Receiving system of dual-frequency image sonar

Abstract

The utility model relates to the field of sonar, in particular to the field of sonar receiving systems, and provides a receiving system of a double-frequency image sonar. In order to solve the problem that the improvement of the imaging effect and the improvement of the effective detection distance cannot coexist, the utility model provides the following scheme: the receiving system of the dual-frequency image sonar comprises a front-end amplification circuit, a primary gating circuit, a variable gain circuit, a frequency mixing circuit, a filter circuit and an A / D (Analog to Digital) acquisition circuit, the front-end amplification circuit firstly amplifies double-frequency input image sonar signals, the first-stage gating circuit screens out required signals, the variable gain circuit adjusts gains of the selected signals to optimize signal quality, the frequency mixing circuit performs frequency mixing processing on the optimized signals, and the second-stage gating circuit performs frequency mixing processing on the optimized signals. And then the filter circuit removes higher harmonic interference in the frequency mixing output signal. And finally, the A / D acquisition circuit converts the filtered analog signal into a digital signal. The device has a good application prospect in the fields of marine geological exploration and the like.

Description

Technical Field

[0001] The utility model relates to the field of sonar, and specifically to the field of sonar receiving systems. Background Art

[0002] Synthetic Aperture Sonar (SAS) is a revolutionary underwater imaging technology that obtains high-resolution underwater images by simulating a large-aperture sonar array. The core of this technology lies in using the movement trajectory of the sonar device underwater, combining the transmitted and received acoustic wave data, and generating clear images through complex computer processing. Compared with traditional sonar systems, synthetic aperture sonar can provide higher-quality images, which is crucial for the exploration and research of the underwater environment. The working principle of synthetic aperture sonar is similar to Synthetic Aperture Radar (SAR) in aerial photography. When the sonar device moves underwater, it emits a series of acoustic wave pulses and receives the echoes reflected from the seabed or other underwater objects. By precisely controlling the movement path and speed of the sonar device, and performing complex post-processing on the acoustic wave data, high-resolution images equivalent to those obtained by a large fixed sonar array can be generated. The application fields of synthetic aperture sonar are very extensive. In marine geological exploration, it can be used to map the seabed topographic map to help scientists understand the seabed geological structure and resource distribution. In the field of underwater archaeology, synthetic aperture sonar can help researchers discover and record sunken ship sites and other ancient relics. In military reconnaissance, synthetic aperture sonar can be used to monitor underwater activities, such as tracking and monitoring submarines.

[0003] However, despite the great potential of synthetic aperture sonar technology, there are relatively few mature synthetic aperture sonar products on the market currently, and the technological gap between domestic and foreign is obvious. This is mainly because the research and development of synthetic aperture sonar technology requires a large amount of capital investment, as well as a high degree of professional knowledge and technical accumulation. In imaging technology, to improve the imaging effect, the most direct method is to increase the frequency of the detection signal. High-frequency acoustic waves can provide higher spatial resolution, making the image clearer. However, increasing the frequency also brings some problems. First, the propagation distance of high-frequency acoustic waves in seawater is shorter because seawater absorbs high-frequency acoustic waves more, which will result in a smaller effective detection distance of the device. Second, high-frequency acoustic waves are more likely to be scattered and attenuated when encountering complex terrain or objects, which will also affect the imaging quality. Therefore, in the development process of synthetic aperture sonar technology, how to balance the contradiction between "detecting far" and "detecting fine" is an important challenge. Summary of the Utility Model

[0004] In order to solve the problem that improving the imaging effect and increasing the effective detection distance cannot coexist, the utility model proposes the following solutions:

[0005] A receiving system for a dual - frequency image sonar, the system comprising: a front - end amplifier circuit, a first - stage gating circuit, a variable - gain circuit, a mixing circuit, a filtering circuit, and an A / D acquisition circuit;

[0006] The front - end amplifier circuit is used to amplify the dual - frequency input image sonar signal, obtain an amplified image sonar signal and send it to the first - stage gating circuit;

