JP5510673B2 - Drive circuit, optical transceiver, communication system, and communication control method - Google Patents

Description

  The present invention relates to a drive circuit, an optical transceiver, a communication system, and a communication control method, and in particular, a drive circuit for driving a light emitting element for transmitting an optical signal, an optical transceiver including the same, and a communication system using the light emitting element. The present invention relates to a communication control method.

  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.

  Here, a laser drive circuit used in a transmitter for optical communication is disclosed in Japanese Patent Application Laid-Open No. 2010-267924 (Patent Document 1). That is, the laser drive circuit can obtain a modulation circuit for supplying a modulation current to the laser diode in accordance with the input burst data, a bias circuit for supplying a bias current to the laser diode, and a desired emission intensity and extinction ratio for the laser diode. And an APC circuit for controlling the modulation current and the bias current. When the transmission enable signal is on, burst driving is performed according to burst data input by the laser diode, and when the transmission enable signal is off, the laser diode is extinguished. The modulation circuit includes a modulation current cut-off circuit that cuts off the modulation current when the transmission enable signal is off, and the bias circuit includes a bias current cut-off circuit that cuts off the bias current when the transmission enable signal is off.

IEEE Std 802.3ah (registered trademark) -2004

JP 2010-267924 A

  By the way, in the PON system, a time division multiplexing system is adopted as an upstream communication system from the home side apparatus to the station side apparatus. In this time division multiplexing system, the home side device transmits a burst signal to the station side device. For this reason, in the home apparatus, it is necessary to supply a current to a light emitting element such as a laser diode during a period in which an optical signal is to be transmitted, and to stop supplying the current in other periods.

  When it is assumed that the laser drive circuit described in Patent Document 1 is used in a home device of a PON system, for example, as a configuration for stopping supply of a bias current, a method of opening a bias circuit by turning off a transistor Alternatively, a method of controlling the output current of the bias circuit to zero can be considered.

  On the other hand, when starting transmission of burst signals, supply modulation current to the laser diode before supplying modulation current to the laser diode so that unnecessary optical output and unstable optical output are not made to the optical communication line. It is necessary to stabilize the bias current.

  However, in any configuration for stopping the bias current, the time from when the bias current supply is stopped until the desired bias current is supplied becomes longer due to a decrease in response speed due to parasitic parameters. There is a possibility.

  That is, since a waiting time is required until the bias current is stabilized, the interval between burst signals from each home side device in the upstream communication from the home side device to the station side device adopting the time division multiplexing method. However, there is a problem that the throughput of the PON system is lowered.

  In particular, in 10G-EPON, as compared with GE-PON, the transmission time of burst signals from each home side device is shortened by increasing the line speed, and the number of home side devices that can be connected to the station side device is increased. For this reason, if the interval between burst signals from each home-side device is increased, the throughput of the PON system is significantly reduced.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a drive circuit, an optical transceiver, a communication system, and a communication circuit that can improve throughput in a communication system that employs a time division multiplexing system. It is to provide a communication control method.

  In order to solve the above problems, a drive circuit according to an aspect of the present invention is a drive circuit used in a home side device in a communication system in which optical signals from a plurality of home side devices to a station side device are time-division multiplexed. A bias current source for generating a bias current to be supplied to the light emitting element for transmitting the optical signal, and a bias for supplying the bias current generated by the bias current source to the light emitting element. A current supply circuit; and a delay circuit for giving a delay time to supply of the bias current by the bias current supply circuit, wherein the bias current supply circuit has the delay time after the generation of the bias current is started. When the time has elapsed, the bias current is supplied to the light emitting element.

  With such a configuration, the response speed of the stable output of the optical signal can be improved. As a result, effective upstream data is not transmitted from a certain home-side device in the station-side device, but unnecessary light is output from the home-side device to the optical communication line, and effective upstream data is transmitted from other home-side devices. The period during which data cannot be transmitted can be shortened. That is, since the bias current is not supplied to the light emitting element in the period in which the delay time is given, unnecessary light output and unstable light output to the optical communication line can be prevented in the period. As a result, the station-side device can transmit an upstream optical signal from another home-side device during the period, so that the interval of burst signals from each home-side device can be shortened, and the throughput of the communication system can be reduced. Can be improved.

  Preferably, the bias current source generates the bias current prior to supplying the light emitting element with a modulation current having a level corresponding to data to be transmitted to the station-side device, and the delay time is the bias time The supply start timing of the current to the light emitting element is set to be before or simultaneously with the supply start timing of the modulation current to the light emitting element.

  With such a configuration, each home-side device can be used even if data such as dummy data or preamble, which has no problem even if it cannot be transmitted normally or has little influence, is not added to the head of the data to be transmitted to the station-side device. , The interval between burst signals can be shortened, and the throughput of the communication system can be improved.

  Preferably, the bias current supply circuit includes the bias current source and forms a first current path that does not include the light-emitting element, thereby operating the bias current source to generate the first current. An operation of flowing the bias current through the path, and a second current path including the light emitting element and the bias current source are formed to operate the bias current source and to operate the bias current through the second current path. The operation of flowing can be switched.

