CN116232281A - Control method of custom filter - Google Patents
Control method of custom filter Download PDFInfo
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- CN116232281A CN116232281A CN202310233069.8A CN202310233069A CN116232281A CN 116232281 A CN116232281 A CN 116232281A CN 202310233069 A CN202310233069 A CN 202310233069A CN 116232281 A CN116232281 A CN 116232281A
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- 239000003990 capacitor Substances 0.000 claims description 25
- 238000010586 diagram Methods 0.000 description 9
- 238000001914 filtration Methods 0.000 description 9
- 238000007493 shaping process Methods 0.000 description 2
- 238000006467 substitution reaction Methods 0.000 description 2
- 230000007704 transition Effects 0.000 description 2
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H17/00—Networks using digital techniques
- H03H17/0045—Impedance matching networks
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H17/00—Networks using digital techniques
- H03H17/02—Frequency selective networks
- H03H17/0248—Filters characterised by a particular frequency response or filtering method
- H03H17/0261—Non linear filters
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/40—Arrangements for reducing harmonics
Abstract
The invention belongs to the technical field of filters, and in particular relates to a control method of a custom filter, which is provided with a control unit electrically connected with an upper computer, wherein the upper computer sends passband cut-off frequency, stopband cut-off frequency, passband maximum attenuation coefficient, stopband minimum attenuation coefficient and filter type of the custom type filter to the control unit, the control unit calculates the required order of the filter according to the passband cut-off frequency, stopband cut-off frequency, passband maximum attenuation coefficient and stopband minimum attenuation coefficient, then calculates the resistance of a digital potentiometer according to the filter type, and the control unit calculates the obtained order control switch S by calculating the obtained order control switch S 0 ～S x Changing the order of the filter. The invention adopts a single operational amplifier to realize a high-order filter; the order of the filter can be adjusted at any time according to the requirements; the type of the filter can be adjusted at any time according to the requirements.
Description
Technical Field
The invention belongs to the technical field of filters, and particularly relates to a control method of a custom filter.
Background
The narrower the transition band of the filter, the better the selectivity and the ideal the filtering characteristic. Increasing the order of the filter can significantly narrow the transition band of the filter, but infinitely increasing the order of the filter can cause the output signal to oscillate around the passband cut-off frequency, so the order of the filter must be reasonably selected according to the application conditions.
The conventional filter analog circuit has to fix its order in the circuit design stage, and then calculate the required RLC parameters according to the desired filter type (Butterworth type, cheebyshev type, bessel type, etc.). When the filtering requirements (passband frequency, stopband frequency, filter type) need to be changed, the order and type of the filter may be changed accordingly, and the circuit topology and element parameters of the filter need to be redesigned. In summary, the analog circuit of the conventional filter has poor flexibility, and is difficult to meet frequent switching among various filtering requirements.
Disclosure of Invention
In order to solve the technical problems, the invention provides a control method of a custom filter. The technical scheme adopted by the invention is as follows:
a control method of a custom filter comprises the following steps:
step 1, setting a control unit electrically connected with an upper computer, wherein the control unit adopts a singlechip, a DSP or an FPGA.
And 2, the upper computer sends the passband cut-off frequency, the stopband cut-off frequency, the passband maximum attenuation coefficient, the stopband minimum attenuation coefficient and the filter type of the custom type filter to the control unit.
And 3, the control unit calculates the required order of the filter according to the passband cutoff frequency, the stopband cutoff frequency, the passband maximum attenuation coefficient and the stopband minimum attenuation coefficient, and then calculates the resistance of the digital potentiometer according to the filter type, wherein the resistance of the digital potentiometer is used for realizing the type of the selected filter, which is a conventional technical means in the field.
Step 4, the control unit calculates the obtained step number control switch S 0 ～S x Changing the order of the filter.
