JP2012205099A - Received light power monitoring method, manufacturing method of received light power monitoring circuit, communication system, optical transceiver and received light power monitoring circuit - Google Patents

Abstract

Even when the power of an optical signal is small, a sufficient measurement range of the received light power is secured by obtaining a digital value that accurately indicates the received light power.
A light reception power monitor circuit 31 includes a light reception current supply circuit 51 for supplying a current corresponding to an output current of a light reception element for receiving an optical signal, and a current supplied from the light reception current supply circuit 51. Digital conversion circuit 52 for converting the level into a digital value, and the current supplied to the digital conversion circuit 52, or an offset for adjusting the offset of the voltage converted from the current into the digital value. And an adjustment circuit 53.
[Selection] Figure 4

Description

  The present invention relates to a received light power monitoring method, a received light power monitor circuit manufacturing method, a communication system, an optical transceiver, and a received light power monitor circuit, and more particularly, a received light power monitor method for measuring received light power based on an output current of a light receiving element. The present invention relates to a method for manufacturing a received light power monitor circuit, a communication system, an optical transceiver, and a received light power monitor circuit.

  In recent years, the Internet has become widespread, and users can access various information on sites operated in various parts of the world and obtain the information. Along with this, devices capable of broadband access such as ADSL (Asymmetric Digital Subscriber Line) and FTTH (Fiber To The Home) are rapidly spreading.

  In IEEE Std 802.3ah (registered trademark) -2004 (non-patent document 1), a plurality of home side devices (ONU: Optical Network Unit) share an optical communication line, and a station side device (OLT: Optical Line Terminal). One method of a passive optical network (PON), which is a medium-sharing communication that performs data transmission with the network, is disclosed. That is, EPON (Ethernet (registered trademark) PON) in which all information is communicated in the form of an Ethernet (registered trademark) frame, including user information passing through the PON and control information for managing and operating the PON, and EPON An access control protocol (MPCP (Multi-Point Control Protocol)) and an OAM (Operations Administration and Maintenance) protocol are defined. By exchanging MPCP frames between the station side device and the home side device, the home side device joins and leaves, and uplink access multiplexing control is performed. Non-Patent Document 1 describes a registration method for a new home device, a report indicating a bandwidth allocation request, and a gate indicating a transmission instruction using an MPCP message.

  In addition, IEEE 802.3av (registered trademark) -2009 is standardized as the next generation technology of GE-PON (Giga Bit Ethernet (registered trademark) Passive Optical Network), which is an EPON realizing a communication speed of 1 gigabit / second. Even in the 10 G-EPON, that is, the EPON corresponding to a communication speed of 10 gigabits / second, the access control protocol is premised on MPCP.

  By the way, there is a case where a function for measuring the received light power is required in the home side apparatus or the station side apparatus in order to confirm the state of the optical communication line.

  As an example of a technique for measuring the received light power in the PON system, for example, Japanese Patent Laying-Open No. 2010-212900 (Patent Document 1) discloses the following configuration. That is, the received light power monitor circuit includes a first A / D converter that identifies a burst cell to be measured from the analog reception signal, and a second A / D that continuously A / D converts the analog reception signal. Based on the difference between the converter, storage means for storing the minimum value of the measurement value from the second A / D converter, and the measurement result from the first A / D converter and the minimum value And a control arithmetic circuit for correcting the offset.

IEEE Std 802.3ah (registered trademark) -2004

JP 2010-212900 A

  In such a received light power monitor circuit using an A / D converter, the digital output value of the A / D converter may become zero when the power of the optical signal input to the apparatus is small. In such a case, the digital value indicating the received power until the power of the optical signal increases to some extent from the no-input state where no optical signal is input to the device is uniformly zero, so the received power measurement range Becomes narrower.

  However, Patent Document 1 does not disclose a configuration for solving such a problem.

  The present invention has been made in order to solve the above-described problems. The purpose of the present invention is to obtain a digital value that accurately indicates the received light power even when the power of the optical signal is low, thereby increasing the measurement range of the received power. To provide a light reception power monitoring method, a light reception power monitor circuit manufacturing method, a communication system, an optical transceiver, and a light reception power monitor circuit that can be sufficiently secured.

  In order to solve the above-described problems, a light receiving power monitoring method according to an aspect of the present invention provides a light receiving current supply for supplying a current corresponding to an output current of a light receiving element for receiving an optical signal from an optical communication line. A light receiving power monitor circuit comprising: a circuit; and a digital conversion circuit for converting a level of a current supplied from the light receiving current supply circuit into a digital value. The current supplied to the digital conversion circuit or the voltage converted from the current is converted into the digital value so that the digital value in a state where the power monitor circuit is not receiving becomes zero or more. Adjusting the voltage offset; inputting optical signals of different powers to the light receiving element; and taking the digital values corresponding to the powers. A step of calculating a correspondence relationship between the digital value and the power value of the optical signal based on each acquired digital value and the corresponding power value of the optical signal; and Operating in a state connected to the optical communication line, and measuring the power of the optical signal using the correspondence.

  With such a method, even when the power of the optical signal is small, it is possible to prevent the digital conversion value of the digital conversion circuit from becoming zero, so that a sufficient measurement range of the received light power can be ensured.

  In order to solve the above problems, a method of manufacturing a light receiving power monitor circuit according to an aspect of the present invention includes a light receiving current supply circuit for supplying a current corresponding to an output current of a light receiving element for receiving an optical signal, and Preparing a light receiving power monitor circuit comprising a digital conversion circuit for converting the level of the current supplied from the light receiving current supply circuit into a digital value; and the light receiving power monitor circuit receives the optical signal. The offset of the current supplied to the digital conversion circuit or the voltage converted from the current and converted to the digital value is adjusted so that the digital value in a state of not being is zero or more. Inputting optical signals of different powers to the light receiving element and acquiring the digital values corresponding to the powers, and acquiring Each said digital values, and based on the power value of the corresponding of the optical signal, and calculates a correspondence between the power value of the digital value and the optical signal, and a step of storing in the optical power monitoring circuit.

