Voltage-controlled magnetic tuning device and frequency control method

Abstract

The invention discloses a voltage-controlled magnetic tuning device and a frequency control method, and belongs to the technical field of magnetic devices, the voltage-controlled magnetic tuning device comprises a magnetic circuit (11), a coil (12) and a resonance circuit (13), and is characterized by further comprising a temperature compensation resistor (14), the coil (12) is connected with the temperature compensation resistor (14) in series, the resistance value RL of the coil (12) is far larger than the resistance value Rb of the temperature compensation resistor (14), and the resistance value Rb of the temperature compensation resistor (14) is larger than the resistance value Rb of the temperature compensation resistor (14). The resistance temperature coefficient of the coil (12) is opposite to that of the temperature compensation resistor (14), and the resistance temperature coefficient of the coil (12) is far smaller than that of the temperature compensation resistor (14); when the voltage-controlled magnetic tuning device is applied, a traditional current exciter can be omitted, so that the application size is greatly reduced, the application cost is reduced, in addition, the joint debugging and temperature compensation processes of a filter and the exciter are omitted, the production efficiency is further improved, and the production cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic devices, and particularly to a voltage-controlled magnetic tuning device and a frequency control method. Background Art

[0002] The operating frequency of a magnetic tuning device can be set according to the user's usage requirements. The accuracy and temperature stability of the set frequency are the prerequisites for application. The working principle of a magnetic tuning device is the ferromagnetic resonance principle, that is, on the premise of meeting the resonance conditions, the resonance frequency of the ferrite resonator (i.e., the working frequency of the filter) is proportional to the externally applied magnetic field. The magnetic circuit and the coil are combined to form an electromagnet. The air gap of the magnetic circuit is used to provide the magnetic field. Ignoring the losses of the magnetic circuit, the magnitude of the magnetic field (resonance frequency) is proportional to the coil NI (N number of turns, I current) and inversely proportional to the length of the air gap of the magnetic circuit. The number of turns of the coil and the air gap of the magnetic circuit are set. When the current is stable, the magnetic field (resonance frequency) is stable. Therefore, the stability of the current is the main factor for the frequency stability of the magnetic tuning filter. There are also some secondary factors affecting frequency stability, such as the temperature instability of the soft magnetic alloy material μ of the magnetic circuit, the Ms of the ferrite single crystal small ball, and the size of the air gap of the magnetic circuit.

[0003] In the prior art, in order to solve the problem of the frequency stability of a magnetic tuning filter, a common method is to use a magnetic tuning device in combination with an exciter. Specifically, such as Figure 1As shown in the figure, the lead-out ends of the coil 12 of the magnetic tuning device 1 are connected to the current output end of the current exciter 2; the magnetic tuning device is composed of three main units: a magnetic circuit 11, a coil 12, and a resonant circuit 13. The magnetic circuit 11 and the coil 12 form an electromagnet. The magnetic circuit 11 is provided with an air gap. The resonator unit in the RF circuit is placed in the air gap. When the coil is energized, a magnetic field is generated at the air gap, and the magnetic field excites the resonator to resonate at the corresponding frequency. If different forms of RF circuits are designed, filters (band-pass / band-stop) or oscillators with magnetic field-controlled frequencies can be obtained. In the prior art, all the electromagnet coils are wound with copper enameled wires. The temperature coefficient of copper enameled wires is about 4000 ppm, and there is about a 40% resistance change in a 100°C wide temperature range. If a fixed voltage is applied to the coil, the current changes by 40%, and the device frequency will also change by 40%. Obviously, a DC voltage cannot be directly applied to the coil. Therefore, in the prior art, the magnetic tuning device uses the current exciter 2 to supply power to the coil 12. The reason is that the current exciter has a very large internal resistance, which can obtain a stable current regardless of the large change in the resistance of the coil 12. At the same time, the current exciter 2 can also be designed with a temperature compensation network to compensate for other frequency instability factors from current to frequency stability. The current exciter 2 uses a current negative feedback amplifier circuit. Taking the analog exciter as an example, the current exciter circuit mainly includes basic units such as a digital-to-analog conversion unit 21, a reference voltage unit 22, an operational amplifier unit 23, a current amplification unit 24, a sampling resistor Rs, a temperature compensation network T, and supporting resistors, capacitors and other components. The circuit is complex. If it is a digital exciter, a control unit such as a CPU or FPGA needs to be added, and the circuit structure is more complex and the cost is higher.

