JP6818064B2 - Error rate measuring device and error rate measuring method - Google Patents

Description

The present invention relates to an error rate measuring device and an error rate measuring method, and more particularly, error rate measurement for measuring a bit error rate (BER) of a PAM4 signal output from a test object (Device Under Test: DUT). The present invention relates to an apparatus and an error rate measuring method.

With the spread of next-generation 5G mobile communication and cloud communication services, further increase in data communication traffic is expected. Along with this, in data centers and the like, which are the infrastructures thereof, in addition to speeding up, it is considered to expand the transmission capacity by using a multi-value modulation signal such as a PAM4 signal.

In the quality evaluation of the equipment constituting the data center as described above, the error rate for detecting a bit error by comparing the pulse pattern signal transmitted from the DUT with the known pulse pattern signal to be transmitted from the DUT. A measuring device is used.

As shown in FIG. 13A, the PAM4 signal is composed of four symbols consisting of "00", "01", "10", and "11". The most significant bit of these symbols is called the MSB (Most Significant Bit), and the least significant bit is called the LSB (Least Significant Bit). FIG. 14 shows an example of an eye pattern obtained by superimposing PAM4 signals on a symbol-by-symbol basis. The voltage range of the openings of the three eye patterns is divided into a high voltage range H1, a medium voltage range H2, and a low voltage range H3, respectively, from the one with the highest voltage level. In the following, the eye pattern opening in the high voltage range H1 will be referred to as "Upper Eye", the eye pattern opening in the medium voltage range H2 will be referred to as "Middle Eye", and the eye pattern opening in the low voltage range H3 will be referred to as "Lower Eye". Refer to.

In order to measure the BER of the PAM4 signal, first, the reference voltages Vth1, Vht2, and Vth3 are set for the high voltage range H1, the medium voltage range H2, and the low voltage range H3, respectively, and the MSB and LSB are set from the PAM4 signal. The bit string signal will be cut out. Here, the bit string signal of the MSB is cut out by the reference voltage Vth2 as shown in FIG. 13 (b). Specifically, when the voltage level of the PAM4 signal is equal to or higher than the reference voltage Vth2, “1” is obtained as the value of the bit string signal of the MSB, and when the voltage level of the PAM4 signal is less than the reference voltage Vth2, the MSB "0" is obtained as the value of the bit string signal of.

Further, the LSB bit string signal is cut out by the reference voltages Vth1 and Vth3 as shown in FIG. 13C. Specifically, when the voltage level of the PAM4 signal is less than the reference voltage Vth2 and the reference voltage Vth3 or more, "1" is obtained as the value of the bit string signal of the LSB, and the voltage level of the PAM4 signal is less than the reference voltage Vth2 and. When the reference voltage is less than Vth3, "0" is obtained as the value of the bit string signal of the LSB. On the other hand, when the voltage level of the PAM4 signal is the reference voltage Vth2 or more and the reference voltage Vth1 or more, "1" is obtained as the value of the bit string signal of the LSB, and the voltage level of the PAM4 signal is the reference voltage Vth2 or more and the reference voltage Vth1. If it is less than, "0" is obtained as the value of the bit string signal of the LSB.

As shown in FIG. 15, a conventional error rate measuring device using a PAM4 signal as a signal to be measured mainly includes a PAM4 decoder 70, a clock reproduction circuit 71, and an error detecting unit 72. The PAM4 decoder 70 outputs the MSB bit string signal of the measured signal from the MSB channel (MSB CH) and outputs the LSB bit string signal of the measured signal from the LSB channel (LSB CH). The clock regeneration circuit 71 reproduces the clock from the MSB bit string signal output from the MSB CH of the PAM4 decoder 70 and outputs it as the reproduction clock CLK. The error detection unit 72 acquires the data of the bit string signals of the MSB and LSB at the timing of the reproduction clock CLK output from the clock reproduction circuit 71, and measures the BER of the measured signal based on these acquired data. It has become.

By the way, in order to measure the BER of the PAM4 signal with high accuracy, it is necessary to set the reference voltages Vth1 to Vth3 to the optimum values in advance. This optimum value can be determined by measuring the bathtub curve as shown in FIG. 16 while sweeping each reference voltage Vth1 to Vth3 and searching for the value of each reference voltage Vth1 to Vth3 that minimizes the BER. (See, for example, Patent Document 1).

Special Table 2017-512017

However, in the system shown in FIG. 15, which reproduces the clock from the bit string signal of the MSB, when the reference voltage Vth2 is swept to create the bathtub curve for the Middle Eye, the clock cannot be reproduced from the bit string signal of the MSB. , There was a problem that clock loss occurred and it became impossible to analyze the Middle Eye.

The present invention has been made to solve such a conventional problem, and is an error rate measuring device and an error rate measuring method capable of creating a bathtub curve for a Middle Eye without causing a clock loss. The purpose is to provide.

In order to solve the above problems, the error rate measuring device according to the present invention has a PAM4 signal in which the voltage ranges of the openings of the three eye patterns are in the high voltage range, the medium voltage range, and the low voltage range from the highest voltage level, respectively. This is an error rate measuring device for detecting an error of, and outputs 1 as a discrimination signal when the voltage level of the PAM4 signal is equal to or higher than the first reference voltage, and outputs 0 as a discrimination signal in other cases. A second 0/1 discriminator and a second that outputs 1 as a discrimination signal when the voltage level of the PAM4 signal is equal to or higher than the second reference voltage, and outputs 0 as a discrimination signal in other cases. A third 0/1 that outputs 1 as a discrimination signal when the voltage level of the 0/1 discriminator and the PAM4 signal is equal to or higher than the third reference voltage, and outputs 0 as a discrimination signal in other cases. The discriminator, the clock reproduction circuit that reproduces the clock from the discrimination signal output from the second 0/1 discriminator and outputs it as a reproduction clock, and the first to third 0/1 discriminators, respectively. A decoding circuit that generates a plurality of bit string signals including the MSB bit string signal of the PAM4 signal from the output discrimination signal, and the voltage level of the MSB bit string signal output from the decoding circuit is measured at the timing of the reproduction clock. The error rate calculation unit that calculates the error rate of the bit string signal of the MSB based on the voltage level measured by the level measurement unit, and the first to third reference voltages, respectively. A reference voltage setting unit for setting the first to third 0/1 discriminators is provided, and the error rate calculation unit uses the reference voltage setting unit to set the second reference voltage in the medium voltage range. When the first reference voltage is set to a constant value and the first reference voltage is variably set in the medium voltage range, the change in the error rate of the bit string signal of the MSB according to the change in the first reference voltage is changed. It is a configuration to create the bathtub curve shown.

