JP2011119855A - Burst optical receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a burst optical receiver which obviates the need for an ATC circuit, and excels in reception sensitivity characteristics. <P>SOLUTION: The burst optical receiver 1 includes a light-receiving element 2 for converting optical burst signal to a current signal; a differential-type transformer impedance amplifying circuit 3 for converting the current signal into a voltage signal; a differential-type identifying circuit 4 for identifying the voltage signal, from the differential-type transformer impedance amplifying circuit 3; an inductive element 62, having one end connected to a power source and the other end connected to the cathode of the light-receiving element 2; an inductive element 61, having one end connected to the anode of the light-receiving element 2 and the other end connected to the GND; a capacitive element 52, having one end connected to an connection end between the inductive element 62 and the light reception element 2 and the other end connected to the differential-type transformer impedance amplifying circuit 3; and a capacitive element 51, having one end connected to a connection end between the inductive element 61 and the light-receiving element 2 and the other end connected to the differential-type transformer impedance amplifying circuit 3. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical communication system, and more particularly, to a PON (Passive Optical Network) system which is one method of an access optical communication system.

  Conventionally, a point-to-multipoint access optical communication system called a PON (Passive Optical Network) system has been widely used as a system for realizing a public network using optical fibers.

  The PON system is composed of one OLT (Optical Line Terminal) which is a station side device and an ONU (Optical Network Unit) which is a plurality of subscriber terminal devices connected via an optical star coupler. For many ONUs, most of the optical fiber, which is the transmission line, can be shared with the OLT, so that the operating cost can be expected to be economical, and the optical star coupler, which is a passive component, does not require power supply and can be installed outdoors. Since it has the advantage of high reliability, it has been actively introduced as a trump card for realizing a broadband network in recent years.

  For example, in a GE-PON (Gigabit Ethernet (registered trademark) -Passive Optical Network) system with a transmission rate of 1.25 Gbit / s standardized by IEEE802.3ah, the downstream direction from the OLT to the ONU has an optical wavelength of 1480. Using the broadcast communication system using the ˜1500 nm band, each ONU extracts only the data of the assigned time slot. On the other hand, the upstream direction from each ONU to the OLT uses an optical wavelength band of 1260 to 1360 nm and uses a time division multiplex communication system that controls transmission timing so that data of each ONU does not collide.

  Also, in the 10G-EPON system with 10.3 Gbit / s transmission rate standardized by IEEE802.3av, the downlink direction from the OLT to the ONU uses the broadcast communication system using the optical wavelength band of 1574-1580 nm. Each ONU extracts only the data of the assigned time slot. On the other hand, the upstream direction from each ONU to the OLT uses an optical wavelength band of 1260 to 1280 nm and uses a time division multiplex communication system that controls transmission timing so that data of each ONU does not collide.

  Here, in the upstream communication of the PON system as described above, since each ONU is located at a different distance from the optical star coupler, the reception level of each ONU in the OLT is different for each received packet. The optical receiver is required to have a wide dynamic range characteristic for reproducing burst signals having different light reception levels at high speed. Accordingly, in general, an OLT burst optical receiver includes an AGC (Automatic Gain Control) circuit that changes a conversion gain in accordance with a received light level, and an ATC (Automatic Threshold Control) circuit that generates a threshold voltage for identification reproduction. Is provided.

  Various methods have been proposed for burst optical receivers for PON systems. For example, in Non-Patent Document 1, a burst optical receiver is composed of a light receiving element, a transimpedance amplifier circuit, and a differential identification circuit. An AGC circuit that controls the gain of the transimpedance amplifier circuit for each packet according to the received light level, and an ATC that detects the high level and low level of the output voltage waveform of the transimpedance amplifier circuit and uses the center potential as the threshold voltage A system is disclosed that includes a circuit and obtains optimum reception characteristics for each received packet having different light reception levels.

S. Yamashita et al., “Novel Cell-AGC Technique for Burst-Mode CMOS Preamplifier With Wide Dynamic Range and High Sensitivity for ATM-PON System,” IEEE J. Solid-State Circuits, vol. 37, No. 7, pp. .881-886, July 2002.

