JP5399307B2 - LOS signal correction apparatus, LOS signal correction method, LOS signal generation apparatus, and optical receiver - Google Patents

Description

  The present invention relates to a LOS signal correction apparatus and a LOS signal correction method for correcting a LOS signal. The present invention also relates to an LOS signal generation apparatus and an optical receiver that include such an LOS signal correction apparatus.

  Some optical receivers that receive optical signals have a LOS (Loss Of Signal) detection function that detects a no-signal state. The optical receiver having the LOS detection function generates a LOS signal whose value is switched depending on whether or not the reception power is equal to or less than a predetermined value. By referring to the value of the LOS signal, for example, a failure of an optical transmitter that is a transmission source of an optical signal, a disconnection of an optical fiber that is an optical signal transmission medium, or the like can be detected.

  As an optical receiver having an LOS detection function, for example, an optical receiver described in Patent Document 1 is known. In the optical receiver described in Patent Document 1, (1) a photocurrent obtained by a photodiode (hereinafter abbreviated as “PD”) is converted into a voltage signal by a transimpedance amplifier (hereinafter abbreviated as “TIA”). (2) The voltage signal obtained by TIA is converted into a differential signal by a differential amplifier and amplified. (3) The maximum value of the potential difference of the differential signal obtained by the differential amplifier is obtained. A configuration is adopted in which detection is performed by a peak detection circuit, and (4) a maximum value detected by the peak detection circuit is compared with a reference voltage by a comparator. For example, when the input of the optical signal is cut off and the signal transitions to the no-signal state, the output signal (analog signal) of the peak detection circuit falls and the value of the output signal (digital signal) of the comparator is inverted.

  In such an optical receiver, for a while after the input of the optical signal is cut off, a phenomenon called chattering in which the value of the output signal of the comparator repeats inversion occurs. This is because, since a reverse bias voltage is applied to the PD, the value of the output signal of the peak detection circuit oscillates after the input of the optical signal is cut off. For this reason, if the output signal itself of the comparator is used as the LOS signal, malfunction may occur in the host system that refers to the LOS signal. When an avalanche photodiode (hereinafter abbreviated as “APD”) to which a higher reverse bias voltage (usually 30 V or more and 100 V or less) is applied is used as a photodetector, a PD of PN type or PIN type is used as a light detector. Chattering is more noticeable than when it is used as a detector.

  Therefore, the optical receiver described in Patent Document 1 employs a configuration in which the output signal of the comparator is corrected by a microcomputer and a corrected LOS signal is output. Specifically, after the comparator output is inverted, the value of the LOS signal is inverted after confirming that the comparator output is constant over a predetermined period (hereinafter referred to as “dead zone” according to Patent Document 1). By doing so, inversion of the comparator output due to chattering is masked.

JP 2004-304232 (release date: October 28, 2004)

  By the way, the duration of chattering that occurs after the input of the optical signal is cut off is determined depending on the power of the optical signal that has been cut off. Specifically, the greater the power of the optical signal, the longer the chattering duration that occurs after the input of the optical signal is cut off. For example, when an APD is used as a photodetector, the chattering duration that occurs after -20 dBm optical signal input is cut off is about 100 μsec, and the chattering duration that occurs after -10 dBm optical signal input is cut off is 5 msec. It will be about. Therefore, in order to mask the chattering that occurs after the input of the optical signal is cut off by the technique described in Patent Document 1, it is necessary to set the length of the dead zone longer than the assumed chattering duration. .

  For this reason, if it is attempted to mask chattering that occurs after the input of a high-power optical signal is cut off by the technique described in Patent Document 1, it is necessary to set the length of the dead zone longer, and the response of the LOS signal is delayed. (The time from when the input of the optical signal is interrupted until the value of the LOS signal is inverted is increased). On the other hand, if the response of the LOS signal is to be made faster, it is necessary to set the length of the dead zone short, and there arises a problem that chattering that occurs after the input of the high-power optical signal is cut off cannot be masked.

  For example, in an SFP (Small From-factor Pluggable) transceiver, it is a standard (SFP-MAS: Small Form-factor) that the time from when the input of an optical signal is interrupted until the value of the LOS signal is inverted is set to 100 μsec or less. Pluggable Transceiver Multi Source Agreement). For this reason, if the length of the dead zone is set to 100 μsec or more so as to mask chattering that occurs when an optical signal stronger than −20 dBm is input, the standard cannot be satisfied. Conversely, if the dead zone length is set to 100 μsec or less so as to satisfy the standard, it is impossible to mask chattering that occurs when an optical signal stronger than −20 dBm is input.

  Here, the problem related to chattering that occurs after the input of the optical signal to the PD has been described, but chattering occurs after the input of the optical signal to the PD is started, and the same problem occurs.

  The present invention has been made in view of the above problems, and its purpose is to start chattering that occurs after the input of an optical signal is cut off and input of the optical signal without delaying the response of the LOS signal. It is to realize an optical receiver capable of masking chattering that occurs after being performed.

