CN108920762A - A kind of filter circuit - Google Patents
A kind of filter circuit Download PDFInfo
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- CN108920762A CN108920762A CN201810569367.3A CN201810569367A CN108920762A CN 108920762 A CN108920762 A CN 108920762A CN 201810569367 A CN201810569367 A CN 201810569367A CN 108920762 A CN108920762 A CN 108920762A
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Abstract
The invention discloses a kind of filter circuits, including：Source, load end, the first matching network module, the second matching network module and trapper module；Wherein, the source is connect with the input terminal of the first matching network module, and the output end of first matching network is connect with the input terminal of the trapper module；The input terminal of the module of second matching network is connect with the output end of the trapper module, and the output end of the second matching network module is connect with the load end.Using the embodiment of the present invention, passband Insertion Loss can be made smaller, suppressed frequency band Insertion Loss is bigger, more preferable to the inhibitory effect of the High-frequency Interference after the low-frequency disturbance and passband before suppressed frequency band.
Description
Technical field
The present invention relates to field of wireless communications systems more particularly to a kind of filter circuits.
Background technique
In double frequency even multi-frequency radio communication system, interfere with each other between different operating frequency band not can avoid sometimes, institute
To usually require to add interference of the suitable narrow band filter circuit to inhibit another working frequency range signal on signal link, lead to
When often working frequency is higher, usually on signal link and a LC series circuit is connect to ground, LC series circuit resonance is in resistance frequency
Band, to have the function that inhibit interference.For filter, Q value (quality factor) is higher, it is meant that and bandwidth is narrower,
The waveform of frequency response just seems more sharp.Narrow band filter circuit in the prior art is as shown in Figure 1, include source T01, negative
Carry end T02, capacitor C0 and inductance L0.Wherein, capacitor C0 and inductance L0 forms LC series circuit.Narrow band filter shown in FIG. 1
There is very high inhibition effect in LC resonance frequency attachment, passband signals can pass freely through other than resonance frequency, still, existing
The Q value of narrow band filter in technology is not high enough, still has biggish decaying so as to cause in passband signals.
Summary of the invention
The purpose of the embodiment of the present invention is that providing a kind of filter circuit, passband Insertion Loss can be made smaller, suppressed frequency band is inserted
Damage is bigger, more preferable to the inhibitory effect of the High-frequency Interference after the low-frequency disturbance and passband before suppressed frequency band.
To achieve the above object, the embodiment of the invention provides a kind of filter circuits, including：Source, load end, first
Matching network module, the second matching network module and trapper module；Wherein,
The source is connect with the input terminal of the first matching network module, the output end of first matching network with
The input terminal of the trapper module connects；
The input terminal of the module of second matching network is connect with the output end of the trapper module, and described second
The output end of distribution network module is connect with the load end.
Compared with prior art, filter circuit disclosed by the invention by the source and the trapper module it
Between connect the first matching network module, described second is then connected between the load end and the trapper module
Distribution network module, the Q value for solving narrow band filter in the prior art is not high enough, still has so as to cause in passband signals
The problem of biggish decaying, can make passband Insertion Loss smaller, and suppressed frequency band Insertion Loss is bigger, to before suppressed frequency band low-frequency disturbance and
The inhibitory effect of High-frequency Interference after passband is more preferable.
As an improvement of the above scheme, the first matching network module includes first capacitor and the second capacitor；Wherein,
The first end of the first capacitor is connect with the input terminal of the first matching network module, the first capacitor
Second end is connect with the output end of the first matching network module；
The first end of second capacitor is connect with the second end of the first capacitor, the second termination of second capacitor
Ground.
As an improvement of the above scheme, the second matching network module includes third capacitor and the 4th capacitor；Wherein,
The first end of the third capacitor is connect with the input terminal of the second matching network module, the third capacitor
Second end is connect with the output end of the second matching network module；
The first end of 4th capacitor is connect with the first end of the third capacitor, the second termination of the 4th capacitor
Ground.
As an improvement of the above scheme, the trapper module includes the 5th capacitor and inductance；Wherein,
The first end of 5th capacitor is separately connected the input terminal and output end of the trapper module, the 5th electricity
The second end of appearance is connect with the first end of the inductance, the second end ground connection of the inductance.
