JP2007311844A - Optical burst signal receiving circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize high sensitivity and a wide dynamic range without using a special level detecting circuit. <P>SOLUTION: An automatic threshold control circuit 9 detects the peak value of an electric burst signal to be output from an APD 1. A reference voltage of an AGC circuit 5 is set on the basis of the peak value, a voltage switching signal generating circuit 10 is controlled to control an APD bias voltage of an APD driving circuit 2. If the peak value is higher than a threshold value previously set in the voltage switching signal generating circuit 10, the APD bias voltage of the APD driving circuit 2 is switched to a low voltage so that the peak value becomes lower than the threshold value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  The PON system currently widely used in the optical access network is an optical access system that is cost-effective because the optical fiber transmission line and the in-station device can be shared among a plurality of subscriber users.

  FIG. 5 (a) is a diagram showing the configuration of this PON system, 21 is an OLT (Optical Line Terminal) on the station side, 22 is an ONU (Optical Network Unit) on the subscriber user side, 23 is an optical splitter, and 24 is an optical splitter. An optical fiber transmission line. The plurality of ONUs 22 are connected to the OLT 21 via the optical splitter 23. In this PON system, the transmission (downstream) signal from the OLT 21 to each ONU 22 is continuous light, but since the distance between the OLT 21 and the ONU 22 varies depending on the subscriber user, the transmission (upstream) signal from the ONU 22 to the OLT 21 is As shown in FIG. 5 (b), optical burst signals having different optical intensities are obtained depending on subscriber users.

  In the future, the PON system is expected to expand the service area and increase the transmission speed, increase the optical loss due to the PON wide area such as the extension of the transmission distance and the increase in the number of branches, etc. Is a problem.

  Therefore, in order to realize a wide range and high speed of the PON system, the optical burst receiver is strongly required to have high sensitivity and wide dynamic range.

  As an effective means for improving reception sensitivity, there is a method using APD having a multiplication effect. However, when an APD is used, if the optical signal input to the APD becomes excessive, an excessive photocurrent is generated due to the multiplication effect of the APD, resulting in saturation of the electric stage amplifier installed in the subsequent stage. In particular, there was a problem that the dynamic range was narrowed.

  In view of this, an optical burst signal receiving circuit that realizes an improvement in dynamic range by appropriately setting the APD multiplication factor according to the intensity of the optical burst signal has been proposed (for example, Patent Document 1). reference).

  FIG. 6 is a diagram showing this optical burst signal receiving circuit. APD 1 for converting the optical burst signal into an electric burst signal, APD driving circuit 2 for giving an APD bias voltage to APD 1, and a preamplifier 3 for amplifying the output electric burst signal of APD 1 A level detection circuit 4 for determining the intensity of light intensity by inputting an electric burst signal, an AGC (Automatic Gain Control) circuit 5A for amplifying the electric burst signal to a certain level, clock extraction and data by inputting the electric burst signal It comprises an identification timing extraction circuit 6 for performing identification, a bypass circuit 7, and a switch 8 comprising switches SW1 and SW2.

  In this optical burst signal receiving circuit, optical burst signals having different optical intensities inputted to the APD 1 are photoelectrically converted into electric burst signals while being multiplied by the APD 1 and outputted to the preamplifier 3. The electric burst signal amplified by the pudding amplifier 3 is input to the level detection circuit 4 where the received light intensity is determined as a threshold. An APD bias control signal corresponding to the threshold determination result is output from the level detection circuit 4 to the APD drive circuit 2. The APD driving circuit 2 switches the APD bias voltage according to the output of the level detection circuit 4 and controls the multiplication factor of the APD 1. The switch 8 is a circuit for removing the influence of the excessive response signal generated after the burst frame ends, but the description thereof is omitted because it is not directly related to the present invention.

Japanese Patent Laid-Open No. 11-355218

  However, in the optical burst signal receiving circuit shown in FIG. 6, the level detection circuit 4 having a relatively complicated structure is specially required, and simplification of the circuit has been desired.

  An object of the present invention is to use an automatic threshold control circuit for generating a reference voltage for an AGC circuit also for APD bias voltage control, while eliminating the need for a special level detection circuit and increasing the sensitivity and wide dynamic range. It is an object to provide an optical burst signal receiving circuit capable of realizing the above.