  In order to solve the above-described problem, an LOS signal correction apparatus according to the present invention is an LOS signal correction apparatus that corrects an LOS signal generated from an output signal of a photodetector, and detects an edge in an LOS signal before correction. And a first state in which the value of the LOS signal before correction is written in the storage unit, and the value of the LOS signal before correction written in the storage unit is output as the value of the corrected LOS signal, and Correction means having a second state for outputting a value obtained by inverting the value of the LOS signal before correction written in the storage unit in the first state as the value of the LOS signal after correction; and the correction means, Timing means for measuring an elapsed time from the time of transition to the second state, and the correction means triggers that the detection means detects an edge in the LOS signal before correction. Transition from the first state to the second state, and from the second state to the first state triggered by the elapsed time counted by the timing means reaching a predetermined time. It is characterized by a transition.

  According to the above configuration, from the first state in which the value of the LOS signal before correction is output as the value of the LOS signal after correction using the detection of the edge in the LOS signal before correction as a trigger, the first state Transition to the second state in which the value obtained by inverting the value of the LOS signal before correction is output as the value of the LOS signal after correction. For this reason, in the first state, the value of the LOS signal before correction is inverted (that is, the input of the optical signal to the photodetector is cut off, or the input of the optical signal to the photodetector is performed). The value of the corrected LOS signal can be inverted immediately in response to the start of In the second state, since the value obtained by inverting the value of the LOS signal before correction in the first state is output as the value of the LOS signal after correction, the value of the LOS signal before correction is inverted by chattering. Even if it is repeated, the value of the corrected LOS signal does not repeat inversion accordingly. That is, chattering that occurs after the input of the optical signal to the photodetector is cut off and chattering that occurs after the input of the optical signal to the photodetector can be masked.

  In the LOS signal correction apparatus according to the present invention, it is preferable that the predetermined time is longer than the duration of chattering that occurs after the value of the LOS signal before correction is inverted.

  According to the above configuration, it is possible to more reliably mask chattering that occurs after the input of the optical signal to the photodetector is cut off and chattering that occurs after the input of the optical signal to the photodetector is started. it can.

  The LOS signal correction apparatus according to the present invention includes an acquisition unit that acquires the reception power of the optical signal input to the photodetector, and a setting unit that sets the predetermined time according to the reception power acquired by the acquisition unit. The predetermined time set by the setting means is preferably represented by a monotonically increasing function of received power.

  According to the above configuration, when the reception power of the optical signal input to the photodetector is small and the chattering duration is short, the duration of the second state is set short, and the photodetector is When the received power of the input optical signal is large and the chattering duration is long, the duration of the second state can be set long. For this reason, the duration of the second state in which the value of the LOS signal before correction and the value of the LOS signal after correction may not coincide with each other is suppressed to the minimum necessary time for masking chattering. It is possible to respond immediately to changes in the optical signal that occur after the convergence of.

  In the LOS signal correction apparatus according to the present invention, the acquisition unit writes the acquired received power value into the storage unit when an optical signal is input, and stores the storage after the input of the optical signal is cut off. It is preferable to provide the value of the received power written in the unit to the setting means.

  According to the above configuration, even for chattering that occurs after the input of the optical signal is cut off, the duration of the second state is suppressed to the minimum necessary time for masking chattering, and the light that occurs after the chattering converges It is possible to respond immediately to changes in the signal.

  In the LOS signal correction device according to the present invention, it is preferable that the correction means writes the value of the LOS signal before correction sampled when the transition from the second state to the first state is made in the storage unit. .

  According to the above configuration, the value of the corrected LOS signal can be immediately matched with the value of the LOS signal before correction at the time of transition from the second state to the first state. That is, the reliability of the corrected LOS signal can be improved.

  In the LOS signal correction apparatus according to the present invention, it is preferable that the correction means writes the value of the LOS signal before correction periodically sampled in the first state in the storage unit.

  According to the above configuration, even when the value of the LOS signal before correction changes (for example, changes slowly) without detecting an edge, the value of the corrected LOS signal output in the first state is corrected. It can be matched to the value of the previous LOS signal. That is, the reliability of the corrected LOS signal can be further improved.

  In order to solve the above-described problem, the LOS signal correction method according to the present invention writes the value of the LOS signal before correction to the storage unit and the value of the LOS signal before correction written in the storage unit after correction. A first state that is output as the value of the LOS signal, and a value obtained by inverting the value of the LOS signal before correction written in the storage unit in the first state is output as the value of the corrected LOS signal. A method for correcting an LOS signal that corrects a LOS signal generated from an output signal of a photodetector using a correction means having two states, a detection step for detecting an edge in an LOS signal before correction, and the above detection A first transition step of transitioning the state of the correction means from the first state to the second state triggered by the detection of an edge in the LOS signal before correction in the step; The time of the elapsed time from the time when the means transits to the second state, and the time of the elapsed time measured in the time counting process as a trigger, the state of the correction means It is preferable that the process includes a second transition step for transitioning from the second state to the first state.

  According to the above configuration, as with the LOS signal correction device, chattering that occurs when the input of the optical signal is interrupted and input of the optical signal is started without delaying the response of the LOS signal. The chattering that occurs can be masked.

  The LOS signal generation device including the LOS signal correction device and the optical receiver including the LOS signal generation device also have the same effects as the LOS signal correction device.