With this configuration, the error rate measuring device according to the present invention can create a bathtub curve for the Middle Eye without causing a clock loss.

Further, in the error rate measuring device according to the present invention, the decoding circuit is exclusively exclusive with the discrimination signal from the second 0/1 discriminator and the discrimination signal from the third 0/1 discriminator. The OR circuit has an EXOR circuit that outputs a logical sum, an OR circuit that outputs a discriminant signal from the first 0/1 discriminator, and an OR circuit that outputs a logical sum of the output of the EXOR circuit. When the third reference voltage is set to a constant value equal to the second reference voltage in the medium voltage range by the reference voltage setting unit, the discrimination signal from the first 0/1 discriminator is transmitted. It may be configured to be output to the level measurement unit as a bit string signal of the MSB.

Further, the error rate measuring device according to the present invention detects errors in PAM4 signals in which the voltage ranges of the openings of the three eye patterns are in the high voltage range, the medium voltage range, and the low voltage range from the highest voltage level, respectively. A first 0/1 of a rate measuring device that outputs 1 as a discrimination signal when the voltage level of the PAM4 signal is equal to or higher than the first reference voltage, and outputs 0 as a discrimination signal in other cases. A discriminator and a second 0/1 discriminator that outputs 1 as a discriminant signal when the voltage level of the PAM4 signal is equal to or higher than the second reference voltage and outputs 0 as a discriminant signal in other cases. A third 0/1 discriminator that outputs 1 as a discrimination signal when the voltage level of the PAM4 signal is equal to or higher than the third reference voltage, and outputs 0 as a discrimination signal in other cases. From the clock reproduction circuit that reproduces the clock from the discrimination signal output from the 2 0/1 discriminator and outputs it as the reproduction clock, and from the discrimination signals output from the 1st to 3rd 0/1 discriminators, respectively. A decoding circuit that generates a plurality of bit string signals including the MSB bit string signal of the PAM4 signal, a level measuring unit that measures the voltage level of the MSB bit string signal output from the decoding circuit at the timing of the reproduction clock, and a level measuring unit. The error rate calculation unit that calculates the error rate of the bit string signal of the MSB based on the voltage level measured by the level measurement unit, and the first to third reference voltages are set to the first to third reference voltages, respectively. The error rate calculation unit includes a reference voltage setting unit to be set in the 0/1 discriminator of the above, and the reference voltage setting unit sets the second reference voltage to a constant value in the medium voltage range. At the same time, when the third reference voltage is variably set in the medium voltage range, a bathtub curve showing a change in the error rate of the bit string signal of the MSB according to the change in the third reference voltage is created. It is a configuration.

With this configuration, the error rate measuring device according to the present invention can create a bathtub curve for the Middle Eye without causing a clock loss.

Further, in the error rate measuring device according to the present invention, the decoding circuit negates and excludes the discrimination signal from the first 0/1 discriminator and the discrimination signal from the second 0/1 discriminator. The AND circuit includes an EXNOR circuit that outputs a logical sum, an AND circuit that outputs a logical product of a discrimination signal from the third 0/1 discriminator, and the output of the EXNOR circuit. When the first reference voltage is set to a constant value equal to the second reference voltage in the medium voltage range by the reference voltage setting unit, the discrimination signal from the third 0/1 discriminator is transmitted. It may be configured to be output to the level measuring unit as the bit string signal of the MSB.

Further, the error rate measuring method according to the present invention is an error of detecting an error of the PAM4 signal in which the voltage range of the openings of the three eye patterns is the high voltage range, the medium voltage range, and the low voltage range from the highest voltage level, respectively. In the rate measurement method, when the voltage level of the PAM4 signal is equal to or higher than the first reference voltage, 1 is output from the first 0/1 discriminator, and in other cases, 0 is output as the discrimination signal. Is output from the first 0/1 discriminator, and 1 is set as the discriminant signal when the voltage level of the PAM4 signal is equal to or higher than the second reference voltage. The second 0/1 discrimination step, which outputs from the 1 discriminator and outputs 0 as a discrimination signal in other cases from the second 0/1 discriminator, and the voltage level of the PAM4 signal is the third reference. When the voltage is equal to or higher than the voltage, 1 is output as a discrimination signal from the third 0/1 discriminator, and in other cases, 0 is output as a discrimination signal from the third 0/1 discriminator. From the 1 discrimination step, the clock reproduction step of reproducing the clock from the discrimination signal output from the 2nd 0/1 discriminator and outputting it as the reproduction clock, and the 1st to 3rd 0/1 discriminators. A decoding step that generates a plurality of bit string signals including the MSB bit string signal of the PAM4 signal from each output discrimination signal, and a voltage level of the MSB bit string signal output from the decoding step are set at the timing of the reproduction clock. The level measurement step to be measured, the error rate calculation step for calculating the error rate of the bit string signal of the MSB based on the voltage level measured by the level measurement step, and the first to third reference voltages, respectively. The reference voltage setting step set in the first to third 0/1 discriminators is provided, and in the error rate calculation step, the second reference voltage is in the medium voltage range by the reference voltage setting step. When the first reference voltage is variably set in the medium voltage range while being set to a constant value in, the error rate of the bit string signal of the MSB changes according to the change of the first reference voltage. It is a configuration to create a bathtub curve showing.

With this configuration, the error rate measuring method according to the present invention can create a bathtub curve for the Middle Eye without causing a clock loss.

Further, in the error rate measuring method according to the present invention, the decoding step is exclusive to the discrimination signal from the second 0/1 discriminator and the discrimination signal from the third 0/1 discriminator. The OR step includes an EXOR step that outputs a logical sum, an OR step that outputs a discriminant signal from the first 0/1 discriminator, and an OR step that outputs a logical sum of the output of the EXOR step, and the OR step is the reference. When the third reference voltage is set to a constant value equal to the second reference voltage in the medium voltage range by the voltage setting step, the discrimination signal from the first 0/1 discriminator is transmitted to the MSB. It may be configured to be output to the level measurement step as a bit string signal of.

