Error rate measuring device and error rate measuring method

Abstract

To adjust a threshold voltage between signal levels in real time using an error determination results during measurement.SOLUTION: An error rate measurement device includes an error counting unit 13a that calculates, for each adjacent signal level of a PAM signal, a first error count value determined to be an error lower than the original signal level of the PAM signal at any time when a threshold voltage is set within the error section for each adjacent signal level of the two or more-value PAM signal, and a second error count value determined to be an error higher than the original signal level of the PAM signal, and a control unit 6 that adjusts and controls the threshold voltage for each signal level such that the ratio between the first error count value and the second error count value for each adjacent signal level calculated by the error counting unit 13a becomes closest to 1:1.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an error rate measuring device and an error rate measuring method for measuring the error rate of any PAM signal with two or more values including an NRZ signal.

Background Art

[0002] Conventionally, in an error rate measuring device, when determining bits of an NRZ signal composed of two values of signal levels 0 and 1 as shown in FIG. 6, it is necessary to determine a threshold voltage Vth serving as a determination criterion. Generally, as a method for obtaining the threshold voltage Vth, a method is used in which the threshold voltage Vth is swept once, and the threshold voltage Vth that gives the best bit error rate (BER) is selected from among them. This method is expected to have the highest accuracy and the algorithm is simple.

[0003] On the other hand, this method has drawbacks such as the need to interrupt the measurement once to sweep the threshold voltage Vth, and the inability to follow in cases where the threshold voltage Vth of the measurement signal can vary midway, lacking real-time performance.

[0004] Therefore, an error rate measuring device is provided with Auto Adjust as a function for estimating the threshold voltage Vth serving as this determination criterion in real time. This utilizes the fact that in an NRZ signal with a uniform mark rate such as a random pattern, the optimal threshold voltage Vth is equal to the DC average voltage value of the signal, and can be realized by a low-pass filter for extracting the DC average voltage of the signal and an A / D converter: ADC (Analog-to-Digital Converter) for detecting its voltage value.

[0005] Incidentally, while an NRZ signal like the one in Figure 6 has only one threshold voltage Vth, a PAM4 signal like the one in Figure 5, which consists of four signal levels (0, 1, 2, 3), requires three threshold voltages: Vth_Upper, Vth_Middle, and Vth_Lower. Of these, only Vth_Middle can be calculated using DC averaging, and Vth_Upper and Vth_Lower cannot be estimated. Therefore, although Auto Adjust is available for PAM4 signals, currently only Vth_Middle can be implemented, which presents a challenge.

[0006] Here, one method for estimating Vth_Upper and Vth_Lower is to estimate the threshold voltage Vth from the region where the digital value of the A / D converter saturates, and this method is disclosed in Patent Document 1 below. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 6025883 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, with PAM4 signals, the signal levels 0, 1, 2, and 3 are not necessarily evenly distributed with respect to the signal's peak-to-peak voltage. Furthermore, the optimal Vth_Upper is not necessarily exactly midway between signal level 3 and signal level 2, which can lead to estimation errors. Additionally, this method requires sweeping the threshold voltage Vth to determine the region where the digital value saturates, making it unsuitable for real-time estimation applications.

[0009] Therefore, the present invention has been made in view of the above problems, and aims to provide an error rate measuring device and an error rate measuring method that can adjust the threshold voltage between signal levels in real time using the error determination result during measurement. [Means for solving the problem]

