CN117559961A - High/low pass filter circuit configuration with accurately adjustable cut-off frequency - Google Patents

High/low pass filter circuit configuration with accurately adjustable cut-off frequency Download PDF

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Publication number
CN117559961A
CN117559961A CN202311529522.6A CN202311529522A CN117559961A CN 117559961 A CN117559961 A CN 117559961A CN 202311529522 A CN202311529522 A CN 202311529522A CN 117559961 A CN117559961 A CN 117559961A
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input
operational amplifier
analog multiplier
voltage
resistor
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吕炎
吴炳
张宝进
吕金鸽
高杰
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Beijing University of Technology
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Beijing University of Technology
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H11/00—Networks using active elements
    • H03H11/02—Multiple-port networks
    • H03H11/04—Frequency selective two-port networks
    • H03H11/12—Frequency selective two-port networks using amplifiers with feedback
    • H03H11/126—Frequency selective two-port networks using amplifiers with feedback using a single operational amplifier
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F7/00—Methods or arrangements for processing data by operating upon the order or content of the data handled
    • G06F7/38—Methods or arrangements for performing computations using exclusively denominational number representation, e.g. using binary, ternary, decimal representation
    • G06F7/48—Methods or arrangements for performing computations using exclusively denominational number representation, e.g. using binary, ternary, decimal representation using non-contact-making devices, e.g. tube, solid state device; using unspecified devices
    • G06F7/52—Multiplying; Dividing
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics

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  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Computational Mathematics (AREA)
  • Mathematical Analysis (AREA)
  • Mathematical Optimization (AREA)
  • Pure & Applied Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Computing Systems (AREA)
  • General Engineering & Computer Science (AREA)
  • Networks Using Active Elements (AREA)

Abstract

The invention discloses a high/low pass filter circuit configuration with accurately controllable cut-off frequency, and relates to the technical field of nondestructive testing. The input analog signal is connected to the x input end of the analog multiplier U1 through a resistor R1, the y input end of the analog multiplier U1 is connected to a direct-current voltage signal, the output end of the analog multiplier U1 is connected to the inverting input end of the operational amplifier U2 through a resistor R2, the non-inverting input end of the operational amplifier U2 is grounded, the output end of the operational amplifier U2 is connected to the inverting input end of the operational amplifier U2 through a capacitor Cf, and the output end of the operational amplifier U2 is connected to the x input end of the analog multiplier U1 to which the input analog signal is connected through a resistor Rf. The invention can realize low-pass and high-pass filtering of the input analog signals, and the filter cut-off frequency can be accurately adjusted by the size of the control voltage signals, thereby having important practical significance and practical value.

