JP2007129639A - Optical burst cell signal reception circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a high sensitivity and a wide dynamic range, and to eliminate an influence of trailing without using a special circuit. <P>SOLUTION: A level of an electric burst cell signal outputted from an APD 1 is detected by a level detection circuit 4 to determine an intensity of reception light, and a bias voltage applied to the APD 1 by an APD driving circuit 2 is switched to a high voltage in a moment in the case of a low intensity of reception light, and also is switched to a low voltage in a moment in the case of a low intensity of reception light. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical burst cell signal receiving circuit using an APD (avalanche photodiode) in an upstream signal receiver of a PON (Passive Optical Network) system.

  The PON system is a cost-effective system in which an optical fiber transmission line and a station apparatus are shared by a plurality of users. The number of PON service subscribers is increasing rapidly, and research on improvement of transmission efficiency and speeding up is actively conducted (for example, see Non-Patent Document 1). In the future, the service area of the PON system will expand not only in urban areas but also in suburban areas, and it will be necessary to increase the transmission speed by increasing the number of users and the appearance of new services. Therefore, an increase in optical loss in the PON section due to an increase in transmission distance or an increase in the number of branches and a deterioration in reception sensitivity due to speeding up become problems.

  FIG. 4A is a diagram showing the configuration of this PON system, 31 is an OLT (Optical Line Terminal) on the station side, 32 is an ONU (Optical Network Unit) on the user side, 33 is an optical splitter, and 34 is an optical fiber transmission. Road. A plurality of ONUs 32 are connected to the OLT 31 via the optical splitter 33. In this PON system, the transmission (downstream) signal from the OLT 31 to the ONU 32 is continuous light. However, since the distance between the OLT 31 and the ONU 32 differs depending on the user, the transmission (upstream) signal from the ONU 32 to the OLT 31 is shown in FIG. As shown in (b), the optical burst cell signal has different light intensity depending on the user. Accordingly, the receiver on the OLT 31 side is required to have a high dynamic range and a wide dynamic range capable of receiving a different intensity optical burst cell signal.

  As an effective means for improving reception sensitivity, there is a method using APD having a multiplication effect. However, in this case, there is a problem that “slowing”, which will be described later, is caused by the instantaneous response of the APD driving circuit, and the reception of the next weak burst cell signal is hindered particularly when a strong optical burst cell is received.

  To solve this problem, an optical burst cell signal receiving circuit that realizes high sensitivity and wide dynamic range by setting an APD multiplication factor according to the intensity of the optical burst cell signal has been proposed (for example, , See Patent Document 1).

  FIG. 5 is a diagram showing this optical burst cell signal receiving circuit. APD1, APD driving circuit 9, preamplifier 3, level detecting circuit 4, AGC (Automatic Gain Control) circuit 5, identification timing extracting circuit 6, bypass circuit 7, The switch 8 is composed of switches SW1 and SW2.

  In this optical burst cell signal receiving circuit, the input optical burst cell signals having different optical intensities are photoelectrically converted into electric burst cell signals by the APD 1 and output to the preamplifier 3. The output of the print amplifier 3 is input to the level detection circuit 4, and after the received optical power level is determined as a threshold, it is output to the APD drive circuit 9. The APD drive circuit 9 changes the APD bias voltage based on the output of the level detection circuit 4 and controls the multiplication factor of the APD 1. The switching unit 8 is a circuit for removing the influence of “slow pull”. “Sosohiki” is a phenomenon in which when a weak burst cell signal is received immediately after a strong burst cell signal, the influence interferes with the weak burst cell signal and degrades reception sensitivity.

