JP2009177577A - Burst signal reception method, burst signal receiver, station side terminal, and pon system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a burst signal reception method, a burst signal receiver, a station side device and a PON system for improving responsiveness to a burst signal. <P>SOLUTION: This burst signal receiver includes: a photodiode 101 for receiving a burst signal based on a binary signal; an amplifier 102 for amplifying the output; a time constant circuit 105 for outputting a first voltage which follows up the burst signal output by the amplifier 102 with a time constant, wherein the time constant is variable; a comparator 104 for setting a signal voltage to be output by the amplifier 102 as a second voltage, and for generating the result of the comparison of the first voltage with the second voltage as an output; and a control circuit 108 for setting the time constant to the time constant circuit 105. Then, the control circuit 108 is configured to switch the time constant so that the time constant to be set in the first half of the signal when receiving the burst signal is set so as to be shorter than the time constant to be set in the second half of the signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention provides, for example, a method and apparatus for receiving a burst signal intermittently transmitted from a home-side apparatus in a station-side apparatus that forms a PON (Passive Optical Network) system together with a plurality of home-side apparatuses, and the apparatus The present invention relates to a station-side device and a PON system that use the.

  The PON system uses an optical fiber network that branches a station side device as an aggregation station and a home side device installed in a plurality of subscriber homes into a plurality of optical fibers via an optical coupler from a single optical fiber. Are connected (for example, see Patent Document 1). When transmission is performed from a plurality of home-side devices to the station-side device at the same time, transmission data collides, and therefore the station-side device gives the home-side device permission regarding the transmission timing and the amount of transmission data. Upon receiving this permission, the home side apparatus transmits the permitted amount to the station side apparatus at a timing permitted from the station side apparatus.

  The signal transmitted from the home side device is an optical burst signal based on a binary signal of 0 or 1. The distance between the station-side device and the home-side device varies depending on the installation location of the home-side device, and the signal strength is not constant. Accordingly, the burst signal is intermittently received from the plurality of home side devices with various strengths to the station side device. In the station side device, a photodiode that receives an optical burst signal and converts it into an electrical burst signal, an amplifier that amplifies the burst signal output from the photodiode, and compares the amplified burst signal with a threshold value Then, a burst signal receiving device including a comparator that outputs a binary signal (digital signal) is provided (for example, see Patent Document 2). The burst signal is composed of a leading preamble section and a subsequent data section.

Japanese Patent Laying-Open No. 2004-64749 (FIG. 4) Japanese Patent Laying-Open No. 2005-175596 (FIG. 2)

In the conventional burst signal receiving apparatus as described above, the center (average value) of the signal amplitude in the burst signal transmitted for each home-side apparatus is obtained, and this is used as a threshold value to set the signal to 0 or 1. Can be determined. In order to obtain the center of the signal amplitude, a time constant circuit can be used. In this case, it is necessary to set the time constant long enough not to interfere with bit determination in the data section. However, if the time constant is long, it takes time to obtain the center of the signal amplitude in the preamble section, and the response to the burst signal becomes poor.
In view of the conventional problems, an object of the present invention is to provide a burst signal receiving method, a burst signal receiving device, a station side device, or a PON system that improves the response to a burst signal.

  The burst signal receiving method of the present invention receives a burst signal based on a binary signal, amplifies the burst signal, outputs a first voltage that follows the amplified burst signal with a variable time constant, and is amplified. A burst signal receiving method for generating one of a signal voltage of a burst signal and a constant reference voltage as a second voltage and outputting a result of comparing the second voltage with the first voltage, wherein the burst signal is The time constant is switched so that the time constant set in the initial stage of the signal when received is shorter than the time constant set in the late stage of the signal.

  In the burst signal receiving method as described above, the time constant of the initial signal including the preamble is set to be shorter than the time constant of the latter period of the signal, and the first voltage that is the target of determination or reference of 0 or 1 is quickly set. Can be detected.

In the burst signal receiving method, the time constant set in the interval between burst signals in which the burst signal is not received may be shorter than the time constant set in the latter period of the signal.
In this case, the first voltage can be quickly returned to the no-signal level even immediately after receiving a burst signal having a large signal strength (amplitude). Therefore, the no-signal period can be shortened, and the band can be utilized more effectively.
In particular, by setting the time constant to be set to the initial stage of the signal as τ1, the time constant to be set to the late stage of the signal as τ2, and the time constant to be set as the interval between the burst signals as τ3, by setting so that τ3 ≦ τ1 <τ2. The first voltage can be quickly returned to the no signal level.

