JP2019016832A - Error detector and error detection method - Google Patents

Abstract

To allow a general user to automatically adjust parameters without conscious of complicated adjustment procedures.SOLUTION: A voltage threshold level calculating section 13 calculates the voltage having the lowest error rate measured in an error rate measurement section 12, when the voltage threshold level Vth2 is changed in a prescribed step, as the voltage threshold level Vth2 after adjustment, a voltage capable of measuring the error rate in the error rate measurement section 12 while changing the voltage threshold levels Vth1, Vth3 within a prescribed voltage range is detected, the voltage having the lowest error rate measured in the error rate measurement section 12 when changing the voltage threshold level Vth1 by a prescribed step at that voltage is calculated as the voltage threshold level Vth1 after adjustment, and the voltage having the lowest error rate measured in the error rate measurement section 12 when changing the voltage threshold level Vth3 by a prescribed step is calculated as the voltage threshold level Vth3 after adjustment. A decoder setting section 11 sets the voltage threshold levels Vth1, Vth2, Vth3 calculated in the voltage threshold level calculating section 13 in a decoder 2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an error detection apparatus and an error detection method for detecting an error rate of a PAM4 signal by a quaternary pulse amplitude modulation method (hereinafter referred to as PAM4 method) in which the amplitude is divided into four types for each symbol.

  Various digital communication apparatuses are required to have a larger capacity transmission capability as the number of users increases and multimedia communication spreads. Also, as one of the indexes for evaluating the quality of digital signals in these digital communication apparatuses, a bit error rate defined as a comparison between the number of received code errors and the total number of received data is known. Yes.

  In the digital communication apparatus described above, a test signal including fixed data is transmitted to a device under test such as a photoelectric conversion component to be tested, and becomes a reference to the signal under measurement input via the device under test. As an error rate measurement device that compares the reference signal with a bit unit and measures the error rate of the signal under measurement, for example, a bit error measurement device disclosed in Patent Document 1 below is known.

  A bit error measurement device disclosed in Patent Document 1 below measures error bits by comparing input data received from a measurement object with known data to be received from the measurement object. The bit error measuring apparatus disclosed in Patent Document 1 compares a comparison data storage unit having a plurality of blocks with received data and known data in order to easily analyze the cause of error bits. A comparison unit that sequentially stores comparison data of a bit string including one or a plurality of detection bits detected under a predetermined detection condition into a plurality of blocks according to the detection, and a comparison stored in each of the plurality of blocks A display control unit configured to display each bit string obtained from the data on a display device in a line with a position according to a predetermined arrangement condition as a reference.

  By the way, a bit string consisting of “0 (low level voltage)” and “1 (high level voltage)” is converted into a pulse signal of four voltage levels as a pulse amplitude modulation signal in which the amplitude of the information signal is encoded by a series of pulse signals. The PAM4 system that modulates and transmits is known. The PAM4 signal in this PAM4 system is divided into four types of amplitudes for each symbol, and has four different voltage levels V1, V2, V3, V4 as shown in FIG. Is divided into a high voltage range H1, a medium voltage range H2, and a low voltage range H3 from the higher voltage level, and consists of a continuous range of three eye pattern openings.

  Then, in order to perform real-time error rate measurement of this type of PAM4 signal with an error rate measuring device, a decoder for the PAM4 signal is required. In order to correctly decode the PAM4 signal composed of three eye pattern openings, it is necessary to determine three voltage thresholds for each eye pattern opening. Furthermore, in order to measure the error rate of the signal decoded by the decoder, it is necessary to adjust the punching timing (phase, voltage threshold) of the input signal (decoded signal) of the error rate measuring device.

JP 2007-274474 A

  However, in order to adjust the parameters described above, it is necessary to adjust individual parameters while checking the error rate with an error rate measuring device. However, since all parameters affect the error rate measurement results, It was necessary to make adjustments in order.

  For this reason, the adjustments described above have been made only by some experienced engineers. In addition to the error rate measurement device and the decoder, adjustment is performed while confirming the waveform output from the decoder using an oscilloscope, and it is difficult for a general user to perform the above-described adjustment.

  Therefore, the present invention has been made in view of the above-described problems, and an error detection apparatus and error detection capable of automatically adjusting individual parameters without a general user being aware of complicated adjustment procedures. It aims to provide a method.

