Simulation method for restoring real impedance of element to be tested and application

Abstract

The invention relates to a simulation method for restoring the real impedance of a to-be-tested element, and the method comprises the steps: building a link model of a long line, and enabling the link model to have an initial impedance value; measuring an impedance curve of the link model, and recording the measurement duration; applying a direct-current voltage to the link model, and measuring the direct-current resistance of the link model; calculating the change rate of the direct-current resistance from the starting moment to the abrupt increasing moment; and subtracting the DC resistance change rate curve from the measured impedance curve to correct the impedance curve. Based on the linear accumulation characteristic of the direct-current resistance, an equivalent link model of a to-be-measured element is established, the change of the direct-current resistance is quantified, difference correction is completed by using a resistance change rate curve and an actually measured impedance curve, the influence of the floating effect is finally eliminated, and the real impedance of the to-be-measured element is restored.

Description

Technical Field

[0001] The present invention relates to the field of electronic circuit testing, and in particular to a simulation method and application for restoring the real impedance of a component to be tested. Background Art

[0002] Printed Circuit Board (PCB) is a key part of electronic products’ physical support and signal transmission. Its performance directly affects the overall function of electronic products. With the rapid development of electronic technology, the design of PCB boards has become more and more complex, and the requirements for signal transmission quality have become higher and higher. The precise measurement and control of impedance has become a key factor in ensuring stable signal transmission.

[0003] In the test phase of PCB boards, due to the influence of impedance drift, the test results often have large errors. From the test principle, the impedance drift is due to the accumulation of DC resistance of the object to be tested, which makes the impedance fluctuate more as the distance from the test point increases during the test. Taking the test of a transmission line as an example, it is found in the actual test that its impedance continues to increase as it moves away from the test point, resulting in the inability to measure the true impedance value. When there are other impedance discontinuities such as vias or connectors in the circuit of the PCB board, the problem becomes more complicated.

[0004] In summary, in long transmission lines or circuits containing discontinuities (such as vias and connectors), DC resistance will accumulate with the length of the line, causing the impedance value of the test point to continuously drift upward with increasing distance, that is, the impedance value deviates from the true value. Existing test methods cannot distinguish between the influence of the true impedance and the drift effect, especially at the intermediate discontinuity points, which are difficult to measure accurately.

[0005] Therefore, how to eliminate the influence of impedance drift and accurately restore the true impedance of the object to be tested has become a key technical problem that needs to be solved urgently in the field of PCB board testing. Summary of the invention

[0006] In order to overcome the shortcomings of the prior art, the present invention provides a simulation method and application for restoring the true impedance of the component to be tested. By building a specific simulation model, combining the measurement and calculation of the DC resistance, and subtracting the DC resistance change rate curve from the original impedance curve, the influence of impedance drift can be effectively eliminated and the true impedance of the component to be tested can be accurately restored.

[0007] The technical solution of the present invention is as follows:

[0008] A simulation method for restoring the real impedance of a component to be tested comprises the following steps:

[0009] Step 1: Build a link model of a long line, where the line length of the long line is not less than 10000 mil, and the link model has an initial impedance value;

[0010] Step 2: Measure the impedance curve of the link model and record the measurement duration.

[0011] Step 3: Apply a DC voltage to the link model and measure the DC resistance of the link model.

[0012] Step 4: Calculate the change rate of the DC resistance during the measurement duration.

[0013] Step 5: Subtract the DC resistance change rate curve obtained in Step 4 from the impedance curve measured in Step 2 to correct the impedance curve.

[0014] As a preferred solution of the present invention, the model parameters of the link model include wire length, wire width, differential line spacing, initial impedance value, circuit layer board where the trace is located, dielectric constant, and board thickness.

[0015] As a preferred solution of the present invention, in Step 1, the wire length range of the long trace is 10000 mil to 20000 mil, and the setting error of the initial impedance value does not exceed ±1%.