  That is, chattering that occurs when the input of an optical signal is interrupted and chattering that occurs when the input of the optical signal is started can be masked without delaying the response of the LOS signal. And an optical receiver can be realized.

  As described above, the LOS signal correction device according to the present invention is a LOS signal correction device that corrects the LOS signal generated from the output signal of the photodetector, and detects the edge in the LOS signal before correction. And a first state in which the value of the LOS signal before correction is written in the storage unit, and the value of the LOS signal before correction written in the storage unit is output as the value of the LOS signal after correction, and Correction means having a second state for outputting a value obtained by inverting the value of the LOS signal before correction written in the storage unit in the state 1 as the value of the LOS signal after correction; Time measuring means for measuring the elapsed time from the time of transition to the state, and the correction means triggers the detection of an edge in the LOS signal before correction by the detection means. Transitions to the second state from the state transition elapsed time measured by said time measuring means from said second state as a trigger that has reached a predetermined time to said first state.

  Therefore, by using the LOS signal correction device according to the present invention, chattering that occurs after the input of the optical signal is cut off and chattering that occurs after the input of the optical signal is started without delaying the response of the LOS signal. An optical receiver capable of masking can be realized.

It is a block diagram which shows the structure of the microcomputer (LOS signal correction apparatus) which concerns on embodiment of this invention. It is a block diagram which shows the structure of the optical receiver provided with the microcomputer shown in FIG. It is a graph showing the length of the interruption prohibition period set by the microcomputer shown in FIG. It is a flowchart which shows the flow of operation | movement of the microcomputer shown in FIG. It is a timing chart which shows the operation | movement flow of the microcomputer shown in FIG. 1, (a)-(g) shows the operation | movement of the microcomputer after the input of an optical signal was interrupted, (h)-(n) The operation of the microcomputer after the input of the optical signal is resumed is shown. In particular, (a) and (h) indicate the value of the optical signal, (b) and (i) indicate the value of the hardware LOS signal, and (c) and (j) indicate the value of the last state. (D) and (k) show the value of the module LOS signal, (e) and (l) show the value of the received power, and (f) and (m) show the timer flag (1: Timer stop, 0: timer operation), and (g) and (n) indicate interrupt flag values.

  An embodiment of the present invention will be described below with reference to the drawings. The LOS signal correction apparatus according to the present embodiment is realized by a microcomputer (micro controller) that controls the optical receiver, and is hereinafter referred to as a “microcomputer”.

[Configuration of optical receiver]
A configuration of the optical receiver 1 including the microcomputer 10 according to the present embodiment will be described with reference to FIG. FIG. 2 is a block diagram showing a configuration of the optical receiver 1. Each block included in the LOS processing unit 11 will be briefly described as follows for each function.

  As shown in FIG. 2, the optical receiver 1 includes an avalanche photodiode (hereinafter abbreviated as “APD”) 21 and a transimpedance amplifier (hereinafter abbreviated as “TIA”) 22 connected to the anode terminal of the APD 21. ing. The APD 21 is a configuration for generating a photocurrent having a magnitude corresponding to the power of the optical signal, and the TIA 22 is a configuration for converting the photocurrent generated by the APD 21 into a differential signal. In the optical receiver 1 according to the present embodiment, the APD 21 is used as a photodetector, but the present invention is not limited to this. That is, instead of the APD 21, a non-avalanche type photodiode may be used as a photodetector, or a phototransistor may be used as a photodetector.

  Further, as shown in FIG. 2, the optical receiver 1 includes a driver amplifier 31, a limiting amplifier 32, and an output buffer amplifier 33 as a configuration for amplifying the differential signal generated by the TIA 22. Yes. The differential signals RD + / RD− amplified by these amplifier groups are output to the outside via the output terminals OUT + / OUT−.

  In addition, as shown in FIG. 2, the optical receiver 1 has a peak detector 34, a comparator 35, and a reference voltage source 36 as generation means for generating a LOS signal from the differential signal generated by the TIA 22. It has. The peak detector 34 is configured to detect the maximum value of the potential difference of the differential signal generated by the TIA 22, and the comparator 35 uses the maximum value detected by the peak detector 34 as the reference voltage source 36. This is a configuration for comparing with the reference voltage Vref generated in (1). A digital signal indicating the comparison result obtained by the comparator 35 is input to the microcomputer 10. Hereinafter, this digital signal generated by the comparator 35 is referred to as a “hardware LOS signal”.

  Further, the optical receiver 1 includes a current mirror circuit 40 connected to the cathode terminal of the APD 21 as shown in FIG. The current mirror circuit 40 is a current mirror circuit with a current mirror ratio = 1: N, and generates a mirror current having a magnitude N times the photocurrent generated by the APD 21. The mirror current generated by the current mirror circuit 40 is converted into a voltage and then supplied to the microcomputer 10 via the AD converter 12 and used to monitor the received power.

  In order to operate the APD 21, it is necessary to apply a reverse bias voltage of 30 V or more. Therefore, the optical receiver 1 includes a reverse bias generation circuit 50 that generates a reverse bias voltage to be applied to the APD 21 as shown in FIG. The reverse bias generation circuit 50 is a circuit for obtaining a reverse bias voltage to be applied to the APD 21 by boosting the power supply voltage (+3.3 V in the case of an SFP transceiver).

