JP2005020417A - Receiving amplifier used in optical communication network and method for controlling receiving gain - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiving amplifier (preamplifier 1) which is used in a station side device of an optical communication network in which two-way communication is performed between the station side device and a plurality of subscriber devices, can make a detection time constant of a power detection circuit 3 long to some extent, can completely follow a high-speed packet of the subscriber devices and provides stable optical receiving intensity. <P>SOLUTION: The receiving amplifier is provided with a photodetector PD for detecting an optical signal from the subscriber devices, an amplifier circuit 2 for amplifying an input current generated from the photodetector PD, the power detection circuit 3 for detecting the value of optical input intensity on the basis of an output of the amplifier circuit 2, a gain control circuit 4 for changing an amplification gain of the amplifier circuit 2, and a control part 5 for reading the value of the optical input intensity detected by the power detection circuit 3 to store the value into a memory 6, reading the value of the optical input intensity stored in the memory 6 before an optical signal input from the same subscriber is predicted, outputting a control signal CNT for determining the controlled variable of the gain control circuit 4 on the basis of the read value of the optical input intensity and supplying the control signal CNT to the gain control circuit 4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a receiving amplifier used in an optical communication network that performs bidirectional communication between a station-side device and a plurality of subscriber devices. This receiving amplifier is a PON (Passive Optical Network) system in which a station side device and an optical branching unit are connected by a trunk optical fiber, and an optical branching unit and a plurality of subscriber devices are connected by branch optical fibers. It is suitably used for such as.
[0002]
[Prior art]
In a system for bidirectional communication between a station-side device and a plurality of subscriber devices using an optical data communication network, the station-side device and each subscriber device are each radially radiated by one optical fiber. A network configuration for tying has been put into practical use (Single Star). In this network configuration, the system and equipment configuration is simplified, but one subscriber device occupies one optical fiber (if the number of subscriber devices is N, N optical fibers are required), It is difficult to reduce the price of the system.
[0003]
Therefore, a PON (Passive Optical Network) system (also referred to as PDS (Passive Double Star)) in which one optical fiber is shared by a plurality of subscriber apparatuses has been proposed. In this PON system, a station side device and an optical branching unit are connected by a trunk optical fiber, and an optical branching unit and a plurality of subscriber devices are connected by a plurality of branch optical fibers. In some cases, another optical branching device is connected to one of the branches of the optical branching device, and branches from there to a plurality of subscriber devices.
[0004]
In this PON system, an optical signal is distributed in broadcast form from a station side device to a subscriber device, and a subscriber device that matches the destination information included in the optical signal captures this optical signal. Since the upstream packet from the subscriber apparatus collides unless some sort of traffic control is performed, each subscriber apparatus transmits an upstream optical signal using a time division slot designated by the station side apparatus.
The distance between the optical branching device and the plurality of subscriber devices varies depending on the subscriber device, and the attenuation of light differs depending on this distance. Also, a large difference in the attenuation of light occurs depending on how many optical branching devices are inserted between the station side device and the subscriber unit. For this reason, the upstream optical signal received by the station-side device has a large light intensity difference for each subscriber device.
[0005]
For this reason, the preamplifier used for the optical receiver of the station side device is required to have a low noise and a wide dynamic range. As such a preamplifier, for example, there is a technique disclosed in Japanese Patent Laid-Open No. 10-284955.
FIG. 9 shows a circuit diagram of this preamplifier. The preamplifier includes a photodiode PD that detects an optical signal from the optical fiber, an amplifier circuit 2 that amplifies a current generated from the photodiode PD, a power detection circuit 3 that detects an average output power of the amplifier circuit 2, and a gain. A control circuit 4 is provided.
[0006]
The amplifier circuit 2 includes a source grounded FET amplifier circuit 21 and a feedback circuit 22 that applies negative feedback to the input from the output of the FET amplifier circuit 21. The amplification factor of the FET amplifier circuit 21 is represented by -A (A> 0). The feedback circuit 22 includes a feedback resistor RB and a feedback FET 23 having a drain and a source coupled in parallel at both ends thereof.
The gain control circuit 4 is a circuit in which two FETs 41 and 42 are connected. The output voltage Vs of the amplifier circuit 2 is applied to the gate of the upper FET 42 and the output of the power detection circuit 3 is applied to the gate of the lower FET 41. A voltage Vp is applied. In this gain control circuit 4, the output voltage Vg is taken out from the drain of the lower stage FET 41.