[0016] As a preferred solution of the present invention, in Step 2, the impedance curve is measured using the time domain reflectometry method, the sampling interval ≤ 10 ps, and the measurement accuracy reaches ±0.1 Ω.

[0017] As a preferred solution of the present invention, in Step 3, the applied DC voltage value is 1 V ± 0.1 V, and the DC resistance is obtained by calculating the ratio of the DC voltage value to the steady-state current value.

[0018] As a preferred solution of the present invention, the calculation formula for the change rate of the DC resistance in Step 4 is: R 测 / Δt, where R 测 is the DC resistance value measured in Step 3, and Δt is the measurement duration for measuring the impedance curve.

[0019] As a preferred solution of the present invention, after Step 1, there is also a calibration step: connect a standard impedance module to the head end of the link model, and remove the standard impedance module after verifying that the measurement error ≤ 0.5%.

[0020] As a preferred solution of the present invention, the link model is constructed in the ADS simulation environment and includes the following sub-modules: ideal DC voltage source, current measurer, differential trace module.

[0021] As a preferred solution of the present invention, the ratio of the differential line spacing to the wire width is 1.5:1 to 3:1, the dielectric constant range of the circuit layer board is 3.5 to 4.5, and the board thickness is 0.8 mm ± 0.05 mm.

[0022] The present invention also provides an application of the simulation method for restoring the true impedance of a component to be measured based on the above solution, including the following steps:

[0023] Step 1, measure the measured impedance curve of the connector, and use the measurement duration as the total duration;

[0024] Step 2, build a link model of the equivalent connector using the S-parameters of the connector; and obtain the DC resistance value;

[0025] Step 3, determine the calculation duration according to the measurement time corresponding to the connector impedance influence area in the measured impedance curve;

[0026] Step 4, calculate the change rate of the DC resistance within the total duration to obtain the DC resistance change rate curve;

[0027] Step 5, subtract the DC resistance change rate curve from the measured impedance curve to restore the true impedance curve of the connector.

[0028] According to the present invention of the above solution, its beneficial effects are as follows:

[0029] Based on the linear cumulative characteristic of the DC resistance, the present invention quantifies the change of the DC resistance by establishing an equivalent link model of the component to be measured, and uses the resistance change rate curve and the measured impedance curve to complete the difference correction, finally eliminating the influence of the upward drift effect and restoring the true impedance of the component to be measured; and using this method, the true impedance situation at any position of the entire link can be seen, so as to accurately judge the situation of the discontinuity point in the middle of the link. Description of the Drawings

[0030] Figure 1 It is a flowchart of the method according to Embodiment 1 of the present invention;

[0031] Figure 2 It is a schematic structural diagram of Embodiment 1 of the present invention;

[0032] Figure 3 It is an impedance curve diagram before repair in Embodiment 1;

[0033] Figure 4 It is a DC resistance change rate curve calculated in Embodiment 1;

[0034] Figure 5 It is a comparison diagram of impedance curves before and after repair in Embodiment 1;

[0035] Figure 6 It is an impedance curve diagram before repair in Embodiment 2;

[0036] Figure 7 It is a DC resistance change rate curve calculated in Embodiment 2;

[0037] Figure 8It is a comparison diagram of impedance curves before and after repair in the second embodiment.

[0038] In the figure, 1 is a DC voltage source; 2 is a current measurer; 3 is a differential trace module. Detailed implementation manner

[0039] To better understand the purpose, technical solution and technical effect of the present invention, the present invention will be further explained below in conjunction with the drawings and embodiments. It should be noted that similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, it is declared that the embodiments described below are only used to explain the present invention and are not used to limit the present invention.

[0040] It should be noted that when an element is referred to as "fixed to" or "disposed on" another element, it can be directly on the other element or there may also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "first" and "second" are only used for the purpose of description and cannot be construed as indicating or implying relative importance or implicitly indicating the number of technical features.