As an improvement of the above scheme, the first capacitor and the capacitance of the third capacitor are equal, second electricity
Hold equal with the capacitance of the 4th capacitor.
As an improvement of the above scheme, the first matching network module to the source meets formula of impedance, the resistance
Anti- formula：
Wherein, ZAImpedance for first matching network to the source, Z0For the impedance of the source, C1It is described
The capacitance of first capacitor, C2For the capacitance of second capacitor, j is pure imaginary number, and ω is angular frequency.
As an improvement of the above scheme, the admittance of the first matching network module to the source is matched with described second
The admittance of network module to the load end is equal；Wherein, the admittance of the first matching network module to the source meets
First admittance formula, the first admittance formula are：
Wherein, YAAdmittance for first matching network to the source, Z0For the impedance of the source, C1It is described
The capacitance of first capacitor, C2For the capacitance of second capacitor, j is pure imaginary number, and ω is angular frequency.
As an improvement of the above scheme, the trapper is passed through in the admittance of the first matching network module to the source
Block transforms at the second matching network module to the load end admittance when conjugate complex number form meet conjugation formula,
The conjugation formula is：
Wherein,The conjugate complex number form of admittance for the second matching network module to the load end, YAIt is described
Admittance of first matching network to the source, L0For the inductance value of the inductance, C0For the capacitance of the 5th capacitor, j is
Pure imaginary number, ω are angular frequency.
As an improvement of the above scheme, it is public to meet the first centre frequency for the suppressed frequency band centre frequency of the filter circuit
Formula, the first centre frequency formula are：
Wherein, f1For the suppressed frequency band centre frequency, L0For the inductance value of the inductance, C0For the electricity of the 5th capacitor
Capacitance.
As an improvement of the above scheme, the passband mid-band frequency of the filter circuit meets second central frequency public affairs
Formula, the second central frequency formula are：
Wherein, f1For passband mid-band frequency, ω is angular frequency.
Detailed description of the invention
Fig. 1 is the circuit structure diagram for the narrow band filter circuit that the prior art provides；
Fig. 2 is a kind of structural schematic diagram of filter circuit provided in an embodiment of the present invention；
Fig. 3 is a kind of circuit structure diagram of filter circuit provided in an embodiment of the present invention；
Fig. 4 is the simulation result diagram in a kind of filter circuit provided in an embodiment of the present invention；
Fig. 5 is another simulation result diagram in a kind of filter circuit provided in an embodiment of the present invention；
Fig. 6 is the simulation result of the narrow band filter of a kind of filter circuit provided in an embodiment of the present invention and the prior art
Figure；
Fig. 7 is in the suppressed frequency band of the narrow band filter of a kind of filter circuit provided in an embodiment of the present invention and the prior art
The simulation result diagram of frequency of heart；
Fig. 8 is in the passband of the narrow band filter of a kind of filter circuit provided in an embodiment of the present invention and the prior art
The simulation result diagram of frequency of heart.
Specific embodiment
Following will be combined with the drawings in the embodiments of the present invention, and technical solution in the embodiment of the present invention carries out clear, complete
Site preparation description, it is clear that described embodiments are only a part of the embodiments of the present invention, instead of all the embodiments.It is based on
Embodiment in the present invention, it is obtained by those of ordinary skill in the art without making creative efforts every other
Embodiment shall fall within the protection scope of the present invention.
Referring to fig. 2, Fig. 2 is a kind of structural schematic diagram of filter circuit provided in an embodiment of the present invention；Including：Source 1,
Load end 5, the first matching network module 2, the second matching network module 4 and trapper module 3；Wherein,
The source 1 is connect with the input terminal IN1 of the first matching network module 2, first matching network 2 it is defeated
Outlet OUT1 is connect with the input terminal IN2 of the trapper module 3；
The input terminal IN3 of the module 4 of second matching network is connect with the output end OUT2 of the trapper module 3,
The output end OUT3 of the second matching network module 4 is connect with the load end 5.
It preferably, is a kind of circuit structure diagram of filter circuit provided in an embodiment of the present invention referring to Fig. 3, Fig. 3；It is described
First matching network module 2 includes first capacitor C1 and the second capacitor C2；Wherein, the first end of the first capacitor C1 with it is described
The input terminal IN1 connection of first matching network module 1, the second end of the first capacitor C1 and the first matching network module
1 output end OUT1 connection；The first end of the second capacitor C2 is connect with the second end of the first capacitor C1, and described second
The second end of capacitor C2 is grounded.