[0007]
In the above preamplifier, when light is input to the photodiode PD, an input current is generated, and this current is inverted and amplified by the amplifier circuit 2 and output. The power detection circuit 3 detects the average intensity from the output waveform, generates a voltage Vp corresponding to the average intensity, and the voltage Vp is supplied to the gate of the FET 41 of the gain control circuit 4.
The output voltage Vg extracted from the drain of the FET 41 of the gain control circuit 4 becomes the gate voltage of the feedback FET 23 of the feedback circuit 22 and controls the resistance value between the source and drain of the feedback FET 23. Accordingly, the resistance value of the feedback circuit 22 changes and the gain of the amplifier circuit 2 can be changed. That is, it is possible to secure a wide dynamic range by increasing the gain as the intensity of the input optical signal increases and increasing the gain as the intensity of the input optical signal decreases. Further, such a preamplifier detects an average value of the optical input intensity, so that it is possible to remove noise components contained in the input light.
[0008]
On the other hand, in recent years, the optical communication speed has been further increased, and accordingly, the optical signal communicated between the station side apparatus and the subscriber apparatus has also been increased. Specifically, the bit period of the 0; 1 data signal (referred to as a burst signal) constituting the optical signal is shortened to about 1 nanosecond.
[0009]
[Patent Document 1] Japanese Patent Laid-Open No. 10-284955
[Patent Document 2] JP-A-5-304422
[0010]
[Problems to be solved by the invention]
In the preamplifier, it is preferable that the output voltage Vp of the power detection circuit 3 can completely follow the change of the optical input after the optical input from a certain subscriber apparatus until the optical input of the next subscriber apparatus. For this reason, if the strength detection time constant of the integrating circuit is shortened, the response is improved.
However, if it is too short, the power detection circuit 3 follows the pattern “0” and “1” of the burst signal, and the amplification gain of the preamplifier is not stable. For example, when the 0 (Low) signal continues, the output of the power detection circuit 3 is greatly increased, and the amplification gain of the preamplifier increases. When the 1 (High) signal continues, the output of the power detection circuit 3 is reduced to a small value, and the amplification gain of the preamplifier decreases. As described above, when the amplification gain of the preamplifier changes depending on the signal pattern, the output signal is distorted and causes jitter. Therefore, it is desirable that the output of the power detection circuit 3 is constant without depending on the signal pattern of the received data signal while receiving a signal from the same subscriber unit. For this reason, the intensity detection time constant of the integrating circuit needs to be lengthened to some extent.
[0011]
By the way, the pause time from receiving a signal from one subscriber unit to receiving a signal from the next subscriber unit is set short in order to increase data transmission efficiency. The preamble period of the data signal cannot be long. Therefore, if the intensity detection time constant of the integration circuit is lengthened, the amplification gain of the preamplifier is dragged by the optical reception intensity of the subscriber unit that has been received previously, and a stable optical reception intensity cannot be obtained.
SUMMARY OF THE INVENTION An object of the present invention is to provide a reception amplifier that can increase the time constant of intensity detection to a certain extent and that can completely follow the optical reception intensity of a subscriber unit and obtain a stable optical reception intensity.
[0012]
[Means for Solving the Problems]
The receiving amplifier of the present invention is used in an optical communication network for bidirectional communication between a station side device and a plurality of subscriber devices, and is generated from a light receiving element for detecting an optical signal from the subscriber device, and the light receiving element. An amplification circuit that amplifies the input current, a power detection circuit that detects a value of optical input intensity based on the output of the amplification circuit, a gain control circuit that changes the amplification gain of the amplification circuit, and a detection by the power detection circuit The optical input intensity value is read and stored in the memory, and the optical input intensity value stored in the memory is read at the time before the optical signal input from the same subscriber is expected, And a control unit that outputs a control signal for determining a control amount of the gain control circuit and supplies the control signal to the gain control circuit (claim 1).
[0013]
According to this receiving amplifier, the value of the optical input intensity of the subscriber is read and stored in the memory, and when the optical signal input from the same subscriber is expected, the gain control is performed based on the stored value. Determine the control amount of the circuit. Therefore, even if the optical input level differs for each subscriber, the amplification gain of the amplifier circuit also becomes a value corresponding to this stored value, and the output level of the amplifier circuit does not vary greatly from subscriber to subscriber.