The switching device 8 turns off the switch SW2 of the switching device 8 and connects the switch SW1 to the bypass circuit 7 while the “slowing” occurs so that this “slowing” is not input to the identification timing extraction circuit 6. To do. Then, the switch SW1 is turned off again, the switch SW2 is turned on again, and the electric burst cell signal converted by the APD1 is input to the identification timing extraction circuit 6 during the time when the influence of “soohiki” does not appear. As described above, the effect of “Sosohiki” is eliminated, and high sensitivity and wide dynamic range are realized.
Xing-Zhi Qiu, Peter Ossieur, Johan Bauwelinck, Yanchun Yi, Dieter Verhulst, Jan Vandewege, Benoit De Vos, and Paolo Solina, "Development of GPON Upstream Physical-Media-Dependent Prototypes", JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL.22 NO.11, NOVEMBER 2004, p2498-2508. Japanese Patent Laid-Open No. 11-355218

  As described above, in Patent Document 1, the APD 1 is connected to the bypass circuit 7 using the switch 8 only during the period in which the “slowing” occurs, thereby eliminating the influence of the “slowing” of the APD 1. However, this method requires the switch 8 and the bypass circuit 7 and has a problem that its configuration and switching control are complicated. There is also a problem that the noise current density input to the preamplifier becomes large due to the influence of the large parasitic capacitance component of the switch 8.

  The present invention has been made under such a background, and controls the APD multiplication factor by using a circuit capable of instantaneously changing the bias voltage to achieve high sensitivity and wide dynamic range. It is an object of the present invention to provide an optical burst cell signal receiving circuit that does not require a special circuit for eliminating the influence of "soaking".

In order to solve the above problems, an optical burst cell signal receiving circuit according to a first aspect of the present invention detects an APD that converts an input optical burst cell signal into an electric burst cell signal, and a level of the electric burst cell signal. A level detection circuit that determines the received light intensity, and an APD drive circuit that switches a bias voltage applied to the APD according to the received light intensity determined by the level detection circuit. Switch means that turns on when received light intensity determined by the level detection circuit is high, and turns off when low, and outputs a low bias voltage when the switch means turns on, and outputs a high bias voltage when the switch means turns off And a voltage dividing circuit.
According to a second aspect of the present invention, in the optical burst cell signal receiving circuit according to the first aspect, the APD driving circuit switches the bias voltage applied to the APD to a high voltage in an initial state, and is determined by the level detection circuit. The APD driving circuit is switched to a low voltage when the received light intensity is high and switched to a high voltage when the received light intensity is low.
According to a third aspect of the present invention, in the optical burst cell signal receiving circuit according to the second aspect, the APD driving circuit differentiates the signal indicating the received light intensity determined by the level detecting circuit to differentiate the burst cell signal. A high-pass filter that generates a differential pulse at the start time and end time, and is reset in an initial state, and is set when the differential pulse indicating the start time of the high-pass filter exceeds a first reference value to indicate the end time A latch circuit that is reset when the differential pulse falls below the second reference value, and the bias voltage applied to the APD is switched to a high voltage when the latch circuit is reset, and the voltage is lowered when the latch circuit is set. And switch means for switching.

  According to the present invention, it is possible to instantaneously change the bias voltage that determines the multiplication factor of the APD, so that a switching device that bypasses the influence of “slowing” becomes unnecessary. Further, by removing the large parasitic capacitance component of the switch, the noise current density input to the preamplifier is reduced, and the reception sensitivity improvement effect of the entire reception system can be obtained at the same time. Therefore, high reception sensitivity and wide dynamic range can be realized at the same time, and high-efficiency transmission that does not require an increase in PON frame overhead is possible.

[First embodiment]
FIG. 1 is a block diagram showing a configuration of an optical burst cell signal receiving circuit according to a first embodiment of the present invention. 1 is an APD that converts an optical burst cell signal into an electric burst cell signal, and 2 is a bias voltage applied to APD 1. APD driving circuit, 3 is a preamplifier, 4 is a level detection circuit that receives an electric burst cell signal and compares it with a threshold value to determine the level of light intensity, and 5 is an AGC (Automatic Gain) that amplifies the electric burst cell signal to a certain level. Control) circuit 6 is an identification timing extraction circuit for inputting an electric burst cell signal and performing clock extraction and data identification.