  With such a method, even when the power of the optical signal is small, the digital conversion value of the digital conversion circuit can be prevented from becoming zero, so the received light power that can sufficiently secure the measured range of received light power A monitor circuit can be provided.

  In order to solve the above problems, a communication system according to an aspect of the present invention includes a station-side device and a home-side device for transmitting and receiving optical signals to and from the station-side device via an optical communication line. The home-side apparatus supplies a light receiving current supply circuit for supplying a current corresponding to an output current of a light receiving element for receiving an optical signal from the optical communication line, and a power supplied from the light receiving current supply circuit. A digital conversion circuit for converting a level of a current to be converted into a digital value, wherein the communication system is configured so that the digital value becomes zero or more in a state where the optical signal is not received. An offset adjustment unit for adjusting an offset of the current supplied to the voltage or a voltage converted from the current and converted into the digital value; and the light receiving element When an optical signal with different power is output, the digital value acquisition unit for acquiring the digital value corresponding to each of the powers, the digital value acquired by the digital value acquisition unit, and the corresponding The correspondence calculation unit for calculating the correspondence between the digital value and the power value of the optical signal based on the power value of the optical signal, and the state where the light receiving power monitor circuit is connected to the optical communication line And a power measuring unit for measuring the power of the optical signal using the correspondence relationship.

  With such a configuration, even when the power of the optical signal is small, it is possible to prevent the digital conversion value of the digital conversion circuit from becoming zero, so that a sufficient measurement range of the received light power can be secured.

  In order to solve the above-described problems, an optical transceiver according to an aspect of the present invention is an optical transceiver that is detachable from an optical communication device for transmitting / receiving an optical signal to / from another device, and receives the optical signal. And a light receiving power monitor circuit for measuring the power of the optical signal, and the light receiving power monitor circuit generates a current corresponding to an output current of the light receiving element for receiving the optical signal. A light receiving current supply circuit for supplying, a digital conversion circuit for converting a level of current supplied from the light receiving current supply circuit into a digital value, and the current supplied to the digital conversion circuit, or the current An offset adjustment circuit for adjusting an offset of the converted voltage that is converted to the digital value, and the optical transceiver further includes: Storing the correspondence between the power value of the digital value and the optical signal converted by the digital conversion circuit, the relationship comprises a readable storage unit from the optical communication apparatus.

  As described above, the correspondence relationship is stored in the optical transceiver that can be attached to and detached from the optical communication device, and the correspondence relationship is read from the optical communication device, so that the optical transceiver is replaced with a new optical transceiver having different electrical characteristics. However, the received light power can be measured appropriately.

  In order to solve the above problems, a light receiving power monitor circuit according to an aspect of the present invention includes a light receiving current supply circuit for supplying a current corresponding to an output current of a light receiving element for receiving an optical signal, and the light receiving power. A digital conversion circuit for converting the level of the current supplied from the current supply circuit into a digital value, and the current supplied to the digital conversion circuit or a voltage obtained by converting the current into the digital value. And an offset adjustment circuit for adjusting the offset of the applied voltage.

  With such a configuration, even when the power of the optical signal is small, it is possible to prevent the digital conversion value of the digital conversion circuit from becoming zero, so that a sufficient measurement range of the received light power can be secured.

  Preferably, the offset adjustment circuit includes a resistor connected between a node to which a fixed voltage is supplied and an input terminal of the digital conversion circuit for receiving a current supplied from the light receiving current supply circuit.

  With such a configuration, even when the power of the optical signal is small, it is possible to prevent the digital conversion value of the digital conversion circuit from becoming zero, so that a sufficient measurement range of the received light power can be secured. In addition, the configuration in which a bias current is applied using a resistor can extend the measurement range of received light power with a simple circuit.

  Preferably, the offset adjustment circuit includes a digital / analog converter for supplying a current of a level corresponding to a given digital value to the digital conversion circuit, and the digital conversion circuit is connected to the light receiving current supply circuit. The level of the combined current of the supplied current and the current supplied from the digital / analog converter is converted into a digital value.

  As described above, since the bias current is supplied using the digital / analog converter, the offset current level can be easily changed, so that the optimum adjustment can be performed according to the variation in the electrical characteristics of each circuit. It becomes. In addition, it is easy to adjust the digital conversion value of the digital conversion circuit to zero when no optical signal is input. In addition, as the digital / analog converter, for example, a built-in CPU can be used, and an increase in circuit scale can be prevented.

  Preferably, the digital conversion circuit includes a current / voltage conversion circuit for converting a current supplied from the light receiving current supply circuit into a voltage, and a level of the voltage converted by the current / voltage conversion circuit into a digital value. An analog / digital converter for converting, and the offset adjustment circuit includes a first resistor connected between a node to which a first fixed voltage is supplied and an input terminal of the analog / digital converter. A second resistor connected between a node to which a second fixed voltage is supplied and an input end of the analog / digital converter, an output end of the current / voltage conversion circuit, and the first resistor And a third resistor connected between the connection node of the second resistor.

  With such a configuration, even when the power of the optical signal is small, it is possible to prevent the digital conversion value of the digital conversion circuit from becoming zero, so that a sufficient measurement range of the received light power can be secured.

  Preferably, the light reception power monitor circuit further includes a storage unit for storing a correspondence relationship between the digital value converted by the digital conversion circuit and the power value of the optical signal.

  As described above, since the correspondence relationship is stored in the light reception power monitor circuit, for example, a light reception power value can be calculated in a device including the light reception power monitor circuit and output to a personal computer or the like connected to the device. The received light power value can be easily obtained.

  According to the present invention, even when the power of an optical signal is low, a sufficient measurement range of received light power can be secured by obtaining a digital value that accurately indicates the received light power.