In addition, since the control unit only has to read the value of the optical input intensity and store it in the memory when the optical input signal becomes stable after rising (claim 2), the time constant of the power detection circuit is the optical input It can be set as long as the signal normally lasts. Therefore, distortion and jitter do not occur in the output signal of the receiving amplifier, and an output signal with less noise can be obtained.
[0014]
The receiving amplifier of the present invention is used in an optical communication network, and a light receiving element for detecting an optical signal from a subscriber unit, an amplifier circuit for amplifying an input current generated from the light receiving element, and an output of the amplifier circuit A power detection circuit that detects an optical input intensity value using an integrating circuit, and a gain control circuit that changes an amplification gain of the amplifier circuit based on the optical input intensity value detected by the power detection circuit And the optical input intensity value detected by the power detection circuit is read and stored in the memory, and the optical input intensity stored in the memory at the time before the optical signal input from the same subscriber is expected. And a control unit for outputting a control signal for determining a control amount of the gain control circuit based on the value and inputting the control signal to the integration circuit of the power detection circuit. And that (claim 3).
[0015]
According to this receiving amplifier, the value of the optical input intensity of the subscriber is read and stored in the memory, and when the optical signal input from the same subscriber is expected, a control signal is output based on the stored value. The output intensity signal value of the power detection circuit is forcibly set by inputting to the integration circuit of the power detection circuit. Therefore, even if the optical input intensity differs for each subscriber, the amplification gain of the amplifier circuit also becomes a value corresponding to this stored value, and the output signal level of the amplifier circuit does not vary greatly from subscriber to subscriber.
[0016]
Further, since the gain control circuit changes the amplification gain of the amplifier circuit based on the value of the optical input intensity detected by the power detection circuit, even if the control unit should not work, the conventional optical input intensity Based on this value, real-time amplification gain control can be performed.
Further, when the optical input signal is stabilized after rising, the control unit may read the value of the optical input intensity from the integrating circuit of the power detection circuit and store it in the memory (Claim 4). The integration circuit time constant of the circuit can be set as long as the period during which the subscriber's optical input signal normally lasts. Therefore, distortion and jitter do not occur in the output signal, and an output signal with less noise can be obtained.
[0017]
The receiving amplifier inputs a signal corresponding to the value of the optical input intensity detected by the power detection circuit and an integration circuit of the power detection circuit to a signal corresponding to the value of the optical input intensity stored in the memory. A terminal can be provided in common (Claim 5). This common terminal requires only one input / output interface for the receiving amplifier. When the receiving amplifier is integrated, the circuit configuration can be simplified and the size can be reduced.
[0018]
Further, the reception gain control method of the present invention detects an optical signal from a subscriber unit, amplifies an input current generated from a light receiving element, detects a value of an optical input intensity based on the amplified output, The value of the light input intensity detected by the power detection circuit is read and stored in the memory, and the value of the light input intensity stored in the memory is stored at a time before an optical signal input from the same subscriber is expected. In this method, the gain for amplifying the input current generated from the light receiving element is changed based on the read value.
[0019]
According to this method, the value of the optical input intensity of the subscriber is read and stored in the memory, and when the optical signal input is expected, the amplification gain of the amplifier circuit is determined based on the stored value. Therefore, even if the optical input level differs for each subscriber, the amplification gain of the amplifier circuit also becomes a value corresponding to this stored value, and the output level of the amplifier circuit does not vary greatly from subscriber to subscriber.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram showing a PON system. The PON system component in the station building is referred to as a station-side device 100, and the PON system component in the subscriber premises is referred to as a subscriber-side device 500. The PON system includes a station-side device 100, a plurality of subscriber-side devices 500, and an optical branching device 300. The station-side device 100 and the optical branching device 300 are connected by a trunk optical fiber 200. And the subscriber-side device 500 are connected by branch optical fibers 400, respectively. The trunk optical fiber 200 and the branch optical fiber 400 are collectively referred to as “optical fiber”. A single mode fiber is used as the optical fiber. The optical branching device 300 is configured by a star coupler.
