Active analog standard inductor and value setting method therefor

Abstract

The present invention relates to the field of precision electromagnetic metering, and specifically to an active analog standard inductor and a value setting method therefor. A resistor R2 in the active analog standard inductor is connected by means of a four-wire method and is divided into a high end and a low end, wherein the high end is divided into a high voltage end and a high current end, and the low end is divided into a low voltage end and a low current end; the high current end is connected to a high-level test wiring end H of the inductor, and the high voltage end is connected to a forward input end of a voltage follower F2; the low current end is connected to an output end of a voltage follower F1, and the low voltage end is connected to a negative input end of the voltage follower F1; one end of a capacitor C is connected in series to one end of a resistor R1, the other end of the capacitor C is connected to an output end of the voltage follower F2, and a negative input end of the voltage follower F2 is connected to the output end; a positive input end of the voltage follower F1 is connected to a node between the capacitor C and the resistor R1; and the other end of the resistor R1 is connected to a low-level test wiring end L of the inductor. The present invention has both long-term stability and a high Q value.

Description

Active analog standard inductor and its setting method TECHNICAL FIELD

[0001] The present application belongs to the field of precision electromagnetic measurement, and particularly relates to an active analog standard inductor and its setting method. BACKGROUND

[0002] A standard inductor is a physical measuring tool for calibrating inductance measuring instruments of various grades. According to different structures, the standard inductor can be divided into a wire-wound standard inductor, a network analog standard inductor and an electronic standard inductor. The standard inductor is generally defined by two ends, and has two inductance definition connection terminals, i.e., a high end (H) and a low end (L). The main defects of the standard inductor in the prior art are as follows: (1) the wire-wound standard inductor has a large volume, and the instability of the mechanical structure of the coil limits the long-term stability index of the standard inductor; and (2) the T-type network analog standard inductor has the disadvantages of low Q value (quality factor of inductance) and non-two-end definition type inductance, although the T-type network analog standard inductor has fewer resistance and capacitance elements and better stability. SUMMARY

[0003] The present application aims to solve the problems in the prior art, and provides an active analog standard inductor, which has long-term stability and a high Q value, can simulate the equivalent inductance value of inductance, and can simulate the impedance characteristics similar to those of the wire-wound standard inductor.

[0004] The present application is implemented by the following technical scheme:

[0005] An active analog standard inductor comprises a resistance R1, a resistance R2, a capacitance C, a voltage follower F1 and a voltage follower F2.

[0006] Two ends of the resistance R2 are a high end and a low end, respectively. The high end branch is a high-voltage end and a high-current end, and the low end branch is a low-voltage end and a low-current end.

[0007] The high-current end is connected with an inductor high-position test connection terminal H, and the high-voltage end is connected with a positive input end of the voltage follower F2. The low-current end is connected with an output end of the voltage follower F1, and the low-voltage end is connected with a negative input end of the voltage follower F1.

[0008] One end of the capacitance C is connected with one end of the resistance R1 in series, the other end of the capacitance C is connected with an output end of the voltage follower F2, and a negative input end of the voltage follower F2 is connected with the output end. A positive input end of the voltage follower F1 is connected with a node between the capacitance C and the resistance R1. The other end of the resistance R1 is connected with an inductor low-position test connection terminal L.

[0009] The resistance R2 has four terminals: high voltage terminal, high current terminal, low voltage terminal and low current terminal, and forms a four-wire connection through the four terminals, which can effectively reduce the influence of the resistance of the wire on the measurement accuracy.

[0010] In order to eliminate the current on the capacitor C branch, the voltage follower F2 is connected between the high voltage terminal H V and the capacitor C, and the positive input terminal and the negative input terminal of the voltage follower F2 have a "virtual break" characteristic, which is equivalent to being disconnected, so that the capacitor C branch will not have current flowing through it, thereby accurately realizing the four-wire definition of the resistance R2 and ensuring the accuracy of the final analog inductance value.

[0011] The connection of the resistance R2 realizes accurate four-wire definition, so even if the resistance R2 has a very small resistance value, it can still be accurately measured. The equivalent resistance R s of the active analog standard inductor of the present application is R2, and according to the general calculation formula of the Q value of inductance: Q=2πfL s / R s , it can be known that the smaller the equivalent resistance R s , the larger the Q value, so the active analog standard inductor of the present application can obtain a higher Q value by matching a smaller resistance R2.

[0012] Since the equivalent inductance value is no longer affected by the frequency, the nominal value of the equivalent inductance of the active analog standard inductor of the present application is determined according to the following formula: L s =CR1R2.

