Design method of active band-pass filter for ocean short-wave communication

Abstract

The invention discloses an active band-pass filter design method for ocean short-wave communication, which comprises the following steps of: a, determining a design index according to a communication requirement; b, selecting a circuit structure according to the design indexes proposed in the step a; c, selecting a proper operational amplifier to adapt to circuit requirements; d, calculating device parameters according to the selected circuit structure; e, replacing the theoretical circuit value obtained in the step d with an actual value; f, performing S parameter simulation by utilizing EDA software, and verifying whether the performance of the filter meets a design index or not based on the actual value obtained in the step e; g, if the result of the step f meets the design index, performing the next step; if not, the influence degree of the device is judged according to the unsatisfied indexes in combination with the calculation formula in the step e, the theoretical value of the device with the large influence degree is properly increased or decreased, and then the step e and the step f are repeated; h, selecting a proper substrate to design a PCB layout; and i, the PCB layout designed in the step h is processed and manufactured, and entity manufacturing of the filter is completed.

Description

Technical Field

[0001] The invention relates to the technical field of communication and information processing, and in particular to a design method of an active bandpass filter for marine shortwave communication. Background Art

[0002] In the process of wireless communication based on shortwave frequency band, due to the mutual interference of signals between multiple frequency bands, the signal quality received at the receiving end is poor and there is a lot of interference. Therefore, a filter is needed to filter out the signal of the target frequency band and suppress the signals of other frequency bands to further improve the quality of the received signal. As an important component of the wireless communication system, the performance of the filter has a direct impact on the performance of the communication system. How to select the target signal from many frequencies without distortion and reduce useless or interfering signals, this demand puts forward higher requirements for the design of the filter.

[0003] In marine communications, due to the greater weather interference, the requirements for the communication system are higher, so choosing shortwave can better reduce the requirements of the communication system. Taking the ocean 1,000-kilometer unrelayed shortwave communication system as an example, the longest distance from the transmitter to the receiver can reach 2,000 kilometers. In this process, it is necessary to consider the impact of multiple-input multiple-output (MIMO) technology and the worst weather conditions. In addition, the escape phenomenon of the ionosphere will also have a significant impact on signal propagation, resulting in a maximum attenuation of the entire communication process of up to -113dB.

[0004] Generally speaking, the sensitivity range of the analog-to-digital converter (ADC) is 0 to -7dB, so the receiver part needs to amplify the received signal to within the adjustment range of the ADC. The expected gain of the Yagi antenna is 15 to 20dB, the expected gain of the low noise amplifier (LNA) module is 20 to 30dB, and the adjustment range of the automatic gain control (AGC) is 0 to 30dB. Therefore, the receiver needs to use an amplifier with at least 33dB gain to ensure that the signal can be effectively amplified and enter the effective working range of the ADC.

[0005] In the current era of continuous development and iteration of various electronic circuit technologies, active filters are popular because of their better filter effects, amplification functions, and strong adjustability. Summary of the invention

[0006] Based on this, it is necessary to propose an active bandpass filter design method for marine shortwave communication to address the above problems.

[0007] The embodiment of the present invention provides a method for designing an active bandpass filter for marine shortwave communication, comprising the following steps:

[0008] a. Determine the design indicators according to communication requirements;

[0009] b. Select the circuit structure according to the design indicators proposed in step a;

[0010] c. Select the appropriate operational amplifier (OPA) to suit the circuit requirements;

[0011] d. Calculate device parameters according to the selected circuit structure, including circuit gain H0, bandpass filter center frequency ω0 and quality factor Q;

[0012] e. Replace the theoretical value of the circuit obtained in step d with the actual value;

[0013] f. Use EDA software to perform S parameter simulation, and verify whether the performance of the filter meets the design specifications based on the actual value obtained in step e;

[0014] g. If the result of step f meets the design index, proceed to the next step; if not, the impact of the device is determined based on the unsatisfied index and the calculation formula in step e, and the theoretical value of the device with a greater impact is appropriately increased or decreased, and then steps e and f are repeated;

[0015] h. Select a suitable substrate to design the PCB layout;

[0016] i. Process and manufacture the PCB layout designed in step h to complete the physical production of the filter.