Further, the error rate measuring method according to the present invention is an error of detecting an error of the PAM4 signal in which the voltage range of the openings of the three eye patterns is the high voltage range, the medium voltage range, and the low voltage range from the highest voltage level, respectively. In the rate measurement method, when the voltage level of the PAM4 signal is equal to or higher than the first reference voltage, 1 is output from the first 0/1 discriminator, and in other cases, 0 is output as the discrimination signal. Is output from the first 0/1 discriminator, and 1 is set as the discriminant signal when the voltage level of the PAM4 signal is equal to or higher than the second reference voltage. The second 0/1 discrimination step, which outputs from the 1 discriminator and outputs 0 as a discrimination signal in other cases from the second 0/1 discriminator, and the voltage level of the PAM4 signal is the third reference. When the voltage is equal to or higher than the voltage, 1 is output as a discrimination signal from the third 0/1 discriminator, and in other cases, 0 is output as a discrimination signal from the third 0/1 discriminator. From the 1 discrimination step, the clock reproduction step of reproducing the clock from the discrimination signal output from the 2nd 0/1 discriminator and outputting it as the reproduction clock, and the 1st to 3rd 0/1 discriminators. A decoding step that generates a plurality of bit string signals including the MSB bit string signal of the PAM4 signal from each output discrimination signal, and a voltage level of the MSB bit string signal output from the decoding step are set at the timing of the reproduction clock. The level measurement step to be measured, the error rate calculation step for calculating the error rate of the bit string signal of the MSB based on the voltage level measured by the level measurement step, and the first to third reference voltages, respectively. The reference voltage setting step set in the first to third 0/1 discriminators is provided, and in the error rate calculation step, the second reference voltage is in the medium voltage range by the reference voltage setting step. When the third reference voltage is set to a constant value and the third reference voltage is variably set in the medium voltage range, the error rate of the bit string signal of the MSB changes according to the change of the third reference voltage. It is a configuration to create a bathtub curve showing.

With this configuration, the error rate measuring method according to the present invention can create a bathtub curve for the Middle Eye without causing a clock loss.

Further, in the error rate measuring method according to the present invention, in the decoding step, the discrimination signal from the first 0/1 discriminator and the discrimination signal from the second 0/1 discriminator are negatively excluded. The AND step includes an EXNOR step that outputs a target logical sum, an AND step that outputs a logical product of the discrimination signal from the third 0/1 discriminator, and the output of the EXNOR step. When the first reference voltage is set to a constant value equal to the second reference voltage in the medium voltage range by the reference voltage setting step, the discrimination signal from the third 0/1 discriminator is transmitted. It may be configured to be output to the level measurement step as a bit string signal of MSB.

The present invention provides an error rate measuring device and an error rate measuring method capable of creating a bathtub curve for a Middle Eye without causing a clock loss.

It is a block diagram (the 1) which shows the structure of the error rate measuring apparatus which concerns on 1st Embodiment of this invention. It is a figure which shows the relationship between the PAM4 signal, the reference voltage and the output in the PAM4 decoder provided in the error rate measuring apparatus which concerns on 1st Embodiment of this invention. It is a figure which shows the truth table of the PAM4 decoder provided in the error rate measuring apparatus which concerns on 1st Embodiment of this invention. It is a block diagram (the 2) which shows the structure of the error rate measuring apparatus which concerns on 1st Embodiment of this invention. It is a flowchart (the 1) which shows the process of the error rate measuring method using the error rate measuring apparatus which concerns on 1st Embodiment of this invention. It is a flowchart (the 2) which shows the process of the error rate measuring method using the error rate measuring apparatus which concerns on 1st Embodiment of this invention. It is a flowchart (3) which shows the process of the error rate measuring method using the error rate measuring apparatus which concerns on 1st Embodiment of this invention. It is a block diagram which shows the structure of the error rate measuring apparatus which concerns on 2nd Embodiment of this invention. It is a figure which shows the truth table of the PAM4 decoder provided in the error rate measuring apparatus which concerns on 2nd Embodiment of this invention. It is a flowchart (the 1) which shows the process of the error rate measuring method using the error rate measuring apparatus which concerns on 2nd Embodiment of this invention. It is a flowchart (No. 2) which shows the process of the error rate measuring method using the error rate measuring apparatus which concerns on 2nd Embodiment of this invention. It is a flowchart (the 3) which shows the process of the error rate measurement method using the error rate measuring apparatus which concerns on 2nd Embodiment of this invention. It is a figure which shows an example of the PAM4 signal generated by the synthesis of the bit string signal of MSB and the bit string signal of LSB. It is a figure which shows the eye pattern of a PAM4 signal. It is a block diagram which shows the structure of the conventional error rate measuring apparatus. It is a figure which shows an example of the bathtub curve which shows the change of the BER of a PAM4 signal according to the change of a reference voltage.

Hereinafter, embodiments of the error rate measuring device and the error rate measuring method according to the present invention will be described with reference to the drawings. As shown in FIG. 14, the present invention detects errors in PAM4 signals in which the voltage ranges of the openings of the three eye patterns are the high voltage range H1, the medium voltage range H2, and the low voltage range H3, respectively, from the one with the highest voltage level. It relates to an error rate measuring device and an error rate measuring method.

(First Embodiment)
As shown in FIG. 1, the error rate measuring device 100 according to the first embodiment of the present invention detects an error in the PAM4 signal output from the DUT 200, and includes a PAM4 decoder 10 and a clock reproduction circuit 20. An error detection unit 30, a display unit 40, an operation unit 50, and a control unit 60 are provided.

The DUT 200 is adapted to output a PAM4 signal as a signal to be measured to the error rate measuring device 100. Examples of standards supported by the DUT200 include PCI Express (registered trademark), USB (registered trademark) (Universal Serial Bus), CEI (Common Electrical Interface), Ethernet (registered trademark), and InfiniBand.

The PAM4 decoder 10 generates a plurality of bit string signals from the PAM4 signal output from the DUT 200, and is a first 0/1 discriminator 11, a second 0/1 discriminator 12, and a third 0. It includes a / 1 discriminator 13, a reference voltage setting unit 14, and a decoding circuit 15. The first to third 0/1 discriminators 11 to 13 are connected in parallel to the transmission line through which the PAM4 signal is transmitted.

The first 0/1 discriminator 11 discriminates 0/1 of the PAM4 signal input from the DUT 200 by comparison with the first reference voltage Vth1. That is, as shown in FIG. 14, the first 0/1 discriminator 11 compares the voltage level of the PAM4 signal with the first reference voltage Vth1, and the voltage level of the PAM4 signal is equal to or higher than the first reference voltage Vth1. When is, D1 = "1" is output as a discrimination signal, and when the voltage level of the PAM4 signal is less than the first reference voltage Vth1, D1 = "0" is output as a discrimination signal.