It is a figure which shows the structure of the PON system which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure of the home side apparatus in the PON system which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure by the side of reception of the optical transceiver in the home side apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the structure of the light reception power monitor circuit in the home side apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the relationship between the input voltage of an analog / digital converter, and a digital conversion value at the time of assuming that the offset adjustment circuit is not provided in the light reception power monitor circuit which concerns on the 1st Embodiment of this invention. It is a figure which shows the relationship between the input voltage and digital conversion value of an analog / digital converter in the light reception power monitor circuit which concerns on the 1st Embodiment of this invention. It is a figure which shows the other example of the relationship between the input voltage and digital conversion value of an analog / digital converter in the light reception power monitor circuit which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the procedure of the manufacturing method of the light reception power monitor in the PON system which concerns on the 1st Embodiment of this invention, and the light reception power monitor method. It is a figure which shows an example of the measurement result of the input power and digital conversion value of an optical signal. It is a figure which shows an example of the measurement result of the input power and digital conversion value of an optical signal. It is a figure which shows the structure of the light reception power monitor circuit which concerns on the 2nd Embodiment of this invention. It is a figure which shows the structure of the light reception power monitor circuit which concerns on the 3rd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<First Embodiment>
FIG. 1 is a diagram showing a configuration of a PON system according to the first embodiment of the present invention.

  Referring to FIG. 1, a PON system 301 is, for example, a 10G-EPON, and includes home-side devices 202A, 202B, 202C, and 202D, a station-side device 201, and splitters SP1 and SP2. Home-side devices 202A, 202B, 202C and station-side device 201 are connected via splitters SP1 and SP2 and optical fiber OPTF, and transmit / receive optical signals to / from each other. The home side apparatus 202D and the station side apparatus 201 are connected via the splitter SP2 and the optical fiber OPTF, and transmit / receive optical signals to / from each other.

  FIG. 2 is a diagram showing the configuration of the home device in the PON system according to the first embodiment of the present invention.

  Referring to FIG. 2, home device 202 includes optical transceiver 21, PON reception processing unit 22, buffer memory 23, UN transmission processing unit 24, UNI (User Network Interface) port 25, and UN reception processing. Unit 26, buffer memory 27, PON transmission processing unit 28, and control unit 29.

  The optical transceiver 21 is detachable from the home device 202. The optical transceiver 21 receives the downstream optical signal transmitted from the station-side device 201, converts it into an electrical signal, and outputs it.

  The PON reception processing unit 22 reconstructs a frame from the electrical signal received from the optical transceiver 21 and distributes the frame to the control unit 29 or the UN transmission processing unit 24 according to the type of the frame. Specifically, the PON reception processing unit 22 outputs the data frame to the UN transmission processing unit 24 via the buffer memory 23 and outputs the control frame to the control unit 29.

  The control unit 29 generates a control frame including various control information and outputs the control frame to the UN transmission processing unit 24.

  The UN transmission processing unit 24 transmits the data frame received from the PON reception processing unit 22 and the control frame received from the control unit 29 to a user terminal such as a personal computer (not shown) via the UNI port 25.

  The UN reception processing unit 26 outputs the data frame received from the user terminal via the UNI port 25 to the PON transmission processing unit 28 via the buffer memory 27, and the control frame 29 receives the control frame received from the user terminal via the UNI port 25. Output to.

  The control unit 29 performs home-side processing related to control and management of the PON line between the station-side device 201 and the home-side device 202, such as MPCP and OAM. That is, various controls such as access control are performed by exchanging MPCP messages and OAM messages with the station-side apparatus 201 connected to the PON line. The control unit 29 generates a control frame including various control information and outputs it to the PON transmission processing unit 28. In addition, the control unit 29 performs various setting processes for each unit in the home device 202.

  The PON transmission processing unit 28 outputs the data frame received from the UN reception processing unit 26 and the control frame received from the control unit 29 to the optical transceiver 21.

  The optical transceiver 21 converts the data frame and control frame received from the PON transmission processing unit 28 into optical signals and transmits them to the station apparatus 201.

  FIG. 3 is a diagram showing a configuration on the receiving side of the optical transceiver in the home-side apparatus according to the first embodiment of the present invention.

  Referring to FIG. 3, optical transceiver 21 includes light receiving element APD, TIA (transimpedance amplifier) 81, LIA (limit amplifier) 82, CDR (Clock and Data Recovery) 83, equalizer circuit 84, and output. It includes a buffer 85, capacitors C3 to C6, power supplies 86 to 90, a received light power monitor circuit 31, a CPU (Central Processing Unit) 70, and a master I / F (interface) 71. The CPU 70 includes a storage unit 73 that is, for example, an EEPROM (Electrically Erasable Programmable Read Only Memory).

  The light receiving element APD is an avalanche photodiode, for example, and converts the optical signal received from the station side device 201 into a current and outputs the current.

  When the distance on the optical fiber between the home-side device 202 and the station-side device 201 is short, the output current of the light receiving element APD is, for example, about 2 milliamperes, and on the optical fiber between the home-side device 202 and the station-side device 201 When the distance is long, the output current of the light receiving element APD is, for example, about 10 microamperes.

  The TIA 81 converts the current received from the light receiving element APD into a voltage and outputs the voltage to the LIA 82 via the capacitors C3 and C4.

  The LIA 82 binarizes the voltage level received from the TIA 81 and outputs it as received data.

  The CDR 83 reshapes the received data received from the LIA 82, extracts the timing from the received data, and performs the retiming of the received data based on the extracted timing, thereby establishing synchronization with the station side device 201. To do.

  The equalizer circuit 84 performs waveform shaping of received data received from the CDR 83, for example, corrects phase distortion and outputs the result.

  The output buffer 85 amplifies the reception data received from the equalizer circuit 84 and outputs the amplified data to the PON reception processing unit 22 via the capacitors C5 and C6. For example, the output buffer 85 outputs the received data from the signal lines OUTP and OUTN as a balance signal.

