Test and measurement apparatus and calibration signal generation method

Abstract

To provide a test measuring device and a calibration signal generation method that generate a calibration signal of a stressed eye signal used for a compliance test of a device under test in a shorter time.SOLUTION: First and second parameters are set to initial values (30), and the parameters are used to generate an initial eye diagram 32, first and second difference between the first and second characteristics and the first and second target characteristics are obtained, respectively (34). The next first value that makes a first difference zero is estimated (36), the first parameter is set to the next first value (38), the next eye diagram is generated (40), these estimation, setting, and generation are repeated until the first characteristic of the latest next eye diagram falls within the first target characteristic, and the final first parameter value is set to the latest next first value (44), the final second parameter value is set to the initial second value (58) when the second characteristic of the latest next eye diagram is within the second target characteristic, and a calibration signal is generated according to the final first and second parameter values.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This disclosed technology relates to the calibration of a test signal for testing a receiver with a stressed test signal, and more particularly to a test measurement apparatus and a calibration signal generation method for generating a calibrated test signal (calibration signal) more quickly. [Background technology]

[0002] In high-speed receiver testing, such as PCI Express devices operating at 32 GT / s (Gigatransfers per second), a test signal is generated that simulates actual reception conditions or is intentionally distorted by stress exceeding actual reception conditions. This test signal is then applied to the receiver to verify its stress tolerance. These stressed test signals (stressed signals) must be calibrated to a target of less than 1 millivolt and less than 1 picosecond. Signals exhibiting "bad" characteristics such as large sinusoidal jitter (SJ), differential mode interference (DMI), and intersymbol interference (ISI) are referred to in this application as "stressed eye signals" or "stressed signals." The receiver (receiving device) must be able to detect data signals with eyes that are under very high stress in one or more of these characteristics. To meet these requirements, the receiver also needs to be calibrated with these stressed eye signals. This requirement applies to numerous receiver test techniques, such as characterizing bit error rate (BER) and jitter tolerance (JTOL). In the final stage of this calibration process, some stress adjustments are necessary to bring the eye diagram within the desired target eye width and eye height to match a specific BER. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2020-115128 [Patent Document 2] Japanese Patent Application Laid-Open No. 2020-112553 [Summary of the Invention] [Problems to be Solved by the Invention]

[0004] Calibration of the stressed-eye signal generally takes a procedure that takes several hours, which is a very troublesome issue for customers in calibration for receiver tests of high-speed technologies. The specification of the standard obliges the use of calibrated stress levels in the compliance test of the device under test. Therefore, it is necessary to execute a long calibration process of the stressed-eye signal before actually conducting the test.

[0005] In one calibration process of the stressed-eye signal, in order to meet the requirements of the specified eye height and eye width, the selected parameters (usually SJ and DMI parameters) are continuously changed (swept). In the existing method, it mainly develops in a way that examines all combinations of stress parameters carefully (exhaustively) over the entire investigation range of SJ and DMI and repeats them until converging to the target eye parameters. This approach is the biggest cause that requires a long time in the calibration of the stressed-eye signal.

[0006] Embodiments of the disclosed device and method attempt to solve the drawbacks of the prior art. [Means for Solving the Problems]

[0007] Hereinafter, examples beneficial for understanding the technology disclosed in the present application are presented. Embodiments of this technology may include one or more of the examples described below and any combinations thereof.

[0008] Example 1 is a test measurement device, comprising a user interface, at least one channel configured to be connected to a device under test, a memory, and one or more processors. The one or more processors perform a process of setting a first parameter to an initial first value and setting a second parameter to an initial second value, a process of generating an initial eye diagram using the initial first value and the initial second value, a process of obtaining a first difference between a first characteristic of the initial eye diagram and a first target characteristic and a second difference between a second characteristic of the initial eye diagram and a second target characteristic, a process of estimating a next first value that makes the first difference zero, a process of setting the first parameter to the next first value, a process of generating a next eye diagram, a process of repeating the estimating process, the setting process, and the generating process until a first characteristic of the latest next eye diagram falls within the first target characteristic, a process of setting a final first parameter value to the latest next first value, a process of setting a final second parameter value to the initial second value if a second characteristic of the latest next eye diagram is within the second target characteristic, and a process of generating a calibration signal according to the final first parameter value and the final second parameter value, by causing the one or more processors to execute code (program).

