KR100847977B1 - Optical receiver and discrimination-threshold generating method - Google Patents

Abstract

An optical receiver for receiving a burst-shaped optical signal or the like, which prevents unintentional switching of gain and generation of a false identification level when there is a transient response to the received signal.

An optical receiver having a preamplifier for converting and amplifying the output current signal of the light receiving element into a voltage signal, and an identification reproducing unit having an identification circuit for identifying the input signal level based on a predetermined threshold of the output signal of the preamplifier. In the preamplifier, the preamplifier is provided with a first average value detection circuit for detecting an average value of its own output signal, and the amplification gain thereof is controlled based on the output of the first average value detection circuit and the comparison output of the predetermined reference voltage. do. The identification reproducing section is also provided with a second average value detection circuit for detecting the average value of the input signal, and the output of the second average value detection circuit is output to the identification circuit as a threshold for signal identification.

Description

Optical receiver and its identification threshold generation method {OPTICAL RECEIVER AND DISCRIMINATION-THRESHOLD GENERATING METHOD}

The present invention relates to an optical receiver, and more particularly, to an optical receiver suitable for a passive optical network (PON) system for transmitting a burst-shaped optical signal and a method of generating an identification threshold thereof.

As an optical receiver applied to a conventional PON system, for example, a burst digital optical receiver shown in Patent Document 1 below exists. The optical receiver includes a photoelectric conversion element for converting a received burst digital optical signal into an electrical signal, and a preamplifier for outputting a first normal signal and a first reverse phase signal of a differential output obtained by amplifying the electrical signal to a predetermined level. A pre-amplifier), a second normal signal obtained by taking a two-value average value of the value of the first normal signal and the first reverse phase signal, and a peak hold of the first normal signal at the time of the signal and the value of the first reverse phase signal. Automatic threshold control (ATC: Auto outputting a second reversed phase signal in reverse phase with a second normal signal that takes a two-valued average value of the offset voltage set to a value higher than this value when it is one value and no signal. Threshold Control circuit and the second normal signal and the second reversed-phase signal, the logic value "0" is determined at the time of no signal of the burst digital optical signal, and the signal is logic to the middle value of the amplitude value of the burst digital optical signal. Judging Rigap the "1" and "0" is configured to include an identifier for the output.

In this optical receiver, first, the preamplifier connected to the photoelectric conversion element controls its gain according to the detection level obtained by peak detection of the optical output signal level from the photoelectric conversion element at high speed. In addition, the automatic threshold control circuit connected to the output side of the preamplifier includes two signal outputs of a differential output signal output from the preamplifier, and two detection outputs for peak detection (PD) and bottom detection (BD). The identification output (level) obtained by averaging the selected circuit output generated on the basis of the input is inputted to a later identifier.

[Patent Document 1] Japanese Patent Application Laid-Open No. 9-181687

However, since the transient response inevitably occurs in the actual burst emission, the detection output level in response to the transient response amplitude fluctuating due to the transient response is highly likely to cause gain switching regardless of the need for gain switching. In addition, since the automatic threshold control circuit generates a threshold value according to the transient response amplitude, there is a problem in that a false identification level is likely to be generated.

The present invention has been made in view of the above, and even if there is a transient response to a received signal, it is possible to prevent unintentional switching of gain and generation of an incorrect identification level, and to generate an identification level equivalent to that in the absence of a transient response. An object of the present invention is to provide an optical receiver and a method for generating an identification threshold thereof.

In order to solve the above problems and achieve the object, the optical receiver according to the present invention, a preamplifier for voltage conversion amplifying the output of the light receiving element for converting the received signal into a current signal, and the output signal of the preamplifier An optical receiver comprising an identification reproducing unit which is a signal and has an identification circuit for identifying a signal of the input signal on the basis of a threshold value generated based on the input signal, wherein the preamplifying unit is a signal of the output signal. A first average value detection circuit for detecting an average value, and controlling an amplification gain thereof based on the output of the first average value detection circuit and a comparison output of a predetermined reference voltage, wherein the identification and reproduction section is provided to the identification circuit. And a second average value detection circuit for detecting the average value of the input signal, and outputting the output of the second average value detection circuit to a signal expression of the input signal. As a threshold for performing is characterized in that the output to the discrimination circuit.

