CN211791460U - Low-pass filter - Google Patents
Low-pass filter Download PDFInfo
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- CN211791460U CN211791460U CN202020204072.9U CN202020204072U CN211791460U CN 211791460 U CN211791460 U CN 211791460U CN 202020204072 U CN202020204072 U CN 202020204072U CN 211791460 U CN211791460 U CN 211791460U
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- 239000003990 capacitor Substances 0.000 claims abstract description 73
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- 230000008859 change Effects 0.000 abstract description 7
- 230000001629 suppression Effects 0.000 abstract description 5
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- 238000001914 filtration Methods 0.000 description 6
- 238000004088 simulation Methods 0.000 description 6
- 238000010586 diagram Methods 0.000 description 3
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- 230000005764 inhibitory process Effects 0.000 description 2
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Abstract
The utility model discloses a low pass filter, include: a signal input terminal; a signal output terminal; the filter circuit is arranged between the signal input end and the signal output end and is provided with one or more groups; each group of filter circuits comprises: the filter circuit comprises a filter inductor, a filter capacitor and a parallel capacitor, wherein the filter inductor is arranged between a signal input end and a signal output end, one end of the filter capacitor is connected between the output end of the filter inductor and the signal output end, the other end of the filter capacitor is grounded, and the parallel capacitor is connected with the filter inductor in parallel. The utility model discloses to current K type wave filter not enough, provide the K type wave filter who improves the structure, can solve the little problem of near-end decay, increase the steepness of outband decay for the signal reduces the impedance change that arouses because frequency variation in order to reach the signal suppression effect of ideal at outband fast decay simultaneously.
Description
Technical Field
The utility model relates to a signal processing field, in particular to low pass filter.
Background
The existing K-type filter is based on a traditional structure, realizes a filtering function by utilizing the frequency selection characteristics of a capacitor and an inductor, is mainly applied to a high-frequency circuit, and filters out-of-band signals in a transmitting or receiving link so as to enable useful signals to be effectively transmitted or received.
The K-type filter of the prior structure has the following disadvantages:
first, the stopband attenuation for passband in and out is small, i.e., the attenuation of the signal is small at frequencies close to the passband. Therefore, the K-type filtering structure can only attenuate signals at a far position of a passband, and has poor inhibition effect on near-end signals;
secondly, the gradient of the attenuation frequency characteristic curve is small, namely, the attenuation of out-of-band signals is slow, effective suppression cannot be achieved in a link with high suppression on near-end stray signals, and the effect of rapid filtering cannot be achieved;
finally, the passband affects impedance frequency transformation to a large extent, and with the change of different frequency bands, the high-frequency impedance change of the structure is very large, which causes impedance mismatch in the passband to affect signal quality.
SUMMERY OF THE UTILITY MODEL
The utility model provides a low pass filter to solve the above-mentioned technical problem who exists among the prior art.
In order to solve the above technical problem, the utility model provides a low pass filter, include: a signal input terminal; a signal output terminal; the filter circuit is arranged between the signal input end and the signal output end and is provided with one or more groups; each group of filter circuits comprises: the filter circuit comprises a filter inductor, a filter capacitor and a parallel capacitor, wherein the filter inductor is arranged between a signal input end and a signal output end, one end of the filter capacitor is connected between the output end of the filter inductor and the signal output end, the other end of the filter capacitor is grounded, and the parallel capacitor is connected with the filter inductor in parallel.
Preferably, the filter inductor, the filter capacitor and the parallel capacitor are all welded on a printed circuit board, and a corresponding printed circuit is built on the printed circuit board.
Preferably, the signal input terminal and the signal output terminal are respectively installed at both ends of the printed circuit board and electrically connected to the printed circuit board.
Preferably, the initial values of the filter inductor, the filter capacitor and the parallel capacitor are obtained by a calculation formula of a K-type filter model.
Preferably, when a group of filter circuits is provided, the initial values of the filter inductors and the filter capacitors in all the filter circuits are calculated values.
Preferably, when the filter circuit is provided with a plurality of sets: the initial value of the filter inductance in the first group of filter circuits is a calculated value, the initial value of the filter inductance in the other groups of filter circuits is 2 times of the calculated value, and the initial value of the filter capacitance in the last group of filter circuits is the calculated value; the initial value of the filter capacitors in the other groups of filter circuits is 2 times of the calculated value; or,
the initial value of the filter capacitors in the first group of filter circuits is a calculated value, the initial values of the filter capacitors in the other groups of filter circuits are 2 times of the calculated value, and the initial values of the filter inductors in the last group of filter circuits are the calculated values; the initial value of the filter inductance in the rest groups of filter circuits is 2 times of the calculated value.