[0009] Example 2 is the test measurement device of Example 1. When a second characteristic of the latest next eye diagram is not within the second target characteristic, the code further causes the one or more processors to perform a process of estimating a next second value that makes the second difference zero, a process of setting the second parameter to the next second value, a process of generating a next eye diagram, a process of repeating the estimating process, the setting process, and the generating process until the second characteristic of the latest next eye diagram falls within the second target characteristic, and a process of setting the final second parameter value to the latest next second value.

[0010] Example 3 is the test measurement apparatus of Example 2, wherein the code further causes one or more of the processors to perform a process to set the difference between the first characteristic and the first target characteristic to a constant value.

[0011] Example 4 is a test measurement apparatus according to any of Examples 1 to 3, wherein the code that causes one or more processors to perform the process of estimating the next first value of the first parameter that makes the first difference zero includes the code that causes one or more processors to perform the process of determining the changes in the first parameter and the second parameter that correlate with the first difference and the second difference, and the process of estimating the first parameter based on the changes in the first parameter.

[0012] Example 5 is a test measurement apparatus according to any of Examples 1 to 4, wherein the code that causes one or more of the processors to perform the process of estimating the first parameter includes the code that causes one or more of the processors to perform the process of estimating the first parameter based on the change in the first parameter and the process of mapping the change in the second parameter to the first parameter.

[0013] Example 6 is a test and measurement apparatus according to any of Examples 1 to 5, wherein the above repetition process is performed only once, and the final second parameter value is set to the initial second value.

[0014] Example 7 is a test measurement apparatus according to any of Examples 1 to 6, wherein the first parameter is differential mode interference and the second parameter is sinusoidal jitter.

[0015] Example 8 is a test measurement apparatus according to any of Examples 1 to 7, wherein the first parameter is sinusoidal jitter and the second parameter is amplitude.

[0016] Example 9 is a test measurement apparatus according to any of Examples 1 to 8, wherein the first parameter is random jitter and the second parameter is differential mode interference.

[0017] Embodiment 10 is a method for generating a calibration signal, comprising: setting a first parameter to an initial first value and setting a second parameter to an initial second value; generating an initial eye diagram using the initial first value and the initial second value; finding the first difference between the first characteristic and the first target characteristic of the initial eye diagram and the second difference between the second characteristic and the second target characteristic of the initial eye diagram; estimating the next first value that makes the first difference zero; setting the first parameter to the next first value; generating the next eye diagram; repeating the estimation process, the setting process and the generation process until the first characteristic of the latest next eye diagram falls within the first target characteristic; setting the final first parameter value to the latest next first value; setting the final second parameter value to the initial second value if the second characteristic of the latest next eye diagram falls within the second target characteristic; and generating a calibration signal according to the final first parameter value and the final second parameter value.

[0018] Example 11 is the method of Example 10, further comprising: a process of estimating the next second value that will make the second difference zero if the second characteristic of the latest next eye diagram is not within the second target characteristic; a process of setting the second parameter to the next second value; a process of generating the next eye diagram; a process of repeating the estimation process, the setting process and the generation process until the second characteristic of the latest next eye diagram is within the second target characteristic; and a process of setting the final second parameter value to the latest next second value.

[0019] Example 12 is the method of Example 11, further comprising a process of setting the difference between the first characteristic and the first target characteristic to a constant value.

[0020] Example 13 is a method of any of Examples 10 to 12 in which the process of estimating the next first value of the first parameter that makes the first difference zero includes a process of finding the changes in the first parameter and the second parameter that correlate with the first difference and the second difference, and a process of estimating the first parameter based on the changes in the first parameter.

[0021] Example 14 is the method of Example 13, wherein the process for estimating the first parameter includes a process for estimating the first parameter based on the change in the first parameter, and a process for mapping the change in the second parameter to the first parameter.

[0022] Example 15 is one of the methods from Examples 10 to 14, wherein the iterative process is performed only once, and the final second parameter value is set to the initial second value.

[0023] Example 16 is a method according to any of Examples 10 to 15, wherein the first parameter is differential mode interference and the second parameter is sinusoidal jitter.

[0024] Example 17 is a method according to any of Examples 10 to 16, wherein the first parameter is sinusoidal jitter and the second parameter is amplitude.

