TWI447401B - Method for circuit stability compensation - Google Patents

Description

Circuit stability compensation method

The present invention relates to a circuit stability compensation method, and more particularly to a circuit stability compensation method for calculating a feedback circuit characteristic of an impedance measurement circuit and compensating for a phase of the impedance measurement circuit.

Generally, in the impedance measurement module, each component is connected to each other through a cable. However, during the measurement signal transmission, the cable tends to cause a phase difference of the measurement signal, so that the impedance measurement is performed. There are errors in the results. Therefore, when the conventional impedance measurement module uses the four-terminal pairs method for impedance measurement in the low frequency range, a calibration procedure is required. For example, Hideki's conventional method of impedance measurement is mentioned in U.S. Patent No. 6,054,867. Among them, Hideki pointed out that at least three or more standard impedances with different measured values need to be used in the impedance measurement, and are respectively connected to the impedance measuring module for three or more calibrations. That is to say, the traditional impedance measurement method uses three or more calibrations to eliminate the influence factors of the cable connecting the device under test (DUT), such as the cable material, length, or other reasons. Accurate measurement.

However, multiple replacements of the standard impedance increase the calibration time that is required, and other errors may occur when replacing the standard impedance. Furthermore, as the measurement frequency increases, the phase shift angle (Phase Shift) generated by the connection line connecting the objects to be tested not only reduces the accuracy of the measurement, but also the feedback circuit in the impedance measurement module. The displacement of the phase causes instability of the overall system. Therefore, in order to maintain the stability of the measurement, the conventional design method imposes strict restrictions (including material, length, etc.) on the cable used for measurement in the feedback path, and reduces the use of the impedance measurement module. Flexibility.

Therefore, a new circuit stability compensation method is needed for the above problem, so that in the high-frequency impedance measurement, the phase compensation can be used to solve the problem of measurement accuracy and stability caused by different cables during high-frequency measurement.

The invention discloses a circuit stability compensation method, which enables the impedance measuring device to calculate the phase shift angle of the feedback circuit in the impedance measuring device when performing the high-frequency impedance measurement, and solve the high-frequency measurement amount through the phase compensation. Measure accuracy and stability issues.

The invention provides a circuit stability compensation method for calibrating an impedance measuring device having a feedback circuit. The circuit stability compensation method comprises the steps of: providing a first standard impedance to perform a first measurement procedure; providing a second standard impedance to perform a second measurement procedure; and measuring results by the first measurement procedure and the second measurement procedure Calculating a phase shift angle of one of the feedback circuits; performing a calibration procedure according to the phase shift angle, the calibration procedure adjusting the frequency response characteristic of the impedance measuring device.

In an exemplary embodiment, the first measurement procedure of the present invention includes the steps of: providing a first standard voltage in a first current loop of one of the impedance measuring devices; generating a corresponding first standard impedance from the first current loop One of the first measurement voltages; in the second current loop of one of the impedance measuring devices, a second standard voltage is provided; and from the second current loop, a second measurement voltage corresponding to one of the first standard impedances is generated. In addition, the second measurement procedure includes the steps of: providing a first standard voltage in the first current loop of the impedance measuring device; generating a third measuring voltage corresponding to one of the second standard impedances from the first current loop; A second standard voltage is provided in the second current loop of the device; and a fourth measured voltage corresponding to one of the second standard impedances is generated from the second current loop.

Therefore, the circuit stability compensation method of the present invention utilizes two objects of known impedance and two sets of controllable signal sources to determine the feedback circuit characteristics of the impedance measuring device, so that when the impedance measuring device is placed into any test In the case of the object, the optimal phase compensation amount can be adjusted so that the impedance measuring device is not limited by the feedback circuit and the test cable, and the accuracy and stability of the system can be maintained.

The advantages and spirit of the present invention will be further understood from the following detailed description of the invention.

Please refer to Figure 1A and Figure 1B together. Figure 1A is a functional block diagram showing an impedance measuring apparatus to which the present invention is applied. The circuit stability compensation method of the present invention is used to calibrate the impedance measuring device 2, and the impedance measuring device 2 has at least one feedback circuit. The flow of the circuit stability compensation method of the present invention and the corresponding components will be separately described below.

As shown in FIG. 1A, the impedance measuring device 2 is a four-wire measuring carrier, such that the measuring object carrier 60 is connected to the measuring cable 20, the measuring cable 30, the measuring cable 40 and the measuring cable 50, respectively. . The resistor 21, the current loop switch 22 and the signal source 23 are connected to the first end 61 of the object carrier 60 through the measuring cable 20, and the current loop switch 22 is used to switch the measuring cable 20 to be connected to the signal source. 23 or connect to the potential ground. The test object stage 60 is used to set a standard impedance and other unknown impedance objects to be tested. In addition, the vector potentiometer 31 is connected to the first end 61 of the object-mounting stage 60 through the measuring cable 30.