  In the present embodiment, the microcomputer 10 refers to the reverse bias voltage generated by the reverse bias generation circuit 50 so that the reverse bias voltage applied to the APD 21 matches the target value. A feedback mechanism that controls the boost ratio is employed. Note that the value of the reverse bias voltage that maximizes the sensitivity of the APD 21 varies depending on the temperature. For this reason, in the present embodiment, the microcomputer 10 periodically resets the target value of the reverse bias voltage to a value at which the sensitivity of the APD 21 becomes maximum at the monitored temperature (for example, at a cycle of 25 ms), thereby performing temperature compensation. The structure which performs is adopted. In such a configuration, for example, a table in which the temperature and the reverse bias voltage at which the sensitivity of the APD 21 is maximized at that temperature is stored in advance is stored in a memory or the like that can be read from the microcomputer 10. Can be realized.

  As described above, since the reverse bias voltage of 30 V or more is applied to the APD 21, the APD 21 has the reverse bias voltage when the input of the optical signal is started or when the input of the optical signal is cut off. Generates current noise due to fluctuations. As a result, after the input of the optical signal is started or after the input of the optical signal is cut off, chattering may occur in which the value of the output signal of the comparator 35 is repeatedly inverted. Therefore, the optical receiver 1 is provided with the LOS processing unit 11 in the microcomputer 10 and corrects the hardware LOS signal so as to mask chattering that occurs after the input of the optical signal is started or after the input of the optical signal is cut off. The corrected LOS signal (hereinafter referred to as “module LOS signal” and distinguished from the above-mentioned “hardware LOS signal”) is output to a host system or the like.

  In the present embodiment, the APD 21 and the TIA 22 are integrated in a single small light receiving module 20 called ROSA (Receiver Optical Sub Assembly). Further, the driver amplifier 31, the limiting amplifier 32, the output buffer amplifier 33, the peak detector 34, and the comparator 35 are integrated in a single integrated circuit 30. The reference voltage source 36 is externally attached to the integrated circuit 30.

[Configuration of microcomputer]
With regard to the configuration of the microcomputer 10, in particular, the configuration of the LOS processing unit 11 provided in the microcomputer 10 will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of the LOS processing unit 11 provided in the microcomputer 10.

  As shown in FIG. 1, the LOS processing unit 11 includes an edge detection unit 101 (detection unit), an LOS output unit 102 (correction unit), an interrupt prohibition period setting unit 103 (setting unit), a timer 104 (time measurement unit), A reception power acquisition unit 105 (acquisition means) and an internal register 110 (storage unit) are provided. The internal register 110 also includes an interrupt flag 111 indicating whether or not interrupt processing described later is permitted, a received power value 112 indicating received power, and a module LOS signal output in the first state described later. The last state 113 indicating the value of is recorded. In the following description, the value of the interrupt flag 111 is “1” when the interrupt process is permitted, and the value of the interrupt flag is “0” when the interrupt process is prohibited. However, this is merely determined for convenience of explanation, and is not limited to this.

  The edge detection unit 101 is means for detecting an edge of the hardware LOS signal. The edge is detected both when the hardware LOS signal rises from the L level to the H level and when the hardware LOS signal falls from the H level to the L level.

  The LOS output unit 102 is a unit for correcting the hardware LOS signal that is the LOS signal before correction and generating the module LOS signal that is the LOS signal after correction. The LOS output unit 102 has a first state in which a module LOS signal having the same value as the input hardware LOS signal is output, and a value obtained by inverting the value of the last state 113 recorded in the internal register 110. A second state in which a module LOS signal is output.

  The LOS output unit 102 is configured to record the value of the module LOS signal output in the first state (same as the value of the hardware LOS signal input in the first state) as the last state 113. . For this reason, the value of the module LOS signal output in the second state is a value obtained by inverting the value of the module LOS signal output in the first state, in other words, the hardware LOS signal input in the first state. Matches the inverted value of.

  In the state transition of the LOS output unit 102, the edge detection unit 101 and the interrupt prohibition period setting unit 103 set the interrupt flag 111 (value “1” in the first state and value “0” in the second state). This is realized by operating while setting and referring to the timer 104.

  That is, when the edge detection unit 101 detects an edge when the value of the interrupt flag 111 is “1”, the edge detection unit 101 notifies the LOS output unit 102 and the interrupt prohibition period setting unit 103 that an edge has been detected. The LOS output unit 102 that has received notification that an edge has been detected transitions the state from the first state to the second state. At the same time, upon receiving notification that an edge has been detected, the interrupt prohibition period setting unit 103 sets (1) the value of the interrupt flag 111 to “0” and (2) an interrupt prohibition period according to the received power (3) The timer 104 is instructed to notify when the set interruption prohibition period has expired. When the interrupt prohibition period expires, the timer 104 notifies the LOS output unit 102 and the interrupt prohibition period setting unit 103 that the interrupt prohibition period has expired. The LOS output unit 102 that has received the notification that the interrupt prohibition period has expired transitions the state from the second state to the first state. At the same time, upon receiving notification that the interrupt prohibition period has expired, the interrupt prohibition period setting unit 103 sets the value of the interrupt flag 111 to “1”.

