A method for measuring differential probe gain using a two-port vector network analyzer

Abstract

This invention discloses a method for measuring the gain of a differential probe using a two-port vector network analyzer, comprising the following steps: calibrating the two-port vector network analyzer; constructing a differential test fixture; obtaining the S-parameters corresponding to the differential test fixture; obtaining the S-parameter matrix corresponding to a through-type calibration component; obtaining the S-parameter matrix corresponding to a line calibration component; obtaining the half-side transmission parameters of the differential test fixture; obtaining the differential-mode gain of the differential probe using the half-side transmission parameters of the differential test fixture and the S-parameters corresponding to the differential test fixture; replacing the differential test fixture with a common-mode test fixture, and obtaining the common-mode gain of the differential probe using the same method as steps S3 to S7. This method achieves voltage gain measurement of the differential probe in a balanced state, eliminating the measurement phase error caused by the offset between the measurement plane and the reference plane in traditional differential probe testing methods.

Description

Technical Field

[0001] This invention relates to the field of differential probe gain measurement, and more specifically to a method for measuring differential probe gain using a two-port vector network analyzer. Background Technology

[0002] With the ever-increasing speed and bandwidth of baseband signals in all types of electronic systems today, differential probe pairs have shown significant advantages over single-ended signal lines. Their immunity to strong noise and environmental coupling, the broadband characteristics afforded by their two-conductor TEM configuration, and low radiated emissions make them the preferred option for high-speed SerDes and fast signal transmission.

[0003] While traditional differential probe measurement methods meet the application scenarios of some test circuits, they are unbalanced. Differential and common-mode voltages exist simultaneously between the positive and negative inputs; that is, the differential probe obtains its output under conditions of both differential and common-mode inputs. This cannot reproduce the differential and common-mode gains of the differential probe in a balanced state, nor can it obtain the common-mode rejection ratio (CMRR). Furthermore, the deviation between the measurement plane and the reference plane will inevitably result in a portion of the transmission network not being embedded in the calibration process of the vector network analyzer, leading to mixed measurement data and unavoidable phase errors in the voltage gain. Summary of the Invention

[0004] To address the aforementioned shortcomings in the prior art, this invention provides a method for measuring differential probe gain using a dual-port vector network analyzer, which eliminates the measurement phase error caused by the offset between the measurement plane and the reference plane in traditional differential probe testing methods.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0006] A method for measuring differential probe gain using a two-port vector network analyzer is provided, comprising the following steps:

[0007] S1. Calibrate the two-port vector network analyzer;

[0008] S2. Construct a differential test fixture; the differential test fixture has a left-right symmetrical structure, and from left to right are the first interface, the first balun, the differential microstrip line, the second balun, and the second interface;

[0009] S3. Connect the calibrated dual-port vector network analyzer and differential probe to the differential test fixture, and obtain the S-parameters corresponding to the differential test fixture;

[0010] S4. Replace the differential test fixture with a through calibration piece, and connect the calibrated dual-port vector network analyzer and differential probe to the through calibration piece using the same method as in step S3, and obtain the S-parameter matrix corresponding to the through calibration piece.

[0011] S5. Replace the differential test fixture with the line calibration component, and connect the calibrated dual-port vector network analyzer and differential probe to the line calibration component using the same method as in step S3, and obtain the S-parameter matrix corresponding to the line calibration component.

[0012] S6. Obtain the half-side transmission parameters of the differential test fixture based on the S-parameter matrix corresponding to the through calibration component and the S-parameter matrix corresponding to the line calibration component.

[0013] S7. Obtain the differential mode gain of the differential probe by using the half-side transmission parameters of the differential test fixture and the S-parameters corresponding to the differential test fixture.

[0014] S8. Replace the differential test fixture with a common-mode test fixture, and use the same method as steps S3 to S7 to obtain the common-mode gain of the differential probe; wherein the common-mode test fixture is the differential test fixture after removing the first balun and the second balun.