[0025] Example 18 is a method of any of Examples 10 to 17, wherein the first parameter is random jitter and the second parameter is differential mode interference.

[0026] The aspects, features, and effects of the embodiments of the present invention will become clear from the accompanying drawings and the following description of the embodiments. [Brief explanation of the drawing]

[0027] [Figure 1] Figure 1 shows an embodiment of the test and measurement device. [Figure 2]Figure 2 graphically shows the variation in the width or height of the eye signal as a function of two parameters. [Figure 3] Figure 3 shows a flowchart illustrating an embodiment of a method for adjusting the parameters of the eye signal to meet inspection requirements. [Figure 4A] Figure 4A shows a flowchart illustrating a specific example of how to adjust the eye signal parameters to meet the inspection requirements. [Figure 4B] Figure 4B shows a flowchart illustrating a specific example of how to adjust the eye signal parameters to meet the inspection requirements. [Figure 5] Figure 5 shows an embodiment of the user interface for a test and measurement device. [Modes for carrying out the invention]

[0028] In testing high-speed receivers such as PCI Express devices operating at 32 GT / s (Gigatransfers per second), the test signal is intentionally stressed, resulting in a test signal with intentionally distorted eye diagrams (stressed eye signal). This stressed eye signal is then supplied to the receiver under test to verify that the receiver can demodulate the data. In such tests, the "stressed eye signal" needs to be calibrated to a target of less than 1 millivolt and less than 1 picosecond. In electrical signal testing, the signal is repeatedly sampled and applied to a vertical input, while the data rate is used to trigger a horizontal sweep, creating what is called an "eye pattern," "eye diagram," or "eye signal." A signal with an "open eye" corresponds to low signal distortion. Signals exhibiting "bad" characteristics such as large sinusoidal jitter (SJ), differential-mode interference (DMI), intersymbol interference (ISI), and random jitter (RJ) are referred to in this application as "stressed eye signals" or "stressed signals." Receivers are required to detect data signals with very stressed eyes relating to one or more of these characteristics. For a receiver to meet these requirements, it is necessary to calibrate the receiver with a signal exhibiting a stressed eye diagram (referred to in this application as a stressed eye signal).

[0029] The proposed method of the embodiments described in this disclosure efficiently utilizes data to arrive at the appropriate stress combination with the fewest number of iterations, thereby enabling the customer to quickly begin testing. By using the method of this application, the customer can complete the calibration of the stressed eye signal in under an hour, saving a significant amount of time.

[0030] These embodiments reveal an efficient method for completing the final step in calibrating a stressed eye signal in PCI Express Generation 5 systems, modeling crosstalk using SJ and DMI. This technique can be generalized to other technologies (e.g., IEEE, Thunderbolt, USB, DisplayPort, etc.) by "closing" the eye diagram using various stresses. In other words, the eye diagram used can be matched to the parameters of a specific specification of the stressed eye signal. Such examples, but not limited to, include USB with SJ and amplitude parameters, and PCI Generation 3 with random jitter (RJ) and DMI parameters.

[0031] Figure 1 shows an embodiment of a test and measurement apparatus capable of carrying out the method of the present invention. The test and measurement apparatus performs a receiver test (Rx test). The following process is performed before the Rx test.

[0032] The test measurement device 10 may include an oscilloscope or other test equipment. The test measurement device 10 may also have an input channel 12 to which a probe or other type of test connector is connected and to which input data from the device under test (DUT) 20 is supplied. The input data is used for analysis and display. One or more processors 14 of the test measurement device 10 receive this data and operate for analysis. One or more processors 14 may receive input from a user interface (U / I) 18. The user interface 18 provides the processors 14 with parameters for the tests to be performed on the DUT 20, for example. Memory 16 may store both the code (program) executed by the processors 14 and the data from the DUT 20. The test measurement device 10 may also have a waveform generator (signal generator) that generates an eye diagram.

[0033] In the following description, a method for calibrating a stressed eye signal used to test a DUT against the PCI Express Gen 5 specification by utilizing the selection of SJ and DMI parameters will be described. However, as described above, these two parameters are not limited to SJ and DMI and may be composed of various parameters. Generally speaking, the width and height of the eye signal are two-dimensional functions of SJ and DMI, and in the following description, SJ and DMI may also be referred to as S and D.