[0013] Therefore, by matching the parameters of the resistance R1, the resistance R2 and the capacitor C, the required equivalent inductance value Ls can be obtained, and the same magnitude range as the wire-wound standard inductor can be easily obtained, and inductances of the order of μH-H can be simulated. Moreover, since there is no mechanical structure of the coil, the long-term stability is determined by the resistance and capacitance elements, and compared with the wire-wound standard inductor, the active analog standard inductor has better long-term stability.

[0014] In order to realize fine adjustment of the active analog inductance value, preferably, the other end of the resistance R1 is connected to the low position test connection terminal of the inductor in series with the resistance R3. By regarding the resistance R3 as part of the resistance R1, the resistance value of the resistance R1 can be adjusted by adjusting the resistance value of the resistance R3, and the equivalent inductance of the active analog standard inductor can be adjusted by adjusting the resistance value of the resistance R1, thereby improving the accuracy of the nominal value of the active analog inductor. When the maximum resistance value of the resistance R3 is less than one thousandth of the resistance value of the resistance R1, the influence of the stability of the resistance R3 on the overall stability of the analog inductor can be ignored, and when the adjustable resolution of the resistance R3 is less than one ten-thousandth of the resistance value of the resistance R1, the nominal value error of the active analog inductor can be controlled within 0.01%.

[0015] When the inductance is simulated below mH value, the resistance of R2 needs to be less than or equal to 100Ω to obtain higher Q value. When the simulated inductance is tested (test voltage is applied), the voltage drop on the output impedance of voltage follower F1 will affect the following accuracy of voltage follower F1, and the influence is about 10 -5 ~10 -4 orders of magnitude, thus resulting in the change of simulated inductance value, and finally resulting in the load coefficient of active simulated inductor.

[0016] In order to reduce the load coefficient of active simulated inductor, preferably, a voltage follower F3 is inserted between voltage follower F1 and resistance R2: the positive input end of voltage follower F3 is connected with the output end of voltage follower F1, the output end of voltage follower F3 is connected with the low current end of resistance R2, and the negative input end of voltage follower F3 is connected with the output end through a wire. By combining the followers to form a closed loop feedback, the output impedance is reduced to micro-ohm (μΩ) order of magnitude, and for mH level inductance, the load coefficient of active simulated standard inductor can be reduced to ppm order of magnitude.

[0017] The active simulated standard inductor is packaged with a metal shielded shell, and the ground end G of the inductor is connected with the metal shielded shell. In order to realize the two-terminal definition of active simulated standard inductor, the voltage followers in the application are all powered by floating power supply, and the reference ground of floating power supply and the reference ground of input test signal are independent of each other, so that the active simulated inductor becomes an independent device to be measured.

[0018] Compared with the prior art, the beneficial effects of the application include:

[0019] 1. The stability index of the active simulated standard inductor of the application mainly depends on the stability index of three resistance-capacitance elements, and compared with the wire-wound standard inductor, the long-term stability can be achieved, and the long-term stability index can be less than 3uH / H, and the temperature coefficient index can be controlled within 3ppm / ℃.

[0020] 2. Compared with the T-type network simulated standard inductor, the application has higher Q value and wider range of inductance value.

[0021] 3. The nominal value error of the active simulated standard inductor of the application is extremely small, and can be adjusted to within 0.01%. BRIEF DESCRIPTION OF DRAWINGS

[0022] Fig. 1 is a schematic diagram of a T-type network simulated standard inductor in the prior art;

[0023] Fig. 2 is a schematic diagram of an active simulated inductor circuit in the prior art;

[0024] Fig. 3 is a schematic diagram of an active analog standard inductor according to the present application;

[0025] Fig. 4 is a schematic diagram of an active analog standard inductor according to the present application in Example 1;

[0026] Fig. 5 is a schematic diagram of an active analog standard inductor according to the present application in Example 2. DETAILED DESCRIPTION

[0027] As shown in Fig. 1, the T-network analog standard inductor has good long-term stability, but its equivalent resistance R S = R1+R2, according to the general formula for the Q value of an inductor: Q = 2πfL s / R s , it can be seen that due to its large equivalent resistance, it is difficult to obtain a high Q value, and when the equivalent inductance is in the order of μH or mH, the low Q value will not be able to well simulate the impedance characteristics of the inductor, so the range of inductance values that can be simulated is very limited.

[0028] The present application combines a voltage follower with a precise four-wire defined resistor to greatly reduce the equivalent resistance of the active analog standard inductor, improve the Q value, and widen the range of inductance values.