[0007] The first - stage gating circuit is used to screen the amplified image sonar signal, obtain a selected signal and send it to the variable - gain circuit;

[0008] The variable - gain circuit is used to adjust the gain of the selected signal, obtain an optimized - gain signal and send it to the mixing circuit;

[0009] The mixing circuit is used to mix the optimized - gain signal, obtain a mixed - output signal and send it to the filtering circuit;

[0010] The filtering circuit is used to filter out the high - order harmonic interference of the mixed - output signal, obtain a filtered analog signal and send it to the A / D acquisition circuit;

[0011] The A / D acquisition circuit is used to convert the filtered analog signal into a digital signal.

[0012] Furthermore, the frequencies of the dual - frequency input image sonar signals are 750 kHz and 1.2 MHz.

[0013] Furthermore, the front - end amplifier circuit is implemented by using a chip of model AD8421.

[0014] Furthermore, the first - stage gating circuit is implemented by using an ADG719 chip.

[0015] Furthermore, the variable - gain circuit is implemented by using an AD8338 chip.

[0016] Furthermore, the mixing circuit includes: an analog switch and an emitter follower;

[0017] The analog switch is used to mix the optimized - gain signal, obtain the mixed - output signal and send it to the emitter follower;

[0018] The emitter follower is used to provide buffering for the mixed - output signal and send the buffered mixed - output signal to the filtering circuit.

[0019] Furthermore, the filtering circuit is implemented by using a MAX7424 filter.

[0020] Further, the A / D acquisition circuit includes: a differential ADC driver and an analog-to-digital conversion circuit;

[0021] The differential ADC driver is configured to convert the filtered analog signal into a differential form, obtain the differential analog signal and send it to the analog-to-digital conversion circuit;

[0022] The analog-to-digital conversion circuit is configured to convert the differential analog signal into the digital signal.

[0023] Further, the system further includes a driving circuit;

[0024] The driving circuit is configured to provide power for the front-end amplification circuit, the variable gain circuit, the mixing circuit, the filtering circuit, and the A / D acquisition circuit.

[0025] The beneficial effects of the present utility model are as follows: By adopting an image sonar system operating at dual frequencies of 750 kHz and 1.2 MHz, it can balance the requirements of long-distance detection and high-resolution imaging. The low-frequency sonar improves the detection depth, and the high-frequency sonar enhances the imaging details, adapting to different water depth conditions, reducing the influence of sound absorption, improving the detection efficiency, and enhancing the target recognition ability. Description of the Drawings

[0026] Figure 1 It is a block diagram of the receiving system of the dual-frequency image sonar in Embodiment 1, where INA is the front-end amplification circuit, MUX is the first-stage gating circuit, VGA is the variable gain circuit, MIX is the mixing circuit, LIP is the filtering circuit, and AMP is the differential ADC driver in the A / D acquisition circuit;

[0027] Figure 2 It is the internal structure diagram of the AD8421 chip in Embodiment 3;

[0028] Figure 3 It is the schematic diagram of the front-end amplification circuit in Embodiment 3;

[0029] Figure 4 It is the schematic diagram of the first-stage gating circuit in Embodiment 4;

[0030] Figure 5 It is the functional block diagram of the AD8338 chip in Embodiment 5;

[0031] Figure 6 It is the schematic diagram of the AD8338 in Embodiment 5;

[0032] Figure 7 It is the schematic diagram of the gain control circuit in Embodiment 5;

[0033] Figure 8Schematic diagram of the circuit composed of a analog switch and an emitter follower in Embodiment 6;

[0034] Figure 9 Internal structure diagram of MAX7424 in Embodiment 7;

[0035] Figure 10 Schematic diagram of the MAX7424 circuit in Embodiment 7;

[0036] Figure 11 Schematic diagram of the filter circuit in Embodiment 7;

[0037] Figure 12 Schematic diagram of the differential ADC drive circuit in Embodiment 8;