The second 0/1 discriminator 12 discriminates 0/1 of the PAM4 signal input from the DUT 200 by comparison with the second reference voltage Vth2. That is, as shown in FIG. 14, the second 0/1 discriminator 12 compares the voltage level of the PAM4 signal with the second reference voltage Vth2, and the voltage level of the PAM4 signal is equal to or higher than the second reference voltage Vth2. When is, D2 = "1" is output as a discrimination signal, and when the voltage level of the PAM4 signal is less than the second reference voltage Vth2, D2 = "0" is output as a discrimination signal.

The third 0/1 discriminator 13 discriminates 0/1 of the PAM4 signal input from the DUT 200 by comparison with the third reference voltage Vth3. That is, as shown in FIG. 14, the third 0/1 discriminator 13 compares the voltage level of the PAM4 signal with the third reference voltage Vth3, and the voltage level of the PAM4 signal is equal to or higher than the third reference voltage Vth3. When is, D3 = "1" is output as a discrimination signal, and when the voltage level of the PAM4 signal is less than the third reference voltage Vth3, D3 = "0" is output as a discrimination signal.

The reference voltage setting unit 14 sets the first to third reference voltages Vth1 to Vth3 in the first to third 0/1 discriminators 11 to 13, respectively.

The decoding circuit 15 is composed of a logic circuit, and generates a plurality of bit string signals from the discrimination signals D1 to D3 output from the first to third 0/1 discriminators 11 to 13, respectively. It has become. For example, the decoding circuit 15 has an EXOR circuit 15a that outputs an exclusive OR of the discrimination signal D2 from the second 0/1 discriminator 12 and the discrimination signal D3 from the third 0/1 discriminator 13. , The OR circuit 15b that outputs the logical sum of the discrimination signal D1 from the first 0/1 discriminator 11 and the output of the EXOR circuit 15a.

In the OR circuit 15b, as shown in FIG. 14, the reference voltage setting unit 14 causes the first to third reference voltages Vth1 to Vth3 to have high voltage ranges H1, medium voltage range H2, and low voltage range H3, for example, center voltages. When set in the vicinity, the LSB bit string signal of the PAM4 signal is output from the LSB channel (LSB CH).

Further, as shown in FIG. 14, when the reference voltage setting unit 14 sets the second reference voltage Vth2 in the medium voltage range H2, for example, near the center voltage, the decoding circuit 15 determines the MSB of the PAM4 signal. The bit string signal (discrimination signal D2) is output from the MSB channel (MSB CH).

The clock regeneration circuit 20 reproduces the clock from the discrimination signal D2 output from the second 0/1 discriminator 12 and outputs it as the reproduction clock CLK.

The error detection unit 30 detects an error in the bit string signal output from the MSB CH and the LSB CH of the decoding circuit 15, and includes a level measurement unit 31, a comparison pattern generation unit 32, and an error rate calculation unit 33. ,including.

The level measuring unit 31 measures the voltage level of the bit string signal output from the MSB CH of the decoding circuit 15 at the timing of the reproduction clock CLK output from the clock reproduction circuit 20. Further, the level measuring unit 31 measures the voltage level of the bit string signal output from the LSB CH of the decoding circuit 15 at the timing of the reproduction clock CLK output from the clock reproduction circuit 20.

The comparison pattern generation unit 32 is a known bit string signal to be output from the MSB CH and LSB CH of the decoding circuit 15 according to the PAM4 signal output from the DUT 200 (hereinafter, also referred to as “comparison pulse pattern signal”). Are to be generated respectively. FIG. 1 shows an example in which the comparison pattern generation unit 32 outputs the MSB bit string signal to the MSB CH of the error rate calculation unit 33 and outputs the LSB bit string signal to the LSB CH of the error rate calculation unit 33. There is.

The error rate calculation unit 33 compares the voltage level measured by the level measurement unit 31 with the comparison pulse pattern signal output from the comparison pattern generation unit 32, and the MSB CH and LSB CH of the decoding circuit 15 are compared. The number of erroneous bits included in the bit string signals output from is counted, and the BER of each of those bit string signals is calculated.

Hereinafter, an operation example in which the error rate measuring device 100 according to the present embodiment creates a bathtub curve with respect to the bit string signal output from the LSB CH of the decoding circuit 15 will be described with reference to FIGS. 2 to 4 and the like. .. In this case, as shown in FIG. 2, the reference voltage setting unit 14 sets the second reference voltage Vth2 and the third reference voltage Vth3 to constant values equal to each other in the medium voltage range H2, for example, near the center voltage. The first reference voltage Vth1 is variably set (swept) in the medium voltage range H2.

As shown in the truth table of FIG. 3, when the second reference voltage Vth2 and the third reference voltage Vth3 are equal (that is, D2 = D3), the EXOR circuit 15a is input to one input A of the OR circuit 15b. Always outputs "0". Further, since the OR circuit 15b always inputs "0" to the input A, the value of the discrimination signal D1 is always output as it is. That is, as shown in FIG. 4, in the OR circuit 15b, the reference voltage setting unit 14 sets the third reference voltage Vth3 to a constant value equal to the second reference voltage Vth2 in the medium voltage range H2. When the reference voltage Vth1 of 1 is variably set in the medium voltage range H2, the discrimination signal D1 from the first 0/1 discriminator 11 is used as the Middle Eye measurement signal (MSB bit string signal) and is leveled from the LSB CH. It is designed to output to the measuring unit 31. At this time, the comparison pattern generation unit 32 outputs the MSB bit string signal as the comparison pulse pattern signal to the LSB CH of the error rate calculation unit 33.

Further, since the second reference voltage Vth2 is fixed in the middle voltage range H2, for example, near the center voltage, the decoding circuit 15 outputs the discrimination signal D2 for clock reproduction from the MSB CH to the clock reproduction circuit 20.

The error rate calculation unit 33 includes the voltage level of the Middle Eye measurement signal output from the LSB CH of the level measurement unit 31 and the bit string of the MSB as the comparison pulse pattern signal output from the LSB CH of the comparison pattern generation unit 32. Based on the comparison with the signal, a bathtub curve as shown in FIG. 16 showing the change in BER of the Middle Eye measurement signal according to the change in the first reference voltage Vth1 is created. The error-free section in FIG. 16 indicates a section in which the error bit cannot be detected by the error rate calculation unit 33 within the preset measurement time.