[0010] To achieve the above objective, the error rate measuring device described in claim 1 of the present invention sets an initial value of a first threshold voltage within the error interval between signal levels 0 and 1 of the PAM4 signal, an initial value of a second threshold voltage within the error interval between signal levels 1 and 2 of the PAM4 signal, and an initial value of a third threshold voltage within the error interval between signal levels 2 and 3 of the PAM4 signal. An error counting unit 13a counts a first error count value determined to be an error lower than the original signal level of the PAM4 signal during the measurement time, and a second error count value determined to be an error higher than the original signal level of the PAM4 signal, for each adjacent signal level. Each function asymptotically approaches +1 when the signal level is shifted towards a higher level, approaches -1 when the signal level is shifted towards a lower level, and is 0 when balanced, and for the first threshold voltage, Subtract the number of errors in which the PAM4 signal was determined to be higher than its original signal level 0 from the number of errors in which the PAM4 signal was determined to be lower than its original signal level 1, and divide that value by the total number of symbols. It is a function, and for the second threshold voltage, Subtract the number of errors in which the PAM4 signal was determined to be higher than its original signal level 1 from the number of errors in which the PAM4 signal was determined to be lower than its original signal level 2, and divide that value by the total number of symbols. It is a function, and for the third threshold voltage, Subtract the number of errors in which the PAM4 signal was determined to be at a level higher than its original signal level 2 from the number of errors in which the PAM4 signal was determined to be at a level lower than its original signal level 3, and divide that value by the total number of symbols. Each function is a function An evaluation function calculation unit 6a defines an evaluation function and calculates the evaluation functions for the first threshold voltage, the second threshold voltage, and the third threshold voltage from the detection result of the error count value of the error count unit, The system includes an operation variable calculation unit 6b that estimates the deviations of the first threshold voltage, second threshold voltage, and third threshold voltage using the evaluation functions of the first threshold voltage, second threshold voltage, and third threshold voltage calculated by the evaluation function calculation unit, and calculates the voltage operation amounts of the first threshold voltage, second threshold voltage, and third threshold voltage from the estimation results, The system is characterized by automatically adjusting the voltage manipulation amounts of the first, second, and third threshold voltages, respectively, calculated by the manipulation amount calculation unit, by adding or subtracting these amounts to the currently set first, second, and third threshold voltages, respectively, so that the absolute value of the evaluation function is minimized. The error rate measuring device described in claim 2 of the present invention is the error rate measuring device of claim 1, When the error-free interval is wide, the first threshold voltage, the second threshold voltage, and the third threshold voltage are each set until an error is detected. Up and down The method is characterized by sweeping and finding the midpoint of the sweep result. The error rate measuring device described in claim 3 of the present invention is an error rate measuring device according to claim 1, A first bit determination device 11A compares the signal voltage level when a predetermined position in the time axis direction of the eye aperture of the PAM4 signal is punched with the first threshold voltage to perform bit determination, A second bit determination device 11B compares the signal voltage level when a predetermined position in the time axis direction of the eye aperture of the PAM4 signal is punched with the second threshold voltage to perform bit determination, The system includes a third bit determination device 11C that compares the signal voltage level when a predetermined position in the time axis direction of the eye aperture of the PAM4 signal is punched with the third threshold voltage to perform bit determination, The first threshold voltage, the second threshold voltage, and the third threshold voltage are bit-determined as the initial value for the first time, and as an adjusted value obtained by adding or subtracting the voltage manipulation amount calculated by the manipulation amount calculation unit 6b for the second time and thereafter. The error rate measuring device described in claim 4 of the present invention is an error rate measuring device according to claim 1, The system is characterized by performing automatic adjustment of the first, second, and third threshold voltages by repeatedly calculating the evaluation functions for the first, second, and third threshold voltages by the evaluation function calculation unit and calculating the voltage manipulation amounts for the first, second, and third threshold voltages by the manipulation amount calculation unit, so that the absolute value of the evaluation function is minimized.

[0011] The error rate measurement method described in claim 5 of the present invention includes the steps of setting an initial value of a first threshold voltage within the error interval between signal levels 0 and 1 of the PAM4 signal, an initial value of a second threshold voltage within the error interval between signal levels 1 and 2 of the PAM4 signal, and an initial value of a third threshold voltage within the error interval between signal levels 2 and 3 of the PAM4 signal, Step ST6 involves the error counting unit 13a calculating a first error count value for each adjacent signal level, which is determined to be an error lower than the original signal level of the PAM4 signal during the measurement time, and a second error count value for each adjacent signal level, which is determined to be an error higher than the original signal level of the PAM4 signal. Each function asymptotically approaches +1 when the signal level is shifted towards a higher level, approaches -1 when the signal level is shifted towards a lower level, and is 0 when balanced, and for the first threshold voltage, Subtract the number of errors in which the PAM4 signal was determined to be higher than its original signal level 0 from the number of errors in which the PAM4 signal was determined to be lower than its original signal level 1, and divide that value by the total number of symbols. It is a function, and for the second threshold voltage, Subtract the number of errors in which the PAM4 signal was determined to be higher than its original signal level 1 from the number of errors in which the PAM4 signal was determined to be lower than its original signal level 2, and divide that value by the total number of symbols. It is a function, and for the third threshold voltage, Subtract the number of errors in which the PAM4 signal was determined to be at a level higher than its original signal level 2 from the number of errors in which the PAM4 signal was determined to be at a level lower than its original signal level 3, and divide that value by the total number of symbols. Each function is a function Step ST7, in which an evaluation function is defined and the evaluation function for the first threshold voltage, the second threshold voltage, and the third threshold voltage is calculated by the evaluation function calculation unit 6a from the detection result of the error count value of the error count unit, Step ST8 involves using the evaluation functions for the first threshold voltage, second threshold voltage, and third threshold voltage calculated by the evaluation function calculation unit to estimate the deviations of the first threshold voltage, second threshold voltage, and third threshold voltage, and then calculating the voltage manipulation amounts for the first threshold voltage, second threshold voltage, and third threshold voltage using the manipulation amount calculation unit 6b based on the estimation results. The method is characterized by including the step of automatically adjusting the first threshold voltage, second threshold voltage, and third threshold voltage, each of which is currently set, by adding or subtracting the voltage manipulation amounts calculated by the manipulation amount calculation unit, to each of the first threshold voltage, second threshold voltage, and third threshold voltage, respectively, so that the absolute value of the evaluation function is minimized. The error rate measurement method described in claim 6 of the present invention is the error rate measurement method of claim 5, When the error-free interval is wide, the first threshold voltage, the second threshold voltage, and the third threshold voltage are each set until an error is detected. Up and down The method is characterized by including the steps of sweeping and finding the midpoint of the sweep result. The error rate measurement method described in claim 7 of the present invention is the error rate measurement method of claim 5, The first bit determination device 11A compares the signal voltage level when the eye aperture of the PAM4 signal is punched at a predetermined position in the time axis direction with the first threshold voltage and determines the bit, The steps include comparing the signal voltage level when the eye aperture of the PAM4 signal is punched at a predetermined position in the time axis direction with the second threshold voltage using the second bit determination device 11B to determine the bit, The third bit determination device 11C compares the signal voltage level when the eye aperture of the PAM4 signal is punched at a predetermined position in the time axis direction with the third threshold voltage and performs a bit determination. The method is characterized by including a step of bit determination of the first threshold voltage, the second threshold voltage, and the third threshold voltage as the initial value for the first time, and as an adjusted value obtained by adding or subtracting a voltage manipulation amount calculated by the manipulated amount calculation unit 6b for the second time and thereafter. The error rate measurement method described in claim 8 of the present invention is the error rate measurement method of claim 5, where the calculation of the evaluation function for each of the first threshold voltage, the second threshold voltage, and the third threshold voltage by the evaluation function calculation unit and the calculation of the voltage operation amount for each of the first threshold voltage, the second threshold voltage, and the third threshold voltage by the operation amount calculation unit are repeated so that the absolute value of the evaluation function becomes minimum, and an automatic adjustment of the first threshold voltage, the second threshold voltage, and the third threshold voltage is executed. This is characterized by including the step of

