Narrow-band filter

Abstract

A narrow-band filter comprises a first operational amplifier U1A, a second operational amplifier U1B, a third operational amplifier U2A, a fourth operational amplifier U2B and the like. The first operational amplifier U1A, the second operational amplifier U1B, the resistor R8, the resistor R1, the capacitor C1, the capacitor C17, the resistor R2, the resistor R3, the capacitor C2 and the capacitor C3 form a second-order low-pass unit; and the third operational amplifier U2A, the fourth operational amplifier U2B, the capacitor C7, the resistor R5, the capacitor C4, the resistor R6, the capacitor C6, the resistor R4, the capacitor C8 and the resistor R7 form a second-order high-pass unit. An integrated operational amplifier is used for designing a four-order band-pass filter, noise elimination of low-pass signals is achieved, and band-pass filtering with the requirement that the pass-band gain is 0dB, the flatness is 1dB and the 3dB cut-off frequency is 6kHz-197kHz is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of signal processing engineering, and relates to filter technology, in particular to a narrow-band filter based on operational amplifier design. BACKGROUND

[0002] In the field of signal processing engineering, almost all the signals used belong to sound signals, light signals or electric signals, etc. The message intensity of the signals is low, small and weak, and the signals are not easy to be received, sensed or received by equipment. Noise covers the detection of various weak signals, and more and more attention is paid to it. In order to extract useful signals in strong interference signals, a filter and an amplification circuit are usually added to realize the filtering and processing of signals, remove noise, interference and other unnecessary frequency components, and thus improve the quality and stability of the signals. The filters in the prior art are various, and even the filters with the same bandwidth are different in Q value (quality factor), which leads to uneven performance of the filters and is difficult to meet the design or product requirements of the filters. CONTENT OF THE INVENTION

[0003] In order to solve the above problems of the prior art, the application provides a narrow-band filter based on operational amplifier design, which uses an integrated operational amplifier to design a 4th-order band-pass filter to realize the noise removal of low-frequency signals.

[0004] In order to achieve the above purpose, the application adopts the following technology:

[0005] A narrow-band filter comprises a first operational amplifier U1A, a second operational amplifier U1B, a third operational amplifier U2A and a fourth operational amplifier U2B.

[0006] The non-inverting input end of the first operational amplifier U1A is connected with one end of a resistor R1 and one end of a capacitor C1, the inverting input end is connected with one end of a capacitor C17, the output end is connected with the inverting input end and one end of a resistor R2, the other end of the resistor R1 is connected with the other end of the capacitor C17 and one end of a resistor R8, and the other end of the capacitor C1 is connected with GND.

[0007] The non-inverting input end of the second operational amplifier U1B is connected with one end of a resistor R3 and one end of a capacitor C3, the inverting input end is connected with one end of a capacitor C2, the output end is connected with the inverting input end and one end of a capacitor C7, the other end of the resistor R3 is connected with the other end of the capacitor C2 and the other end of the resistor R2, and the other end of the capacitor C3 is connected with GND.

[0008] The non-inverting input end of the third operational amplifier U2A is connected with one end of a resistor R6 and one end of a capacitor C4, the inverting input end is connected with one end of a resistor R5, the output end is connected with the inverting input end and one end of a capacitor C6, the other end of the resistor R5 is connected with the other end of the capacitor C4 and the other end of the capacitor C7, and the resistor R5 is connected with GND.

[0009] The non-inverting input end of the fourth operational amplifier U2B is connected with one end of the resistor R7 and one end of the capacitor C8, the inverting input end is connected with one end of the resistor R4, the output end is connected with the inverting input end, the other end of the resistor R4 is connected with the other end of the capacitor C8 and the other end of the capacitor C6, and the resistor R7 is connected with GND;

[0010] The other end of the resistor R8 is used for connecting a signal source, and the output end of the fourth operational amplifier U2B is the output end of the filter.

[0011] Further, the first operational amplifier U1A and the second operational amplifier U1B are realized by one double-channel operational amplifier device, and the third operational amplifier U2A and the fourth operational amplifier U2B are realized by another double-channel operational amplifier device.

[0012] Further, the first operational amplifier U1A, the second operational amplifier U1B, the resistor R8, the resistor R1, the capacitor C1, the capacitor C17, the resistor R2, the resistor R3, the capacitor C2 and the capacitor C3 constitute a second-order low-pass unit, and the third operational amplifier U2A, the fourth operational amplifier U2B, the capacitor C7, the resistor R5, the capacitor C4, the resistor R6, the capacitor C6, the resistor R4, the capacitor C8 and the resistor R7 constitute a second-order high-pass unit.

[0013] The utility model has the advantages that:

[0014] 1. The integrated operational amplifier is used to design a fourth-order band-pass filter, and the noise of a low-frequency signal is removed.

[0015] 2. The attenuation amplitude can be adjusted by adjusting the resistance value and the capacitance value in the filter, such as increasing or decreasing the same multiple.