[0017] In the above solution, the circuit structure includes types including a Salen-Key structure and an MFB structure, wherein the MFB structure is particularly suitable for the case where the amplification factor is greater than 1.

[0018] In the above scheme, for the circuit structure selected in step b, when the amplification factor is 1, the Sallen-Key structure is preferably selected; when the amplification factor is greater than 1, the MFB structure is selected.

[0019] In the above scheme, when calculating the device parameters in step d, the second-order bandpass filter transfer function must be satisfied. Where H0 is the circuit gain, ω0 is the center frequency of the bandpass filter, and Q is the quality factor.

[0020] In the above scheme, H0 and Q satisfy the following formula: where F H and F L is the frequency when the corresponding maximum value of the circuit differs by 3dB, H is the circuit gain, and H0 is the filter gain.

[0021] The embodiment of the present invention further provides a marine shortwave communication receiver according to the above-mentioned active bandpass filter design method for marine shortwave communication, wherein the marine shortwave communication receiver comprises:

[0022] Yagi antenna module, used to receive and amplify signals in the 19MHz band, with an amplification factor of about 15-20dB;

[0023] The active bandpass filter module is connected to the Yagi antenna module and is used to perform the first limiting filter on the received signal. The filter frequency band is 19MHz and the bandwidth is 2MHz.

[0024] The low noise amplifier (LNA) module is connected to the active bandpass filter module to further amplify the signal and reduce the system noise, with an amplification factor of about 20-30dB;

[0025] Automatic gain control (AGC) module, connected to the LNA module, is used to adjust the signal amplification factor. The operating frequency range supports the shortwave frequency band and the control gain range is 0-30dB;

[0026] Active bandpass filter and amplifier (OPA) module, connected to the AGC module, is used to selectively amplify the target signal with an amplification factor of about 40-50dB;

[0027] The analog-to-digital converter (ADC) module is connected to the OPA module and is used to receive and convert the amplified signal. The receiving sensitivity range is about 0-7dB.

[0028] The embodiments of the present invention have the following beneficial effects:

[0029] The present invention is designed based on the entire design process of the active bandpass filter, integrates the existing technology into the shortwave frequency band filter design, and is used to construct a receiver for the marine shortwave communication system, which can better improve the performance of the South China Sea shortwave communication system and ensure a good received signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

[0031] in:

[0032] Figure 1 The present invention provides a flow chart of a method for designing an active bandpass filter for marine shortwave communication;

[0033] Figure 2 is the circuit structure of the present invention;

[0034] Figure 3After the parameters are calculated in the present invention, they are replaced with the device circuit diagram provided by the manufacturer;

[0035] Figure 4 This is the schematic diagram after adding the interface in the present invention;

[0036] Figure 5 It is the layout of the active bandpass filter in the present invention;

[0037] Figure 6 It is a principle block diagram of the marine shortwave communication receiver in the present invention. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in 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. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] The embodiment of the present invention refers to Arthur B. Willi ams, Fred J. Taylor "Electronic Filter Design" [M]. Beijing: Science Press, 2008 to study the design of active bandpass filters, and obtains a filter schematic and layout that can be actually processed. Based on the filter design process, it is achieved that the receiving end in the South China Sea shortwave communication system can obtain a received and amplified signal with good performance.

[0040] An embodiment of the present invention provides a method for designing an active bandpass filter for marine shortwave communication, the method comprising the following steps:

[0041] Step 1: Determine the design indicators according to communication requirements;

[0042] Specifically, in the South China Sea shortwave project, communication will be based on the frequency band of 18MHz-20MHz, so the filter indicators are set as: center frequency F0=19MHz, passband bandwidth BW=2MHz, attenuation at bandwidth 18MHz-20MHz <=3dB, and amplification factor>30dB.