Advantages of the Invention

[0012] According to the present invention, based on the estimation according to the error determination result during measurement, the threshold voltage Vth between signal levels can be adjusted in real time in the direction of decreasing errors.

Brief Description of the Drawings

[0013] [Figure 1] It is a block diagram showing the internal configuration of an error rate measurement device according to the present invention. [Figure 2] It is a block diagram related to the automatic adjustment function (Auto Adjust) of the threshold voltage in FIG. 1. [Figure 3] It is a flowchart of an automatic adjustment method of a threshold voltage by an error rate measurement device according to the present invention. [Figure 4] It is a flowchart of an automatic adjustment method of a threshold voltage by an error rate measurement device according to the present invention following FIG. 3. [Figure 5] It is a diagram showing an example of the relationship between the signal levels 0, 1, 2, 3 of a PAM4 signal and the threshold voltages Vth_Upper, Vth_Middle, Vth_Lower. [Figure 6] It is a diagram showing an example of the relationship between the signal levels 0, 1 of a NRZ signal and the threshold voltages Vth1, Vth2, Vth3.

Embodiments for Carrying out the Invention

[0014] The embodiments for carrying out the present invention will be described in detail below with reference to the attached drawings.

[0015] [Summary of the Invention] The error rate measurement device and error rate measurement method according to the present invention employ a method that focuses on the distribution of error counts of bits and symbols, and has a function to automatically adjust the threshold voltage Vth in real time for any two- or more PAM signals, including NRZ signals.

[0016] First, to make the function of the present invention easier to understand, we will explain the case using a binary NRZ signal as an example, referring to Figure 6.

[0017] In Figure 6, the optimal threshold voltage Vth is Vth1, but if we move it upwards to, for example, Vth2, the frequency of incorrectly identifying bits that should be at signal level 1 as signal level 0 increases. Furthermore, if we move the threshold voltage Vth even higher to Vth3, all bits that should be at signal level 1 will be incorrectly identified as signal level 0.

[0018] Thus, an error in which a bit that should be at signal level 1 is mistakenly identified as signal level 0 is called an omission error, and the opposite is called an insertion error. However, for the sake of extension to the PAM signal described later, we will represent omission errors as L1_Omittion and insertion errors as L0_Insertion here.

[0019] Next, in Figure 6, if we consider moving the threshold voltage Vth downwards from Vth1, then conversely, L0_Insertion, which mistakes a bit with signal level 0 for a signal level 1, will increase. From this, we can consider that by evaluating whether L0_Insertion or L1_Omittion is dominant, we can estimate whether the current threshold voltage Vth is shifted upwards or downwards. Then, by moving the threshold voltage Vth based on this estimation, we consider the point where the ratio of L0_Insertion and L1_Omittion is balanced to be the optimal point for the threshold voltage Vth.

[0020] Next, we apply this to the PAM4 signal. For example, using the PAM4 signal in Figure 5, the threshold voltages Vth (Vth_Upper, Vth_Middle, Vth_Lower) can be estimated from the error counts shown below.

[0021] Furthermore, an error where the PAM4 signal is judged to be lower than its original signal level 3 is expressed as L3_Omittion, an error where the PAM4 signal is judged to be lower than its original signal level 2 is expressed as L2_Omittion, and an error where the PAM4 signal is judged to be lower than its original signal level 1 is expressed as L1_Omittion.

[0022] In contrast, an error that determines the PAM4 signal level is higher than its original level 2 is expressed as L2_Insertion, an error that determines the PAM4 signal level is higher than its original level 1 is expressed as L1_Insertion, and an error that determines the PAM4 signal level is higher than its original level 0 is expressed as L0_Insertion.