In order to achieve the above object, in the error detection device according to claim 1 of the present invention, the entire amplitude voltage range H is changed from a higher voltage level to a high voltage range H1, a medium voltage range H2, and a low voltage range H3. An error detection apparatus 1 that is divided and decodes a PAM4 signal having a continuous range by three eye pattern openings by a decoder 2 and detects an error rate from the decoded signal.
An error rate measuring unit 12 that measures an error rate when the voltage threshold Vth1 of the high voltage range, the voltage threshold Vth2 of the medium voltage range, and the voltage threshold Vth3 of the low voltage range are changed in predetermined steps;
When the voltage threshold value in the medium voltage range is changed in a predetermined step, the voltage at which the error rate measured by the error rate measurement unit is lowest is calculated as the adjusted voltage threshold value in the medium voltage range, and the high voltage The error rate measuring unit detects a voltage capable of measuring the error rate while changing the voltage threshold of the range and the voltage threshold of the low voltage range within a predetermined voltage range, and the detected error rate can be measured In voltage, when the voltage threshold of the high voltage range is changed in a predetermined step, the voltage at which the error rate measured by the error rate measuring unit is lowest is calculated as the adjusted voltage threshold of the high voltage range The voltage threshold calculation for calculating the voltage at which the error rate measured by the error rate measurement unit is lowest when the voltage threshold of the low voltage range is changed in a predetermined step as the adjusted voltage threshold of the low voltage range And part 13,
And a decoder setting unit 11 for setting the voltage threshold value in the high voltage range, the voltage threshold value in the medium voltage range, and the voltage threshold value in the low voltage range calculated by the voltage threshold value calculation unit in the decoder. And

The error detection device according to claim 2 is the error detection device according to claim 1,
A parameter setting unit 14 is provided, which sets a position at which the error rate becomes the lowest by changing the phase and voltage as the punching timing of the signal input to the error rate measurement unit 12.

In the error detection method according to claim 3, the entire amplitude voltage range H is divided into a high voltage range H1, a medium voltage range H2, and a low voltage range H3 from the higher voltage level to three eye pattern openings. An error detection method for decoding a PAM4 signal having a continuous range by a decoder 2 and detecting an error rate from the decoded signal,
Measuring the error rate while changing the voltage threshold Vth2 of the intermediate voltage range in a predetermined step, and setting the voltage at which the error rate is lowest to the adjusted voltage threshold of the intermediate voltage range;
Measuring an error rate while changing the voltage threshold Vth1 of the high voltage range and the voltage threshold Vth3 of the low voltage range within a predetermined voltage range, and detecting a voltage capable of measuring the error rate;
In the voltage where the error rate can be measured, the error rate is measured while changing the voltage threshold of the high voltage range in a predetermined step, and the voltage with the lowest error rate is adjusted to the adjusted voltage threshold of the high voltage range. Steps to set,
In the voltage where the error rate can be measured, the error rate is measured while changing the voltage threshold of the low voltage range in a predetermined step, and the voltage with the lowest error rate is adjusted to the adjusted voltage threshold of the low voltage range. And a setting step.

The error detection method according to claim 4 is the error detection method according to claim 3,
It includes a step of setting a position where the error rate is lowest by changing the phase and voltage as the punching timing of the input signal.

  According to the present invention, when detecting an error rate of a PAM4 signal, a general user can automatically adjust individual parameters and use a decoder without being aware of complicated adjustment procedures. In addition, the adjustment time can be shortened compared with conventional manual adjustments, and individual parameters are automatically adjusted based only on the error rate measurement results, so there is no need to use a measuring instrument such as an oscilloscope.

1 is a block diagram of an error detection apparatus according to the present invention. It is explanatory drawing in the case of adjusting the voltage threshold value Vth2 of the intermediate voltage range H2 in this invention. It is explanatory drawing in the case of roughly adjusting the voltage threshold Vth1 of the high voltage range H1 and the voltage threshold Vth3 of the low voltage range H3 in the present invention. It is explanatory drawing in the case of adjusting the punching timing of an input signal in this invention. It is a flowchart including the adjustment procedure of voltage threshold Vth1, Vth2, Vth3 of each voltage range H1, H2, H3 in this invention. It is explanatory drawing of a PAM4 signal.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings.