In the burst signal receiving method, when performing discovery of a device that is a burst signal transmission source, a special burst signal including a preamble long set for discovery is transmitted from the device, and time constant switching is performed. The time constant for the burst signal may be maintained at a constant value longer than the time constant to be set at the initial stage of the signal.
In this case, in the discovery period, the follow-up of the first voltage at the beginning of the preamble is delayed due to a relatively long time constant, but a special burst signal including a preamble having a sufficient length with respect to the time constant arrives. The preamble can be received without any trouble. As a result, a special burst signal can be received from a discovery target device without controlling transmission / reception timing.

  On the other hand, the burst signal receiving apparatus of the present invention includes a receiving element that receives a burst signal based on a binary signal, an amplifier that amplifies the output of the receiving element, and a burst signal that is output from the amplifier with a time constant. One of a time constant circuit that outputs a voltage of 1 and the time constant is variable, a signal voltage output from the amplifier and a constant reference voltage is set as a second voltage, and this is used as the first voltage. Comparator that produces the result of comparing with voltage as output, and time constant can be set for the time constant circuit, and the time constant to be set to the initial signal when the burst signal is received is set to the late signal And a control circuit for switching the time constant so as to be shorter than the time constant.

  In the burst signal receiving apparatus configured as described above, the first voltage that is the target or reference for determination of 0 or 1 is set by setting the initial time constant including the preamble shorter than the time constant of the latter period of the signal. Can be detected quickly.

In the burst signal receiving apparatus, the time constant set in the interval between burst signals in which the burst signal is not received may be shorter than the time constant set in the latter half of the signal.
In this case, the first voltage can be quickly returned to the no-signal level even immediately after receiving a burst signal having a large signal strength (amplitude). Therefore, the no-signal period can be shortened, and the band can be utilized more effectively.
In particular, by setting the time constant to be set to the initial stage of the signal as τ1, the time constant to be set to the late stage of the signal as τ2, and the time constant to be set as the interval between the burst signals as τ3, by setting so that τ3 ≦ τ1 <τ2. The first voltage can be quickly returned to the no signal level.

  Further, the present invention is a station-side device that constitutes a PON system together with a plurality of home-side devices, a receiving element that receives an optical burst signal based on a binary signal and outputs an electrical signal; An amplifier that amplifies the output, a first voltage that follows a burst signal output from the amplifier with a time constant, and a time constant circuit that can switch the time constant to three stages, and a signal output from the amplifier Either a voltage or a constant reference voltage is used as a second voltage, and the result of comparing this with the first voltage is output, and the time constant can be set for the time constant circuit. The time constant for setting the initial signal when the burst signal is received is τ1, the time constant for setting the signal late is τ2, and the time constant for setting the interval between burst signals not receiving the burst signal is τ. As, in which a control circuit for setting to be a relationship τ3 ≦ τ1 <τ2.

In the station side device configured as described above, the time constant of the initial signal including the preamble is set to be shorter than the time constant of the latter period of the signal, and the first voltage that is the target of determination or reference of 0 or 1 is set. It can be detected quickly.
In addition, the first voltage can be quickly returned to the no-signal level immediately after receiving a burst signal having a large signal strength (amplitude). Therefore, the no-signal period can be shortened, and the band can be utilized more effectively.

In addition, the present invention is a PON system including a station side device and a plurality of home side devices, and the station side device includes:
A receiving element that receives a burst signal based on a binary signal, an amplifier that amplifies the output of the receiving element, and a first voltage that follows the burst signal output from the amplifier with a time constant is output. A variable time constant circuit, and a comparator that generates, as an output, a result obtained by comparing one of a signal voltage output from the amplifier and a constant reference voltage as a second voltage and comparing the second voltage with the first voltage. The time constant can be set for the time constant circuit, and the time constant is set so that the time constant set at the initial stage of the signal when the burst signal is received is shorter than the time constant set at the latter stage of the signal. And a control circuit for performing
When performing the discovery of the home side device, the home side device transmits a special burst signal including a preamble long set for discovery, and the control circuit performs the time constant switching without performing the time constant switching. The time constant for the burst signal is maintained at a constant value longer than the time constant set at the initial stage of the signal.