  Japan's first FTTH service introduced in the world is STM-PON (16Mbps) from 1997, B-PON (622Mbps / 156Mbps) from 2002, GE-PON (1.25Gbps) from 2004 With the introduction of the system, it has been in widespread use, and research and development related to 10G-EPON (10.3 Gbps) is being actively conducted as a next-generation PON system. Furthermore, the demand for subscriber optical networks is expected to increase further in the future due to various services centered on video distribution, and the transmission speed is expected to be 25 Gbps or 100 Gbps.

  Here, as also shown in Non-Patent Document 1, a burst optical receiver is generally composed of a light receiving element, a transimpedance amplifier circuit, and a differential identification circuit. In order to increase the sensitivity, it is effective to maximize the gain of the transimpedance amplifier circuit. However, since the gain and the band of the transimpedance amplifier circuit are normally in a trade-off relationship, As the speed increases, the gain of the transimpedance amplifier circuit must be reduced. When the gain of the transimpedance amplifier circuit is high, the reception sensitivity characteristic of the burst optical receiver hardly depends on the identification sensitivity of the differential identification circuit at the subsequent stage, but when the gain of the transimpedance amplifier circuit is low, Since the output voltage amplitude of the transimpedance amplifier circuit is small, insufficient identification sensitivity of the differential identification circuit at the subsequent stage may be a cause of deterioration in reception sensitivity. Therefore, in particular, in order to realize a future 25 Gbps or 100 Gbps PON system, it is necessary to pay sufficient attention to the identification sensitivity of the differential identification circuit at the subsequent stage.

  However, in the technique disclosed in Non-Patent Document 1, one of the input signals to the subsequent differential identification circuit is detected from the output voltage signal of the transimpedance amplifier circuit and the other is detected from the output voltage signal of the transimpedance amplifier circuit. Compared with the case where the center potential of the high level and the low level, that is, the DC voltage, and the differential signal is input, this is equivalent to halving the amplitude of the input signal, and there is a problem that the reception sensitivity is likely to deteriorate. .

  The present invention has been made in view of the above, and in a PON system in which burst signals of different received light levels are mixed by time division multiplexing, an ATC that generates a threshold voltage for identifying and reproducing each packet at high speed An object of the present invention is to obtain a burst optical receiver that does not require a circuit and has excellent reception sensitivity characteristics.

  In order to solve the above-described problems and achieve the object, the present invention relates to a received optical burst in a burst optical receiver that receives optical burst signals transmitted from a plurality of subscriber side devices via an optical transmission line. A light receiving element that converts a signal into a current signal, a differential transimpedance amplifier circuit that converts the current signal into a voltage signal, and a differential identification circuit that identifies a voltage signal from the differential transimpedance amplifier circuit; A first inductive element having one end connected to the power source and the other end connected to the cathode of the light receiving element, and a second inductive element connected to the anode of the light receiving element and the other end connected to GND. One end of the inductive element is connected to the connection end of the other end of the first inductive element and the cathode of the light receiving element, and the other end is one input of the differential transimpedance amplifier circuit. A capacitive element connected to one end, one end connected to one end of the second inductive element and the anode of the light receiving element, and the other end to the other input of the differential transimpedance amplifier circuit And a capacitive element connected to the end.

  According to the present invention, it is possible to obtain a burst optical receiver that does not require an ATC circuit and has excellent reception sensitivity characteristics.

FIG. 1 is a diagram illustrating a configuration of a burst optical receiver according to a first embodiment of the present invention. FIG. 2 is a schematic diagram of a transient response waveform of each part in the burst optical receiver when a burst signal is received. FIG. 3 is a diagram showing the configuration of the burst optical receiver according to the second embodiment of the present invention. FIG. 4 is a diagram illustrating a configuration of a burst optical receiver according to the third embodiment of the present invention.