  The power supplies 86 to 90 supply, for example, current as electric power to the TIA 81, LIA 82, CDR 83, equalizer circuit 84, and output buffer 85, respectively. The power supplies 88 to 90 supply power to the CDR 83, the equalizer circuit 84, and the output buffer 85, respectively, when the reception disable signal is inactive, and the power when the reception disable signal is activated. Stop supplying.

  The light receiving power monitor circuit 31 is connected between the power supply node N1 to which the power supply voltage Vapd is supplied and the cathode of the light receiving element APD, and measures the output current of the light receiving element APD. Here, the power supply voltage Vapd is generated, for example, by boosting the power supply voltage Vdd of the optical transceiver 21 so that a sufficient reverse bias voltage is applied to the light receiving element APD.

  For example, the CPU 70 exchanges various data with the control unit 29 via an I2C bus including the signal line SCL and the signal line SDA. The storage unit 73 in the CPU 70 stores an offset adjustment amount of an offset adjustment circuit 53 to be described later, and a coefficient of a power conversion function indicating a correspondence relationship between a digital conversion value of the digital conversion circuit 52 and the power of the optical signal.

  The master I / F 71 provides an interface function between the CPU 70 and the I2C bus.

  FIG. 4 is a diagram showing a configuration of a received light power monitor circuit in the home-side apparatus according to the first embodiment of the present invention.

  Referring to FIG. 4, light reception power monitor circuit 31 includes a current mirror circuit (light reception current supply circuit) 51, a digital conversion circuit 52, and a storage unit 73. The received light power monitor circuit 31 includes a digital / analog converter (DAC) 53 as an offset adjustment circuit. The digital conversion circuit 52 includes a current / voltage conversion circuit 54 and an analog / digital converter (ADC) 55.

  The current mirror circuit 51 is connected between the power supply node N1 and the cathode of the light receiving element APD, and generates a mirror current corresponding to the output current of the light receiving element APD, that is, the current flowing between the power supply node N1 and the light receiving element APD. This is supplied to the conversion circuit 52.

  Thus, by providing the current mirror circuit 51, the circuit on the side for measuring the light reception power of the light receiving element APD, that is, the light receiving power monitor circuit 31 is electrically connected to the main signal circuit on the light receiving element APD side operating at a high speed of 10 GHz. It can prevent affecting the characteristics.

  The digital conversion circuit 52 converts the level of the current supplied from the current mirror circuit 51 into a digital value. More specifically, in the digital conversion circuit 52, the current / voltage conversion circuit 54 converts the current supplied from the current mirror circuit 51 into the voltage VADC. The analog / digital converter 55 converts the level of the voltage VADC converted by the current / voltage conversion circuit 54 into a digital value.

  The offset adjustment circuit 53 adjusts the offset of the current supplied to the digital conversion circuit 52 by supplying a bias current to the digital conversion circuit 52. More specifically, the digital / analog converter 53 supplies a current of a level corresponding to the given digital value to the digital conversion circuit 52. The digital conversion circuit 52 converts the level of the combined current of the current supplied from the current mirror circuit 51 and the current supplied from the digital / analog converter 53 into a digital value.

  The storage unit 73 stores the correspondence between the digital value converted by the digital conversion circuit 52 and the power value of the optical signal. This correspondence can be read from the control unit 29 in the home device 202.

  Here, the optical signal from the station-side apparatus 201 is a pulse-like signal, and is controlled so that the ratio of the logic high level and the logic low level in a certain period is substantially equal.

  The operating frequency band of the light receiving power monitor circuit 31 is limited by the conversion speed of the analog / digital converter 55, and is, for example, 1 MHz band. That is, the analog / digital converter 55 converts the current level into a digital value at a sampling period longer than the period of the optical signal.

  With such a configuration in which analog / digital conversion is performed on such an optical signal at a sampling period longer than the period of the optical signal, an average value of received light power can be obtained.

  FIG. 5 is a diagram showing the relationship between the input voltage of the analog / digital converter and the digital conversion value when it is assumed that no offset adjustment circuit is provided in the received light power monitor circuit according to the first embodiment of the present invention. is there.

  Referring to FIG. 5, consider the case where analog / digital converter 55 has a negative offset. That is, when the input voltage VADC of the analog / digital converter 55 is V1 larger than zero, the digital conversion value of the analog / digital converter 55 is zero.

  In this case, even when the input voltage VADC of the analog / digital converter 55 is not zero, that is, when the input voltage VADC is V1 or less, the digital conversion value of the analog / digital converter 55 is zero. Become.

  Then, with respect to the received light power from the no-input state until the input voltage VADC becomes V1, the digital conversion value of the analog / digital converter 55 indicating the measurement result of the output current of the light receiving element APD becomes zero. It cannot be measured.

  That is, the required measurement range is the range from the no-input state to the input voltage VADC being V3, whereas the minimum value of the actual measurable range is V1.

  Specifically, the minimum reception sensitivity standard of the home side device in 10G-EPON is “−28.5 dBm”, the maximum reception sensitivity standard is “−10 dBm”, and the damage threshold, that is, the light receiving element APD is damaged. The minimum value of power that can be generated is “−9 dBm”.

  For this reason, the measurement range including the front and rear margins is set to, for example, “−30 dBm (1 μW) to −7 dBm (200 μW)”. In this case, the dynamic range of the analog / digital converter 55 is at least 23 dB.

  Here, the resolution of the analog / digital converter 55 is 16 bits (= 65536), and the range of the input voltage VADC is 0V to 1.8V. That is, about 27.5 μV / digit.

When the offset voltage of the analog / digital converter 55 is 0 V, that is, when V1 shown in FIG. 5 is zero, the dynamic range is 10 × log ₁₀ (2 ¹⁶ ) = 48.16 [dB].

However, when V1 is, for example, 15 mV, 48.16-10 × log ₁₀ (15000 / 27.5) = 20.8 [dB]. That is, the analog / digital converter 55 cannot satisfy the minimum required dynamic range of 23 dB.