[0041] Embodiment 1

[0042] As Figures 1 to 5 shown, a simulation method for restoring the true impedance of a device under test includes the following steps:

[0043] Step 1: Build a link model of a long trace. The length of the long trace is not less than 10000 mil, and the link model has an initial impedance value. This step constructs a link model through a long trace (≥10000 mil) to simulate the linear cumulative characteristic of resistance with wire length in an actual circuit and ensure that the model is consistent with the actual physical behavior.

[0044] Step 2: Measure the impedance curve of the link model and record the measurement duration, referring to Figure 3 ; This step records the measurement duration to locate the impedance rising interval caused by the upward drift effect and provide a time reference for subsequent correction.

[0045] Step 3: Apply a DC voltage to the link model and measure the DC resistance of the link model. This step quantifies the resistance cumulative value by applying a DC voltage and measuring the DC resistance as a correction basis.

[0046] Step 4: Calculate the change rate of the DC resistance during the measurement duration, referring to Figure 4 ; This step quantifies the change of the DC resistance over time.

[0047] Step 5: Subtract the DC resistance change rate curve obtained in Step 4 from the impedance curve measured in Step 2 to correct the impedance curve, referring to Figure 5 ; Through curve subtraction operation in this step, the influence of the upward drift effect is eliminated from the measured impedance, and the intrinsic impedance of the component under test is directly extracted.

[0048] Based on the linear cumulative characteristic of DC resistance, the present invention quantifies the change of DC resistance by establishing an equivalent link model of the component under test, and uses the resistance change rate curve and the measured impedance curve to complete the difference correction, systematically eliminating the DC resistance cumulative effect (upward drift effect) in the long transmission line, and accurately restoring the true impedance of the component under test.

[0049] In the present invention, the link model is constructed in the ADS simulation environment. The link model includes the following sub-modules: an ideal DC voltage source 1, a current measurer 2, and a differential trace module 3. Among them, the differential trace module includes a first long trace and a second long trace arranged in parallel, accurately simulating the actual differential transmission line of the component under test, and comprehensively considering the influence of signal integrity on impedance. The ADS environment supports high-frequency circuit simulation to ensure controllable model parameters. The ideal DC voltage source can provide a stable voltage input, the current measurer can accurately measure the current, and the differential trace module can simulate the differential signal transmission in the actual circuit.

[0050] In the present invention, the model parameters of the link model include line length, line width, and differential line spacing to define the geometric parameters of the trace, so that the electrical characteristics of the link model are consistent with those of the component under test; the model parameters also include the circuit layer board where the trace is located, dielectric constant, board thickness, and initial impedance value. The initial impedance value is used as the initial value not affected by the DC resistance upward drift. Accurately setting the above model parameters is beneficial to improving the matching degree between the model and the actual circuit, and ensuring the reliability and repeatability of the simulation results.

[0051] In the present invention, the line length range of the long trace in Step 1 is 10000 mil to 20000 mil, and the setting error of the initial impedance value does not exceed ±1%. The line length is long enough to effectively simulate the long transmission line phenomenon far from the test point. The initial impedance error ≤ ±1% ensures that the initial conditions of the model are closer to the real situation, which is beneficial to reducing the model construction error and making the subsequent simulation calculation based on this model more accurate.

[0052] In the present invention, in step 2, the impedance curve is measured using the time domain reflectometry method, with a sampling interval ≤ 10 ps and a measurement accuracy reaching ±0.1 Ω. In this step, the impedance discontinuity points are located through the time difference of the reflected signals. Combining with the sampling interval ≤ 10 ps ensures the accuracy of the time axis. The high-sensitivity device with a measurement accuracy reaching ±0.1 Ω can reduce data noise, provide a high signal-to-noise ratio input for subsequent correction, thus facilitating the improvement of the resolution of the impedance curve, accurately capturing the details of impedance mutations, being able to measure the impedance curve of the device under test more precisely, obtaining more detailed impedance change information, and providing a more accurate data basis for subsequent correction steps. The time domain reflectometry method is a commonly used method for measuring impedance, which determines the impedance by transmitting a pulse signal and analyzing the reflected signal. A smaller sampling interval can collect data more densely and capture the subtle changes in the impedance curve. A higher measurement accuracy reduces the errors in the measurement process, making the obtained impedance curve closer to the true value.