[0023] Vth_Upper:L3_Omittion and L2_Insertion Vth_Middle:L2_Omittion and L1_Insertion Vth_Lower: L1_Omittion and L0_Insertion

[0024] More specifically, if Symbol_total is the total number of symbols measured per arbitrary time, then a function can be realized using the following calculation formulas (Equations (1) to (3)) such that the threshold voltage Vth (Vth_Upper, Vth_Middle, Vth_Lower) asymptotically approaches +1 if it is shifted upward, approaches -1 if it is shifted downward, and is 0 if it is balanced. In this embodiment, this function is defined as the evaluation function.

[0025] Vth_Upper:(L3_Omittion-L2_Insertion) / Symbol_total…Formula (1)

[0026] The threshold voltage Vth_Upper is calculated using equation (1) above by subtracting the number of errors that determined the PAM4 signal was higher than its original signal level 2 from the number of errors that determined the PAM4 signal was lower than its original signal level 3, and then dividing that value by the total number of symbols.

[0027] Vth_Middle:(L2_Omittion-L1_Insertion) / Symbol_total…Formula (2)

[0028] The threshold voltage Vth_Middle is calculated using equation (2) above by subtracting the number of errors in which the PAM4 signal was determined to be higher than its original signal level 1 from the number of errors in which the PAM4 signal was determined to be lower than its original signal level 2, and then dividing that value by the total number of symbols.

[0029] Vth_Lower:(L1_Omittion-L0_Insertion) / Symbol_total…Formula (3)

[0030] The threshold voltage Vth_Lower is calculated using equation (3) above by subtracting the number of errors in which the PAM4 signal was determined to be higher than its original signal level 0 from the number of errors in which the PAM4 signal was determined to be lower than its original signal level 1, and then dividing that value by the total number of symbols.

[0031] [Configuration of the error rate measuring device] Next, the configuration of the error rate measurement device when automatically adjusting the threshold voltage of the PAM4 signal described above will be explained with reference to Figure 1.

[0032] As shown in Figure 1, the error rate measurement device 1 is generally configured to include a clock source 2, a variable delay unit 3, a bit error measurement unit 4, an operation display unit 5, and a control unit 6. The bit error measurement unit 4, as shown in Figure 1, includes a bit determination unit 11 (11A, 11B, 11C), a decoder 12, and an error determination unit 13. Furthermore, as shown in Figure 2, a threshold voltage adjustment unit 14 (14A, 14B, 14C) is provided between the control unit 6 and each bit determination unit 11 (11A, 11B, 11C).

[0033] Clock source 2 generates a clock at a reference frequency and inputs the generated reference frequency clock to variable delay unit 3.

[0034] When the control unit 6 controls the reference frequency clock from the clock source 2 with a set phase amount, the variable delay unit 3 inputs a punching clock based on the phase amount to each bit determination unit 11 (11A, 11B, 11C).

[0035] The number of bit determination units 11 corresponds to the number of eyepieces in the PAM signal. In this case, since the PAM4 signal is the target signal, there are three bit determination units 11 (11A, 11B, 11C).

[0036] Each bit determination unit 11A, 11B, and 11C is equipped with input terminals for a determination threshold voltage and a punching clock controlled by the control unit 6. The punching clock is synchronized with the PAM signal (data signal), and the punching phase is adjusted by controlling the delay amount of the variable delay unit 3 by the control unit 6.

[0037] The decoder 12 decodes the results obtained from each bit determination unit 11 (11A, 11B, 11C) into determination results as PAM symbols.

[0038] The error determination unit 13 includes an error counting unit 13a and detects errors by comparing the determination result as a PAM symbol decoded by the decoder 12 at an arbitrary time (or a preset measurement time) with a reference pattern sequence. Error determination involves not only counting errors, but also identifying errors that include information about the expected symbol and the actually determined symbol, as expressed as L3_Omittion above.

[0039] When the error determination unit 13 detects an error at any given time (or measurement time), the error counting unit 13a counts errors that are lower than the original signal level of the PAM4 signal (L3_Omittion, L2_Omittion, L1_Omittion) and errors that are higher than the original signal level of the PAM4 signal (L2_Insertion, L1_Insertion, L0_Insertion) for each adjacent signal level (between signal levels 0-1, 1-2, 2-3).

[0040] Then, a first error count value (error count values ​​for L3_Omittion, L2_Omittion, and L1_Omittion) is calculated for errors determined to be lower than the original signal level of the PAM4 signal, and a second error count value (error count values ​​for L2_Insertion, L1_Insertion, and L0_Insertion) is calculated for errors determined to be higher than the original signal level of the PAM4 signal, for each adjacent signal level interval (between signal levels 0-1, 1-2, and 2-3).

[0041] The threshold voltage adjustment units 14 (14A, 14B, 14C) consist of adders and subtractors, and add or subtract the voltage manipulation amount (adjustment amount) of the corresponding threshold voltage Vth calculated by the manipulated variable calculation unit 6b of the control unit 6 (described later) to the initial value of the threshold voltage Vth (Vth_Upper, Vth_Middle, Vth_Lower). Specifically, the threshold voltage adjustment unit 14A adds or subtracts the voltage manipulation amount (adjustment amount) of the threshold voltage Vth_Upper calculated by the manipulated variable calculation unit 6b to the initial value of the threshold voltage Vth_Upper. The threshold voltage adjustment unit 14B adds or subtracts the voltage manipulation amount (adjustment amount) of the threshold voltage Vth_Middle calculated by the manipulated variable calculation unit 6b to the initial value of the threshold voltage Vth_Middle. The threshold voltage adjustment unit 14C adds or subtracts the voltage manipulation amount (adjustment amount) of the threshold voltage Vth_Lower calculated by the manipulated variable calculation unit 6b to the initial value of the threshold voltage Vth_Lower.