  FIG. 2 is a block diagram including specific components of the APD driving circuit 2 in FIG. The APD drive circuit 2 includes an amplifier 21 that amplifies the pulse signal from the level detection circuit 4 to a certain level, an NMOS transistor M1 (switch means) that performs an on / off operation in response to the output of the amplifier 21, and a high multiplication factor. VH output circuit 22 for supplying the bias voltage VH at the time, resistors R1 and R2 for dividing the voltage VH when the transistor M1 is turned on, and a capacitor C1 for stabilizing the bias voltage VH. A common connection point of the resistors R1 and R2 is connected to the cathode of the APD 1 as a bias voltage output point.

  The burst cell signal received by the APD 1 and converted into an electric signal is amplified by the preamplifier 3 and input to the level detection circuit 4. In the level detection circuit 4, a threshold value is determined. If it is determined that the received light intensity is strong, a pulse signal having a pulse width corresponding to the time of the optical burst cell signal is output, and if it is determined to be an appropriate value, no pulse signal is output. . When the output signal of the level detection circuit 4 is input to the amplifier 21 in the APD driving circuit 2, when there is no pulse output of the level detection circuit 4, that is, when the received light intensity is an appropriate value, the output of the amplifier 21 is The level becomes low, and the transistor M1 is turned off. At this time, the voltage VH output from the VH output circuit 22 is applied as a bias voltage to the APD 1 via the resistor R1. At this time, APD1 is set to a high multiplication factor.

  On the other hand, when a pulse signal is output from the level detection circuit 4, that is, when the received light intensity is high, the output of the amplifier 21 is at a high level and the transistor M1 is turned on. Since the bias voltage at this time is a low voltage obtained by dividing the voltage VH by the resistors R1 and R2, the APD1 is set to a low multiplication factor.

  As described above, the bias voltage applied to the APD 1 can be instantaneously switched to a high voltage if the intensity of the received optical burst cell signal is low, and to a low voltage if the intensity is high, thereby realizing high sensitivity and wide dynamic range. It is possible to prevent the influence of “Hiki”.

[Second Embodiment]
FIG. 3 is a block diagram including specific components of the APD driving circuit 2 of the second embodiment. The APD driving circuit 2 includes a capacitor C2 and resistors R3 and R4, a high-pass filter 23 that differentiates a pulse signal output from the level detection circuit 4, and a reference voltage Va and a comparator CP1. The output pulse signal of the high-pass filter 23 is a voltage. A low multiplication factor setting circuit 24 that issues a low multiplication factor setting command when higher than Va, and a high multiplication factor that issues a high multiplication factor setting command when the output pulse signal of the high-pass filter 23 is lower than the voltage Vb. Magnification setting circuit 25, latch circuit 26 that performs set / reset by the output signals (rise to high level) of these setting circuits 24, 25, VH output circuit 27 that provides bias voltage VH for high multiplication factor, A VL output circuit 28 for applying a bias voltage VL for multiplication factor, and a PMOS connected to the CMOS and receiving the output of the latch circuit 26 Transistor M2 and the NMOS transistor M3 is configured from a (switching means).

  2, the signal input to the level detection circuit 4 is subjected to threshold determination, and when the intensity of the received optical burst cell signal is high, a pulse signal is output to the APD driving circuit 2. input. In the APD driving circuit 2, the pulse signal is differentiated by the high-pass filter 23, and a differential pulse signal having a large amplitude is generated at the start and end of the pulse signal, and the low multiplication factor setting circuit 24 and the high multiplication factor setting circuit are generated. 25. In the low multiplication factor setting circuit 24, when a pulse signal having a level higher than the voltage Va is input, a high level signal rises. In the high multiplication factor setting circuit 25, a signal having a level lower than the voltage Vb is input. Therefore, if the output voltage Vo of the high-pass filter 23 is Vb <Vo <Va, the outputs of the low multiplication factor setting circuit 24 and the high multiplication factor setting circuit 25 do not become high, and the latch circuit 26 has the set terminal S. No high level rising signal is input to any of the reset terminals R, and the current state is maintained.

  When the output Q of the latch circuit 26 is high, the transistor M2 is turned off and M3 is turned on to output a bias voltage VL that gives a low multiplication factor. When the output Q is low, the transistor M2 is turned on and M3 is turned off. Thus, a bias voltage VH giving a high multiplication factor is output. In the initial state, the latch circuit 26 is set to the reset state so that a bias voltage VH giving a high multiplication factor is output. The latch circuit 26 stores the previous state until a new input is received.

