A receiving preprocessing circuit for image sonar

Abstract

The present invention relates to the technical field of receiving preprocessing of acoustic signals, and specifically to a receiving preprocessing circuit for image sonar; it includes a preamplifier circuit, a filter circuit and a conditioning module; the input end of the preamplifier circuit is used to receive an analog signal output by an array element, the output end is connected to the input end of the filter circuit, the output end of the filter circuit is connected to the input end of the conditioning module, and the output end of the conditioning module is used to connect to a sampling quantization circuit; in the process of signal preprocessing, the preamplifier circuit, the filter circuit and the conditioning module are used to complete the amplification, filtering and conditioning operations of the signal, so as to achieve high-quality signal preprocessing. It realizes indiscriminate amplification of underwater acoustic signals, filtering of noise, and improving the signal-to-noise ratio of output signals; it adopts a 16-bit, 8-channel synchronous sampling analog-to-digital data acquisition chip; the system can realize the selection of the center frequency of different underwater acoustic signal acquisition and processing by changing the configurable parameters in the circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of acoustic signal reception preprocessing, and in particular to a reception preprocessing circuit for an image sonar. Background Art

[0002] Generally, sonar systems utilize a multi-element array, which has a large number of output signal paths. This requires a multi-channel acquisition system. The hydrophone output signal is very weak, requiring processing such as amplification and filtering before acquisition and quantization. In acquisition systems, the input analog signal typically passes through a preprocessing circuit before sampling and quantization. The purpose of signal preprocessing is to perform operations such as buffering, amplification, attenuation, isolation, and linearization of the sensor signal. During the amplification and filtering process of signal preprocessing, the signal is easily affected by electrical noise and digital circuits, causing signal phase shifts. To ensure amplitude and phase consistency across all channels, high demands are placed on the analog receiver's signal preprocessing circuitry.

[0003] Basic Information on Traditional Technologies: In recent years, with the progress and development of society, humanity has become increasingly interested in understanding the planet they inhabit. Compared to the more familiar landmass, our understanding of the ocean remains relatively limited. The ocean is an indispensable resource for humanity, making it all the more worthy of exploration and development. my country shoulders the important mission and task of building a strong maritime nation, and continuously exploring the unknown ocean has become a key issue in my country's development today. Understanding the ocean requires collecting, analyzing, and processing underwater information. As we all know, most underwater information is transmitted in the form of sound waves, a very effective transmission method. Acoustic signals carrying underwater information can be collected underwater and converted into electrical signals for processing and analysis, thereby achieving the goal of understanding the underwater world. In underwater signal processing, preprocessing circuits are undoubtedly crucial for more accurate processing and analysis of underwater acoustic signals. They are the first step in the signal's entry into the entire underwater acoustic processing system and determine the phase and amplitude consistency of the acquired and stored underwater acoustic signals, thus affecting the accuracy of the processing results. This process is widely used in fields such as sonar and radar.

[0004] Traditional underwater acoustic signal preprocessing circuits have the following main shortcomings:

[0005] Weak signal processing capability: For underwater acoustic signals, the signal output by the transducer is a weak signal with an extremely low signal-to-noise ratio. The preprocessing circuit is used to amplify useful signals, attenuate noise signals, and improve the signal-to-noise ratio of the signal to facilitate detection and processing by subsequent circuits. Its performance determines the system's ability to detect weak signals.

[0006] Fewer data transmission channels: Traditional underwater acoustic data acquisition memory generally has fewer channels. For example, single-channel ones include SP201 and SC247, and dual-channel ones include EG3300 and YE5938. This results in slow data transmission, long working time, and low acquisition efficiency. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention provides a receiver preprocessing circuit for imaging sonar, which achieves indiscriminate amplification of underwater acoustic signals, filters noise, and improves the signal-to-noise ratio of the output signal. This circuit utilizes a 16-bit, 8-channel synchronous sampling analog-to-digital data acquisition chip. The system can select the center frequency for different underwater acoustic signal acquisition and processing by modifying configurable circuit parameters. All components are low-noise, low-current, ensuring the circuit's low power consumption.

[0008] The present invention is achieved through the following technical solutions:

[0009] A receiving preprocessing circuit for an image sonar includes a preamplifier circuit, a filter circuit, and a conditioning module; the preamplifier circuit has an input for receiving an analog signal output by an array element, an output connected to an input of the filter circuit, an output of the filter circuit connected to an input of the conditioning module, and an output of the conditioning module connected to a sampling and quantization circuit;

[0010] During the signal preprocessing process, the signal amplification, filtering and conditioning operations are completed through the preamplifier circuit, the filter circuit and the conditioning module, thereby achieving high-quality signal preprocessing.