[0021]
The downstream optical signal from the station side device 100 to the subscriber side device 500 and the upstream optical signal from the subscriber side device 500 to the station side device 100 are each composed of a packet (also referred to as an optical signal).
The station-side device 100 receives a packet sent from a higher-level network (such as the Internet), sends it to the subscriber-side device 500 through an optical fiber, receives the packet sent from the subscriber-side device 500, It has a function to send to the network.
[0022]
The station-side device 100 includes an optical transmission line termination device OLT (Optical Line Terminals) serving as a connection end to the trunk optical fiber 200, a layer 2 switch, a broadband access router serving as a connection end of a higher-level network, and the like.
The subscriber-side device 500 includes a personal computer installed in a home, an optical subscriber line termination unit ONU (Optical Network Unit) that transmits and receives broadband optical signals of the personal computer to an optical network, and the like.
[0023]
The operation of the PON system will be briefly described. Downstream packets entering the station-side device 100 from the higher-level network are subjected to predetermined processing by the layer 2 switch in the station-side device 100. Then, it is transmitted to the optical fiber through the optical transmission line termination device OLT. The optical signal transmitted to the optical fiber is branched by the optical branching device 300 and transmitted to the subscriber-side device 500 connected to the optical branching device 300. The subscriber-side device 500 having the same destination address matches the optical signal. And decrypt the packet.
[0024]
On the other hand, the uplink packet transmitted from the subscriber side device 500 is transmitted to the station side device 100 via the optical branching device 300. In the station apparatus 100, after predetermined processing is performed by the layer 2 switch, it is transmitted from here to the upper network via the broadband access router.
It is necessary to prevent the upstream packets transmitted from the subscriber apparatus 500 from competing with each other in time. Therefore, when transmitting a packet from the station-side device 100 to the subscriber-side device 500, the station-side device 100 assigns an uplink time slot (hereinafter simply referred to as “slot”) to each subscriber-side device 500. The subscriber side device 500 to which the slot is assigned transmits an uplink packet to the assigned slot. Therefore, contention for upstream packets between the subscriber side devices 500 is avoided. The station side device 100 and the subscriber side device 500 need to share a clock. This time adjustment includes the time information in the packet when performing packet communication. Can be done.
[0025]
-Preamplifier configuration example 1-
FIG. 2 is a circuit diagram of the preamplifier 1 provided in the station side device 100. As in the circuit of FIG. 9, the preamplifier 1 amplifies the input current generated from the photodiode PD that receives optical input to obtain a voltage signal, and the optical power based on the output of the amplifier circuit 2. A power detection circuit 3 for detection and a feedback control circuit 4 are provided.
The detection value of the power detection circuit 3 is referred to as “MON value”. Since the amplifier circuit 2 is an inverting amplifier circuit, the MON value decreases when the optical input is large, and the MON value increases when the optical input is small.
[0026]
The FET described below is composed of an n-channel Schottky field effect transistor formed on a GaAs semiconductor layer, but the present invention is not limited to this and is formed on a silicon substrate or the like. It may be composed of a MOSFET or the like.
The amplifier circuit 2 includes a common source FET amplifier circuit 21 and a feedback circuit 22 in which the drain and source of the feedback FET 23 are coupled in parallel to both ends of the feedback resistor RB. The feedback circuit 22 applies negative feedback from the output of the FET amplifier circuit 21 to the input.
[0027]
The feedback control circuit 4 is a circuit in which two FETs 41 and 42 are connected. The output voltage Vs of the amplifier circuit 2 is applied to the gate of the upper FET 42, and the output voltage Vg is extracted from the drain of the lower FET 41.
A difference from the conventional configuration is that a control unit 5 is provided, and the output voltage Vp of the power detection circuit 3 is input to the control unit 5. The control voltage Vc to be supplied to the gate of the lower stage FET 41 of the feedback control circuit 4 is output from the control unit 5.
[0028]
The controller 5 is attached with a memory 6 that stores the MON value of the power detection circuit 3 detected in the past for each subscriber.
One of the functions of the control unit 5 is to identify which subscriber side is receiving data being received and which subscriber side is next to transmit data, and refer to the memory 6 The control voltage Vc is set for each subscriber side and supplied to the feedback control circuit 4.