The display unit 40 is composed of display devices such as an LCD and a CRT, and displays various display contents such as a bathtub curve created by the error rate calculation unit 33 according to a control signal output from the control unit 60. It has become. Further, the display unit 40 displays operation targets such as buttons, soft keys, pull-down menus, and text boxes for setting various conditions.

The operation unit 50 is for receiving an operation input by the user, and is composed of, for example, a touch panel provided on the display unit 40. Alternatively, the operating unit 50 may be configured to include an input device such as a keyboard or mouse. Further, the operation unit 50 may be configured by an external control device that performs remote control by a remote command or the like. The operation input to the operation unit 50 is detected by the control unit 60. For example, the operation unit 50 can arbitrarily set the first to third reference voltages Vth1 to Vth3 of the first to third 0/1 discriminators 11 to 13.

The control unit 60 is composed of, for example, a microcomputer including a CPU, ROM, RAM, HDD, etc., a personal computer, or the like, and controls the operation of each of the above units constituting the error rate measuring device 100. Further, the control unit 60 can configure the error rate calculation unit 33 by software by transferring a predetermined program stored in the ROM or the like to the RAM and executing the program. The error rate calculation unit 33 can also be configured by a digital circuit such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). Alternatively, the error rate calculation unit 33 can be configured by appropriately combining hardware processing by a digital circuit and software processing by a predetermined program.

Hereinafter, an example of the processing of the error rate measuring method using the error rate measuring device 100 of the present embodiment will be described with reference to the flowcharts of FIGS. 5 and 6.

First, the reference voltage setting unit 14 sets the second reference voltage Vth2 and the third reference voltage Vth3 as constant values equal to each other in the medium voltage range H2, for example, near the center voltage, and sets the second and third 0/1, respectively. Set in the discriminators 12 and 13 (reference voltage setting step S1).

Next, the reference voltage setting unit 14 sets the initial value of the first reference voltage Vth1 in the medium voltage range H2 in the first 0/1 discriminator 11 (reference voltage setting step S2).

Next, the DUT 200 transmits a PAM4 signal as a signal to be measured to the error rate measuring device 100 (step S3).

Next, the first 0/1 discriminator 11 outputs the Middle Eye measurement signal as the discriminant signal D1 (first 0/1 discriminant step S4). Further, the second 0/1 discriminator 12 outputs the discrimination signal D2 (second 0/1 discrimination step S5). Further, the third 0/1 discriminator 13 outputs the discrimination signal D3 (third 0/1 discrimination step S6).

Next, the clock regeneration circuit 20 reproduces the clock from the discrimination signal D2 output from the second 0/1 discriminator 12 and outputs it as the reproduction clock CLK (clock reproduction step S7).

Next, the decoding circuit 15 generates a plurality of bit string signals including the MSB bit string signal of the measured signal from the discrimination signals D1 to D3 output from the first to third 0/1 discriminators 11 to 13, respectively. .. That is, the decoding circuit 15 outputs the MSB bit string signal of the signal to be measured obtained by the second reference voltage Vth2 from the MSB CH, and also outputs the Middle Eye measurement signal (MSB) obtained by the first reference voltage Vth1. The bit string signal) is output from the LSB CH (decoding step S8).

Next, the level measuring unit 31 clocks the voltage level of the MSB bit string signal output from the MSB CH in the decoding step S8 and the voltage level of the Middle Eye measurement signal output from the LSB CH in the decoding step S8. The measurement is performed at the timing of the reproduction clock CLK output from S7 (level measurement step S9).

Next, the comparison pattern generation unit 32 outputs the MSB bit string signal as the comparison pulse pattern signal to the MSB CH and the LSB CH of the error rate calculation unit 33 (step S10).

Next, the error rate calculation unit 33 was output from the MSB CH of the decoding circuit 15 based on the comparison between the voltage level measured in the level measurement step S9 and the comparison pulse pattern signal output from step S10. The BER of the bit string signal of the MSB and the BER of the Middle Eye measurement signal output from the LSB CH are calculated respectively (error rate calculation step S11).

Next, the control unit 60 determines whether or not the processes up to step S11 have been executed for all the first reference voltages Vth1 (step S12). If the processes up to step S11 have not been executed for all the first reference voltages Vth1, the control unit 60 executes the processes of step S13. On the other hand, when the processes up to step S11 are executed for all the first reference voltages Vth1, the control unit 60 executes the processes of step S14.

In step S13, the reference voltage setting unit 14 sets a new first reference voltage Vth1 in the medium voltage range H2 in the first 0/1 discriminator 11 (reference voltage setting step S13). Next, the control unit 60 executes the processes after step S4 again.

In step S14, the error rate calculation unit 33 measures the Middle Eye according to the change in the first reference voltage Vth1 based on the BER of the Middle Eye measurement signal for all the first reference voltage Vth1 obtained in step S11. A bathtub curve showing a change in the BER of the signal is created (error rate calculation step S14).

Next, the display unit 40 displays the bathtub curve created in the error rate calculation step S14 (step S15).

Hereinafter, an example of the processing of the decoding step S8 of FIG. 5 will be described with reference to the flowchart of FIG. 7.

First, the EXOR circuit 15a outputs "0" as the exclusive OR of the discrimination signal D2 from the second 0/1 discriminator 12 and the discrimination signal D3 from the third 0/1 discriminator 13. (EXOR step S41).

Next, the OR circuit 15b outputs the discrimination signal D1 as the logical sum of the discrimination signal D1 from the first 0/1 discriminator 11 and the output of the EXOR step S41 (OR step S42). That is, in the OR step S42, the reference voltage setting step S1 sets the second reference voltage Vth2 and the third reference voltage Vth3 to constant values equal to each other in the medium voltage range H2, so that the Middle Eye measurement signal ( The discrimination signal D1) is output to the level measurement step S9.

As described above, the error rate measuring device 100 according to the present embodiment sets the first reference voltage Vth1 to a medium value in a state where the second reference voltage Vth2 related to clock reproduction is fixed to a constant value in the medium voltage range H2. Since it can be set variably in the voltage range H2, it is possible to create a bathtub curve for the Middle Eye without causing clock loss.