[Configuration of error detection device]
As shown in FIG. 1, the error detection apparatus 1 of the present embodiment is roughly configured to include a decoder 2 and an error detector 3. As shown in FIG. 6, the error detection apparatus 1 is divided into four types of amplitudes for each symbol, and has voltage levels V1, V2, V3, V4 having four different amplitudes, and the entire amplitude voltage range H is a voltage. The error rate of the PAM4 signal, which is divided into a high voltage range H1, a medium voltage range H2, and a low voltage range H3 from the higher level, and consists of a continuous range by three eye pattern openings is detected.

  The decoder 2 decodes the input PAM4 signal into, for example, an NRZ signal, and outputs the decoded signal (decoded signal) to the error detector 3. The PAM4 signal is generated by a pattern generation unit (not shown) (PAM signal generation unit provided in the error detection device 1 or a PAM signal generation unit configured separately) to fold the device under test (DUT). It is input by transmission from a device under test (DUT) itself having a transmission function.

  The error detector 3 detects an error rate of the decoded signal input from the decoder 2 and includes a decoder setting unit 11, an error rate measuring unit 12, a voltage threshold value calculating unit 13, and a parameter setting unit 14. .

  The decoder setting unit 11 sets parameters (voltage threshold, phase) necessary for correctly decoding the PAM4 signal, and includes a voltage threshold variable unit 11a and a voltage threshold setting unit 11b.

  When the voltage threshold variable unit 11a automatically adjusts and sets the voltage threshold Vth2 of the medium voltage range H2 of the PAM4 signal by an automatic adjustment method described later, the voltage threshold variable unit 11a changes the voltage threshold Vth2 of the medium voltage range H2 in a predetermined step. Set in decoder 2.

  The voltage threshold variable unit 11a automatically adjusts and sets the voltage threshold Vth1 of the high voltage range H1 and the voltage threshold Vth3 of the low voltage range H3 of the PAM4 signal by an automatic adjustment method described later. The voltage threshold value Vth1 and the voltage threshold value Vth3 of the low voltage range H3 are changed in a predetermined step every time the error rate BER is measured and set in the decoder 2.

  Furthermore, the voltage threshold variable unit 11a changes the decoder in predetermined steps in the amplitude axis direction when the voltage threshold is automatically adjusted and set as the punching timing of the input signal of the error measuring unit 12 by an automatic adjustment method described later. Set to 2.

  The voltage threshold setting unit 11b uses the automatic adjustment method to be described later, and the voltage threshold Vth1 of the high voltage range H1 of the PAM4 signal calculated by the voltage threshold calculation unit 12, the voltage threshold Vth2 of the medium voltage range H2, and the voltage of the low voltage range H3. The threshold value Vth3 is set in the decoder 2 as an automatically adjusted voltage threshold value.

  The error rate measurement unit 12 automatically adjusts the voltage thresholds Vth1, Vth2, and Vth3 of the voltage ranges H1, H2, and H3 of the PAM4 signal and sets them in the decoder 2 by the decoder setting unit 11 by an automatic adjustment method described later. Then, the error rate of the decoded signal input from the decoder 2 is measured.

  Further, the error rate measuring unit 12 performs the decoder 2 at the punching timing (phase, voltage threshold) set by the parameter setting unit 14 by the automatic adjustment method described later in the actual measurement after finishing the automatic adjustment method described later. The error rate of the decoded signal input from is measured.

  Based on the error rate measurement result measured by the error rate measurement unit 12, the voltage threshold value calculation unit 13 uses the automatic adjustment method described later, and the voltage threshold value Vth1 of the high voltage range H1 and the voltage threshold value Vth2 of the medium voltage range H2 of the PAM4 signal. The voltage threshold Vth3 of the low voltage range H3 is calculated.

  The parameter setting unit 14 sets the punching timing (phase and voltage threshold) automatically adjusted by the automatic adjustment method described later in the error rate measuring unit 12.

  That is, the parameter setting unit 14 sets the phase in the time axis direction in a predetermined step (for example, 10 mUI) when the phase is automatically adjusted and set as the punching timing of the input signal of the error measurement unit 12 by an automatic adjustment method described later. Change to set in the error measurement unit 12. Further, the parameter setting unit 14 changes the voltage threshold in a predetermined step and automatically sets the error threshold when the voltage threshold is automatically adjusted and set as the punching timing of the input signal of the error measurement unit 12 by an automatic adjustment method described later. Set to 12.