[0029] In order to make the present application easier to understand, before formally introducing the technical solutions of the present application, an active analog inductor circuit of Fig. 2 is provided for comparative description.

[0030] The effective series inductance value L s , the equivalent series resistance R s and the Q value of the active analog inductor circuit in Fig. 2 are as follows: R s ≈R2 (2) Q=ωC(R1-R2) / (1+ω 2 C 2 R1R2) (3)

[0031] As can be seen from formulas (1)-(3), the equivalent series resistance R s of Fig. 2 is approximately equal to R2, but its equivalent inductance L s and Q value are both frequency-dependent.

[0032] In Fig. 2, there is still a small current in the branch of resistance R2 connected to the capacitor C, and the size of the current changes with frequency, and its influence makes the simulated inductance value frequency-dependent. That is, under different frequency test signals, the simulated inductance in Fig. 2 changes with frequency, so it is not suitable for use in a metrological standard.

[0033] In addition, the active analog standard inductor circuit in Figure 2 belongs to a grounded inductor, while the conventional standard inductor is floating. In order to realize the two-terminal definition of the active analog standard inductor, as shown in Figure 3, the application adopts a metal shielded housing package, and the ground terminal G of the inductor is connected to the metal shielded housing. The application adopts a floating power supply to supply power to the active circuit, and the reference ground of the floating power supply and the reference ground of the input test signal are independent of each other, so that the active analog inductor becomes an independent device to be measured. In order to eliminate the correlation between the equivalent inductance and the frequency, the application adds a voltage follower F2, as shown in Figure 3, and proposes an active analog standard inductor, which comprises a resistor R1, a resistor R2, a capacitor C, a voltage follower F1 and a voltage follower F2.

[0034] The resistor R2 is connected by a four-wire method and is divided into a high end and a low end. The high end branch is a high voltage end and a high current end, and the low end branch is a low voltage end and a low current end.

[0035] The high current end is connected to the high position test connection end of the inductor, and the high voltage end is connected to the positive input end of the voltage follower F2. The low current end is connected to the output end of the voltage follower F1, and the low voltage end is connected to the negative input end of the voltage follower F1.

[0036] One end of the capacitor C is connected in series with one end of the resistor R1, and the other end of the capacitor C is connected to the output end of the voltage follower F2. The negative input end and the output end of the voltage follower F2 are connected by a wire. The positive input end of the voltage follower F1 is connected to the node between the capacitor C and the resistor R1. The other end of the resistor R1 is connected to the low position test connection end of the inductor.

[0037] Because the positive input end and the negative input end of the voltage follower F2 have a "virtual break" characteristic, which is equivalent to being disconnected, the capacitor C branch will no longer have current flowing through it, which can eliminate the correlation between the equivalent inductance and the frequency, and ensure that the four-wire definition of the resistor R2 is accurately realized, and the accuracy of the final analog inductance value is ensured. Therefore, the equivalent inductance value L s , the equivalent resistance value R s and the Q value of the active analog inductor standard device of the application are as follows: L s = CR1R2 (4) R s = R2 (5) Q = ωCR1 (6)

[0038] As can be seen from formulas (4) to (6), the equivalent series inductance L s and the Q value of the active analog inductor in Figure 3 are independent of the frequency, and the equivalent series resistance R s value is equal to R2.

[0039] The equivalent resistance R of the active analog standard inductor of the present application s = R2, according to the general calculation formula of the Q value of inductance: Q = 2πfL / R s , it can be known that the equivalent resistance R s is smaller, the Q value is larger, therefore the active analog standard inductor of the present application can obtain a higher Q value by matching a smaller resistance R2.

[0040] In addition, the output impedance of the single follower F1 in Fig. 2 is generally in the order of milliohms (mΩ), if the resistance R2 is set to 10Ω or below, when testing the analog inductance (applying a test voltage), the voltage drop on the output impedance of the precision follower F1 will affect the following precision of the follower F1, which will affect the analog inductance value in the order of 10 -5 ~ 10 -4 orders of magnitude, ultimately resulting in a certain load coefficient of the active analog inductor.

[0041] Embodiment 1

[0042] In order to reduce the load coefficient of the active analog inductor, according to Fig. 4, the present application inserts a voltage follower F3 between the voltage follower F1 and the resistance R2: the positive input end of the voltage follower F3 is connected with the output end of the voltage follower F1, the output end of the voltage follower F3 is connected with the low current end of the resistance R2, and the negative input end of the voltage follower F3 is connected with the output end through a wire. By combining the followers to form a closed loop feedback, the output impedance is reduced to the order of micro-ohms (μΩ), and for mH-level inductors, the load coefficient of the active analog standard inductor can be reduced to the order of ppm.