  Further, the offset of the current supplied to the current / voltage conversion circuit 54, that is, the dark current supplied to the current / voltage conversion circuit 54 in the no-input state varies, for example, in the range of 10 μA to 20 μA due to individual differences, and is averaged. 15 μA.

If the light receiving sensitivity R of the light receiving element APD is 1.0 [A / W] and the multiplication factor M is 10, the output current Iapd of the light receiving element APD is expressed by the following equation.
Iapd [A] = Pin [W] × M × R [A / W] = 10 [A / W] × Pin [W]

  From this equation, when the current offset is 15 μA as described above, an optical signal of 1.5 μW≈−28.24 dBm or less cannot be measured correctly, and the measurement range cannot be satisfied.

  FIG. 6 is a diagram showing the relationship between the input voltage of the analog / digital converter and the digital conversion value in the received light power monitor circuit according to the first embodiment of the present invention.

  Referring to FIG. 6, for example, if V1 shown in FIG. 5 is 15 mV, offset adjustment circuit 53 sets the level of the bias current supplied to current / voltage conversion circuit 54 to the state in which the bias current is not supplied. In comparison, the input voltage VADC is set to a value that increases more than 15 mV.

  Thereby, the analog / digital converter 55 can have a positive offset. That is, when the input voltage VADC of the analog / digital converter 55 is zero, the digital conversion value of the analog / digital converter 55 can be a positive value.

  In this case, even if the level of the input voltage VADC of the analog / digital converter 55 is small, the digital conversion value of the analog / digital converter 55 does not become zero. It is also possible to distinguish between an optical signal input state and a no-input state. Therefore, the received light power can be accurately measured over a wide range. However, when the bias current is set in this way, the maximum value V2 of the measurable range is smaller than that shown in FIG. 5, so that the maximum value of the required measurement range is shown in FIG. V2 may be smaller than V3.

  FIG. 7 is a diagram showing another example of the relationship between the input voltage of the analog / digital converter and the digital conversion value in the received light power monitor circuit according to the first embodiment of the present invention.

  Referring to FIG. 7, for example, if V1 shown in FIG. 5 is 15 mV, offset adjustment circuit 53 sets the level of the bias current supplied to current / voltage conversion circuit 54 to the state in which the bias current is not supplied. In comparison, the input voltage VADC is set to a value that increases by 15 mV.

  Thus, when the input voltage VADC of the analog / digital converter 55 is zero, the digital conversion value of the analog / digital converter 55 is zero, and when the input voltage VADC of the analog / digital converter 55 is greater than zero, The digital conversion value of the analog / digital converter 55 can be a positive value.

  Further, since the maximum value V2 of the measurable range is larger than that shown in FIG. 6, V2 can be more reliably increased than the required maximum value V3 of the measurement range. Further, the measurable range 0 to V2 in the case shown in FIG. 7 is the same length on the drawing as the measurable range V1 to V2 in the case shown in FIG. 5, but the dynamic range converted in decibels is the case shown in FIG. Larger than Therefore, the received light power can be correctly measured in a wider range.

  FIG. 8 is a flowchart showing a method of manufacturing a received light power monitor and a received light power monitor method in the PON system according to the first embodiment of the present invention.

  Referring to FIG. 8, first, a received light power monitor circuit 31 is prepared (step S1).

  Next, the offset of the current supplied to the digital conversion circuit 52 is adjusted so that the digital value in a state where the received light power monitor circuit 31 does not receive the optical signal becomes zero or more (step S2).

  Next, optical signals having different powers are input to the light receiving element APD, and digital values corresponding to the respective powers are acquired (step S3).

  Next, based on each acquired digital value and the power value of the corresponding optical signal, a correspondence relationship between the digital conversion value and the power value of the optical signal is calculated and stored in the storage unit 73 (step S4).

  Next, the light receiving power monitor circuit 31 is operated in a state where it is connected to the optical communication line, that is, the optical fiber OPTF, and the power of the optical signal is measured using the above correspondence (step S5).

  Here, as a method of calculating the correspondence between the digital conversion value and the power value of the optical signal, for example, a method of calculating a function indicating the correspondence using a multiple simultaneous equation is conceivable.

  9 and 10 are diagrams illustrating examples of measurement results of the input power of the optical signal and the digital conversion value.

  Referring to FIG. 9, for example, a digital conversion value DAT when the input power of the optical signal is 1 μW, a digital conversion value DAT when it is 10 μW, and a digital conversion value DAT when it is 200 μW are acquired.

  Referring to FIG. 10, in this measurement result, the digital conversion value DAT is zero when there is no input, the digital conversion value DAT is 100 when the input power of the optical signal is 1 μW, and the input power of the optical signal is The digital conversion value DAT is 1300 when the power is 10 μW, and the digital conversion value DAT is 40000 when the input power of the optical signal is 200 μW.

  Then, the measurement results at three points other than when the digital conversion value DAT is zero are substituted into the simultaneous equations, and the coefficient of the power conversion function indicating the correspondence between the digital conversion value DAT and the power value of the optical signal is calculated. Then, the calculated coefficient is stored in the storage unit 73.

  The method for calculating the relationship between the digital conversion value and the power value of the optical signal is not limited to the method using the multiple simultaneous equations, and for example, the following method can be considered.

  That is, a digital conversion value corresponding to the maximum power value of the optical signal, a minimum power value of the optical signal, that is, a digital conversion value corresponding to 0 watt, and one or more powers between the minimum power value and the maximum power value of the optical signal Get the digital conversion value corresponding to the value. Then, using these measurement results, the horizontal axis is the input power, the vertical axis is the digital conversion value, and a polygonal line approximation is performed.

  When measuring the received light power of the home side device 202, for example, the CPU 70 uses the coefficient of the power conversion function stored in the storage unit 73 and uses the power value corresponding to the digital value DAT received from the analog / digital converter 55. Is output to the control unit 29 via the I2C bus.