[0004] That is, the prior art has at least some disadvantages: 1) The frequency-temperature coefficient stability of a single magnetic tuning device is poor, and it cannot be directly powered by a DC voltage and frequency controlled; 2) The magnetic tuning filter must be externally connected to a current exciter to work properly. Currently, there is no general current exciter for the application of magnetic tuning devices, and all need to be designed in cooperation with the product. The volume and cost of the exciter need to be increased during use; 3) Whether the current exciter is provided by the product manufacturer or self-assembled by the user, it must be independently paired and adjusted with the magnetic tuning filter. There are processes such as control frequency setting and temperature compensation in the tuning process, resulting in a large amount of process costs; 4) The current amplification unit of the current exciter is powered by a fixed voltage V E , and the value of V E needs to meet the provided current to ensure that the filter works at the highest frequency. However, when the filter works at other frequencies, the value of V E is in a surplus state. The lower the frequency, the more surplus V E is, and the surplus voltage is consumed ineffectively in the exciter amplification unit. Summary of the Invention

[0005] The object of the present invention is to provide a voltage-controlled magnetic tuning device to solve the above problems.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A voltage-controlled magnetic tuning device includes a magnetic circuit, a coil, and a resonant circuit, and further includes a temperature compensation resistor. Among them, the coil is connected in series with the temperature compensation resistor, and the resistance value R of the coil L is more than ten times that of the temperature compensation resistor value Rb. The temperature coefficient of resistance of the coil is opposite to that of the temperature compensation resistor, and the temperature coefficient of resistance of the temperature compensation resistor is more than a hundred times that of the temperature coefficient of resistance of the coil.

[0007] The solution of the voltage-controlled magnetic tuning device proposed by the present invention lies in that the coil of the electromagnet is connected in series with a temperature compensation resistor, which solves the key problem of the unstable temperature environment of the coil resistance of the magnetic tuning filter.

[0008] The temperature compensation resistor connected in series with the coil in the present invention has a temperature coefficient of resistance opposite to that of the coil resistance, and can perform resistance stability compensation on the current loop.

[0009] As a preferred technical solution, the resistance of the coil is a positive temperature coefficient resistor, and the temperature compensation resistor is a negative temperature coefficient resistor.

[0010] The resistance value R of the coil of the present invention L is much larger than the resistance value R of the temperature compensation resistor b , and the temperature coefficient of resistance of the temperature compensation resistor of the present invention is much larger than that of the coil resistance, which can not only reduce the useless power consumption caused by the voltage division of the temperature compensation resistor, but also weaken the nonlinear problem of the negative temperature coefficient temperature compensation resistor.

[0011] The frequency temperature drift introduced by the magnetic circuit material, air gap, small ball resonator, etc. in the magnetic tuning filter of the present invention can also be compensated by the temperature compensation resistor, and the overall temperature compensation effect can be adjusted by designing the change range of the resistance value of the temperature compensation resistor.

[0012] As a preferred technical solution, the coil is wound with an enameled wire with a low temperature coefficient of resistance below 100 ppm / °C. The temperature change of the coil resistance value is reduced, and the frequency change rate caused by the temperature change of the coil resistance value is reduced by an order of magnitude compared with the copper enameled wire.

[0013] The second object of the present invention is to provide a frequency control method for the above voltage-controlled magnetic tuning device. The technical solution adopted is to directly supply power by connecting a DC power supply in series with the coil and the temperature compensation resistor in sequence, and the frequency of the voltage-controlled magnetic tuning device is adjusted by directly adjusting the voltage of the DC power supply.

[0014] When the present invention is applied, the user can directly use the voltage Ve to control to obtain a stable operating frequency, and directly adjusting Ve can achieve frequency adjustment.

[0015] The third object of the present invention is to provide another frequency control method of the above-mentioned voltage-controlled magnetic tuning device, the technical solution adopted is that a current exciter is used for power supply, one end of the coil is directly grounded, and the feedback end is directly connected to the other end of the coil.

[0016] That is, the magnetically tuned filter of the present invention can also continue to be powered by a current exciter. Figure 3 As shown, however, it can be cancelled when applied Figure 1 The sampling resistor Rs and the temperature compensation network T of the current exciter in the prior art are directly grounded at one end of the coil, and the feedback end is directly connected to the other end of the coil, which can simplify the current exciter. And because the frequency of the device itself is stable, the amplitude of the feedback compensation of the current exciter is greatly reduced, and the stability and control accuracy of the filter frequency are improved.

[0017] That is to say, the key invention point of the present invention is that the magnetic tuning device is designed with stable coil resistance, stable coil current, and comprehensive temperature drift compensation of temperature compensation resistor, and when applied, voltage control can be directly used to obtain a stable operating frequency.