  When the edge detection unit 101 detects an edge, if the value of the interrupt flag 111 is “1”, the edge detection unit 101 notifies the LOS output unit 102 that the edge has been detected, and if the value of the interrupt flag 111 is “0”. For example, the LOS output unit 102 is not notified that an edge has been detected. Therefore, when the value of the interrupt flag 111 is “1”, the LOS output unit 102 outputs the value of the last state 113 recorded in the internal register 110 (as it is) as a module LOS signal. When the value of the embedded flag 111 is “0”, the LOS output unit 102 outputs a module LOS signal having a value obtained by inverting the value of the last state 113 recorded in the internal register 110.

  The interrupt prohibition period setting unit 103 prohibits interrupt prohibition according to the reception power value (reception power value 112 read from the internal register 110) before the optical signal is interrupted when the input of the optical signal is interrupted. When the period is set and the input of the optical signal is started, the interrupt prohibition period according to the value of the reception power after the input of the optical signal is started (the value of the reception power acquired from the reception power acquisition unit 105) Set. In any case, when the value of the reception power is large, the length of the interrupt prohibition period is set long, and when the value of the reception power is small, the length of the interrupt prohibition period is set short.

  The length of the interrupt prohibition period set by the interrupt prohibition period setting unit 103 only needs to be expressed by a monotonically increasing function of received power (a monotonically increasing function in a broad sense including a step function). An example of setting the interrupt prohibition period is shown in FIG. FIG. 3 is a graph showing the length of the interrupt prohibition period with respect to the magnitude of the received power. As shown in FIG. 3, the length of the interrupt prohibition period is represented by a linear function of reception power, or by a step function obtained by stepping a linear function of reception power. Can be set. Also, it may be set so as to be expressed by an n-order function (n is an integer of 2 or more) of received power, an exponential function, a logarithmic function, or the like, or expressed by a step function obtained by stepping these functions. Good.

  As described above, the timer 104 counts the set interruption prohibition period. When the timer count overflows, that is, when the interrupt prohibition period expires, the timer 104 notifies the LOS output unit 102 and the interrupt prohibition period setting unit 103 that the interrupt prohibition period has expired. As a signal for notifying the LOS output unit 102 and the interrupt prohibition period setting unit 103 that the interrupt prohibition period has expired, for example, when it is an interrupt prohibition period, it is set to L level and is not an interrupt prohibition period. In this case, a binary signal having an H level can be used, but the present invention is not limited to this.

  The reception power acquisition unit 105 samples (AD converts) the photocurrent supplied from the current mirror circuit 40 (more precisely, a voltage signal obtained by voltage-converting the photocurrent), and the sampled photocurrent The received power value calculated from the value is recorded as the received power value 112 in the internal register 110. Separately, the reception power acquisition unit 105 samples and samples the photocurrent supplied from the current mirror circuit 40, triggered by the edge detection unit 101 detecting an edge in the hardware LOS signal. The reception power value calculated from the photocurrent value is provided to the interrupt prohibition period setting unit 103.

[Operation of microcomputer]
An interrupt process performed by the LOS processing unit 11 included in the microcomputer 10 will be described below with reference to FIGS. FIG. 4 is a flowchart showing the flow of interrupt processing performed by the LOS processing unit 11. FIGS. 5A to 5G are timing charts showing the operation of the LOS processing unit 11 when the input of the optical signal is interrupted. FIGS. 5H to 5N are optical timing diagrams. It is a timing chart which shows operation | movement of the LOS process part 11 when the input of a signal is started.

  As shown in FIG. 5A, when the input of the optical signal is cut off (that is, when the optical signal is changed from the input state to the non-input state), as shown in FIG. The value of the hardware LOS signal rises from the L level to the H level. At this time, current noise is generated from the APD 21 due to fluctuations in the reverse bias voltage, and as a result, chattering occurs in the hardware LOS signal. The time from when the input of the optical signal is interrupted until the hardware LOS signal first rises is about 20 μs, and the pulse width of the first pulse constituting the chattering is about 2 μs at the shortest. Thereafter, chattering continues for a maximum of 5 ms.

  Similarly, as shown in FIG. 5 (h), the input of the optical signal starts (that is, when the optical signal is changed from the input state to the input state), as shown in FIG. 5 (i). The value of the hardware LOS signal falls from the H level to the L level. At this time, current noise is generated from the APD 21 due to fluctuations in the reverse bias voltage, and as a result, chattering occurs in the hardware LOS signal. The time from when the input of the optical signal is started until the hardware LOS signal first falls is about 20 μs, and the pulse width of the first pulse constituting the chattering is about 2 μs at the shortest. Thereafter, chattering continues for a maximum of 5 ms.

  Each of the interrupt processing executed when the first rising edge in the hardware LOS signal shown in FIG. 5B or the first falling edge of the hardware signal shown in FIG. The steps will be described with reference to FIGS.