  In this way, by switching the current path to switch the presence or absence of current supply to the light-emitting element, the influence of a decrease in the response speed of the circuit due to parasitic parameters is reduced, and switching of the bias current supply destination to the light-emitting element is stabilized. Can be done quickly.

  More preferably, the bias current supply circuit is connected between a node to which a power supply voltage is supplied and the bias current source, and is turned on to form a first current path. And a second switch that is connected in series with the light emitting element between a node to which a power supply voltage is supplied and the bias current source, and forms the second current path by being turned on.

  In this way, by configuring the bias current supply circuit with a differential circuit including a switch pair, it is possible to quickly switch the presence / absence of supply of the bias current to the light emitting element with a simple configuration.

  In order to solve the above problems, an optical transceiver according to an aspect of the present invention is detachable from a home-side device in a communication system in which optical signals from a plurality of home-side devices to a station-side device are time-division multiplexed. An optical transceiver, comprising: a light emitting element for transmitting the optical signal; and a drive circuit for driving the light emitting element, wherein the drive circuit generates a bias current to be supplied to the light emitting element. A bias current source, a bias current supply circuit for supplying the bias current generated by the bias current source to the light emitting element, and a delay time for supplying the bias current by the bias current supply circuit The bias current supply circuit includes a delay circuit, and the bias current supply circuit, when the delay time elapses after generation of the bias current is started, The current supplied to the light emitting element, the optical transceiver is further configured to store the delay time, the delay time is provided readable storage unit from the optical network unit.

  In this way, the delay time is stored in the optical transceiver that can be attached to and detached from the home-side device, and the home-side device reads the delay time, so that even if a replacement with a new optical transceiver with a different delay time is performed, An appropriate delay time can be notified to the station side device.

  In order to solve the above-described problem, a communication system according to an aspect of the present invention is a communication system including a plurality of home-side devices and a station-side device for transmitting and receiving optical signals to and from each home-side device. A transmission planning unit for creating a transmission plan of the optical signals from the home devices so that the optical signals from the home devices to the station devices are time-division multiplexed; Transmission for notifying the transmission planning unit of preparation time required in the home side device prior to transmission of the optical signal from the device to the station side device, or whether or not the preparation time in the home side device can be shortened A preparation information notification unit, wherein the transmission plan unit creates the transmission plan based on the notification from the transmission preparation information notification unit, and the preparation time transmits the optical signal included in the home-side device. Light emitting device Is the time required for preparation for supplying modulation current and a bias current having a level corresponding to the data to be transmitted to the station side device.

  With such a configuration, in the station-side device, valid uplink data is not transmitted from a certain home-side device, but unnecessary light is output from the home-side device to the optical communication line. It is possible to obtain from each home-side apparatus whether or not it is possible to shorten the period during which valid uplink data cannot be transmitted. As a result, the station side device can create a transmission plan in which the interval of burst signals from each home side device is shortened, so that the throughput of the communication system can be improved.

  In order to solve the above-described problem, a communication control method according to an aspect of the present invention includes a plurality of home-side devices, and transmission / reception of optical signals to / from each home-side device and from each home-side device to the station-side device. A communication control method in a communication system comprising: a station side device for creating a transmission plan of the optical signal from each home side device so that the optical signal to be time-division multiplexed; A step of notifying the station side device of a preparation time required prior to transmission of the optical signal to the station side device, or whether or not the preparation time can be shortened; Creating the transmission plan based on the notification from the device, and the preparation time should be transmitted to the station-side device to a light emitting element for transmitting the optical signal provided in the home-side device Have a level depending on the data Modulation current, and the time required for preparation for supplying a bias current.

  With such a configuration, in the station-side device, valid uplink data is not transmitted from a certain home-side device, but unnecessary light is output from the home-side device to the optical communication line. It is possible to obtain from each home-side apparatus whether or not it is possible to shorten the period during which valid uplink data cannot be transmitted. As a result, the station side device can create a transmission plan in which the interval of burst signals from each home side device is shortened, so that the throughput of the communication system can be improved.

  According to the present invention, it is possible to improve throughput in a communication system that employs time division multiplexing.

It is a figure which shows the structure of the PON system which concerns on embodiment of this invention. It is a figure which shows the structure of the home side apparatus in the PON system which concerns on embodiment of this invention. It is a figure which shows in detail the structure by the side of the transmission of the optical transceiver in the home side apparatus which concerns on embodiment of this invention. It is a figure which shows the state of the optical output in the optical transceiver of the home side apparatus which concerns on embodiment of this invention, a control signal, and each circuit. It is a figure which shows the flow of the data between the station side apparatus in a PON system which concerns on embodiment of this invention, and a home side apparatus.

  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.

  FIG. 1 is a diagram showing a configuration of a PON system according to an 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. In the PON system 301, optical signals from the home side devices 202A, 202B, 202C, 202D to the station side device 201 are time-division multiplexed.

  FIG. 2 is a diagram showing a configuration of a home device in the PON system according to the 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 in detail the configuration of the transmission side of the optical transceiver in the home-side apparatus according to the embodiment of the present invention.