On the other hand, between the measurement cable 40 and the measurement cable 50 is a feedback circuit. One end of the measurement cable 40 is connected to the second end 62 of the test object stage 60, and the other end of the measurement cable 40 is connected to the input amplifier 41, the vector potentiometer 42, the current loop switch 43, the narrowband high gain amplifier 44, Current loop switch 45, signal source 46, and output amplifier 47. Further, a resistor 51 is connected between the output of the output amplifier 47 and the measurement cable 50, and the resistor 51 is connected to the second end 62 of the object carrier 60 through the measurement cable 50.

For convenience of explanation, FIG. 1A is simplified here as the Thevenin equivalent circuit as shown in FIG. Figure 1B is a schematic diagram showing an equivalent circuit of an impedance measuring apparatus to which the present invention is applied. As shown in FIG. 1B, the impedance Z ₁ and the impedance Z ₂ are respectively the wearer equivalent impedance values seen from the first end 61 and the second end 62 to the ground, and the signal source 70 and the signal source 71 respectively represent two. The Thevenin equivalent signal source, the input amplifier 73 has an open loop gain value A. Wherein, when the signal source 23 is used to provide the E ₁ voltage, and the signal source 46 is used to provide the E _φ voltage, the signal source 70 and the signal source 71 respectively provide the K ₁ E ₁ voltage and the K _φ E _φ voltage, K ₁ , K _φ , A, Z ₁ , and Z ₂ are all complex variables. In the following, with the circuit stability compensation method of the present invention, how to obtain these variables by switching the different signal sources and the measured values of the vector potentiometer 72.

The current loop switch 74 integrates the current loop switch 43 and the current loop switch 45. For example, when the current loop switch 43 is not turned on and the current loop switch 45 is connected to the ground potential, it is equivalent to being seen from the second end 62 of the object carrier 60, and the current loop switch 74 is connected to the potential. ground.

Please refer to FIG. 1B, FIG. 2 and FIG. 3 together. FIG. 2 is a flow chart showing a circuit stability compensation method according to an exemplary embodiment of the present invention. Figure 3 is a flow chart showing a first measurement procedure in accordance with the present invention. As shown in the figure, in step S10, the standard impedance Z _{xs1 is first} placed in the object carrier 60 to perform a first measurement procedure. Here, the first measurement procedure can be further explained by steps S102 to S108. In step S102, when the standard impedance Z _{xs1 is} placed in the object carrier 60, a current loop is formed, which is determined by the current loop switch 22 and the current loop switch 74. In this step, the current loop switch 22 of the impedance measuring device 2 is connected to a signal source 70 which is connected to the potential ground. Thereby, a current source of the signal source 70, the impedance Z ₁ , the standard impedance Z _xs1 and the impedance Z ₂ to be grounded can be formed in the impedance measuring device 2.

In step S104, the vector potentiometer 72 can generate a measured voltage V _φ1 corresponding to one of the standard impedances Z _xs1 in the current loop of step S102, wherein the measured voltage can be calculated from the equivalent circuit of the impedance measuring device 2 of FIG. V _{φ1 is} as shown in the following formula (1).

In step S106, the impedance measuring device 2 is further switchable to another current loop such that the current loop switch 22 is connected to the potential ground, and the current loop switch 74 is connected to the signal source 71. Thereby, a current source of the signal source 71, the impedance Z ₂ , the standard impedance Z _xs1 and the impedance Z ₁ to be grounded can be formed in the impedance measuring device 2.

In step S108, the vector potentiometer 72 can generate a measurement voltage V _φ2 corresponding to one of the standard impedances Z _xs1 in the current loop of step S106, wherein the equivalent circuit of the impedance measuring device 2 of FIG. 1B can calculate the first The voltage V _{φ2 is} measured as shown in the following equation (2).

Similarly, in step S12, the impedance measuring device 2 can generate two current loops by switching the current loop switcher 22 and the current loop switcher 74 to generate the measured voltage V _φ3 corresponding to the standard impedance Z _xs2 and the measured voltage V. _{Φ4 is} as shown in the following formulas (3) and (4).

Next, in step S14, by using the known standard impedances Z _xs1 and Z _xs2 and the respective measured voltages, it is possible to separately derive the Thevenin equivalent of the impedance measuring device 2 at the first end 61 and the second end 62 to the ground. Impedance Z ₁ and impedance Z ₂ . They are shown in the following equations (5) and (6), respectively.

Among them, the four transfer function values C ₁ , C ₂ , C ₃ and C ₄ are (V _φ1 /E ₁ ), (V _φ2 /E _φ ), (V _φ3 /E ₁ ) and (V _φ4 /E _{φ , respectively).} And, of course, the transfer function values C ₁ , C ₂ , C _{3 ,} and C ₄ described above are derived from equations (1), (2), (3), and (4), respectively, and are not described herein. In practice, the transfer function values C ₁ , C ₂ , C ₃ and C ₄ can be considered as known, for example, when the signal source 23 provides the E ₁ voltage and the measured voltage V _φ1 is known, the transfer function value C ₁ Of course, it can be easily learned.