1 is a block diagram showing a configuration of an optical receiver according to a first embodiment of the present invention;

2-1 is a view for explaining the operation when not considering the transient response in the optical receiver to which the prior art is applied,

2-2 is a view for explaining the operation in the case of considering the transient response in the conventional optical receiver,

3 is a view for explaining the operation in the case of considering the transient response in the optical receiver of the first embodiment;

4 is a block diagram showing a configuration of an optical receiver according to a second embodiment of the present invention;

5 is a view for explaining the operation of the optical receiver according to a third embodiment of the present invention;

6 is a view for explaining the operation of the optical receiver according to a fourth embodiment of the present invention.

Explanation of the sign

1: light receiving element 2: preamplifier

3: identification playback section 6: AGC section

7: ATC part 12: inverting amplifier (AMP)

13: feedback resistance (Rf) 14, 19: average value detection circuit

15: reference voltage 16, 22: comparison circuit

17: feedback resistance drive circuit 18, 21: identification circuit

23: S / H circuit 24: control signal

25: offset adjustment circuit 26: buffer portion

Hereinafter, preferred embodiments of the optical receiver and its identification threshold generation method according to the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by this Example.

(Example 1)

1 is a block diagram showing the configuration of an optical receiver according to a first embodiment of the present invention. The optical receiver shown in FIG. 1 includes a light receiving element 1 for receiving an optical signal and a preamplification unit 2 for inputting an output current of the light receiving element 1, converting the input current signal into a voltage signal, and outputting the voltage signal. And an identification reproducing section 3 for inputting the output voltage of the preamplifying section 2 and identifying the voltage level of the inputted output voltage. In addition, as a detailed structure, the buffer part 26 of the preamplifier 2 is a transimpedance amplifier (hereinafter abbreviated as "TIA") 5 and an automatic gain control part (hereinafter abbreviated as "AGC part") ( 6). On the other hand, the identification reproducing unit 3 includes an automatic threshold control unit (hereinafter, abbreviated as "ATC unit") 7 for generating and outputting a predetermined threshold level, the input signal to the self and the ATC unit 7. And an identification circuit 18 for identifying the input signal (level) based on the output.

As a detailed configuration, the TIA 5 includes an inverting amplifier 12 and a feedback resistor Rf 13, and the AGC unit 6 detects an average value of the output levels of the preamplifier 2. The feedback value Rf which variably controls the resistance value of the average value detection circuit 14, the comparison circuit 16 which compares the output level of the average value detection circuit 14, and the reference voltage Vref 15, and the feedback resistor Rf. ) Drive circuit 17 and feedback resistor (Rf) 13. In addition, since the feedback resistor 13 has both the conversion action of converting the current signal into the voltage signal and the gain control action of the inverting amplifier 12, the TIA 5 and the AGC section 6 as described above. Included in each component of the.

Next, the operation of the optical receiver shown in FIG. 1 will be described. In Fig. 1, the optical signal received by the light receiving element 1 is converted into a current signal and then converted into a voltage signal by the TIA 5 and amplified. Then, the average value of the output amplitude is continuously detected by the average value detection circuit 14 which is the first average value detection circuit, and the difference voltage with the reference voltage 15 is generated by the comparison circuit 16. The feedback resistance drive circuit 17 drives (variable control) the value of the feedback resistor 13 based on the output signal of the comparison circuit 16. By such control, for example, when the output amplitude of the TIA 5 is larger than the reference voltage 15, AGC control is performed so that the amplitude determined by the reference voltage 15 is set.

In the identification reproduction unit 3, as a result of outputting from the ATC unit 7 to the identification circuit 18 by the average value detection circuit 19, which is the second average value detection circuit, a predetermined threshold voltage is generated and outputted. The above-described identification and reproduction processing is performed based on the identification level according to the light reception power of the light receiving element 1.

By the way, in the actual optical burst signal, the amplitude fluctuation component which generate | occur | produced by the transient response exists as demonstrated in the above-mentioned subject. So, the following describes the transient response operation in the optical receiver to which the prior art is applied.

First, the operation in the optical receiver in the case where the transient response is not considered (assuming that no transient response exists) will be described with reference to Fig. 2-1. 2-1 is a figure for demonstrating operation | movement (ideal operation in the case of not considering a transient response) in the optical receiver to which the prior art was applied. In addition, description of each operation in FIG. 2-1 and FIG. 2-2 mentioned later assumes the optical receiver of the general structure to which the prior art was applied.

