Voltage-controlled adjustable center frequency point band-pass filter and excitation signal modulation device

Abstract

The utility model relates to a voltage-controlled adjustable center frequency point band-pass filter and an excitation signal modulation device. After a reverse-phase low-pass filter circuit amplifies or attenuates received control voltage, negative voltage matched with pinch-off voltage parameters of a field-effect tube in a frequency-selecting filter is output; the non-linear compensation circuit compensates the negative voltage and then transmits the negative voltage to the frequency-selecting filter; and the frequency-selecting filter adjusts the center frequency by utilizing an internal field-effect tube according to the received negative voltage, and modulates the received PWM signal into a same-frequency sine wave signal according to the adjusted center frequency. And the control voltage can be adjusted according to actual requirements, so that the frequency-selecting filter modulates the received PWM signal into the same-frequency sine wave signal according to the adjusted center frequency, the center frequency point is supported to be continuously adjustable on line, and the use reliability in a complex electromagnetic environment is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of signal modulation, in particular to a voltage-controlled adjustable center frequency point band-pass filter and an excitation signal modulation device. BACKGROUND

[0002] In the high-quality continuous casting process of a steel billet, the liquid level height of a molten steel crystallizer is a very important control index. Excessive liquid level fluctuation not only seriously affects the quality of the steel billet, degrades the quality of the steel billet, but also may cause forced shutdown, even a safety accident of molten steel leakage, and cause serious economic losses and personnel danger. Therefore, an electromagnetic sensor needs to be used to detect the liquid level height. In a traditional electromagnetic sensor (CN 216138077 U), a complete detection loop is formed through a primary coil, a secondary coil and a cable interface, the liquid level of the molten steel crystallizer is detected, and the liquid level is monitored in real time. However, in the electromagnetic sensor, the frequency of an excitation signal transmitted to the primary coil is fixed and cannot be adjusted online, and the electromagnetic sensor has the defect of low reliability in complex electromagnetic environments. CONTENT OF THE UTILITY MODEL

[0003] Therefore, it is necessary to provide a voltage-controlled adjustable center frequency point band-pass filter and an excitation signal modulation device which can improve the reliability in complex electromagnetic environments in view of the above problems.

[0004] A voltage-controlled adjustable center frequency point band-pass filter comprises a frequency selection filter, a non-linear compensation circuit and an inverting low-pass filter circuit, the frequency selection filter is connected to the non-linear compensation circuit, and the inverting low-pass filter circuit is connected to the non-linear compensation circuit.

[0005] The inverting low-pass filter circuit amplifies or attenuates a received control voltage and outputs a negative voltage matched with pinch-off voltage parameters of a field effect tube in the frequency selection filter, the non-linear compensation circuit compensates the negative voltage and then transmits the negative voltage to the frequency selection filter, the frequency selection filter adjusts a center frequency by using an internal field effect tube according to the received negative voltage, and modulates a received PWM signal into a same-frequency sine wave signal according to the adjusted center frequency.

[0006] In one of the embodiments, the frequency selection filter comprises an operational amplifier U1A, a resistor R1, a resistor R2, a resistor R4, a resistor R5, a resistor R8, a capacitor C1, a capacitor C2 and a field effect transistor Q1, a control terminal and a first terminal of the field effect transistor Q1 are connected to the non-linear compensation circuit, a second terminal of the field effect transistor Q1 is grounded, a first terminal of the resistor R8 is connected to the first terminal of the field effect transistor Q1 and a first terminal of the resistor R4, a second terminal of the resistor R8 is grounded, a second terminal of the resistor R4 is connected to a first terminal of the resistor R1, a first terminal of the capacitor C1 and a first terminal of the capacitor C2, a second terminal of the resistor R1 is connected to a PWM signal, a second terminal of the capacitor C1 is connected to an output terminal of the operational amplifier U1A, a second terminal of the capacitor C2 is connected to an inverting input terminal of the operational amplifier U1A, a non-inverting input terminal of the operational amplifier U1A is grounded through the resistor R5, a first terminal of the resistor R2 is connected to the inverting input terminal of the operational amplifier U1A, a second terminal of the resistor R2 is connected to the output terminal of the operational amplifier U1A, and the output terminal of the operational amplifier U1A outputs a same-frequency sine wave signal.