Further, in the technical field to which the present invention pertains, a person skilled in the art can further derive a feedback loop transfer function G of the impedance measuring device 2 through the calculation result of the step S14, as shown in the following formula (7).

Here, Z ₀ = Z ₁ + Z ₂ , K ^' _φ = AK _φ , and Z _x can be any impedance or standard impedance Z _xs1 , Z _xs2 . In general, the feedback loop transfer function G can be expressed in the following form as shown in the following formula (8).

When the equations (7) and (8) are compared, K _p and K _q can be derived by the following equation (9) and the following equation (10).

When expressed by the transfer function values C ₁ , C ₂ , C ₃ and C ₄ described above, K _p and K _q can further represent the following formula (11) and the following formula (12).

Z ₀ can be expressed as shown in the following formula (13).

It can be seen from equations (11), (12), (13) that the circuit stability compensation method of the present invention can utilize two known standard impedances (Z _xs1 and Z _xs2 ), and four transfer function values C _{1 .} , C ₂ , C ₃ , C ₄ , can calculate the three parameter values of K _p , K _q , Z _o . In practical applications, when any impedance Z _x is brought in, the feedback loop transfer function G may correspond to the impedance Z _x to a complex plane, and the corresponding result impedance Z _x should fall on the right half of the complex plane.

Please refer to Figure 4. Figure 4 is a schematic diagram showing the corresponding impedance of the feedback loop transfer function to the complex plane. As shown, when any impedance Z _x is brought in, the impedance Z _x is located on the right half of the complex plane, and the centroid coordinate value can be calculated, and then the phase shift angle a of the center of the circle and the real axis of the complex plane is obtained. However, it should be apparent to those skilled in the art that the narrowband high gain amplifier has a phase characteristic of ±90° in the strip, so the phase range of the loopback transfer function of Figure 4 covers the positive real axis of the complex plane. From the point of view of the characteristic equation of the control theory, if the feedback loop covers the coordinates (1, 0) in Figure 4, the impedance measuring device will oscillate, resulting in unstable measurement.

Therefore, in order to prevent the impedance measuring device from oscillating, the present invention performs a calibration procedure in accordance with the phase shift angle described above in step S16, and the calibration procedure can adjust the frequency response characteristic of the impedance measuring device. In this step, the present invention adjusts the phase range of the feedback loop transfer function so that it does not cover the positive real axis of the complex plane. Take Figure 5 as an example, please refer to Figure 5. Figure 5 is a schematic diagram showing the adjustment feedback loop transfer function. As shown in FIG. 5, the calibration procedure of the present invention converts the phase range of the feedback loop transfer function to the left half of the complex plane, and limits the center coordinate position to the negative real axis to avoid coordinates on the complex plane (1) , 0) location. Further, if the phase shift angle a has been calculated in advance, it is of course possible to use a variable phase shifter to make a phase shift of 180° -a such that the phase angle of the feedback loop encompasses the positive real axis of the complex plane. Here, since there are many methods for adjusting the phase range of the feedback loop transfer function, the present invention is not limited, and those skilled in the art can determine at their own discretion.

It is worth noting that the traditional impedance measurement method usually includes open measurement, short measurement, and load measurement. That is, the impedance of the object to be measured should be infinite. Large, zero, and other impedance values. However, it should be understood by those having ordinary skill in the art that when performing high frequency testing, the object to be tested tends to couple signals in the environment, so it is quite difficult to require the impedance of the object to be measured to be infinitely large, and at the same time It is easy to cause measurement errors.

However, the present invention differs from the conventional impedance measurement method in that the present invention only needs to pass two standard impedances to calculate the feedback circuit characteristics of the impedance measuring device. Thereby, the present invention does not necessarily select an open circuit measurement, but can select a short circuit measurement and a load measurement, which not only reduces the non-ideal situation at the time of high frequency measurement, but also more accurately calculates the feedback circuit characteristic of the impedance measuring device.

In summary, the circuit stability compensation method of the present invention utilizes two objects of known impedance and two sets of controllable signal sources to determine the feedback circuit characteristics of the impedance measuring device. Compared with the conventional technology, the conventional technology often needs to use three or more known impedances of the object to determine the feedback circuit characteristics of the impedance measuring device. Therefore, the present invention can further simplify the measurement process and speed up the measurement. In addition, when the impedance measuring device is placed in any object to be tested, the present invention can adjust the optimal phase compensation amount so that the impedance measuring device is not limited by the feedback circuit and the test cable, and the accuracy of the system can be maintained. stability.