  Referring to FIG. 3, the optical transceiver 21 includes a pre-buffer circuit 61, an equalizer circuit 62, an output buffer circuit 63, power supplies 64-66, a timing circuit 67, a bias circuit (drive circuit) 68, and light emission. A circuit 75, a master I / F (interface) 91, a CPU (Central Processing Unit) 92, a slave I / F 93, a control register 94, and capacitors C1 and C2 are included. The prebuffer circuit 61 includes a termination resistor R11. The light emitting circuit 75 includes a light emitting element LD and inductors L1 and L2. Bias circuit 68 includes a delay circuit 71, an inverter 72, a level shift circuit 81, a bias current supply circuit 82, a bias current source 83, and a resistor R3. Level shift circuit 81 includes transistors TR4 and TR5, resistors R1 and R2, and a capacitor C3. Bias current supply circuit 82 includes transistors TR2 and TR3. Bias current source 83 includes a transistor TR1 and a constant current source 73. The CPU 92 includes a storage unit 95 that is, for example, an EEPROM (Electrically Erasable Programmable Read Only Memory).

  The pre-buffer circuit 61 receives the transmission data, which is the data frame from the UN reception processing unit 26 and the control frame from the control unit 29, via the capacitors C1 and C2, and receives and amplifies the transmission data. To do. For example, the prebuffer circuit 61 receives the transmission data from the signal lines INP and INN as a balance signal.

  The equalizer circuit 62 performs waveform shaping of the transmission data received from the pre-buffer circuit 61, for example, corrects phase distortion and outputs the result.

  The output buffer circuit 63 includes, for example, a differential circuit composed of two transistors, and supplies a modulation current to the light emitting circuit 75 based on transmission data received from the equalizer circuit 62. This modulation current has a level corresponding to the logical value of data to be transmitted to the station side device 201.

  The light emitting circuit 75 transmits the upstream optical signal to the station side device 201. In the light emitting circuit 75, the light emitting element LD is connected to the power supply node to which the power supply voltage Vcc2 is supplied via the inductor L1, and is connected to the bias circuit 68 via the inductor L2. The light emitting element LD emits light based on the bias current supplied from the bias circuit 68 and the modulation current supplied from the output buffer circuit 63, and changes the light emission intensity.

  The power supplies 64 to 66 can supply, for example, current as power to the pre-buffer circuit 61, the equalizer circuit 62, and the output buffer circuit 63, respectively, and control the start and stop of power supply. More specifically, the power supplies 64 to 66 switch whether to supply current to the pre-buffer circuit 61, the equalizer circuit 62, and the output buffer circuit 63 based on the transmission enable signal received from the control unit 29.

  Specifically, the power supplies 64 to 66 supply power to the pre-buffer circuit 61, the equalizer circuit 62, and the output buffer circuit 63, respectively, when the transmission enable signal is activated, and the transmission enable signal is deactivated. If this is the case, the power supply is stopped.

  The timing circuit 67 performs control to forcibly stop the supply of the modulation current from the output buffer circuit 63 to the light emitting element LD.

  The bias circuit 68 supplies a bias current as power to the light emitting circuit 75. The bias circuit 68 switches whether to supply a bias current to the light emitting circuit 75 based on the transmission enable signal received from the control unit 29.

  In light emitting circuit 75, inductor L1 has a first end connected to a power supply node to which power supply voltage Vcc2 is supplied, and a second end. The light emitting element LD is a laser diode, for example, and has an anode connected to the second end of the inductor L1 and a cathode connected to the first end of the inductor L2. The modulation current output from the output buffer circuit 63 flows from the anode to the cathode of the light emitting element LD.

  In bias circuit 68, resistor R3 has a first end connected to a power supply node supplied with power supply voltage Vcc2, and a second end. In level shift circuit 81, transistor TR4 is, for example, an NPN transistor, a collector connected to the second end of resistor R3, and a base connected to a connection node of resistor R1, resistor R2, capacitor C3, and transistor TR5; And an emitter. Resistor R1 has a first end connected to a power supply node supplied with power supply voltage Vcc1, and a second end. Resistor R2 has a first end connected to the second end of resistor R1, and a second end connected to a ground node to which a ground voltage is supplied. Capacitor C3 has a first end connected to the second end of resistor R1, and a second end connected to a ground node to which a ground voltage is supplied. Transistor TR5 is an NPN transistor, for example, and has a collector connected to the second end of inductor L2, a base connected to a connection node of resistors R1, R2, capacitor C3 and transistor TR4, and an emitter.

  In bias current supply circuit 82, transistor TR2 is an NPN transistor, for example, and has a collector connected to the emitter of transistor TR4, a base that receives a signal from inverter 72, and an emitter. Transistor TR3 is, for example, an NPN transistor, and has a collector connected to the emitter of transistor TR5, a base for receiving a signal from delay circuit 71, and an emitter.

  In bias current source 83, transistor TR1 is an NPN transistor, for example, and is connected to a collector connected to the emitters of transistors TR2 and TR3, a base that receives a transmission enable signal from control unit 29, and constant current source 73. And an emitter. The constant current source 73 is connected between the emitter of the transistor TR1 and a ground node to which a ground voltage is supplied.