[0007] In one of the embodiments, the frequency selection filter further comprises a resistor R3 connected to the output terminal of the operational amplifier U1A.

[0008] In one of the embodiments, the non-linear compensation circuit comprises an operational amplifier U1B, an operational amplifier U1C, a resistor R6, a resistor R7, a resistor R9, a resistor R10 and a capacitor C3, a non-inverting input terminal of the operational amplifier U1B is connected to the first terminal of the field effect transistor Q1 through the resistor R7, an inverting input terminal of the operational amplifier U1B is connected to the output terminal of the operational amplifier U1B and a first terminal of the resistor R6, a second terminal of the resistor R6 is connected to the control terminal of the field effect transistor Q1 and a first terminal of the resistor R9, a second terminal of the resistor R9 is connected to an output terminal of the operational amplifier U1C and an inverting input terminal of the operational amplifier U1C, a non-inverting input terminal of the operational amplifier U1C is connected to a first terminal of the resistor R10 and grounded through the capacitor C3, and a second terminal of the resistor R10 is connected to the inverting low-pass filter circuit.

[0009] In one of the embodiments, the inverting low-pass filter circuit comprises an operational amplifier U1D, a resistor R11, a resistor R12, a resistor R13 and a capacitor C4, the non-inverting input terminal of the operational amplifier U1D is grounded through the resistor R13, the inverting input terminal of the operational amplifier U1D is connected to the control voltage through the resistor R12, the resistor R11 and the capacitor C4 are connected in parallel, one end of which is connected to the inverting input terminal of the operational amplifier U1D, and the other end of which is connected to the output terminal of the operational amplifier U1D, and the output terminal of the operational amplifier U1D is connected to the second end of the resistor R10.

[0010] In one of the embodiments, the field effect tube is a JFET tube.

[0011] The excitation signal modulation device comprises the voltage-controlled adjustable center frequency band-pass filter.

[0012] In one of the embodiments, the excitation signal modulation device further comprises a control module, which is connected to the inverting low-pass filter circuit in the voltage-controlled adjustable center frequency band-pass filter and outputs the control voltage to the inverting low-pass filter circuit.

[0013] In one of the embodiments, the excitation signal modulation device further comprises a signal adjustment module, which is connected to the frequency selection filter in the voltage-controlled adjustable center frequency band-pass filter and outputs the PWM signal to the frequency selection filter.

[0014] In one of the embodiments, the excitation signal modulation device further comprises a power amplification module, which is connected to the electromagnetic coil and the frequency selection filter in the voltage-controlled adjustable center frequency band-pass filter, receives the same-frequency sine wave signal output by the frequency selection filter and outputs the excitation signal to the electromagnetic coil.

[0015] The voltage-controlled adjustable center frequency band-pass filter and the excitation signal modulation device, the inverting low-pass filter circuit amplifies or attenuates the received control voltage, outputs the negative voltage matched with the pinch-off voltage parameter of the field effect tube in the frequency selection filter, and the non-linear compensation circuit compensates the negative voltage and then sends it to the frequency selection filter; the frequency selection filter adjusts the center frequency by using the internal field effect tube according to the received negative voltage, and modulates the received PWM signal into the same-frequency sine wave signal according to the adjusted center frequency. The control voltage can be adjusted according to actual needs, so that the frequency selection filter modulates the received PWM signal into the same-frequency sine wave signal according to the adjusted center frequency, supports the online continuous adjustment of the center frequency, and improves the use reliability in complex electromagnetic environment. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 It is a structural block diagram of the voltage-controlled adjustable center frequency band-pass filter in one of the embodiments.