[0029]
FIG. 3 is a flowchart showing the flow of processing of the control unit 5 when the control unit 5 is configured by a computer or the like and the function is realized by software. However, the function of the control unit 5 does not necessarily need to be realized by software, and it should be noted in advance that the control unit 5 may be configured by a circuit element.
With reference to FIG. 3, the control part 5 specifies the subscriber X who receives an optical signal next (step S1). As described above, since the station apparatus 100 allocates a slot to each subscriber apparatus 500, the subscriber X can be identified based on the allocation information.
[0030]
The MON value corresponding to the subscriber X stored in the memory 6 is read (step S2). When the optical signal is received from the subscriber X for the first time, the MON value is set to the maximum level as a default.
Then, a voltage signal (referred to as a CNT signal) to be supplied to the gate of the lower stage FET 41 of the feedback control circuit 4 is obtained as a function CNT (MON) of the MON value (step S3).
[0031]
The function CNT (MON) may be the MON value itself detected and stored from the previous subscriber X (in this case, the function form CNT (X) = X). However, this may cause the amplification gain to overshoot and not quickly converge to an appropriate gain.
Therefore, the following statistical processing may be performed. The function CNT (MON) may be an average of the MON values as long as the optical signal has been received from the subscriber X in the past several times (N times) (in this case, CNT (X) = (1 / N) Σxi; i is a subscript indicating the number of stored data and is from 1 to N).
[0032]
Further, the previously set CNT signal value may be included in the function so as not to deviate significantly from the previously set CNT signal value. For example, if the CNT signal value set at the time of reception from the previous subscriber X is written as CNT (previous) and (MON value read this time−MON value read last time) is written as ΔMON, CNT (MON) = CNT (Previous) + αΔMON (α is a positive constant for weighting; 0 <α <1; convergence is faster as α is closer to 1, but may jump out; convergence is slower as α is closer to 0 But the risk of jumping out is less).
[0033]
The CNT signal is output to the feedback control circuit 4 (step S4). The feedback control circuit 4 extracts an output voltage (referred to as a gate voltage) Vg from the drain of the lower stage FET 41 of the feedback control circuit 4 in accordance with the input CNT signal. This gate voltage Vg is applied to the gate of the feedback FET 23 of the feedback circuit. As a result, the feedback amount of the feedback circuit is determined, and the amplification gain of the amplifier circuit 2 is determined accordingly.
That is, when the previous MON value is large, the CNT signal is large, the voltage Vc is large, the gate voltage Vg is small, the VGS is small, the resistance value between the source and drain of the feedback FET 23 is large, and the feedback amount is small. It is set large. On the other hand, when the previous MON value is small, the amplification gain of the amplifier circuit 2 is set small.
[0034]
Next, when an optical signal is received from the subscriber-side device 500 of the subscriber X (step S5), this optical signal is amplified with the amplification gain of the amplification circuit 2 corresponding to the CNT signal.
The MON value in this case is measured in real time (step S6). Then, the measured MON value is stored in the memory 6 as the latest MON value (step S7). The value stored in this way is used for adjusting the amplification gain when the optical signal of the subscriber X is received next time.
[0035]
FIG. 4 is a waveform diagram for explaining an amplification gain adjusting method when optical signals of a plurality of subscribers A and B are received. FIG. 4A shows the respective received light levels when the optical signal of subscriber A is received and the optical signal of subscriber B is subsequently received a plurality of times. FIG. 4B shows the detected MON value of the power detection circuit 3 in real time. FIG. 4C shows the amplification gain of the amplifier circuit 2.
It is assumed that the optical signal of the subscriber A has been received last time, and the MON value is stored in the memory 6. Therefore, an appropriate amplification gain is obtained throughout the reception period by the control of FIG. 3 (see time point E). However, the optical signal is received from the subscriber B for the first time, and the default value which is the maximum level is stored as the MON value. For this reason, the optical signal (see time point A) from the subscriber B is amplified with the maximum gain (see time point B). Since the MON value of the optical signal from the subscriber B (see time point A) is stored in the memory 6, when the optical signal is subsequently received from the subscriber B (see time point C), the MON value stored in the memory 6 is stored. Based on the above, an appropriate gain can be set by the control of FIG. 3 (see time point D). In this way, the gain of the amplifier circuit 2 can be changed according to the optical signal level from the subscriber, so that a wide dynamic range can be ensured.