In the PON system configured as described above, the time constant of the initial signal including the preamble is set to be shorter than the time constant of the latter period of the signal, and the first voltage that is the target of determination or reference of 0 or 1 is quickly set. Can be detected.
In the discovery period, the tracking of the first voltage in the initial stage of the preamble is delayed due to a relatively long time constant. However, a special burst signal including a preamble having a sufficient length with respect to the time constant is generated from the home side device. By receiving, the preamble can be received without any trouble. As a result, a special burst signal can be received from the home device to be discovered without performing transmission / reception timing control.

According to the burst signal receiving method, the burst signal receiving apparatus, the station side apparatus, and the PON system of the present invention, the responsiveness to the burst signal can be improved.

  FIG. 1 is a connection diagram of a PON system related to a burst signal receiving method, a burst signal receiving apparatus, and a station side apparatus according to an embodiment of the present invention. In the figure, the station side device 1 is installed as a central station for a plurality of home side devices 2-4. The home side devices 2 to 4 are respectively installed in the subscriber homes of the PON system. An optical fiber network (5 to 9) is configured to branch from a single optical fiber 5 connected to the station side device 1 to a plurality of optical fibers (branches) 7 to 9 via an optical coupler 6. The home devices 2 to 4 are connected to the ends of the optical fibers 7 to 9, respectively. Furthermore, the station side device 1 is connected to the host network 11, and the home side devices 2 to 4 are connected to the respective user networks 12 to 14.

  In FIG. 1, three home-side devices 2 to 4 are shown, but it is possible to connect 32 home-side devices by branching, for example, 32 from one optical coupler 6. Although only one optical coupler 6 is used in FIG. 1, more home-side devices can be connected to the station-side device 1 by providing a plurality of optical couplers in a column. The distance from the station side device 1 to each of the home side devices 2 to 4 is not constant. Therefore, the intensity of the signal received from each of the home side devices 2 to 4 is not constant.

In FIG. 1, data is transmitted at a wavelength λ ₁ in the upstream direction from each of the home side devices 2 to 4 to the station side device 1. Conversely, data is transmitted at the wavelength λ ₂ in the downstream direction from the station side device 1 to the home side devices 2 to 4. These wavelengths λ ₁ and λ ₂ are determined based on Clause 60 of IEEE standard 802.3ah-2004 in the case of GE-PON, for example.

  In the PON system as described above, transmission from the station side device 1 to the home side devices 2 to 4 can be performed at any time. On the other hand, transmission from the home side devices 2 to 4 to the station side device 1 is performed under the control of the station side device 1, and each home side device 2, 3 and 4 is permitted to transmit at the time when transmission permission is obtained. The amount of data obtained is transmitted.

<< First Embodiment >>
FIG. 2 is a circuit diagram of the burst signal receiving apparatus according to the first embodiment of the present invention provided in the station side apparatus 1. In the figure, a photodiode 101 as a receiving element receives a burst signal based on a binary signal (digital signal), converts it into an electric signal, and outputs it. The output of the photodiode 101 is amplified by an amplifier 102 having a feedback resistor 103 connected between the input and output. The amplified burst signal output from the amplifier 102 is directly input to one input terminal of the comparator 104 as a signal voltage. In addition, a voltage at which the burst signal is output via the time constant circuit 105 is input to the other input terminal of the comparator 104 as a threshold voltage.

  The time constant circuit 105 is a low-pass filter including a resistor 106 whose resistance value is variable by external control, and a capacitor 107 having one end connected to the resistor 106 and the other end being a ground potential. When the resistance value 106 is R and the capacitance of the capacitor 107 is C, the time constant τ is τ = R · C. The comparator 104 compares the signal voltage with the threshold voltage, and outputs the comparison result as a binary signal (digital signal) Dout of 0 or 1, and its logical inversion signal. The resistance value of the resistor 106 can be changed by the control circuit 108. The control circuit 108 controls the transmission of each home-side device, and determines when the burst signal is sent from each home-side device and the amount of transmission data (the length of the preamble section, the length of the data section). Always know.

  FIG. 3 is a diagram showing an example of a more specific circuit configuration for making the resistance 106 variable in the time constant circuit 105 of FIG. In the figure, a time constant circuit 105 includes a resistor R0 (resistance value R0) and a capacitor 107, which are provided between the output terminal of the amplifier 102 and the ground potential, and a resistor connected in parallel to the resistor R0. R1 (resistance value R1) and a switching element (for example, a MOS-FET) 111 in series, and a resistor R2 (resistance value R2) and switching element 112 connected in parallel to the resistance R0. Yes. The switching elements 111 and 112 are ON / OFF controlled by a control circuit 108 connected to each control terminal (for example, the gate of a MOS-FET).

