Band-pass filtering method and circuit for depth finder

Abstract

The invention relates to a band-pass filtering method and circuit for a depth finder. According to the method, two stages of MFB type band-pass filters with different center frequencies are cascaded to process underwater acoustic echo signals, the center frequency of the first stage is 432 kHz, the center frequency of the second stage is 476 kHz, two-stage filtering is executed by two channels integrated in the same dual-channel operational amplifier chip, and passband flatness and rapid stop-band attenuation are achieved through parameter collaborative setting. A corresponding circuit adopts an OPA2830 operational amplifier, and through optimized resistor-capacitor network configuration, the area of a printed board is remarkably reduced, the wiring complexity and cost are reduced, and meanwhile, the filtering consistency and the anti-interference capability are improved. According to the scheme, noise interference in signals received by the depth finder can be effectively filtered out, the signal-to-noise ratio is remarkably improved, and the accuracy and reliability of water depth measurement are guaranteed.

Description

Technical Field

[0001] This invention relates to the field of underwater acoustic signal processing technology, and in particular to a bandpass filtering method and circuit for depth sounders. Background Technology

[0002] As a key piece of equipment for underwater exploration, the performance of an echo sounder directly depends on the ability of its receiving circuit to process underwater acoustic echo signals. In actual working environments, the received signals are mixed with a large amount of marine environmental noise, equipment noise, and electromagnetic interference. Therefore, designing high-performance bandpass filters to accurately extract effective echo signals within a specific frequency range has become a core technical issue for improving the performance of echo sounders.

[0003] Currently, common bandpass filtering implementations mainly include cascaded multi-stage identical filters and combinations of low-pass and high-pass filters. These existing technologies have significant shortcomings in both methodology and circuit structure.

[0004] Traditional filtering methods typically employ cascaded filtering with identical parameters or simple frequency band splicing. This approach struggles to achieve a good balance between passband flatness, stopband attenuation speed, and signal processing efficiency. The signal must pass through multiple similar or independent processing stages, introducing additional noise and distortion, and increasing the complexity and delay of signal processing.

[0005] In terms of circuit structure, cascading multiple identical filters requires arranging multiple similar filter units, while a combination of low-pass and high-pass filters requires two independent filter circuits and corresponding operational amplifiers. These structures lead to an increase in the number of electronic components, a complex printed circuit board layout, a large space occupation, and high material costs. At the same time, the discreteness of component parameters affects the consistency of filtering performance.

[0006] Therefore, there is an urgent need in this field for an innovative filtering method and corresponding circuit structure that can optimize the signal processing path from the method flow perspective, simplify the circuit design from the physical structure perspective, and achieve miniaturization, low cost and high reliability of the device while ensuring excellent filtering performance (including passband flatness and fast stopband attenuation). Summary of the Invention

[0007] To solve the above-mentioned technical problems, the present invention provides a bandpass filtering method for depth sounders, comprising the following steps:

[0008] Receives underwater acoustic echo signals mixed with noise;

[0009] The electrical signal is input to a first-stage MFB bandpass filter for preliminary filtering. The first-stage MFB bandpass filter is configured to have a first center frequency to selectively pass echo signals within a first frequency band and initially suppress first out-of-band noise.

[0010] The signal that has been initially filtered by the first-stage MFB bandpass filter is input to the second-stage MFB bandpass filter for secondary filtering. The second-stage MFB bandpass filter is configured to have a second center frequency different from the first center frequency in order to further filter and enhance the target echo signal in the second frequency band, while achieving fast stopband attenuation.

[0011] Among them, the first and second stage MFB type bandpass filters form a flat amplitude-frequency characteristic in the passband by coordinating the center frequency and bandwidth, and deeply suppress out-of-band noise, thereby outputting a filtered signal with a significantly improved signal-to-noise ratio.

[0012] Furthermore, the preliminary filtering and secondary filtering steps are performed by two operational amplifier channels integrated within the same dual-channel high-speed low-noise operational amplifier chip.

[0013] In one embodiment of the present invention, the first center frequency is 432 kHz and the second center frequency is 476 kHz.

[0014] In one embodiment of the present invention, the bandwidth of the first-stage MFB bandpass filter is 47kHz, and the bandwidth of the second-stage MFB bandpass filter is 50kHz.