[0034] Since changes in both S and D result in changes in both width W and height H, they are two-dimensional. Thus, if function w represents width W and function h represents height H, then W = w(S, D) and H = h(S, D). These width and height may more generally be referred to as the first characteristic and the second characteristic in order to avoid limiting the method to either characteristic. Similarly, the two parameters may be referred to as the first parameter and the second parameter in order to avoid limiting the application of the method to only SJ and DMI. In the following description, as further terms, there are ΔW and ΔH as the amounts of increase in the eye width and height, and ΔS and ΔD as the amounts of increase in SJ and DMI. The initial values of S and D are S , ,

[0035] , nominal , nominal , nominal , nominal , nominal , nominal , , , , and D nominal and are called, and the target values of the width and height are w target and h target and will be called.

[0035] Figure 2 shows the variation of W on the surface of the figure. H also varies similarly, but assuming the target point shown by (S nominal , D nominal ), its shape may be different. Using the first-order Taylor series approximation using the partial derivatives of W and H at (S nominal , D nominal ), we get W ≈ w(S nominal , D <00***010>) + ΔW. Using partial derivatives, ΔW can be described as follows. [[ID=**0]]

Equation

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[0036] Thus, the process obtains ΔS and ΔD with respect to the desired increases ΔW and ΔH, as calculated previously. In other words, if the desired changes in width W and height H, represented by ΔW and ΔH, are known, then the changes in SJ and DMI (i.e., ΔS and ΔD) required to achieve the desired changes ΔW and ΔH can be calculated using equation I.

[0037] The procedure described herein dramatically improves the efficiency of obtaining the desired parameters through this calculation. Using this formula eliminates the currently used brute-force approach of calculating and examining every possible value. This improves the speed at which the eye signal converges toward a specific target during the calibration process. Using this formula, the process can make significant progress toward a specific eye width and eye height target in a single iterative calculation.

[0038] The following explanation uses the example of S and D, but will work well with general processes as well. Figure 3 shows a flowchart of an embodiment of this process. The process begins at step 30, when the first and second parameters are set to their initial values ​​(initial first value and initial second value). In this example, the S and D parameters at the start of the calibration of the stressed eye are (S nominal ,D nominal ) and for these, the eye width and eye height measured for the eye diagram generated in step 32 are (w nominal ,h nominal I'll consider it that way.

[0039] In step 34, the process determines the difference between the eye height and eye width obtained from the initial eye diagram generated in step 32 and the eye height and eye width of the target eye diagram (referred to as the target eye height and target eye width in this application) as follows: [Equation 4] (w SpecTarget -w nominal ,h SpecTarget -h nominal )≡(ΔW First Diff ,ΔH First Diff ) Here, w SpecTarget This represents the target eye width, h SpecTarget This represents the target eye height.

[0040] Next, the above equation is (ΔW First Diff ,ΔH First Diff (ΔS) corresponds to the range of ) First Diff ,ΔD First Diff It is used to obtain ( ).

[0041] One of the constraints imposed on the disclosed algorithm is to minimize the variation in SJ towards the end of the calibration. The process following the above process uses the following equation to obtain the ΔS obtained in the initial calculation. First Diff This is the ΔD obtained in the initial calculation. First Diff ΔD above MappedThis involves mapping to the additional DMI level indicated by [the symbol].

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[0042] At the end of the first calculation, stress level (S nominal ,D nominal +ΔD First Diff +ΔD Mapped The following is required: This first parameter is estimated in step 36, and this estimate of the first parameter is used in step 38 to measure the eye height and eye width. In this example, the first parameter will be adjusted, and this is the DMI parameter. In other examples and embodiments, it may be SJ.

[0043] The above process is SJ is S nominal While maintaining this, in step 42, steps 38, 40, and 42 are repeated, changing only the DMI by setting the DMI to the latest estimate in step 38, until the eye height enters the specified target range. As a result, at this point, (S nominal ,D Final A stress level is generated, indicated by ). At this time, the final value of the first parameter (in this example, the D parameter) (in this example, D Final ) is set in step 44 as the latest next estimate obtained from the above process. At this point, the eye height should be within the specified target range.

[0044] At this point in the calibration process, in step 50, there are two possibilities regarding the eye width. If the eye width target is also met, the process sets the second parameter (S in this case) to the latest next estimate in step 58. If the eye width target is met, the S parameter is initially set to S nominal Since it was set to (S nominal ,D Final It will be set to ).