[0017] Figure 2 This is a schematic diagram of the structure of a voltage-controlled adjustable center frequency bandpass filter in one embodiment. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. It is understood that the term "connection" in the following embodiments, if the connected circuits, modules, units, etc., transmit electrical signals or data to each other, should be understood as "electrical connection," "communication connection," etc.

[0020] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0021] In one embodiment, such as Figure 1 As shown, a voltage-controlled adjustable center frequency bandpass filter is provided, including a frequency-selective filter 110, a nonlinear compensation circuit 120, and an inverting low-pass filter circuit 130. The frequency-selective filter 110 is connected to the nonlinear compensation circuit 120, and the nonlinear compensation circuit 120 is connected to the inverting low-pass filter circuit 130. The inverting low-pass filter circuit 130 amplifies or attenuates the received control voltage and outputs a negative voltage that matches the pinch-off voltage parameter of the field-effect transistor in the frequency-selective filter 110. The nonlinear compensation circuit 120 compensates for the negative voltage and then sends it to the frequency-selective filter 110. The frequency-selective filter 110 adjusts the center frequency using its internal field-effect transistor according to the received negative voltage, and modulates the received PWM (Pulse Width Modulation) signal into a sinusoidal signal of the same frequency according to the adjusted center frequency.

[0022] The voltage-controlled adjustable center frequency band-pass filter is specifically a frequency selection filter, which is used to separate and extract a signal of a specific frequency or a signal located in a certain frequency band from other signals of different frequencies. The inverting low-pass filter circuit 130 can be connected to a control module of the excitation signal modulation device to receive a control voltage. The frequency selection filter 110 can be connected to a signal adjustment module and a power amplification module of the excitation signal modulation device to receive a PWM signal output by the signal adjustment module and output a same-frequency sine wave signal to the power amplification module.

[0023] Specifically, the control module outputs a PWM signal of a target frequency to the signal adjustment module and sends a control voltage corresponding to the target frequency to the inverting low-pass filter circuit 130 in the voltage-controlled adjustable center frequency band-pass filter. The signal adjustment module amplifies the input PWM signal and outputs an amplified PWM signal of the same frequency to the frequency selection filter 110. The frequency selection filter 110 modulates the received PWM signal into a same-frequency sine wave signal according to the adjusted center frequency. The power amplification module amplifies the same-frequency sine wave signal output by the frequency selection filter 110 and outputs an excitation signal to the electromagnetic coil. The electromagnetic coil can be a primary electromagnetic coil of an electromagnetic sensor. The excitation signal is output to the primary electromagnetic coil by the excitation signal modulation device, and the electromagnetic sensor analyzes the induced signal generated by the secondary electromagnetic coil to detect the liquid level. The specific value of the target frequency is not unique and can be set according to actual needs and saved in the control module. The control module also saves the amplitude of the control voltage corresponding to different frequencies.

[0024] In one embodiment, as shown in FIG. 1, Figure 2 The frequency selection filter 110 includes an operational amplifier U1A, a resistor R1, a resistor R2, a resistor R4, a resistor R5, a resistor R8, a capacitor C1, a capacitor C2, and a field effect transistor Q1. The control end and the first end of the field effect transistor Q1 are connected to the non-linear compensation circuit 120. The second end of the field effect transistor Q1 is grounded. The first end of the resistor R8 is connected to the first end of the field effect transistor Q1 and the first end of the resistor R4. The second end of the resistor R8 is grounded. The second end of the resistor R4 is connected to the first end of the resistor R1, the first end of the capacitor C1, and the first end of the capacitor C2. The second end of the resistor R1 is connected to the PWM signal. The second end of the capacitor C1 is connected to the output end of the operational amplifier U1A. The second end of the capacitor C2 is connected to the inverting input end of the operational amplifier U1A. The non-inverting input end of the operational amplifier U1A is grounded through the resistor R5. The first end of the resistor R2 is connected to the inverting input end of the operational amplifier U1A. The second end of the resistor R2 is connected to the output end of the operational amplifier U1A. The output end of the operational amplifier U1A outputs a same-frequency sine wave signal.