  The control unit 29 transfers the power value received from the CPU 70 to an information processing terminal such as a personal computer connected to the home device 202, and the power value is displayed on the information processing terminal. This power value is, for example, an absolute value such as watts or dBm.

  Instead of the CPU 70 obtaining the power value, the CPU 70 outputs the digital conversion value of the analog / digital converter 55 via the I2C bus, and the personal computer or the like connected to the home side device 202 calculates and displays the power value. It may be configured to.

  By the way, in the light receiving power monitor circuit using the A / D converter, the digital output value of the A / D converter may become zero when the power of the optical signal input to the apparatus is small. In such a case, the digital value indicating the received power until the power of the optical signal increases to some extent from the no-input state where no optical signal is input to the device is uniformly zero, so the received power measurement range Becomes narrower.

  In contrast, in the light receiving power monitor circuit according to the first embodiment of the present invention, the current mirror circuit 51 supplies a current corresponding to the output current of the light receiving element APD for receiving the optical signal. The digital conversion circuit 52 converts the level of the current supplied from the current mirror circuit 51 into a digital value. The offset adjustment circuit 53 adjusts the offset of the current supplied to the digital conversion circuit 52.

  With such a configuration, even when the power of the optical signal is small, it is possible to prevent the digital conversion value of the digital conversion circuit from becoming zero, so that a sufficient measurement range of the received light power can be secured.

  FIG. 8 of Patent Document 1 discloses a configuration in which a current load is connected to a connection node between a current mirror circuit and a light receiving element. However, the current load is provided in order to improve the response of the current mirror circuit, and its purpose is completely different from that of the offset adjustment circuit according to the first embodiment of the present invention. In addition, the bias current supplied to the analog / digital converter 55 by the offset adjustment circuit 53 is sufficient. On the other hand, in order to improve the response of the current mirror circuit, the light receiving element is used when the power of the optical signal is large. It is necessary to pass a current equivalent to the current flowing through the current load, and the current levels of the two are completely different. In addition, in such a configuration using a current load, it is necessary to pass a larger amount of current through the current mirror circuit, so that there are cases where selection of components such as transistors used in the current mirror circuit is limited.

  In the light receiving power monitor circuit according to the first embodiment of the present invention, the digital / analog converter 53 supplies a current of a level corresponding to the given digital value to the digital conversion circuit 52 as an offset adjustment circuit. To do. The digital conversion circuit 52 converts the level of the combined current of the current supplied from the current mirror circuit 51 and the current supplied from the digital / analog converter 53 into a digital value.

  As described above, the configuration in which the bias current is supplied using the digital / analog converter makes it possible to easily change the offset current level, so that the optimum adjustment can be performed according to the electrical characteristics of each optical transceiver 21. It becomes. In addition, it is easy to adjust the digital conversion value of the digital conversion circuit 52 to zero when the optical signal is not input. Further, the digital / analog converter 53 can be diverted from the one built in the CPU 70, and an increase in the circuit scale of the optical transceiver 21 can be prevented.

  Further, in the received light power monitor circuit according to the first embodiment of the present invention, the storage unit 73 stores the correspondence between the digital value converted by the digital conversion circuit 52 and the power value of the optical signal.

  As described above, since the light receiving power monitor circuit stores the above correspondence relationship, the home side device 202 can calculate the light receiving power value and output it to a personal computer or the like connected to the home side device 202. The power value can be easily acquired.

  For example, when the optical transceiver 21 used for the home device 202 is manufactured by a plurality of manufacturers, the correspondence between the digital conversion value of the analog / digital converter 55 and the received light power value is determined by the manufacturer of the optical transceiver 21. May be different.

  On the other hand, the optical transceiver according to the first embodiment of the present invention is detachable from the home device 202. In the optical transceiver 21, the storage unit 73 stores the correspondence between the digital value converted by the digital conversion circuit 52 and the power value of the optical signal, and this correspondence can be read from the home device 202.

  As described above, the correspondence relationship is stored in the optical transceiver 21 that can be attached to and detached from the home side device 202, and the correspondence relationship is read from the home side device 202, so that the optical transceiver 21 can be replaced with a new optical transceiver having different electrical characteristics. Even if is performed, the received light power can be appropriately measured.

  In the light receiving power monitor circuit according to the first embodiment of the present invention, an example in which the bias current is adjusted so that the digital conversion value of the analog / digital converter 55 becomes zero when no optical signal is input. Although not limited to this, the bias current is adjusted so that the digital conversion value of the analog / digital converter 55 in the no-input state of the optical signal is larger than zero as shown in FIG. Thus, it is possible to secure a sufficient measurement range of the received light power.

  Moreover, although the light reception power monitor circuit according to the first embodiment of the present invention is configured to include the current mirror circuit 51, the present invention is not limited to this. The circuit is not limited to the current mirror circuit, and may be any circuit as long as it is electrically connected to the light receiving element APD and can supply a current corresponding to the output current of the light receiving element APD.

  In the PON system according to the first embodiment of the present invention, the digital conversion circuit is configured so that the digital value in the state where the home apparatus 202 is not receiving the optical signal is zero or more as the offset adjustment unit. The offset of the current supplied to 52 is adjusted. In addition, the home device 202 acquires a digital value corresponding to each power when an optical signal with different power is output to the light receiving element APD as a digital value acquisition unit. Further, the home device 202 serves as a correspondence calculation unit, and the correspondence between the digital conversion value and the power value of the optical signal based on each digital value acquired by the digital value acquisition unit and the power value of the corresponding optical signal. Calculate the relationship. When the home device 202 operates as a power measurement unit with the light reception power monitor circuit 31 connected to the optical communication line, the optical signal is transmitted using the correspondence calculated by the correspondence calculation unit. Measure the power.