[0045] However, if the target eye width (also called the target of the second characteristic) is not met by these parameters in step 50, the process proceeds to step 52, in which the process estimates a value for the second parameter that makes the difference zero. For example, S is estimated based on the difference between the current eye signal and its target. In this application, this difference is called the "residual" difference. If the target eye width is not met, the residual difference of the eye width (residual width) "ΔW" Residual If the condition that needs adjustment is met, then, similar to equation I above, use the following equation III to adjust the vector [ΔS Residual ,ΔD Residual Obtain ].

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[0046] At this stage of the calibration process, the eye height is already satisfied, so in this example, the remaining difference in eye height (remaining height) "ΔH" is used. Residual It should be noted that the voltage is maintained at a very small value of 0.25mV. Due to this fact, in order to avoid further changes in DMI, and therefore further changes in eye height, ΔD Residual As before, ΔS Mapped It is mapped to. In step 54, the second parameter is set to the next estimate using the new estimate obtained in step 52. The eye signal is measured in step 56 with respect to the new eye signal (S nominal +ΔS Mapped ,D Final This is executed using the stress set by the ). The above process is repeated in step 50 until the eye width converges to within the specified target, and then in step 58 the second parameter is set to its final value.

[0047] Figures 4A and 4B show flowcharts applying the above method to the SJ and DMI embodiments, corresponding to the more general case of the above process.

[0048] This method allows the calibration signal used for testing to be obtained much faster than the current process. As shown by equation I above, this process can quickly approach the parameters necessary to obtain the desired signal. In many cases, the first part of the process is performed only once, and in other cases, the first part is performed only twice. The second part of the process is often not even necessary. This saves the user time and allows the actual test to be performed much faster than before.

[0049] The user does not need to see any of the above processes. Figure 5 shows an example of a user interface on a test measurement device. The system may offer "Calibration" or other options, or the system may provide an "Answer" on the user interface so that the user can input initial values ​​for two parameters of their choice and then proceed with the test.

[0050] Embodiments of the disclosed technology can operate on a specially programmed general-purpose computer, including specially created hardware, firmware, digital signal processors, or processors that operate according to programmed instructions. The terms “controller” or “processor” in this application mean microprocessors, microcomputers, ASICs, and dedicated hardware controllers, etc. Embodiments of the disclosed technology can be implemented by one or more computers (including monitoring modules) or other devices, using computer-readable data such as program modules and computer-executable instructions. Generally, program modules include routines, programs, objects, components, data structures, etc., which, when executed by a processor in a computer or other device, perform specific tasks or implement specific abstract data formats. Computer-executable instructions may be stored on computer-readable storage media such as hard disks, optical disks, removable storage media, solid-state memory, RAM, etc. As will be understood by those skilled in the art, the functions of the program modules may be combined or distributed as needed in various embodiments. Furthermore, these functions can be embodied in whole or in part in firmware or hardware equivalents such as integrated circuits or field-programmable gate arrays (FPGAs). One or more aspects of the disclosed technology can be more effectively implemented using specific data structures, such data structures are considered to be within the scope of computer-executable instructions and computer-usable data described herein.

[0051] The disclosed embodiments may, in some cases, be implemented in hardware, firmware, software, or any combination thereof. The disclosed embodiments may also be implemented as instructions carried or stored in one or more computer-readable media that can be read and executed by one or more processors. Such instructions may be referred to as computer program products. The computer-readable media described herein means any medium accessible by a computing device. For example, but not limited to, computer-readable media may include computer storage media and communication media.

[0052] Computer storage media means any medium that can be used to store computer-readable information. Examples of computer storage media include, but are not limited to, random-access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory and other memory technologies, compact disc read-only memory (CD-ROM), DVD (Digital Versatile Disc) and other optical disc storage devices, magnetic cassettes, magnetic tapes, magnetic disk storage devices and other magnetic storage devices, and any other volatile or non-volatile removable or non-removable media implemented by any technology. Computer storage media exclude signals themselves and temporary forms of signal transmission.

[0053] A communication medium means any medium that can be used for the communication of computer-readable information. Examples of communication mediums, though not limited to them, include coaxial cables, fiber optic cables, air, or any other medium suitable for the communication of electrical, optical, radio frequency (RF), infrared, sound, or other forms of signals.