Description

High/low pass filter circuit configuration with accurately adjustable cut-off frequency
Technical Field
The invention belongs to the technical field of nondestructive testing, and particularly relates to a high/low pass filter circuit configuration with accurately adjustable cut-off frequency.
Background
In the field of ultrasonic nondestructive testing, an ultrasonic microscopic detection technology is used as a common detection means, and the surface and internal information of a test piece are displayed in an image mode through the reflection characteristic of ultrasonic waves, so that the detection and 3D reconstruction of defects of industrial materials are realized.
The ultrasonic excitation/receiver is used as a core instrument of an ultrasonic microscopic system and is used for ultrasonic excitation and signal conditioning and receiving, and the conditioning function mainly comprises amplification and filtering of ultrasonic echo signals. Aiming at different detection precision requirements of scanning of an ultrasonic microscope, ultrasonic transducers with different center frequencies need to be replaced, thereby causing uncertainty of working frequency of an ultrasonic excitation/receiver, and in order to avoid clutter interference outside a target frequency band, a filter with an adjustable filter passband range needs to be realized.
The program-controlled filter mainly comprises the following three methods: the first is to switch the passive circuit network by an analog switch, and the adjustment accuracy of the first is dependent on the number of the passive circuit networks; the second is to use active integrated filter chip, which has the characteristics of complete filter function, better stability, programmable cut-off (or center) frequency (generally within 200 kHz), but larger circuit noise, and smooth filter addition; the third is to use DSP chip (Digital Signal Processor chip) to carry out Digital filtering to the signal collected by the Analog-to-Analog Converter, then output by DAC, the speed is limited by the device used, and the accuracy of the Analog signal is limited by the number of collected/output bits.
In summary, the prior filtering technology lacks a brand new analog active filtering circuit configuration which can realize high adjustment precision, high frequency band, large adjustable range and low noise. The filter circuit design with different filtering ranges can be realized through the combination of different active devices and passive devices based on the circuit configuration, and the filter circuit design can be applied to the field of ultrasonic detection and other circuit application scenes with accurate filtering requirements.
Disclosure of Invention
Aiming at the defects of the prior filtering technology, the invention provides an analog filtering circuit configuration capable of accurately adjusting the filtering range, low-pass filtering and high-pass filtering of an input analog signal can be realized, and the filtering cut-off frequency can be accurately adjusted by the size of a control voltage signal.
In order to solve the technical problems, the invention adopts the following technical scheme: the utility model provides a high/low pass filter circuit configuration of accurate controllable cutoff frequency, including operational amplifier U2, analog multiplier U1 and a plurality of passive component, input analog signal inserts analog multiplier U1's x input through resistance R1, analog multiplier U1's y input inserts direct current voltage signal, operational amplifier U2's inverting input is inserted through resistance R2 to analog multiplier U1's output, operational amplifier U2's non-inverting input ground connection, operational amplifier U2's output is connected to operational amplifier U2's inverting input through capacitor Cf, operational amplifier U2's output is connected to the x input of input analog multiplier U1 that the input analog signal inserts through a resistance Rf again.
Preferably, the analog multiplier may be replaced by a controllable gain amplifying device.
Preferably, the circuit configuration can realize low-pass filtering or high-pass filtering of the input analog signal, wherein the output end of the low-pass filtering is the output end of the operational amplifier, the output end of the high-pass filtering is the x input end of the analog multiplier to which the input analog signal is connected, and the cut-off frequency of the low-pass filtering or the high-pass filtering is controlled by the direct-current voltage signal input by the analog multiplier.
The output voltage of the analog multiplier U1 is equal to the product of the input voltages at two ends, the usage in the invention is that the output is equal to the product of the input analog signal and the control voltage signal, and the function can be realized by a controllable gain amplifier.
A bandwidth-controllable inverting filter is designed, and the positive direction of current is set to flow from an input Vin to a resistor Rf through a resistor R1. In an ideal state, the input impedance of the analog multiplier U1 is regarded as infinity, the operational amplifier U2 satisfies an ideal amplifying state, and the frequency domain relationship between the output voltage and the voltages at a point and b point can be known according to the analog multiplier calculation formula and the operational amplifier amplifying principle, wherein the a point is the x input end of the analog multiplier U1, and the b point is the output end of the analog multiplier U1, as shown in formulas (2-1) and (2-2). Vo is an operational amplifierOutput terminal voltage of amplifier U2, V a For the voltage at the x input of the analog multiplier U1, V b For the voltage at the output of the analog multiplier U1, V y For the voltage at the y input of the analog multiplier U1, R 2 C is the resistor connected between the output end of the analog multiplier U1 and the inverting input end of the operational amplifier U2 f Is the capacitance connected between the inverting input terminal and the output terminal of the operational amplifier U2, J is the imaginary unit representing the phase rotation of the voltage signal, ω is the frequency of the voltage signal, vin is the input voltage, I R1 To flow through the resistor R1, I R2 Is the current flowing through resistor R2.
V b ＝V y ×V a (2-2)
The multiplier U1 and the operational amplifier U2 are regarded as a whole, the amplification factor-A is shown as a formula (2-3), and the peripheral circuit accords with the precondition of negative feedback design. The positive direction of the current is set to flow from the input Vin to the resistor Rf through the resistor R1, and the formulas (2-4), (2-5) and (2-6) can be obtained.