[Control Example 1]
The time constant circuit 105 in FIG. 3 is controlled as in Control Example 1 shown in Table 1 below, for example. FIG. 4 is a diagram illustrating an example of a burst signal. Each burst signal is composed of a preamble (preamble section) and data (data section). The control circuit 108 (FIG. 3) grasps in advance the time t1 at which the preamble portion is first received, the time t3 at which the data portion is first received, and the time t4 at which reception of the burst signal ends. . In addition, the time t5 at which the next burst signal starts to arrive after passing through the no-signal section is grasped in advance (the same applies hereinafter).

3 and 4, in Table 1, in the control example 1, the resistance values R1 and R2 have a relationship of R2 <R1. Regarding the on / off of the switching elements 111 and 112, different control is performed for each signal initial stage of the burst signal, signal late stage, and no-signal section of the burst signal. First, in a part (time t1 to t2) of the preamble period at the initial stage of the signal, the switching element 111 is turned on and the switching element 112 is turned off. Thus, when the on-resistance of the switching element 111 is Rs1, the time constant circuit 105 has a configuration in which a capacitor 107 (capacitance C) is connected to a parallel resistance of the resistor R0 and the resistor (R1 + Rs1). ,
τ1 = {R0 · (R1 + Rs1) / (R0 + R1 + Rs1)} · C. . . (1)
It becomes.
Note that the time t2 can be set to a predetermined time slightly before the time t3, which is the end of the preamble.

Subsequently, in the other part (time t2 to t3) and the data period (time t3 to t4)) of the preamble period in the latter half of the signal, that is, from time t2 to t4, the switching elements 111 and 112 are both turned off. As a result, the resistors R1 and R2 of the time constant circuit 105 become invalid, and become a time constant by only the resistor R0 and the capacitor 107 (capacitance C).
τ2 = R0 · C. . . (2)
It becomes.

Subsequently, in the non-signal period (time t4 to t5), the switching element 111 is turned off and the switching element 112 is turned on. As a result, when the on-resistance of the switching element 112 is Rs2, the time constant is determined by the parallel resistance of the resistors R0 and R2 + Rs2 and the capacitor 107 (capacitance C).
.tau.3 = {R0. (R2 + Rs2) / (R0 + R2 + Rs2)}. C. . . (3)
It becomes.

In the above formulas (1) to (3), when another resistor (R1 or R2) is connected in parallel to the resistor R0, the resistance value of the entire parallel resistor becomes smaller than the resistor R0, and the resistance value connected in parallel Is smaller, the resistance value of the entire parallel resistor is smaller. Therefore,
τ3 <τ1 <τ2. . . (4)
It becomes. In terms of the relative relationship of the lengths of the time constants, the initial signal is “medium”, the late signal is “long”, and the non-signal period is “short”. By switching the time constant, the time constant becomes relatively shorter in the preamble period (t1 to t2) in the initial stage of the signal than in the later stage of the signal. Therefore, the threshold voltage that is the output voltage of the time constant circuit 105 is set to the preamble. Can quickly follow the median of. In particular, when a bit-inverted repetitive signal such as 0, 1, 0, 1,... Is used for the preamble, the frequency component of the signal becomes high (only one bit continues in the same sign). By setting the constant short, the median can be detected early. Thereby, the responsiveness with respect to a burst signal can be improved.

On the other hand, from the latter half of the preamble period in the latter part of the signal to the data period (t2 to t4), the time constant is set longer than that in the initial stage of the signal according to the encoding format of the data period. Thereby, the threshold voltage in the data section can be stabilized so as not to deviate from the center of the amplitude.
Furthermore, the threshold voltage can be quickly returned to the no-signal level by making the time constant the shortest in the no-signal section. As a result, the threshold voltage can be quickly returned to the no-signal level even immediately after receiving a burst signal having a large optical signal intensity (amplitude). Therefore, the no-signal period can be shortened, and the band can be utilized more effectively.

[Control Example 2]
The time constant circuit 105 in FIG. 3 can be controlled as in Control Example 2 shown in Table 2 below, for example.