[0054] In addition, the description of this application refers to certain features. It should be understood that the disclosures herein include all possible combinations of these specific features. Where a particular feature is disclosed in relation to a particular aspect or example, that feature may, to the extent possible, also be used in relation to other aspects and examples.

[0055] For the sake of explanation, specific embodiments of the present invention have been illustrated and described, but it should be understood that various modifications are possible without deviating from the gist and scope of the present invention. Therefore, the present invention should not be limited to anything other than the appended claims. [Explanation of Symbols]

[0056] 10 Test and measurement device 12 input channels 14 processors 16 memory 18. User Interface (U / I) 20. Device under test (DUT)

Claims

1. A test and measurement device, User interface and, At least one channel configured to be connected to the device under test, Memory and One or more processors and Equipped with, One or more of the above processors, A process to set the first parameter to its initial first value and the second parameter to its initial second value, The process of generating an initial eye diagram using the above initial first value and the above initial second value, The process involves determining the first difference between the first characteristic and the first target characteristic of the initial eye diagram, and the second difference between the second characteristic and the second target characteristic of the initial eye diagram. The process involves estimating the next first value that makes the above first difference zero, The process of setting the above first parameter to the above next first value, The process of generating the next eye diagram, The process of estimating, setting, and generating is repeated until the first characteristic of the latest next eye diagram falls within the range of the first target characteristic. The process of setting the final first parameter value to the latest next first value, If the second characteristic of the latest next eye diagram above is within the second target characteristic above, the final second parameter value is set to the initial second value above. If the second characteristic of the latest next eye diagram is not within the second target characteristic, the process involves estimating the next second value that will make the second difference zero, setting the second parameter to the next second value, generating the next eye diagram, and repeating the estimation process, setting process, and generation process until the second characteristic of the latest next eye diagram falls within the second target characteristic, thereby setting the final second parameter value to the latest next second value. A process to generate a calibration signal according to the above final first parameter value and the above final second parameter value. It is configured to execute code that causes one or more of the above processors to perform the following: A test and measurement device in which the first characteristic and the second characteristic described above are two-dimensional functions of the first parameter and the second parameter described above.

2. Code that causes one or more of the above processors to perform the process of estimating the next first value of the above first parameter that makes the above first difference zero, A process to determine the amount of change in the first parameter and the second parameter necessary to achieve the first difference and the second difference described above, The process of mapping the above change amount of the second parameter to the above change amount of the first parameter is used to estimate the next first value of the first parameter. A test and measurement device according to claim 1, having a code to perform the following.

3. A process to set the first parameter to its initial first value and the second parameter to its initial second value, The process of generating an initial eye diagram using the above initial first value and the above initial second value, The process involves determining the first difference between the first characteristic and the first target characteristic of the initial eye diagram, and the second difference between the second characteristic and the second target characteristic of the initial eye diagram. The process involves estimating the next first value that makes the above first difference zero, The process of setting the above first parameter to the above next first value, The process of generating the next eye diagram, The process of estimating, setting, and generating is repeated until the first characteristic of the latest next eye diagram falls within the range of the first target characteristic. The process of setting the final first parameter value to the latest next first value, If the second characteristic of the latest next eye diagram above is within the second target characteristic above, the final second parameter value is set to the initial second value above. If the second characteristic of the latest next eye diagram is not within the second target characteristic, the process involves estimating the next second value that will make the second difference zero, setting the second parameter to the next second value, generating the next eye diagram, and repeating the estimation process, setting process, and generation process until the second characteristic of the latest next eye diagram falls within the second target characteristic, thereby setting the final second parameter value to the latest next second value. A process to generate a calibration signal according to the above final first parameter value and the above final second parameter value. A calibration signal generation method comprising the above-mentioned first characteristic and the above-mentioned second characteristic being two-dimensional functions of the above-mentioned first parameter and the above-mentioned second parameter.

4. The process of estimating the next first value of the first parameter that makes the above first difference zero is, A process to determine the amount of change in the first parameter and the second parameter necessary to achieve the first difference and the second difference described above, The process of mapping the above change amount of the second parameter to the above change amount of the first parameter is used to estimate the next first value of the first parameter. A calibration signal generation method according to claim 3, comprising:

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