[0011] Preferably, the preamplifier circuit uses an AD8421 chip, and the AD8421 chip serves as the front stage of the preprocessing circuit.

[0012] Preferably, when the AD8421 chip is used as a preamplifier circuit, the gain is set to 1 to 10,000 by configuring a resistor; the reference pin is used to apply a precise offset to the output voltage.

[0013] Preferably, the 8-channel analog signals at the input end are amplified by the AD8421 chip, and the input underwater acoustic signal is amplified 10 times by configuring the gain resistor Rg=1kΩ, and output to the next-level analog filter circuit.

[0014] Preferably, the filtering circuit adopts the LT1568 chip, so that the LT1568 chip is used as a second-order Butterworth low-pass filter or a band-pass filter; the low-pass cutoff frequency is set at 2.5MHz by adjusting the resistance value of the external resistor, the total voltage input is 5V, and the corresponding current is 28mA~38mA.

[0015] Preferably, the 8-channel analog signals at the analog signal input end of the filtering circuit are filtered by the LT1568 chip with a center frequency of fs=2.5MHz, which effectively filters the interfering low-frequency signals to prevent interference with the collected target signals, and then output them to the next-level conditioning module circuit.

[0016] Preferably, the conditioning module adopts a VCA8500 chip, which is an 8-channel variable gain amplifier consisting of a low-noise preamplifier and a variable post-gain amplifier.

[0017] Preferably, the gain of the low noise preamplifier is fixed at 20 dB and has good noise and signal handling characteristics; the post gain amplifier is programmed to four gain settings: 20 dB, 25 dB, 27 dB or 30 dB gain.

[0018] Preferably, the working principle of the underwater acoustic signal preprocessing circuit is:

[0019] First, the 8-channel analog signals at the input end are amplified by the AD8421 chip, and the input underwater acoustic signal is amplified 10 times by configuring the gain resistor Rg=1kΩ, and output to the next-level analog filter circuit. Then, the 8-channel analog signals at the analog signal input end of the filter circuit are filtered by the LT1568 chip with a center frequency of fs=2.5MHz, which effectively filters the interfering low-frequency signals to prevent interference with the collected target signals, and then output to the next-level conditioning module circuit. Finally, the conditioning module uses the VCA8500 chip as the variable gain amplifier in the conditioning module, which is internally controlled by the single-chip microcomputer STM32. By controlling the high and low levels of the VCA8500 control pins, the 8-channel input signals are conditioned and amplified, and the single-ended input signals are converted into differential signal outputs, thereby eliminating common-mode noise and improving the signal-to-noise ratio, and then output to the A / D acquisition module.

[0020] The beneficial effects of the present invention are:

[0021] 1. The present invention studies the role of narrowband systems in improving signal-to-noise ratio and detection capability. In the circuit, weak signals can be amplified by a low-noise amplifier, and then a bandpass filter composed of an extremely low-noise high-frequency active RC filter chip is used to filter out noise signals to improve the signal-to-noise ratio. By designing an eight-channel high-frequency signal acquisition, it can correspond to multi-element array acquisition and ensure the integrity of underwater acoustic signal preprocessing.

[0022] 2. Signal-to-noise ratio of underwater acoustic signals: It consists of a preamplifier circuit with a wide and flat bandwidth and a narrow and shiftable bandpass filter. It can not only amplify the underwater acoustic signal indiscriminately, but also filter the noise, thereby improving the signal-to-noise ratio of the output signal.

[0023] 3. Synchronous storage of multiple underwater acoustic sensors: using 16-bit, 8-channel synchronous sampling analog-to-digital data acquisition chip.

[0024] 4. Bandwidth and low power consumption: The system can select the center frequency for different underwater acoustic signal acquisition and processing by changing the configurable parameters in the circuit. All components are low-noise and low-current components to ensure the circuit's low power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 It is a circuit structure diagram of the present invention;

[0027] Figure 2 It is the principle diagram of the AD8421 preamplifier circuit in the present invention;

[0028] Figure 3 It is a schematic diagram of the filter circuit in the present invention.

[0029] In the figure: 1-preamplifier circuit, 2-filter circuit, 3-conditioning module. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention. Example

[0031] See also Figures 1-3As shown, this embodiment specifically discloses a technical solution for a receiver preprocessing circuit for an imaging sonar. The circuit utilizes a low-noise, low-power preamplifier chip, the AD8421, as the pre-stage of the preprocessing circuit. The LT1568, an extremely low-noise, high-frequency active RC filter, serves as the filtering module within the preprocessing circuit. Finally, a low-noise preamplifier chip, the VCA8500, comprising a variable-gain amplifier, completes the post-conditioning circuit. This circuit integrates several novel architectural components designed for optimal performance, higher integration, and lower power consumption, achieving a higher level of system performance. To achieve optimal system performance, a balanced combination of these high-performance components is essential.