[0036]
Further, as can be seen from FIG. 4C, the MON value is stored in the memory 6, and an appropriate amplification is performed based on the stored MON value before the optical signal is next received from the subscriber. Since the gain can be set in advance, stable optical amplification can be performed even when the burst signal rises (see time point F in FIG. 4A).
In addition, the power detection circuit 3 sets the time constant of the integration circuit to the extent that the intensity can be detected during reception of one optical signal, and when the detection signal of the power detection circuit 3 becomes stable (see time points A and C), MON Since the value only has to be taken in, the time constant of the power detection circuit 3 may not be so small. That is, the response of the power detection circuit 3 may not be so fast.
[0037]
FIG. 5 is a specific circuit diagram of the power detection circuit 3. The power detection circuit 3 can be realized by an integration circuit of a resistor R and a capacitor C as shown in FIG.
-Preamplifier configuration example 2-
Next, another configuration example of the preamplifier will be described. The preamplifier 1 shown in FIG. 2 has two terminals, a PWR_MON terminal that outputs a detection signal of the power detection circuit 3 and a CNT terminal for inputting the CNT signal to the feedback control circuit 4. In this case, when the power detection circuit 3 is incorporated and the preamplifier 1 is integrated, it is necessary to provide a pad for each input / output interface on the IC substrate, which is disadvantageous in terms of area. Therefore, these two terminals are made common.
[0038]
FIG. 6 is a circuit diagram showing the preamplifier 1 ′ having the common terminal MUT and the control unit 5 connected thereto. The power detection circuit 3 of the preamplifier 1 'is realized by an integration circuit of a resistor R and a capacitor C shown in FIG.
The preamplifier 1 'obtains the following two functions through this common terminal MUT. One is a function to output the detection signal of the power detection circuit 3 as before, and the other one is to forcibly charge or discharge the integration circuit in the power detection circuit 3 so as to be in an initial state. It is a function to make.
[0039]
The charging voltage or discharging voltage is a voltage based on the CNT value described above. The CNT value may be a voltage based on the MON value. However, if there is a possibility that the amplification gain overshoots and does not converge quickly to an appropriate gain, as described above, the average of the MON values received from the subscriber X in the past multiple times may be used. Good. Further, the previously set CNT signal value may be included in the function so as not to deviate significantly from the previously set CNT signal value.
[0040]
In FIG. 6, the control unit 5 has a PWR_MON terminal that takes in a detection signal of the power detection circuit 3, an INIT terminal that sets the power detection circuit 3 to an initial state, and a switch 7 that switches ON / OFF of the initialization function. . When the power detection circuit 3 is set to the initial state from the controller 5, the switch 7 is turned on. In the state where the switch 7 is turned on, the control unit 5 can charge and discharge the capacitor C constituting the integrating circuit in the power detection circuit 3. The time constant of charge / discharge is determined by the capacitance of the capacitor C and the output impedance R ′ of the INIT terminal. If R ′ is smaller than the resistance value R of the power detection circuit 3, the charge / discharge time can be made faster than the normal response time of the power detection circuit 3 to the optical input signal. The power detection circuit 3 smoothes the output of the preamplifier 1 ', and its voltage fluctuation range is about 1V at most. Assuming that the output of the power detection circuit 3 having a 100 pF capacitor is changed by 1 V, the output voltage can be changed in 100 nsec by charging and discharging a current of 1 mA from the INIT terminal of the control unit 5. .
[0041]
The control unit 5 turns on the switch 7 before the start of reception when the optical input signal changes greatly, calculates the CNT value based on the MON value stored in the memory 6, and uses this CNT value as the power detection circuit 3. , The power detection circuit 3 is brought into an initial state. As a result, the voltage of the integration circuit of the power detection circuit 3 is forced to a CNT value. The power detection circuit 3 inputs this CNT value directly to the feedback control circuit 4. Thus, the amplification gain can be set to an appropriate value before the optical input signal enters.
[0042]
Next, when the output of the power detection circuit 3 is stabilized, the switch 7 is turned OFF to take in the voltage of the integration circuit in the power detection circuit 3. That is, at this time, the common terminal functions as a PWR_MON terminal.