[0038] Figure 13 Schematic diagram of the analog-to-digital conversion circuit in Embodiment 8;

[0039] Figure 14 Schematic diagram of the drive circuit in Embodiment 9;

[0040] Figure 15 PCB design diagram in Embodiment 10. Specific embodiments

[0041] Embodiment 1: With reference to Figure 1 This embodiment will be described. A receiving system of a dual-frequency image sonar, the system includes: a front-end amplifier circuit, a first-stage gating circuit, a variable gain circuit, a mixing circuit, a filter circuit, and an A / D acquisition circuit;

[0042] The front-end amplifier circuit is used to amplify the dual-frequency input image sonar signal to obtain an amplified image sonar signal and send it to the first-stage gating circuit;

[0043] The first-stage gating circuit is used to screen the amplified image sonar signal to obtain a selected signal and send it to the variable gain circuit;

[0044] The variable gain circuit is used to adjust the gain of the selected signal to obtain an optimized gain signal and send it to the mixing circuit;

[0045] The mixing circuit is used to mix the optimized gain signal to obtain a mixed output signal and send it to the filter circuit;

[0046] The filter circuit is used to filter out the high-order harmonic interference of the mixed output signal to obtain a filtered analog signal and send it to the A / D acquisition circuit;

[0047] The A / D acquisition circuit is used to convert the filtered analog signal into a digital signal.

[0048] Figure 1 It is a block diagram of the receiving system of a dual - frequency image sonar. From the figure, it can be seen that the dual - frequency image sonar receiving system enhances the signal through the front - end amplification circuit, then adjusts the signal intensity through the variable - gain circuit, mixes the signals through the mixing circuit, removes interference through the filtering circuit, and finally digitizes the signal through the A / D acquisition circuit. In short, this is an image sonar signal receiving system that includes signal amplification, gain adjustment, mixing, filtering, and digital processing.

[0049] Embodiment 2: This embodiment further limits the receiving system of a dual - frequency image sonar described in Embodiment 1. In this embodiment, the frequencies of the dual - frequency input image sonar signals are 750 kHz and 1.2 MHz.

[0050] Embodiment 3: Combining Figure 2 and Figure 3 to illustrate this embodiment. This embodiment further limits the receiving system of a dual - frequency image sonar described in Embodiment 1. In this embodiment, the front - end amplification circuit is implemented using an AD8421 - type chip.

[0051] Figure 2 It is the internal structure diagram of the AD8421 chip. The AD8421 is a high - speed instrumentation amplifier with low cost, low power consumption, and extremely low noise, and is very suitable for various signal conditioning and data acquisition applications. This chip has an extremely high common - mode rejection ratio, allowing the extraction of level signals in the presence of high - frequency common - mode noise. At the same time, the bandwidth of this chip is 10 MHz, the slew rate is 35 V / μs, and the settling time for 0.001% is 0.6 μs, enabling the AD8421 to amplify high - speed signals and perform well in applications that require high - channel - number multiplexing systems. Even at higher gains, the current - feedback architecture can maintain high performance. The AD8421 provides 3 nV / √Hz input voltage noise and 200 fA / √Hz current noise, and the quiescent current is only 2 mA, making it an ideal choice for measuring low - level signals. At the same time, it can be powered by a ±2.5 V to ±18 V dual - power supply or a 5 V to 36 V single - power supply. This chip uses a unique protection method to ensure a robust input while maintaining extremely low noise. This protection allows the input voltage to reach up to 40 V without damaging the device.

[0052] Figure 3 It is the schematic diagram of the front - end amplification circuit. In this system, +5 V is used for power supply. C80, C81, C84, and C85 are all filter capacitors. The reference voltage is 2.8 V. The dual - frequency input image sonar signals of 750 kHz and 1.2 MHz are input through in_L_b_n and in_L_b_p and in_H_b_n and in_H_b_p respectively, and the amplified image sonar signal is output from the VOUT terminal.