[0015] Furthermore, the specific method for calibrating the two-port vector network analyzer in step S1 is as follows:

[0016] Connect the first port of the two-port vector network analyzer to the calibration device via a 50-ohm characteristic impedance cable, so that the reference plane for the measurement of the first port is the end connector of the 50-ohm characteristic impedance cable; connect the second port of the two-port vector network analyzer to the calibration device via a 50-ohm characteristic impedance cable, so that the reference plane for the measurement of the second port is the end connector of the 50-ohm characteristic impedance cable.

[0017] Connect the cables of the first and second ports using the through calibration connector, adjust the parameters of the two-port vector network analyzer so that the voltage ratio fluctuation of the two ports is within 0.1dB, and complete the calibration of the two-port vector network analyzer.

[0018] Furthermore, the specific method for obtaining the S-parameter matrix corresponding to the differential test fixture in step S3 is as follows:

[0019] Connect the front probe of the differential probe to the differential microstrip line; connect the first port of the calibrated two-port vector network analyzer to the first interface of the differential test fixture via a 50-ohm characteristic impedance cable, and connect the second port of the calibrated two-port vector network analyzer to the second interface of the differential test fixture via a 50-ohm characteristic impedance cable. Obtain the voltage ratio between the second port and the first port of the calibrated two-port vector network analyzer at this time, and record it as the S-parameter G.CA ;

[0020] Maintaining the connection configuration of the first port of the calibrated two-port vector network analyzer, connect the second port of the calibrated two-port vector network analyzer to the output terminal of the differential probe via a 50-ohm characteristic impedance cable. Obtain the voltage ratio between the second port and the first port of the calibrated two-port vector network analyzer at this point, and record it as the S-parameter G. DA .

[0021] Furthermore, in step S4, the S-parameter matrix T Mt And the S-parameter matrix T in step S5 Ml These include the voltage ratio of incident current to reflected current at the first port of the calibrated two-port vector network analyzer, the voltage ratio of the first port to the second port of the calibrated two-port vector network analyzer, the voltage ratio of the second port to the first port of the calibrated two-port vector network analyzer, and the voltage ratio of incident current to reflected current at the second port of the calibrated two-port vector network analyzer.

[0022] Furthermore, the specific method for obtaining the half-side transmission parameters of the differential test fixture in step S6 is as follows:

[0023] According to the formula:

[0024] T Mt =T C T Nt T D

[0025] T Ml =T C T Nl T D

[0026] For the half-side transmission parameter T of the differential test fixture C Perform a joint solution; where T Nt T is the identity matrix; D To transmit parameters to the other side of the differential test fixture, T Nl Let l be the transmission matrix of an ideal transmission line of unit length l.

[0027] Furthermore, the specific method for obtaining the differential mode gain of the differential probe in step S7 is as follows:

[0028] Based on the subsequent load and voltage division ratio, parameter T is transferred from one half of the differential test fixture. C Obtaining S-parameter G CB According to the formula:

[0029]

[0030] Obtain the differential mode gain G of the differential probe DB .

[0031] The beneficial effects of this invention are as follows: This method realizes voltage gain measurement under the balanced state of differential probe, eliminates the measurement phase error caused by the offset between the measurement plane and the reference plane in the traditional differential probe test method, and performs differential gain measurement and common-mode gain measurement separately. The common-mode rejection ratio of the differential probe can be obtained using only a two-port vector network analyzer. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating the method.

[0033] Figure 2 The equivalent circuit diagram for differential-mode gain testing;

[0034] Figure 3 Equivalent circuit diagram for differential gain testing after de-embedding;

[0035] Figure 4 This is a simulation schematic diagram of the method in ADS;

[0036] Figure 5 This is a schematic diagram of a differential probe simulation device consisting of a 25k resistor and a fully differential amplifier ADL5580;

[0037] Figure 6 for Figure 5 The diagram shows a comparison of the magnitudes of the test values ​​and the actual values ​​in the simulation.

[0038] Figure 7 for Figure 5 The diagram shown illustrates the phase comparison between the test value and the actual value in the simulation.