[0015] In one embodiment of the present invention, the dual-channel high-speed low-noise operational amplifier chip is model OPA2830.

[0016] In one embodiment of the present invention, the first center frequency is set by configuring the parameters of the first resistor network (R1, R2, R3) and the first capacitor network (C1, C2); the second center frequency is set by configuring the parameters of the second resistor network (R4, R5, R6) and the second capacitor network (C3, C4).

[0017] The present invention also provides a bandpass filter circuit for implementing the above-described bandpass filter method, comprising:

[0018] First-stage MFB bandpass filter and second-stage MFB bandpass filter;

[0019] The output of the first-stage MFB bandpass filter is cascaded with the input of the second-stage MFB bandpass filter;

[0020] The first-stage MFB bandpass filter and the second-stage MFB bandpass filter are implemented by a dual-channel high-speed low-noise operational amplifier.

[0021] In one embodiment of the present invention, the first-stage MFB type bandpass filter includes resistors R1, R2, R3 and capacitors C1, C2; the second-stage MFB type bandpass filter includes resistors R4, R5, R6 and capacitors C3, C4.

[0022] Compared with the prior art, the above-mentioned technical solution of the present invention has the following advantages: The bandpass filtering method of the present invention can effectively filter out noise interference in the depth sounder received signal, significantly improve the signal-to-noise ratio, and ensure the accuracy and reliability of water depth measurement. Furthermore, the corresponding circuit uses an OPA2830 operational amplifier, and through optimized resistor-capacitor network configuration, significantly reduces the printed circuit board area, lowers wiring complexity and cost, while improving filtering consistency and anti-interference capability. Attached Figure Description

[0023] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0024] Figure 1 This is a flowchart of the bandpass filtering method in this invention.

[0025] Figure 2 This is a system block diagram of the bandpass filter circuit described in this invention.

[0026] Figure 3 This is a circuit schematic diagram of a specific embodiment of the present invention.

[0027] Figure 4 This is an alternative simulation circuit diagram for circuit simulation using the OPA830 operational amplifier.

[0028] Figure 5 yes Figure 4 The simulation diagram of the frequency response of the first-stage bandpass filter shows its center frequency and bandwidth.

[0029] Figure 6 yes Figure 4 The simulation diagram of the frequency response of the second-stage bandpass filter shows its center frequency and bandwidth.

[0030] Figure 7 This is a simulation diagram of the overall frequency response of the two-stage cascaded bandpass filter circuit of the present invention. Detailed Implementation

[0031] Example 1

[0032] like Figure 1 and Figure 2 As shown, this embodiment provides a bandpass filtering method for depth sounders, including the following steps:

[0033] First, receive the noisy underwater acoustic echo signal from the underwater acoustic transducer. This signal typically includes marine ambient noise, equipment noise, and electromagnetic interference.

[0034] Next, the received electrical signal is input to the first-stage MFB bandpass filter for preliminary filtering. By configuring the parameters of the first resistor network (R1, R2, R3) and the first capacitor network (C1, C2), this stage of the filter is given a specific first center frequency (432kHz in this embodiment). This step mainly achieves selective passage of echo signals within the first frequency band and preliminary suppression of the first out-of-band noise.

[0035] Then, the signal after the first-stage filtering is input to the second-stage MFB bandpass filter for secondary filtering. By configuring the parameters of the second resistor network (R4, R5, R6) and the second capacitor network (C3, C4), this stage of the filter has a second center frequency (476kHz in this embodiment) that is different from the first center frequency. This step further filters and enhances the target echo signal in the second frequency band, while achieving rapid stopband attenuation.

[0036] The two-stage filtering process described above is performed by two operational amplifier channels integrated within the same dual-channel high-speed low-noise operational amplifier chip (preferably OPA2830 in this embodiment). By collaboratively setting the center frequency and bandwidth of the two-stage filters (47kHz for the first stage and 50kHz for the second stage), a flat amplitude-frequency response is ultimately formed within the passband, deeply suppressing out-of-band noise and resulting in a filtered signal with a significantly improved signal-to-noise ratio.