  Step S101: When the edge detection unit 101 detects the first rising edge in the hardware LOS signal shown in FIG. 5B or the first falling edge of the hardware signal shown in FIG. The LOS output unit 102 and the interrupt prohibition period setting unit 103 are notified of the detection. Using the notification from the edge detection unit 101 as a trigger, the interrupt prohibition period setting unit 103 allows the interrupt processing to be performed with the value of the interrupt flag 111 as shown in FIGS. 5 (g) and 5 (n). From the value “1” indicating that the interrupt processing is prohibited to the value “0” indicating that the interrupt processing is prohibited. As described above, the edge detection unit 101 is configured to notify the interrupt prohibition period setting unit 103 that an edge has been detected only when the value of the interrupt flag 111 is “1”. ing. Therefore, the value of the interrupt flag 111 is updated only when the interrupt processing is permitted, triggered by the detection of an edge in the hardware LOS signal.

  Step S102: Using the notification from the edge detection unit 101 as a trigger, the LOS output unit 102 last outputs the value of the module LOS signal to be output to the internal register 110 as shown in FIGS. 5 (d) and 5 (k). The value of the hardware LOS signal recorded as the state 113 is switched to the value obtained by inverting the value of the hardware LOS signal recorded as the last state 113 in the internal register 110.

  Steps S103 to S105: After rewriting the value of the interrupt flag 111 to “0”, the interrupt prohibition period setting unit 103 sets an interrupt prohibition period. Specifically, in step S103, it is determined whether or not the input of the optical signal is cut off. If the input of the optical signal is cut off (YES in step S103), it is recorded in the internal register 110 in step S104. If the optical signal input is not interrupted (NO in step S103), the reception power value calculated by the reception power acquisition unit 105 is acquired in step S105. Then, the interrupt prohibition period setting unit 103 sets the interrupt prohibition period according to the value of the reception power read from the internal register 110 in step S104 or the value of the reception power acquired from the reception power acquisition unit 105 in step S105. The timer 104 is set so that an alarm is issued at the time (time t + Δt) when the interrupt prohibition period (time Δt) has elapsed from the current time (time t).

  Note that the determination executed by the interrupt prohibition period setting unit 103 in step S103 is realized by referring to the value of the last state 113 recorded in the internal register 110, for example. In this case, as shown in FIG. 5C, if the value of the last state 113 after detecting the edge is L level (inversion of H level), it is determined that the input of the optical signal is cut off. As shown in FIG. 5 (j), if the value of the last state 113 after detecting the edge is H level (inversion of L level), it can be determined that the input of the optical signal is not cut off. .

  The reception power acquisition unit 105 samples (AD converts) the photocurrent supplied from the current mirror circuit 40 (more precisely, a voltage signal obtained by converting the voltage of the photocurrent). The reception power value calculated from the photocurrent value is recorded in the internal register 110 as the reception power value 112. The sampling period of the reception power acquisition unit 105 is, for example, 25 ms. In this case, the reception power value recorded in the internal register 110 is updated every 25 ms. (In FIG. 5 (e) and FIG. 5 (l), the reception power calculation timing executed for each sampling period is indicated by a white circle). Therefore, in step S <b> 104, the interrupt prohibition period setting unit 103 reads from the internal register 110 the value of the reception power immediately before detecting an edge in the hardware LOS signal. The reception power acquisition unit 105 samples the photocurrent supplied from the current mirror circuit 40 using the edge detection unit 101 detecting an edge in the hardware LOS signal as a trigger, and calculates the value of the sampled photocurrent. The calculated reception power value is configured to be provided to the interrupt prohibition period setting unit 103 (in FIG. 5L, the reception power calculation timing triggered by edge detection is indicated by a black circle. Shown). Therefore, in step S <b> 105, the interrupt prohibition period setting unit 103 acquires from the reception power acquisition unit 105 the value of reception power immediately after detecting an edge in the hardware LOS signal.

  In step S101, the interrupt prohibition period setting unit 103 rewrites the value of the interrupt flag 111 (inhibits interrupt processing). In step S102, the value of the module LOS signal output by the LOS output unit 102 is switched. Both the processing (outputting a value obtained by inverting the last state) and the processing in which the interrupt prohibition period setting unit 103 sets the interrupt prohibition period in steps S103 to S105 are performed by the edge detection unit 101 using hardware. This is a process executed with the detection of an edge in the LOS signal as a trigger, and the execution order thereof is not limited to that shown in FIG. That is, it may be executed as shown in FIG. 4, may be executed in a different order, or may be executed in parallel (in parallel).

  Steps S106 to S107: When the interrupt prohibition period starts, the timer 104 lowers the value of the timer flag to L level as shown in FIGS. 5F and 5M, and the interrupt prohibition period expires. Until this is done (until determined as YES in step S107), the value of the timer flag is maintained at the L level as shown in FIGS. 5 (f) and 5 (m). When the interrupt prohibition period expires (when it is determined YES in step S107), the value of the timer flag is raised to the H level as shown in FIGS. 5 (f) and 5 (m).