[0042] The operation display unit 5 combines the functions of an operation unit, which consists of various keys, switches, buttons, and soft keys on the display screen equipped on the main body of the error rate measuring device 1, with the functions of a display unit, which consists of a display device such as a liquid crystal display, an EL (electroluminescent) display, or a CRT.

[0043] The operation display unit 5 allows the user to input various information necessary for automatic adjustment of the threshold voltage Vth of the PAM signal and measurement of the error rate (for example, initial values ​​of the threshold voltage Vth (Vth_Upper, Vth_Middle, Vth_Lower), phase amount (delay element operation amount), pattern sequence, and ON / OFF of the automatic adjustment function (Auto Adjust) of the threshold voltage Vth). The control unit 6 then controls the display of setting item screens and measurement result screens for setting the above information, and displays buttons, soft keys, pull-down menus, input boxes, and other objects for operation on the setting item screen to set various conditions.

[0044] In this embodiment, the operation display unit 5 is shown as having a configuration that combines both an operation unit and a display unit, but the operation display unit 5 may also have separate configurations for the operation unit and the display unit.

[0045] As shown in Figures 1 and 2, the control unit 6 includes an evaluation function calculation unit 6a and a manipulated variable calculation unit 6b.

[0046] The evaluation function calculation unit 6a calculates the evaluation function for each threshold voltage Vth (Vth_Upper, Vth_Middle, Vth_Lower) based on the error count value detection result from the error count unit 13a.

[0047] The manipulated variable calculation unit 6b uses the evaluation function for each threshold voltage Vth (Vth_Upper, Vth_Middle, Vth_Lower) calculated by the evaluation function calculation unit 6a to estimate the deviation of the threshold voltage Vth (Vth_Upper, Vth_Middle, Vth_Lower), and calculates the voltage manipulated variable (adjustment amount) for each threshold voltage Vth (Vth_Upper, Vth_Middle, Vth_Lower) from the estimation results.

[0048] The control unit 6 then comprehensively controls the variable delay unit 3, the operation display unit 5, the bit determination unit 11 (11A, 11B, 11C), and the error determination unit 13 in order to automatically adjust the threshold voltage Vth, which will be described later.

[0049] Specifically, the control unit 6 receives various information necessary for automatic adjustment of the threshold voltage Vth of the PAM signal and measurement of the error rate (for example, initial values ​​of the threshold voltage Vth (Vth_Upper, Vth_Middle, Vth_Lower), phase amount (delay device operation amount), pattern sequence, and automatic adjustment function of the threshold voltage Vth (Auto The operation display unit 5 controls the operation input (such as turning Adjust ON / OFF), controls the display of the operation display unit 5 (such as setting item screens and measurement result screens), controls the variable delay 3 by the set phase amount (delay control amount), controls the input of the threshold voltage adjustment unit 14 (14A, 14B, 14C) to the bit determination unit 11 (11A, 11B, 11C) to the threshold voltage adjustment unit 14 (14A, 14B, 14C) to the initial value of the threshold voltage Vth (Vth_Upper, Vth_Middle, Vth_Lower) and the voltage adjustment amount (adjustment amount) calculated by the operation amount calculation unit 6b, controls the input of the pattern sequence to the error determination unit 13, and determines whether the ratio of the first error count value and the second error count value for each signal level is closest to 1:1 (or whether the absolute value of the evaluation function is small).

[0050] [Method for automatically adjusting the threshold voltage Vth] Next, a method for automatically adjusting the threshold voltage Vth of the PAM4 signal using the error rate measuring device 1 configured as described above will be explained with reference to Figures 3 and 4.

[0051] To automatically adjust the threshold voltage Vth of the PAM4 signal, the operation display unit 5 is used to set the initial value of the threshold voltage Vth (Vth_Upper, Vth_Middle, Vth_Lower), the phase amount (delay switch operation amount), the pattern sequence, and the automatic adjustment function for the threshold voltage Vth (Auto Adjust): ON (ST1).

[0052] The initial value of the threshold voltage Vth is set within the error intervals between adjacent signal levels of the PAM4 signal (between signal levels 0-1, 1-2, and 2-3). Specifically, the initial value of the threshold voltage Vth_Lower is set within the error interval between signal levels 0-1 of the PAM4 signal, the initial value of the threshold voltage Vth_Middle is set within the error interval between signal levels 1-2 of the PAM4 signal, and the initial value of the threshold voltage Vth_Upper is set within the error interval between signal levels 2-3 of the PAM4 signal.

[0053] Furthermore, in this embodiment, the bit determination unit 11 (11A, 11B, 11C) and the decoder 12 are always in operation, but the user can also arbitrarily set the measurement time using the operation display unit 5.

