JP4190840B2 - Optical receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical receiver used for optical transmission, in particular, an identification reference voltage and a phase control voltage for maintaining the code error rate of the optical receiver at a desired value when transmission path characteristics and environmental conditions change. Related to automatic adjustment.
[0002]
[Prior art]
In general, in an optical receiver, an optical signal is converted into an electric signal by a light receiving unit corresponding to a terminal of an optical transmission line, an electric signal is amplified by an amplifying unit, and identification reproduction is performed at a clock timing by an identification reproducing unit. Then, the error rate is monitored using a code error rate measurement circuit after the identification reproduction unit, and the control unit adjusts the phase of the clock timing, the identification reference voltage to the identification regenerator, and the identification reproduction. By adjusting the amplification factor of the equalization amplifier, it is possible to reproduce the transmission signal with a desired code error rate.
[0003]
In this case, the identification reference voltage value for identification reproduction and the voltage for adjusting the phase of the clock are adjusted so as to be the center of the eye opening that minimizes the code error rate, and the value of the variable parameter is held. . However, if the transmission path characteristics and environmental conditions are changed, the shape of the eye opening may change and the code error rate may deteriorate.
[0004]
Therefore, in the conventional optical receiver, as an automatic adjustment method of the code error rate, the control unit adjusts in the following order (1), (2), (3) to obtain the optimum point of the code error rate. (For example, refer to Patent Document 1).
[0005]
(1) The identification reference voltage value used in the identification reproduction unit is adjusted and fixed so that the code error rate is minimized. (2) The phase of the clock timing used in the discriminating / reproducing unit is changed and adjusted and fixed so that the code error rate is minimized. (3) The ratio for amplifying the signal received by the optical receiver is changed and adjusted so that the code error rate is minimized and fixed.
[0006]
[Patent Document 1]
JP-A-6-85752
[Problems to be solved by the invention]
However, in the above-described conventional method, when the code error rate is within a predetermined range, the identification level, the phase, and the amplification factor of the light receiving element are sequentially adjusted. If the error information does not reach the optimum value even after adjusting the value, the element is set to the initial value and then the next element is adjusted, so the transmission line characteristics and environmental conditions change, as shown in FIG. If the identification reference voltage value or clock phase deviates from the optimal value and the eye opening (dotted line) at the time of adjustment changes to the operating eye opening (solid line), the optimum code error rate cannot be found. There is.
[0008]
Therefore, an object of the present invention is to provide an optical receiver that always sets the code error rate to a desired value regardless of individual variations of the optical receiver itself, the shape and position of the eye opening that changes due to changes in transmission path characteristics and environmental conditions. Is to provide a vessel.
[0009]
The eye opening here refers to the phase control of the clock signal, which is two variable parameters, when the optical signal that has passed through the transmission path is converted into an electrical signal by the optical receiver and restored to the original signal. The point where the measured code error rate data is the same for the signal and the identification reference voltage value that determines the identification level of the identification reproduction unit is plotted on a plane with the phase control signal and the identification reference voltage value as coordinates. An elliptical figure drawn.
[0011]
[Means for Solving the Problems]
An optical receiver according to the present invention includes an optical receiver (1 in FIG. 1) that converts an optical signal received from a transmission path into an electrical signal and performs equalization amplification, and a clock that generates a clock signal from a data signal from the optical receiver. An extraction unit (2 in FIG. 1), a phase shift unit (3 in FIG. 1) for shifting the phase of the clock signal, an identification reproduction unit (4 in FIG. 1) for identifying and reproducing the main signal from the optical reception unit, An error monitoring circuit (5 in FIG. 1) that measures the code error rate of the main signal that has been identified and reproduced, and outputs the result as code error rate data, and the entire area in the data waveform of the main signal that has been identified and reproduced. exhaustive, and includes a matrix of data tables that the values corresponding to each of the at least the phase control voltage and the identification reference voltage coordinate values, reads the value on the data table when the optical receiver is operated, the phase control Voltage is phase shifted, The reference voltage output to the reproducing unit, the by the code error rate data for the phase control voltage and the identification reference voltage, setting the phase control voltage and the identification reference voltage that satisfies the bit error rate value of the target that has been set in advance And a control unit (6 in FIG. 1).
