average voltage of the first voltage signal, and outputs the first voltage as a first average voltage; and A control unit that continuously controls the gain of the preamplifier, a low-pass filter that changes the passband based on the transmission speed, and outputs the second voltage signal with the first voltage signal as an input;
A second detection circuit that changes its own time constant based on the transmission speed, detects an average voltage of the second voltage signal, and outputs it as a second average voltage; the second voltage signal; and And a differential amplifier that amplifies and outputs a difference voltage from the second average voltage.

  According to the optical receiver of the present invention, the preamplifier that changes the conversion gain according to the transmission speed of the burst signal, the band variable low-pass filter that changes the noise equalization band, the time constant variable average value for gain control that changes the time constant of the AGC A detection / control circuit and a time constant variable average value detection circuit for threshold control that changes the time constant of ATC are provided. Optimum reception sensitivity is obtained, and a wide dynamic range characteristic that stably reproduces packets with different light reception levels. Thus, in a PON system in which burst signals having different transmission rates are mixed by time division multiplexing, an effect is achieved that high throughput characteristics can be realized.

  Embodiments of an optical receiver according to the present invention will be described below in detail with reference to the accompanying drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
(Configuration of optical receiver)
FIG. 1 is a diagram of a configuration of the optical receiver according to the first embodiment. The optical receiver includes, as main components, a preamplifier 11, a light receiving element 10 having a cathode connected to a power source and an anode connected to an input terminal of the preamplifier 11, and a gain control time constant for performing gain control (AGC) of the preamplifier 11. Variable average value detection / control circuit (hereinafter simply referred to as “control circuit”) 12, band variable low-pass filter (hereinafter simply referred to as “LPF”) 13 for performing noise equalization, threshold control for performing threshold control (ATC) The circuit includes a constant variable average value detection circuit (hereinafter simply referred to as “detection circuit”) 14 and a limiting amplifier 15 that is a differential amplifier circuit.

  The variable resistance element 21 and the variable resistance element 22 are variable resistances that constitute a feedback resistance that determines the conversion gain of the preamplifier 11. The variable resistance element 21 is a variable resistance element whose resistance value changes continuously according to the control voltage of the time constant variable average value detection / control circuit 12 for gain control, and the variable resistance element 22 is used for the received burst signal. The variable resistance element is controlled according to the transmission speed.

(Operation of optical receiver)
Next, the operation of the optical receiver will be described. The light receiving element 10 outputs a current signal corresponding to the received light level of the received optical burst signal. The preamplifier 11 converts the current signal output from the light receiving element 10 into a voltage signal that is a first voltage signal and outputs the voltage signal. One of the voltage signals output from the preamplifier 11 is subjected to noise equalization by the LPF 13, and the other is detected by the control circuit 12 as an average voltage with respect to the input signal and converted into a desired voltage value. Applied. The resistance value of the variable resistance element 21 continuously changes according to the control voltage of the control circuit 12, and decreases as the light receiving level increases. That is, the preamplifier 11 operates so that the conversion gain becomes small. One of the second voltage signals output from the LPF 13 is input to one end of the limiting amplifier 15, and the other detects a threshold voltage (average voltage) with respect to the input signal by the detection circuit 14 which is a second detection circuit. And input to the other end of the limiting amplifier 15. The limiting amplifier 15 amplifies and outputs the difference voltage between the threshold voltage output from the LPF 13 and the detection circuit 14 and the second voltage signal. The control circuit 12 may be divided into a first detection circuit that detects the average voltage and a control unit that controls the variable resistance element 21.

  The variable resistance element 22, the control circuit 12, the LPF 13, and the detection circuit 14 operate so that the resistance value, the time constant, and the pass band change according to the rate switching signal input from the outside. This rate switching signal is a multi-level signal corresponding to the transmission rate, and is input to each of the above-described units immediately before or after receiving burst signals having different transmission rates.