V o ＝-A×V a (2-4)
In an ideal state, the input impedance of the multiplier U1 is considered to be infinite, and the current does not enter the input end thereof, so I R1 ＝I Rf ，ω 0 For the cut-off frequency, the a-point voltage Va, the output voltage Vo of the operational amplifier U2 is obtained when rf=r1Frequency domain relation to input voltage Vin:
wherein the cutoff frequency omega 0 The control formula of (2) is:
in combination with the above formula, the circuit configuration takes Vo as output and can be used as a low-pass filter, and takes Va as output and can be used as a high-pass filter, and the cut-off frequency is determined by the control voltage Vy, the resistor R2 and the capacitor Cf, and the upper limit of the filtering precision of the circuit configuration depends on the regulation precision of the control voltage under the condition of resistance-capacitance determination.
The beneficial effects of adopting above-mentioned technical scheme to produce lie in:
1. the circuit configuration can realize low-pass and high-pass filtering of input analog signals, and the filter cut-off frequency can be accurately adjusted by the size of a control voltage signal, so that the circuit configuration has important practical significance and practical value.
2. The filter circuit design with different filtering ranges can be realized through the combination of different active devices and passive devices based on the circuit configuration, and each device can be freely allocated according to the needs, so that the filter circuit can be applied to the field of ultrasonic detection and other circuit application scenes with accurate filtering requirements.
Drawings
FIG. 1 is a schematic circuit configuration;
FIG. 2 is a schematic circuit diagram;
fig. 3 is a diagram of simulation results.
Detailed Description
The following description of the embodiments of the present application will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all, of the embodiments of the present application. All other embodiments, which can be made by one of ordinary skill in the art based on the embodiments herein without making any inventive effort, are intended to be within the scope of the present application.
The circuit configuration comprises an analog multiplier, an operational amplifier and a plurality of passive devices. As shown in fig. 1, an input analog signal is connected to an X input end of an analog multiplier U1 through a resistor R1, a Y input end of the analog multiplier U1 is connected to a dc voltage signal, an output end of the analog multiplier U1 is connected to an inverting input end of an operational amplifier U2 through a resistor R2, a non-inverting input end of the operational amplifier U2 is grounded, an output end of the operational amplifier U2 is connected to the inverting input end of the operational amplifier U2 through a capacitor Cf, and an output end of the operational amplifier U2 is connected to an X input end of the analog multiplier U1 to which the input analog signal is connected through a resistor Rf.
The circuit configuration can realize low-pass filtering or high-pass filtering of an input analog signal, wherein the output end of the low-pass filtering is the output end of an operational amplifier, the output end of the high-pass filtering is the x input end of an analog multiplier to which the input analog signal is connected, and the two filtering cut-off frequencies are controlled by a direct-current voltage signal input by the analog multiplier. The control precision of the filter cut-off frequency of the device in an ideal working state is completely dependent on the control voltage signal precision.
The invention is further described in connection with simulations. Fig. 2 is a high/low pass filter circuit with precisely adjustable cut-off frequency built using Multism simulation software. The performance of the circuit configuration is verified by simulation analysis from the circuit principle characteristic level, meanwhile, the influence of device factors in an actual circuit can be avoided, and the designed circuit configuration can be well verified.
The analog multiplier U1 selects a standard analog multiplier with a Multism, the model of the operational amplifier U2 selects AD8047AR, the gain bandwidth product of the operational amplifier is 250MHz, the amplification requirement within 50MHz is enough to be realized, R2 is selected to be 50Ω, cf is set to be 39pF, the resistors R1 and Rf are both set to be 384 Ω according to the device characteristics of the AD8047AR, and R7 is used as the output impedance of the signal input source V1. Multism is set as frequency response simulation to obtain the amplitude-frequency characteristic curves of the circuit network 5 (point a in fig. 1) and the network 2 (point Vo in fig. 1) and the input so as to verify the correctness of the formula.
Fig. 3 shows the result of amplitude-frequency characteristic curve simulation of the network 2 and the network 5 when Vy takes different values. In the figure, different colors represent different input voltages of Vy, a solid line is an output amplitude-frequency characteristic curve of the network 2, and a dotted line is an output amplitude-frequency characteristic curve of the network 5. From the graph, the absolute value of the amplification factor of the system Vo in the passband is basically stabilized near 1, va is between 0.51 and 0.6, and the amplification factor accords with the formula prediction.
Table 1 shows that when the control amount Vy is different, the frequency of the pass band-3 dB point of the attenuation of the amplitude-frequency characteristic of the network 2 is FL, and the-3 dB point of the network 5 is FH. The results show that the amplification and cut-off frequency substantially meet the estimate of the cut-off frequency in equation (2-9).
TABLE 1V y Calculating the cut-off frequency omega 0 And simulation result numerical table
It should be noted that Vo is the output of the active device U2, which has a strong loading capability, and the output will be inverted in the passband. However, the point a is used as a signal input terminal of the active device U1, and the load carrying capability is weak, so that a power amplifier needs to be mounted in practical application.
The present invention is not limited to the above-mentioned embodiments, and any person skilled in the art, based on the technical solution of the present invention and the inventive concept thereof, can be replaced or changed within the scope of the present invention.