Preferably, the topology of implementing the custom low pass filter is as follows: the control unit controls the n-channel numerical control alternative analog switch S through digital quantity n And a digital potentiometer R f 、R 1 Resistance value of (2); z is an operational amplifier, and the positive input end of the operational amplifier passes through a resistor R 0 The negative input ends are respectively connected with the digital potentiometer R 1 Numerical control two-in-one analog switch S 0 Terminal 0 and negative feedback capacitance C of (2) f The output end is connected with a digital potentiometer R f And negative feedback capacitor C f The method comprises the steps of carrying out a first treatment on the surface of the Numerical control two-out-of-one analog switch S 0 Is a common terminal of (a) and a digital potentiometer R f Are connected; numerical control two-out-of-one analog switch S 1 Is a common terminal of (a) and a digital potentiometer R 1 Are connected; numerical control two-out-of-one analog switch S 0 Terminal 1 of (2) and digital control alternative analog switch S 1 Is connected to terminal 0 of (2); input signal U in And numerical control one-out-of-two analog switch S 1～x Is connected to terminal 1 of (2); resistor R x Is connected with a numerical control alternative analog switch S x Common terminal of (2) and digital control alternative analog switch S x-1 Terminal 0 of (a); capacitor C x Is connected with a numerical control alternative analog switch S x-1 Between terminal 0 and 0 potential point GND, x>2。
Preferably, the topology of implementing the custom high pass filter is as follows: the control unit controls the n-channel numerical control alternative analog switch S through digital quantity n And a digital potentiometer R f Resistance value of (2); z is an operational amplifier, and the positive input end of the operational amplifier passes through a resistor R 0 The negative input ends are respectively connected with the capacitor C 1 Numerical control two-in-one analog switch S 0 Terminal 0 and digital potentiometer R f The output end is connected with a digital potentiometer R f And negative feedback capacitor C f The method comprises the steps of carrying out a first treatment on the surface of the Numerical control two-out-of-one analog switch S 0 Common terminal of (2) and negative feedback capacitor C f Are connected; numerical control two-out-of-one analog switch S 1 Common terminal of (C) and capacitor C 1 Are connected; numerical control two-out-of-one analog switch S 0 Terminal 1 of (2) and digital control alternative analog switch S 1 Is connected to terminal 0 of (2); input signal U in And numerical control one-out-of-two analog switch S 1～x Is connected to terminal 1 of (2); capacitor C x Is connected with a numerical control alternative analog switch S x Common terminal of (2) and digital control alternative analog switch S x-1 Terminal 0 of (a); resistor R x Is connected with a numerical control alternative analog switch S x-1 Between terminal 0 and 0 potential point GND, x>2。
The invention has the beneficial effects that:
the invention adopts a single operational amplifier to realize a high-order filter; the order of the filter can be adjusted at any time according to the requirements; the type of the filter can be adjusted at any time according to the requirements.
Drawings
In order to more clearly illustrate the embodiments of the present invention, or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It is apparent that the drawings in the following description are specific embodiments of the invention and that other drawings within the scope of the application can be obtained from these drawings by those skilled in the art without inventive effort.
FIG. 1 is a logic flow diagram of a method for controlling a custom filter according to an embodiment of the present invention;
FIG. 2 is a schematic circuit diagram of an infinite gain multipath feedback second-order low-pass filter in the prior art;
FIG. 3 is a topology structure diagram of a single op-amp custom low pass filter according to a second embodiment of the present invention;
FIG. 4 is a schematic diagram of a circuit structure of an infinite gain multi-path feedback second-order high-pass filter in the prior art;
fig. 5 is a topology structure diagram of a single op-amp custom high pass filter according to a third embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made apparent and complete in conjunction with the accompanying drawings, in which it is evident that the embodiments described are some, but not all embodiments of the present invention.
Embodiment one: a control method of a custom filter.
Fig. 1 is a logic flow diagram of a method for controlling a custom filter according to a first embodiment of the present invention. A control method of a custom filter comprises the following steps:
step 1, setting a control unit electrically connected with an upper computer, wherein the control unit adopts a singlechip, a DSP or an FPGA.
And 2, the upper computer sends the passband cut-off frequency, the stopband cut-off frequency, the passband maximum attenuation coefficient, the stopband minimum attenuation coefficient and the filter type of the custom type filter to the control unit.