[0053] The gain of the AD8421 can be expressed as:

[0054]

[0055] Corresponding to R in this system G They are R138 and R139, and the gain is calculated to be 20 dB through the formula. The gain can be changed by changing the resistance value of the resistor, and the structure is simple and the operation is convenient.

[0056] Embodiment 4: Combining Figure 4 To illustrate this embodiment, this embodiment further limits the receiving system of a dual-frequency image sonar described in Embodiment 1. In this embodiment, the first-stage gating circuit is implemented by using an ADG719 chip.

[0057] The ADG719 chip is powered by a single power supply from 1.8V to 5.5V, with a maximum on-resistance of 4Ω, a resistance flatness of 0.75Ω, a -3dB bandwidth greater than 200MHz, and rail-to-rail output; at the same time, it can provide a fast switching time, t ON is 12ns, t OFF is 6ns.

[0058] Among them, the gating circuit is controlled by the SW signal. When SW is at a low level, the switch is turned to pin 6 of the chip, and the high-frequency signal conducts and works; when SW is at a high level, the switch is turned to pin 4 of the chip, and the low-frequency signal conducts and works.

[0059] Embodiment 5: Combining Figures 5 - 7 To illustrate this embodiment, this embodiment further limits the receiving system of a dual-frequency image sonar described in Embodiment 1. In this embodiment, the variable gain circuit is implemented by using an AD8338 chip.

[0060] Through Figures 5 - 7 It can be known that in the AD8338 chip, the gain control method is voltage control, that is, the gain is controlled by an externally set voltage. The gain code sent by the main control chip is first converted into an analog signal by a D / A chip, and after smoothing and filtering, it is input to the VGA chip. In this way, one D / A chip can drive multiple VGAs, which is suitable for multi-channel integration.

[0061] The AD8338 is a low-noise, low-power variable gain amplifier, with a power supply range of 3V to 5V, a power supply current of only 3mA, and an input voltage noise of 4.5nV / √Hz.

[0062] A passive RC network is used for filtering and DC isolation at the input end to filter out DC noise interference and differential-mode noise outside the band. Since the maximum gain of the AD8338 is 80 dB, even very weak signals will be amplified to generate great interference. Therefore, adding a passive filter at the input end is crucial.

[0063] The MODE pin of the AD8338 is used to configure the positive and negative gradients of the gain. In this design, this pin is grounded and the gain is set to the negative gradient. That is, the larger the external input voltage, the smaller the gain, and the smaller the input voltage, the larger the gain.

[0064] Its GAIN pin is for control voltage input, with a range of 0.1V to 1.1V. The gain can be changed by changing the voltage input. The selected signal is input through pins 1 and 4 of the chip, and the optimized gain signal obtained after gain amplification is output from pin 10 of the chip.

[0065] The D / A chip uses the MAX5441 digital-to-analog converter, and its main characteristics are as follows

[0066] 1. Ultra-low power consumption, with a working current of only 120 μA, and can be powered by a single +5V power supply.

[0067] 2. The settling time does not exceed 1 μs, and it can respond faster to rapidly changing control codes.

[0068] 3. It has high control resolution and control accuracy, supports a maximum control word length of 16 bits, and the offset error is only 2 LSB (least significant bit).

[0069] 4. The highest serial input is 25 MHz, and data transmission can be completed with only 3 lines, and the interface has strong versatility.

[0070] 5. The chip uses a uMAX package, with a small size of only 3mm x 5mm, saving circuit area.

[0071] 6. The reference voltage VREF can be externally configured.

[0072] The MAX5441 is suitable for single-polarity output, which is consistent with the requirements of the gain control voltage of the AD8338.

[0073] Embodiment 6: Combination Figure 8 This embodiment will be described. This embodiment further limits the receiving system of a dual-frequency image sonar described in Embodiment 1. In this embodiment, the mixing circuit includes: an analog switch and an emitter follower;

[0074] The analog switch is used to mix the optimized gain signal to obtain the mixed output signal and send it to the emitter follower;

[0075] The emitter follower is used to buffer the mixed-frequency output signal and send the buffered mixed-frequency output signal to the filtering circuit.