  FIG. 2 is a timing chart for explaining the operation of each part whose state changes in response to a rate switching signal input to the optical receiver. The variable resistance element 22 and the LPF 13 operate so as to obtain optimum reception sensitivity according to the transmission speed of the received burst signal, that is, the rate switching signal, as in the above-mentioned Patent Document 2. Specifically, when the rate switching signal is High, the resistance value of the variable resistance element 22 changes so as to increase, and the pass band of the LPF 13 changes so as to narrow, so that a burst signal with a transmission rate of 1.25 Gbit / s. Optimum receiving sensitivity corresponding to can be obtained. On the other hand, when the rate switching signal is low, the resistance value of the variable resistance element 22 changes so as to be small, and the pass band of the LPF 13 changes so as to widen, so that it corresponds to a burst signal with a transmission speed of 10.3 Gbit / s. Optimum reception sensitivity can be obtained. Note that the variable resistance element 21 operates so as to obtain optimum reception sensitivity even when the reception levels of burst signals having the same transmission speed are different.

  The control circuit 12 and the detection circuit 14 operate in accordance with the rate switching signal and the code string so as to have an optimal time constant that achieves both high-speed response and the same code continuity tolerance. Specifically, when the rate switching signal is High, the time constants of the control circuit 12 and the detection circuit 14 change so as to be short, and the optimal time constant corresponding to the burst signal and code string having a transmission rate of 1.25 Gbit / s. (For example, 300 ns to 400 ns) is obtained. On the other hand, when the rate switching signal is Low, the time constants of the control circuit 12 and the detection circuit 14 change so as to be short, and the optimal time constant (for example, corresponding to the burst signal and code string of the transmission rate 10.3 Gbit / s) 600 ns to 800 ns) is obtained. The time constant indicates the time from when the burst signal is received until the above-described first voltage signal waveform and second voltage signal waveform converge stably.

  FIG. 3 is a timing chart for explaining the relationship between the output signal of the optical receiver and the received burst signal. In a system that accommodates both a GE-PON system and a 10G-EPON system, when the optical receiver according to the present embodiment receives a burst signal of 1.25 Gbit / s (see the upper side of FIG. 3), the receiver settling of the output signal For example, when the time is about 300 ns to 400 ns (see the lower side of FIG. 3) and a 10.3 Gbit / s burst signal is received, the Receiver Settling Time is about 600 ns to 800 ns, for example. Operate.

  As described above, the optical receiver according to the present embodiment changes the preamplifier 11 that changes the conversion gain according to the transmission speed and reception level of the burst signal, and the noise equalization band according to the transmission speed of the burst signal. Since the LPF 13 is provided, an optimum reception sensitivity is obtained in accordance with the transmission speed, and an operation is performed so as to have a wide dynamic range characteristic for stably reproducing packets having different light reception levels. In addition, since the control circuit 12 that changes the AGC time constant according to the burst signal transmission rate and the detection circuit 14 that changes the ATC time constant according to the burst signal transmission rate are provided, it is optimal for the transmission rate. Operates to obtain a time constant. As a result, the optical receiver according to the present embodiment can realize high throughput characteristics in a PON system in which burst signals of different transmission rates are mixed by time division multiplexing.

Embodiment 2. FIG.
The optical receiver according to the first embodiment supplies the rate switching signal from the outside. However, the optical receiver according to the present embodiment includes the transmission speed detection / control circuit 16 that generates and outputs the rate switching signal. It is configured. Hereinafter, the same parts as those of the optical receiver according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 4 is a diagram of a configuration of the optical receiver according to the second embodiment. The transmission rate detection / control circuit 16 outputs the generated rate switching signal to the variable resistance element 22, the control circuit 12, the LPF 13, and the detection circuit 14. Connected to the input section. Similar to the first embodiment, the transmission speed detection / control circuit 16 determines the resistance value of the variable resistance element 22, the pass band of the LPF 13, the control circuit 12 and the detection circuit 14 according to the detected transmission speed of the burst signal. It operates to optimally control the time constant of the. In FIG. 4, the transmission speed detection / control circuit 16 is connected to the output unit of the preamplifier 11, but the connection location is not limited as long as it is inside the optical receiver.