And 3, the control unit calculates the required order of the filter according to the passband cut-off frequency, the stopband cut-off frequency, the passband maximum attenuation coefficient and the stopband minimum attenuation coefficient, and then calculates the resistance of the digital potentiometer according to the filter type.
For analog filters, the design criteria are α p 、f p 、α s And f s . Wherein f p And f s Respectively referred to as passband cut-off frequency and stopband cut-off frequency, alpha p Is passband (f=0 to f) p ) Maximum attenuation coefficient, alpha s Is a stop band (f>f p ) Is a minimum attenuation coefficient of (a) p 、α s Is typically in dB.
Taking a Butterworth type low-pass filter as an example, the calculation method of the order in step 3 will be briefly described.
Assuming the passband cut-off frequency f is required p =1khz, passband maximum attenuation α p =1 dB, stop band cut-off frequency f s =2khz, stop band minimum attenuation α s ＝30dB。
Order the
The required filter order +.>
Wherein, gamma sp To normalize the frequency, k sp Is the normalized amplitude of the filter. k (k) sp The detailed derivation process is prior art and will not be described in detail herein.
Bringing the desired parameters into the above formula yields the required filter order of 6. Based on the second embodiment of the present invention, the transfer function of the desired low-pass filter can be determined as follows:
the resistance and capacitance are known conditions, and the quality factor of the circuit is related to the digital potentiometer R f And R is 1 The quality factor of the Butterworth type low-pass filter is 0.96, and the proper resistance value is matched according to the conditions and the selectable resistance value of the digital potentiometer.
Step 4, the control unit calculates the obtained step number control switch S 0 ～S x Changing the order of the filter.
Embodiment two: a custom low pass filter.
Fig. 2 is a schematic circuit structure of an infinite gain multipath feedback second-order low-pass filter in the prior art. Transfer function of the low pass filter:
passband cut-off frequency:
quality factor:
in summary, the low-pass filter is a second-order low-pass filter circuit, the order of the low-pass filter cannot be changed after the design and shaping of the circuit, and if the pass/stop band cut-off frequency and the quality factor need to be changed, the resistance-capacitance element needs to be welded again. Therefore, the low-pass filter is not suitable for application in the case where the filter requirement is frequently changed.
When the passband cut-off frequency and the stopband cut-off frequency of the low-pass filter are changed, the required order of the low-pass filter may be changed, and on the premise that only one operational amplifier is adopted, the circuit structure needs to be changed, namely, an RC circuit is connected in series before the current input end, and then the RC parameter (quality factor Q) is recalculated according to the type of the expected low-pass filter.
On the premise of adopting a plurality of operational amplifiers, the change of the filter order can be realized by connecting low-order low-pass filters in series, but the RC parameters of the circuit also need to be recalculated according to the type of the low-pass filters.
In summary, in any of the above modes, in an application environment where the filtering parameters need to be changed frequently, the topology structure of the existing low-pass filter is difficult to change, and is not suitable for mass application.
In the second embodiment of the present invention, a self-defined low-pass filter with frequently-changed filter parameters is provided, and the filter parameters are only required to be input to the control unit without changing the circuit structure, and the control unit controls the filter circuit to combine the low-pass filter meeting the filter requirements.
Fig. 3 is a topology structure diagram of a single op-amp custom low-pass filter according to a second embodiment of the present invention.
In the figure:
U in : inputting a signal;
U out : outputting a signal;
S n : n-channel numerical control alternative analog switch (n=0, 2-x);
C n : capacitors (n=2, 3 to x);
R n : resistors (n=0, 2 to x);
R f 、R 1 : digital potentiometers (digitally controlled programmable resistors);
z: an operational amplifier.
GND:0 potential site.