  However, the PON system 301 is not limited to such a configuration. In other words, the station side device 201 may include an offset adjustment unit, a digital value acquisition unit, a correspondence relationship calculation unit, and a power measurement unit, or an illustration other than the home side device 202 and the station side device 201 in the PON system 301 is illustrated. The apparatus which does not carry out may be the structure provided with an offset adjustment part, a digital value acquisition part, a correspondence calculation part, and a power measurement part.

  In the PON system according to the first embodiment of the present invention, the home-side device 202 measures the light reception current, that is, the output current of the light receiving element APD, and calculates the light reception power value. It is not limited. The home-side device 202 may notify the station-side device 201 of the digital conversion value of the received light current acquired by the home-side device 202, and the station-side device 201 may calculate the light-receiving power value.

  In the optical transceiver according to the first embodiment of the present invention, the storage unit 73 stores the coefficient of the power conversion function. However, the present invention is not limited to this. The storage unit 73 may simply be configured to store the digital conversion value of the digital conversion circuit 52. Alternatively, a storage unit that stores the digital conversion value of the digital conversion circuit 52 or the coefficient of the power conversion function may be provided outside the optical transceiver 21 such as the control unit 29.

  Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Second Embodiment>
The present embodiment relates to a received light power monitor circuit in which a bias current supply method is changed as compared with the received light power monitor circuit according to the first embodiment. The contents other than those described below are the same as those of the received light power monitor circuit according to the first embodiment.

  FIG. 11 is a diagram showing a configuration of the received light power monitor circuit according to the second embodiment of the present invention.

  Referring to FIG. 11, light reception power monitor circuit 32 further includes a clamp diode D <b> 1 as compared with the light reception power monitor circuit according to the first embodiment of the present invention, and performs offset adjustment instead of offset adjustment circuit 53. A circuit 56 is included. The offset adjustment circuit 56 includes a resistor R1.

  The resistor R1 and the clamp diode D1 are connected in parallel to each other between the connection node of the current mirror circuit 51 and the current / voltage conversion circuit 54 and the power supply node N2 to which the power supply voltage Vdd is supplied.

  The clamp diode D1 is provided to prevent application of an excessive voltage to the analog / digital converter 55.

  The resistor R1 is connected between the power supply node N2 and the input terminal of the current / voltage conversion circuit 54 for receiving the current supplied from the current mirror circuit 51. A bias current is supplied from the power supply node N2 to the current / voltage conversion circuit 54 via the resistor R1. The current / voltage conversion circuit 54 converts the combined current of the current supplied from the current mirror circuit 51 and the current supplied via the resistor R1 into a voltage VADC.

  Thereby, similarly to the light receiving power monitor circuit according to the first embodiment of the present invention, even when the power of the optical signal is small, it is possible to prevent the digital conversion value of the digital conversion circuit from becoming zero. A sufficient measurement range of the received light power can be secured.

  In addition, the configuration in which a bias current is applied using a resistor can extend the measurement range of received light power with a simple circuit.

  Since other configurations and operations are the same as those of the received light power monitor circuit according to the first embodiment, detailed description thereof will not be repeated here.

  Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Third Embodiment>
The present embodiment relates to a received light power monitor circuit that supplies a bias voltage instead of a bias current as compared with the received light power monitor circuit according to the first embodiment. The contents other than those described below are the same as those of the received light power monitor circuit according to the first embodiment.

  FIG. 12 is a diagram showing a configuration of a received light power monitor circuit according to the third embodiment of the present invention.

  Referring to FIG. 12, light reception power monitor circuit 33 includes an offset adjustment circuit 57 instead of offset adjustment circuit 53, as compared with the light reception power monitor circuit according to the first embodiment of the present invention. Offset adjustment circuit 57 includes resistors R11 to R13.

  The offset adjustment circuit 57 supplies a bias voltage to the analog / digital converter 55, thereby offsetting the voltage VADC converted by the current / voltage conversion circuit 54, that is, the voltage converted into a digital value by the analog / digital converter 55. Adjust.

  The resistor R12 is connected between the power supply node N2 to which the power supply voltage Vdd is supplied and the input terminal of the analog / digital converter 55. The resistor R13 is connected between a ground node to which a ground voltage is supplied and an input terminal of the analog / digital converter 55. The resistor R11 is connected between the output terminal of the current / voltage conversion circuit 54 and the connection node of the resistors R12, R13 and the input terminal of the analog / digital converter 55.

  With such a configuration, the digital conversion value of the digital conversion circuit can be prevented from becoming zero even when the power of the optical signal is small, as in the case of the received light power monitor circuit according to the first embodiment of the present invention. Therefore, the measurement range of the received light power can be secured sufficiently.

  Specifically, when the power supply voltage Vdd is 3.3 V, for example, the resistance value of the resistor R12 is set to 200 kΩ, for example, and the resistance value of the resistor R13 is set to 1 kΩ, for example.

  If the resistance value of the resistor R11 is too small, the voltage divided by the resistors R11 and R13 becomes the input voltage VADC, and it becomes difficult to adjust the offset of the input voltage ADC of the analog / digital converter 55.

  If the resistance value of the resistor R11 is too large, the voltage divided by the resistors R12 and R13 becomes the input voltage VADC, and the input voltage VADC becomes constant regardless of the output current level of the light receiving element APD.

  Therefore, the resistance value of the resistor R11 needs to be set to a value that does not cause the above problem.

  That is, the light reception power monitor circuit according to the first embodiment of the present invention and the second embodiment of the present invention has an offset adjustment compared to the light reception power monitor circuit according to the third embodiment of the present invention. Circuit design and adjustment is easy.

  Since other configurations and operations are the same as those of the received light power monitor circuit according to the first embodiment, detailed description thereof will not be repeated here.