[0016] 3. The band-pass filter with a passband gain of 0dB, a flatness of 1dB and a 3dB cutoff frequency of 6kHz-197kHz is realized. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is the circuit principle and test simulation environment diagram of the embodiment of the application.

[0018] Figure 2 It is the simulation result of the starting point 6KHz of the narrow-band filter of the embodiment of the application.

[0019] Figure 3 It is the simulation result of the cutoff point 197KHz of the narrow-band filter of the embodiment of the application. DETAILED DESCRIPTION

[0020] In order to make the purpose, the technical scheme and the advantages of the embodiments of the utility model clearer, the embodiments of the utility model are described in detail below with reference to the drawings, but the embodiments described in the utility model are part of the embodiments of the utility model, rather than all the embodiments.

[0021] The embodiment of the application provides a kind of narrow band filter, utilize integrated operational amplifier design 4 order band-pass filter, realize the denoising of low communication signal.Assume that input signal amplitude is 1Vp, passband gain is required to be 0dB, 3dB cut-off frequency is 6K~197KHz respectively, pass gain requirement flatness is 1dB, circuit load is 1kΩ.According to the above requirements, the circuit is designed, and the amplitude-frequency characteristic of the circuit is simulated.

[0022] As shown in Figure 1 Narrow band filter includes first operational amplifier U1A, second operational amplifier U1B, third operational amplifier U2A and fourth operational amplifier U2B.

[0023] Specifically, first operational amplifier U1A and second operational amplifier U1B are realized by a double-channel operational amplifier device, and third operational amplifier U2A and fourth operational amplifier U2B are realized by another double-channel operational amplifier device.The double-channel operational amplifier device can use ADA4096-2ACPZ.

[0024] Each operational amplifier is matched with resistance and capacitance, the resistance is selected as E96 series value, the capacitance is selected as 10% series, and the cut-off frequency error is required to be within 20%.

[0025] The non-inverting input terminal of the first operational amplifier U1A is connected to one end of the resistance R1 and one end of the capacitance C1, the inverting input terminal is connected to one end of the capacitance C17, the output terminal is connected to the inverting input terminal and one end of the resistance R2, the other end of the resistance R1 is connected to the other end of the capacitance C17 and one end of the resistance R8, the other end of the capacitance C1 is connected to GND.The other end of the resistance R8 is used to connect the signal source.Simulation test, as shown in Figure 1 The other end of the resistance R8 is connected to the signal source XFG1, and is also connected to IN+ of the Bode plot instrument XBP1 and IN+ of the Bode plot instrument XBP3.

[0026] The non-inverting input terminal of the second operational amplifier U1B is connected to one end of the resistance R3 and one end of the capacitance C3, the inverting input terminal is connected to one end of the capacitance C2, the output terminal is connected to the inverting input terminal and one end of the capacitance C7, the other end of the resistance R3 is connected to the other end of the capacitance C2 and the other end of the resistance R2, the other end of the capacitance C3 is connected to GND.During simulation test, the output terminal of the second operational amplifier U1B is connected to OUT+ of the Bode plot instrument XBP1.

[0027] The non-inverting input terminal of the third operational amplifier U2A is connected to one end of the resistance R6 and one end of the capacitance C4, the inverting input terminal is connected to one end of the resistance R5, the output terminal is connected to the inverting input terminal and one end of the capacitance C6, the other end of the resistance R5 is connected to the other end of the capacitance C4 and the other end of the capacitance C7, and the resistance R5 is connected to GND.During simulation test, the non-inverting input terminal of the third operational amplifier U2A is connected to A end of the channel oscilloscope XSC1.

[0028] The non-inverting input terminal of the fourth operational amplifier U2B is connected to one end of the resistor R7 and one end of the capacitor C8, the inverting input terminal is connected to one end of the resistor R4, the output terminal is connected to the inverting input terminal, the other end of the resistor R4 is connected to the other end of the capacitor C8 and the other end of the capacitor C6, the resistor R7 is connected to GND, and the output terminal of the fourth operational amplifier U2B is the output terminal of the filter.

[0029] The first operational amplifier U1A, the second operational amplifier U1B, the resistor R8, the resistor R1, the capacitor C1, the capacitor C17, the resistor R2, the resistor R3, the capacitor C2, and the capacitor C3 constitute a second-order low-pass unit. The third operational amplifier U2A, the fourth operational amplifier U2B, the capacitor C7, the resistor R5, the capacitor C4, the resistor R6, the capacitor C6, the resistor R4, the capacitor C8, and the resistor R7 constitute a second-order high-pass unit.

[0030] Optionally, the resistance value of the resistor R2 is equal to the resistance value of the resistor R8, the resistance value of the resistor R1 is equal to the resistance value of the resistor R3, and the capacitance value of the capacitor C1 is equal to the capacitance value of the capacitor C3, which functions to expand the upper sideband and adjust the cutoff point of the low-pass, i.e., to adjust the lower limit cutoff frequency fp2.