[0039] Figure 8 This is a simulation schematic of the differential probe common-mode gain test in ADS.

[0040] Figure 9 A simulation model for differential probe common-mode gain testing;

[0041] Figure 10 for Figure 9 The diagram shows a comparison of the magnitudes of the test values ​​and the actual values ​​in the simulation.

[0042] Figure 11 for Figure 9 The diagram shown illustrates the phase comparison between the test value and the actual value in the simulation.

[0043] Figure 12 This is a structural diagram of the line calibration component;

[0044] Figure 13 This is a structural diagram of the through-calibration component. Detailed Implementation

[0045] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0046] like Figure 1 As shown, the method for measuring differential probe gain using a two-port vector network analyzer includes the following steps:

[0047] S1. Calibrate the two-port vector network analyzer;

[0048] S2. Construct a differential test fixture; the differential test fixture has a left-right symmetrical structure, and from left to right are the first interface, the first balun, the differential microstrip line, the second balun, and the second interface;

[0049] S3. Connect the calibrated dual-port vector network analyzer and differential probe to the differential test fixture, and obtain the S-parameters corresponding to the differential test fixture;

[0050] S4. Replace the differential test fixture with a through calibration piece, and connect the calibrated dual-port vector network analyzer and differential probe to the through calibration piece using the same method as in step S3, and obtain the S-parameter matrix corresponding to the through calibration piece.

[0051] S5. Replace the differential test fixture with the line calibration component, and connect the calibrated dual-port vector network analyzer and differential probe to the line calibration component using the same method as in step S3, and obtain the S-parameter matrix corresponding to the line calibration component.

[0052] S6. Obtain the half-side transmission parameters of the differential test fixture based on the S-parameter matrix corresponding to the through calibration component and the S-parameter matrix corresponding to the line calibration component.

[0053] S7. Obtain the differential mode gain of the differential probe by using the half-side transmission parameters of the differential test fixture and the S-parameters corresponding to the differential test fixture.

[0054] S8. Replace the differential test fixture with a common-mode test fixture, and use the same method as steps S3 to S7 to obtain the common-mode gain of the differential probe; wherein the common-mode test fixture is the differential test fixture after removing the first balun and the second balun.

[0055] In the specific implementation process, the differential probe to be tested is brought into contact with the differential test fixture, and the front probe of the differential probe is connected to the differential microstrip line (or coupling line). Due to the presence of the balun, the voltage on the coupling line is a differential voltage with the same amplitude but opposite polarity. The positive terminal of the differential probe is connected to the positive voltage line in the coupling line, and the negative terminal is connected to the negative voltage line, thus realizing the measurement in a balanced state. Figure 2 The equivalent circuit diagram for differential-mode gain testing is shown below. Figure 2 In the diagram, 50 Ohm represents the equivalent resistance inside the two-port vector network analyzer, and Port1, Port2, and Port3 are the connection points of the two-port vector network analyzer.

[0056] The specific method for calibrating the two-port vector network analyzer in step S1 is as follows:

[0057] Connect the first port of the two-port vector network analyzer to the calibration device via a 50-ohm characteristic impedance cable, so that the reference plane for the measurement of the first port is the end connector of the 50-ohm characteristic impedance cable; connect the second port of the two-port vector network analyzer to the calibration device via a 50-ohm characteristic impedance cable, so that the reference plane for the measurement of the second port is the end connector of the 50-ohm characteristic impedance cable.

[0058] Connect the cables of the first and second ports using the through calibration connector, adjust the parameters of the two-port vector network analyzer so that the voltage ratio fluctuation of the two ports is within 0.1dB, and complete the calibration of the two-port vector network analyzer.

[0059] After the two-port vector network analyzer has been calibrated, both ports of the analyzer will be connected to external devices via cables with a characteristic impedance of 50 ohms in subsequent operations.

[0060] In the specific implementation process, the simulation diagrams of the line calibration component and the through calibration component are as follows: Figure 12 and Figure 13 As shown, it consists of two ports and a microstrip line. One end of the calibration device is the input, and the other end is the output.