In Fig. 2-1, Fig. 2-1 (a) is a diagram showing an ideal optical signal waveform when no transient response is considered (assuming no transient response exists). When this optical signal is converted into a current signal by the light receiving element and input to the preamplifier, the AGC gain decreases instantaneously because the head pulse of the burst signal exceeds the level (level 1) at which the AGC operates. The output amplitude is thus limited (Fig. 2-1 (b)). On the other hand, when the output signal of the preamplifier of limited output amplitude is inputted to the identification playback section, the identification playback section 3 operates the ATC so that the threshold level for identification is the upper limit level ("High" level) of the signal pulse. It is set to the intermediate level of the lower limit level ("Low" level) (Fig. 2-1 (c)). As described above, in the optical receiver of the general configuration to which the prior art is applied, in the normal operation in which the transient response is not considered, the AGC operates when gain switching is necessary, and the ATC unit also adjusts the identification level according to the input signal amplitude to itself. To generate it. Therefore, it can be said that in the optical receiver of the general configuration to which the prior art is applied, it is difficult to find the existence of a problem as long as the operation in the case where there is no transient response is considered.

Next, operation in the optical receiver in the case where the transient response is considered (assuming that there is a transient response) will be described with reference to Figs. 2-2. 2-2 is a figure for demonstrating operation | movement at the time of considering the transient response in the optical receiver to which the prior art was applied.

In FIG. 2-2, FIG. 2-2 (a) is a figure which shows the optical signal waveform at the time of considering the transient response. When this optical signal is converted into a current signal by the light receiving element and input to the preamplifier, in the example shown in Fig. 2-2 (b), the second pulse of the burst signal is the level at which AGC operates (level 1 ), The AGC gain is reduced and the output amplitude is limited. In addition, in FIG. 2-2 (b), the waveform shown by the solid line is a waveform when AGC has operated, while the waveform shown by a broken line is a waveform when assuming that AGC does not operate. As shown in Fig. 2-2 (b), when there is a transient response, the AGC operation works even when it is not necessary to operate the AGC. As a result, an undesired decrease in output amplitude occurs. 2-2 (c) is a waveform which shows the output signal of the preamplifier part when AGC does not operate. When this signal is input to the identification reproducing unit, the ATC operates in the identification reproducing unit so that the threshold level for identification is, for example, the upper limit level ("High" level) and the lower limit level ("Low") of the third pulse of the burst signal. Level). When this threshold level is set, the seventh pulse or later of the burst signal input to the identification reproducing unit 3 is incorrectly identified. In addition, when considering the AGC operation (assuming that the AGC operates), since the signal level input to the identification reproducing unit is further lowered, the identification error rate is further degraded.

Thus, in the optical receiver of the general structure to which the prior art is applied, unintentional gain switching in the AGC unit is performed depending on the degree of transient response of the input optical signal waveform, and inadvertent threshold in the ATC unit. The value level (identification level) may be generated, indicating that there is a problem that the identification level is set incorrectly.

Next, an operation in the case where the transient response in the optical receiver of the present embodiment is considered (assuming that a transient response exists) will be described with reference to FIG. 3. 3 is a figure for demonstrating operation | movement at the time of considering the transient response in the optical receiver of a present Example.

In FIG. 3, FIG. 3 (a) is a figure which shows the optical signal waveform at the time of considering the transient response similar to FIG. 2-2 (a). When this optical signal is converted into a current signal by the light receiving element 1 of FIG. 1 and input to the preamplifier 2, for example, as shown in FIG. Even if the output level of 6 pulses exceeds the reference voltage 15 which is one input signal input to the comparison circuit 16, the average value detection circuit 14 which is the other input signal input to the comparison circuit 16 Since the average value output from does not exceed the reference voltage 15, or because the amount of decrease in AGC gain is small even if it exceeds, the AGC hardly operates within this transient response period, so that the signal waveform of the light receiving element output signal is maintained. As a result, unintentional gain switching in the AGC unit is prevented.

The signal waveform shown in FIG. 3B is input to the identification and playback section 3 as the output waveform of the preamplification section 2. In the identification reproduction unit 3, the average value detection circuit 19 of the ATC unit 7 is operated so that the threshold level for identification is the upper limit level (" High " level) and the lower limit level of each pulse of the burst signal. "Low" level). Therefore, since the threshold level follows the approximate median value (average value) of the upper limit level and the lower limit level of each pulse, a threshold level at which no identification and reproduction processing is made wrong is generated.