3 and 4, in Table 2, in the control example 2, the resistance values R1 and R2 may not be R2 <R1, may be R1 = R2, or may be R1 <R2. Regarding the on / off of the switching elements 111 and 112, different control is performed for each signal initial stage of the burst signal, signal late stage, and no-signal section of the burst signal. First, in a part (time t1 to t2) of the preamble period at the initial stage of the signal, the switching element 111 is turned on and the switching element 112 is turned off. As a result, when the on-resistance of the switching element 111 is Rs1, the time constant circuit has a form in which the capacitor 107 (capacitance C) is connected to the parallel resistance of the resistor R0 and the resistor (R1 + Rs1).
τ1 = {R0 · (R1 + Rs1) / (R0 + R1 + Rs1)} · C. . . (5)
(Same as equation (1)).
Note that the time t2 can be set to a predetermined time slightly before the time t3, which is the end of the preamble.

Subsequently, in the other part (time t2 to t3) and the data period (time t3 to t4)) of the preamble period in the latter half of the signal, that is, from time t2 to t4, the switching elements 111 and 112 are both turned off. As a result, the resistors R1 and R2 of the time constant circuit 105 become invalid, and become a time constant by only the resistor R0 and the capacitor 107 (capacitance C).
τ2 = R0 · C. . . (6)
(Same as equation (2)).

Subsequently, in the non-signal period (time t4 to t5), the switching elements 111 and 112 are both turned on. As a result, when the on-resistance of the switching element 112 is Rs2, the time constant due to the parallel resistance of the resistors R0, R1 + Rs1, R2 + Rs2 and the capacitor 107 (capacitance C) is obtained.
[tau] 3 = {R0. (R1 + Rs1). (R2 + Rs2) / (R0 + R1 + Rs1 + R2 + Rs2)}. . . (7)
It becomes.

From the above formulas (5) to (7),
τ3 <τ1 <τ2. . . (8)
(Same as equation (4)), the same effect as in the case of the control example 1 is obtained.

[Control Example 3]
Further, the time constant circuit 105 of FIG. 3 can be controlled as in Control Example 3 shown in Table 3 below, for example.

FIG. 5 is a diagram showing an example of a burst signal in a discovery section in addition to a burst signal from a known home device.
Referring to FIG. 5, in Table 3, the control example 3 is obtained by adding control corresponding to discovery to the control example 1. The control of the initial signal stage, the late signal stage, and the no-signal section of the burst signal is the same as in Control Example 1, and thus the description thereof is omitted.

  In the initial state where the home device is newly connected to the PON system (FIG. 1), the home device is not yet under the control of the station device 1 (FIG. 1). I do not know when to receive the signal from the side device. Therefore, a special section (band) called a discovery section is periodically provided to discover a new home-side device, and the station-side device 1 is in a state of listening to transmission from the home-side device. Further, it is assumed that the new home-side device transmits a special burst signal including a preamble longer than a normal preamble of a known home-side device, that is, a preamble set longer for discovery.

  In FIG. 5, times t6 to t7 are prepared as discovery intervals. During this interval, the control circuit 108 (FIG. 3) sets the time constant by turning off the switching elements 111 and 112 (FIG. 3). It is assumed that τ2 is the same as the normal data section. Thus, in the discovery period, the station side device 1 fixes the time constant to a long state like the data period, and waits for a burst signal with the time constant τ2. The tracking of the threshold voltage at the beginning of the preamble is delayed due to the long time constant τ2, but the station side apparatus 1 receives the preamble without any trouble by receiving a burst signal of a preamble with a sufficient length with respect to the time constant τ2. In addition, data can be received without switching the time constant thereafter. Thereby, it is possible to receive a burst signal from the home device to be discovered without performing transmission / reception timing control.

  Note that discovery is not frequently performed, and the discovery interval is set to a maximum communication distance between the station-side device 1 and the home-side device that is longer than the time required for the optical signal to arrive. Even if it becomes a little longer, the overall communication efficiency is hardly affected.

In the above control examples 1 to 3, the relationship between the three time constants is τ3 <τ1 <τ2, but it is also possible to reverse the magnitude relationship between τ3 and τ1 so that τ1 <τ3 <τ2. It is.
In any of the above control examples 1 to 3, three time constants (τ1, τ2, τ3) can be set. However, two time constants (τ1, τ2) may be set as τ3 = τ1. That is, τ1 that satisfies the relationship of τ1 <τ2 may be applied to the no-signal section. In this case, the series circuit of the resistor R2 and the switching element 112 in FIG. 3 is not necessary.