The control unit (single chip microcomputer/DSP/FPGA, etc.) controls the n-channel numerical control one-out-of-two analog switch S through digital quantity n And a digital potentiometer R f 、R 1 Resistance value of (2); z is an operational amplifier, the positive input end of which passes through a resistor R 0 The negative input ends are respectively connected with the digital potentiometer R 1 Numerical control two-in-one analog switch S 0 Terminal 0 and negative feedback capacitance C of (2) f The output end is connected with a digital potentiometer R f And negative feedback capacitor C f The method comprises the steps of carrying out a first treatment on the surface of the Numerical control two-out-of-one analog switch S 0 Is a common terminal of (a) and a digital potentiometer R f Are connected; numerical control two-out-of-one analog switch S 1 Is a common terminal of (a) and a digital potentiometer R 1 Are connected; numerical control two-out-of-one analog switch S 0 Terminal 1 of (2) and digital control alternative analog switch S 1 Is connected to terminal 0 of (2); input signal U in And numerical control one-out-of-two analog switch S 1～x Is connected to terminal 1 of (2); resistor R x (x>2) Is connected with a numerical control alternative analog switch S x Common terminal of (2) and digital control alternative analog switch S x-1 Terminal 0 of (a); capacitor C x (x>2) Is connected with a numerical control alternative analog switch S x-1 Between terminal 0 and 0 potential point GND.
Referring to fig. 3, the upper computer transmits a desired passband cut-off frequency, a passband maximum attenuation coefficient, a stopband minimum attenuation coefficient, and a filter type to the control unit, and the control unit calculates the required order of the low-pass filter according to the passband cut-off frequency, the passband maximum attenuation coefficient, and the stopband minimum attenuation coefficient, and then calculates the resistance of the digital potentiometer according to the selected low-pass filter type, and controls the switch S by calculating the obtained order 0 ～S x The state of which changes the order of the low-pass filter.
When the low-pass filter order k set by the upper computer is equal to or greater than 2, and the resistance values of the resistors are all R and the capacitance values of the capacitors are all C, the transfer function of the low-pass filter circuit shown in FIG. 3 is as follows:
from the transfer function, the pass band cut-off frequency and the quality factor of the k (k.gtoreq.2) order low-pass filter are related to R 1 、R f Is reasonable to configure R 2 、R f The desired cut-off frequency and quality factor can be obtained. In the formula, s is the Laplacian, the other is the element parameter value, the selection of the element parameter value is the prior art, and the description is omitted here。
With reference to FIG. 3, x (x>1) The order butterworth low-pass filter exemplifies its workflow. After the target pass (block) band cut-off frequency is input into the control unit, the control unit calculates the proper filter order as x, and the control unit controls the switch S 0 In position 1, switch S x The other switches are arranged at the position 1 and the position 0, so that an x-order low-pass filter can be obtained; then according to the target Butterworth low-pass filter, its quality factor (Q value) is 0.96, C is included in the circuit n 、R n After the determination, the required R can be calculated by combining the orders f 、R 1 Values. When a first-order low-pass filter is needed, a switch S is needed 0 Is arranged at the position 0, the switch S 1 The device is placed at the position 1.
Embodiment III: a custom high pass filter.
Fig. 4 is a schematic circuit diagram of an infinite gain multipath feedback second-order high-pass filter in the prior art.
Transfer function of the high pass filter:
passband cut-off frequency:
quality factor:
in summary, the high-pass filter is a second-order filter circuit, the order of the high-pass filter cannot be changed after the design and shaping of the circuit, and if the pass/stop band cut-off frequency and the quality factor need to be changed, the resistance-capacitance element needs to be welded again. Therefore, the high-pass filter is not suitable for application in the occasion where the filter requirement frequently changes.
When the passband cutoff frequency and the stopband cutoff frequency of the high-pass filter are changed, the required order of the high-pass filter may be changed, and on the premise that only one operational amplifier is adopted, the circuit structure needs to be changed, namely, an RC circuit is connected in series before the current input end, and then the RC parameter (quality factor Q) is recalculated according to the expected filter type.
On the premise of adopting a plurality of operational amplifiers, the change of the order of the high-pass filter can be realized by connecting low-order high-pass filters in series, but the RC parameters of the circuit also need to be recalculated according to the type of the high-pass filter.