As described above, according to the optical receiver of this embodiment, the preamplification unit controls its amplification gain based on the output of the first average value detecting circuit which detects the average value of its output signal and the comparison output of the predetermined reference voltage. In addition, since the identification reproducing unit outputs the output of the second average value detecting circuit which detects the average value of the input signal to the identification circuit to the identification circuit as a threshold for performing signal identification of the input signal, the intention of the preamplification unit is as follows. Gain switching that is not performed can be prevented, thereby generating a threshold level in which the identification reproduction processing is not misplaced.

In this embodiment, the configuration for controlling the gain of the TIA, that is, the gain of the preamplification unit, based on the feedback resistance control of the feedback resistance drive circuit is shown, but is not limited to this configuration. For example, if it is a structure which can control the gain of a preamplification part based on the comparison result of the output of an average value detection circuit, and a predetermined reference voltage, it is contained in this invention.

(Example 2)

4 is a block diagram showing the configuration of an optical receiver according to a second embodiment of the present invention. The identification and reproducing section 3 of the optical receiver shown in FIG. 4 is provided with an identification circuit 21 for outputting normal output and reversed-phase output instead of the configuration of the identification circuit 18 of the first embodiment. 21. The output of the comparison circuit 22 (difference voltage) is maintained based on the signal level of the control signal 24 and the comparison circuit 22, which is a second comparison circuit that generates the difference voltage between the phase outputs of the present invention. ATC unit 7 stores an offset adjustment signal generated based on the output of the S / H circuit 23 and a sample hold circuit (hereinafter referred to as an "S / H circuit") 23 for controlling whether to output to a short circuit. It is comprised so that it may further include the offset adjustment circuit 25 which outputs to. In addition, in the structure of Example 1, the ATC part 7 is connected to the output side of the average value detection circuit 19, and the buffer part 26 into which the output (offset adjustment signal) of the offset adjustment circuit 25 is input. It is further provided, and is configured so that the output of the buffer unit 26 is input to the identification circuit 21. In addition, about the other structure, it is the same as or equivalent to the structure part of Example 1 shown in FIG. 1, The same code | symbol is attached | subjected to these structure parts, and the description is abbreviate | omitted. In addition, in the following description, it demonstrates centering on operation different from Example 1. FIG.

Next, the operation of the identification reproduction unit 3 shown in FIG. 4 will be described. The characteristic of the operation of the identification reproducing unit 3 according to this embodiment is different from that in the first embodiment in that the initial offset of the identification reproducing unit 3 is automatically adjusted to the minimum. More specifically, the comparison circuit 22 generates the difference voltage between the normal output and the reverse phase output of the identification circuit 21 and outputs it to the S / H circuit 23. Here, although the control signal 24 is input to the S / H circuit 23, this control signal 24 instructs the operation mode of the S / H circuit 23 which consists of a sample mode and a hold mode. When the signal level of the control signal 24 indicates the hold mode, the S / H circuit 23 maintains the sampled voltage, and when the signal level of the control signal 24 indicates the sample mode, The sampled voltage is output to the offset adjustment circuit 25. Moreover, when the sampled voltage is output to the offset adjustment circuit 25, the output voltage of the buffer part 26 of the ATC part 7 is changed based on the output of the offset adjustment circuit 25, and the The feedback loop causes the voltage difference between the normal output and the reverse phase output to become almost zero, thereby canceling the circuit offset components of the identification circuit 21 and the ATC unit 7. This operation also reduces the sensitivity deviation of the optical receiver itself.

As described above, according to this embodiment, the offset component included in the output of the second average value detection circuit is controlled based on the output of the sample and hold circuit which holds or transmits the comparison output comparing the differential outputs of the identification circuits. Since the feedback control is performed so that the voltage difference between the differential outputs of the identification circuits becomes almost zero, the sensitivity deviation of the optical receiver itself can be reduced.

(Example 3)

5 is a view for explaining the operation of the optical receiver according to a third embodiment of the present invention. In Fig. 5, Fig. 5A shows a burst signal having an optical signal waveform in which a transient response has occurred. 5B shows each output of the optical receiver, i.e., the solid line portion, for example, shows the normal output of the identification circuit 21, and the broken line portion, for example, shows the reverse phase output of the identification circuit 21. As shown in FIG. 5C shows an example of a control signal waveform of the control signal 24 input to the S / H circuit 23.