<< Second Embodiment >>
FIG. 6 is a circuit diagram of a burst signal receiving apparatus according to the second embodiment of the present invention provided in the station side apparatus 1. In the figure, a photodiode 101 as a receiving element receives a burst signal based on a binary signal (digital signal), converts it into an electric signal, and outputs it. The output of the photodiode 101 is amplified by an amplifier 102 having a feedback resistor 103 connected between the input and output. The amplified burst signal output from the amplifier 102 is input to one input terminal of the comparator 104 via the time constant circuit 105. In addition, a constant voltage supplied from the DC power supply 113 is input to the other input terminal of the comparator 104 as a threshold voltage.

  The time constant circuit 105 includes a resistor 106 whose resistance value is variable by external control, and a capacitor 107 having one end connected to the resistor 106 and the other end connected to the output terminal of the amplifier 102. When the resistance value of the resistor 106 is R and the capacitance of the capacitor 107 is C, the time constant τ is τ = R · C. The comparator 104 compares the signal voltage at the connection point between the capacitor 107 and the resistor 106 with the threshold voltage, and outputs the comparison result as a binary signal (digital signal) Dout of 0 or 1, and its logical inversion signal. The resistance value of the resistor 106 can be changed by the control circuit 108. The control circuit 108 controls the transmission of each home-side device, and determines when the burst signal is transmitted from each home-side device and the amount of transmission data (the length of the preamble section, the length of the data section). Always know.

  FIG. 7 is a diagram showing an example of a more specific circuit configuration for making the resistance 106 variable in the time constant circuit 105 of FIG. In the figure, a time constant circuit 105 includes a resistor R0 (resistance value R0) provided between a capacitor 107 and a DC power source 103, a resistor R1 (resistance value R1) connected in parallel to the resistor R0, and a switching element. (For example, a MOS-FET) 111 and a series body of a resistor R2 (resistance value R2) and a switching element 112 connected in parallel to the resistor R0. The switching elements 111 and 112 are ON / OFF controlled by a control circuit 108 connected to each control terminal (for example, the gate of a MOS-FET).

Since the control example of the burst signal receiving apparatus according to the second embodiment is the same as that of the first embodiment, a description thereof will be omitted.
Comparing the time constant circuits 105 of both embodiments, the time constant circuit 105 (FIG. 3) in the first embodiment outputs a threshold voltage that follows the burst signal output from the amplifier 102 with a time constant as the first voltage. The time constant is variable. Further, the comparator 104 in the first embodiment is configured to generate a signal voltage output from the amplifier 102 as a second voltage, and a result obtained by comparing the signal voltage with the first voltage as an output. On the other hand, the time constant circuit 105 (FIG. 7) in the second embodiment outputs a signal voltage that follows the burst signal output from the amplifier 102 with a time constant as the first voltage, and the time constant is variable. . Further, the comparator 104 in the second embodiment generates a constant reference voltage (the output voltage of the DC power supply 113) as the second voltage (threshold voltage), and outputs the result of comparing this with the first voltage. It is configured as follows.

<< Third Embodiment >>
FIG. 8 is a circuit diagram of a burst signal receiving apparatus according to the third embodiment of the present invention provided in the station side apparatus 1. The difference from the burst signal receiving apparatus according to the first embodiment is that the time constant circuit 105 has a feedback circuit configuration, and the other configurations and operations are the same. In FIG. 8, the time constant circuit 105 includes a resistor 106 whose resistance value is variable under the control of the control circuit 108, and a capacitor 107 having one end connected to the resistor 106 and the other end being a ground potential. In addition to the low-pass filter, a differential amplifier 114 and a midpoint potential generation circuit 115 are provided.

  The voltage signal from the amplifier 102 and the threshold voltage are input to the differential amplifier 114, and output signals (analog level voltage signals) corresponding to the potential difference between these two inputs are output as a positive phase output and a negative phase output. Is output in the form. The midpoint potential generation circuit 115 outputs an average value of the two outputs from the differential amplifier 114, that is, a midpoint potential. Due to this midpoint potential, a threshold voltage is generated at the connection point between the resistor 106 and the capacitor 107.