[0053] In the present invention, the DC voltage value applied in step 3 is 1 V ± 0.1 V to avoid errors introduced by voltage fluctuations. The DC resistance is calculated by the ratio of the DC voltage value to the steady-state current value. This step excludes the influence of transient responses, accurately reflects the static characteristics of the DC resistance, ensures the accuracy and consistency of the DC resistance measurement, and makes the subsequent calculated DC resistance change rate more reliable.

[0054] In the present invention, the calculation formula for the DC resistance change rate in step 4 is: R_measured / Δt, where R_measured is the DC resistance value measured in step 3, and Δt is the measurement duration of measuring the impedance curve. It can be seen that based on the linear increase of the DC resistance in the uniform transmission line, the total resistance change amount is evenly distributed to the unit time during the measurement period, simplifying the calculation process; based on the measured impedance curve, from the total duration from the 0 moment to the end of the measurement, the change of the DC resistance over time within the same time period is accurately introduced. The change rate curve calculated based on this is matched with the impedance curve for subsequent correction of the impedance curve.

[0055] In a preferred embodiment, after step 1, there is also a calibration step: a standard impedance module is connected to the head end of the link model, and after verifying that the measurement error ≤ 0.5%, the standard impedance module is removed. The standard impedance module provides a known impedance value (such as 50 Ω) to calibrate the baseline error of the measurement system; verify the accuracy of the model to ensure the reliability of the input data for the correction algorithm. It can be seen that by adding a calibration step after building the link model, the measurement error can be effectively reduced, the accuracy and reliability of the entire simulation process can be improved, and it is ensured that the finally restored true impedance is closer to the actual value.

[0056] In a preferred embodiment, the ratio of the differential line pitch to the line width is 1.5:1 to 3:1, the dielectric constant range of the circuit layer board material is 3.5 to 4.5, and the board thickness is 0.8 mm ± 0.05 mm. Since the ratio of the differential line pitch to the line width affects the coupling degree and impedance matching of differential signals, a differential line pitch to line width ratio of 1.5:1 to 3:1 is beneficial to balancing signal coupling and loss and maintaining impedance consistency. The dielectric constant and board thickness affect the signal transmission speed and characteristic impedance. Limiting these parameters within a certain range can make the electrical characteristics of the model closer to the actual circuit and improve the accuracy of simulation.

[0057] Embodiment 2

[0058] A fixture board combination of two circuit boards connected by a connector in the middle. The impedance curve measured from one of the boards is affected by the impedance drift of the connector and cannot truly measure the impedance of the connector itself, that is, the situation of the discontinuity point in the middle of the link cannot be judged.

[0059] As Figures 6 to 8 described, the present invention proposes an application method of a simulation method for restoring the true impedance of a device under test based on the above solution, including the following steps:

[0060] Step 1: Measure the measured impedance curve of the connector, referring to Figure 6 , and the measurement duration is used as the total duration;

[0061] Step 2: Use the S-parameters of the connector to build an equivalent link model of the connector; and obtain the DC resistance value;

[0062] Step 3: Determine the calculation duration from the measurement time corresponding to the connector impedance influence area in the measured impedance curve;

[0063] Step 4: Calculate the change rate of the DC resistance within the total duration to obtain the DC resistance change rate curve, referring to Figure 7 ;

[0064] Step 5: Subtract the DC resistance change rate curve from the measured impedance curve to restore the true impedance curve of the connector. Figure 8 The dotted line in is the impedance test result under the upward drift effect before repair, and the solid line is the impedance result after repair. The true impedance of the connector itself can be obtained, the situation of the discontinuity point in the middle of the link can be judged, and the true impedance at any position of the entire link can be seen.