  The power supply voltage Vcc2 is higher in level than the power supply voltage Vcc1. The power supply voltage Vcc1 is also supplied to, for example, the pre-buffer circuit 61, the equalizer circuit 62, and the output buffer circuit 63.

  Delay circuit 71 delays the transmission enable signal received from control unit 29 by delay time TDL and outputs the delayed signal. Specifically, for example, the delay circuit 71 outputs a transmission enable signal obtained by delaying the timing at which the transmission enable signal is activated by a delay time TDL. This delay time TDL is, for example, several tens of nanoseconds.

  Inverter 72 inverts the logic level of the transmission enable signal received from delay circuit 71 and outputs the result.

  Level shift circuit 81 performs level shift so that a voltage lower than power supply voltage Vcc2 is applied to bias current supply circuit 82 and bias current source 83 side. That is, the level shift circuit 81 obtains a voltage obtained by subtracting the base-emitter voltage of the transistors TR4 and TR5 from the voltage obtained by dividing the power supply voltage Vcc1 by the resistors R1 and R2, and the bias current supply circuit 82 and the bias current source 83 side. Apply to. Thereby, it is possible to prevent an excessive level of voltage from being applied to the bias current supply circuit 82 and the bias current source 83 side.

  The bias current source 83 generates a bias current to be supplied to the light emitting element LD for transmitting the optical signal, based on the transmission enable signal, prior to supply of the modulation current to the light emitting element LD by the output buffer circuit 63.

  In the bias current source 83, the transistor TR1 is turned on when the transmission enable signal received from the control unit 29 is activated, and turned off when the transmission enable signal is deactivated.

  The constant current source 73 generates a bias current. Here, in the optical transceiver 21, the value of the bias current is set so that the light emitting element LD emits light when the bias current is supplied to the light emitting element LD in a state where the modulation current is not supplied to the light emitting element LD. .

  The bias current supply circuit 82 is a differential circuit composed of, for example, two transistors TR2 and TR3. The bias current supply circuit 82 controls the supply of the bias current generated by the bias current source 83 to the light emitting element LD.

  In the bias current supply circuit 82, the transistor TR2 is turned on when the transmission enable signal received from the inverter 72 is activated and turned off when the transmission enable signal is deactivated. The transistor TR3 is turned on when the transmission enable signal received from the delay circuit 71 is activated, and turned off when the transmission enable signal is deactivated. That is, transistors TR2 and TR3 are turned on and off in a complementary manner.

  The delay circuit 71 gives the aforementioned delay time TDL to the supply of the bias current by the bias current supply circuit 82. The delay time TDL is set so that the supply start timing of the bias current to the light emitting element LD is before or simultaneously with the supply start timing of the modulation current to the light emitting element LD.

  The bias current supply circuit 82 supplies the bias current to the light emitting element LD when the delay time TDL elapses after the generation of the bias current is started.

  The bias current supply circuit 82 includes a bias current source 83 and forms a current path A that does not include the light emitting element LD, thereby operating the bias current source 83 to flow a bias current through the current path A. By forming the current path B including the light emitting element LD and the bias current source 83, the operation of operating the bias current source 83 and flowing the bias current through the current path B can be switched.

  More specifically, current path A is a path from a power supply node supplied with power supply voltage Vcc2 to a ground node via resistor R3, transistor TR4, transistor TR2, transistor TR1, and constant current source 73. The current path B is a path from the power supply node to which the power supply voltage Vcc2 is supplied to the ground node via the inductor L1, the light emitting element LD, the inductor L2, the transistor TR5, the transistor TR3, the transistor TR1, and the constant current source 73. It is.

  In the bias current supply circuit 82, the transistor TR2 is connected between the node to which the power supply voltage Vcc2 is supplied and the bias current source 83, and forms a current path A when turned on. The transistor TR3 is connected in series with the light emitting element LD via the inductor L2 and the transistor TR5 between the node to which the power supply voltage Vcc2 is supplied and the bias current source 83, and forms a current path B by being turned on.

  Note that the power supply voltage in the current path A, that is, the power supply voltage supplied to the power supply node connected to the resistor R3, and the power supply voltage in the current path B, that is, the power supply voltage supplied to the power supply node connected to the inductor L1 are different. It may be a voltage. However, as shown in FIG. 3, with the configuration in which the power supply voltages of the current paths A and B are the same, the value of the bias current before and after the bias current supply to the light emitting element LD, that is, before and after the switching of the current paths A and B is substantially Since they can be made equal, the circuit operation can be stabilized.

  For example, the CPU 92 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 95 in the CPU 92 stores the delay time TDL.

  The master I / F 91 provides an interface function between the CPU 92 and the I2C bus.

  The slave I / F 93 provides an interface function between the CPU 92 and the control register 94.

  The CPU 92 writes various control data to the control register 94 via the slave I / F 93.

  The power supply 66 changes the amount of current supplied to the output buffer circuit 63 based on the control data APC1 written in the control register 94.

  The bias circuit 68 changes the amount of current supplied to the light emitting circuit 75 based on the control data APC2 written in the control register 94.