[Operation of error detection device]
Next, as an operation of the error detection apparatus 1 configured as described above, automatic adjustment of each parameter (voltage thresholds Vth1, Vth2, Vth3 of each voltage range H1, H2, H3 of the PAM4 signal, input signal punching timing) is performed. The method will be described with reference to FIGS. Each parameter before automatic adjustment is assumed to be set to a predetermined initial value or a value arbitrarily set by the user.

  When the start button for performing automatic adjustment is pressed, the voltage threshold value Vth2 of the intermediate voltage range H2 of the decoder 2 is set to 0, and automatic adjustment of the voltage threshold value Vth2 of the intermediate voltage range H2 is started (ST1).

In this automatic adjustment of the voltage threshold Vth2, the error rate BER is measured while changing the voltage threshold Vth2 of the intermediate voltage range H2 in a predetermined step (for example, 1 mV) (ST2). Then, as shown in FIG. 2, the inverse error function Erfc ⁻¹ vs. the voltage threshold Vth2 of the medium voltage range H2 is calculated from the voltage threshold Vth2 of the medium voltage range H2 vs. the error rate BER (10 ⁻⁵ to 10 ⁻¹⁰ ). (ST3). Subsequently, a straight line approximation by the least square method is performed on the inverse error function Erfc ⁻¹ plane to calculate an intersection of two straight lines (ST4). Then, the voltage threshold value Vth2 of the intermediate voltage range H2 in which the error rate is lowest at the intersection of the two straight lines is set in the decoder 2 as the voltage threshold value Vth2 of the automatically adjusted intermediate voltage range H2 (ST5).

The inverse error function Erfc ⁻¹ is a value obtained by substituting the error rate BER into the following equation (1).

  Next, coarse adjustment of the voltage threshold Vth1 of the high voltage range H1 and the voltage threshold Vth3 of the low voltage range H3 is started (ST6). In this rough adjustment, the point with the lowest error rate BER is taken as the adjustment result.

  However, the error rate BER is measured by actually setting all the voltage thresholds of the voltage threshold Vth1 of the high voltage range H1 and the voltage threshold Vth3 of the low voltage range H3, and the measurement result is the point where the error rate BER is the lowest. Is ideal.

  However, since the time required for the measurement is actually enormous, it is not realistic. Therefore, in the automatic adjustment of the voltage threshold Vth1 of the high voltage range H1 and the voltage threshold Vth3 of the low voltage range H3, the first adjustment is a rough adjustment, and the second adjustment is a main adjustment, and the adjustment is performed in two stages. .

  Here, since adjustment of the voltage threshold Vth1 of the high voltage range H1 and the voltage threshold Vth3 of the low voltage range H3 affects the measurement result of the error rate, both voltage thresholds Vth1 and Vth3 must be adjusted to optimum values. . However, if one of the voltage thresholds has a large difference from the center voltage of the upper and lower eye pattern openings, the error rate becomes a very large value, and the other voltage threshold approaches the center voltage of the eye pattern opening. Adjustment becomes impossible. For this reason, it is necessary to set the voltage threshold value Vth1 of the high voltage range H1 and the voltage threshold value Vth3 of the low voltage range H3 at rough intervals, measure the respective error rates, and find a setting value that can adjust the voltage threshold values Vth1 and Vth3. is there.

  The least significant bit LSB can measure the error rate BER only when both the voltage threshold Vth1 of the high voltage range H1 and the voltage threshold Vth3 of the low voltage range H3 are set near the center of the eye pattern opening.

  Therefore, in the coarse adjustment, an error occurs while changing the voltage threshold Vth1 of the high voltage range H1 and the voltage threshold Vth3 of the low voltage range H3 within a predetermined voltage range in a coarser step (eg, 20 mV) than the step of actual adjustment (eg, 1 mV). The rate BER is measured (ST7). Then, a combination of the voltage threshold Vth1 of the high voltage range H1 and the voltage threshold Vth3 of the low voltage range H3, which is a region where the error rate BER can be measured, is detected from the measurement result of the error rate BER (ST8).

