JP2009060203A - Optical receiving signal interruption detection circuit and optical receiving signal interruption detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical receiving signal interruption detection circuit and an optical receiving signal interruption detection method preventing false detection. <P>SOLUTION: A signal interruption detection operation is improved by controlling a bias voltage circuit by utilizing a loss of signal obtained by a signal interruption detection circuit by input amplitude of clock data recovery, varying a multiplication factor of an avalanche photodiode to affect the input amplitude of the clock data recovery, and improving signal-to-noise ratio. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical reception signal interruption detection circuit and an optical reception signal interruption detection method.

In recent years, with an increase in demand for fiber optical communication, improvement in communication quality is desired. For this reason, various optical reception signal disconnection detection circuits that detect signal disconnection have been proposed (see, for example, Patent Documents 1 and 2).
The optical reception signal interruption detection circuit uses the fact that the electric output amplitude of the avalanche photodiode (hereinafter referred to as APD) is proportional to the optical input at the signal interruption detection level, and uses the APD electric output amplitude and the signal interruption detection reference. The APD optical input interruption is detected as a loss of signal (hereinafter referred to as LOS) by comparing the voltage with clock data recovery (hereinafter referred to as CDR). In addition, it has been proposed that a plurality of states can be detected and hysteresis can be obtained by preparing a plurality of signal interruption detection reference voltages.
JP 2005-101913 A JP-A 63-178633

  However, in the related art described above, there is a case where noise from an amplifier used as appropriate in an APD or a circuit using an APD exceeds the signal disconnection detection reference voltage and is erroneously detected. This is particularly noticeable when a plurality of signal interruption detection reference voltage differences are small.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical reception signal interruption detection circuit and an optical reception signal interruption detection method that prevent erroneous detection.

  According to a first circuit of the present invention, the avalanche photodiode is used to improve a signal-to-noise ratio by using clock data recovery to which an output of an avalanche photodiode is input and a loss of signal from an amplifier at the previous stage of the clock data recovery. And a bias voltage control circuit for changing the multiplication factor.

  The second circuit according to the present invention is obtained from an avalanche photodiode used for optical communication, clock data recovery for separating a clock and data from an output signal of the avalanche photodiode, and an amplifier in the previous stage of the clock data recovery. And a bias voltage control circuit for changing the multiplication factor of the avalanche photodiode by using a loss of signal to act on the input amplitude of the clock data recovery and improving the signal-to-noise ratio.

  A third circuit according to the present invention includes an avalanche photodiode used for optical communication, an amplifier that amplifies the output of the avalanche photodiode, clock data recovery that separates a clock and data from an output signal of the avalanche photodiode, Bias voltage control for improving the signal-to-noise ratio by changing the multiplication factor of the avalanche photodiode using the loss of signal obtained from the amplifier in the previous stage of the clock data recovery and acting on the input amplitude of the clock data recovery And a bias voltage circuit for applying a bias voltage to the avalanche photodiode based on a control signal from the bias voltage control circuit.

  According to a first method of the present invention, when an output signal of an avalanche photodiode is amplified by an amplifier and input to clock data recovery, a gain of the avalanche photodiode is changed using a loss of signal obtained by the amplifier. It is characterized by improving the signal-to-noise ratio.

  According to a second method of the present invention, an avalanche photodiode used for optical communication is prepared, and an output signal of the avalanche photodiode is amplified by an amplifier and input to clock data recovery. A signal is used to change a multiplication factor of the avalanche photodiode to affect an input amplitude of the clock data recovery, thereby improving a signal-to-noise ratio.

  A third method according to the present invention is to prepare an avalanche photodiode used for optical communication, amplify the output of the avalanche photodiode by an amplifier, and input the amplified output signal of the avalanche photodiode to clock data recovery. The gain of the avalanche photodiode is changed using a loss-of-signal obtained from the amplifier in the previous stage of the clock data recovery, and the bias voltage circuit controls the avalanche photodiode based on a control signal from the bias voltage control circuit. A bias voltage is applied to act on the input amplitude of the clock data recovery to improve the signal-to-noise ratio.