[0061] The specific method for obtaining the S-parameter matrix corresponding to the differential test fixture in step S3 is as follows:

[0062] Connect the front probe of the differential probe to the differential microstrip line; connect the first port of the calibrated two-port vector network analyzer to the first interface of the differential test fixture via a 50-ohm characteristic impedance cable, and connect the second port of the calibrated two-port vector network analyzer to the second interface of the differential test fixture via a 50-ohm characteristic impedance cable. Obtain the voltage ratio between the second port and the first port of the calibrated two-port vector network analyzer at this time, and record it as the S-parameter G. CA ;

[0063] Maintaining the connection configuration of the first port of the calibrated two-port vector network analyzer, connect the second port of the calibrated two-port vector network analyzer to the output terminal of the differential probe via a 50-ohm characteristic impedance cable. Obtain the voltage ratio between the second port and the first port of the calibrated two-port vector network analyzer at this point, and record it as the S-parameter G. DA .

[0064] Since the test fixture is not included in the calibration, the measurement plane offset from the reference plane, which is common in traditional differential probe measurement methods, is avoided, and the measured S-parameters are error-free. However, this introduces a new problem: the differential test fixture is included in the measured S-parameters, therefore the measurement architecture cannot be directly equivalent to a lumped parameter circuit. To further simplify the model, a de-embedding method must be used. The equivalent circuit diagram for differential-mode gain testing after de-embedding is shown below. Figure 3 As shown. Figure 3 Port1 and Port2 are differential ports, T B The T matrix is ​​the equivalent of a two-port transmission network on one side of the differential test fixture, i.e., T C , Its generalized reverse transmission matrix, i.e., T D . Figure 3 Point A is the contact point between the first port of the calibrated two-port vector network analyzer and the differential test fixture; point B is the contact point between the front probe of the differential probe and the differential test fixture; point C is the contact point between the second port of the calibrated two-port vector network analyzer and the differential test fixture; and point D is the contact point between the output end of the differential probe and the second port of the calibrated two-port vector network analyzer.

[0065] In step S4, the S-parameter matrix T Mt And the S-parameter matrix T in step S5 Ml These include the voltage ratio of incident current to reflected current at the first port of the calibrated two-port vector network analyzer, the voltage ratio of the first port to the second port of the calibrated two-port vector network analyzer, the voltage ratio of the second port to the first port of the calibrated two-port vector network analyzer, and the voltage ratio of incident current to reflected current at the second port of the calibrated two-port vector network analyzer.

[0066] The specific method for obtaining the half-side transmission parameters of the differential test fixture in step S6 is as follows: According to the formula:

[0067] T Mt =T C T Nt T D

[0068] T Ml =T C TNl T D

[0069] For the half-side transmission parameter T of the differential test fixture C Perform a joint solution; where T Nt T is the identity matrix; D To transmit parameters to the other side of the differential test fixture, T Nl Let l be the transmission matrix of an ideal transmission line of unit length l.

[0070] To test the differential mode gain of the differential probe, the ratio of the voltage at point D to that at point B, i.e., G, needs to be measured. DB The specific method for obtaining the differential mode gain of the differential probe in step S7 is as follows:

[0071] Based on the subsequent load and voltage division ratio, parameter T is transferred from one half of the differential test fixture. C Obtaining S-parameter G CB The corresponding expression is:

[0072]

[0073] Where T 11 T 12 T 21 and T 22 All are half-side transmission parameters T C The elements in.

[0074] Then, according to the formula:

[0075]

[0076] The differential gain G of the differential probe can then be obtained. DB .

[0077] In practical implementation, similar to the differential probe differential-mode gain measurement method, the common-mode test fixture is equivalent to a cascade of two symmetrical two-port networks, thus simplifying circuit analysis. After equating the output port of the power divider to a common-mode port, T... C The T-matrix represents the equivalent transmission network on one side of the common-mode test fixture. Its generalized inverse transfer matrix is ​​obtained by using the same method as the differential-mode gain measurement process to obtain G in the common-mode test. CA and G DA Then, by de-embedding the common-mode test fixture, we obtain... This allows us to obtain the ratio of the voltage at point C to the voltage at point B required to calculate the common-mode gain, thus enabling us to determine the common-mode gain.