[0043] Embodiment 2

[0044] Although theoretically, high-precision metal foil resistors and high-precision multilayer ceramic capacitors can obtain high-precision equivalent inductance, some stray distributed parameters will inevitably exist in the circuit, resulting in a decrease in the precision of the equivalent inductance, i.e. an increase in the error between the actual value and the nominal value of the equivalent inductance.

[0045] In order to realize fine adjustment of the active analog inductance value, on the basis of Embodiment 1, in the present embodiment, the other end of the resistance R1 is connected with the low-position test wiring end L after being connected in series with the resistance R3. The resistance R3 can be a fixed resistance or an adjustable resistance.

[0046] The resistance R3 is regarded as a part of the resistance R1, and the resistance R1 can be adjusted by adjusting the resistance R3. According to the formula (4), the equivalent inductance of the active analog inductor can be adjusted by adjusting the resistance R1, and the precision of the nominal value of the active analog inductor can be improved. When the maximum resistance of the resistance R3 is less than one ten-thousandth of the resistance of the resistance R1, the stability of the resistance R3 can be ignored. When the adjustable resolution of the resistance R3 is less than one hundredth of the resistance of the resistance R1, the nominal value error of the active analog inductor can be controlled within 0.01%.

[0047] When setting the value, the actual value of the capacitance parameter is configured to be slightly lower than the nominal value, for example, the nominal value is 100 nF, but the actual value is 99.98 nF. In this way, the resistance R1 is increased by adjusting the resistance R3, and the resistance R1 is increased to the extent that the stray interference is balanced to obtain the equivalent inductance within the nominal value error range.

[0048] Embodiment 3

[0049] In this embodiment, the active analog inductor with the required equivalent inductance value is obtained by matching the resistance and capacitance parameters of the active analog inductor in Embodiment 2. According to the formula for calculating the nominal value of the equivalent inductance of the active analog inductor: L s = CR1R2, the resistance and capacitance parameters are matched to meet the required equivalent inductance value; in the formula, L s represents the equivalent inductance value, C represents the capacitance value of the capacitance C, R1 represents the resistance value of the resistance R1, and R2 represents the resistance value of the resistance R2.

[0050] The configuration parameters of the 100 μH-1 H analog inductor are shown in Table 1.

[0051] Table 1

[0052] As shown in Table 1, to realize the active analog inductor with high stability, the resistance unit uses a precision metal foil resistance, the capacitance unit uses a high-precision multilayer ceramic capacitor (NP0) unit, and the related resistance and capacitance units are screened by parameters. The long-term stability index of the active analog inductor can be less than 3 uH / H, and the temperature coefficient index can be controlled within the range of 3 ppm / °C.

[0053] According to the parameters in Table 1, when the order of magnitude of the required equivalent inductance value is μH or mH, the resistance value R1 of the resistance R1 is much greater than the resistance value R2 of the resistance R2: the resistance value R1 of the resistance R1 is more than 100 times the resistance value R2 of the resistance R2; and the resistance value R2 of the resistance R2 is within the range of 100 Ω, and a Q value comparable to a wound standard inductor can be obtained.

[0054] Embodiment 4

[0055] In order to realize the two-terminal definition of the active analog standard inductor, the voltage follower is powered by a floating power supply (such as +VCC and -VCC in Figures 3, 4 and 5), and in the embodiment, the floating power supply simultaneously powers the voltage follower F1, the voltage follower F2 and the voltage follower F3. The reference ground of the floating power supply is independent of the reference ground of the input test signal, so that the active analog standard inductor becomes an independent device to be measured.

[0056] The floating power supply can be an isolated DC power supply or a battery.

[0057] The application further comprises a metal shielding shell for packaging the active analog standard inductor, and the ground terminal G of the active analog standard inductor is connected to the metal shielding shell. The metal shielding shell encapsulates the resistor R1, the resistor R2, the capacitor C, the voltage follower F1, the voltage follower F2, the voltage follower F3 and the resistor R3.

[0058] The measuring instrument (LCR meter) can be tested by connecting the high and low test terminals of the Kelvin clip to the high terminal test terminal H and the low terminal test terminal L of the active analog standard inductor. There are two methods for inductance testing: a) two-terminal method: the high and low test terminals are connected to the H terminal and the L terminal of the inductor, and the ground terminal G is connected to the L terminal in short circuit; b) three-terminal method: the high and low test terminals are connected to the H terminal and the L terminal of the inductor, and the shell ground of the measuring instrument is connected to the ground terminal G of the standard inductor.