More specifically, the error rate measuring device 100 according to the present embodiment is used for clock reproduction by setting the third reference voltage Vth3 to a constant value equal to the second reference voltage Vth2 in the medium voltage range H2. While supplying the discrimination signal D2 to the MSB CH, the Middle Eye measurement signal can be analyzed by the LSB CH.

(Second Embodiment)
Subsequently, the error rate measuring device 110 according to the second embodiment of the present invention will be described with reference to the drawings. The description of the same configuration as that of the first embodiment will be omitted as appropriate. Further, description of the same operation as that of the first embodiment will be omitted as appropriate. As shown in FIG. 8, in this embodiment, the configuration of the PAM4 decoder 10 is different from that in the first embodiment.

The decoding circuit 16 included in the PAM4 decoder 10 of the present embodiment is composed of a logic circuit, and is derived from the discrimination signals D1 to D3 output from the first to third 0/1 discriminators 11 to 13, respectively. It is designed to generate multiple bit string signals. For example, the decoding circuit 16 outputs the negative and exclusive logical sum of the discrimination signal D1 from the first 0/1 discriminator 11 and the discrimination signal D2 from the second 0/1 discriminator 12a. And an AND circuit 16b that outputs a logical product of the discrimination signal D3 from the third 0/1 discriminator 13 and the output of the EXNOR circuit 16a.

In the AND circuit 16b, when the first to third reference voltages Vth1 to Vth3 are set by the reference voltage setting unit 14 in the high voltage range H1, the medium voltage range H2, and the low voltage range H3, for example, near the center voltage, respectively. Outputs the LSB bit string signal of the PAM4 signal from the LSB channel (LSB CH).

Further, in the decoding circuit 16, when the second reference voltage Vth2 is set in the medium voltage range H2, for example, near the center voltage by the reference voltage setting unit 14, the MSB bit string signal (discrimination signal D2) of the PAM4 signal. Is output from the MSB channel (MSB CH).

On the other hand, an operation example when the error rate measuring device 110 according to the present embodiment creates a bathtub curve with respect to the bit string signal output from the LSB CH of the decoding circuit 16 is as follows. That is, as shown in FIG. 8, the reference voltage setting unit 14 sets the first reference voltage Vth1 and the second reference voltage Vth2 to constant values equal to each other in the medium voltage range H2, for example, near the center voltage. The reference voltage Vth3 of 3 is variably set (swept) in the medium voltage range H2.

As shown in the truth table of FIG. 9, the EXNOR circuit 16a is connected to one input B of the AND circuit 16b when the first reference voltage Vth1 and the second reference voltage Vth2 are equal (that is, D1 = D2). Always outputs "1". Further, since the AND circuit 16b always inputs "1" to the input B, the value of the discrimination signal D3 is always output as it is. That is, as shown in FIG. 8, in the AND circuit 16b, the reference voltage setting unit 14 sets the first reference voltage Vth1 to a constant value equal to the second reference voltage Vth2 in the medium voltage range H2, and at the same time, When the reference voltage Vth3 of 3 is variably set in the medium voltage range H2, the discrimination signal D3 from the third 0/1 discriminator 13 is used as the Middle Eye measurement signal (MSB bit string signal) and is leveled from the LSB CH. It is designed to output to the measuring unit 31. At this time, the comparison pattern generation unit 32 outputs the MSB bit string signal as the comparison pulse pattern signal to the LSB CH of the error rate calculation unit 33.

Further, since the second reference voltage Vth2 is fixed in the middle voltage range H2, for example, near the center voltage, the decoding circuit 16 outputs the discrimination signal D2 for clock reproduction from the MSB CH to the clock reproduction circuit 20.

Hereinafter, an example of the processing of the error rate measuring method using the error rate measuring device 110 of the present embodiment will be described with reference to the flowcharts of FIGS. 10 and 11.

First, the reference voltage setting unit 14 sets the first reference voltage Vth1 and the second reference voltage Vth2 as constant values equal to each other in the medium voltage range H2, for example, near the center voltage, and sets the first and second 0/1, respectively. It is set in the discriminators 11 and 12 (reference voltage setting step S21).

Next, the reference voltage setting unit 14 sets the initial value of the third reference voltage Vth3 in the medium voltage range H2 in the third 0/1 discriminator 13 (reference voltage setting step S22).

Next, the DUT 200 transmits a PAM4 signal as a signal to be measured to the error rate measuring device 110 (step S23).

Next, the first 0/1 discriminator 11 outputs the discrimination signal D1 (first 0/1 discrimination step S24). Further, the second 0/1 discriminator 12 outputs the discriminant signal D2 (second 0/1 discriminant step S25). Further, the third 0/1 discriminator 13 outputs the Middle Eye measurement signal as the discriminant signal D3 (third 0/1 discriminant step S26).

Next, the clock regeneration circuit 20 reproduces the clock from the discrimination signal D2 output from the second 0/1 discriminator 12 and outputs it as the reproduction clock CLK (clock reproduction step S27).

Next, the decoding circuit 16 generates a plurality of bit string signals including the MSB bit string signal of the measured signal from the discrimination signals D1 to D3 output from the first to third 0/1 discriminators 11 to 13, respectively. .. That is, the decoding circuit 16 outputs the MSB bit string signal of the signal to be measured obtained by the second reference voltage Vth2 from the MSB CH, and also outputs the Middle Eye measurement signal (MSB) obtained by the third reference voltage Vth3. The bit string signal) is output from the LSB CH (decoding step S28).

Next, the level measuring unit 31 clocks the voltage level of the MSB bit string signal output from the MSB CH in the decoding step S28 and the voltage level of the Middle Eye measurement signal output from the LSB CH in the decoding step S28. The measurement is performed at the timing of the reproduction clock CLK output from S27 (level measurement step S29).

Next, the comparison pattern generation unit 32 outputs the MSB bit string signal as the comparison pulse pattern signal to the MSB CH and the LSB CH of the error rate calculation unit 33 (step S30).

Next, the error rate calculation unit 33 was output from the MSB CH of the decoding circuit 16 based on the comparison between the voltage level measured in the level measurement step S29 and the comparison pulse pattern signal output from step S30. The BER of the bit string signal of the MSB and the BER of the Middle Eye measurement signal output from the LSB CH are calculated respectively (error rate calculation step S31).

Next, the control unit 60 determines whether or not the processes up to step S31 have been executed for all the third reference voltages Vth3 (step S32). If the processes up to step S31 have not been executed for all the third reference voltages Vth3, the control unit 60 executes the processes of step S33. On the other hand, when the processes up to step S31 are executed for all the third reference voltages Vth3, the control unit 60 executes the processes of step S34.