  The above embodiment should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 21 Optical transceiver 22 PON reception process part 23 Buffer memory 24 UN transmission process part 25 UNI port 26 UN reception process part 27 Buffer memory 28 PON transmission process part 29 Control part 31, 32, 33 Light reception power monitor circuit 51 Current mirror circuit (light reception) Current supply circuit)
52 Digital Conversion Circuit 53 Digital / Analog Converter (Offset Adjustment Circuit)
54 Current / Voltage Conversion Circuit 55 Analog / Digital Converter 56, 57 Offset Adjustment Circuit 70 CPU
71 Master I / F
73 storage unit 81 TIA
82 LIA
83 CDR
84 Equalizer circuit 85 Output buffer 86-90 Power supply 201 Station side device 202A, 202B, 202C, 202D Home side device 301 PON system APD Light receiving element C3-C6 Capacitor D1 Clamp diode R1, R11-R13 Resistor SP1, SP2 Splitter OPTF Optical fiber

Claims (9)

A light receiving current supply circuit for supplying a current corresponding to an output current of a light receiving element for receiving an optical signal from an optical communication line, and a level of a current supplied from the light receiving current supply circuit is converted into a digital value. A received light power monitoring method using a received light power monitor circuit comprising a digital conversion circuit for
The current supplied to the digital conversion circuit, or a voltage converted from the current, so that the digital value in a state where the light reception power monitor circuit does not receive the optical signal is zero or more, Adjusting the offset of the voltage converted to a digital value;
Inputting optical signals of different powers to the light receiving elements, and obtaining the digital values corresponding to the powers;
Calculating a correspondence relationship between the digital value and the power value of the optical signal based on each acquired digital value and the power value of the corresponding optical signal;
Operating the light reception power monitor circuit in a state connected to the optical communication line, and measuring the power of the optical signal using the correspondence relationship. A light receiving current supply circuit for supplying a current corresponding to an output current of a light receiving element for receiving an optical signal, and a digital conversion circuit for converting the level of the current supplied from the light receiving current supply circuit into a digital value Preparing a received power monitor circuit comprising:
The current supplied to the digital conversion circuit, or a voltage converted from the current, so that the digital value in a state where the light reception power monitor circuit does not receive the optical signal is zero or more, Adjusting the offset of the voltage converted to a digital value;
Inputting optical signals of different powers to the light receiving elements, and obtaining the digital values corresponding to the powers;
Calculating a correspondence relationship between the digital value and the power value of the optical signal based on each of the acquired digital values and the corresponding power value of the optical signal, and storing the calculated relationship in the received light power monitor circuit. , A method for manufacturing a light receiving power monitor circuit. A communication system comprising a station side device and a home side device for transmitting and receiving optical signals to and from the station side device via an optical communication line,
The home device includes a light receiving current supply circuit for supplying a current corresponding to an output current of a light receiving element for receiving an optical signal from the optical communication line, and a current supplied from the light receiving current supply circuit. A digital conversion circuit for converting the level into a digital value,
The communication system is:
The current supplied to the digital conversion circuit or the voltage converted from the current is converted into the digital value so that the digital value in a state where the optical signal is not received becomes zero or more. An offset adjustment unit for adjusting a voltage offset;
In the case where optical signals of different power are output to the light receiving element, a digital value acquisition unit for acquiring the digital value corresponding to each of the powers;
A correspondence calculation unit for calculating a correspondence between the digital value and the power value of the optical signal based on each digital value acquired by the digital value acquisition unit and the power value of the corresponding optical signal. When,
A communication system comprising: a power measurement unit configured to measure the power of the optical signal using the correspondence relationship when the light reception power monitor circuit is operating in a state of being connected to the optical communication line. An optical transceiver detachable from an optical communication device for transmitting / receiving an optical signal to / from another device,
A light receiving element for receiving the optical signal;
A light receiving power monitor circuit for measuring the power of the optical signal,
The light receiving power monitor circuit is:
A light receiving current supply circuit for supplying a current corresponding to an output current of a light receiving element for receiving the optical signal;
A digital conversion circuit for converting the level of current supplied from the light receiving current supply circuit into a digital value;
An offset adjustment circuit for adjusting an offset of the current supplied to the digital conversion circuit, or a voltage converted from the current and converted into the digital value,
The optical transceiver further includes:
An optical transceiver comprising: a storage unit that stores a correspondence relationship between the digital value converted by the digital conversion circuit and a power value of the optical signal, and the correspondence relationship can be read from the optical communication device. A light receiving current supply circuit for supplying a current corresponding to the output current of the light receiving element for receiving the optical signal;
A digital conversion circuit for converting the level of current supplied from the light receiving current supply circuit into a digital value;
A received light power monitor circuit comprising: an offset adjustment circuit for adjusting an offset of the current supplied to the digital conversion circuit or a voltage converted from the current and converted into the digital value. The offset adjustment circuit includes:
6. The received light power monitor circuit according to claim 5, further comprising a resistor connected between a node to which a fixed voltage is supplied and an input terminal of the digital conversion circuit for receiving a current supplied from the received light current supply circuit. . The offset adjustment circuit includes:
A digital / analog converter for supplying a current of a level corresponding to a given digital value to the digital conversion circuit;
6. The received light power monitor circuit according to claim 5, wherein the digital conversion circuit converts a level of a combined current of the current supplied from the received light current supply circuit and the current supplied from the digital / analog converter into a digital value. . The digital conversion circuit includes:
A current / voltage conversion circuit for converting a current supplied from the light receiving current supply circuit into a voltage;
An analog / digital converter for converting the level of the voltage converted by the current / voltage conversion circuit into a digital value;
The offset adjustment circuit includes:
A first resistor connected between a node to which a first fixed voltage is supplied and an input terminal of the analog / digital converter;
A second resistor connected between a node to which a second fixed voltage is supplied and an input terminal of the analog / digital converter;
6. The received light power monitor circuit according to claim 5, further comprising a third resistor connected between an output terminal of the current / voltage conversion circuit and a connection node of the first resistor and the second resistor. The light receiving power monitor circuit further includes:
The received light power monitor according to claim 5, further comprising a storage unit for storing a correspondence relationship between the digital value converted by the digital conversion circuit and the power value of the optical signal. circuit.

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