  Hereinafter, embodiments of a burst optical receiver according to the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by this embodiment.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration of a burst optical receiver 1 according to the first exemplary embodiment of the present invention. In FIG. 1, a burst optical receiver 1 includes, as main components, a light receiving element 2, a differential transimpedance amplifier circuit (hereinafter simply referred to as a “TIA circuit”) 3, a differential identification circuit 4, a capacitive element 51, 52, and inductive elements 61 and 62. The cathode terminal of the light receiving element 2 is connected to a power source via an inductive element (first inductive element) 62, and the anode terminal of the light receiving element 2 is connected via an inductive element 61 (second inductive element). Connected to GND. At the same time, the cathode terminal of the light receiving element 2 is connected to the input part of the TIA circuit 3 via the capacitive element 52, and the anode terminal of the light receiving element 2 is connected to the input part of the TIA circuit 3 via the capacitive element 51. That is, the burst optical receiver 1 shown in FIG. 1 has an inductive element 62 having one end connected to the power supply and the other end connected to the cathode of the light receiving element 2, and one end connected to the anode of the light receiving element 2. Is connected to GND, one end is connected to the other end of the inductive element 62 and the cathode of the light receiving element 2, and the other end is connected to one input end of the TIA circuit 3. And a capacitive element 51 having one end connected to the connection end of one end of the inductive element 61 and the anode of the light receiving element 2 and the other end connected to the other input end of the TIA circuit 3. Yes. The output part of the TIA circuit 3 is connected to the input part of the differential type identification circuit 4, and the output part of the differential type identification circuit 4 is the output part of the burst optical receiver 1.

  Next, the operation will be described. The light receiving element 2 whose cathode terminal is connected to the power supply via the inductive element 62 and whose anode terminal is connected to the GND via the inductive element 61 is in a reverse-biased state in terms of DC and receives the received optical signal ( A current (current signal) corresponding to the received light level of the optical burst signal is output. Since the light receiving element 2 and the TIA circuit 3 are connected via the capacitive elements 51 and 52, the high frequency component of the output current of the light receiving element 2 is input to the TIA circuit 3 as a differential current signal. It is converted into a differential voltage signal (voltage signal) by the TIA circuit 3. Further, the differential voltage signal from the TIA circuit 3 is discriminated and amplified by the differential discriminating circuit 4, and a reproduced binary signal is output.

  FIG. 2 is a schematic diagram of a transient response waveform of each part in the burst optical receiver 1 at the time of burst signal reception. Here, as shown in FIG. 2, the current waveform of the light receiving element 2 is defined as A, the output voltage waveform of the TIA circuit 3 is defined as B and C, and the output voltage waveform of the differential type identification circuit 4 is defined. Are defined as D and E. Since the light receiving element 2 is an element that linearly converts light into current, the current waveform A has a waveform equivalent to the received burst optical signal. Since the light receiving element 2 and the TIA circuit 3 are capacitively coupled by the capacitive elements 51 and 52, the voltage waveforms B and C are waveforms obtained by differentiating the current waveform A. In addition, the voltage waveforms D and E are waveforms obtained by amplifying the voltage waveforms B and C. In the differential type identification circuit 4, the output amplitude is constant because the limiting operation is performed beyond a desired voltage amplitude. It becomes a waveform.

  Here, the capacitance values of the capacitive elements 51 and 52 and the inductance values of the inductive elements 61 and 62 need to satisfy the following conditions. First, regarding the capacitance values of the capacitive elements 51 and 52, it is necessary to pass a necessary frequency component (predetermined frequency component) included in the burst signal converted into a current signal by the light receiving element 2, particularly in a low frequency range. The value needs to be larger than the desired capacitance value through which the component passes. At the same time, the capacitance value and the response time constant of the differential waveform are in a proportional relationship, and in order to realize high speed when reproducing a signal, it is necessary to set a value smaller than a desired capacitance value. That is, the capacitance values of the capacitive elements 51 and 52 need to be larger than the capacitance value that passes the necessary frequency component of the received signal and smaller than the capacitance value that realizes the necessary high-speed response.

  On the other hand, regarding the inductance values of the inductive elements 61 and 62, it is necessary to block a necessary frequency component (predetermined frequency component) included in the burst signal converted into a current signal by the light receiving element 2, and at the same time, the light receiving element It is necessary to pass a low frequency component including DC so that a reverse bias can be applied to 2 in a DC manner. That is, the inductance value of the inductive elements 61 and 62 needs to be larger than the inductance value that blocks the necessary frequency component of the received signal.