[0078] In one embodiment of the present invention, such as Figure 4As shown, to simulate the balun test, the S-parameter file of BAL-0032SSG was used, along with a section of the MCLN model included with ADS as the model without differential lines. The amplifier in the differential probe was simulated using the ADL5580 fully differential amplifier file. Since the differential probe is a semi-differential structure, one of the ADL5580's output pins needs to be connected to ground at 50 Ohms. Two 25kΩ ideal resistors were used to simulate the input attenuation network at the front end of the differential probe. The cascaded structure of the 25kΩ resistors and the ADL5580 fully differential amplifier simulates the entire differential probe.

[0079] In the simulation, the steps are simplified by directly connecting the output of the differential probe (i.e., the output of the ADL5580 fully differential amplifier) ​​to the third 50 Ohm terminus (equivalent to the third port of a two-port vector network analyzer, except that the third port does not exist in actual measurements; instead, two S21 values ​​are obtained through the secondary measurement in step S3). This allows us to obtain G. CA and G DA Next, the influence of the test fixture will be eliminated, and the ratio of its single-ended output voltage to the differential input voltage, i.e., G, will be obtained through a simulator. CB .

[0080] To verify the error between the actual value and the actual value, a separate simulation was performed on the differential probe analog device composed of a 25k resistor and a fully differential amplifier ADL5580. The simulation schematic is attached. Figure 5 As shown. (Through) Figure 5 The simulation model compares the test values ​​with the actual values, and the results are as follows: Figure 6 and Figure 7 As shown, the measured value of the differential voltage gain of the differential probe is almost identical to the actual value. The very small error is caused by the amplitude-phase imbalance of the balun. Furthermore, the phase comparison diagram shows that this measurement method does not cause phase deviation.

[0081] The simulation schematic of the differential probe common-mode gain testing method in ADS is attached. Figure 8 As shown in the diagram, a voltage divider network composed of three 50kΩ ideal resistors connected in parallel simulates a power divider. Since the resistor models in ADS lack frequency selectivity and phase delay, and the power divider used for simulation verification cannot be too ideal, a microstrip line is added to ensure phase delay. Furthermore, parallel capacitors and series inductors are added to simulate the parasitic capacitance and inductance of the transmission network, giving it frequency characteristics. The entire architecture is symmetrical to ensure amplitude and phase balance. The differential probe simulation is also a cascaded network composed of a 25kΩ ideal resistor and a fully differential amplifier ADL5580.

[0082] pass Figure 9 The simulation model will G DBThe common-mode voltage gain was compared with that of the differential probe analog device. Figure 10 and Figure 11 It can be seen that when the power divider is in phase-amplitude balance, the measured common-mode gain is identical to the actual value in both amplitude and phase.

[0083] In summary, this invention achieves voltage gain measurement under balanced conditions, eliminates the measurement phase error caused by the offset between the measurement plane and the reference plane in traditional differential probe testing methods, and can obtain the common-mode rejection ratio of the differential probe using only two-port vector network analysis.