[0032] Preamplifier Circuit 1: The AD8421 is a low-cost, low-power, extremely low-noise, ultra-low bias current, high-speed instrumentation amplifier ideal for a wide range of signal conditioning and data acquisition applications. It can extract low-level signals in the presence of high-frequency common-mode noise over a wide temperature range. Its superior performance and parameters make the AD8421 a standout in applications requiring high-channel-count multiplexed systems. Even with higher gains, the current feedback architecture maintains high performance, achieving a settling time of 0.8µs at G = 100 and a 2MHz bandwidth, for example. The AD8421's excellent distortion performance makes it suitable for use in demanding circuit environments.

[0033] The AD8421 offers 3nV / √Hz input voltage noise and 200fA / √Hz current noise, with only 2mA of quiescent current, making it ideal for measuring low-level signals. For applications with high source impedance, the AD8421 uses innovative process technology and design techniques to provide noise performance limited only by the sensor.

[0034] The AD8421 uses a unique protection method to ensure a strong input while still maintaining very low noise. This protection allows input voltages up to 40V from the opposite supply rail without damaging the part.

[0035] When using the AD8421 chip as preamplifier circuit 1, the gain can be set from 1 to 10000 by configuring a resistor. The reference pin can be used to apply a precise offset to the output voltage.

[0036] When designing the circuit, it is necessary to configure the resistance parameters of the AD8421 chip. Figure 2 AD8421 preamplifier circuit 1 schematic diagram: Figure 2 It can be seen that the 8-channel analog signals at the input end are amplified by AD8421, and the input underwater acoustic signal is amplified 10 times by configuring the gain resistor Rg = 1kΩ, and output to the next-level analog filter circuit 2.

[0037] Filtering Module: The LT1568 chip is an easy-to-use active RC filter building block with rail-to-rail input and output. The IC's internal capacitors and the GBW product of its internal low-noise operational amplifier are trimmed to achieve consistent and repeatable filter response. Using a single resistor value, the LT1568 provides a pair of matched two-pole Butterworth low-pass filters with unity gain suitable for I / Q channels. By using asymmetrical external resistors, these two two-pole filter sections can produce different frequency responses or gains. Furthermore, the two stages can be cascaded to form a four-pole filter with a programmable response. The LT1568 can achieve cutoff frequencies up to 10MHz, making it ideal for anti-aliasing or channel filtering in high-speed data communications. It can also be used as a bandpass filter. The LT1568 offers very low noise, supporting a signal-to-noise ratio exceeding 90dB. It also provides single-ended to differential signal conversion for direct driving of high-speed A / D converters. The LT1568 features a shutdown mode that reduces supply current to approximately 0.5mA when operating from a 5V supply.

[0038] In this embodiment, the LT1568 chip is used as a second-order Butterworth low-pass filter, which can also function as a bandpass filter. The low-pass cutoff frequency is set to 2.5MHz by adjusting the value of an external resistor. A total voltage input of 5V corresponds to a current range of 28mA to 38mA. Furthermore, this filter can also be used for single-ended to differential conversion, eliminating phase noise and improving the signal-to-noise ratio.

[0039] The filter circuit 2 of LT1568 is designed as follows Figure 3 Shown: From Figure 3 It can be seen that the 8-channel analog signals at the analog signal input end of the filter circuit 2 are filtered by LT1568 with a center frequency of fs=2.5MHz, which effectively filters the interfering low-frequency signals to prevent interference with the target signals we collected, and then output them to the next-level conditioning module 3 circuit.

[0040] Conditioning Module 3: The VCA8500 is an 8-channel variable-gain amplifier consisting of a low-noise preamplifier and a variable-gain attenuator. This combination, along with the device's functionality, makes it an ideal choice for a variety of ultrasound systems. The low-noise preamplifier has a fixed gain of 20dB and offers excellent noise and signal handling characteristics. The voltage-controlled attenuator's gain can be varied over a 45dB range across all channels of the VCA8500 using a 0V to 1.2V control voltage.

[0041] The post-gain amplifier can be programmed to four gain settings: 20 dB, 25 dB, 27 dB, or 30 dB gain. As a means of improving system overload recovery time, the VCA8500 provides an internal clamping function with post-gain amplifier settings and the clamp is controlled via the series connections.