[Operation]
Next, the operation when the drive circuit according to the embodiment of the present invention controls the current supply to the light emitting element will be described with reference to the drawings.

  FIG. 4 is a diagram showing the optical output, the control signal, and the state of each circuit in the optical transceiver of the home-side apparatus according to the embodiment of the present invention. In FIG. 4, an optical output A is an optical output when it is assumed that no delay time is given to the bias current supply to the light emitting element LD in the driving circuit according to the embodiment of the present invention. The light output B is the light output when the drive circuit according to the embodiment of the present invention is used. In the optical output waveform, the portion indicated by “data” is actually the level of only the “bias” portion, the “bias” portion, and the “data” portion in accordance with the logical value of the transmission data. The waveform changes with the level.

  Referring to FIG. 4, first, the transmission enable signal is deactivated in a period in which transmission of the upstream optical signal is not permitted from station-side apparatus 201. In this case, the transistor TR1 is in an off state, the transistor TR2 is in an on state, and the transistor TR3 is in an off state. For this reason, the constant current source 73 does not operate and no bias current is generated.

  Next, transmission of the upstream optical signal is permitted from the station side device 201, and the transmission enable signal is activated in order to transmit the upstream optical signal from the home side device 202. Then, the transistor TR1 is turned on. Further, the transistor TR2 remains on, and the transistor TR3 remains off. As a result, a current path A is formed, the constant current source 73 starts operating, and a bias current is generated.

  When the transmission enable signal is activated, the power supplies 64 to 66 start operating, and current is supplied to the pre-buffer circuit 61, the equalizer circuit 62, and the output buffer circuit 63, respectively. However, the modulation current from the output buffer circuit 63 is not supplied to the light emitting element LD under the control of the timing circuit 67 (timing t1).

  Next, at timing t2 after the delay time TDL has elapsed from timing t1, the output signal of the delay circuit 71 is activated. Then, the transistor TR2 is turned off and the transistor TR3 is turned on. Further, the transistor TR1 remains on. As a result, the current path of the bias current is switched from the current path A to the current path B, and the bias current is supplied to the light emitting element LD (timing t2).

  Here, at the timing t2 when the delay time TDL has elapsed from the timing t1 at which the constant current source 73 starts to operate and the bias current starts to flow, the bias current is stable at a predetermined level, and the light emitting element LD is stabilized. Thus, light can be emitted. However, the light output from the light emitting element LD due to the bias current reaches a predetermined level a little after the timing t2, and is stabilized. This is because it takes some time for the circuit in the current path B to become stable.

  The timing circuit 67 forcibly stops the supply of the modulation current from the output buffer circuit 63 to the light emitting element LD during the period from the timing t1 to the timing t2 and from the timing t2 to the timing t3 after the elapse of time TA. As a result, it is possible to prevent the occurrence of overshoot or the like caused by the modulation current flowing in a state where the level of the bias current is unstable, so that the circuit operation can be stabilized.

  If there is no problem even if the circuit stabilization time associated with switching from the current path A to the current path B is not considered, the timing circuit 67 outputs the output buffer circuit 63 only during the period from the timing t1 to the timing t2. Alternatively, the supply of the modulation current to the light emitting element LD may be forcibly stopped.

  Next, when the supply of the modulation current to the light emitting element LD is started, a preamble which is invalid data starts to be transmitted, and thereafter, transmission of valid data is started (timing t3).

  Next, in order to stop transmission of the upstream optical signal from the home side apparatus 202, the transmission enable signal is deactivated. Then, the transistor TR1 is turned off, the transistor TR2 is turned on, and the transistor TR3 is turned off. As a result, the constant current source 73 stops operating, and the generation of the bias current is stopped (timing t4).

  Here, in the case of the optical output A, since the delay time TDL is not given to the supply of the bias current to the light emitting element LD, the bias current is equal to the timing t1 when the constant current source 73 starts generating the bias current. The light is supplied to the light emitting element LD. Then, an unnecessary light output or an unstable light output is made to the optical communication line until a timing t3 when the bias current is stably supplied to the light emitting element LD from the timing t1 and the modulation current is supplied to the light emitting element LD. It will be. During the period TWAIT from timing t1 to timing t3, no valid uplink data is transmitted from a certain home device 202 to the station device 201, but unnecessary light is output from the home device 202 to the optical fiber OPTF. This is a period during which valid uplink data cannot be transmitted from the other home side apparatus 202.

  On the other hand, in the optical output B, since the bias current is not supplied to the light emitting element LD during the period from the timing t1 to the timing t2, unnecessary optical output or unstable optical output is output to the optical communication line during the period. Can be prevented. On the other hand, since the generation of the bias current is started at the timing t1, a stable bias current of a predetermined level can be immediately supplied to the light emitting element LD.

  FIG. 5 is a diagram showing a data flow between the station side device and the home side device in the PON system according to the embodiment of the present invention.