Preferably, the initial values of the parallel capacitors in all the filter circuits are the same and are calculated values of the initial values of the filter capacitors.
Preferably, simulation software is adopted to optimally tune initial values of the filter inductor, the filter capacitor and the parallel capacitor so as to increase the external suppression performance of the low-pass filter.
Compared with the prior art, the utility model discloses not enough to current K type wave filter provides the K type wave filter who improves the structure, can solve the little problem of near-end decay, increases the steepness of outband decay for the signal reduces the impedance change that arouses because frequency variation in order to reach the signal suppression effect of ideal at outband fast decay.
In addition, compared with filters with other structures and processes with the same functions, the cost of the filter is reduced by more than 60 times; the indexes can be flexibly adjusted, the building speed is high, and no influence is caused by the cargo life; the impedance is variable, the volume is small, and the differential circuit can be used for signal processing.
Drawings
Fig. 1 is a schematic circuit diagram of a low-pass filter according to the present invention;
FIG. 2 is a diagram illustrating simulation results of a conventional K-type filter;
fig. 3 is a schematic diagram of a simulation result of the low-pass filter of the present invention.
Detailed Description
In order to make the above objects, features and advantages of the present invention more comprehensible, embodiments of the present invention are described in detail below with reference to the accompanying drawings. It should be noted that the drawings of the present invention are simplified and use non-precise ratios, and are only used for the purpose of facilitating and clearly assisting the description of the embodiments of the present invention.
As shown in fig. 1, the present invention provides a low pass filter, including:
a signal input terminal T1 for receiving an input signal.
And a signal output terminal T2 for outputting a filtered output signal.
And the filter circuit is arranged between the signal input end T1 and the signal output end T2 and is used for filtering the input signal. The filter circuit is provided with one or more groups, that is, the low-pass filter of the embodiment is a second-order filter or a multi-order filter, and the specific order can be adjusted according to the use requirement. When the filter is selected, the design index and the area of the printed circuit board need to be considered, the performance of the filter can be optimized by properly increasing the order, but the area of the printed circuit board is occupied more.
With continued reference to fig. 1, each set of filter circuits includes: the filter inductor is arranged between a signal input end T1 and a signal output end T2, one end of the filter capacitor is connected between the output end of the filter inductor and the signal output end T2, the other end of the filter capacitor is grounded, and the parallel capacitor is connected with the filter inductor in parallel.
That is to say, the filter inductor is connected in series with the signal circuit between the signal input end T1 and the signal output end T2, the filter capacitor is connected in parallel between the signal circuit and the ground, the characteristics of the alternating current and the direct current are realized by the cooperation of the signal circuit and the ground, the filtering function is realized, the parallel capacitor is connected in parallel with the filter inductor, the out-of-band rejection effect of the existing K-type filter is improved, the stray signals can be filtered quickly, and the ideal effect is achieved. Taking the sixth-order low-pass filter shown in fig. 1 as an example, the filter circuit has three sets, so that the corresponding filter inductors, filter capacitors and parallel capacitors are also three sets, respectively, where the first inductor L1, the second inductor L2 and the third inductor L3 are filter inductors and are connected in series to the signal circuit, the first capacitor C1, the second capacitor C2 and the third capacitor C3 are filter capacitors and are connected in parallel between the signal circuit and ground, and the fourth capacitor C4, the fifth capacitor C5 and the sixth capacitor C6 are parallel capacitors and are connected in parallel with the first inductor L1, the second inductor L2 and the third inductor L3, respectively.
Therefore, the filter inductor and the filter capacitor jointly form a K-type filter circuit, the parallel capacitor is connected to the filter inductor in parallel, and the K-type filter circuit is improved, so that the improved circuit can effectively inhibit a near-end signal and achieve the effect of rapid filtering; meanwhile, the parallel capacitor can also reduce impedance change caused by frequency change, and the signal quality is ensured.