Preferably, the second matching network module 4 includes third capacitor C3 and the 4th capacitor C4；Wherein, the third
The first end of capacitor C3 is connect with the input terminal IN3 of the second matching network module 4, the second end of the third capacitor C3 with
The output end OUT3 connection of the second matching network module 4；The first end of the 4th capacitor C4 and the third capacitor C3
First end connection, the 4th capacitor C4 second end ground connection.
Preferably, the trapper module 3 includes the 5th capacitor C5 and inductance L；Wherein, the first of the 5th capacitor C5
End is separately connected the input terminal IN2 and output end OUT2 of the trapper module 2, the second end of the 5th capacitor C5 with it is described
The first end of inductance L connects, the second end ground connection of the inductance L.The trapper module 3 is for eliminating certain garbage signals
(being interfered with each other between different operating frequency band), to reduce the interference to useful signal.
Preferably, the capacitance of the first capacitor C1 and the third capacitor C3 are equal, the second capacitor C2 and institute
The capacitance for stating the 4th capacitor C4 is equal.Specifically, the first matching network module and the second matching network module are left
It is right symmetrical, it enables to passband impedance matching effect more preferable, while blocking may be implemented, inhibits low-frequency disturbance.
Preferably, as shown in Figure 3, to the source, (i.e. circuit disconnects the first matching network module from A point, and A point is left
Impedance of the lateral circuit to ground) meet formula of impedance, the formula of impedance：
Wherein, ZAImpedance for first matching network to the source, Z0For the impedance of the source, Z0=
50ohm, C1For the capacitance of the first capacitor, C2For the capacitance of second capacitor, j is pure imaginary number, and ω is angular frequency.
Preferably, admittance and the second matching network module of the first matching network module to the source are to institute
The admittance for stating load end is equal；Wherein, the admittance of the first matching network module to the source meets the first admittance formula,
The first admittance formula is：
Wherein, YAAdmittance for first matching network to the source, Z0For the impedance of the source, C1It is described
The capacitance of first capacitor, C2For the capacitance of second capacitor, j is pure imaginary number, and ω is angular frequency.
By circuit symmetry, (i.e. circuit is from B point off for admittance from the second matching network module to the load end
It opens, impedance of the circuit to ground on the right side of B point)：
Wherein, YBAdmittance for the second matching network module to the load end, Z0For the impedance of the source, C1
For the capacitance of the first capacitor, C2For the capacitance of second capacitor, j is pure imaginary number, and ω is angular frequency.
Preferably, the admittance of the first matching network module to the source passes through the trapper block transforms into institute
It states conjugate complex number form when admittance of the second matching network module to the load end and meets conjugation formula, the conjugation formula
For：
Wherein,The conjugate complex number form of admittance for the second matching network module to the load end, YAFor institute
State the admittance of the first matching network to the source, L0For the inductance value of the inductance, C0For the capacitance of the 5th capacitor.
So having：
Met by the imaginary part that formula (2 ') and formula (3 ') can obtain the mutual conductance complex function on the left of A point：
And then following equations can be obtained：
Wherein, formula (6 ') is one with ω2For the quadratic equation with one unknown of variable, analytic solutions can be found out.
Preferably, the suppressed frequency band centre frequency of the filter circuit meets the first centre frequency formula, in described first
Frequency of heart formula is：
Wherein, f1For the suppressed frequency band centre frequency, L0For the inductance value of the inductance, C0For the electricity of the 5th capacitor
Capacitance.
Preferably, the passband mid-band frequency of the filter circuit meets second central frequency formula, in described second
Frequency of heart formula is：
Wherein, f1For passband mid-band frequency；ω is angular frequency, by ω in formula (6 ')2Solution substitute into, ω be greater than 0.
Preferably, C is taken1=3.3pF, C2=0.3pF, L0=2.2nH, C0=1.2pF substitutes into formula (4) and acquires the filter
The suppressed frequency band centre frequency of wave device circuit is approximately equal to 2796MHz, substitutes into formula (5) and acquires in the passband of the filter circuit
Frequency of heart is approximately equal to 4238MHz.