  According to the present invention, the bias voltage circuit is controlled using the loss of signal obtained by the signal interruption detection circuit based on the input amplitude of clock data recovery, the multiplication factor of the avalanche photodiode is changed, and the input amplitude of clock data recovery is changed. The signal interruption detection operation can be improved by acting on and improving the signal-to-noise ratio.

  One embodiment of an optical reception signal break detection circuit according to the present invention uses a clock data recovery to which an output of an avalanche photodiode is input, and a signal-to-noise ratio using a loss-of-signal from an amplifier in the previous stage of the clock data recovery. And a bias voltage control circuit for changing the multiplication factor of the avalanche photodiode for improvement.

  According to the above configuration, the signal interruption detection operation is improved by improving the signal-to-noise ratio using the clock data recovery to which the output of the avalanche photodiode is input and the loss of signal from the amplifier at the previous stage of the clock data recovery. Can be made.

  Another embodiment of an optical reception signal break detection circuit according to the present invention includes an avalanche photodiode used for optical communication, clock data recovery for separating a clock and data from an output signal of the avalanche photodiode, and clock data recovery. A bias voltage control circuit that improves the signal-to-noise ratio by changing the gain of the avalanche photodiode using the loss-of-signal obtained from the amplifier in the previous stage and affecting the input amplitude of clock data recovery. And

  According to the above configuration, the clock and data are separated from the output signal of the avalanche photodiode used for optical communication, and the multiplication factor of the avalanche photodiode is changed using the loss of signal obtained from the amplifier in the previous stage of clock data recovery. Thus, by acting on the input amplitude of clock data recovery and improving the signal-to-noise ratio, it is possible to improve the signal-to-noise ratio and improve the signal break detection operation.

  Another embodiment of the optical reception signal break detection circuit according to the present invention includes an avalanche photodiode used for optical communication, an amplifier for amplifying the output of the avalanche photodiode, and a clock and data separated from the output signal of the avalanche photodiode. Bias that improves the signal-to-noise ratio by changing the gain of the avalanche photodiode using the loss of signal obtained from the amplifier before the clock data recovery and the clock data recovery, and changing the gain of the clock data recovery. And a bias voltage circuit for applying a bias voltage to the avalanche photodiode based on a control signal from the bias voltage control circuit.

  According to the above configuration, the output of the avalanche photodiode used for optical communication is amplified, the clock and data are separated from the output signal of the avalanche photodiode, and the loss of signal obtained from the amplifier in the previous stage of clock data recovery is used. By changing the multiplication factor of the avalanche photodiode to affect the input amplitude of clock data recovery and improving the signal-to-noise ratio, it is possible to improve the signal-to-noise ratio and improve the signal break detection operation.

  According to an embodiment of the present invention, there is provided an optical avalanche photodiode loss detection method, wherein when an output signal of an avalanche photodiode is amplified by an amplifier and input to clock data recovery, the loss of signal obtained by the amplifier is used to increase the avalanche photodiode. The signal-to-noise ratio is improved by changing the magnification.

  According to the above configuration, when the output signal of the avalanche photodiode is amplified by the amplifier and input to the clock data recovery, the loss of signal obtained by the amplifier is used to change the multiplication factor of the avalanche photodiode to improve the signal-to-noise ratio. By doing so, the signal interruption detection operation can be improved.

  Another embodiment of the optical reception signal disconnection detection method according to the present invention prepares an avalanche photodiode used for optical communication, amplifies the output signal of the avalanche photodiode with an amplifier, and inputs it to clock data recovery. The gain of the avalanche photodiode is changed by using the loss of signal obtained from the amplifier to affect the input amplitude of clock data recovery, thereby improving the signal-to-noise ratio.

  According to the above configuration, the avalanche photodiode is prepared by using the loss of signal obtained from the amplifier when the avalanche photodiode used for optical communication is prepared, and the output signal of the avalanche photodiode is amplified by the amplifier and input to the clock data recovery. The signal loss detection operation can be improved by improving the signal-to-noise ratio by changing the gain of the signal to affect the input amplitude of the clock data recovery and improving the signal-to-noise ratio.