[0018] The working principle of the present invention is: The main contradiction in using voltage to directly control the frequency of the device and achieve frequency stability is that the current flowing through the coil achieves temperature stability (including ambient temperature and self-heating). Figure 3 The main goal is to stabilize the current when the medium load voltage is static. The principle of the solution adopted is: First, a temperature compensation resistor is connected in series with the coil resistor. Increasing the temperature compensation resistor requires increasing the voltage to provide the current required by the coil, which has the negative problem of increasing power consumption. If the resistance value of the increased temperature compensation resistor R b The resistance value R is much smaller than the coil resistance L Then the negative can be omitted; Second, the coil resistance and the temperature compensation resistor are positive and negative temperature coefficients respectively. The resistance value of the temperature compensation resistor is R b The resistance value R is much smaller than the coil resistance L As long as the temperature coefficient of the temperature compensation resistor is much larger than the temperature coefficient of the coil resistance, full positive and negative compensation can be achieved. Third, in addition to compensating for the coil, the temperature compensation resistor can also compensate for other factors that affect the frequency stability. By properly adjusting the resistance value R of the temperature compensation resistor b Or temperature coefficient, it is possible to achieve fine adjustment of coil current to compensate for comprehensive frequency stability.

[0019] When the device uses a single crystal ferrite ball with a large anisotropy field, the present invention can also use the debugging method of the ferrite single crystal ball deviating from the temperature stable axis to perform frequency temperature compensation, replace the function of the temperature compensation resistor, and even cancel the temperature compensation resistor.

[0020] It should be noted that: after the single-crystal small ball is oriented, there is a temperature stability axis. During debugging, there is a process of rotating the small ball to find the temperature stability axis. This process is an important debugging step for the frequency stability of the magnetic tuning device, and the purpose is that the operating frequency of the device will not be affected by temperature changes. If the single-crystal small ball is not debugged to work on the temperature stability axis, there will be positive and negative temperature drifts in the resonance frequency. Deviating to the right of the temperature stability axis is a negative temperature drift, and deviating to the left of the temperature stability axis is a positive temperature drift. The greater the anisotropy field of the single-crystal small ball, the farther the rotating small ball deviates from the temperature stability axis, the greater the frequency temperature drift, and the stronger the ability to reverse-compensate the frequency temperature drift introduced by other factors of the device.

[0021] Compared with the prior art, the advantages of the present invention are as follows: (1) When the voltage-controlled magnetic tuning device of the present invention is applied, the traditional current exciter can be cancelled. Since the cost and volume of the current exciter unit are almost the same as those of the magnetic tuning device unit, the application volume and cost of the device can be reduced by several times. (2) When the voltage-controlled magnetic tuning device of the present invention is applied, the joint debugging of the filter and the exciter and the temperature compensation process are cancelled, further improving the production efficiency and reducing the production cost. (3) When the voltage-controlled magnetic tuning device of the present invention is working, voltage control is directly adopted, and the voltage and the operating frequency of the magnetic tuning device are in a linear proportional relationship. Description of the Drawings

[0022] Figure 1 is a combined application and structural schematic diagram of a traditional magnetic tuning device and a current exciter; Figure 2 is one of the frequency control schematic diagrams of the voltage-controlled magnetic tuning device of the present invention; Figure 3 is another frequency control schematic diagram of the voltage-controlled magnetic tuning device of the present invention; Figure 4 is a structural cross-sectional schematic diagram of the L-band voltage-controlled magnetic tuning filter in Embodiment 1 of the present invention; In the figure: 1. Magnetic tuning device; 11. Magnetic circuit; 12. Coil; 13. Resonant circuit; 14. Temperature compensation resistor; 2. Current exciter; 21. Digital-to-analog conversion unit; 22. Reference voltage unit; 23. Operational amplifier unit; 24. Current amplification unit; T. Temperature compensation network; Detailed Embodiments

[0023] The present invention will be further described below in conjunction with the embodiments.