  Step S108: The LOS output unit 102 updates the last state 113 recorded in the internal register 110, triggered by the expiration of the interrupt prohibition period and the value of the timer flag rising to H level. The update of the last state 113 is realized by, for example, sampling the hardware LOS signal supplied from the comparator 35 and recording the value of the sampled hardware LOS signal in the internal register 110 as the last state 113. The

  Step S109: When the update of the last state 113 is completed, the LOS output unit 102 inverts the value of the module LOS signal to be output with the value of the last state 113 recorded in the internal register 110 (the value before the update). The changed value is switched to the last state 113 value (updated value) recorded in the internal register 110.

  Step S110: Triggered by the expiration of the interrupt prohibition period and the value of the timer flag rising to the H level, the interrupt prohibition period setting unit 103, as shown in FIGS. 5 (g) and 5 (n) The value of the interrupt flag 111 is rewritten from a value “0” indicating that the interrupt processing is prohibited to a value “1” indicating that the interrupt processing is prohibited. In this example, the configuration for updating the value of the interrupt flag 111 is described using the expiration of the interrupt prohibition period as a trigger. However, the interrupt is triggered by the switching of the value of the output module LOS signal. A configuration for updating the value of the flag 111 may be adopted. When the latter configuration is adopted, the LOS output unit 102 notifies the interrupt prohibition period setting unit 103 that the value of the module LOS signal has been switched, or the interrupt prohibition period setting unit 103 notifies the internal register 110. A configuration in which the value of the recorded last state 113 is monitored may be employed.

  In the present embodiment, a configuration is adopted in which the LOS output unit 102 outputs a value obtained by inverting the value of the last state 113 as the value of the module LOS signal, triggered by detection of an edge in the hardware LOS signal. doing. This specifies the direction of the edge (that is, whether the value of the hardware LOS signal has changed from H level to L level or from L level to H level), and the module LOS signal's direction depends on the specified edge direction. In the case where the configuration for determining the value is adopted, the inventors have studied that the value of the module LOS signal is likely to be an erroneous value due to a pulse having a small pulse width generated in the early stage (especially at the beginning) of chattering. This is because it became clear.

  In addition, since the interruption prohibition period is set based on the reception power, when the optical signal is small and the chattering period is short, a short interruption prohibition period can be set. As a result, it is possible to immediately cope with a change in the optical signal that occurs after the short chattering converges.

  The interrupt process described above is a process from step S101 to step S110 that is started by using a change in the hardware LOS signal, that is, an edge as a trigger. The interrupt prohibition period is a period during which, when a new edge is detected during the interrupt process, it is prohibited to start the interrupt process using the newly detected edge as a trigger. Accordingly, even if an edge caused by chattering is detected, it is possible to prevent the value of the module LOS signal from changing accordingly.

  Further, when an edge is detected, the interrupt process is performed by interrupting the main operation of the microcomputer 10 shown in FIG. When the interrupt process ends, the microcomputer 10 resumes the main operation of the microcomputer 10 from the operation at the time when the interrupt process interrupted.

  In the present embodiment, the configuration in which the interrupt prohibition period is set according to the value of the reception power has been described, but the present invention is not limited to this. That is, the interrupt prohibition period may be constant (for example, 5 ms) regardless of the value of the reception power. In this case, for example, a configuration in which the interrupt prohibition period setting unit 103 and the reception power acquisition unit 105 are omitted, and the edge detection unit 101 directly sets the timer 104 can be employed.

  In the present embodiment, the LOS output unit 102 records the last state recorded in the internal register 110 when the interrupt prohibition period expires (at the time of transition from the second state to the first state). Although the configuration in which 113 is updated only once has been described, the present invention is not limited to this. That is, after the interrupt prohibition period expires, the LOS output unit 102 updates the value of the last state 113 at regular intervals regardless of whether or not an edge in the hardware LOS signal is detected. It may be adopted. In this case, even if it fails to match the value of the module LOS signal with the value of the hardware LOS signal when the interrupt prohibition period expires, the value of the module LOS signal is changed after the interrupt prohibition period expires. It can be matched with the value of the hardware LOS signal. For this reason, the reliability of the alarm quality based on the module LOS signal can be improved.

(Program and recording medium)
The LOS processing unit 11 included in the microcomputer 10 may be configured by hardware logic. Alternatively, it may be realized by software using a CPU (Central Processing Unit) as follows.

  In other words, the LOS processing unit 11 includes a CPU such as an MPU that executes instructions of a program that realizes each function, a ROM (Read Only Memory) that stores the program, and a RAM (Random Access) that expands the program into an executable format. Memory) and a storage device (recording medium) such as a memory for storing the program and various data.

  The object of the present invention is not limited to the case where the program memory of the LOS processing unit 11 is fixedly supported, and the program code (executable program, intermediate code program, or source program) of the above program is recorded. This can also be achieved by supplying a recording medium to the microcomputer 10 and reading and executing the program code recorded on the recording medium.

  The recording medium is not limited to a specific structure or type. That is, the recording medium includes, for example, a tape system such as a magnetic tape and a cassette tape, a magnetic disk such as a floppy (registered trademark) disk / hard disk, and an optical disk such as a CD-ROM / MO / MD / DVD / CD-R. System, a card system such as an IC card (including a memory card) / optical card, or a semiconductor memory system such as a mask ROM / EPROM / EEPROM / flash ROM.