[0025] The second end of the resistor R1 is connected to the signal adjusting module, and receives the same frequency amplified PWM signal VI output by the signal adjusting module. The field effect tube Q1 can be a JFET tube or other type of field effect tube. In the embodiment, the field effect tube Q1 is a JFET-N tube, the gate is the control end, the drain is the first end, and the source is the second end. The frequency selection filter 110 can further include a resistor R3. The output end of the operational amplifier U1A is connected to the power amplification module through the resistor R3, and outputs the same frequency sine wave signal VO to the power amplification module.

[0026] In the frequency selection filter 110, the resistor R1 and the resistor R2 mainly determine the filter gain. The capacitance C1 and the capacitance C2 can be set to have the same capacitance value. The resistor R2 and the resistor R4, the resistor R8, and the equivalent resistor composed of the field effect tube Q1 in series and parallel together determine the center frequency point of the frequency selection filter. The resistor R3 is an output current limiting resistor. Since the field effect tube Q1 is a JFET tube, it has relatively large noise and relatively large temperature drift than the resistor. Therefore, the resistor R8 is connected in parallel with the field effect tube Q1, so that the noise and the temperature drift are reduced at the cost of reducing the variable resistance range of the equivalent resistor. The resistor R4 is generally set to be more than twice the maximum resistance value of the equivalent resistor composed of the field effect tube Q1 and the resistor R8 in parallel. This makes the proportion of the resistor R4 in the equivalent resistor composed of the resistor R4, the field effect tube Q1, and the resistor R8 mainly affected. This is also to further reduce the noise and the temperature drift caused by the JFET tube. In some applications that do not require a very large range of center frequency point adjustment range, the circuit can achieve a practical range through such design.

[0027] When the capacitance C1, the capacitance C2, the resistor R1, and the resistor R2 have fixed parameters, the equivalent resistor composed of the resistor R4, the resistor R8, and the field effect tube Q1 in series and parallel determines the center frequency point of the frequency selection filter 110. When the control voltage VC is 0V, the field effect tube Q1 is equivalent to a small resistor. The on-resistance of the field effect tube Q1 is connected in parallel with the resistor R8, and then connected in series with the resistor R4 to obtain an equivalent resistor. The equivalent resistor, together with the capacitance C1, the capacitance C2, and the resistor R2, determines the initial center frequency of the frequency selection filter 110. When the control voltage VC gradually increases, due to the pinch effect of the JFET tube, the equivalent resistance of the field effect tube Q1 gradually increases, which causes the equivalent resistance composed of the field effect tube Q1, the resistor R4, and the resistor R8 to gradually increase, and the center frequency point of the frequency selection filter 110 gradually decreases. When the control voltage VC increases to the fully pinched region of the field effect tube Q1, the center frequency point of the frequency selection filter 110 reaches the minimum.

[0028] Further, the non-linear compensation circuit 120 comprises an operational amplifier U1B, an operational amplifier U1C, a resistor R6, a resistor R7, a resistor R9, a resistor R10 and a capacitor C3, the non-inverting input terminal of the operational amplifier U1B is connected to the first terminal of the field effect transistor Q1 through the resistor R7, the inverting input terminal of the operational amplifier U1B is connected to the output terminal of the operational amplifier U1B and the first terminal of the resistor R6, the second terminal of the resistor R6 is connected to the control terminal of the field effect transistor Q1 and the first terminal of the resistor R9, the second terminal of the resistor R9 is connected to the output terminal of the operational amplifier U1C and the inverting input terminal of the operational amplifier U1C, the non-inverting input terminal of the operational amplifier U1C is connected to the first terminal of the resistor R10 and grounded through the capacitor C3, and the second terminal of the resistor R10 is connected to the inverting low-pass filter circuit 130.