[0043] Step 2: Select the circuit structure according to the index proposed in step 1;

[0044] Specifically, active filters are divided into two structures: the Sale-Key structure and the MFB structure. The Sale-Key structure is suitable for the case where the gain is 1, and the number of devices required for this structure is the smallest in this case; the MFB structure is suitable for the case where the gain is greater than 1, and the active filter of the MFB structure requires fewer devices for the case where there is a need for amplification, and the device sensitivity is smaller than that of the Sale-Key structure, and is more suitable for marine shortwave communications. Therefore, the present invention will be designed based on the MFB active filter structure.

[0045] Step 3, select a suitable operational amplifier (OPA);

[0046] Specifically, the selection of operational amplifiers is mainly determined by the input and output voltage range and the gain-bandwidth product (GBW), where the gain-bandwidth product satisfies:

[0047] GBW=H×BW (1)

[0048] Where H is the target gain factor and BW is the passband bandwidth. The gain-bandwidth product of the selected device should meet the following conditions:

[0049] GBW OPA >GBW 实际 (2)

[0050] Step 4: Calculate device parameters according to the selected circuit structure;

[0051] Specifically, the following formula must be satisfied:

[0052] The transfer function of the second-order bandpass filter is:

[0053]

[0054] Where H0 is the circuit gain, ω0 is the center frequency of the bandpass filter, and Q is the quality factor. H0 and Q satisfy the following formula:

[0055]

[0056] Among them, F H and F L It is the frequency when the corresponding maximum value of the circuit differs by 3dB.

[0057]

[0058] Among them, H is the circuit gain, and H0 is the filter gain.

[0059]

[0060] Among them, F0 is the center frequency and BW is the passband bandwidth.

[0061] The MFB bandpass filter transfer function is:

[0062]

[0063] Let C1=C2=C=30pF, R1=R, R2=nR, R3=mR in equation (7), and combine equations (3)-(6) to obtain the circuit parameter values, as shown in Table 1.

[0064] Table 1

[0065] Devices Device Value C1 30pF C2 30pF R1 1.32kΩ R2 14.89Ω R3 5.31kΩ

[0066] Step 5: Replace the theoretical value of the circuit obtained in step 4 with the nominal value;

[0067] Specifically, select the relatively close nominal values ​​shown in Table 1 and replace them in the circuit. The final replacement results are shown in Table 2 below:

[0068] Table 2

[0069] Devices Device Value C1 30pF C2 30pF R1 1.33kΩ R2 15Ω R3 5.36kΩ

[0070] Step 6: Based on the device results obtained in Step 4 and Step 5, use EDA software to perform S parameter simulation to observe whether the final result meets the requirements. If so, proceed to the next step. If not, the impact of the device can be determined based on the unsatisfied indicators and the calculation formula in Step 5, and the theoretical value of the device with a greater impact can be appropriately increased or decreased.

[0071] Step 7: Select a suitable substrate to design the PCB layout;

[0072] Step 8: Process the substrate in step 9, such as Figure 5 As shown,

[0073] The shortwave frequency band filter designed through the above steps is used in marine shortwave communication receivers.

[0074] like Figure 6 As shown, the marine shortwave communication receiver comprises:

[0075] Yagi antenna module, used to receive and amplify signals in the 19MHz band, with an amplification factor of about 15-20dB;

[0076] The active bandpass filter module is connected to the Yagi antenna module and is used to perform the first limiting filter on the received signal. The filter frequency band is 19MHz and the bandwidth is 2MHz.

[0077] The low noise amplifier (LNA) module is connected to the active bandpass filter module to further amplify the signal and reduce the system noise, with an amplification factor of about 20-30dB;

[0078] Automatic gain control (AGC) module, connected to the LNA module, is used to adjust the signal amplification factor. The operating frequency range supports the shortwave frequency band and the control gain range is 0-30dB;

[0079] Active bandpass filter and amplifier (OPA) module, connected to the AGC module, is used to selectively amplify the target signal with an amplification factor of about 40-50dB;

[0080] The analog-to-digital converter (ADC) module is connected to the OPA module and is used to receive and convert the amplified signal. The receiving sensitivity range is about 0-7dB.

