Filter design method

Abstract

The invention relates to the technical field of filters, and discloses a filter design method, which comprises the following steps of: firstly, determining target frequency response characteristics and input and output impedance requirements of a filter according to an actual scene, and considering group delay characteristic requirements; then, model selection is carried out from low-pass filters according to indexes, a prototype is built based on the selected type, and the realizability and cost order selection are considered; then, element values are calculated and normalized according to the actual frequency conversion prototype; and finally, establishing a circuit by using lumped or distributed parameters, performing simulation analysis, considering non-ideal characteristics of elements, performing fine adjustment and topology adjustment if indexes are not met, and reselecting types if the indexes are not met until the design reaches the standard. The method has the advantages that the requirements of complex frequency response characteristics and group delay characteristics can be accurately designed, and meanwhile, the non-ideal characteristics of actual elements are fully considered.

Description

Technical Field

[0001] The present invention relates to the technical field of filters, and specifically refers to a filter design method. Background Art

[0002] As a circuit that is selective for signal frequencies, filters are widely used in many fields such as communication, electronics, and power. In a communication system, filters are used to separate signals of different frequencies to achieve functions such as signal modulation, demodulation, and multiplexing; in electronic devices, filters are used to remove power supply noise and suppress interference signals to ensure the normal operation of the devices; in a power system, filters are used to improve power quality and reduce the impact of harmonics on the power grid.

[0003] With the continuous development of technology, the performance requirements for filters are increasing day by day. Traditional filter design methods have certain limitations in meeting complex frequency response characteristics, group delay characteristics, and considering the non-ideal characteristics of actual components. For example, some traditional design methods cannot effectively control the change of group delay when realizing specific passband and stopband characteristics, resulting in signal distortion during transmission; in practical applications, due to non-ideal characteristics such as parasitic parameters of components, filters designed according to the ideal model often cannot meet the expected performance indicators. Therefore, a new filter design method is needed to overcome these problems. Summary of the Invention

[0004] In order to solve the above various problems, the present invention proposes a filter design method that can accurately design a filter to meet the requirements of complex frequency response characteristics and group delay characteristics, while fully considering the non-ideal characteristics of actual components.

[0005] To solve the above technical problems, the technical solution proposed by the present invention is: a filter design method, including the following steps:

[0006] Step 1: Determine the filter design specifications

[0007] According to the actual application scenario, clarify the target frequency response characteristics of the filter, including the passband and stopband frequency ranges, the maximum attenuation value in the passband, and the minimum attenuation value in the stopband;

[0008] Determine the requirements for the input and output impedances of the filter;

[0009] Step 2: Select the filter type

[0010] According to the filter design specifications, select a suitable type from low-pass, high-pass, band-pass, and band-stop filters;

[0011] If the target frequency response requires that signals in a specific low-frequency band pass through without attenuation and are greatly attenuated in the high-frequency band, select a low-pass filter;

[0012] If a specific high-frequency band signal needs to pass through without attenuation and the low-frequency band is significantly attenuated, select a high-pass filter;

[0013] If a signal within a specific frequency range needs to pass through without attenuation and the outside of the range is significantly attenuated, select a band-pass filter;

[0014] If a signal within a specific frequency range needs to be significantly attenuated and the outside of the range passes through without attenuation, select a band-stop filter;

[0015] Step 3: Establish a filter prototype

[0016] Based on the selected type, use a specific prototype establishment method to construct the initial prototype of the filter;

[0017] Butterworth prototype: Let the order be n, and calculate the frequency response according to the magnitude-squared function ∣H(jω)∣ 2 =1 / (1+(ω / ω c ) 2n ), where ω is the angular frequency and ωc is the cut-off angular frequency;

[0018] Chebyshev prototype: According to the magnitude-squared function ∣H(jω)∣ 2 =1 / (1+∈ 2 Tn 2 (ω / ω c )) to build the prototype, ∈ is related to the passband ripple, Tn(x) is the nth-order Chebyshev polynomial, and ω c is the cut-off angular frequency;

[0019] Elliptic prototype: Constructed using elliptic function theory, and its frequency response has equiripple passband and stopband characteristics;

[0020] Step 4: Frequency transformation and component value calculation

[0021] According to the actual passband and stopband frequencies, perform frequency transformation on the filter prototype to convert the prototype frequency characteristics into characteristics that meet the design specifications;