  Referring to FIG. 5, let us consider a state in which the home device 202A is unregistered and the home device 202B is registered in the station device 201. The station-side device 201 transmits a discovery gate frame to each home-side device 202. With this discovery gate frame, the transmission timing of the upstream optical signal is notified to the unregistered home device 202A. Further, the station side device 201 includes an inquiry as to whether or not the period TWAIT shown in FIG. 4 can be shortened in this discovery gate frame (step S1).

  Next, the unregistered home-side device 202A receives the discovery gate frame from the station-side device 201, and transmits a register request frame that is a registration request to the station-side device 201 at the transmission timing indicated by the discovery-gate frame. To 201.

  Here, in response to the inquiry indicated by the discovery gate frame, home device 202A has a configuration that determines whether or not itself can shorten period TWAIT, that is, provides a delay time for supplying bias current to light emitting element LD. The answer of NO is included in the register request frame.

  If the home side device 202 can shorten the period TWAIT, it may include the shortened time, that is, the delay time TDL in the answer. Specifically, for example, the control unit 29 in the home-side apparatus 202 acquires information about whether or not the period TWAIT can be shortened, or the delay time TDL from the storage unit 95 in the optical transceiver 21 (step S2).

  Next, the station side device 201 receives the register request frame from the home side device 202A and transmits the register frame to the home side device 202A. With this register frame, LLID (Logical Link Identification) is notified as a registration result to the unregistered home device 202A (step S3).

  Next, the station-side device 201 creates a transmission plan for each home-side device 202 based on the answer indicated by the register request frame received from the home-side device 202A. A bandwidth and transmission timing are calculated (step S4). Note that the execution order of step S3 and step S4 may be reversed.

  Next, the station side device 201 transmits a gate frame to each home side device 202. With this gate frame, each home-side device 202 is notified of the transmission band and transmission timing of the upstream optical signal (step S5).

  Next, the home apparatus 202A notified of the LLID receives the gate frame from the station apparatus 201, and transmits a register ACK frame, which is a reception response of the register frame, at the transmission timing indicated by the gate frame. (Step S6).

  By the way, when it is assumed that the laser driving circuit described in Patent Document 1 is used in the home device of the PON system, for example, as a configuration for stopping supply of the bias current, the bias circuit is opened by turning off the transistor. Or a method of controlling the output current of the bias circuit to zero.

  However, in any configuration for stopping the bias current, the time from when the bias current supply is stopped until the desired bias current is supplied becomes longer due to a decrease in response speed due to parasitic parameters. There is a possibility.

  That is, since a waiting time is required until the bias current is stabilized, the interval between burst signals from each home side device in the upstream communication from the home side device to the station side device adopting the time division multiplexing method. However, there is a problem that the throughput of the PON system is lowered.

  On the other hand, in the drive circuit according to the embodiment of the present invention, the bias current source 83 uses the bias current to be supplied to the light emitting element LD for transmitting the optical signal to be transmitted to the station side device 201. Is generated prior to the supply of the modulation current having a level corresponding to the light emitting element LD. The delay circuit 71 gives a delay time TDL to the supply of the bias current by the bias current supply circuit 82. The bias current supply circuit 82 supplies the bias current to the light emitting element LD when the delay time TDL elapses after the generation of the bias current is started. The delay time TDL is set so that the supply start timing of the bias current to the light emitting element LD is before or simultaneously with the supply start timing of the modulation current to the light emitting element LD.

  Specifically, for example, a switch circuit, that is, a transistor TR1 is provided in the upper stage of the constant current source 73. When the transmission enable signal is activated and returns from the bias current supply stop state, first, the transistor TR1 is turned on, and a bias current flows through the opposite phase side of the bias circuit 68, that is, through the current path A. Thereafter, the transmission enable signal that has passed through the delay circuit 71 is input to the transistor TR3, and a bias current flows through the positive phase side of the bias circuit 68, that is, through the current path B. Since the bias current generated by the bias current source 83 is already stable at the time of switching the current path, the response speed of the stable output of the optical signal can be improved.

  With such a configuration, effective upstream data is not transmitted from a certain home-side device 202 in the station-side device 201, but unnecessary light is output from the home-side device 202 to the optical fiber OPTF. It is possible to shorten a period during which valid uplink data cannot be transmitted from the side device 202.

  In other words, since the bias current is not supplied to the light emitting element LD during the period in which the delay time TDL is given, unnecessary light output and unstable light output can be prevented from being made to the optical communication line during the period. . As a result, the station-side device 201 can transmit the upstream optical signal from the other home-side device 202 during the period, so that the interval of the burst signal from each home-side device can be shortened. Throughput can be improved.

  Further, in the drive circuit according to the embodiment of the present invention, the bias current supply circuit 82 includes the bias current source 83 and forms a current path A that does not include the light emitting element LD. And the bias current source 83 is operated to generate a bias current through the current path B by forming the current path B including the light emitting element LD and the bias current source 83. The flow operation can be switched.

  In this way, by switching the current path to switch the presence / absence of current supply to the light emitting element LD, the influence of a decrease in the response speed of the circuit due to the parasitic parameter is reduced, and the bias current supply destination to the light emitting element LD is switched. It can be performed stably and quickly.