So far, the suppressed frequency band centre frequency and the passband mid-band frequency can be found out, it is preferred that above-mentioned solution passband
The process of mid-band frequency and suppressed frequency band centre frequency can be calculated by MATLAB, then again by ADS software to this programme
The filter circuit and narrow band filter circuit in the prior art are emulated, and this programme and the prior art can be obtained
Difference, while obtain this programme compared with prior art brought by beneficial effect.
Preferably, referring to fig. 4, Fig. 4 is the simulation result diagram in a kind of filter circuit provided in an embodiment of the present invention.Figure
4 indicate be S21 (parameter point) Smith chart, the m1 Frequency point in Fig. 4 indicates that matching is worst in origin (at 0), from original
Point more near match is poorer, and signal is less susceptible to pass through, therefore m1 Frequency point is the suppressed frequency band centre frequency, is indicated in suppressed frequency band
The frequency inhibitory effect of heart point is good.M2 Frequency point is farthest from origin, and matching is best, and signal is easier to be passed through, therefore m2 Frequency point
For the passband mid-band frequency, indicating passband, nearby frequency Insertion Loss is small, i.e., signal is almost without inhibition.
Specifically, Fig. 5 is another simulation result in a kind of filter circuit provided in an embodiment of the present invention referring to Fig. 5
Figure.Insertion Loss reduces at passband as seen from Figure 5, and centre frequency processing thinks that Insertion Loss is 0, and the Insertion Loss of suppressed frequency band is big.
Specifically, Fig. 6 is the narrowband of a kind of filter circuit and the prior art provided in an embodiment of the present invention referring to Fig. 6
The simulation result diagram of filter.M3 Frequency point in Fig. 6 is the Frequency point of the filter circuit of this programme, and m4 is the prior art
The Frequency point of narrow band filter.It can be obtained by Fig. 6, this programme is compared with traditional scheme has the effect of blocking, and in trap
Low frequency inhibitory effect before frequency of heart point is more preferable；This programme is to the high frequency after the low-frequency disturbance and passband before suppressed frequency band
The inhibitory effect of interference is better than traditional scheme；This programme may be implemented in passband mid-band frequency (m3 Frequency point) ideal situation
Lower zero Insertion Loss, and traditional scheme only just has ideal zero Insertion Loss in passable frequency far super suppressed frequency band centre frequency.This programme
Q (quality factor) value of filter is improved, while can reduce the decaying to passband inband signaling, improves the resistance in passband
Anti- matching reduces the reflection and distortion of signal.
Specifically, Fig. 7 is the narrowband of a kind of filter circuit and the prior art provided in an embodiment of the present invention referring to Fig. 7
The simulation result diagram of the suppressed frequency band centre frequency of filter.Fig. 7 is the partial enlarged view that Fig. 6 is 2.74-2.84GHz in frequency,
M1 Frequency point in Fig. 7 is the suppressed frequency band centre frequency of the filter circuit of this programme, and m1 ' Frequency point is the narrowband of the prior art
The suppressed frequency band centre frequency of filter.It can be obtained by Fig. 7, this programme is equal with the suppressed frequency band centre frequency of prior art, but
Be this programme after -40db when design frequency range it is slightly wide.
Specifically, Fig. 8 is the narrowband of a kind of filter circuit and the prior art provided in an embodiment of the present invention referring to Fig. 8
The simulation result diagram of the passband mid-band frequency of filter.Fig. 8 is the partial enlarged view that Fig. 6 is 3.0-6.0GHz in frequency, Fig. 8
In m2 Frequency point be this programme filter circuit passband mid-band frequency, m2 ' is the narrow band filter of the prior art
Passband mid-band frequency.It can be obtained by Fig. 8, this programme may be implemented in passband mid-band frequency ideally zero Insertion Loss, and pass
System scheme only just has ideal zero Insertion Loss in passable frequency far super suppressed frequency band centre frequency.
Compared with prior art, filter circuit disclosed by the invention passes through in the source 1 and the trapper module 3
Between connect the first matching network module 2, then between the load end 5 and the trapper module 3 connection described in
Second matching network module 4, the Q value for solving the narrow band filter of the prior art is not high enough, so as to cause in passband signals
Still there is the problem of biggish decaying, passband Insertion Loss can be made smaller, suppressed frequency band Insertion Loss is bigger, to the low frequency before suppressed frequency band
The inhibitory effect of High-frequency Interference after interference and passband is more preferable.This programme makes different operating frequency range in wireless communication system
Between interfere smaller, system performance is stronger.