FIG. 7 is a graph showing the time transition of the MON value / CNT value of the control unit 5 described above. FIG. 7A shows the respective received light levels when the optical signal of subscriber A is received and then the optical signal of subscriber B is received a plurality of times. FIG. 7B is a waveform diagram of the MON value / CNT value, and FIG. 7C is a voltage waveform diagram of the common terminal MUT of the power detection circuit 3.
[0043]
It is assumed that the optical signal of the subscriber A has been received before and the MON value is stored in the memory 6. Before the optical signal of the subscriber A enters, the switch 7 is turned on, and the power detection circuit 3 is initialized by using the CNT value calculated based on the MON value of the subscriber A stored in the memory 6. (See (1) in FIG. 7). This CNT value is an appropriate value based on the MON value stored in the memory 6. When the optical signal of the subscriber A enters, the switch 7 is turned off and the detection signal of the power detection circuit 3 is detected. The detected MON value slightly changes from the CNT value, but the CNT value is a value calculated based on the previously received MON value of the subscriber A, and the change is small and does not cause a problem. Therefore, the gain is stable throughout the reception period (see (2) in FIG. 7).
[0044]
Next, before the optical signal of the subscriber A ends and the optical signal of the subscriber B comes in, the switch 7 is turned on, and the calculation is performed based on the MON value of the subscriber B stored in the memory 6 The power detection circuit 3 is initialized by using the CNT value. The subscriber B is receiving for the first time, and the memory 6 stores the default maximum level as the MON value as described above. Therefore, the maximum CNT value is output. For this reason, the amplification gain of the preamplifier is maximized (see FIG. 7 (3)).
[0045]
When the optical signal of subscriber B is received, switch 7 is turned off. Due to the time constant of the power detection circuit 3, the detected MON value of the power detection circuit 3 gradually decreases to a predetermined level (see (4) in FIG. 7). Thereby, the amplification gain of the preamplifier gradually decreases from the maximum gain state. The control unit 5 takes in the MON value and stores it in the memory 6 when the detected MON value of the power detection circuit 3 settles (see time point E). This stored MON value becomes the initial value set when the optical signal of subscriber B is received next time.
[0046]
Next, before the optical signal of the same subscriber B enters, the switch 7 is turned on, and the power is detected using the CNT value calculated based on the MON value of the subscriber B stored in the memory 6 The circuit 3 is set to an initial state (see (5) in FIG. 7). When the optical signal of the subscriber B enters, the switch 7 is turned off and the detection signal of the power detection circuit 3 is taken in (see (6) in FIG. 7). The acquired MON value is not different from the MON value in the initial state.
[0047]
Therefore, as in FIG. 4, an appropriate amplification gain is obtained throughout the optical signal reception period except for the first subscriber. In this manner, the gain of the amplifier circuit 2 is changed according to the optical signal level from the subscriber, and a wide dynamic range can be ensured.
In the embodiment of FIGS. 6 and 7, the control unit 5 forcibly charges or discharges the integration circuit in the power detection circuit 3 at the start of reception when the optical input greatly changes, and amplifies it. By measuring and storing the state of the integrating circuit of the power detection circuit 3 when the gain is stabilized and the optical input is stabilized, it is possible to prepare for the next optical input from the same subscriber. In order to realize these functions, the preamplifier 1 ′ need only have one common terminal MUT. Therefore, when the preamplifier 1 'is integrated, only one input / output interface is required on the IC substrate, so that the configuration of the integrated circuit can be simplified and the area can be reduced.
[0048]
Further, since the detection output of the power detection circuit 3 is directly input to the feedback control circuit 4, even when the function of the control unit 5 fails or is stopped, the real-time amplification gain based on the detected value of the optical input intensity is the same as in the past. Control can be performed. This is a useful measure as a safety measure against a failure of the control unit 5.
Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above-described embodiments. For example, the control unit 5 in FIG. 6 internally generates a CNT value for setting the power detection circuit 3 in an initial state, and supplies the CNT value to the power detection circuit 3 through the switch 7. However, as shown in FIG. 8, voltage sources corresponding to several CNT values may be prepared in advance, a predetermined voltage source may be selected by the switch 7a, and supplied to the power detection circuit 3 therefrom. . In addition, various modifications can be made within the scope of the present invention.