[0031] The capacitance value of the capacitor C7 is equal to the capacitance value of the capacitor C7, the capacitance value of the capacitor C4 is equal to the capacitance value of the capacitor C8, and the resistance value of the resistor R6 is equal to the resistance value of the resistor R7, which functions to reduce the lower sideband and adjust the starting point of the high-pass, i.e., to adjust the upper limit cutoff frequency fp1.

[0032] In the second-order low-pass unit: the passband gain Ap=1, the feedback resistor RF is 0, and because the upper limit cutoff frequency fp1 is 193 kHz, according to the nonlinear relationship between the cutoff frequency and C, C is taken as 47 pF, and the nonlinear relationship between the cutoff frequency and C is as follows: C1=C3=C=47 pF; K0=100 / fc*C=193 / 3; R8=R2=0.136*K0; R1=R3=4.28*K0.

[0033] In the second-order high-pass unit: the passband gain Ap=1, the feedback resistor RF is 0, and because the lower limit cutoff frequency fp2 is 6 kHz, according to the nonlinear relationship between the cutoff frequency and C, C is taken as 820 pF, and the nonlinear relationship between the cutoff frequency and C is as follows: C6=C7=C=820 pF; K0=100 / fc*C=20 / 3; R6=R7=7.5*K0.

[0034] The simulation results are as follows Figures 2-3 The band-pass filter with a passband gain of 0 dB, a flatness of 1 dB, and a 3 dB cutoff frequency of 6 kHz-197 kHz is realized.

[0035] The above descriptions are merely some embodiments of the present application, but are not intended to limit the present application. It is apparent that those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application.

Claims

1. A narrowband filter, characterized by, The first operational amplifier U1A, the second operational amplifier U1B, the third operational amplifier U2A, and the fourth operational amplifier U2B are connected in series. The non-inverting input terminal of the first operational amplifier U1A is connected to one end of the resistor R1 and one end of the capacitor C1, the inverting input terminal is connected to one end of the capacitor C17, and the output terminal is connected to the inverting input terminal and one end of the resistor R2. The other end of the resistor R1 is connected to the other end of the capacitor C17 and one end of the resistor R8, and the other end of the capacitor C1 is connected to GND. The non-inverting input terminal of the second operational amplifier U1B is connected to one end of the resistor R3 and one end of the capacitor C3, the inverting input terminal is connected to one end of the capacitor C2, and the output terminal is connected to the inverting input terminal and one end of the capacitor C7. The other end of the resistor R3 is connected to the other end of the capacitor C2 and the other end of the resistor R2, and the other end of the capacitor C3 is connected to GND. The non-inverting input terminal of the third operational amplifier U2A is connected to one end of the resistor R6 and one end of the capacitor C4, the inverting input terminal is connected to one end of the resistor R5, and the output terminal is connected to the inverting input terminal and one end of the capacitor C6. The other end of the resistor R5 is connected to the other end of the capacitor C4 and the other end of the capacitor C7, and the resistor R5 is connected to GND. The non-inverting input terminal of the fourth operational amplifier U2B is connected to one end of the resistor R7 and one end of the capacitor C8, the inverting input terminal is connected to one end of the resistor R4, and the output terminal is connected to the inverting input terminal. The other end of the resistor R4 is connected to the other end of the capacitor C8 and the other end of the capacitor C6, and the resistor R7 is connected to GND.

2. The narrowband filter of claim 1, wherein, The other end of the resistor R8 is used to connect a signal source, and the output terminal of the fourth operational amplifier U2B is the output terminal of the filter.

3. The narrowband filter of claim 1, wherein, The first operational amplifier U1A and the second operational amplifier U1B are implemented by a double-channel operational amplifier device, and the third operational amplifier U2A and the fourth operational amplifier U2B are implemented by another double-channel operational amplifier device.

4. The narrowband filter of claim 1, wherein, The double-channel operational amplifier device uses ADA4096-2ACPZ.

5. The narrowband filter of claim 1, wherein, The first operational amplifier U1A, the second operational amplifier U1B, the resistor R8, the resistor R1, the capacitor C1, the capacitor C17, the resistor R2, the resistor R3, the capacitor C2, and the capacitor C3 constitute a second-order low-pass unit.

6. The narrowband filter of claim 1, wherein, The third operational amplifier U2A, the fourth operational amplifier U2B, the capacitor C7, the resistor R5, the capacitor C4, the resistor R6, the capacitor C6, the resistor R4, the capacitor C8, and the resistor R7 constitute a second-order high-pass unit.

7. The narrowband filter of claim 1, wherein, The resistance value of the resistor R2 is equal to the resistance value of the resistor R8, the resistance value of the resistor R1 is equal to the resistance value of the resistor R3, and the capacitance value of the capacitor C1 is equal to the capacitance value of the capacitor C3.

8. The narrowband filter of claim 1, wherein, The capacitance value of the capacitor C7 is equal to the capacitance value of the capacitor C7, the capacitance value of the capacitor C4 is equal to the capacitance value of the capacitor C8, and the resistance value of the resistor R6 is equal to the resistance value of the resistor R7.

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