Claims (4)

1. The high/low pass filter circuit configuration with the accurately controllable cut-off frequency is characterized by comprising an operational amplifier U2, an analog multiplier U1 and a plurality of passive devices, wherein an input analog signal is connected to an x input end of the analog multiplier U1 through a resistor R1, a y input end of the analog multiplier U1 is connected to a direct-current voltage signal, an output end of the analog multiplier U1 is connected to an inverting input end of the operational amplifier U2 through a resistor R2, an in-phase input end of the operational amplifier U2 is grounded, an output end of the operational amplifier U2 is connected to an inverting input end of the operational amplifier U2 through a capacitor Cf, and an output end of the operational amplifier U2 is connected to an x input end of the analog multiplier U1 connected to the input analog signal through a resistor Rf.
2. A high/low pass filter circuit configuration with precisely controllable cut-off frequency according to claim 1 wherein the analog multiplier U1 is replaced by a controllable gain amplifying device.
3. The circuit configuration according to claim 1, wherein the circuit configuration is capable of realizing low-pass filtering or high-pass filtering of an input analog signal, wherein the output end of the low-pass filtering is the output end of the operational amplifier U2, the output end of the high-pass filtering is the x input end of an analog multiplier to which the input analog signal is connected, and the cut-off frequency of the low-pass filtering or the high-pass filtering is controlled by a direct-current voltage signal input by the analog multiplier.
4. The high/low pass filter circuit configuration with precisely controllable cut-off frequency according to claim 1, wherein the output voltage of the analog multiplier U1 is equal to the product of the input voltages at both ends, the output is equal to the product of the input analog signal and the control voltage signal, and the function is realized by a controllable gain amplifier;
designing a bandwidth controllable inverting filter, wherein the positive direction of current is set to flow from an input Vin to a resistor Rf through a resistor R1; in an ideal state, the input impedance of the analog multiplier U1 is regarded as infinity, the operational amplifier U2 meets an ideal amplifying state, and the frequency domain relation between the output voltage and the voltage at the point a and the voltage at the point b can be known according to an analog multiplier calculation formula and an operational amplifier amplifying principle, wherein the point a is an x input end of the analog multiplier U1, and the point b is an output end of the analog multiplier U1, as shown in formulas (1) and (2); vo is an operational amplifier U2Output terminal voltage, V a For the voltage at the x input of the analog multiplier U1, V b For the voltage at the output of the analog multiplier U1, V y For the voltage at the y input of the analog multiplier U1, R 2 C is the resistor connected between the output end of the analog multiplier U1 and the inverting input end of the operational amplifier U2 f Is the capacitance connected between the inverting input terminal and the output terminal of the operational amplifier U2, J is the imaginary unit representing the phase rotation of the voltage signal, ω is the frequency of the voltage signal, vin is the input voltage, I R1 To flow through the resistor R1, I R2 Is the current flowing through resistor R2;
V b ＝V y ×V a (2)
taking the multiplier U1 and the operational amplifier U2 as a whole, wherein the amplification factor-A is shown in a formula (3), and the peripheral circuit accords with the precondition of negative feedback design; the positive direction of the current is set to be that the input Vin flows to the resistor Rf through the resistor R1 to obtain formulas (4), (5) and (6);
V o ＝-A×V a (4)
in an ideal state, the input impedance of the multiplier U1 is considered to be infinite, and the current does not enter the input end thereof, so I R1 ＝I Rf ，ω 0 For the cut-off frequency, the a-point voltage Va, operation is obtained when rf=r1Frequency domain relationship of the output voltage Vo of the amplifier U2 to the input voltage Vin:
wherein the cutoff frequency omega 0 The control formula of (2) is:
in combination with the above formula, the circuit configuration takes Vo as an output and takes Va as an output as a low-pass filter, and the cut-off frequency is determined by the control voltage Vy, the resistor R2 and the capacitor Cf together, and in the case of resistance-capacitance determination, the upper limit of the filtering precision of the circuit configuration depends on the regulation precision of the control voltage.
CN202311529522.6A 2023-11-16 2023-11-16 High/low pass filter circuit configuration with accurately adjustable cut-off frequency Pending CN117559961A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202311529522.6A CN117559961A (en) 2023-11-16 2023-11-16 High/low pass filter circuit configuration with accurately adjustable cut-off frequency

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202311529522.6A CN117559961A (en) 2023-11-16 2023-11-16 High/low pass filter circuit configuration with accurately adjustable cut-off frequency

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CN117559961A true CN117559961A (en) 2024-02-13

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