[0024] Embodiment 1:

[0025] See Figure 4, An L-band voltage-controlled magnetically tuned bandpass filter, comprising a magnetic circuit 11, a coil 12, a resonant circuit 13, and a temperature compensation resistor 14; the magnetic circuit 11 is designed with a self-shielded can structure, the coil 12 is sleeved on the magnetic pole column of the magnetic circuit to form an electromagnet with the magnetic circuit, and the resonator unit of the resonant circuit is placed in the air gap of the magnetic circuit; the material of the coil 12 is made of copper-nickel alloy enameled wire with a positive temperature coefficient, its resistance temperature coefficient is 40 ppm / °C, the number of turns is designed according to the current tuning sensitivity of 10 MHz / mA, and the coil normal temperature resistance is designed to be about 50 Ω by selecting the wire diameter, the voltage tuning sensitivity is designed to be 200 MHz / V, and the coil resistance change value is about 49.8 Ω to 50.2 Ω in the temperature environment of -20 °C to 60 °C; the temperature compensation resistor 14 uses a commercially available NTC resistor with a negative temperature coefficient, the normal temperature resistance value is 2 Ω, and the resistance value changes from about 3 Ω to 1 Ω in the temperature environment of -20 °C to 60 °C; It should be noted that the temperature compensation resistor 14 used in this embodiment changes from 3 Ω to 1 Ω, which is greater than the change value of the coil resistance. The reason is that the temperature characteristics of the magnetic circuit, ferrite resonator, etc. are also considered to cause frequency changes of the filter. These changes have a basically positive temperature coefficient on the frequency of the device, with a positive frequency drift at low temperature and a negative frequency drift at high temperature; For the L-band voltage-controlled magnetically tuned filter of this embodiment, the filter has an external dimension of 30×30×15 mm 3 , The voltage control tuning frequency coverage is 1000 MHz to 2000 MHz, the corresponding control voltage is between 5 V and 10 V, the corresponding current is about between 100 mA and 200 mA, and the corresponding power consumption is about 0.5 W to 2 W; Table 1 shows the measured data of the frequency stability of the voltage-controlled magnetically tuned filter in this embodiment at three temperatures (-20 °C, 20 °C, 60 °C). The test method is to preheat the filter for 5 minutes at room temperature (20 °C) and then adjust the control voltage Ve to make the filter work at three frequency points of 1000 MHz, 1500 MHz, and 2000 MHz respectively, record the control voltage value (the rightmost voltage value in Table 1), and then record the operating frequency after working at room temperature, low temperature, and high temperature for 1 h based on this voltage value. The maximum temperature drift of this embodiment is controlled within 4 MHz, which has basically reached the level of controlling the frequency temperature drift using a current exciter in this frequency band. Since the frequency stability test of the device shows a positive temperature drift characteristic, it may be caused by the slightly larger change range of the temperature compensation resistor. If the change range of the temperature compensation resistor is adjusted to be smaller, the temperature drift should be further reduced.

[0026] Table 1 Test data of the three-temperature frequency stability of the L-band voltage-controlled magnetically tuned filter , Table 2 shows the measured data of the linear relationship between the voltage-controlled magnetically tunable filter and voltage in this embodiment. The test method is as follows: After power-on and preheating for 5 minutes, record the data of the preset frequency and the corresponding voltage. The voltage data shows that the non-linearity of the control voltage is about ±0.01 V, which is converted to a frequency non-linearity of about 2 MHz. This index is consistent with the control level of the current exciter in this frequency band.

[0027] Table 2 Relationship between the frequency and the corresponding voltage of the L-band voltage-controlled magnetically tunable filter , Example

[0028] See Figure 3 , a P-band magnetically tunable filter assembly (configured with a current exciter), including a magnetically tunable filter 1 and a current exciter 2. The magnetically tunable filter 1 is composed of a magnetic circuit 11, a coil 12, a resonant circuit 13, and a temperature compensation resistor 14. The magnetic circuit 11 is designed with a self-shielded can structure. The coil 12 is sleeved on the magnetic pole column of the magnetic circuit to form an electromagnet with the magnetic circuit. The resonant element unit of the resonant circuit is placed in the air gap of the magnetic circuit; the coil 12 is made of copper-nickel alloy enameled wire with a positive temperature coefficient, and its resistance temperature coefficient is 40 ppm. The number of turns is designed according to the current tuning sensitivity of 5 MHz / mA. The current exciter 2 mainly includes a digital-to-analog conversion unit 21, a reference voltage unit 22, an operational amplifier unit 23, and a current amplification unit 24, and reduces the sampling resistor Rs and the temperature compensation network unit compared with the traditional current exciter. In this combination, the coil is both the load of the exciter current output and serves as the sampling resistor of the exciter.