[0049]
【The invention's effect】
As described above, according to the present invention, the value of the optical input intensity of the subscriber is read and stored in the memory, and when the optical signal input is expected, the amplification of the preamplifier is performed based on the stored value. Since the gain is determined, even if the optical input level is different for each subscriber, the amplification gain of the amplifier circuit becomes a value corresponding to this, and the output level of the amplifier circuit is kept constant. Therefore, even when the optical input level changes for each subscriber, it is possible to secure a wide dynamic range.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a PON system.
2 is a circuit diagram of a preamplifier 1 provided in the station side device 100. FIG.
FIG. 3 is a flowchart showing a processing flow of the control unit 5 when the control unit 5 is configured by a computer or the like and the function is realized by software.
FIG. 4 is a waveform diagram for explaining an amplification gain adjustment method when optical signals of a plurality of subscribers A and B are received.
FIG. 5 is a specific circuit diagram of the power detection circuit 3;
6 is a circuit diagram showing a preamplifier 1 ′ having a common terminal MUT and a control unit 5. FIG.
FIG. 7 is a graph showing a time transition of the MON value / CNT value of the control unit 5;
FIG. 8 is a circuit diagram showing a control unit 5 in which a predetermined voltage source is selected by a switch 7a.
FIG. 9 is a circuit diagram of a conventional preamplifier.
[Explanation of symbols]
1 Preamplifier
2 Amplifier circuit
3 Power detection circuit
4 Feedback control circuit
5 Control unit
6 memory
7,7a switch
21 FET amplifier circuit
22 Feedback circuit
23 Feedback FET
41 Lower FET
42 Upper FET
100 station side equipment
500 Subscriber side equipment
300 Optical splitter
200 Trunk optical fiber
400 Branch line optical fiber
PD photodiode

Claims (6)

A receiving amplifier used in an optical communication network for bidirectional communication between a station-side device and a plurality of subscriber devices,
A light receiving element for detecting an optical signal from the subscriber unit;
An amplifier circuit for amplifying an input current generated from the light receiving element;
A power detection circuit that detects a value of optical input intensity based on the output of the amplifier circuit;
A gain control circuit for changing the amplification gain of the amplifier circuit;
The value of the optical input intensity detected by the power detection circuit is read and stored in the memory, and the optical input intensity value stored in the memory at the time before the optical signal input from the same subscriber is expected. And a control unit that outputs a control signal for determining a control amount of the gain control circuit based on the value and supplies the control signal to the gain control circuit. 2. The receiving amplifier according to claim 1, wherein the control unit reads the value of the optical input intensity and stores it in a memory when the optical input signal is stabilized after rising. A receiving amplifier used in an optical communication network for bidirectional communication between a station-side device and a plurality of subscriber devices,
A light receiving element for detecting an optical signal from the subscriber unit;
An amplifier circuit for amplifying an input current generated from the light receiving element;
A power detection circuit that detects a value of light input intensity based on an output of the amplification circuit using an integration circuit;
A gain control circuit that changes the amplification gain of the amplifier circuit based on the value of the optical input intensity detected by the power detection circuit;
The value of the optical input intensity detected by the power detection circuit is read and stored in the memory, and the optical input intensity value stored in the memory at the time before the optical signal input from the same subscriber is expected. And a control unit that outputs a control signal for determining a control amount of the gain control circuit based on the value, and inputs the control signal to the integration circuit of the power detection circuit. A characteristic receiving amplifier. 4. The reception amplifier according to claim 3, wherein the control unit reads the value of the optical input intensity from the integrating circuit of the power detection circuit and stores it in a memory when the optical input signal is stabilized after rising. A terminal for outputting the value of the light input intensity detected by the power detection circuit and a terminal for inputting a signal corresponding to the value of the light input intensity stored in the memory to the integration circuit of the power detection circuit The receiving amplifier according to claim 3, wherein the receiving amplifier is provided. A method for controlling a reception gain of a reception amplifier used in an optical communication network for bidirectional communication between a station side device and a plurality of subscriber devices,
Detect the optical signal from the subscriber unit,
Amplifies the input current generated from the light receiving element,
Detecting the value of light input intensity based on the amplified output;
Reading the value of the detected light input intensity and storing it in a memory;
At the time before optical signal input from the same subscriber is expected, the value of the optical input intensity stored in the memory is read out,
A receiving gain control method, wherein a gain for amplifying an input current generated from the light receiving element is changed based on the value.

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