  According to another embodiment of the present invention, there is provided an avalanche photodiode used for optical communication, amplifying an output of the avalanche photodiode by an amplifier, and outputting an amplified output signal of the avalanche photodiode. When inputting to the clock data recovery, the gain of the avalanche photodiode is changed using the loss of signal obtained from the amplifier in the previous stage of the clock data recovery, and the bias voltage circuit is used to control the avalanche based on the control signal from the bias voltage control circuit. A bias voltage is applied to the photodiode to affect the input amplitude of clock data recovery, thereby improving the signal-to-noise ratio.

According to the above configuration, the avalanche photodiode used for optical communication is prepared, the output of the avalanche photodiode is amplified by the amplifier, and the output signal of the amplified avalanche photodiode is input to the clock data recovery. The gain of the avalanche photodiode is changed using the loss-of-signal obtained from the amplifier in the previous stage, and the bias voltage is applied to the avalanche photodiode based on the control signal from the bias voltage control circuit by the bias voltage circuit. By operating on the input amplitude and improving the signal-to-noise ratio, the signal interruption detection operation can be improved.
The above-described embodiment shows an example of a preferred embodiment of the present invention, and the present invention is not limited thereto, and various modifications can be made without departing from the scope of the invention. is there.

[Configuration of Example]
FIG. 1 is a block diagram showing an embodiment of an optical reception signal interruption detection circuit to which an optical reception signal interruption detection method according to the present invention is applied.
FIG. 1 shows an optical input signal 1-1, an APD 1-2 that receives the optical input signal 1-1, an electrical signal 1-3 that has undergone photoelectric conversion, and an amplifier 1 that amplifies the electrical signal 1-3. -4, amplified electrical signal 1-5, and CDR that obtains data 1-6, clock 1-7, and LOS (Loss Of Signal) 1-8 from the amplified electrical signal 1-5 (Clock Data Recovery) 1-9, a bias voltage circuit 1-11 for applying a bias voltage 1-10 to the APD 1-2, and a bias voltage control circuit for controlling the bias voltage circuit 1-10 by the LOS 1-8 1-12 and bias voltage control signal 1-13, and signals 1-14 and 1-15 for setting LOS emission and release levels are shown.

  An optical reception signal disconnection detection circuit according to the present invention includes an APD 1-2 that receives an optical input signal 1-1, an amplifier 1-4 that amplifies an electrical signal 1-3 that is photoelectrically converted by the APD 1-2, and an amplifier. CDR 1-9 for obtaining data 1-6, clock 1-7 and LOS 1-8 from the electric signal 1-5 amplified in 1-4, and bias voltage circuit 1 for applying a bias voltage 1-10 to APD 1-2 11 and a bias voltage control circuit 1-12 for controlling the bias voltage circuit 1-10 by the LOS 1-8.

The optical input signal 1-1 is scrambled in advance and mixed with clock information.
The LOS is obtained by comparing the signals 1-14 and 1-15 that set the LOS emission and release levels with the amplified electrical signal 1-5.

FIG. 5 is a block diagram showing an example of clock data recovery used in the optical reception signal loss detection circuit shown in FIG.
The clock data recovery 1-9 shown in FIG. 5 includes the amplifier 1-4 shown in FIG.
In FIG. 1, the amplifier 1-4 and the CDR 1-9 are described separately, but the amplifier 1-4 and the CDR 1-9 are generally integrated as shown in FIG. In FIG. 1, LOS 1-8 is set and described in CDR 1-9 as a place to be obtained. FIG. 5 describes the amplifier 1-4. 1 and 5, the function of detecting the amplitude after the signal from the APD 1-2 is amplified by the amplifier 1-4 is the same.
The clock data recovery shown in FIG. 5 is an ADN2856 manufactured by Analog Devices, and a circuit such as a phase shifter, a VCO, a low-pass filter, and a D flip-flop is integrated in an IC to convert a data signal having clock information into a clock and data. To separate. A detailed description of the configuration is left to the catalog and the like, and the description thereof is omitted.
Here, the clock data recovery is to receive a signal (data) on a transmission line in which a clock is superimposed on data in information communication, and to separate the data into a clock and data.
In order to transmit / receive a digital signal, it is necessary to determine each data bit at a correct timing on the receiving side. For this reason, a transmission path for transmitting timing information (clock) is often provided in parallel with a transmission path for transmitting data.