[0022] Low-pass to low-pass: The prototype cut-off frequency is ωp0, and the target cut-off frequency is ωp. The transformation formula is ω=(ωp / ωp0)Ω, where Ω is the prototype angular frequency and ω is the target angular frequency;

[0023] Low-pass to high-pass: The transformation formula is ω=-ωpωp0 / Ω;

[0024] Low-pass to band-pass: The center frequency of the band-pass is ω0, and the bandwidth is B. The transformation formula is ω=(ω0 2 / B)(Ω + 1 / Ω);

[0025] Low-pass to band-stop: The transformation formula is ω=Bω0 / (Ω 2 - 1);

[0026] After frequency transformation, calculate the values of each component of the filter according to circuit theory and formulas;

[0027] Step Five: Filter Circuit Implementation and Optimization

[0028] Build the filter circuit using lumped parameters or distributed parameters according to the calculated component values;

[0029] Use circuit simulation software for simulation analysis to observe whether the actual frequency response meets the design specifications;

[0030] If not satisfied, fine-tune the component values or adjust the circuit topology, and re-simulate until the design specifications are met.

[0031] Preferably, in the said Step One, it further includes determining the requirements for the group delay characteristic of the filter, and the requirements for the group delay characteristic include the maximum change value of the group delay within the passband.

[0032] Preferably, in the said Step Three, when establishing the filter prototype, also consider the realizability and cost of the filter, select the appropriate order of the prototype filter, and while meeting the design specifications, achieve the optimal balance between the complexity and cost of the filter.

[0033] Preferably, in the said Step Four, after frequency transformation and component value calculation, normalize the calculated component values to facilitate subsequent circuit design and analysis.

[0034] Preferably, in the said Step Five, when using circuit simulation software for simulation analysis, consider the non-ideal characteristics of actual components, such as the parasitic inductance and capacitance of resistors, the series resistance and inductance of capacitor effects, and the DC resistance and parasitic capacitance of inductors, and model and compensate for these non-ideal characteristics to improve the simulation accuracy.

[0035] Preferably, in the said Step Five, if adjusting the component values and the circuit topology still does not meet the design specifications, return to Step Two, re-select the filter type, and repeat the subsequent steps until a filter that meets the design specifications is designed.

[0036] The advantages of the present invention compared with the prior art are as follows:

[0037] Through a clear step process, the present invention can accurately design a filter that meets the requirements of complex frequency response characteristics. Whether it is the control of the passband and stopband frequency ranges, or the maximum attenuation value in the passband and the minimum attenuation value in the stopband, it is more precise, improving the applicability of the filter in various application scenarios.

[0038] Considering the requirements for the group delay characteristic of the filter, it can effectively reduce the phase distortion of the signal during transmission, ensure the integrity and accuracy of the signal, and is particularly suitable for fields such as communication and audio processing that have high requirements for the signal phase.

[0039] When establishing the filter prototype, the factors of realizability and cost are comprehensively considered. By selecting an appropriate order of the prototype filter, it is possible to reduce the complexity and cost of the filter while meeting the performance requirements, thereby enhancing the market competitiveness of the product.

[0040] After frequency transformation and component value calculation, normalization is carried out, which facilitates subsequent circuit design and analysis and improves the design efficiency.

[0041] During the circuit implementation and optimization process, the non-ideal characteristics of actual components are fully considered, modeled, and compensated, enabling the designed filter to be closer to the ideal performance in practical applications and improving the reliability and stability of the filter.

[0042] The design method provided by the present invention has a good iterative optimization mechanism. When the design result does not meet the specifications, it is possible to continuously optimize the design by reselecting the filter type and adjusting design parameters until the design requirements are met. Description of the Drawings

[0043] Figure 1 It is the principle flowchart of the present invention. Detailed Description of the Invention

[0044] The present invention will be further described in detail below with reference to the accompanying drawings.

[0045] Embodiment 1

[0046] Determine the filter design specifications

[0047] The actual application scenario is audio signal processing, and a low-pass filter needs to be designed to remove high-frequency noise above 10 kHz. Therefore, the passband frequency range is set to 0 Hz - 10 kHz, the maximum passband attenuation value is set to 3 dB, the stopband frequency range is set to 15 kHz and above, and the minimum stopband attenuation value is set to 40 dB. The input and output impedance requirements are 600 Ω to match the interface of audio equipment.

[0048] Select the filter type

[0049] According to the above design specifications, since it is necessary to allow the low-frequency audio signal to pass through without attenuation and significantly attenuate the high-frequency noise, a low-pass filter is selected.