  As described above, since the optical receiver according to the present embodiment detects the transmission speed of the received burst signal by the optical receiver main body and can self-generate the rate switching signal, the control signal supplied from the outside The high throughput characteristics similar to those of the optical receiver according to the first embodiment can be realized without depending on.

Embodiment 3 FIG.
FIG. 5 is a diagram illustrating a configuration of the first detection circuit, the LPF, and the detection circuit of the control circuit in the optical receiver according to the third embodiment. The circuit shown in FIG. 5 includes a resistance element 81 constituting an LPF for 1.25 Gbit / s, a resistance element 82 constituting an LPF for 10.3 Gbit / s, a switch 84 whose conduction path is switched according to a rate switching signal, and 1.25 A common capacitive element 83 constituting the LPF for Gbit / s and 10.3 Gbit / s is provided.

  In the circuit shown in FIG. 5, in response to the rate switching signal, when the lower path of the switch 84 is conductive, the resistor element 81 and the capacitor element 83 constitute a 1.25 Gbit / s LPF 85. Further, when the upper path of the switch 84 is in a conductive state, the resistor element 82 and the capacitor element 83 constitute a 10.3 Gbit / s LPF 86. The circuit shown in FIG. 5 corresponds to two burst signals with transmission speeds of 1.25 Gbit / s and 10.3 Gbit / s, but is configured to support other transmission speeds and three or more burst signals. It may be. Further, although FIG. 5 illustrates a first-order LPF, a higher-order LPF may be used.

  FIG. 6 is a diagram showing a circuit configuration in which the components of the circuit shown in FIG. 5 are changed. The circuit shown in FIG. 6 is a comparison target for facilitating and supplementing the description of the circuit of FIG. 5. Compared with the circuit of FIG. 5, a capacitive element 87 constituting a 1.25 Gbit / s LPF and 10.3 Gbit and a capacitive element 88 that constitutes the / s LPF. Hereinafter, the same parts as those of the circuit shown in FIG.

  Comparing FIG. 5 and FIG. 6 showing the present embodiment, in the circuit of FIG. 5, the switch 84 whose conduction path is switched according to the rate switching signal is provided only at one position on the output side. Further, the capacitive elements 83 constituting the LPFs 85 and 86 are shared for different transmission rates. Here, when a capacitive element is configured using an MIM capacitor or the like in an IC, generally, the layout area of the capacitive element is much larger than that of a resistive element. Therefore, when the resistive elements 81 and 82 and the capacitive elements 87 and 88 that constitute the LPFs 85 and 86 are arranged for each transmission speed as in the circuit shown in FIG. This is disadvantageous in terms of economy.

  As described above, the first detection circuit, the LPF 13 and the detection circuit 14 of the control circuit 12 according to the present embodiment are configured by the LPFs 85 and 86 including the resistance element 81 or the resistance element 82 and the capacitance element 83, and receive bursts. Regardless of the signal transmission speed, one capacitive element 83 is shared. Therefore, in addition to the effects obtained in the first or second embodiment, it is possible to realize a small and economical optical receiver.

Embodiment 4 FIG.
FIG. 7 is a diagram illustrating a configuration of the first detection circuit, the LPF, and the detection circuit of the control circuit in the optical receiver according to the fourth embodiment. The circuit shown in FIG. 7 includes a resistive element 81, a resistive element 82, a switch 84, a capacitive element 87, a capacitive element 88, and a common inductive element 89 that constitutes LPF 85 and LPF 86.

  In the circuit shown in FIG. 7, in response to the rate switching signal, when the left path of the switch 84 is conductive, the inductive element 89 and the capacitive element 87 constitute a 1.25 Gbit / s LPF 85. When the path on the right side of the switch 84 is conductive, the inductive element 89 and the capacitive element 88 constitute a 10.3 Gbit / s LPF 86. The circuit shown in FIG. 7 corresponds to two burst signals with transmission speeds of 1.25 Gbit / s and 10.3 Gbit / s, but has a configuration corresponding to other transmission speeds and three or more burst signals. It may be. Further, although the circuit shown in FIG. 7 is an example of a primary LPF, it may be configured as a high-order LPF.