  As described above, the capacitance values of the capacitive elements 51 and 52 are set to be equal to or larger than the capacitance value passing through the predetermined frequency component included in the burst signal, and the inductance values of the inductive elements 61 and 62 are included in the burst signal. The inductance value is set to be equal to or higher than the predetermined frequency component.

  Here, as the light receiving element 2, a PIN photodiode, an avalanche photodiode, or the like is representative. In particular, an avalanche photodiode is a light receiving element that uses a current multiplication effect obtained by applying a large reverse bias voltage of about several tens of volts to a pn junction of a semiconductor, and has an advantage that a large signal-to-noise ratio can be obtained. have. In this case, a voltage of about several tens of volts is applied between the anode terminal and the cathode terminal of the light receiving element 2, but the light receiving element 2 and the TIA circuit 3 are connected via the capacitive elements 51 and 52. Therefore, a voltage of about several tens of volts is not applied between the input terminals of the TIA circuit 3. In general, the breakdown voltage of a high-speed semiconductor integrated circuit is about several volts, but even when an avalanche photodiode is applied as the light receiving element 2 as described above, the light receiving element 2 and the TIA circuit 3 are capacitive. Since the capacitors 51 and 52 are capacitively coupled, that is, they are DC cut, it is possible to achieve both high reverse bias voltage application to the light receiving element and the breakdown voltage of the semiconductor integrated circuit.

  In addition, since both terminals of the light receiving element 2 are connected to the TIA circuit 3 at a high frequency, a differential signal is input to the TIA circuit 3, and a single-phase signal is converted into a differential signal in the conventional example. Therefore, the ATC circuit which is necessary for this is not necessary.

  At the same time, not only the discharge current of the light receiving element 2 but also the sink current can be amplified by the TIA circuit 3, so that the burst optical receiver 1 having excellent reception sensitivity characteristics can be obtained.

  Furthermore, since the differential signal is naturally input to the differential type identification circuit 4, it is equivalent to the input signal amplitude being doubled as compared with the conventional example in which one side of the input is a DC voltage, The burst optical receiver 1 having excellent reception sensitivity characteristics can be obtained.

  Thus, in the burst optical receiver 1 according to the present embodiment, both terminals of the light receiving element 22 are capacitively coupled to the TIA circuit 3, a reverse bias is applied to the light receiving element 2 in a DC manner, and the received signal is converted into a received signal. Inductive elements 61 and 62 are provided so that the included frequency components flow only in the TIA circuit 3 at the subsequent stage, and the TIA circuit 3 and the differential type identification circuit 4 are configured by a differential type amplifier circuit. Therefore, it is possible to realize an economical burst optical receiver 1 that has excellent reception sensitivity characteristics and does not require an ATC circuit as compared with the conventional example.

Embodiment 2.
FIG. 3 is a diagram showing a configuration of the burst optical receiver 1 according to the second exemplary embodiment of the present invention. 3, 1-4, 51, 52, 61, and 62 are the same as those shown in FIG. 1 according to the first embodiment, and the TIA circuit 3 is a pair of the same circuit and the same layout that is excellent in pairing. It is composed of single-phase transimpedance amplifier circuits (hereinafter simply referred to as “single-phase TIA circuits”) 31, 32.

  In general, in a semiconductor integrated circuit, even if the same circuit is used, characteristic variations occur due to fluctuations in manufacturing conditions in an integrated circuit manufacturing process. This variation in characteristics can be reduced by arranging symmetrically in the same layout at close locations in the same wafer. The pair of single-phase TIA circuits 31 and 32 has the same circuit and the same layout. It is characterized by excellent pairing. More specifically, in the differential amplifier circuit, if an offset occurs between the input normal phase signal and the negative phase signal, there is a concern about sensitivity degradation. However, the TIA circuit 3 is the same circuit and the same circuit. By comprising the pair of single-phase TIA circuits 31 and 32 excellent in layout pairing, it is possible to suppress the offset of the input and output biases. That is, the input bias offset of the TIA circuit 3 and the input bias offset of the differential type identification circuit 4 can be reduced as much as possible, and the fear of sensitivity deterioration in the differential type amplifier circuit can be eliminated.