Claims

1. A method for measuring the gain of a differential probe using a two-port vector network analyzer, characterized in that, Includes the following steps: S1. Calibrate the two-port vector network analyzer; S2. Construct a differential test fixture; the differential test fixture has a left-right symmetrical structure, and from left to right are the first interface, the first balun, the differential microstrip line, the second balun, and the second interface; S3. Connect the calibrated dual-port vector network analyzer and differential probe to the differential test fixture, and obtain the S-parameters corresponding to the differential test fixture; S4. Replace the differential test fixture with a through calibration piece, and connect the calibrated dual-port vector network analyzer and differential probe to the through calibration piece using the same method as in step S3, and obtain the S-parameter matrix corresponding to the through calibration piece. S5. Replace the differential test fixture with the line calibration component, and connect the calibrated dual-port vector network analyzer and differential probe to the line calibration component using the same method as in step S3, and obtain the S-parameter matrix corresponding to the line calibration component. S6. Obtain the half-side transmission parameters of the differential test fixture based on the S-parameter matrix corresponding to the through calibration component and the S-parameter matrix corresponding to the line calibration component. S7. Obtain the differential mode gain of the differential probe by using the half-side transmission parameters of the differential test fixture and the S-parameters corresponding to the differential test fixture. S8. Replace the differential test fixture with a common-mode test fixture, and use the same method as steps S3 to S7 to obtain the common-mode gain of the differential probe; wherein the common-mode test fixture is the differential test fixture after removing the first balun and the second balun.

2. The method for measuring differential probe gain using a two-port vector network analyzer according to claim 1, characterized in that, The specific method for calibrating the two-port vector network analyzer in step S1 is as follows: Connect the first port of the two-port vector network analyzer to the calibration device via a 50-ohm characteristic impedance cable, so that the reference plane for the measurement of the first port is the end connector of the 50-ohm characteristic impedance cable. Connect the second port of the two-port vector network analyzer to the calibration device via a 50-ohm characteristic impedance cable, so that the reference plane for the second port measurement is the end connector of the 50-ohm characteristic impedance cable. Connect the cables of the first and second ports using the through calibration connector, adjust the parameters of the two-port vector network analyzer so that the voltage ratio fluctuation of the two ports is within 0.1dB, and complete the calibration of the two-port vector network analyzer.

3. The method for measuring differential probe gain using a two-port vector network analyzer according to claim 1, characterized in that, The specific method for obtaining the S-parameter matrix corresponding to the differential test fixture in step S3 is as follows: Connect the front probe of the differential probe to the differential microstrip line; connect the first port of the calibrated two-port vector network analyzer to the first interface of the differential test fixture via a 50-ohm characteristic impedance cable, and connect the second port of the calibrated two-port vector network analyzer to the second interface of the differential test fixture via a 50-ohm characteristic impedance cable. Obtain the voltage ratio S between the second port and the first port of the calibrated two-port vector network analyzer at this time. 21 And denote it as S-parameter G CA ; Maintaining the connection configuration of the first port of the calibrated two-port vector network analyzer, connect the second port of the calibrated two-port vector network analyzer to the output of the differential probe via a 50-ohm characteristic impedance cable. Obtain the voltage ratio S between the second port and the first port of the calibrated two-port vector network analyzer at this point. 31 And denote it as S-parameter G DA .

4. The method for measuring differential probe gain using a two-port vector network analyzer according to claim 3, characterized in that, In step S4, the S-parameter matrix T Mt And the S-parameter matrix T in step S5 Ml These include the voltage ratio of incident current to reflected current at the first port of the calibrated two-port vector network analyzer, the voltage ratio of the first port to the second port of the calibrated two-port vector network analyzer, the voltage ratio of the second port to the first port of the calibrated two-port vector network analyzer, and the voltage ratio of incident current to reflected current at the second port of the calibrated two-port vector network analyzer.

5. The method for measuring differential probe gain using a two-port vector network analyzer according to claim 4, characterized in that, The specific method for obtaining the half-side transmission parameters of the differential test fixture in step S6 is as follows: According to the formula: T Mt =T C T Nt T D T Ml =T C T Nl T D For the half-side transmission parameter T of the differential test fixture C Perform a joint solution; where T Nt T is the identity matrix; D To transmit parameters to the other side of the differential test fixture, T Nl Let l be the transmission matrix of an ideal transmission line of unit length l.

6. The method for measuring differential probe gain using a two-port vector network analyzer according to claim 5, characterized in that, The specific method for obtaining the differential mode gain of the differential probe in step S7 is as follows: Based on the subsequent load and voltage division ratio, parameter T is transferred from one half of the differential test fixture. C Obtaining S-parameter G CB According to the formula: Obtain the differential mode gain G of the differential probe DB .

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