[0081] The marine shortwave communication receiver is connected in sequence through a Yagi antenna module, an active bandpass filter module, an LNA module, an AGC module, an OPA module and an ADC module, which together constitute a signal processing link of the receiver, realize signal reception, filtering, amplification, regulation and conversion, and is used for signal transmission in a 19MHz frequency band in long-distance marine communication. The wavelength of this frequency band is about 15 meters, and the longest communication distance can reach 2,000 kilometers, which is approximately equal to 130,000 wavelengths.

[0082] When the maximum attenuation multiple (considering MIMO and the worst weather condition of high humidity) is about 1.7x10^10, i.e. about 103dB attenuation, and the ionospheric escape is about 10dB, the receiver can ultimately withstand a total attenuation of about 113dB through its overall architectural design.

[0083] Furthermore, the marine shortwave communication receiver also includes auxiliary modules, such as a power management module, a signal processing module, etc., to support the normal operation and signal processing functions of the receiver.

[0084] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A design method for an active bandpass filter for marine shortwave communication, characterized in that: The following steps are involved: a. Determine the design indicators according to communication requirements; b. Select the circuit structure according to the design indicators proposed in step a; c. Select the appropriate operational amplifier (OPA) to suit the circuit requirements; d. Calculate device parameters according to the selected circuit structure, including circuit gain H0, bandpass filter center frequency ω0 and quality factor Q; e. Replace the theoretical value of the circuit obtained in step d with the actual value; f. Use EDA software to perform S parameter simulation, and verify whether the performance of the filter meets the design specifications based on the actual value obtained in step e; g. If the result of step f meets the design index, proceed to the next step; if not, the impact of the device is determined based on the unsatisfied index and the calculation formula in step e, and the theoretical value of the device with a greater impact is appropriately increased or decreased, and then steps e and f are repeated; h. Select a suitable substrate to design the PCB layout; i. Process and manufacture the PCB layout designed in step h to complete the physical production of the filter.

2. The active bandpass filter design method for ocean shortwave communication according to claim 1 is characterized in that: The circuit structure includes types including a Sal len-Key structure and an MFB structure, wherein the MFB structure is particularly suitable for the case where the amplification factor is greater than 1.

3. The method for designing an active bandpass filter for ocean shortwave communication according to claim 1 or 2, characterized in that: For the circuit structure selected in step b, when the amplification factor is 1, the Sallen-Key structure is preferably selected; when the amplification factor is greater than 1, the MFB structure is selected.

4. The method for designing an active bandpass filter for ocean shortwave communication according to claim 3, characterized in that: When calculating the device parameters in step d, the second-order bandpass filter transfer function must be satisfied. Where H0 is the circuit gain, ω0 is the center frequency of the bandpass filter, and Q is the quality factor.

5. The method for designing an active bandpass filter for ocean shortwave communication according to claim 4, characterized in that: The H0 and Q satisfy the following formula: where F H and F L is the frequency when the corresponding maximum value of the circuit differs by 3dB, H is the circuit gain, and H0 is the filter gain.

6. A marine shortwave communication receiver according to any one of claims 1 to 5, characterized in that: The marine shortwave communication receiver comprises: Yagi antenna module, used to receive and amplify signals in the 19MHz band, with an amplification factor of about 15-20dB; The active bandpass filter module is connected to the Yagi antenna module and is used to perform the first limiting filter on the received signal. The filter frequency band is 19MHz and the bandwidth is 2MHz. The low noise amplifier (LNA) module is connected to the active bandpass filter module to further amplify the signal and reduce the system noise, with an amplification factor of about 20-30dB; Automatic gain control (AGC) module, connected to the LNA module, is used to adjust the signal amplification factor. The operating frequency range supports the shortwave frequency band and the control gain range is 0-30dB; Active bandpass filter and amplifier (OPA) module, connected to the AGC module, is used to selectively amplify the target signal with an amplification factor of about 40-50dB; The analog-to-digital converter (ADC) module is connected to the OPA module and is used to receive and convert the amplified signal. The receiving sensitivity range is about 0-7dB.

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