[0050] Establish the filter prototype

[0051] Considering the high requirement for passband flatness, a Butterworth prototype is selected. Through calculation and analysis, the order is determined to be 4. At this time, it is possible to ensure good flatness in the passband while meeting the requirements of the maximum passband attenuation value and the minimum stopband attenuation value.

[0052] Frequency transformation and component value calculation

[0053] Since the actual low-pass filter is designed from a low-pass prototype, it belongs to the low-pass to low-pass transformation. After determining the frequency transformation relationship, calculate the values of each component of the filter according to circuit theory. For a low-pass filter circuit composed of a resistor R and a capacitor C, it is calculated that R = 10 kΩ and C = 1.59 nF. After calculation, normalize the component values for convenient subsequent design.

[0054] Implementation and Optimization of Filter Circuit

[0055] Build a low-pass filter circuit using lumped parameter components resistor R and capacitor C. Use circuit simulation software for simulation analysis. Consider non-ideal characteristics such as the parasitic inductance and capacitance of the resistor, and the equivalent series resistance and inductance of the capacitor in the simulation. It is found that the attenuation near 10 kHz in the simulation results is slightly less than the design requirements. By fine-tuning the capacitance value, adjust C to 1.6 nF and simulate again. The actual frequency response meets the design specifications.

[0056] Example 2

[0057] Determine Filter Design Specifications

[0058] Applied to a wireless communication receiving system, a band-pass filter needs to be designed to receive signals with a center frequency of 900 MHz and a bandwidth of 20 MHz. The passband frequency range is set to 890 MHz - 910 MHz, the maximum attenuation value in the passband is set to 2 dB, the stopband frequency range is set to less than 880 MHz and greater than 920 MHz, and the minimum attenuation value in the stopband is set to 50 dB. The input and output impedance requirements are 50 Ω to match the RF circuit.

[0059] Select Filter Type

[0060] According to the design specifications, signals within a specific frequency range need to pass through without attenuation, and be greatly attenuated outside the range. Therefore, a band-pass filter is selected.

[0061] Establish Filter Prototype

[0062] Since a steeper transition band is required, a Chebyshev prototype is selected. Determine the order to be 5 through calculation, and the passband ripple parameter is also determined.

[0063] Frequency Transformation and Component Value Calculation

[0064] Perform frequency transformation from the low-pass prototype to the band-pass filter. Calculate the values of each component of the filter. For a band-pass filter circuit composed of an inductor L and a capacitor C, it is calculated that L = 10 nH and C = 3.06 pF. After calculation, normalize the component values.

[0065] Implementation and Optimization of Filter Circuit

[0066] Due to the relatively high operating frequency, a distributed-parameter element microstrip line is used to build the band-pass filter circuit. Circuit simulation software is used for simulation analysis, taking into account the non-ideal characteristics such as the loss and parasitic parameters of the microstrip line. The simulation results show that there are some ripples in the passband. By adjusting the length and width of the microstrip line and changing the circuit topology, and then simulating again, the actual frequency response meets the design specifications.

[0067] Embodiment 3

[0068] Determine the filter design specifications

[0069] Applied to the power system, the purpose is to suppress the 50Hz harmonic interference while ensuring the normal transmission of electrical energy at other frequencies. Therefore, the passband frequency range is set to the frequency interval other than 49Hz - 51Hz, the maximum attenuation value in the passband is set to 1dB, the stopband frequency range is set to 49Hz - 51Hz, and the minimum attenuation value in the stopband is set to 60dB. The input and output impedance requirements are the standard impedance of the power system to achieve good access.

[0070] Select the filter type

[0071] According to the design specifications, signals in a specific frequency range need to be significantly attenuated, and there is no attenuation for signals outside this range. Therefore, a band-stop filter is selected.

[0072] Establish the filter prototype

[0073] Taking into account both cost and performance, an elliptical prototype is selected. Through a series of calculations, the appropriate order is determined to meet the design requirements.

[0074] Frequency transformation and component value calculation

[0075] Perform frequency transformation from the low-pass prototype to the band-stop filter. According to circuit theory, the values of each component (resistor, capacitor, inductor) of the filter are calculated, and then the component values are normalized.