In step S33, the reference voltage setting unit 14 sets a new third reference voltage Vth3 in the medium voltage range H2 in the third 0/1 discriminator 13 (reference voltage setting step S33). Next, the control unit 60 executes the processes after step S24 again.

In step S34, the error rate calculation unit 33 measures the Middle Eye according to the change in the third reference voltage Vth3 based on the BER of the Middle Eye measurement signal for all the third reference voltage Vth3 obtained in step S31. A bathtub curve showing a change in the BER of the signal is created (error rate calculation step S34).

Next, the display unit 40 displays the bathtub curve created in the error rate calculation step S34 (step S35).

Hereinafter, an example of the processing of the decoding step S28 of FIG. 10 will be described with reference to the flowchart of FIG.

First, the EXNOR circuit 16a outputs "1" as a negative exclusive OR of the discrimination signal D1 from the first 0/1 discriminator 11 and the discrimination signal D2 from the second 0/1 discriminator 12. (EXNOR step S43).

Next, the AND circuit 16b outputs the discrimination signal D3 as a logical product of the discriminant signal D3 from the third 0/1 discriminator 13 and the output of the EXNOR step S43 (AND step S44). That is, in the AND step S44, the reference voltage setting step S21 sets the first reference voltage Vth1 and the second reference voltage Vth2 to constant values equal to each other in the medium voltage range H2, so that the Middle Eye measurement signal ( The discrimination signal D3) is output to the level measurement step S29.

As described above, the error rate measuring device 110 according to the present embodiment sets the third reference voltage Vth3 to medium in a state where the second reference voltage Vth2 related to clock reproduction is fixed to a constant value in the medium voltage range H2. Since it can be set variably in the voltage range H2, it is possible to create a bathtub curve for the Middle Eye without causing clock loss.

More specifically, the error rate measuring device 110 according to the present embodiment is used for clock reproduction by setting the first reference voltage Vth1 to a constant value equal to the second reference voltage Vth2 in the medium voltage range H2. While supplying the discrimination signal D2 to the MSB CH, the Middle Eye measurement signal can be analyzed by the LSB CH.

10 PAM4 decoder 11 1st 0/1 discriminator 12 2nd 0/1 discriminator 13 3rd 0/1 discriminator 14 Reference voltage setting unit 15, 16 Decoding circuit 15a EXOR circuit 15b OR circuit 20 Clock playback circuit 30 Error detection unit 31 Level measurement unit 33 Error rate calculation unit 100, 110 Error rate measurement device 200 DUT

Claims (8)