  Further, even if the LOS processing unit 11 (or the microcomputer 10) is configured to be connectable to a communication network, the object of the present invention can be achieved. In this case, the program code is supplied to the LOS processing unit 11 via the communication network. This communication network is not limited to a specific type or form as long as it can supply the program code to the LOS processing unit 11. For example, the Internet, intranet, extranet, LAN, ISDN, VAN, CATV communication network, virtual private network, telephone line network, mobile communication network, satellite communication network, etc. may be used.

  The transmission medium constituting the communication network may be any medium that can transmit the program code, and is not limited to a specific configuration or type. For example, even with wired lines such as IEEE 1394, USB, power line carrier, cable TV line, telephone line, ADSL (Asymmetric Digital Subscriber Line) line, infrared rays such as IrDA and remote control, Bluetooth (registered trademark), 802.11 wireless, HDR, mobile phone It can also be used by radio such as a telephone network, a satellite line, and a terrestrial digital network. The present invention can also be realized in the form of a computer data signal embedded in a carrier wave in which the program code is embodied by electronic transmission.

[Additional Notes]
The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in the embodiments are also included. It is included in the technical scope of the present invention.

  The present invention can be suitably used for an optical receiver such as an SFP transceiver.

1 Optical receiver (optical receiver)
10 Microcomputer (LOS signal correction device)
11 LOS processing unit 12 AD conversion unit 13 Master I / F
14 Slave I / F
20 Small light-receiving module 21 Avalanche photodiode (photodetector)
22 Transimpedance amplifier 30 Integrated circuit 31 Driver amplifier 32 Limiting amplifier 33 Output buffer amplifier 34 Peak detector (generation means)
35 Comparator (Generation means)
36 Reference voltage source (generation means)
40 Current mirror circuit 50 Reverse bias generation circuit 101 Edge detection unit (detection means)
102 LOS output unit (correction means)
103 Interrupt prohibition period setting section (setting means)
104 Timer (time measuring means)
105 Received power acquisition unit (acquisition means)
110 Internal register (storage unit)
111 Interrupt flag 112 Received power value 113 Last state

Claims (9)

A LOS signal correction device for correcting a LOS signal generated from an output signal of a photodetector,
Detecting means for detecting an edge in the LOS signal before correction;
A first state in which the value of the LOS signal before correction is written in the storage unit, and the value of the LOS signal before correction written in the storage unit is output as the value of the LOS signal after correction, and the first Correction means having a second state for outputting a value obtained by inverting the value of the LOS signal before correction written in the storage unit in a state as the value of the LOS signal after correction;
Timing means for measuring an elapsed time from the time when the correction means transitions to the second state,
The correction means transitions from the first state to the second state triggered by the detection means detecting an edge in the LOS signal before correction, and the elapsed time measured by the time measurement means is predetermined. Transition from the second state to the first state is triggered by reaching the time of
A LOS signal correction apparatus characterized by the above. The predetermined time is longer than the duration of chattering that occurs after the value of the LOS signal before correction is inverted,
The LOS signal correction apparatus according to claim 1, wherein Acquisition means for acquiring the received power of the optical signal input to the photodetector;
The apparatus further comprises setting means for setting the predetermined time according to the reception power acquired by the acquisition means, and the predetermined time set by the setting means is represented by a monotonically increasing function of reception power.
The LOS signal correction apparatus according to claim 1 or 2, wherein The acquisition means writes the acquired received power value in the storage unit when an optical signal is input, and the received power value written in the storage unit after the optical signal input is cut off. Provide to the setting means,
4. The LOS signal correction apparatus according to claim 3, wherein The correction means writes the value of the LOS signal before correction sampled when transitioning from the second state to the first state into the storage unit.
The LOS signal correction apparatus according to claim 1, wherein the LOS signal correction apparatus is one of the first to fourth aspects. The correction means writes the value of the LOS signal before correction periodically sampled in the first state into the storage unit;
The LOS signal correction apparatus according to claim 1, wherein the LOS signal correction apparatus is one of the first to fourth aspects.   7. A LOS signal generation apparatus comprising: the LOS signal correction apparatus according to claim 1; and generation means for generating the LOS signal before correction. A first state in which the value of the LOS signal before correction is written in the storage unit, and the value of the LOS signal before correction written in the storage unit is output as the value of the LOS signal after correction, and the first From the output signal of the photodetector, using correction means having a second state that outputs a value obtained by inverting the value of the LOS signal before correction written in the storage unit in the state as the value of the LOS signal after correction. A LOS signal correction method for correcting a generated LOS signal, comprising:
A detection step of detecting an edge in the LOS signal before correction;
A first transition step for transitioning the state of the correction means from the first state to the second state triggered by the detection of an edge in the LOS signal before correction in the detection step;
A time measuring step for measuring an elapsed time from the time when the correction means transits to the second state;
A second transition step for transitioning the state of the correction means from the second state to the first state, triggered by the fact that the elapsed time counted in the time counting step has reached a predetermined time; Including,
And a LOS signal correction method.   An optical receiver comprising the LOS signal generation device according to claim 7.

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