  For example, as shown in FIG. 3, the error threshold BER is measured while the voltage threshold Vth3 of the low voltage range H3 is fixed to AmV and the voltage threshold Vth1 of the high voltage range H1 is changed from AmV within a predetermined voltage range, for example, in 20 mV steps. To do. Subsequently, the voltage threshold Vth3 of the low voltage range H3 is fixed to A + 20 mV, and the error rate BER is measured while changing the voltage threshold Vth1 of the high voltage range H1 from AmV within a predetermined voltage range in 20 mV steps. 3. Measure in the order of 0, 1, 2,..., N, n + 1,. In the example of FIG. 3, a combination of voltage thresholds Vth1 and Vth3 surrounded by a thick line is a voltage region in which the error rate BER can be measured (error count is possible).

Next, the main adjustment of the voltage threshold Vth1 of the high voltage range H1 and the voltage threshold Vth3 of the low voltage range H3 is started (ST9). This adjustment is performed by the same method as the automatic adjustment of the voltage threshold Vth2 in the medium voltage range H2 described above. That is, in this adjustment of the voltage threshold Vth1, the error rate BER is measured while changing the voltage threshold Vth1 of the high voltage range H1 in a predetermined step (for example, 1 mV). Then, from the voltage threshold Vth1 of the high voltage range H1 versus the error rate BER (10 ⁻⁵ to 10 ⁻¹⁰ ), data of the inverse error function Erfc ⁻¹ vs. the voltage threshold Vth1 of the high voltage range H1 is calculated. Subsequently, a straight line approximation by the least square method is performed on the inverse error function Erfc ⁻¹ plane to calculate an intersection of two straight lines. Then, the voltage threshold value Vth1 of the high voltage range H1 with the lowest error rate at the intersection of the two straight lines is set in the decoder 2 as the voltage threshold value Vth1 of the high voltage range H1 after automatic adjustment.

In the main adjustment of the voltage threshold Vth3, the error rate BER is measured while changing the voltage threshold Vth3 of the low voltage range H3 in a predetermined step (for example, 1 mV). Then, from the voltage threshold Vth3 of the low voltage range H3 versus the error rate BER (10 ⁻⁵ to 10 ⁻¹⁰ ), data of the inverse error function Erfc ⁻¹ vs. the voltage threshold Vth3 of the low voltage range H3 is calculated. Subsequently, a straight line approximation by the least square method is performed on the inverse error function Erfc ⁻¹ plane to calculate an intersection of two straight lines. Then, the voltage threshold Vth3 of the low voltage range H3 in which the error rate is lowest at the intersection of the two straight lines is set in the decoder 2 as the voltage threshold Vth3 of the low voltage range H3 after automatic adjustment.

  As described above, in adjusting the voltage threshold value Vth1 of the high voltage range H1 and the voltage threshold value Vth3 of the low voltage range H3, an area in which the error rate BER can be measured by coarse adjustment is obtained, and then finer steps than the coarse adjustment are performed. The error rate BER is measured while changing the voltage threshold. As a result, a point with the lowest error rate BER can be searched efficiently.

  Next, the punching timing (phase, voltage threshold) of the input signal in the error detector 3 is set by a conventionally known method (ST10). The punching timing of the input signal is set to a position where the error rate BER is lowest when the phase and voltage are changed in predetermined steps. Specifically, in the horizontal axis (time axis) direction of FIG. 4, the phase is changed by a predetermined step (for example, 10 mUI), and the point with the lowest error rate BER is detected as the optimum point. Further, in the amplitude direction (vertical axis direction in FIG. 4) of the optimum point of the error rate BER, the voltage is changed in a predetermined step, and the point with the lowest error rate BER is detected as the optimum point. Then, the phase and voltage at the position of the detected optimum point are set as the punching timing (phase and voltage threshold).

If there is an error-free area in 1 second measurement, the optimum point cannot be uniquely determined. In this case, the optimum point is obtained by performing the approximate calculation using the least square method on the inverse error function Erfc ⁻¹ plane described above from the measurement result at the timing at which the error rate BER can be measured.

  As described above, according to the present embodiment, when detecting the error rate of the PAM4 signal, a general user is not aware of the complicated adjustment procedure, and the individual parameters (the voltages in the voltage ranges H1, H2, and H3). The decoder can be used by automatically adjusting the threshold values Vth1, Vth2, Vth3, and the input signal punching timing. In addition, the adjustment time can be shortened as compared with the conventional manual adjustment. Furthermore, individual parameters can be automatically adjusted based only on error rate measurement results, and there is no need to use a measuring instrument such as an oscilloscope.