Preferably, the filter inductor, the filter capacitor and the parallel capacitor are all welded on a printed circuit board, and of course, a corresponding printed circuit is built on the printed circuit board. The signal input terminal T1 and the signal output terminal T2 are respectively mounted at both ends of the printed circuit board and electrically connected to the printed circuit board, thereby forming a complete low pass filter, and in order to protect the printed circuit board and devices thereon, a protective case may be further provided, which reserves openings at both ends thereof for the signal input terminal T1 and the signal output terminal T2. The signal input end and the signal output end respectively adopt a signal terminal to realize the signal connection function.
Preferably, the initial values of the filter inductor, the filter capacitor and the parallel capacitor are obtained through a calculation formula of a K-type filter model. Then substitute the calculated value in simulation software, utilize simulation software low pass filter to simulate, and then can optimize tuning to the initial value of filter inductance, filter capacitance and parallelly connected electric capacity, because printed circuit board's panel, and LAYOUT's structure, the stromatolite, the line width and the line spacing of microstrip line are different, the distribution parameter is to the influence of performance in the high frequency circuit, simultaneously because the precision of the own of electric capacity and inductance and the influence that the cascade error brought, when practical application is on printed circuit board, probably need do the fine setting to the value of electric capacity and inductance, in order to obtain final parameter, form the utility model discloses a low pass filter, this low pass filter can increase low pass filter's external inhibition performance.
Since the order of the low-pass filter is adjusted according to the actual use requirement, the initial value in the filter circuit is different under different conditions. Specifically, when the filter circuit is provided with one group, the initial values of the filter inductors and the filter capacitors in all the filter circuits are calculated values. When the filter circuit is provided with a plurality of groups: the initial value of the filter inductance in the first group of filter circuits is a calculated value, the initial value of the filter inductance in the other groups of filter circuits is 2 times of the calculated value, and the initial value of the filter capacitance in the last group of filter circuits is the calculated value; the initial value of the filter capacitors in the other groups of filter circuits is 2 times of the calculated value; or the initial value of the filter capacitor in the first group of filter circuits is a calculated value, the initial values of the filter capacitors in the other groups of filter circuits are 2 times of the calculated value, and the initial value of the filter inductor in the last group of filter circuits is the calculated value; the initial value of the filter inductance in the rest groups of filter circuits is 2 times of the calculated value.
Preferably, the initial values of the parallel capacitors in all the filter circuits are the same and are calculated values of the initial values of the filter capacitors.
Referring to fig. 1 to 3, the design process of the low pass filter of the present invention is described in detail as follows:
firstly, a printed circuit is built on a printed circuit board, the order of the filter can be selected according to actual requirements, design indexes and the area of the printed circuit board need to be considered during selection, the performance of the filter can be optimized by properly increasing the order, but the area of the printed circuit board is occupied more.
Then, the value of the component is preliminarily estimated by using the calculation formula of the existing K-type filter model, and the calculation process is as follows:
in the known K-type filter model, the characteristic impedance Z is normalized0And normalized characteristic frequency f0：
Z0＝1Ω
Let the cut-off frequency of the low-pass filter to be designed be f1The low-pass filter to be designed has a termination impedance of Z1Then, the calculation formula of each component is as follows:
the filter inductance L in each filter circuit can be calculated by the formulaNewAnd a filter capacitor CNewThe value of (c). If the order of the low-pass filter is 2, the initial values of the filter inductance and the filter capacitance in the low-pass filter are the calculated values. If the order of the low-pass filter is greater than 2 orders, the initial value of the first filter capacitor (or the first filter inductor) and the initial value of the last filter capacitor (or the last filter inductor) in the low-pass filter are calculated values, and the device values in the middle of the low-pass filter are all 2 times of the calculated values.
Then, a parallel capacitor is connected in parallel to each filter inductor, and the initial value of the parallel capacitor can be close to the calculated value of the filter capacitor in the above step.
And finally, optimizing and tuning the component values in simulation software to obtain the improved K-type filter with optimized out-of-band rejection performance. According to final result of optimizing, can obtain on pasting printed circuit board with the components and parts that correspond the utility model discloses a low pass filter is in kind.