  However, in the case of a signal from a read head such as a magnetic disk or an optical disk, or high-speed serial transmission or the like, timing information is superimposed on a data signal and transmitted without providing a separate clock. In wireless communication, transmission is performed using an NRZ signal synchronized with a stable transmission clock. The receiving side detects the edge (signal transition) of the data signal and adjusts the phase of the internal reference clock to reproduce the timing information. This process is called clock data recovery.

  In order to correctly perform clock recovery, it is necessary that edges appear frequently in the data signal. Otherwise, synchronization will be lost due to drift of the internal reference clock on the receiving side. The maximum length of consecutive identical bit patterns that appear for each data necessary for clock data recovery to correctly regenerate the clock is called CID (maximum consecutive digits (CID) specification). In order to ensure that sufficient edges appear in the data signal, encoding such as Manchester code, 8b / 10b code, Run Length Limited encoding (RLL), Eight Fourteen Modulation (EFM) is often performed.

The following (1) to (4) are listed as clock data recovery configuration methods.
(1) Phase synchronization circuit (PLL)
This is the most common method, and the edge timing of data is detected by a phase comparator and the oscillation frequency and phase of the VCO are adjusted.

(2) Phase interpolation method A multi-phase clock is generated from a reference clock by a phase interpolation circuit (interpolator), and an optimum clock phase is selected according to the edge timing of the data signal. Since there is no oscillation circuit inside the clock data recovery, the jitter of the recovered clock can be reduced by using a highly accurate reference clock. Also, precise control is possible by performing phase comparison and low-pass filter with a digital logic circuit. On the other hand, the circuit scale and power consumption tend to increase in order to increase the accuracy of phase interpolation.

(3) Gated ring oscillator Insert a NAND gate into the ring oscillator loop and reset the phase of the ring oscillator at the edge of the data. Since it can be synchronized in a very short time after being stopped, it is suitable for burst transmission.

(4) Tank circuit Using the flywheel effect (continuation of vibration) of the tank circuit (resonator), the clock signal is output without interruption even when there is no edge.

[Description of Operation of Example]
Next, the operation will be described with reference to FIG.
During normal operation, the optical input signal 1-1 is converted into an electric signal 1-3 by inputting an appropriate signal to the APD 1-2. The converted electric signal 1-3 is amplified by the amplifier 1-4, becomes an amplified electric signal 1-5, and is input to the CDR 1-9. Data 1-6 and clock 1-7 are extracted by CDR 1-9.

Utilizing the fact that the amplitude of the amplified electric signal 1-5 is proportional to the optical input signal 1-1, generation of the amplified electric signal 1-5 and LOS corresponding to a certain optical input signal level 1-1 Comparing the three signals of level 1-14 and release level 1-15, CDR 1-9 outputs LOS 1-8. That is, the data amplitude and a certain voltage (for example, LOS emission / cancellation set voltage) are compared by the comparator and output. The LOS emission level 1-14 and the release level 1-15 can be obtained by using two comparators (not shown).
The amplitude of the amplifier in FIG. 5 and the voltage set by THRADJ are compared by the LOS detector, and LOS 1-8 is output.

The bias voltage control circuit 1-12 is controlled corresponding to the LOS 1-8, outputs a bias voltage control signal 1-13, and the bias voltage circuit 1-11 is controlled. A bias voltage 1-10 generated by the bias voltage circuit 1-11 is applied to the APD 1-2 and acts on the electric signal 1-3.
If the threshold value is below the LOS emission threshold, the APD noise can be reduced by lowering the APD bias voltage, and a margin for the malfunction of the LOS release can be secured. This is because when the multiplication factor of APD is high, the shot noise increases as the multiplication factor increases, so that the shot noise can be reduced by lowering the multiplication factor.
Furthermore, since noise generated in the APD decreases exponentially with respect to a decrease in bias voltage, the LOS release threshold can be set lower than the LOS emission threshold.