[0037] Example 2

[0038] To implement the above filtering method, this embodiment provides a corresponding circuit implementation. For example... Figure 3 The circuit schematic shown indicates that the bandpass filter circuit includes:

[0039] A first-stage MFB bandpass filter and a second-stage MFB bandpass filter. The first-stage MFB bandpass filter consists of resistors R1, R2, and R3, capacitors C1 and C2, and the first channel (U1:A) of a dual-channel operational amplifier U1. The second-stage MFB bandpass filter consists of resistors R4, R5, and R6, capacitors C3 and C4, and the second channel (U1:B) of U1. The output of the first-stage filter is cascaded with the input of the second-stage filter.

[0040] Specific simulation verification; since the OPA2830 model may not be available in the simulation software, its single-channel version, OPA830, can be used as an alternative for simulation. The simulation circuit is as follows: Figure 4 As shown.

[0041] Simulation results show that:

[0042] The frequency response of the first-stage bandpass filter (composed of R1, R2, R3, C1, C2, and U1:A) is as follows: Figure 5 As shown, its center frequency is 432kHz and its bandwidth is 47kHz.

[0043] The frequency response of the second-stage bandpass filter (composed of R4, R5, R6, C3, C4, and U1:B) is as follows: Figure 6 As shown, its center frequency is 476kHz and its bandwidth is 50kHz.

[0044] The overall frequency response after cascading the two filters is as follows: Figure 7 As shown, this filter circuit exhibits good passband flatness and fast stopband attenuation characteristics.

[0045] This embodiment, through the aforementioned method and circuit, achieves a significant reduction in printed circuit board area, wiring complexity, and material costs while maintaining excellent filtering performance. The two operational amplifier channels within the same chip exhibit stronger consistency in response to temperature and power supply fluctuations, resulting in better common-mode rejection ratio (CMRR) and power supply rejection ratio (PSRR) performance, and superior anti-interference capabilities. Applying this circuit to the depth sounder's receiving circuit effectively filters out interference signals while retaining useful echo signals, thereby improving the signal-to-noise ratio and enhancing the accuracy and reliability of depth measurement.

[0046] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A bandpass filtering method for depth sounders, characterized in that, Includes the following steps: Receives underwater acoustic echo signals mixed with noise; The electrical signal is input to a first-stage MFB bandpass filter for preliminary filtering. The first-stage MFB bandpass filter is configured to have a first center frequency to selectively pass echo signals within a first frequency band and initially suppress first out-of-band noise. The signal that has been initially filtered by the first-stage MFB bandpass filter is input to the second-stage MFB bandpass filter for secondary filtering. The second-stage MFB bandpass filter is configured to have a second center frequency different from the first center frequency in order to further filter and enhance the target echo signal in the second frequency band, while achieving fast stopband attenuation. Among them, the first and second stage MFB type bandpass filters form a flat amplitude-frequency characteristic in the passband by coordinating the center frequency and bandwidth, and deeply suppress out-of-band noise, thereby outputting a filtered signal with a significantly improved signal-to-noise ratio. Furthermore, the preliminary filtering and secondary filtering steps are performed by two operational amplifier channels integrated within the same dual-channel high-speed low-noise operational amplifier chip.

2. The bandpass filtering method according to claim 1, characterized in that: The first center frequency is 432kHz, and the second center frequency is 476kHz.

3. The bandpass filtering method according to claim 2, characterized in that: The bandwidth of the first-stage MFB bandpass filter is 47kHz, and the bandwidth of the second-stage MFB bandpass filter is 50kHz.

4. The bandpass filtering method according to claim 1, characterized in that: The dual-channel high-speed low-noise operational amplifier chip is model OPA2830.

5. The bandpass filtering method according to claim 1, characterized in that: The first center frequency is set by configuring the parameters of the first resistor network and the first capacitor network; the second center frequency is set by configuring the parameters of the second resistor network and the second capacitor network.

6. A bandpass filter circuit for implementing the bandpass filter method according to any one of claims 1 to 5, characterized in that, include: First-stage MFB bandpass filter and second-stage MFB bandpass filter; The output of the first-stage MFB bandpass filter is cascaded with the input of the second-stage MFB bandpass filter; The first-stage MFB bandpass filter and the second-stage MFB bandpass filter are implemented by a dual-channel high-speed low-noise operational amplifier.

7. The bandpass filter circuit according to claim 6, characterized in that: The first-stage MFB bandpass filter includes resistors R1, R2, and R3, and capacitors C1 and C2; the second-stage MFB bandpass filter includes resistors R4, R5, and R6, and capacitors C3 and C4.

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