[0076] Filter circuit implementation and optimization

[0077] Use lumped-parameter elements to build the band-stop filter circuit. Use circuit simulation software for simulation analysis, taking into account the non-ideal characteristics of the actual components. It is found that the attenuation at the edge of the stopband in the simulation results is not ideal enough. By slightly adjusting the inductor value and then simulating again, the actual frequency response meets the design specification requirements.

[0078] As described above, it is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A filter design method, characterized in that, It includes the following steps: Step 1: Determine the filter design specifications According to the actual application scenario, clarify the target frequency response characteristics of the filter, including the passband and stopband frequency ranges, the maximum attenuation value in the passband, and the minimum attenuation value in the stopband; Determine the requirements for the input and output impedances of the filter; Step 2: Select the filter type Based on the filter design specifications, select a suitable type from low-pass, high-pass, band-pass, and band-stop filters; If the target frequency response requires that signals in a specific low-frequency band pass through without attenuation and are significantly attenuated in the high-frequency band, select a low-pass filter; If it is required that signals in a specific high-frequency band pass through without attenuation and are significantly attenuated in the low-frequency band, select a high-pass filter; If it is required that signals in a specific frequency range pass through without attenuation and are significantly attenuated outside the range, select a band-pass filter; If it is required that signals in a specific frequency range are significantly attenuated and pass through without attenuation outside the range, select a band-stop filter; Step 3: Establish the filter prototype Based on the selected type, use a specific prototype establishment method to construct the initial prototype of the filter; Butterworth prototype: Let the order be n, and calculate the frequency response according to the magnitude-squared function |H(jω)| 2 = 1 / (1 + (ω / ω c ) 2n ), where ω is the angular frequency and ω c is the cut-off angular frequency; Chebyshev prototype: According to the magnitude-squared function |H(jω)| 2 = 1 / (1 + ∈ 2 Tn 2 (ω / ω c )) to build the prototype, ∈ is related to the passband ripple, Tn(x) is the Chebyshev polynomial of the nth order, ω c is the cut-off angular frequency; Elliptic prototype: Constructed using elliptic function theory, its frequency response has equiripple passband and stopband characteristics; Step 4: Frequency transformation and component value calculation According to the actual passband and stopband frequencies, perform a frequency transformation on the filter prototype to convert the prototype frequency characteristics into characteristics that meet the design specifications; Low-pass to low-pass: The cut-off frequency of the prototype is ωp0, and the target cut-off frequency is ωp. The transformation formula is ω = (ωp / ωp0)Ω, where Ω is the prototype angular frequency and ω is the target angular frequency; Low-pass to high-pass: The transformation formula is ω = -ωpωp0 / Ω; Low-pass to band-pass: Band-pass center frequency ω0, bandwidth B, transformation formula ω = (ω0 2 / B)(Ω + 1 / Ω); Low-pass to band-stop: transformation formula ω = Bω0 / (Ω 2 - 1); After the frequency transformation, calculate the values of each component of the filter according to circuit theory and formulas; Step 5: Filter circuit implementation and optimization Based on the calculated component values, build the filter circuit using lumped parameters or distributed parameters; Use circuit simulation software for simulation analysis to observe whether the actual frequency response meets the design specifications; If not satisfied, fine-tune the component values or adjust the circuit topology, and re-simulate until the design specifications are met.

2. The filter design method according to claim 1, wherein: In the above Step 1, it also includes determining the requirements for the group delay characteristics of the filter. The requirements for the group delay characteristics include the maximum change value of the group delay in the passband.

3. A filter design method according to claim 1, characterized in that: In the above Step 3, when establishing the filter prototype, also consider the realizability and cost of the filter, select the appropriate order of the prototype filter, and achieve the optimal balance between the filter complexity and cost while meeting the design specifications.

4. A filter design method according to claim 1, characterized in that: In the above Step 4, after the frequency transformation and component value calculation, perform normalization on the calculated component values to facilitate subsequent circuit design and analysis.

5. A filter design method according to claim 1, characterized in that: In the above Step 5, when using circuit simulation software for simulation analysis, consider the non-ideal characteristics of actual components, such as the parasitic inductance and capacitance of resistors, the series resistance and inductance of the effective capacitance of capacitors, and the DC resistance and parasitic capacitance of inductors, and model and compensate for these non-ideal characteristics to improve the simulation accuracy.

6. A filter design method according to claim 1, characterized in that: In the above Step 5, if adjusting the component values and the circuit topology still does not meet the design specifications, return to Step 2, re-select the filter type, and repeat the subsequent steps until a filter that meets the design specifications is designed.

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