The characteristic of this embodiment is that in the output form of the control signal 24 shown in Fig. 5 (c), the control is made so that the operation mode of the S / H circuit 23 becomes the sample mode only during the no signal period after the power is turned on. The signal 24 is output. Therefore, the output offset of the no signal period after power-on is minimized. In addition, since the output offset of the no signal period after power-on is minimized, the signal-free period similar to the no signal period after power-on (in the example of FIG. 5, between the first packet between the first packet and the second packet, And between the second packet after the second packet), it is possible to maintain the output offset minimization state.

As described above, according to this embodiment, since the offset control by the offset adjustment circuit is performed in the no signal period after the power is turned on, the output offset minimization state can be effectively maintained.

(Example 4)

6 is a view for explaining the operation of the optical receiver according to a fourth embodiment of the present invention. In the third embodiment, the operation mode of the S / H circuit 23 is instructed to be the sample mode only in the non-signal period after the power is turned on. In this embodiment, the operation mode of the S / H circuit 23 is defined as the optical signal. It is instructed to be in sample mode in all no signal areas. In the example of FIG. 6, the signal-free period after the power is turned on is set to the hold mode, but of course, the operation mode of this period may be set to be the sample mode.

Here, when the optical receiver is operating continuously, there is a possibility that the output offset component is accumulated and gradually increases. On the other hand, in this embodiment, by setting the operation mode of the S / H circuit 23 to all the non-signal areas of the optical signal in the sample mode, accumulation of the output offset component is inhibited, resulting in deterioration of the offset component over time or It is possible to reduce aging deterioration.

As described above, according to this embodiment, since the offset control by the offset adjustment circuit is performed in the non-signal period between the light receiving signals, the accumulation of the output offset component is suppressed, and the offset component is time-lapsed. Deterioration or secular deterioration can be reduced.

According to the optical receiver according to the present invention, the preamplification unit controls its amplification gain on the basis of the output of the first average value detecting circuit which detects the average value of its output signal and the predetermined reference voltage, thereby identifying and reproducing it. Since the output unit outputs the output of the second average value detection circuit that detects the average value of the input signal to the identification circuit to the identification circuit as a threshold for signal identification of the input signal, unintentional gain switching in the preamplifier. This is prevented, and it has the effect of generating the threshold level which does not make the identification reproduction process wrong.

As described above, the optical receiver according to the present invention is useful, for example, in a PON system for transmitting a burst-shaped optical signal, and particularly, when the transient response of an input signal becomes a problem.

Claims (5)

A preamplifier for voltage conversion amplifying the output of the light receiving element for converting the received signal into a current signal; and the input signal based on the threshold value generated based on the input signal, using the preamplifier for outputting the preamplifier; An optical receiver comprising an identification reproducing unit having an identification circuit for identifying a signal of The preamplifier includes a first average value detection circuit that detects an average value of its output signal, and continuously controls its amplification gain based on the output of the first average value detection circuit and a comparison output of a predetermined reference voltage. and, The identification reproducing section includes a second average value detection circuit that detects an average value of the input signal to the identification circuit, and uses the output of the second average value detection circuit as the threshold for performing signal identification of the input signal. Output Optical receiver, characterized in that. The method of claim 1, The identification playback unit, A comparison circuit having both outputs of the in-phase output and the reverse phase output of the identification circuit as differential inputs; A buffer circuit for holding an output of said second average value detecting circuit; A sample and hold circuit for holding or transmitting the output of the comparison circuit; An offset adjustment circuit for controlling an offset component of the buffer circuit based on an output of the sample and hold circuit Optical receiver further comprising. The method of claim 2, Offset control by said offset adjustment circuit is performed in the no signal period after power supply. The method of claim 2, The offset control by the offset adjustment circuit is performed in the no signal period between the received signals. A preamplifier for voltage conversion amplifying the output of the light receiving element for converting the received signal into a current signal; and an output signal of the preamplifier for an input signal, and based on the threshold value generated based on the input signal. An identification threshold value generating method of an optical receiver having an identification reproducing unit having an identification circuit for identifying a signal, the method comprising: A gain control step of controlling an amplification gain of the preamplifier according to a comparison output between the first average value detection output detecting the average value of the output signal of the preamplifier and a predetermined reference voltage; An identification threshold generation output step of generating and outputting, to the identification circuit, a second average value detection output that has detected an average value of the input signal to the identification circuit as the threshold for performing signal identification of the input signal; Identification threshold generation method of the optical receiver comprising a.

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