  As described above, in the burst optical receiver 1 according to the present embodiment, the TIA circuit 3 is composed of a pair of single-phase TIA circuits 31 and 32 excellent in pairing with the same circuit and the same layout. In addition to the effects obtained in the first embodiment, it is possible to realize the burst optical receiver 1 having further excellent reception sensitivity characteristics.

Embodiment 3.
FIG. 4 is a diagram illustrating the configuration of the burst optical receiver 1 according to the third embodiment of the present invention. 4, 1-4, 51, 52, 61, and 62 are the same as those shown in FIG. 1 according to the first embodiment, and the TIA circuit 3 includes a differential limiting amplifier circuit 33. .

  The differential limiting amplifier circuit 33 operates to linearly amplify when the amplitude of the input signal is small, and to output a constant amplitude for an input signal having a desired amplitude or higher.

  As shown in Non-Patent Document 1, the burst optical receiver 1 that is normally used in the PON system is provided with an AGC circuit in order to realize a wide dynamic range. In a general single-phase TIA circuit, the gain is determined by the feedback resistance value, but in a region where the output voltage amplitude value determined by the product of the feedback resistance value and the input current amplitude value exceeds a certain value, the circuit Because of saturation, the amplification operation does not work normally. In order to avoid this, it is common to use an AGC circuit that detects the input current amplitude or the output voltage amplitude and variably controls the feedback resistance value based on the detection result.

  On the other hand, a general differential limiting amplifier circuit operates so as to switch the branch ratio of a fixed current value by ON / OFF operation of a pair of transistors arranged in the positive phase and the reverse phase, respectively. When a signal with a desired amplitude or more is input, the branching ratio is completely switched between 0% to 100% or 100% to 0%. Outputs a constant amplitude.

  Therefore, when the TIA circuit 3 is constituted by the differential limiting amplifier circuit 33, a wide dynamic range can be realized without providing a conventional AGC circuit.

  As described above, in the burst optical receiver 1 according to the present embodiment, the TIA circuit 3 is configured by the differential limiting amplifier circuit 33, so that the AGC circuit that has been conventionally required is not necessary and can be implemented. In addition to the effects obtained in the first embodiment, the burst optical receiver 1 that is more economical can be realized.

  As described above, the present invention can be applied to a PON system that is one method of an access optical communication system, and in particular, to obtain a burst optical receiver that does not require an ATC circuit and has excellent reception sensitivity characteristics. It is useful as an invention that can

DESCRIPTION OF SYMBOLS 1 Burst light receiver 2 Light receiving element 3 Differential type transimpedance amplifier circuit 4 Differential type identification circuit 31, 32 Single phase type transimpedance amplifier circuit 33 Differential type limiting amplifier circuit 51, 52 Capacitive element 61 Inductive element (Second inductive element)
62 Inductive element (first inductive element)

Claims (4)

In a burst optical receiver that receives optical burst signals 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 differential transimpedance amplifier circuit that converts the current signal into a voltage signal;
A differential identification circuit for identifying a voltage signal from the differential transimpedance amplifier circuit;
A first inductive element having one end connected to a power source and the other end connected to the cathode of the light receiving element;
A second inductive element having one end connected to the anode of the light receiving element and the other end connected to GND;
A capacitive element having one end connected to the connecting end of the other end of the first inductive element and the cathode of the light receiving element, and the other end connected to one input end of the differential transimpedance amplifier circuit; ,
A capacitive element having one end connected to a connection end between one end of the second inductive element and the anode of the light receiving element, and the other end connected to the other input end of the differential transimpedance amplifier circuit;
A burst optical receiver. Each capacitive element is set to a capacitance value that passes a predetermined frequency component included in the optical burst signal,
2. The burst optical receiver according to claim 1, wherein each inductive element is set to have an inductance value that is greater than an inductance value that blocks the predetermined frequency component.   3. The burst light according to claim 1, wherein the differential transimpedance amplifier circuit includes a pair of single-phase transimpedance amplifier circuits having the same circuit and the same layout. Receiver.   3. The differential transimpedance amplifier circuit includes a differential limiting amplifier circuit that outputs a constant amplitude with respect to an input signal having a desired amplitude or higher. Burst light receiver.

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