[0029] See Figure 3 , a P-band magnetically tunable filter assembly (configured with a current exciter), including a magnetically tunable filter 1 and a current exciter 2. The magnetically tunable filter 1 is composed of a magnetic circuit 11, a coil 12, a resonant circuit 13, and a temperature compensation resistor 14. The magnetic circuit 11 is designed with a self-shielded can structure. The coil 12 is sleeved on the magnetic pole column of the magnetic circuit to form an electromagnet with the magnetic circuit. The resonant element unit of the resonant circuit is placed in the air gap of the magnetic circuit; the coil 12 is made of copper-nickel alloy enameled wire with a positive temperature coefficient, and its resistance temperature coefficient is 40 ppm. The number of turns is designed according to the current tuning sensitivity of 5 MHz / mA. The current exciter 2 mainly includes a digital-to-analog conversion unit 21, a reference voltage unit 22, an operational amplifier unit 23, and a current amplification unit 24, and reduces the sampling resistor Rs and the temperature compensation network unit compared with the traditional current exciter. In this combination, the coil is both the load of the exciter current output and serves as the sampling resistor of the exciter.

[0030] See Figure 3, a P-band magnetically tunable filter component (configured with a current exciter), includes a magnetically tunable filter 1 and a current exciter 2. The magnetically tunable filter 1 consists of a magnetic circuit 11, a coil 12, a resonant circuit 13, and a temperature compensation resistor 14. The magnetic circuit 11 is designed with a self-shielded can structure. The coil 12 is sleeved on the magnetic pole column of the magnetic circuit to form an electromagnet with the magnetic circuit. The resonant element unit of the resonant circuit is placed in the air gap of the magnetic circuit. The coil 12 is made of copper-nickel alloy enameled wire with a positive temperature coefficient, and its resistance temperature coefficient is 40 ppm. The number of turns is designed according to the current tuning sensitivity of 5 MHz / mA. The current exciter 2 mainly includes a digital-to-analog conversion unit 21, a reference voltage unit 22, an operational amplifier unit 23, and a current amplification unit 24, and reduces the sampling resistor Rs and the temperature compensation network unit compared with the traditional current exciter. In this combination, the coil is both the load for the current output of the exciter and serves as the sampling resistor of the exciter.

[0031] In this embodiment, the magnetically tunable filter 1 does not use a temperature compensation resistor. During the debugging process, the debugging method of deviating the temperature stability axis is used to make the filter frequency exhibit a positive temperature drift characteristic of 3 - 5 MHz.

[0032] This embodiment of the driver 2 V E Adopts a 12V voltage. Table 3 shows the measured data of the frequency stability of the magnetically tunable filter component (configured with a current exciter) in this embodiment at -20°C and 60°C. The test method is to preheat the filter for 5 minutes at room temperature (20°C) and then adjust the control code to make the filter work at two frequency points of 400 MHz and 700 MHz respectively. Then, record the operating frequency after working at -20°C and 60°C for 1 hour respectively. The maximum temperature drift of this embodiment is controlled within 3 MHz, which is consistent with the level of controlling the frequency temperature drift using the existing technology current exciter in this frequency band.

[0033] Table 3 Temperature Test Data of Frequency Stability in Embodiment 2 。

[0034] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A voltage-controlled magnetic tuning device, comprising a magnetic circuit (11), a coil (12) and a resonant circuit (13), characterized in that, It further includes a temperature compensation resistor (14), wherein the coil (12) is connected in series with the temperature compensation resistor (14), and the resistance value R of the coil (12) L is more than ten times the resistance value R of the temperature compensation resistor (14) b The temperature coefficient of resistance of the coil (12) is opposite to that of the temperature compensation resistor (14), and the temperature coefficient of resistance of the temperature compensation resistor (14) is more than a hundred times that of the coil (12).

2. The voltage-controlled magnetic tuning device according to claim 1, characterized in that, The resistance of the coil (12) is a positive temperature coefficient resistor, and the temperature compensation resistor (14) is a negative temperature coefficient resistor.

3. The voltage-controlled magnetic tuning device according to claim 1, characterized in that The coil (12) is wound with enameled wire having a temperature coefficient of resistance below 100 ppm / °C.

4. A frequency control method for a voltage-controlled magnetically tunable device according to any one of claims 1 to 3, characterized in that, The DC power supply is directly connected in series with the coil (12) and the temperature compensation resistor (14) in sequence for power supply, and the frequency of the voltage-controlled magnetic tuning device is adjusted by directly adjusting the voltage of the DC power supply.

5. A frequency control method for a voltage-controlled magnetically tunable device according to any one of claims 1 to 3, characterized in that, Power supply is provided by a current exciter, one end of the coil (12) is directly grounded, and the feedback end is directly connected to the other end of the coil (12).

6. A frequency control method for a voltage-controlled magnetically tunable device, characterized in that, Frequency temperature compensation is performed by using the debugging method of the ferrite single crystal small ball deviating from the temperature stability axis.

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