  Such a time constant circuit 105 has a circuit configuration in which a threshold voltage is given by feedback. Specifically, for example, when the threshold voltage is smaller than the median value of the voltage signal from the amplifier 102, the positive phase output of the differential amplifier 114 is larger than the negative phase output, thereby increasing the threshold voltage. . On the other hand, when the threshold voltage is larger than the median value of the voltage signal from the amplifier 102, the negative-phase output of the differential amplifier 114 becomes larger than the positive-phase output, thereby lowering the threshold voltage. Therefore, finally, the threshold voltage follows the median value of the voltage signal from the amplifier 102 with a time constant.

  Since the time constant circuit 105 forms a feedback loop, the time constant depends on the open loop gain of the feedback loop. Assuming that the potential difference between the two inputs (voltage signal, threshold voltage) to the differential amplifier 114 in FIG. 8 is ΔVin and the threshold voltage is ΔVout, the open loop gain A (f) as a function of frequency is A (f) = ΔVout. / ΔVin. When the resistance value of the resistor 106 is R and the capacitance of the capacitor 107 is C, the time constant τ of the time constant circuit 105 is τ = A (f) · R · C.

  Here, the bandwidth of the differential amplifier 114 and the midpoint potential generation circuit 115 is set sufficiently wider than the bandwidth of the low-pass filter (1 / (2π · R · C)) by the resistor 106 and the capacitor 107. It can be considered that A (f) = A (a constant value) in a band lower than the band of the low-pass filter. Therefore, the time constant τ can be controlled by controlling the resistance value R of the resistor 106 to be switched.

Since the control example of the burst signal receiving apparatus according to the third embodiment is the same as that of the first embodiment, a description thereof will be omitted.
When the time constant circuits 105 of both embodiments are compared, a threshold voltage that follows the burst signal output from the amplifier 102 with a time constant is output as the first voltage, and the time constant is variable, and the comparator 104. Is the same in that the signal voltage output from the amplifier 102 is used as the second voltage and the result obtained by comparing the signal voltage with the first voltage is used as the output.

  In FIG. 8, the voltage signal and the threshold signal are not directly input to the comparator 104, and the differential amplifier 114 is interposed in the middle. However, the comparator 104 is a multistage connection of differential amplifiers. (Differential amplifier 114 + comparator 104) can be regarded as one comparator with respect to the input of the voltage signal and the threshold signal. Therefore, for example, the circuit shown in FIG. 9 is also a circuit equivalent to FIG. When the comparator is composed of a multistage differential amplifier, it is preferable to feed back the output of the first stage in order to make the circuit scale as compact as possible.

  In any of the above-described embodiments (first to third), the initial voltage constant including the preamble is set to be shorter than the late signal time constant, and the first voltage that is the target of determination or reference of 0 or 1 Can be detected quickly. Similarly, the time constant of the non-signal period can be set short, and the first voltage can be quickly returned to the non-signal level to prepare for the next burst signal. In this way, the responsiveness to the burst signal can be improved.

  The “no-signal interval” in each of the above embodiments is actually used for the emission interval Ton and the extinction interval Toff in consideration of the transient response of the laser emission / extinction of the laser on the burst signal transmission side, as shown in FIG. May be. In this case, although it can be said that it is not strictly a “no-signal” section, the time constant τ3 is set in the “inter-burst signal section” so as to include such a case.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined not by the above-mentioned meaning but by the scope of claims for patent, and is intended to include all modifications within the scope and meaning equivalent to the scope of claims for patent.

1 is a connection diagram of a PON system related to a burst signal receiving method, a burst signal receiving apparatus, and a station side apparatus according to an embodiment of the present invention. 1 is a circuit diagram of a burst signal receiving device according to a first embodiment of the present invention provided in a station side device. FIG. FIG. 3 is a diagram showing an example of a more specific circuit configuration for making the resistance variable in the time constant circuit of FIG. 2. It is a figure which shows an example of a burst signal. It is the figure which also showed an example of the burst signal of a discovery area other than the burst signal from a known home side apparatus. It is a circuit diagram of the burst signal receiver which concerns on 2nd Embodiment of this invention provided in a station side apparatus. FIG. 7 is a diagram showing an example of a more specific circuit configuration for making the resistance variable in the time constant circuit of FIG. 6. It is a circuit diagram of the burst signal receiver which concerns on 3rd Embodiment of this invention provided in a station side apparatus. FIG. 9 is another circuit diagram equivalent to FIG. 8. It is a figure which shows an example which utilized the area between burst signals for the light emission area Ton and the quenching area Toff of the laser of the burst signal transmission side.