[0042] In this embodiment, the VCA8500 chip is used as the variable gain amplifier in the conditioning module 3, which is internally controlled by the single-chip STM32. By controlling the high and low levels of the VCA8500 control pins, the 8-way input signals are conditioned and amplified, and the single-ended input signals are converted into differential signal outputs, thereby eliminating common-mode noise and improving the signal-to-noise ratio, and then output to the A / D acquisition module.

[0043] System Operating Principle: The underwater acoustic signal preprocessing circuit operates as follows: First, the eight analog signals at the input are amplified by the AD8421. A gain resistor Rg = 1kΩ is configured to amplify the input underwater acoustic signals by a factor of 10 and output them to the next-level analog filter circuit 2. The eight analog signals at the analog signal input of filter circuit 2 are then filtered by the LT1568 with a center frequency fs = 2.5MHz, effectively filtering out interfering low-frequency signals to prevent them from interfering with the acquired target signal. These signals are then output to the next-level conditioning module 3 circuit. Finally, conditioning module 3 uses the VCA8500 chip as its variable gain amplifier. Internally controlled by an STM32 microcontroller, the eight input signals are conditioned and amplified by controlling the high and low levels of the VCA8500 control pins, converting single-ended input signals into differential output signals, thereby eliminating common-mode noise and improving the signal-to-noise ratio. These signals are then output to the A / D acquisition module.

[0044] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A receiving preprocessing circuit for an image sonar, characterized in that: It comprises a preamplifier circuit, a filter circuit and a conditioning module; the input end of the preamplifier circuit is used to receive the analog signal output by the array element, the output end is connected to the input end of the filter circuit, the output end of the filter circuit is connected to the input end of the conditioning module, and the output end of the conditioning module is used to connect to the sampling quantization circuit; In the signal preprocessing process, the signal amplification, filtering and conditioning operations are completed through the preamplifier circuit, the filter circuit and the conditioning module to achieve high-quality signal preprocessing; The working principle of the acoustic signal preprocessing circuit is as follows: first, the 8-channel analog signal at the input end is amplified by the AD8421 chip, and the input underwater acoustic signal is amplified 10 times by configuring the gain resistor Rg=1kΩ, and then output to the next-level analog filter circuit. Then, the 8-channel analog signal at the analog signal input end of the filter circuit is filtered by the LT1568 chip with a center frequency of fs=2.5MHz, which effectively filters the interfering low-frequency signal to prevent interference with the collected target signal, and then outputs it to the next-level conditioning module circuit. Finally, the conditioning module uses the VCA8500 chip as the variable gain amplifier in the conditioning module, which is internally controlled by the single-chip microcomputer STM32. By controlling the high and low levels of the VCA8500 control pins, the 8-channel input signals are conditioned and amplified, and the single-ended input signal is converted into a differential signal output, thereby eliminating common-mode noise and improving the signal-to-noise ratio, and then output to the A / D acquisition module.

2. The receiving preprocessing circuit of image sonar according to claim 1, characterized in that: The preamplifier circuit adopts AD8421 chip, and the AD8421 chip serves as the front stage of the preprocessing circuit.

3. The receiving preprocessing circuit of image sonar according to claim 2, characterized in that: When using the AD8421 chip as a preamplifier circuit, the gain is set from 1 to 10000 by configuring a resistor; the reference pin is used to apply a precise offset to the output voltage.

4. The receiving preprocessing circuit of image sonar according to claim 3, characterized in that: The 8-channel analog signals at the input end are amplified by the AD8421 chip, and the input underwater acoustic signal is amplified 10 times by configuring the gain resistor Rg=1kΩ and output to the next-level analog filter circuit.

5. The receiving preprocessing circuit of image sonar according to claim 1, characterized in that: The filter circuit adopts the LT1568 chip, which is used as a second-order Butterworth low-pass filter or a band-pass filter; the low-pass cutoff frequency is set at 2.5MHz by adjusting the resistance value of the external resistor, the total voltage input is 5V, and the corresponding current is 28mA~38mA.

6. The receiving preprocessing circuit of image sonar according to claim 5, characterized in that: The 8 analog signals at the analog signal input end of the filtering circuit are filtered by the LT1568 chip with a center frequency of fs=2.5MHz, which effectively filters the interfering low-frequency signals to prevent interference with the collected target signals, and then output them to the next-level conditioning module circuit.

7. The receiving preprocessing circuit of image sonar according to claim 1, characterized in that: The conditioning module adopts a VCA8500 chip, which is an 8-channel variable gain amplifier consisting of a low-noise preamplifier and a variable post-gain amplifier.

8. The receiving preprocessing circuit of image sonar according to claim 7, characterized in that: The low noise preamplifier has a fixed gain of 20dB and has good noise and signal handling characteristics; the post gain amplifier is programmed to four gain settings: 20dB, 25dB, 27dB or 30dB gain.

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