  In the drive circuit according to the embodiment of the present invention, in the bias current supply circuit 82, the transistor TR2 is connected between the node to which the power supply voltage Vcc2 is supplied and the bias current source 83, and is turned on so that the current flows. A path A is formed. The transistor TR3 is connected in series with the light emitting element LD between the node to which the power supply voltage Vcc2 is supplied and the bias current source 83, and forms a current path B by being turned on.

  In this way, by configuring the bias current supply circuit 82 with a differential circuit including a switch pair, it is possible to quickly switch the presence / absence of supply of the bias current to the light emitting element LD with a simple configuration.

  For example, when the optical transceiver 21 used in the home device 202 is manufactured by a plurality of manufacturers, the delay time TDL in the optical transceiver 21 may be different depending on the manufacturer of the optical transceiver 21.

  On the other hand, in the optical transceiver according to the embodiment of the present invention, the storage unit 95 stores the delay time TDL provided by the delay circuit 71, and the delay time TDL can be read from the control unit 29 in the home side apparatus 202. is there.

  As described above, the delay time TDL is stored in the optical transceiver 21 that can be attached to and detached from the home-side apparatus 202, and the control unit 29 reads the delay time TDL, so that the optical transceiver 21 can be replaced with a new optical transceiver having a different delay time TDL. Even if it is performed, the station-side apparatus 201 can be notified of an appropriate delay time.

  Further, in the PON system according to the embodiment of the present invention, the station side device 201 transmits the optical signal from each home side device 202 so that the optical signal from each home side device 202 to the station side device 201 is time-division multiplexed. Create a signal transmission plan. The home apparatus 202 notifies the station apparatus 201 of the preparation time required prior to the transmission of the optical signal to the station apparatus 201 or whether the preparation time can be shortened. The station side device 201 creates the transmission plan based on the notification from the home side device 202. The preparation time is a preparation for supplying a modulation current having a level corresponding to data to be transmitted to the station side device 201 and a bias current to the light emitting element LD for transmitting the optical signal provided in the home side device 202. Is the time needed for.

  With such a configuration, in the station-side device 201, valid uplink data is not transmitted from a certain home-side device 202, but unnecessary light is output from the home-side device 202 to the optical communication line. Whether or not it is possible to shorten the period during which valid uplink data cannot be transmitted from the side device 202 can be obtained from each home device 202. Thereby, in the station side apparatus 201, the transmission plan which shortened the space | interval of the burst signal from each home side apparatus 202 can be created, Therefore The throughput of a PON system can be improved.

  In the drive circuit according to the embodiment of the present invention, the generation of the bias current is stopped in a period in which transmission of the upstream optical signal is not permitted from the station side device 201. However, the configuration is limited to this. It is not a thing. The bias current may be set to a level at which the light emitting element LD does not emit light even if the bias current is supplied to the light emitting element LD in the period, and the bias current in the period is not limited to zero.

  In the drive circuit according to the embodiment of the present invention, the bias current source 83 corresponds to the bias current to be supplied to the light emitting element LD for transmitting the optical signal according to the data to be transmitted to the station side device 201. The modulation current having a level is generated prior to the supply to the light emitting element LD, and the delay time TDL is a timing at which the supply start timing of the bias current to the light emitting element LD is the same as the supply start timing of the modulation current to the light emitting element LD. Although it is assumed that the configuration is set to be before or at the same time, the configuration is not limited to this. The configuration may be such that dummy data, preamble, or the like, which has no problem even if it cannot be transmitted normally or has little influence, is added to the head of the data to be transmitted to the station-side apparatus 201. In this case, the bias current source 83 does not have to generate the bias current prior to supplying the modulation current to the light emitting element LD, and the delay time TDL is the timing at which supply of the bias current to the light emitting element LD is started. Further, it may not be set before or at the same time as the supply start timing of the modulation current to the light emitting element LD.

  Further, in the PON system according to the embodiment of the present invention, the home apparatus 202 notifies the transmission preparation information notification section of whether or not the preparation time can be shortened or the shortening time, and the station apparatus 201 notifies the notification as the transmission planning section. Based on the above, it is assumed that the transmission plan of the upstream optical signal from each home-side apparatus 202 is created. However, the present invention is not limited to this. A configuration in which at least one of the notification and the creation of a transmission plan is executed in a device (not shown) other than the home device 202 and the station device 201 in the PON system 301 may be employed.

  That is, in the PON system 301, the transmission planning unit creates a transmission plan of optical signals from each home side device 202 so that the optical signals from each home side device 202 to the station side device 201 are time-division multiplexed. The transmission preparation information notifying unit transmits the preparation time required in the home device 202 prior to transmission of the optical signal from the home device 202 to the station device 201 or whether or not the preparation time in the home device 202 can be shortened. Notify the department. The transmission planning unit creates a transmission plan based on the notification from the transmission preparation information notification unit. The preparation time is for preparing to supply a modulation current having a level corresponding to data to be transmitted to the station apparatus 201 and a bias current to the light emitting element LD for transmitting the optical signal provided in the home apparatus 202. It is time necessary for.