[Explanation of effects]
FIG. 2 is a diagram showing the relationship between the optical input signal level and the APD multiplication factor when the emission threshold value 1-14 and the LOS cancellation threshold value 1-15 in the optical reception signal disconnection detection circuit shown in FIG. 1 are different.
In FIG. 2, the horizontal axis indicates optical input, the vertical axis indicates the electrical signal, and the vertical axis indicates the APD multiplication factor.
As shown in FIG. 2, by controlling the multiplication factor of the APD 1-2 according to the optical input signal 1-1, the amplified electric signal 1-5 is changed, so that a hysteresis loop can be obtained. . Further, since the multiplication factor is reduced, noise is reduced and the frequency of erroneous detection is reduced.

Here, FIG. 3 is an explanatory diagram of an optical reception signal interruption detection method related to the present invention, and FIG. 4 is an explanatory diagram of another optical reception signal interruption detection method related to the present invention.
3 and 4, the horizontal axis indicates optical input, the vertical axis indicates the electrical signal, and the vertical axis indicates the APD multiplication factor.
3 and 4, two comparators are prepared,
Greater than release threshold Release threshold-emission threshold Less than emission threshold Release comparator H L L
Output comparator H H L
A hysteresis loop can be obtained by using each level and its transition. The stability of LOS issuance / cancellation has been ensured by providing a dead zone by this hysteresis loop. However, when the bias voltage of the APD is high, noise exceeding the dead zone may be generated and there is a risk of erroneous release.
Compared with the case where the multiplication factor is not changed by LOS (see FIG. 3), the difference in the LOS issue release threshold for obtaining the same hysteresis loop becomes larger. As a result, even when noise is added to the amplified electrical signal 1-5, the frequency of erroneous detection is reduced.

  Further, as shown in FIG. 4, the hysteresis can be changed by changing the APD multiplication factor or the gain of the amplifier 1-4. However, since noise is also amplified at the same time, the frequency of erroneous detection is reduced. It can be seen that it is less than the present invention.

Although the CDR 1-9 is used in the embodiment shown in FIG. 1, the amplifier 1-4 detects the amplitude of the electric signal 1-3 instead of the CDR 1-9 to generate a signal corresponding to the LOS 1-8. You may comprise.
When the LOS issue threshold value 1-14 and the LOS release threshold value 1-15 are the same, it is considered as shown in FIG.
FIG. 6 is a diagram showing the relationship between the optical input signal level and the APD multiplication factor when the emission threshold 1-14 and the LOS cancellation threshold 1-15 in the optical reception signal disconnection detection circuit shown in FIG. 1 are the same.
As shown in FIG. 6, a hysteresis loop can be obtained by controlling the multiplication factor of the APD 1-2 in accordance with the optical input signal 1-1, and changing the amplified electric signal 1-5. . Further, since the multiplication factor is reduced, noise is reduced and the frequency of erroneous detection is reduced.

[Differences from related technologies]
The technique described in Patent Document 1 is different from the present invention in that the optical signal input break detection circuit may malfunction due to noise as described in the paragraph “0008”. Although attempts are made to solve the problem by using a plurality of CDRs in the present invention, the use of a single one is common in order to satisfy the original function of clock identification reproduction, which is not in line with the current situation.

  Further, the technique described in Patent Document 2 is different from the present invention in that it aims at AGC, the relationship between signal interruption and change in APD multiplication factor is unclear, and the output of the error signal amplifier is used as an APD bias. The configuration is different from the present invention in that it is output to both the control circuit and the variable gain amplifier. Furthermore, although the APD multiplication factor is constant in the technique described in Patent Document 2, it is different from the present invention in which the APD multiplication factor changes when a signal interruption is detected.