[0054] After the above settings are made, when the measurement of the PAM4 signal begins, the control unit 6 inputs the initial values ​​of the set threshold voltages Vth (Vth_Upper, Vth_Middle, Vth_Lower) to the corresponding bit discriminators 11 (11A, 11B, 11C) and controls the variable delay unit 3 with the set phase amount. As a result, the variable delay unit 3 inputs a punching clock based on the phase amount to each bit discriminator 11 (11A, 11B, 11C) (ST2).

[0055] Then, each bit determination unit 11 (11A, 11B, 11C) compares the signal voltage level when the punching clock from the variable delay unit 3 punches a predetermined position in the time axis direction of the eye aperture of the PAM4 signal with the set threshold voltage Vth (Vth_Upper, Vth_Middle, Vth_Lower: initial value for the first time, adjusted value after adding or subtracting the voltage manipulation amount (adjustment amount) for the second time and thereafter) to determine the bit (ST3).

[0056] Next, the decoder 12 decodes the bit determination results of each bit determination unit 11 (11A, 11B, 11C) into determination results as PAM symbols (ST3).

[0057] Then, the error determination unit 13 compares the determination result decoded by each bit determination unit 11 (11A, 11B, 11C) with the set pattern sequence at an arbitrary time (or a predetermined measurement time) to determine whether or not there is an error and detect an error (ST4).

[0058] Furthermore, the error counting unit 13a counts errors (L3_Omittion, L2_Omittion, L1_Omittion) that are lower than the original signal level of the PAM4 signal for an arbitrary time (or measurement time), and errors (L2_Insertion, L1_Insertion, L0_Insertion) that are higher than the original signal level of the PAM4 signal, for each signal level interval (between signal levels 0-1, 1-2, and 2-3) (ST5).

[0059] The error counting unit 13a then calculates a first error count value (error count value for L3_Omittion, L2_Omittion, and L1_Omittion) for errors determined to be lower than the original signal level of the PAM4 signal, and a second error count value (error count value for L2_Insertion, L1_Insertion, and L0_Insertion) for errors determined to be higher than the original signal level of the PAM4 signal, for each adjacent signal level interval (between signal levels 0-1, 1-2, and 2-3) (ST6).

[0060] Next, the evaluation function calculation unit 6a of the control unit 6 calculates the evaluation function for each of the threshold voltages Vth_Upper, Vth_Middle, and Vth_Lower mentioned above from the error count value detection result of the error count unit 13a (ST7).

[0061] Then, the manipulated amount calculation unit 6b of the control unit 6 estimates the direction of the deviation and whether or not convergence occurs in the threshold voltage Vth (Vth_Upper, Vth_Middle, Vth_Lower) using the evaluation function calculated by the evaluation function calculation unit 6a, and calculates the voltage manipulated amount (adjustment amount) for each threshold voltage Vth (Vth_Upper, Vth_Middle, Vth_Lower) from the estimation result (ST8).

[0062] Subsequently, the control unit 6 inputs the voltage manipulation amount (adjustment amount) for each threshold voltage Vth (Vth_Upper, Vth_Middle, Vth_Lower) to the corresponding threshold voltage adjustment unit 14 (14A, 14B, 14C). As a result, the threshold voltage adjustment unit 14 (14A, 14B, 14C) automatically adjusts and sets the threshold voltages Vth (Vth_Upper, Vth_Middle, Vth_Lower) by adding or subtracting the voltage manipulation amount (adjustment amount) for the corresponding threshold voltage Vth to the currently set threshold voltages Vth (Vth_Upper, Vth_Middle, Vth_Lower) (ST9).

[0063] Then, the control unit 6 repeats the processes from ST3 to ST9 until it determines that the ratio of the first error count value to the second error count value for each signal level calculated by the error count unit 13a is closest to 1:1 (or the absolute value of the evaluation function is minimized) (ST10-Yes), and the control unit 6 controls the automatic adjustment of the threshold voltage Vth (Vth_Upper, Vth_Middle, Vth_Lower). When the user performs the operation to terminate the automatic adjustment of the threshold voltage Vth from the operation display unit 5 (ST11-Yes), the process of automatic adjustment of the threshold voltage Vth is terminated.

[0064] Alternatively, the determination process of ST10 in Figure 4 can be omitted, and the control unit 6 can be used to repeat the processes of ST3 to ST9 so that the ratio of the first error count value and the second error count value for each signal level calculated by the error count unit 13a is as close to 1:1 as possible (or so that the absolute value of the evaluation function is minimized), thereby automatically adjusting the threshold voltage Vth (Vth_Upper, Vth_Middle, Vth_Lower).

[0065] By the way, although the above-described embodiment used the case of using an NRZ signal and a PAM4 signal as an example, the explanation is not limited to this and can be similarly applied to any PAM signal.

[0066] Furthermore, as mentioned above, the method of this embodiment provides real-time information on the direction of the threshold voltage Vth deviation and its convergence, but it does not directly determine the position of the threshold voltage Vth. Therefore, it is necessary to repeat the estimation of the direction of the threshold voltage Vth deviation and the adjustment of the threshold voltage Vth several times until convergence occurs, and if the current threshold voltage Vth is far from the optimal point, convergence may take time.