In order to solve the above-mentioned problem, an optical burst signal receiving circuit according to a first aspect of the present invention includes an APD that converts an input optical burst signal into an electric burst signal, an APD drive circuit that applies an APD bias voltage to the APD, A preamplifier for amplifying the output electric burst signal of the APD; an automatic threshold control circuit for detecting a peak value of the output signal of the preamplifier; and a voltage for switching an APD bias voltage according to the peak value detected by the automatic threshold control circuit A voltage switching signal generating circuit for generating a switching signal, and an AGC circuit for amplifying an electric burst signal output from the preamplifier to a constant level using a signal corresponding to the peak value detected by the automatic threshold control circuit as a reference voltage. It is characterized by providing.
According to a second aspect of the present invention, in the optical burst signal receiving circuit according to the first aspect, the voltage switching signal generating circuit is configured such that the peak value detected by the automatic threshold control circuit is lower than a preset upper limit threshold. When exceeding, a voltage switching signal for reducing the APD bias voltage is generated for the APD driving circuit.
According to a third aspect of the present invention, in the optical burst signal receiving circuit according to the first aspect, the voltage switching signal generating circuit is configured such that the peak value detected by the automatic threshold control circuit is lower than a preset lower limit threshold. A voltage switching signal is generated to increase the APD bias voltage for the APD driving circuit when the APD driving circuit is below.
According to a fourth aspect of the present invention, in the optical burst signal receiving circuit according to the first aspect, the voltage switching signal generating circuit is configured such that the peak value detected by the automatic threshold control circuit is lower than a preset upper limit threshold. When exceeding, when generating a voltage switching signal for reducing the APD bias voltage to the APD drive circuit, and when the peak value detected by the automatic threshold control circuit is below the preset lower threshold, A voltage switching signal for increasing the APD bias voltage is generated for the APD driving circuit.

  According to the present invention, the peak value of the electric burst signal is detected by the automatic threshold control circuit, and the detected output is used as the reference voltage of the AGC circuit and at the same time as the signal indicating the level of the APD received light intensity. The voltage switching signal generation circuit is added to the APD, and the APD multiplication factor can be controlled to an appropriate value for each received optical burst signal without using a special level detection circuit. Range can be realized.

  FIG. 1 is a block diagram showing a configuration of an optical burst signal receiving circuit according to an embodiment of the present invention. The same components as those described in FIG. An AGC circuit 5 has a reference voltage input terminal 5a for controlling the gain. 9 is an automatic threshold control circuit (ATC circuit) that detects the peak value of the output signal of the preamplifier 3 and sets the reference voltage of the AGC circuit 5, and 10 is an APD bias according to the peak value detected by the automatic threshold control circuit 9. It is a voltage switching signal generation circuit for generating a voltage switching signal. That is, in this embodiment, the peak value of the output signal of the preamplifier 3 detected by the automatic threshold control circuit 9 is used not only for the reference voltage of the AGC circuit 5, but also as an intensity detection signal of the optical burst signal. This allows the APD bias voltage to be switched. This eliminates the need for the special level detection circuit 4 as shown in FIG.

  Now, the optical burst signal input to the APD 1 is converted into an electric burst signal after being subjected to the multiplication effect of the APD 1. The electric burst signal is amplified by the preamplifier 3 and then input to the automatic threshold control circuit 9. The automatic threshold control circuit 9 is reset by a reset signal R1 generated in synchronization with the optical burst signal input to the APD 1 and detects the peak value of the signal level when the electric burst signal is input from the preamplifier 3. . The detected peak value signal is used as a reference voltage for the AGC circuit 5 and simultaneously input to the voltage switching signal generation circuit 10. The voltage switching signal generation circuit 10 outputs an APD bias voltage switching signal to the APD driving circuit 2 in accordance with the input peak value signal.

  There are three APD bias voltage control methods in the voltage switching signal generation circuit 10 as shown in FIGS. In the control method shown in FIG. 2, the threshold value of the voltage switching signal generation circuit 10 is set in advance to the upper limit value X of the input of the AGC circuit 5, and the peak value detected by the automatic threshold value control circuit 9 sets the upper limit value X. This is a control method for outputting a voltage switching signal for lowering the APD bias voltage to the APD drive circuit 2 so that the level a ′ does not exceed the upper limit value X when the level a exceeds the level a.

  In the control method shown in FIG. 3, the threshold value of the voltage switching signal generation circuit 10 is set in advance to the lower limit value Y of the input of the AGC circuit 5, and the peak value detected by the automatic threshold value control circuit 9 sets the lower limit value Y. This is a control method for outputting a voltage switching signal for increasing the APD bias voltage to the APD driving circuit 2 so that the level b ′ exceeds the lower limit value Y when the level b becomes lower.