[0012]
The data table stores and accumulates the code error rate data measured with respect to the phase control voltage and the identification reference voltage, and sets the minimum value of the accumulated code error rate data as the error. The optimum phase control voltage and identification reference voltage may be set by repeating comparison with the code error rate data from the monitoring circuit.
[0013]
In the present invention, a data table for the identification reference voltage value of the signal identification level and the phase control voltage of the clock signal is prepared in the control unit. This data table is divided so as to cover the entire area of the data waveform as shown in FIG. 3, and the eye opening is always on the data table. For this reason, it is always possible to find an adjustment point in the eye opening, and an optical receiver with an appropriate code error rate is made possible. In addition, by using the data table, even when the position of the eye opening has changed significantly (FIG. 4), which cannot be adjusted by the conventional automatic adjustment method, it is possible to adjust to the optimum code error rate. It has become.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0015]
[Description of configuration]
FIG. 1 is a block diagram showing an embodiment of the optical receiver of the present invention. This optical receiver includes an optical receiver 1, a clock extractor 2, a phase shift unit 3, an identification reproduction unit 4, an error monitoring unit 5, and a control unit 6.
[0016]
The optical receiver 1 converts the optical signal 10 received from the transmission path into an electrical signal, performs equalization amplification, and outputs the main signal 14 to the identification / reproduction unit 4 and the data signal 16 to the clock extraction unit 2. The clock extraction unit 2 creates a clock signal 17 from the data signal 16, and the phase shift unit 3 can vary the phase of the clock signal 17 by the phase control voltage 12 from the control unit 6.
[0017]
Based on the clock signal 18 from the phase shift unit 3, the identification / reproduction unit 4 compares whether the input main signal 14 is higher or lower than the identification reference voltage 11 from the control unit 6. As a result, when the main signal 14 is higher than the identification reference voltage 11, “Hi” is output to the error monitoring unit 5 as “Main” and “Lo” is output as the main signal 15. Therefore, it can be said that the main signal 15 is obtained by digitizing the analog main signal 14 as shown in FIG.
[0018]
The error monitoring unit 5 measures the code error rate of the main signal 15 and outputs the result as code error rate data 13 to the control unit 6. Further, the main signal 19 adjusted to have a desired code error rate is output to the outside.
[0019]
The control unit 6 has a built-in data table. As shown in FIG. 3, this data table is a matrix-like table in which values corresponding to the phase control voltage 12 and the identification reference voltage 11 covering the entire area of the data waveform of the main signal 15 are coordinate values. The code error rate is divided into m and n so as to obtain a desired accuracy. In FIG. 3, three eye openings centering on the optimum adjustment point and using the code error rate as a parameter are shown superimposed on the data waveform and the data table.
[0020]
At the start of operation of the optical receiver, the control unit 6 reads the phase control voltage 12 and the identification reference voltage 11 from the data table and outputs them to the phase shift unit 3 and the identification reproduction unit 4. Then, when the code error rate data 13 is received from the error monitoring unit 5 for each of them, the code error rate data 13 sets a phase control voltage 12 and an identification reference voltage value 11 that satisfy a preset code error rate. The phase control voltage 12 and the identification reference voltage 11 are set as operating points and the optical receiver is put into operation.
[0021]
[Description of operation]
Next, the operation of the embodiment of the present invention will be described along the flowchart of the control unit 6 shown in FIGS.
[0022]
In the operation of this optical receiver, a data table is prepared in the control unit 6 and an acceptance criterion for the code error rate of the data signal is set.
[0023]
First, the control unit 6 sets initial values with the index i = 0 of the identification reference voltage 11 and the index j = 0 of the phase control voltage 12 (step S1 in FIG. 5), and the identification reference voltage 11 (step S2). Then, the phase control voltage 12 is changed (step S3). The phase shift unit 3 outputs the clock signal 18 obtained by shifting the phase of the clock signal 17 by the phase control voltage 12 to the identification reproduction unit 4. The identification / reproduction unit 4 outputs the main signal 15 obtained by identifying and reproducing the main signal 14 using the identification reference voltage 11 and the clock signal 18 to the error monitoring unit 5.