[0065] In summary, starting from the principle of impedance upward drift, the present invention builds a DC resistance simulation link, and the built link model has a trace length of no less than 10000 mils to ensure that the model can truly reflect the linear cumulative characteristic of resistance with wire length. When subtracting the measured impedance curve from the obtained DC resistance change rate curve, the two curves are precisely matched in the time axis and data points, and then the curves are subtracted to effectively correct the impedance curve and accurately restore the true impedance.

[0066] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0067] The above embodiments only express several implementation manners of the present invention, and the description is relatively specific and detailed, but it should not be understood as a limitation to the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A simulation method for restoring the true impedance of a device under test, characterized in that, It includes the following steps: Step 1: Build a link model for the long trace, and the link model has an initial impedance value; Step 2: Measure the impedance curve of the link model and record the measurement duration; Step 3: Apply a DC voltage to the link model and measure the DC resistance of the link model; Step 4: Calculate the change rate of the DC resistance during the measurement duration; Step 5: Subtract the DC resistance change rate curve obtained in Step 4 from the impedance curve measured in Step 2 to correct the impedance curve.

2. The simulation method for restoring the true impedance of the device under test according to claim 1, wherein The model parameters of the link model include line length, line width, differential line spacing, initial impedance value, circuit layer board where the trace is located, dielectric constant, and board thickness.

3. The simulation method for restoring the true impedance of a device under test according to claim 1, characterized in that In Step 1, the line length range of the long trace is from 10000 mil to 20000 mil, and the setting error of the initial impedance value does not exceed ±1%.

4. The simulation method for restoring the true impedance of the element to be measured according to claim 1, characterized in that In Step 2, the impedance curve is measured using the time domain reflectometry method, the sampling interval ≤ 10 ps, and the measurement accuracy reaches ±0.1 Ω.

5. The simulation method for restoring the true impedance of a device under test according to claim 1, characterized in that In Step 3, the applied DC voltage value is 1V ± 0.1V, and the DC resistance is obtained by calculating the ratio of the DC voltage value to the steady-state current value.

6. The simulation method for restoring the true impedance of the element to be measured according to claim 1, characterized in that, The calculation formula for the DC resistance change rate in step 4 is: R 测 / Δt, where R 测 is the DC resistance value measured in step 3, and Δt is the measurement duration of the measurement impedance curve.

7. The simulation method for restoring the true impedance of the device under test according to claim 1, characterized in that, After Step 1, it also includes a calibration step: Connect a standard impedance module to the head end of the link model, and remove the standard impedance module after verifying that the measurement error ≤ 0.5%.

8. The simulation method for restoring the true impedance of the device under test according to claim 1, wherein, The link model is built in the ADS simulation environment and includes the following sub-modules: ideal DC voltage source, current measurer, differential trace module.

9. The simulation method for restoring the true impedance of a device under test according to claim 1, wherein The ratio of the differential line spacing to the line width is from 1.5:1 to 3:1, the dielectric constant range of the circuit layer board is from 3.5 to 4.5, and the board thickness is 0.8mm ± 0.05mm.

10. Application of a simulation method for restoring the true impedance of a device under test according to any one of claims 1 to 9, characterized in that It includes the following steps: Step 1: Measure the measurement impedance curve of the connector, and the measurement duration is used as the total duration; Step 2: Build a link model of the equivalent connector using the S parameters of the connector; and obtain the DC resistance value; Step 3: Determine the calculation duration according to the measurement time corresponding to the connector impedance influence area in the measurement impedance curve; Step 4: Calculate the change rate of the DC resistance within the total duration to obtain the DC resistance change rate curve; Step 5: Subtract the DC resistance change rate curve from the measurement impedance curve to restore the true impedance curve of the connector.

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