Explanation of symbols

1 Station side device 2-4 Home side device 101 Photodiode 102 Amplifier 104 Comparator 105 Time constant circuit 108 Control circuit

Claims (9)

Receiving a burst signal based on a binary signal and amplifying it,
Outputting a first voltage that follows the amplified burst signal with a variable time constant;
A burst signal receiving method for generating one of a signal voltage of an amplified burst signal and a constant reference voltage as a second voltage, and generating a result obtained by comparing the second voltage with the first voltage,
A burst signal receiving method comprising: switching a time constant so that a time constant set at the initial stage of the signal when the burst signal is received is shorter than a time constant set at a later stage of the signal.   2. The burst signal receiving method according to claim 1, wherein a time constant set in an interval between burst signals not receiving the burst signal is shorter than a time constant set in the latter period of the signal.   The time constant set in the initial stage of the signal is τ1, the time constant set in the late stage of the signal is τ2, and the time constant set in the interval between the burst signals is set as τ3, so that the relation of τ3 ≦ τ1 <τ2 is established. 3. A burst signal receiving method according to 2.   When performing discovery of a device that is a transmission source of a burst signal, the burst signal is transmitted without causing the device to transmit a special burst signal including a preamble long set for discovery and without switching the time constant. 2. The burst signal receiving method according to claim 1, wherein the time constant for is maintained at a constant value longer than the time constant to be set at the initial stage of the signal. A receiving element for receiving a burst signal based on a binary signal;
An amplifier for amplifying the output of the receiving element;
A time constant circuit that outputs a first voltage that follows the burst signal output from the amplifier with a time constant, and the time constant is variable;
A comparator that generates, as an output, a result of comparing one of a signal voltage output from the amplifier and a constant reference voltage as a second voltage, and comparing the second voltage with the first voltage;
A time constant can be set for the time constant circuit, and the time constant is set so that the time constant set at the initial stage of the signal when the burst signal is received is shorter than the time constant set at the latter stage of the signal. A burst signal receiving apparatus comprising: a control circuit.   6. The burst signal receiving apparatus according to claim 5, wherein a time constant set in an interval between burst signals not receiving the burst signal is shorter than a time constant set in the latter period of the signal.   The time constant set in the initial stage of the signal is τ1, the time constant set in the late stage of the signal is τ2, and the time constant set in the interval between the burst signals is set as τ3, so that the relation of τ3 ≦ τ1 <τ2 is established. 6. The burst signal receiving device according to 6. A station side device that constitutes a PON system together with a plurality of home side devices,
A receiving element for receiving an optical burst signal based on a binary signal and outputting an electrical signal;
An amplifier for amplifying the output of the receiving element;
A time constant circuit that outputs a first voltage that follows the burst signal output from the amplifier with a time constant, and the time constant can be switched to three stages;
A comparator that generates, as an output, a result of comparing one of a signal voltage output from the amplifier and a constant reference voltage as a second voltage, and comparing the second voltage with the first voltage;
A time constant can be set for the time constant circuit, the time constant for setting the initial signal when the burst signal is received is τ1, the time constant for setting the signal late is τ2, and the burst signal is not received. A station-side apparatus comprising: a control circuit that sets a time constant set in an interval between burst signals as τ3, so that a relationship of τ3 ≦ τ1 <τ2 is established. A PON system composed of a station-side device and a plurality of home-side devices,
A receiving element for receiving a burst signal based on a binary signal;
An amplifier for amplifying the output of the receiving element;
A time constant circuit that outputs a first voltage that follows the burst signal output from the amplifier with a time constant, and the time constant is variable;
A comparator that generates, as an output, a result of comparing one of a signal voltage output from the amplifier and a constant reference voltage as a second voltage, and comparing the second voltage with the first voltage;
A time constant can be set for the time constant circuit, and the time constant is set so that the time constant set at the initial stage of the signal when the burst signal is received is shorter than the time constant set at the latter stage of the signal. A control circuit,
When performing the discovery of the home side device, the home side device transmits a special burst signal including a preamble long set for discovery, and the control circuit performs the time constant switching without performing the time constant switching. A PON system that maintains a time constant for a burst signal at a constant value longer than a time constant to be set at the initial stage of the signal.

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