  In the control method shown in FIG. 4, the upper limit value X and the lower limit value Y of the input of the AGC circuit 5 are set in advance as the threshold of the voltage switching signal generation circuit 10, and the peak value detected by the automatic threshold control circuit 9 is When the level c exceeds the upper limit value X, a voltage switching signal for lowering the APD bias voltage is output to the APD drive circuit 2 so that the level c ′ does not exceed the upper limit value X, while the automatic threshold control circuit 9 Control that outputs a voltage switching signal for increasing the APD bias voltage to the APD drive circuit 2 so that the peak value detected in step S becomes a level d that is lower than the lower limit value Y, and the level d ′ exceeds the lower limit value Y. Is the method.

  The APD driving circuit 2 controls the APD multiplication factor by changing the APD bias voltage according to the voltage switching signal output from the voltage switching signal generation circuit 10 in accordance with any one of the control methods shown in FIGS. . When the APD multiplication factor is changed, the automatic threshold value control circuit 9 is reset by inputting the reset signal R2, and the electric burst signal after the APD multiplication factor change is inputted from the preamplifier 3 to the automatic threshold value control circuit 9. A new peak value is detected, whereby the reference voltage of the AGC circuit 5 is set again.

  The detection signal of this new peak value is also input to the voltage switching signal generation circuit 10, but this voltage switching signal generation circuit 10 is controlled so that the switching signal is not continuously output within the same burst frame. Once switched, the APD multiplication factor does not change within the same burst frame.

  As described above, in the optical burst signal receiving circuit of this embodiment, the automatic threshold control circuit 9 is used to detect the peak value of the electric burst signal, and the detected output is used as the reference voltage of the AGC circuit 5 and at the same time the APD reception is performed. By using it as a signal indicating the light intensity level, the APD gain can be controlled to an appropriate value for each received optical burst signal, realizing high sensitivity and wide dynamic range of the optical burst signal receiving circuit. it can.

It is a block diagram which shows the structure of the optical burst signal receiving circuit of the Example of this invention. It is explanatory drawing of the 1st example of the APD bias voltage control method. It is explanatory drawing of the 2nd example of the APD bias voltage control method. It is explanatory drawing of the 3rd example of the APD bias voltage control method. (a) is a schematic explanatory diagram of the PON system, and (b) is a waveform diagram showing an upstream burst signal of the PON system. It is a block diagram which shows the structure of the conventional optical burst signal receiving circuit.

Explanation of symbols

1: APD, 2: APD drive circuit, 3: preamplifier, 4: level detection circuit, 5, 5A: AGC circuit, 6: identification timing extraction circuit, 7: bypass circuit, 8: switch, 9: automatic threshold control circuit DESCRIPTION OF SYMBOLS 10: Voltage switching signal generation circuit 21: OLT, 22: ONU, 23: Optical splitter, 24: Optical fiber transmission line

Claims (4)

  An APD that converts an input optical burst signal into an electric burst signal, an APD driving circuit that applies an APD bias voltage to the APD, a preamplifier that amplifies the output electric burst signal of the APD, and a peak value of the output signal of the preamplifier An automatic threshold control circuit for detecting, a voltage switching signal generating circuit for generating a voltage switching signal for switching an APD bias voltage according to the peak value detected by the automatic threshold control circuit, and the peak detected by the automatic threshold control circuit An optical burst signal receiving circuit comprising: an AGC circuit that amplifies an electric burst signal output from the preamplifier to a certain level using a signal according to a value as a reference. In the optical burst signal receiving circuit according to claim 1,
The voltage switching signal generation circuit outputs a voltage switching signal for lowering the APD bias voltage to the APD driving circuit when the peak value detected by the automatic threshold control circuit exceeds a preset upper threshold. An optical burst signal receiving circuit generated. In the optical burst signal receiving circuit according to claim 1,
The voltage switching signal generation circuit outputs a voltage switching signal for increasing the APD bias voltage to the APD driving circuit when the peak value detected by the automatic threshold control circuit falls below a preset lower limit threshold. An optical burst signal receiving circuit generated. In the optical burst signal receiving circuit according to claim 1,
The voltage switching signal generation circuit outputs a voltage switching signal for lowering the APD bias voltage to the APD driving circuit when the peak value detected by the automatic threshold control circuit exceeds a preset upper threshold. Occurs and
A light that generates a voltage switching signal for increasing the APD bias voltage to the APD driving circuit when the peak value detected by the automatic threshold control circuit falls below a preset lower limit threshold. Burst signal receiving circuit.

Images