  When a high-intensity optical burst cell signal is input to the APD 1, the output differential pulse level of the high-pass filter 23 exceeds the voltage Va at the beginning of the APD 1, so that the output of the low multiplication factor setting circuit 24 becomes high, and the latch circuit 26, the output Q becomes high, the transistor M3 is turned on, the bias voltage VL is applied to the APD1, and the low multiplication factor is set. At this time, since the level of the output differential pulse of the high-pass filter 23 is lower than Vb thereafter, the output of the high multiplication factor setting circuit 25 becomes high, the latch circuit 26 is reset, and the output Q becomes low, The transistor M3 is turned off and the transistor M2 is turned on, and a bias voltage VH giving a high magnification is output. That is, it is reset to the initial state.

  As described above, also in this embodiment, the bias voltage applied to the APD 1 is instantaneously switched to a high voltage when the intensity of the received optical burst cell signal is low, and to a low voltage when it is high, thereby achieving high sensitivity and a wide dynamic range. This can be realized, and the influence of “sowing” can be prevented. Furthermore, in this embodiment, the bias voltage VH is initially set to be high, but when a high-intensity optical burst cell signal is input, a low bias voltage VL is set, and when the optical burst cell signal ends, the bias voltage VH is high. The bias voltage VH is reset to prepare for reception of the next optical burst cell signal.

1 is a block diagram showing a configuration of an optical burst cell signal receiving circuit according to a first embodiment of the present invention. FIG. It is a block diagram of the principal part of the optical burst cell signal receiving circuit containing the APD drive circuit part of 1st Example. It is a block diagram of the principal part of the optical burst cell signal receiving circuit containing the APD drive circuit part of 2nd Example. (a) is a schematic explanatory diagram of the PON system, and (b) is a waveform diagram showing a PON upstream burst cell signal. It is a block diagram which shows the structure of the conventional optical burst cell signal receiving circuit.

Explanation of symbols

1: APD (avalanche photodiode)
2: APD driving circuit, 21: amplifier, 22: VH output circuit, 23: high-pass filter, 24: low multiplication factor setting circuit, 25: high multiplication factor setting circuit, 26: latch circuit, 27: VH output circuit, 28: VL output circuit 3: Preamplifier 4: Level detection circuit 5: AGC circuit 6: Identification timing extraction circuit 7: Bypass circuit 8: Switch 9: APD drive circuit

Claims (3)

An APD that converts an input optical burst cell signal into an electrical burst cell signal, a level detection circuit that detects the level of the electrical burst cell signal and determines the received light intensity, and the received light intensity determined by the level detection circuit And an APD driving circuit that switches a bias voltage applied to the APD according to
The APD drive circuit is turned on when the received light intensity determined by the level detection circuit is high, and is turned off when the received light intensity is low. When the switch means is turned on, the APD drive circuit outputs a low bias voltage and turns off. And a voltage dividing circuit for outputting a high bias voltage. In the optical burst cell signal receiving circuit according to claim 1,
In the initial state, the APD driving circuit switches the bias voltage applied to the APD to a high voltage, switches to a low voltage when the received light intensity determined by the level detection circuit is high, and switches to a high voltage when the received light intensity is low. An optical burst cell signal receiving circuit, wherein the optical burst cell signal receiving circuit is replaced with a driving circuit. The optical burst cell signal receiving circuit according to claim 2,
The APD driving circuit is reset in an initial state, a high-pass filter that differentiates a signal indicating the received light intensity determined by the level detection circuit and generates a differential pulse at the start time and end time of the burst cell signal, A latch circuit that is set when a differential pulse indicating the start time of the high-pass filter exceeds a first reference value, and reset when the differential pulse indicating the end time falls below a second reference value; and An optical burst cell signal receiving circuit comprising: switching means for switching a bias voltage applied to the APD to a high voltage when reset and switching to a low voltage when the latch circuit is set.

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