  FIG. 8 is a diagram showing a circuit configuration in which the components of the circuit shown in FIG. 7 are changed. The circuit shown in FIG. 8 is a comparison object for facilitating and supplementing the description of the circuit of FIG. 7. Compared with the circuit of FIG. 7, the induction element 90 that constitutes the LPF for 1.25 Gbit / s and 10.3 Gbit and an inductive element 91 constituting the LPF for / s. Hereinafter, the same parts as those of the circuit shown in FIG. 7 are denoted by the same reference numerals, and detailed description thereof is omitted.

  Comparing FIG. 7 and FIG. 8 in the present embodiment, in the circuit of FIG. 7, the switch 84 whose conduction path is switched according to the rate switching signal is provided only at one position on the output side. Further, the inductive elements 89 constituting the LPFs 85 and 86 are shared for different transmission speeds. Here, when an inductive element is configured using a spiral inductor or the like in an IC, in general, the layout area of the inductive element is much larger than that of a resistive element or a capacitive element. Therefore, when the inductive elements 90 and 91 and the capacitive elements 87 and 88 that constitute the LPFs 85 and 86 are arranged for each transmission speed as in the circuit shown in FIG. This is disadvantageous in terms of economy.

  As described above, the first detection circuit, the LPF 13 and the detection circuit 14 of the control circuit 12 according to the present embodiment are configured by the LPFs 85 and 86 including the capacitive element 87 or the capacitive element 88 and the inductive element 89, and receive bursts. Regardless of the signal transmission speed, one inductive element 89 is shared. Therefore, in addition to the effects obtained in the first or second embodiment, it is possible to realize a small and economical optical receiver.

Embodiment 5 FIG.
FIG. 9 is a diagram of the configuration of the first detection circuit, the LPF, and the detection circuit of the control circuit in the optical receiver according to the fifth embodiment. The circuit shown in FIG. 9 includes a variable resistance element 92 whose resistance value changes continuously according to the control voltage, a variable capacitance element 93 whose capacitance value changes continuously according to the control voltage, and converts the input signal to a desired level. And a level conversion circuit 94 for outputting. The rate switching signal is a voltage signal that changes continuously according to the transmission speed of the received burst signal, and the transmission speed and the voltage value have a one-to-one relationship. An example of the variable resistance element 92 is a MOSFET, and an example of the variable capacitance element 93 is a varactor diode, but is not limited thereto. Further, FIG. 9 illustrates the first-order LPF, but a higher-order LPF may be used.

  Here, the rate switching signal that continuously changes according to the transmission speed of the received burst signal has a variable resistance element 92 having a desired resistance value and a variable capacitance element 93 having a desired capacitance value. Each level is converted by the level conversion circuit 94. The level conversion circuit 94 operates so as to control at least one of the resistance value of the variable resistance element 92 and the capacitance value of the variable capacitance element 93 by the level-converted rate switching signal.

  In the circuit shown in FIG. 9, since the LPF is configured by a pair of variable resistance element 92 and variable capacitance element 93 for a plurality of transmission speeds, the circuit shown in the third and fourth embodiments. However, further miniaturization and economy can be achieved. Further, in addition to 1.25 Gbit / s and 10.3 Gbit / s, the effect is great when time-division multiplexing of a large number of burst signals having different transmission rates.

  As described above, the first detection circuit, the LPF 13, and the detection circuit 14 of the control circuit 12 according to the present embodiment include the variable resistance element 92 whose resistance value is continuously changed by the control voltage, and the capacitance value by the control voltage. In addition to the effects obtained in the first or second embodiment, it is possible to realize a smaller and more economical optical receiver in addition to the effect obtained in the first or second embodiment. is there.