In summary, in any of the above modes, in an application environment where the filtering parameters need to be changed frequently, the topology structure of the existing high-pass filter is difficult to change, and is not suitable for mass application.
The third embodiment of the invention provides a high-pass filter which can be suitable for the frequent change of the filtering parameters, and on the premise of not changing the circuit structure, the filtering parameters are only required to be input into the control unit, and the control unit controls the filtering circuit to combine the high-pass filter meeting the filtering requirement.
Fig. 5 shows a topology structure diagram of a single op-amp custom high pass filter according to a third embodiment of the present invention.
In the figure:
U in : inputting a signal;
U out : outputting a signal;
S n : n-channel numerical control alternative analog switch (n=0, 1-x);
C n : capacitors (n=1, 2 to x);
R n : resistors (n=0, 3 to x);
R f 、R 2 : digital potentiometers (digitally controlled programmable resistors);
z: an operational amplifier;
GND:0 potential site.
The control unit (single chip microcomputer/DSP/FPGA, etc.) controls the n-channel numerical control one-out-of-two analog switch S through digital quantity n And a digital potentiometer R f Resistance value of (2); z is an operational amplifier, the positive input end of which passes through a resistor R 0 The negative input ends are respectively connected with the capacitor C 1 Numerical control two-in-one dieQuasi-switch S 0 Terminal 0 and digital potentiometer R f The output end is connected with a digital potentiometer R f And negative feedback capacitor C f The method comprises the steps of carrying out a first treatment on the surface of the Numerical control two-out-of-one analog switch S 0 Common terminal of (2) and negative feedback capacitor C f Are connected; numerical control two-out-of-one analog switch S 1 Common terminal of (C) and capacitor C 1 Are connected; numerical control two-out-of-one analog switch S 0 Terminal 1 of (2) and digital control alternative analog switch S 1 Is connected to terminal 0 of (2); input signal U in And numerical control one-out-of-two analog switch S 1～x Is connected to terminal 1 of (2); capacitor C x (x>2) Is connected with a numerical control alternative analog switch S x Common terminal of (2) and digital control alternative analog switch S x-1 Terminal 0 of (a); resistor R x (x>2) Is connected with a numerical control alternative analog switch S x-1 Between terminal 0 and 0 potential point GND.
The upper computer sends expected passband cut-off frequency, stopband cut-off frequency, passband maximum attenuation coefficient, stopband minimum attenuation coefficient and high-pass filter type to the control unit, the control unit calculates the required order of the high-pass filter according to the passband cut-off frequency, passband maximum attenuation coefficient and stopband minimum attenuation coefficient, then calculates the resistance of the digital potentiometer according to the selected high-pass filter type and the order, and controls the switch S by calculating the obtained order 0 ～S x The state of which changes the order of the high pass filter.
When the order k of the high-pass filter set by the upper computer is equal to or greater than 2, and the resistance values of the resistors are all R and the capacitance values of the capacitors are all C, the transfer function of the high-pass filter circuit shown in FIG. 5:
from the transfer function, the cut-off frequency and the quality factor of the k (k.gtoreq.2) order high pass filter are respectively related to R 2 /R f And R is R 2 /R f Is reasonable to configure R 2 、R f The desired cut-off frequency and quality factor can be obtained.
With reference to FIG. 5, x (x>1) The order butterworth type high-pass filter exemplifies its workflow. After inputting the cut-off frequency of the target pass (block) band, the maximum attenuation coefficient of the pass band and the minimum attenuation coefficient of the stop band to the control unit, the control unit calculates the proper filter order as x, and the control unit controls the switch S 0 In position 1, switch S x The other switches are arranged at the position 1 and the position 0, so that an x-order high-pass filter can be obtained; then according to the target Butterworth high-pass filter, its quality factor (Q value) is 0.96, C is found in the circuit n 、R n After the determination, the required R can be calculated by combining the orders 2 、R f Values. When a first-order high-pass filter is needed, a switch S is needed 0 Is arranged at the position 0, the switch S 1 The device is placed at the position 1.