[0067] Furthermore, in the above-described embodiment, the threshold voltage Vth is adjusted by estimation based on the error detection result during measurement, so it converges in the error-free section. Therefore, if the eye aperture is sufficient and the error-free section is wide, there is a possibility that the threshold voltage Vth may be adjusted by estimating a point shifted from the center of the eye as the optimal point. For this reason, if it is required not only to be error-free but also to be at the center of the error-free section, it is preferable to perform a conventionally known process such as sweeping the threshold voltage Vth up and down until an error is detected and finding the midpoint of the sweep result.

[0068] Thus, according to this embodiment, the threshold voltage Vth between signal levels is adjusted by estimation based on the error judgment result during measurement, making it possible to adjust the threshold voltage Vth between signal levels in real time for any PAM signal with two or more values, including an NRZ signal. In principle, this method can be applied even when, for example, the signal levels 0, 1, 2, and 3 of a PAM4 signal are not evenly distributed, or when the midpoint is not the optimal point for the threshold voltage Vth, and it is possible to adjust the threshold voltage Vth between signal levels in real time in a direction that reduces errors.

[0069] Furthermore, instead of providing a separate circuit for detecting the threshold voltage Vth, the threshold voltage Vth between signal levels is adjusted using the results of the bit determination machine. Therefore, the bit error measurement unit 4 can perform adjustment by estimating the threshold voltage using the same receiver device as conventional error rate measurement devices. This eliminates the need to consider the difference in characteristics between the circuit for adjusting by estimating the threshold voltage Vth and the bit error measurement unit 4, enabling adjustment correlated with the bit error while simultaneously allowing for a simple and inexpensive device configuration.

[0070] The best mode of the error rate measuring device and error rate measuring method according to the present invention has been described above, but the present invention is not limited by this description and drawings. That is, other modes, examples, and operational techniques made by those skilled in the art based on this mode are all included in the scope of the present invention. [Explanation of Symbols]

[0071] 1. Error rate measuring device 2 clock sources 3. Variable delay circuit 4-bit error measurement unit 5 Operation display section 6 Control Unit 6a Evaluation function calculation unit 6b Operation amount calculation section 11 (11A, 11B, 11C) bit determination machine 12 Decoders 13 Error detection unit 13a Error Counting Section 14 (14A, 14B, 14C) Threshold voltage adjustment section

Claims

1. The initial value of the first threshold voltage is set within the error interval between signal levels 0 and 1 of the PAM4 signal, the initial value of the second threshold voltage is set within the error interval between signal levels 1 and 2 of the PAM4 signal, and the initial value of the third threshold voltage is set within the error interval between signal levels 2 and 3 of the PAM4 signal. An error counting unit (13a) counts a first error count value determined to be an error lower than the original signal level of the PAM4 signal during the measurement time, and a second error count value determined to be an error higher than the original signal level of the PAM4 signal, for each adjacent signal level. Each function asymptotically approaches +1 if the signal level is shifted towards a higher level, approaches -1 if the signal level is shifted towards a lower level, and is 0 if it is balanced. The first threshold voltage is a function obtained by subtracting the number of errors determined to be higher than the original signal level 0 of the PAM4 signal from the number of errors determined to be lower than the original signal level 1 of the PAM4 signal, and dividing that value by the total number of symbols. The second threshold voltage is a function obtained by subtracting the number of errors determined to be lower than the original signal level 2 of the PAM4 signal from the original signal level The evaluation function is defined as a function that subtracts the number of errors determined to be higher than level 1 and divides that value by the total number of symbols, and for the third threshold voltage, it is a function that subtracts the number of errors determined to be higher than the original signal level 2 of the PAM4 signal from the number of errors determined to be lower than the original signal level 3 of the PAM4 signal and divides that value by the total number of symbols, and the evaluation function calculation unit (6a) calculates the evaluation functions for the first threshold voltage, the second threshold voltage, and the third threshold voltage from the detection results of the error count value of the error count unit, The system includes an operation variable calculation unit (6b) which uses the evaluation functions for the first threshold voltage, second threshold voltage, and third threshold voltage calculated by the evaluation function calculation unit to estimate the deviations of the first threshold voltage, second threshold voltage, and third threshold voltage, and calculates the voltage operation amounts for the first threshold voltage, second threshold voltage, and third threshold voltage from the estimation results, An error rate measuring device characterized by automatically adjusting the currently set first threshold voltage, second threshold voltage, and third threshold voltage by adding or subtracting the voltage manipulation amounts of the first threshold voltage, second threshold voltage, and third threshold voltage, respectively, calculated by the manipulation amount calculation unit, so that the absolute value of the evaluation function is minimized.

2. The error rate measuring device according to claim 1, characterized in that, when the error-free interval is wide, the first threshold voltage, the second threshold voltage, and the third threshold voltage are each swept up or down until an error is detected, and the midpoint of the sweep result is determined.