[0076] Combined with Figure 8 it can be seen that the optimized gain signal is connected to pin 6 of the ADA4807-1 chip. The center level of the optimized gain signal, 1.5V, is provided by the AD8338. The reference voltage output from pin 16 of the AD8338 is regulated by the emitter follower and then connected to pin 4 of the ADG719. The mixed-frequency output signal is output from pin 5. Among them, CLK MIX is the mixing clock, which is 700kHz at low frequency and 1.15MHz at high frequency.

[0077] Embodiment 7: Combined with Figures 9 - 11 To illustrate this embodiment, this embodiment is a further limitation on the receiving system of a dual-frequency image sonar described in Embodiment 1. In this embodiment, the filtering circuit is implemented using a MAX7424 filter.

[0078] Combined with Figures 9 - 11 it can be seen that the low-pass filtering circuit is composed of a MAX7424, which is a 5th-order Butterworth switched-capacitor filter. Its cut-off frequency can be arbitrarily set within the range of 0 - 60kHz. The setting method is controlled by an externally input square-wave signal. The cut-off frequency of the filter can be expressed as:

[0079]

[0080] In the circuit, C76 and R135 form a passive RC low-pass filter to filter out high-frequency interference from the power supply. The cut-off frequency of this module can be controlled by the external CLKLPF to ensure that the frequency after mixing can work within the normal range. Among them, PD3 is the enable signal for the mixing filter, and it is active high. The mixed-frequency output signal is input through pin 2 of the MAX7424, and the filtered analog signal is output through pin 5.

[0081] The signal is processed by the MAX7424 and then passes through a passive CR high-pass filter at the front end of the ADA4807-1. The cut-off frequency of the high-pass filter is 1.94kHz. The power supply VS+ is provided by PD5, where PD5 represents the enable signal for the ADC driver, and it is active high.

[0082] Embodiment 8: Combined with Figure 12 and Figure 13 To illustrate this embodiment, this embodiment is a further limitation on the receiving system of a dual-frequency image sonar described in Embodiment 1. In this embodiment, the A / D acquisition circuit includes: a differential ADC driver and an analog-to-digital conversion circuit;

[0083] The differential ADC driver is used to convert the filtered analog signal into a differential form, obtain the differential analog signal and send it to the analog-to-digital conversion circuit;

[0084] The analog-to-digital conversion circuit is used to convert the differential analog signal into the digital signal.

[0085] Through Figure 12 and Figure 13 It can be known that the differential ADC driver is composed of the chip AD8137, powered by +5V, with a reference voltage of +2.5V. The signal is divided into in-phase and anti-phase and transmitted to the A / D acquisition chip by means of single-ended input and differential output. The filtered analog signal passes through pin 1 of AD8137. After the gain configuration is completed, it is output to pins 3 and 4 of the chip. The circuit gain can be expressed as:

[0086]

[0087] The LTC2320 chip is used as the analog-to-digital converter, and its main advantages are as follows:

[0088] Low noise, a high-speed 16-bit analog-to-digital converter, with differential input of signals;

[0089] It includes 8 independent analog-to-digital conversion channels and can process 8-channel analog signals simultaneously;

[0090] Low power consumption, with a power consumption of only 20mW per channel.

[0091] In this system, the CMOS working mode of this chip is selected.

[0092] After the differential analog signal enters the LTC2320, after the operation of converting the analog signal of the chip into a digital signal, it is output from pins 27, 28, 29, 30, 35, 36, 39, and 40 of the chip.

[0093] Embodiment Nine: Combining Figure 14 To illustrate this embodiment, this embodiment is a further limitation of the receiving system of a dual-frequency image sonar described in Embodiment One. In this embodiment, the system further includes a drive circuit;

[0094] The drive circuit is used to provide power for the front-end amplification circuit, the variable gain circuit, the mixing circuit, the filtering circuit, and the A / D acquisition circuit.