In the embodiments of the present invention, technical features that are not described in detail are all existing technologies or conventional technical means, and are not described herein.
Finally, it should be noted that: the above examples are only specific embodiments of the present invention, and are not intended to limit the scope of the present invention. Those skilled in the art will appreciate that: any person skilled in the art may modify or easily conceive of changes to the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features within the technical scope of the present disclosure; such modifications, changes or substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention, and are intended to be included in the scope of the present invention.
Claims (3)
1. The control method of the custom filter is characterized by comprising the following steps:
step 1, setting a control unit electrically connected with an upper computer, wherein the control unit adopts a singlechip, a DSP or an FPGA;
step 2, the upper computer sends the passband cut-off frequency, the stopband cut-off frequency, the passband maximum attenuation coefficient, the stopband minimum attenuation coefficient and the filter type of the custom type filter to the control unit;
step 3, the control unit calculates the required order of the filter according to the passband cut-off frequency, the stopband cut-off frequency, the passband maximum attenuation coefficient and the stopband minimum attenuation coefficient, and calculates the resistance of the digital potentiometer according to the filter type;
step 4, the control unit calculates the obtained step number control switch S 0 ～S x Changing the order of the filter.
2. The method for controlling a custom filter according to claim 1, wherein the topology of implementing the custom low-pass filter is as follows:
the control unit controls the n-channel numerical control alternative analog switch S through digital quantity n And a digital potentiometer R f 、R 1 Resistance value of (2); z is an operational amplifier, and the positive input end of the operational amplifier passes through a resistor R 0 The negative input ends are respectively connected with the digital potentiometer R 1 Numerical control two-in-one analog switch S 0 Terminal 0 and negative feedback capacitance C of (2) f The output end is connected with a digital potentiometer R f And negative feedback capacitor C f The method comprises the steps of carrying out a first treatment on the surface of the Numerical control two-out-of-one analog switch S 0 Is a common terminal of (a) and a digital potentiometer R f Are connected; numerical control two-out-of-one analog switch S 1 Is a common terminal of (a) and a digital potentiometer R 1 Are connected; numerical control two-out-of-one analog switch S 0 Terminal 1 of (2) and digital control alternative analog switch S 1 Is connected to terminal 0 of (2); input signal U in And numerical control one-out-of-two analog switch S 1～x Is connected to terminal 1 of (2); resistor R x Is connected with a numerical control alternative analog switch S x Common terminal of (2) and digital control alternative analog switch S x-1 Terminal 0 of (a); capacitor C x Is connected with a numerical control alternative analog switch S x-1 Between terminal 0 and 0 potential point GND, x>2。
3. The method for controlling a custom filter according to claim 1, wherein the topology of implementing the custom high-pass filter is as follows:
the control unit controls the n-channel numerical control alternative analog switch S through digital quantity n And a digital potentiometer R f Resistance value of (2); z is an operational amplifier, and the positive input end of the operational amplifier passes through a resistor R 0 The negative input ends are respectively connected with the capacitor C 1 Numerical control two-in-one analog switch S 0 Terminal 0 and digital potentiometer R f The output end is connected with a digital potentiometer R f And negative feedback capacitor C f The method comprises the steps of carrying out a first treatment on the surface of the Numerical control two-out-of-one analog switch S 0 Common terminal of (2) and negative feedback capacitor C f Are connected; numerical control two-out-of-one analog switch S 1 Common terminal of (C) and capacitor C 1 Are connected; numerical control two-out-of-one analog switch S 0 Terminal 1 of (2) and digital control alternative analog switch S 1 Is connected to terminal 0 of (2); input signal U in And numerical control one-out-of-two analog switch S 1～x Is connected to terminal 1 of (2); capacitor C x Is connected with a numerical control alternative analog switch S x Common terminal of (2) and digital control alternative analog switch S x-1 Terminal 0 of (a); resistor R x Is connected with a numerical control alternative analog switch S x-1 Between terminal 0 and 0 potential point GND, x>2。
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|---|---|
| CN116232281B (en) | 2023-11-14 |
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