3. A first bit determination device (11A) compares the signal voltage level when a predetermined position in the time axis direction of the eye aperture of the PAM4 signal is punched with the first threshold voltage to perform bit determination, A second bit determination device (11B) compares the signal voltage level when a predetermined position in the time axis direction of the eye aperture of the PAM4 signal is punched with the second threshold voltage to perform bit determination, The system includes a third bit determination device (11C) that compares the signal voltage level when a predetermined position in the time axis direction of the eye aperture of the PAM4 signal is punched with the third threshold voltage to perform bit determination, The error rate measuring device according to claim 1, characterized in that the first threshold voltage, the second threshold voltage, and the third threshold voltage are bit-determined as the initial value for the first time, and as adjusted values ​​obtained by adding or subtracting a voltage manipulation amount calculated by the manipulated amount calculation unit (6b) for the second time and thereafter.

4. The error rate measuring device according to claim 1, characterized in that it performs automatic adjustment of the first threshold voltage, second threshold voltage, and third threshold voltage by repeatedly calculating the evaluation functions for the first threshold voltage, second threshold voltage, and third threshold voltage by the evaluation function calculation unit and calculating the voltage manipulation amounts for the first threshold voltage, second threshold voltage, and third threshold voltage by the manipulation amount calculation unit, so that the absolute value of the evaluation function is minimized.

5. The steps include setting an initial value for a first threshold voltage within the error interval between signal levels 0 and 1 of the PAM4 signal, an initial value for a second threshold voltage within the error interval between signal levels 1 and 2 of the PAM4 signal, and an initial value for a third threshold voltage within the error interval between signal levels 2 and 3 of the PAM4 signal, Step (ST6) involves the error counting unit (13a) calculating a first error count value determined to be an error lower than the original signal level of the PAM4 signal during the measurement time, and a second error count value determined to be an error higher than the original signal level of the PAM4 signal, for each adjacent signal level. Each function asymptotically approaches +1 if the signal level is shifted towards a higher level, approaches -1 if the signal level is shifted towards a lower level, and is 0 if it is balanced. The first threshold voltage is a function obtained by subtracting the number of errors determined to be higher than the original signal level 0 of the PAM4 signal from the number of errors determined to be lower than the original signal level 1 of the PAM4 signal, and dividing that value by the total number of symbols. The second threshold voltage is a function obtained by subtracting the number of errors determined to be lower than the original signal level 2 of the PAM4 signal from the number of errors determined to be higher than the original signal level 1 of the PAM4 signal. The function for the third threshold voltage is defined as a function that subtracts the number of errors determined to be lower than the original signal level 3 of the PAM4 signal and divides that value by the total number of symbols, and for the third threshold voltage, it is defined as a function that subtracts the number of errors determined to be higher than the original signal level 2 of the PAM4 signal from the number of errors determined to be lower than the original signal level 3 of the PAM4 signal and divides that value by the total number of symbols, and each of these functions is defined as an evaluation function, and the evaluation function calculation unit (6a) calculates the evaluation functions for the first threshold voltage, the second threshold voltage, and the third threshold voltage from the detection result of the error count value of the error count unit (ST7), Step (ST8): Using the evaluation functions for the first threshold voltage, the second threshold voltage, and the third threshold voltage calculated by the evaluation function calculation unit, the deviations of the first threshold voltage, the second threshold voltage, and the third threshold voltage are estimated, and the voltage manipulation amounts for the first threshold voltage, the second threshold voltage, and the third threshold voltage are calculated by the manipulation amount calculation unit (6b) from the estimation results. An error rate measurement method characterized by including the step of automatically adjusting the first threshold voltage, second threshold voltage, and third threshold voltage, respectively, by adding or subtracting the voltage manipulation amounts of the first threshold voltage, second threshold voltage, and third threshold voltage, respectively, calculated by the manipulation amount calculation unit, to each of the currently set first threshold voltage, second threshold voltage, and third threshold voltage, respectively, so that the absolute value of the evaluation function is minimized.

6. The error rate measurement method according to claim 5, characterized in that, when the error-free interval is wide, the first threshold voltage, the second threshold voltage, and the third threshold voltage are each swept up or down until an error is detected, and the midpoint of the sweep result is determined.

7. The first bit determination device (11A) compares the signal voltage level when a predetermined position in the time axis direction of the eye aperture of the PAM4 signal is punched with the first threshold voltage and performs a bit determination. The steps include comparing the signal voltage level when the eye aperture of the PAM4 signal is punched at a predetermined position in the time axis direction with the second threshold voltage using a second bit determination device (11B) to perform a bit determination, The steps include comparing the signal voltage level when the eye aperture of the PAM4 signal is punched at a predetermined position in the time axis direction with the third threshold voltage using a third bit determination device (11C) to determine the bit, The error rate measurement method according to claim 5, characterized in that it includes the step of bit determination of the first threshold voltage, the second threshold voltage, and the third threshold voltage as the initial value for the first time, and as an adjusted value obtained by adding or subtracting a voltage manipulation amount calculated by the manipulation amount calculation unit (6b) for the second time and thereafter.

8. The error rate measurement method according to claim 5, characterized in that it includes the step of performing automatic adjustment of the first threshold voltage, second threshold voltage, and third threshold voltage by repeatedly calculating the evaluation functions for the first threshold voltage, second threshold voltage, and third threshold voltage by the evaluation function calculation unit and calculating the voltage manipulation amounts for the first threshold voltage, second threshold voltage, and third threshold voltage by the manipulation amount calculation unit, so that the absolute value of the evaluation function is minimized.

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