The above is a preferred embodiment of the present invention, it is noted that for those skilled in the art
For, various improvements and modifications may be made without departing from the principle of the present invention, these improvements and modifications are also considered as
Protection scope of the present invention.
Claims (10)
1. a kind of filter circuit, which is characterized in that including：Source, load end, the first matching network module, the second pair net
Network module and trapper module；Wherein,
The source is connect with the input terminal of the first matching network module, the output end of first matching network with it is described
The input terminal of trapper module connects；
The input terminal of the module of second matching network is connect with the output end of the trapper module, second pair net
The output end of network module is connect with the load end.
2. filter circuit as described in claim 1, which is characterized in that the first matching network module includes first capacitor
With the second capacitor；Wherein,
The first end of the first capacitor is connect with the input terminal of the first matching network module, and the second of the first capacitor
End is connect with the output end of the first matching network module；
The first end of second capacitor is connect with the second end of the first capacitor, the second end ground connection of second capacitor.
3. filter circuit as claimed in claim 2, which is characterized in that the second matching network module includes third capacitor
With the 4th capacitor；Wherein,
The first end of the third capacitor is connect with the input terminal of the second matching network module, and the second of the third capacitor
End is connect with the output end of the second matching network module；
The first end of 4th capacitor is connect with the first end of the third capacitor, the second end ground connection of the 4th capacitor.
4. filter circuit as claimed in claim 3, which is characterized in that the trapper module includes the 5th capacitor and electricity
Sense；Wherein,
The first end of 5th capacitor is separately connected the input terminal and output end of the trapper module, the 5th capacitor
Second end is connect with the first end of the inductance, the second end ground connection of the inductance.
5. filter circuit as claimed in claim 3, which is characterized in that the capacitor of the first capacitor and the third capacitor
It is worth equal, the capacitance of second capacitor and the 4th capacitor is equal.
6. filter circuit as claimed in claim 5, which is characterized in that it is characterized in that, the first matching network module
Meet formula of impedance, the formula of impedance to the source：
Wherein, ZAImpedance for first matching network to the source, Z0For the impedance of the source, C1It is described first
The capacitance of capacitor, C2For the capacitance of second capacitor.
7. filter circuit as claimed in claim 6, which is characterized in that it is characterized in that, the first matching network module
Admittance to the source is equal with the admittance of the second matching network module to the load end；Wherein, described first
The admittance of distribution network module to the source meets the first admittance formula, and the first admittance formula is：
Wherein, YAAdmittance for first matching network to the source, Z0For the impedance of the source, C1It is described first
The capacitance of capacitor, C2For the capacitance of second capacitor, j is pure imaginary number, and ω is angular frequency.
8. filter circuit as claimed in claim 4, which is characterized in that the first matching network module to the source
Conjugate complex when admittance of the trapper block transforms at the second matching network module to the load end is passed through in admittance
Number form formula meets conjugation formula, and the conjugation formula is：
Wherein,The conjugate complex number form of admittance for the second matching network module to the load end, YAIt is described first
Admittance of the matching network module to the source, L0For the inductance value of the inductance, C0For the capacitance of the 5th capacitor, j is
Pure imaginary number, ω are angular frequency.
9. filter circuit as claimed in claim 4, which is characterized in that the suppressed frequency band centre frequency of the filter circuit is full
The first centre frequency formula of foot, the first centre frequency formula are：
Wherein, f1For the suppressed frequency band centre frequency, L0For the inductance value of the inductance, C0For the capacitance of the 5th capacitor.
10. filter circuit as claimed in claim 7, which is characterized in that the passband mid-band frequency of the filter circuit
Meet second central frequency formula, the second central frequency formula is：
Wherein, f1For passband mid-band frequency, ω is angular frequency.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201810569367.3A CN108920762A (en) | 2018-06-05 | 2018-06-05 | A kind of filter circuit |
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|---|---|---|---|
| CN201810569367.3A CN108920762A (en) | 2018-06-05 | 2018-06-05 | A kind of filter circuit |
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Cited By (1)
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| CN110133691A (en) * | 2019-04-29 | 2019-08-16 | 上海艾为电子技术股份有限公司 | A kind of high-performance trap circuit |
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Application publication date: 20181130 |