[0029] In addition, the inverting low-pass filter circuit 130 can specifically comprise an operational amplifier U1D, a resistor R11, a resistor R12, a resistor R13 and a capacitor C4, the non-inverting input terminal of the operational amplifier U1D is grounded through the resistor R13, the inverting input terminal of the operational amplifier U1D is connected to the control voltage VC through the resistor R12, the resistor R11 and the capacitor C4 are connected in parallel, one end of which is connected to the inverting input terminal of the operational amplifier U1D, and the other end of which is connected to the output terminal of the operational amplifier U1D, and the output terminal of the operational amplifier U1D is connected to the second terminal of the resistor R10.

[0030] The control voltage VC output by the control module is generally a positive voltage of zero to several volts, which is amplified or attenuated by a certain proportion through the inverting low-pass filter circuit 130 composed of the operational amplifier U1D, the resistor R11, the resistor R12, the resistor R13 and the capacitor C4, and then a negative voltage matched with the pinch-off voltage parameter of the selected JFET tube is output. The negative voltage can compensate for the non-linearity of the JFET variable resistor through the non-linear compensation circuit 120 composed of the operational amplifier U1B, the operational amplifier U1C and the matching resistors.

[0031] In one embodiment, an excitation signal modulation device is also provided, comprising the voltage-controlled adjustable center frequency band-pass filter described above. The excitation signal modulation device further comprises a control module connected to the inverting low-pass filter circuit in the voltage-controlled adjustable center frequency band-pass filter, and outputs a control voltage to the inverting low-pass filter circuit. Further, the excitation signal modulation device can comprise a signal conditioning module connected to the frequency selection filter in the voltage-controlled adjustable center frequency band-pass filter, and outputs a PWM signal amplified at the same frequency to the frequency selection filter.

[0032] In addition, the excitation signal modulation device can further include a power amplification module connected to the electromagnetic coil and the frequency selection filter in the voltage-controlled adjustable center frequency band pass filter, the power amplification module receives the same frequency sine wave signal output by the frequency selection filter, and outputs the excitation signal to the electromagnetic coil. The power amplification module can be a single power amplification module or a double power amplification module. In the embodiment, the power amplification module is a double power amplification module, and the double power amplification module performs in-phase and anti-phase power amplification according to the same frequency sine wave signal, and outputs two excitation signals with the same amplitude and a phase difference of 180° to both ends of the electromagnetic coil. Specifically, the same frequency amplified PWM signal is obtained after passing through the voltage-controlled adjustable center frequency band pass filter, the same frequency sine wave signal is amplified in phase and anti-phase respectively, and two excitation signals with the same amplitude and a phase difference of 180° are output to both ends of the electromagnetic coil. After this modulation, the amplitude of the sine excitation signal finally output to the electromagnetic coil can be doubled relative to the single power amplification scheme, thereby effectively expanding the design boundary of the electromagnetic sensor coil.

[0033] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, but as long as the combinations of the technical features do not exist, they should be considered as within the scope of the present disclosure.

[0034] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the utility model patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A voltage controlled adjustable center frequency bandpass filter, characterized by, The frequency selection filter, the non-linear compensation circuit and the inverse low-pass filter circuit are connected, and the inverse low-pass filter circuit is connected with the non-linear compensation circuit; The inverse low-pass filter circuit amplifies or attenuates the received control voltage and outputs a negative voltage matched with the pinch voltage parameter of the field effect tube in the frequency selection filter, and the non-linear compensation circuit compensates the negative voltage and sends it to the frequency selection filter; the frequency selection filter adjusts the center frequency by using the internal field effect tube according to the received negative voltage, and modulates the received PWM signal into a same-frequency sine wave signal according to the adjusted center frequency.