Error rate measuring device that detects errors in PAM4 signals in which the voltage range of the openings of the three eye patterns is the high voltage range (H1), medium voltage range (H2), and low voltage range (H3) from the highest voltage level, respectively. (100)
A first 0/1 discriminator (11) that outputs 1 as a discrimination signal when the voltage level of the PAM4 signal is equal to or higher than the first reference voltage and outputs 0 as a discrimination signal in other cases.
A second 0/1 discriminator (12) that outputs 1 as a discrimination signal when the voltage level of the PAM4 signal is equal to or higher than the second reference voltage and outputs 0 as a discrimination signal in other cases.
A third 0/1 discriminator (13) that outputs 1 as a discrimination signal when the voltage level of the PAM4 signal is equal to or higher than the third reference voltage and outputs 0 as a discrimination signal in other cases.
A clock reproduction circuit (20) that reproduces a clock from the discrimination signal output from the second 0/1 discriminator and outputs it as a reproduction clock.
A decoding circuit (15) that generates a plurality of bit string signals including the MSB bit string signal of the PAM4 signal from the discrimination signals output from the first to third 0/1 discriminators, respectively.
A level measuring unit (31) that measures the voltage level of the MSB bit string signal output from the decoding circuit at the timing of the reproduction clock, and
An error rate calculation unit (33) that calculates the error rate of the bit string signal of the MSB based on the voltage level measured by the level measurement unit, and
A reference voltage setting unit (14) for setting the first to third reference voltages in the first to third 0/1 discriminators, respectively, is provided.
In the error rate calculation unit, the second reference voltage is set to a constant value in the medium voltage range by the reference voltage setting unit, and the first reference voltage is variably set in the medium voltage range. In this case, the error rate measuring device is characterized by creating a bathtub curve showing a change in the error rate of the bit string signal of the MSB in response to a change in the first reference voltage. The decoding circuit
An EXOR circuit (15a) that outputs an exclusive OR of the discrimination signal from the second 0/1 discriminator and the discrimination signal from the third 0/1 discriminator.
It has an OR circuit (15b) that outputs a logical sum of the discrimination signal from the first 0/1 discriminator and the output of the EXOR circuit.
The OR circuit is the first 0/1 discriminator when the third reference voltage is set to a constant value equal to the second reference voltage in the medium voltage range by the reference voltage setting unit. The error rate measuring apparatus according to claim 1, wherein the discrimination signal from the above is output to the level measuring unit as a bit string signal of the MSB. Error rate measuring device that detects errors in PAM4 signals in which the voltage range of the openings of the three eye patterns is the high voltage range (H1), medium voltage range (H2), and low voltage range (H3) from the highest voltage level, respectively. (110)
A first 0/1 discriminator (11) that outputs 1 as a discrimination signal when the voltage level of the PAM4 signal is equal to or higher than the first reference voltage and outputs 0 as a discrimination signal in other cases.
A second 0/1 discriminator (12) that outputs 1 as a discrimination signal when the voltage level of the PAM4 signal is equal to or higher than the second reference voltage and outputs 0 as a discrimination signal in other cases.
A third 0/1 discriminator (13) that outputs 1 as a discrimination signal when the voltage level of the PAM4 signal is equal to or higher than the third reference voltage and outputs 0 as a discrimination signal in other cases.
A clock reproduction circuit (20) that reproduces a clock from the discrimination signal output from the second 0/1 discriminator and outputs it as a reproduction clock.
A decoding circuit (16) that generates a plurality of bit string signals including the MSB bit string signal of the PAM4 signal from the discrimination signals output from the first to third 0/1 discriminators, respectively.
A level measuring unit (31) that measures the voltage level of the MSB bit string signal output from the decoding circuit at the timing of the reproduction clock, and
An error rate calculation unit (33) that calculates the error rate of the bit string signal of the MSB based on the voltage level measured by the level measurement unit, and
A reference voltage setting unit (14) for setting the first to third reference voltages in the first to third 0/1 discriminators, respectively, is provided.
In the error rate calculation unit, the second reference voltage is set to a constant value in the medium voltage range by the reference voltage setting unit, and the third reference voltage is variably set in the medium voltage range. In this case, the error rate measuring device is characterized by creating a bathtub curve showing a change in the error rate of the bit string signal of the MSB in response to a change in the third reference voltage. The decoding circuit
An EXNOR circuit (16a) that outputs a negative exclusive OR of the discrimination signal from the first 0/1 discriminator and the discrimination signal from the second 0/1 discriminator.
It has an AND circuit (16b) that outputs a logical product of the discrimination signal from the third 0/1 discriminator and the output of the EXNOR circuit.
The AND circuit is a third 0/1 discriminator when the first reference voltage is set to a constant value equal to the second reference voltage in the medium voltage range by the reference voltage setting unit. The error rate measuring apparatus according to claim 3, wherein the discrimination signal from the above is output to the level measuring unit as a bit string signal of the MSB. Error rate measuring method for detecting errors in PAM4 signals in which the voltage ranges of the openings of the three eye patterns are the high voltage range (H1), the medium voltage range (H2), and the low voltage range (H3) from the highest voltage level, respectively. And
When the voltage level of the PAM4 signal is equal to or higher than the first reference voltage, 1 is output from the first 0/1 discriminator (11) as a discrimination signal, and 0 is output as the discrimination signal in other cases. The first 0/1 discrimination step (S4) output from the 0/1 discriminator of
When the voltage level of the PAM4 signal is equal to or higher than the second reference voltage, 1 is output from the second 0/1 discriminator (12) as a discrimination signal, and 0 is output as the discrimination signal in other cases. The second 0/1 discrimination step (S5) output from the 0/1 discriminator of
When the voltage level of the PAM4 signal is equal to or higher than the third reference voltage, 1 is output from the third 0/1 discriminator (13) as a discrimination signal, and 0 is output as the discrimination signal in other cases. The third 0/1 discrimination step (S6) output from the 0/1 discriminator of
A clock reproduction step (S7) of reproducing a clock from the discrimination signal output from the second 0/1 discriminator and outputting it as a reproduction clock.
A decoding step (S8) for generating a plurality of bit string signals including the MSB bit string signal of the PAM4 signal from the discrimination signals output from the first to third 0/1 discriminators, respectively.
A level measurement step (S9) for measuring the voltage level of the MSB bit string signal output from the decoding step at the timing of the reproduction clock, and
An error rate calculation step (S11) for calculating the error rate of the bit string signal of the MSB based on the voltage level measured by the level measurement step, and
A reference voltage setting step (S1, S2, S13) for setting the first to third reference voltages in the first to third 0/1 discriminators, respectively, is provided.
In the error rate calculation step, the second reference voltage is set to a constant value in the medium voltage range and the first reference voltage is variably set in the medium voltage range by the reference voltage setting step. In this case, the error rate measuring method is characterized in that a bathtub curve showing a change in the error rate of the bit string signal of the MSB in response to a change in the first reference voltage is created. The decoding step
The EXOR step (S41) that outputs the exclusive OR of the discriminant signal from the second 0/1 discriminator and the discriminant signal from the third 0/1 discriminator.
It includes an OR step (S42) that outputs a logical sum of the discrimination signal from the first 0/1 discriminator and the output of the EXOR step.
The OR step is the first 0/1 discriminator when the third reference voltage is set to a constant value equal to the second reference voltage in the medium voltage range by the reference voltage setting step. The error rate measuring method according to claim 5, wherein the discrimination signal from the above is output as a bit string signal of the MSB to the level measurement step. Error rate measuring method for detecting errors in PAM4 signals in which the voltage ranges of the openings of the three eye patterns are the high voltage range (H1), the medium voltage range (H2), and the low voltage range (H3) from the highest voltage level, respectively. And
When the voltage level of the PAM4 signal is equal to or higher than the first reference voltage, 1 is output from the first 0/1 discriminator (11) as a discrimination signal, and 0 is output as the discrimination signal in other cases. The first 0/1 discrimination step (S24) output from the 0/1 discriminator of
When the voltage level of the PAM4 signal is equal to or higher than the second reference voltage, 1 is output from the second 0/1 discriminator (12) as a discrimination signal, and 0 is output as the discrimination signal in other cases. The second 0/1 discrimination step (S25) output from the 0/1 discriminator of
When the voltage level of the PAM4 signal is equal to or higher than the third reference voltage, 1 is output from the third 0/1 discriminator (13) as a discrimination signal, and 0 is output as the discrimination signal in other cases. The third 0/1 discrimination step (S26) output from the 0/1 discriminator of
A clock reproduction step (S27) of reproducing a clock from the discrimination signal output from the second 0/1 discriminator and outputting it as a reproduction clock.
A decoding step (S28) for generating a plurality of bit string signals including the MSB bit string signal of the PAM4 signal from the discrimination signals output from the first to third 0/1 discriminators, respectively.
A level measurement step (S29) for measuring the voltage level of the MSB bit string signal output from the decoding step at the timing of the reproduction clock, and
An error rate calculation step (S31) for calculating the error rate of the bit string signal of the MSB based on the voltage level measured by the level measurement step, and
A reference voltage setting step (S21, S22, S33) for setting the first to third reference voltages in the first to third 0/1 discriminators, respectively, is provided.
In the error rate calculation step, the second reference voltage is set to a constant value in the medium voltage range and the third reference voltage is variably set in the medium voltage range by the reference voltage setting step. A method for measuring an error rate, which comprises creating a bathtub curve showing a change in the error rate of the bit string signal of the MSB in response to a change in the third reference voltage. The decoding step
An EXNOR step (S43) that outputs a negative exclusive OR of the discrimination signal from the first 0/1 discriminator and the discrimination signal from the second 0/1 discriminator.
It includes an AND step (S44) that outputs a logical product of the discrimination signal from the third 0/1 discriminator and the output of the EXNOR step.
The AND step is the third 0/1 discriminator when the first reference voltage is set to a constant value equal to the second reference voltage in the medium voltage range by the reference voltage setting step. The error rate measuring method according to claim 7, wherein the discrimination signal from the above is output as a bit string signal of the MSB to the level measurement step.

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