[0095] Through Figure 14 It can be known that the drive circuit is the drive circuit of the enable signal and the drive circuit of the high and low frequency working mode selection switch.

[0096] Embodiment Ten: Combining Figure 15To illustrate this embodiment, the PCB design of the above embodiment will be exemplified below: By Figure 15 It can be seen that a multi-layer board structure design is adopted in this system, which is divided into a signal layer, a ground layer and a power supply layer. The overall copper plating of the ground layer can effectively play an isolation role. The power supply layer can be divided into two parts: +5V analog power supply and +3.3V digital power supply according to the placement position of the devices. When performing power supply copper plating, the isolation of the two parts is well done; at the same time, multiple vias need to be placed at the power supply to avoid power supply voltage drop. When routing, the power supply line should be as short and wide as possible to ensure less loss during transmission. When routing the signal line, the bending part should be as obtuse as possible to avoid parallel routing and acute-angle bending; when routing the differential line, use the differential routing function in the Altium Designer software to ensure that the line spacing is consistent and close to each other, thereby enhancing the anti-interference ability of the circuit.

Claims

1. A dual-frequency image sonar receiving system, characterized in that: The system comprises: a front-end amplifier circuit, a first-stage gating circuit, a variable gain circuit, a mixing circuit, a filtering circuit and an A / D acquisition circuit; The front-end amplifier circuit is used to amplify the dual-frequency input image sonar signal to obtain an amplified image sonar signal and send it to the first-level gating circuit; The first-level gating circuit is used to screen the amplified image sonar signal, obtain the selected signal and send it to the variable gain circuit; The variable gain circuit is used to adjust the gain of the selected signal to obtain an optimized gain signal and send it to the mixing circuit; The mixing circuit is used to mix the optimized gain signal to obtain a mixed output signal and send it to the filtering circuit; The filtering circuit is used to filter out the high-order harmonic interference of the mixing output signal, obtain the filtered analog signal and send it to the A / D acquisition circuit; The A / D acquisition circuit is used to convert the filtered analog signal into a digital signal.

2. A dual-frequency image sonar receiving system according to claim 1, characterized in that: The frequencies of the dual-frequency input image sonar signal are 750 kHz and 1.2 MHz.

3. The dual-frequency image sonar receiving system according to claim 1, characterized in that: The front-end amplifier circuit is implemented using an AD8421 chip.

4. The dual-frequency image sonar receiving system according to claim 1, characterized in that: The first-level gating circuit is implemented using the ADG719 chip.

5. The dual-frequency image sonar receiving system according to claim 1, characterized in that: The variable gain circuit is implemented using the AD8338 chip.

6. The dual-frequency image sonar receiving system according to claim 1, characterized in that: The mixing circuit comprises: an analog switch and an emitter follower; The analog switch is used to mix the optimized gain signal to obtain the mixed output signal and send it to the emitter follower; The emitter follower is used to provide a buffering effect for the mixed output signal and send the buffered mixed output signal to the filter circuit.

7. The dual-frequency image sonar receiving system according to claim 1, characterized in that: The filtering circuit is implemented by using a MAX7424 filter.

8. The dual-frequency image sonar receiving system according to claim 1, characterized in that: The A / D acquisition circuit includes: a differential ADC driver and an analog-to-digital conversion circuit; The differential ADC driver is used to convert the filtered analog signal into a differential form, obtain the differential analog signal and send it to the analog-to-digital conversion circuit; The analog-to-digital conversion circuit is used to convert the differential analog signal into the digital signal.

9. The dual-frequency image sonar receiving system according to claim 1, characterized in that: The system also includes a drive circuit; The driving circuit is used to provide power for the front-end amplifier circuit, the variable gain circuit, the mixing circuit, the filtering circuit and the A / D acquisition circuit.

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