  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 61 Prebuffer circuit 62 Equalizer circuit 63 Output buffer circuit 64-66 Power supply 67 Timing circuit 68 Bias circuit (Drive circuit)
71 Delay circuit 72 Inverter 73 Constant current source 75 Light emitting circuit 81 Level shift circuit 82 Bias current supply circuit 83 Bias current source 91 Master I / F (interface)
92 CPU
93 Slave I / F
94 control register 95 storage unit 201 station side device 202A, 202B, 202C, 202D home side device 301 PON system C1, C2, C3 capacitor R1, R2, R3 resistance TR1, TR2, TR3, TR4, TR5 transistor R11 termination resistance LD light emission Element L1, L2 Inductor SP1, SP2 Splitter OPTF Optical fiber

Claims (9)

A drive circuit used in a home-side device in a communication system in which optical signals from a plurality of home-side devices to a station-side device are time-division multiplexed,
A bias current source for generating a bias current to be supplied to a light emitting element for transmitting the optical signal;
A bias current supply circuit for supplying the light emitting element with the bias current generated by the bias current source;
A delay circuit for giving a delay time to the supply of the bias current by the bias current supply circuit,
The bias current supply circuit supplies the bias current to the light emitting element when the delay time elapses after generation of the bias current is started ,
Wherein the optical network units, information on whether it has a structure that gives the delay time has is stored, said information Ru notifiable der the station side device, the drive circuit. The bias current source generates the bias current prior to supplying the modulation current having a level corresponding to data to be transmitted to the station side device to the light emitting element,
2. The driving according to claim 1, wherein the delay time is set such that a supply start timing of the bias current to the light emitting element is set before or simultaneously with a supply start timing of the modulation current to the light emitting element. circuit. A drive circuit used in a home-side device in a communication system in which optical signals from a plurality of home-side devices to a station-side device are time-division multiplexed,
A bias current source for generating a bias current to be supplied to a light emitting element for transmitting the optical signal;
A bias current supply circuit for supplying the light emitting element with the bias current generated by the bias current source;
Add dummy data or preamble to the head of data to be transmitted to the station side device ,
Information on whether or not the home side apparatus has a configuration for providing a delay time to supply the bias current by the bias current supply circuit is stored, and the information can be notified to the station side apparatus. Drive circuit.   The bias current supply circuit includes the bias current source and forms a first current path that does not include the light emitting element, thereby operating the bias current source and passing the first current path through the first current path. An operation of flowing a bias current, and an operation of operating the bias current source to flow the bias current through the second current path by forming a second current path including the light emitting element and the bias current source. 4. The drive circuit according to claim 1, wherein the drive circuit can be switched. The bias current supply circuit includes:
A first switch connected between a node to which a power supply voltage is supplied and the bias current source and turning on to form the first current path;
5. A second switch connected in series with the light emitting element between a node to which a power supply voltage is supplied and the bias current source, and forming the second current path by being turned on. The driving circuit described in 1.   6. The drive circuit according to claim 1, wherein the bias current source stops generation of the bias current in a period in which transmission of an optical signal to the station-side device is not permitted. . An optical transceiver detachable from a home side device in a communication system in which optical signals from a plurality of home side devices to a station side device are time-division multiplexed,
A light emitting element for transmitting the optical signal;
A drive circuit for driving the light emitting element,
The drive circuit is
A bias current source for generating a bias current to be supplied to the light emitting element;
A bias current supply circuit for supplying the light emitting element with the bias current generated by the bias current source;
A delay circuit for giving a delay time to the supply of the bias current by the bias current supply circuit,
The bias current supply circuit supplies the bias current to the light emitting element when the delay time elapses after generation of the bias current is started,
The optical transceiver further includes:
The store information about whether it has a structure that gives a delay time, Bei give a readable storage unit the information from the optical network unit,
Said information Ru notifiable der the station side device, the optical transceiver. A plurality of home-side devices;
A communication system comprising each of the home side devices and a station side device for transmitting and receiving optical signals,
A transmission planning unit for creating a transmission plan of the optical signal from each home side device so that the optical signal from each home side device to the station side device is time-division multiplexed;
Prior to transmission of the optical signal from the home side device to the station side device, the transmission planning unit is notified of the preparation time required in the home side device or whether the preparation time in the home side device can be shortened. A transmission preparation information notifying unit for
The transmission plan unit creates the transmission plan based on the notification from the transmission preparation information notification unit,
The preparation time is for preparing to supply a modulation current having a level corresponding to data to be transmitted to the station side device and a bias current to a light emitting element for transmitting the optical signal provided in the home side device. Communication system, which is the time required for A plurality of home-side devices;
A transmission plan of the optical signal from each home side device is transmitted and received with each home side device, and the optical signal from each home side device to the station side device is time-division multiplexed. A communication control method in a communication system comprising a station side device for creating,
The home side device notifying the station side device of preparation time required prior to transmission of the optical signal to the station side device, or whether or not the preparation time can be shortened;
The station side device creating the transmission plan based on the notification from the home side device,
The preparation time is for preparing to supply a modulation current having a level corresponding to data to be transmitted to the station side device and a bias current to a light emitting element for transmitting the optical signal provided in the home side device. Communication control method, which is the time required for communication.

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