[0059] In summary, the application realizes a high-precision inductance measurement standard instrument, solves the technical problems of wide-range inductance value simulation, low analog inductance Q value and poor stability index, and realizes a high-grade inductance measurement instrument with extremely high stability, extremely small nominal value error and temperature coefficient.

[0060] In the description of the application, it should be noted that, unless otherwise specified and limited, the terms "connected", "connected" should be understood broadly, for example, it can be fixedly connected, or detachably connected, or integrally connected; it can be mechanically connected, or electrically connected; it can be directly connected, or indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0061] In the description of the application, unless otherwise stated, the terms "upper", "lower", "left", "right", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the application and simplifying the description, and does not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore it cannot be understood as a limitation on the application.

[0062] The technical solutions described above are only specific embodiments of the present application. Those skilled in the art can make various types of improvements or modifications on the basis of the disclosed principles without being limited to the technical solutions described in the above specific embodiments. Therefore, the above description is only preferred and not limiting.

Claims

1. An active analog standard inductor, characterized in that, This includes resistor R1, resistor R2, capacitor C, voltage follower F1, and voltage follower F2; The resistor R2 is connected using a four-wire method, divided into a high-end and a low-end. The high-end branch is the high-voltage end and the high-current end, and the low-end branch is the low-voltage end and the low-current end. The high current terminal is connected to the high-position test terminal H of the inductor, and the high voltage terminal is connected to the positive input terminal of the voltage follower F2; the low current terminal is connected to the output terminal of the voltage follower F1, and the low voltage terminal is connected to the negative input terminal of the voltage follower F1. One end of the capacitor C is connected in series with one end of the resistor R1, and the other end of the capacitor C is connected to the output terminal of the voltage follower F2. The negative input terminal and the output terminal of the voltage follower F2 are connected by a wire. The positive input terminal of the voltage follower F1 is connected to the node between the capacitor C and the resistor R1. The other end of the resistor R1 is connected to the low-position test terminal L of the inductor.

2. The active analog standard inductor according to claim 1, characterized in that, It also includes a voltage follower F3, whose positive input terminal is connected to the output terminal of voltage follower F1, whose output terminal is connected to the low current terminal of resistor R2, and whose negative input terminal is connected to the output terminal.

3. The active analog standard inductor according to claim 2, characterized in that, It also includes a floating power supply that simultaneously powers voltage followers F1, F2, and F3.

4. The active analog standard inductor according to claim 1, characterized in that, Resistors R1 and R2 are both metal foil resistors, and capacitor C is a multilayer ceramic capacitor.

5. The active analog standard inductor according to claim 1, characterized in that, It also includes a metal shielding housing for encapsulating an active analog standard inductor, with the ground terminal G of the active analog standard inductor connected to the metal shielding housing.

6. The active analog standard inductor according to any one of claims 1 to 5, characterized in that, The other end of resistor R1 is connected in series with resistor R3 and then connected to the low-position test terminal L of the inductor.

7. A method for setting the value of an active analog standard inductor as described in any one of claims 1 to 5, characterized in that, The nominal value of the equivalent inductance of an active analog standard inductor is calculated using the following formula: L s =CR1R2, to perform resistance and capacitance parameter matching to meet the required equivalent inductance value; where L s The values ​​represent the equivalent inductance, C represents the capacitance of capacitor C, R1 represents the resistance of resistor R1, and R2 represents the resistance of resistor R2.

8. The method for setting the value of an active analog standard inductor according to claim 7, characterized in that, When the required equivalent inductance value is on the order of μH or mH, the resistance value R1 of resistor R1 is much larger than the resistance value R2 of resistor R2.

9. The method for setting the value of an active analog standard inductor according to claim 8, characterized in that, The resistance value of resistor R2 is less than or equal to 100Ω, and the resistance value of resistor R1 is more than 100 times that of resistor R2.

10. The method for setting the value of an active analog standard inductor according to claim 7, characterized in that, The other end of resistor R1 is connected in series with resistor R3 and then connected to the low-position test terminal L of the inductor; the maximum resistance of resistor R3 is less than one-thousandth of the resistance of resistor R1. The error between the measured and nominal values ​​of the equivalent inductance of the active analog standard inductor is reduced by adjusting the value of resistor R3.

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