With particular reference to fig. 1 to 3, to actually set the cut-off frequency f of the low-pass filter1Is 450MHz, and a termination impedance Z1For example 50 Ω (6 th order):
from the formula it can be calculated:
corresponding the calculated value of the formula to each component to obtain:
the initial value of the first inductance L1 is:
L1＝17.65nH
the initial values of the second inductance L2 and the third inductance L3 are:
L2＝L3＝2*LNew＝35.3nH
the initial value of the third capacitance C3 is:
C3＝7.1pF
the initial values of the first capacitor C1 and the second capacitor C2 are:
C1＝C2＝2*CNew＝14.2pF
if the simulation result of the conventional K-type filter after tuning the structure (i.e. without the parallel capacitor) is shown in fig. 2, the simulation result shows a 450MHz low-pass filter curve, it can be seen that although the signal starts to attenuate after 450M, the attenuation slope is small, and the spurious signal close to the sideband can not be effectively filtered in practical use (the signal attenuation is only 3.58dB at 500M); the main reason is that the tuning needs to take out-of-band rejection and input and output impedances into account due to the structure of the conventional K-type filter, and a small change in the value of one component may cause the filter parameters to be rapidly deteriorated, so that the actual requirements cannot be met.
If a parallel capacitor is connected in parallel to each filter inductor on the basis of the simulation result, the initial capacitance value is calculated according to the calculation result;
C4＝C5＝C6＝7.1pF
continuing to optimize and tune the values of the components in the simulation software, as can be seen from the simulation result shown in fig. 3, under the condition of meeting the passband of 450M, the out-of-band attenuation slope is very large, and spurious signals outside the sideband (the signal attenuation is 44.93dB at 500M) can be rapidly filtered out, compared with the traditional K-type filter, the out-of-band attenuation is 41.35dB, which indicates that the out-of-band rejection effect is greatly optimized, and the out-of-band spurious signals can be effectively filtered out.
It will be apparent to those skilled in the art that various changes and modifications may be made to the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (8)
1. A low pass filter comprising: a signal input terminal; a signal output terminal; the filter circuit is arranged between the signal input end and the signal output end and is provided with one or more groups; it is characterized in that each group of filter circuits comprises: the filter circuit comprises a filter inductor, a filter capacitor and a parallel capacitor, wherein the filter inductor is arranged between a signal input end and a signal output end, one end of the filter capacitor is connected between the output end of the filter inductor and the signal output end, the other end of the filter capacitor is grounded, and the parallel capacitor is connected with the filter inductor in parallel.
2. The low pass filter according to claim 1, wherein the filter inductor, the filter capacitor and the shunt capacitor are soldered on a printed circuit board on which a corresponding printed circuit is built.
3. A low-pass filter according to claim 2, characterized in that the signal input and output terminals are mounted at both ends of the printed circuit board, respectively, and connected to the printed circuit.
4. The low-pass filter according to claim 1, characterized in that the initial values of the filter inductance, the filter capacitance and the shunt capacitance are obtained from the calculation formula of a K-type filter model.
5. The low-pass filter according to claim 4, wherein when the filter circuits are provided in a group, initial values of filter inductances and filter capacitances in all the filter circuits are calculated values.
6. A low-pass filter as claimed in claim 4, characterized in that the filter circuit is provided with a plurality of sets: the initial value of the filter inductance in the first group of filter circuits is a calculated value, the initial value of the filter inductance in the other groups of filter circuits is 2 times of the calculated value, and the initial value of the filter capacitance in the last group of filter circuits is the calculated value; the initial value of the filter capacitors in the other groups of filter circuits is 2 times of the calculated value; or,
the initial value of the filter capacitors in the first group of filter circuits is a calculated value, the initial values of the filter capacitors in the other groups of filter circuits are 2 times of the calculated value, and the initial values of the filter inductors in the last group of filter circuits are the calculated values; the initial value of the filter inductance in the rest groups of filter circuits is 2 times of the calculated value.
7. A low-pass filter as claimed in claim 5 or 6, characterized in that the initial values of the parallel capacitors in all filter circuits are the same and are calculated values of the initial values of the filter capacitors.
8. A low-pass filter as claimed in claim 4, characterized in that the initial values of the filter inductance, the filter capacitance and the shunt capacitance are optimally tuned by simulation software to increase the rejection performance of the low-pass filter.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202020204072.9U CN211791460U (en) | 2020-02-24 | 2020-02-24 | Low-pass filter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202020204072.9U CN211791460U (en) | 2020-02-24 | 2020-02-24 | Low-pass filter |
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| Publication Number | Publication Date |
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| CN211791460U true CN211791460U (en) | 2020-10-27 |
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| CN202020204072.9U Active CN211791460U (en) | 2020-02-24 | 2020-02-24 | Low-pass filter |
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