  INDUSTRIAL APPLICABILITY The present invention can be used for an optical receiver for optical fiber communication and an optical level monitoring device, and when other embodiments are applied, such as SFP (Small Form Factor Plagable) having no identification / reproduction circuit It can also be used for products.

It is a block diagram which shows one Example of the optical reception signal interruption detection circuit to which the optical reception signal interruption detection method which concerns on this invention is applied. It is a figure which shows the relationship between the optical input signal level and APD multiplication factor in case the emission threshold value 1-14 in the optical reception signal interruption | blocking detection circuit shown in FIG. 1 differs from the LOS cancellation | release threshold value 1-15. It is explanatory drawing of the optical reception signal disconnection detection method relevant to this invention. It is explanatory drawing of the other optical reception signal disconnection detection method relevant to this invention. FIG. 2 is a block diagram showing an example of clock data recovery used in the optical reception signal break detection circuit shown in FIG. 1. It is a figure which shows the relationship between the optical input signal level and APD multiplication factor in case the emission threshold value 1-14 in the optical reception signal interruption | blocking detection circuit shown in FIG. 1 and the LOS cancellation | release threshold value 1-15 are the same.

Explanation of symbols

1-1 Optical input signal 1-2 APD (avalanche photodiode)
1-3 Electrical signal 1-4 Amplifier 1-5 Amplified electrical signal 1-6 Data 1-7 Clock 1-8 LOS
1-9 CDR (clock data recovery)
1-10 Bias voltage 1-11 Bias voltage circuit 1-12 Bias voltage control circuit 1-13 Bias voltage control signal 1-14 LOS emission threshold signal 1-15 LOS release threshold signal

Claims (6)

Clock data recovery to which the output of the avalanche photodiode is input,
A bias voltage control circuit for changing a multiplication factor of the avalanche photodiode in order to improve a signal-to-noise ratio using a loss-of-signal from an amplifier in the previous stage of the clock data recovery. Detection circuit. An avalanche photodiode used for optical communication;
Clock data recovery for separating clock and data from the output signal of the avalanche photodiode;
Bias voltage control circuit for improving the signal-to-noise ratio by changing the multiplication factor of the avalanche photodiode using a loss-of-signal obtained from the amplifier in the previous stage of the clock data recovery and acting on the input amplitude of the clock data recovery An optical reception signal disconnection detection circuit comprising: An avalanche photodiode used for optical communication;
An amplifier for amplifying the output of the avalanche photodiode;
Clock data recovery for separating clock and data from the output signal of the avalanche photodiode;
Bias voltage control for improving the signal-to-noise ratio by changing the multiplication factor of the avalanche photodiode using the loss-of-signal obtained from the amplifier in the previous stage of the clock data recovery and acting on the input amplitude of the clock data recovery Circuit,
And a bias voltage circuit for applying a bias voltage to the avalanche photodiode based on a control signal from the bias voltage control circuit.   When the output signal of the avalanche photodiode is amplified by an amplifier and input to clock data recovery, the signal-to-noise ratio is improved by changing the multiplication factor of the avalanche photodiode using the loss of signal obtained by the amplifier. An optical reception signal loss detection method. Prepare an avalanche photodiode used for optical communication,
When the output signal of the avalanche photodiode is amplified by an amplifier and input to clock data recovery, the gain of the avalanche photodiode is changed using the loss of signal obtained from the amplifier, and the input amplitude of the clock data recovery And a signal-to-noise ratio to improve the received signal loss detection method. Prepare an avalanche photodiode used for optical communication,
The amplifier amplifies the output of the avalanche photodiode,
When the amplified output signal of the avalanche photodiode is input to clock data recovery, the gain of the avalanche photodiode is changed using a loss of signal obtained from the amplifier in the previous stage of the clock data recovery,
A bias voltage circuit applies a bias voltage to the avalanche photodiode based on a control signal from the bias voltage control circuit to affect the input amplitude of the clock data recovery, thereby improving a signal-to-noise ratio. Optical reception signal loss detection method.

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