2. The filter of claim 1, wherein, The frequency selection filter comprises an operational amplifier U1A, a resistor R1, a resistor R2, a resistor R4, a resistor R5, a resistor R8, a capacitor C1, a capacitor C2 and a field effect tube Q1, the control end and the first end of the field effect tube Q1 are connected with the non-linear compensation circuit, the second end of the field effect tube Q1 is grounded, the first end of the resistor R8 is connected with the first end of the field effect tube Q1 and the first end of the resistor R4, the second end of the resistor R8 is grounded, the second end of the resistor R4 is connected with the first end of the resistor R1, the first end of the capacitor C1 and the first end of the capacitor C2, the second end of the resistor R1 is connected with a PWM signal, the second end of the capacitor C1 is connected with the output end of the operational amplifier U1A, the second end of the capacitor C2 is connected with the inverting input end of the operational amplifier U1A, the non-inverting input end of the operational amplifier U1A is grounded through the resistor R5, the first end of the resistor R2 is connected with the inverting input end of the operational amplifier U1A, the second end of the resistor R2 is connected with the output end of the operational amplifier U1A, and the output end of the operational amplifier U1A outputs a same-frequency sine wave signal.

3. The filter of claim 2, wherein, The frequency selection filter further comprises a resistor R3 connected with the output end of the operational amplifier U1A.

4. The filter of claim 2, wherein, The non-linear compensation circuit comprises an operational amplifier U1B, an operational amplifier U1C, a resistor R6, a resistor R7, a resistor R9, a resistor R10 and a capacitor C3, the non-inverting input end of the operational amplifier U1B is connected with the first end of the field effect tube Q1 through the resistor R7, the inverting input end of the operational amplifier U1B is connected with the output end of the operational amplifier U1B and the first end of the resistor R6, the second end of the resistor R6 is connected with the control end of the field effect tube Q1 and the first end of the resistor R9, the second end of the resistor R9 is connected with the output end of the operational amplifier U1C and the inverting input end of the operational amplifier U1C, the non-inverting input end of the operational amplifier U1C is connected with the first end of the resistor R10 and grounded through the capacitor C3, and the second end of the resistor R10 is connected with the inverse low-pass filter circuit.

5. The filter of claim 2, wherein, The inverting low-pass filter circuit comprises an operational amplifier U1D, a resistor R11, a resistor R12, a resistor R13 and a capacitor C4, the non-inverting input terminal of the operational amplifier U1D is grounded through the resistor R13, the inverting input terminal of the operational amplifier U1D is connected to a control voltage through the resistor R12, the resistor R11 and the capacitor C4 are connected in parallel, one end of which is connected to the inverting input terminal of the operational amplifier U1D, and the other end is connected to the output terminal of the operational amplifier U1D, and the output terminal of the operational amplifier U1D is connected to the second end of the resistor R10.

6. The filter according to any one of claims 1 to 5, characterized in that The field effect tube is a JFET tube.

7. An excitation signal modulation apparatus characterized by comprising: The voltage-controlled adjustable center frequency band-pass filter comprises the voltage-controlled adjustable center frequency band-pass filter according to any one of claims 1-6.

8. The apparatus of claim 7, wherein, The control module is further connected to the inverting low-pass filter circuit in the voltage-controlled adjustable center frequency band-pass filter and outputs a control voltage to the inverting low-pass filter circuit.

9. The apparatus of claim 7, wherein, The signal conditioning module is further connected to the frequency selection filter in the voltage-controlled adjustable center frequency band-pass filter and outputs a PWM signal to the frequency selection filter.

10. The apparatus of claim 7, wherein, The power amplification module is further connected to the electromagnetic coil and the frequency selection filter in the voltage-controlled adjustable center frequency band-pass filter, receives a same-frequency sinusoidal wave signal output by the frequency selection filter, and outputs an excitation signal to the electromagnetic coil.

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