  In the above-described embodiment (FIG. 1), the case where the decoder 2 and the error detector 3 are configured separately has been described as an example. However, the decoder 2 is incorporated into the main body of the error detector 3 and integrated. The configured error detection device 1 may be used. In addition, a pattern generation unit that generates a PAM4 signal that is input as a test signal to the device under test (DUT) may be mounted on the error detector 3.

  The best mode of the error detection apparatus and the error detection method according to the present invention has been described above, but the present invention is not limited by the description and drawings according to this mode. That is, it is a matter of course that all other forms, examples, operation techniques, and the like made by those skilled in the art based on this form are included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Error detection apparatus 2 Decoder 3 Error detector 11 Decoder setting part 11a Voltage threshold variable part 11b Voltage threshold setting part 12 Error rate measurement part 13 Voltage threshold calculation part 14 Parameter setting part H Amplitude voltage range H1 High voltage range H2 Medium voltage range H3 Low voltage range V1, V2, V3, V4 Voltage level Vth1, Vth2, Vth3 Voltage threshold

Claims (4)

The entire amplitude voltage range (H) is divided into a high voltage range (H1), a medium voltage range (H2), and a low voltage range (H3) from the higher voltage level, and from a continuous range by three eye pattern openings. An error detection device (1) that decodes a PAM4 signal that is decoded by a decoder (2) and detects an error rate from the decoded signal,
An error rate measuring unit that measures an error rate when the voltage threshold (Vth1) of the high voltage range, the voltage threshold (Vth2) of the medium voltage range, and the voltage threshold (Vth3) of the low voltage range are changed in a predetermined step ( 12)
When the voltage threshold value in the medium voltage range is changed in a predetermined step, the voltage at which the error rate measured by the error rate measurement unit is lowest is calculated as the adjusted voltage threshold value in the medium voltage range, and the high voltage The error rate measuring unit detects a voltage capable of measuring the error rate while changing the voltage threshold of the range and the voltage threshold of the low voltage range within a predetermined voltage range, and the detected error rate can be measured In voltage, when the voltage threshold of the high voltage range is changed in a predetermined step, the voltage at which the error rate measured by the error rate measuring unit is lowest is calculated as the adjusted voltage threshold of the high voltage range The voltage threshold calculation for calculating the voltage at which the error rate measured by the error rate measurement unit is lowest when the voltage threshold of the low voltage range is changed in a predetermined step as the adjusted voltage threshold of the low voltage range Part (13),
A decoder setting unit (11) for setting the voltage threshold value of the high voltage range, the voltage threshold value of the medium voltage range, and the voltage threshold value of the low voltage range calculated by the voltage threshold value calculation unit in the decoder; An error detection device characterized by the above. 2. A parameter setting unit (14) for setting a position at which an error rate becomes lowest by changing a phase and voltage as a punching timing of a signal input to the error rate measurement unit (12). The error detection apparatus described. The entire amplitude voltage range (H) is divided into a high voltage range (H1), a medium voltage range (H2), and a low voltage range (H3) from the higher voltage level, and from a continuous range by three eye pattern openings. The PAM4 signal is decoded by a decoder (2), and an error detection method for detecting an error rate from the decoded signal,
Measuring the error rate while changing the voltage threshold (Vth2) of the medium voltage range in a predetermined step, and setting the voltage at which the error rate is lowest to the adjusted voltage threshold of the medium voltage range;
Measuring an error rate while changing the voltage threshold (Vth1) of the high voltage range and the voltage threshold (Vth3) of the low voltage range within a predetermined voltage range, and detecting a voltage capable of measuring the error rate;
In the voltage where the error rate can be measured, the error rate is measured while changing the voltage threshold of the high voltage range in a predetermined step, and the voltage with the lowest error rate is adjusted to the adjusted voltage threshold of the high voltage range. Steps to set,
In the voltage where the error rate can be measured, the error rate is measured while changing the voltage threshold of the low voltage range in a predetermined step, and the voltage with the lowest error rate is adjusted to the adjusted voltage threshold of the low voltage range. And an error detecting method. 4. The error detection method according to claim 3, further comprising the step of setting a position where the error rate is lowest by changing the phase and voltage as the punching timing of the input signal.

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