  The configurations of the optical receivers shown in Embodiments 1 to 5 show an example of the contents of the present invention, and can be combined with other known techniques and depart from the gist of the present invention. Of course, it is possible to change and configure such as omitting a part within the range.

  As described above, the optical receiver according to the present invention is applicable to a system in which a GE-PON system and a 10G-EPON system are mixedly accommodated, and in particular, has a high throughput with respect to the transmission speed of a plurality of received burst signals. It is useful as an invention that can be enhanced.

1 is a diagram illustrating a configuration of an optical receiver according to a first embodiment. It is a timing chart explaining operation | movement of each part which changes a state by the rate switching signal input into an optical receiver. It is a timing chart explaining the relationship between the output signal of an optical receiver, and a received burst signal. FIG. 4 is a diagram illustrating a configuration of an optical receiver according to a second embodiment. FIG. 7 is a diagram illustrating a configuration of a first detection circuit, an LPF, and a detection circuit of a control circuit in an optical receiver according to a third embodiment. FIG. 6 is a diagram showing a circuit configuration in which the components of the circuit shown in FIG. 5 are changed. FIG. 10 is a diagram illustrating a configuration of a first detection circuit, an LPF, and a detection circuit of a control circuit in an optical receiver according to a fourth embodiment. It is a figure which shows the circuit structure which changed the component of the circuit shown by FIG. FIG. 10 is a diagram illustrating a configuration of a first detection circuit, an LPF, and a detection circuit of a control circuit in an optical receiver according to a fifth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light receiving element 11 Preamplifier 12 Time constant variable average value detection / control circuit for gain control (1st detection circuit, control part)
13 Band-variable low-pass filter (low-pass filter)
14 Time constant variable average value detection circuit for threshold control (second detection circuit)
DESCRIPTION OF SYMBOLS 15 Limiting amplifier 16 Transmission speed detection / control circuit 21, 22, 92 Variable resistance element 81, 82 Resistance element 83, 87, 88 Capacitance element 84 Switch 85 1.25 Gbit / s low pass filter 86 10.3 Gbit / s low pass filter 89 , 90, 91 Inductive element 93 Variable capacitance element 94 Level conversion circuit

Claims (5)

In an optical receiver for receiving an optical burst signal transmitted from a plurality of subscriber side devices via an optical transmission line,
A light receiving element that converts the received optical burst signal into a current signal;
A preamplifier that converts the current signal into a first voltage signal and performs gain control based on a transmission rate of the optical burst signal;
A first detection circuit that changes its own time constant based on the transmission speed, detects an average voltage of the first voltage signal, and outputs the first voltage as a first average voltage;
A control unit for continuously controlling the gain of the preamplifier according to the first average voltage;
A low-pass filter that changes a pass band based on the transmission speed, and outputs a second voltage signal with the first voltage signal as an input;
A second detection circuit that changes its own time constant based on the transmission speed, detects an average voltage of the second voltage signal, and outputs the second voltage as a second average voltage;
A differential amplifier that amplifies and outputs a difference voltage between the second voltage signal and the second average voltage;
An optical receiver comprising:   The optical receiver according to claim 1, further comprising a transmission rate detector that detects the transmission rate. The first detection circuit, the second detection circuit, and the low-pass filter are:
The optical receiver according to claim 1, wherein the optical receiver includes a capacitive element and a plurality of resistance elements, and switches resistance values of the plurality of resistance elements based on the transmission speed. The first detection circuit, the second detection circuit, and the low-pass filter are:
The optical receiver according to claim 1, wherein the optical receiver includes an inductive element and a plurality of capacitive elements, and switches resistance values of the plurality of capacitive elements based on the transmission speed. The first detection circuit, the second detection unit, and the low-pass filter are:
A variable resistance element and a variable capacitance element, and controlling at least one of a resistance value of the variable resistance element and the variable capacitance element based on the transmission speed;
The optical receiver according to claim 1 or 2.

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