[0024]
Since the error monitoring unit 5 measures the main signal 15 and outputs the code error rate data 13, the control unit 6 reads it (step S4). As a result, if the read code error rate data 13 is equal to or less than the set value (YES in step S5), the adjustment is terminated. The phase control voltage 12 and the identification reference voltage 11 are fixed to values corresponding to the indices j and i at that time (step S8), and the present optical receiver is put into operation.
[0025]
However, if the read code error rate data 13 is not less than the set value (NO in step S5) and j = m, that is, the phase control voltage 12 has not been changed to the maximum value on the data table (step The index j is increased by 1 (step S7), and the phase control voltage 12 is raised by one step. Then, the processes in steps S3 to S6 are repeated.
[0026]
In step S5, when j = m and it is found that the phase control voltage 12 has reached the maximum value on the data table (YES in step S6), the index j = 0 is set (step S9). By changing i to the maximum value on the data table (steps S10 and S11), the identification reference voltage 11 is raised step by step from the initial value (step S2).
[0027]
The processes of steps S3 to S8 are repeated under each value of the identification reference voltage 11. If the read code error rate data 13 falls below the set value (YES in step S5), the adjustment is terminated. The phase control voltage 12 and the identification reference voltage 11 are fixed to values corresponding to the indices j and i at that time (step S8), and the present optical receiver is put into operation.
[0028]
On the other hand, if it is determined in step S10 that i = n and the maximum value on the identification reference voltage 11 data table has been reached (YES in step S10), the phase control voltage 12 and the identification reference voltage 11 are set on the data table. Even if it is changed up to the upper limit, the code error rate does not reach the set acceptance criterion, so an error is assumed (step S12).
[0029]
When an optical receiver is shipped and actually incorporated into a transmission line system, the position and shape of the eye opening often changes as shown in FIG. 4 depending on the characteristics and conditions of the transmission line. In that case, the initially set phase control voltage 12 and identification reference voltage 11 may not be able to keep a desired code error rate. However, by performing the processing as described above at the start of operation, the code error rate can always be kept above the set value, and an optical receiver with stable quality can be supplied. FIG. 4 shows the change in the optimum adjustment point of the eye opening, the identification reference voltage, and the phase control voltage superimposed on the data table.
[0030]
Other Embodiments of the Invention
In the above-described embodiment, the phase control voltage 12 and the identification reference voltage 11 are sequentially changed. However, as a second embodiment of the present invention, the data table is randomly searched based on the random number table, The routine may be stopped when the acceptance criterion of the code error rate is reached.
[0031]
In the first embodiment, the low code error rate was searched in order from the end of the data table. However, when the acceptance standard value comes to the last point, it takes time to meet the automatic adjustment. End up. On the other hand, in the second embodiment, since the data table is searched at random, the eye opening can be searched at substantially the same time no matter where the eye opening is located on the data table.
[0032]
Next, as a third embodiment of the present invention, the code error rate data 13 measured by the error monitoring unit 5 is read with respect to the phase control voltage 12 and the identification reference voltage 11, and the phase control voltage 12 and the identification reference voltage are read. A structure that can be stored and accumulated in the data table in the control unit 6 together with the voltage 11 is provided. Then, by comparing the code error rate data 13 obtained by changing the phase control voltage 12 and the identification reference voltage 11 with all the code error rate data stored in the data table, the code error rate data 13 is identified. An optimum adjustment point of the reference voltage 11 can be found.
[0033]
FIG. 6 shows a flowchart of the control unit 6 in the third embodiment. In the third embodiment, the read code error rate ER is written and stored in the data table (step T4 in FIG. 6) (step T5). Then, in the routine (steps T2 to T13) for raising the phase control voltage 12 and the identification reference voltage 11, whether the read code error rate ER is smaller than the minimum code error rate ER (min) in the data table. It is checked (step T7).