The features and spirit of the present invention will be more apparent from the detailed description of the preferred embodiments. On the contrary, the intention is to cover various modifications and equivalents within the scope of the invention as claimed.

2. . . Impedance measuring device

20, 30, 40, 50. . . Measuring cable

21, 51. . . resistance

22, 43, 45, 74. . . Current loop switcher

23, 46, 70, 71. . . signal source

31, 42, 72. . . Vector potentiometer

41, 44, 47, 73. . . Amplifier

60. . . Dust-bearing stage

61. . . First end

62. . . Second end

Z ₁ , Z ₂ . . . impedance

S10~S16, S102~S108. . . Process step

Figure 1A is a functional block diagram showing an impedance measuring apparatus to which the present invention is applied.

Figure 1B is a schematic diagram showing an equivalent circuit of an impedance measuring apparatus to which the present invention is applied.

2 is a flow chart showing a circuit stability compensation method according to an exemplary embodiment of the present invention.

Figure 3 is a flow chart showing a first measurement procedure in accordance with the present invention.

Figure 4 is a schematic diagram showing the corresponding impedance of the feedback loop transfer function to the complex plane.

Figure 5 is a schematic diagram showing the adjustment feedback loop transfer function.

S10~S16. . . Step flow

Claims (7)

A circuit stability compensation method for calibrating an impedance measuring device, the impedance measuring device having a feedback circuit, the method comprising the steps of: providing a first standard impedance to perform a first measurement procedure, wherein the first measurement The program includes the steps of: providing a first standard voltage in a first current loop of the impedance measuring device; and generating, from the first current loop, a first measured voltage corresponding to one of the first standard impedances; Providing a second standard voltage in one of the second current loops of the measuring device; and generating a second measured voltage corresponding to one of the first standard impedances from the second current loop; providing a second standard impedance to perform a first a second measurement program, wherein the second measurement program comprises the steps of: providing the first standard voltage in the first current loop of the impedance measuring device; and generating a corresponding second standard impedance from the first current loop a third measurement voltage; the second standard voltage is provided in the second current loop of the impedance measuring device; and the second current is a fourth measurement voltage corresponding to one of the second standard impedances; a phase shift angle of one of the feedback circuits is calculated by the first measurement program and the measurement result of the second measurement program; and the phase shift angle is determined according to the phase shift angle A calibration procedure is performed that adjusts the frequency response characteristics of the impedance measuring device. The circuit stability compensation method according to claim 1, wherein the step of calculating the phase shift angle of the feedback circuit is based on the first standard impedance, the second standard impedance, and the first standard. The voltage, the second standard voltage, the first measured voltage, the second measured voltage, the third measured voltage, and the fourth measured voltage are used to calculate the phase shift angle. The circuit stability compensation method according to claim 1, wherein the step of calculating the phase shift angle of the feedback circuit includes the following steps: calculating a first standard voltage from the first measurement voltage a first transfer function; calculating a second transfer function from the second standard voltage and the second measured voltage; calculating a third transfer function from the first standard voltage and the third measured voltage; and the second standard voltage The fourth measured voltage calculates a fourth transfer function; and calculates the phase shift angle according to the first transfer function, the second transfer function, the third transfer function, and the fourth transfer function. The circuit stability compensation method of claim 1, wherein the second measurement procedure comprises the steps of: providing a first standard voltage in a first current loop of the impedance measuring device; a third measurement voltage corresponding to one of the second standard impedances is generated in the current loop; a second standard voltage is provided in the second current loop of the impedance measuring device; and a corresponding voltage is generated from the second current loop One of the second standard impedances is the fourth measured voltage. The circuit stability compensation method of claim 4, wherein the first measurement procedure comprises the step of: providing the first standard voltage in the first current loop of the impedance measuring device; a first measurement voltage corresponding to one of the first standard impedances is generated in the current loop; the second standard voltage is provided in the second current loop of the impedance measuring device; and correspondingly generated from the second current loop One of the first standard impedances is the second measured voltage. The circuit stability compensation method according to claim 5, wherein the step of calculating the phase shift angle of the feedback circuit is based on the first standard impedance, the second standard impedance, and the first standard The voltage, the second standard voltage, the first measured voltage, the second measured voltage, the third measured voltage, and the fourth measured voltage are used to calculate the phase shift angle. The circuit stability compensation method of claim 5, wherein the step of calculating the phase shift angle of the feedback circuit comprises the steps of: calculating a first standard voltage from the first measurement voltage a first transfer function; calculating a second transfer function from the second standard voltage and the second measured voltage; calculating a third transfer function from the first standard voltage and the third measured voltage; and the second standard voltage The fourth measured voltage calculates a fourth transfer function; and calculates the phase shift angle according to the first transfer function, the second transfer function, the third transfer function, and the fourth transfer function.