[0034]
As a result, if the read code error rate ER is not smaller than the minimum code error rate ERmin in the data table (NO in step T7), the routine is continued as it is. On the other hand, if the read code error rate ER is smaller than the minimum code error rate ERmin in the data table (YES in step T7), the read code error rate ER is set to the minimum code error rate ERmin (step T9). Then, the index j at that time is set as an index M of the phase control voltage 12 corresponding to the optimal adjustment point, and i is set as an index N of the identification reference voltage 11 corresponding to the optimal adjustment point (step T10).
[0035]
According to the third embodiment, it is possible to adjust the phase control voltage 12 and the identification reference voltage 11 to the point with the lowest code error rate regardless of the position and shape of the eye opening. The optimal adjustment point can be maintained.
[0036]
【The invention's effect】
The optical receiver of the present invention includes a matrix-like data table that covers the entire area of the data waveform of the main signal after identification and reproduction, and that has coordinate values corresponding to the phase control voltage and the identification reference voltage, respectively. When operating an optical receiver, the values on the data table are read out, the code error rate for the phase control voltage and the identification reference voltage is measured, and the identification reference voltage and phase satisfying the desired code error rate value Since the control voltage is set to identify the main signal, the identification reference voltage and phase that always satisfy the desired code error rate value even if the shape and position of the eye opening change significantly due to changes in the transmission path characteristics and environment. The effect that the control voltage can always be found can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of an optical receiver according to the present invention. FIG. 2 is a diagram showing input and output waveforms in an identification reproducing unit of the optical receiver. Fig. 4 shows the optimum adjustment point of the control voltage superimposed on the data waveform and data table. Fig. 4 shows data on changes in the optimum adjustment point of the eye opening, identification reference voltage, and phase control voltage when the transmission line conditions change. FIG. 5 is a flow chart showing automatic adjustment of the identification reference voltage and the phase control voltage according to the first embodiment of the present invention. FIG. 6 is a flowchart showing the identification reference voltage according to the third embodiment of the present invention. Flow chart showing automatic adjustment of phase control voltage 【Explanation of symbols】
DESCRIPTION OF SYMBOLS 1 Optical receiving part 2 Clock extraction part 3 Phase shift part 4 Identification reproduction | regeneration part 5 Error monitoring part 6 Control part 10 Optical signal 11 Identification reference voltage 12 Phase control voltage 13 Code error rate data 14 Main signal 15 Main signal 16 Data signal 17 Clock Signal 18 Clock signal 19 Main signal

Claims (4)

An optical receiver that converts an optical signal received from the transmission path into an electrical signal and performs equalization amplification;
A clock extraction unit that generates a clock signal from the data signal from the optical receiver;
A phase shift unit for shifting the phase of the clock signal;
An identification reproducing unit for identifying and reproducing a main signal from the optical receiving unit;
An error monitoring circuit for measuring a code error rate of the identified and reproduced main signal and outputting the result as code error rate data;
A matrix-like data table that covers the entire area of the data waveform of the main signal after the identification and reproduction and that has coordinate values corresponding to at least the phase control voltage and the identification reference voltage, on the data table The phase control voltage is output to the phase shift unit, the identification reference voltage is output to the identification reproduction unit, and the code error rate data for the phase control voltage and the identification reference voltage is used to set a target value set in advance. An optical receiver comprising: a phase control voltage that satisfies a code error rate value; and a control unit that sets an identification reference voltage for the operation of the optical receiver. The data table stores and stores the code error rate data measured with respect to the phase control voltage and the identification reference voltage, and sets the minimum value of the stored code error rate data as the error. 2. The optical receiver according to claim 1 , wherein an optimum phase control voltage and an identification reference voltage are set by repeating comparison with the code error rate data from the monitoring circuit. Optical receiver according to claim 1 or 2, wherein the data table is characterized in that read sequentially at the address order. Optical receiver according to claim 1 or 2, wherein the data table is characterized in that read randomly.

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