CN112803917A - Low group delay fluctuation and high inhibition filter and implementation method thereof - Google Patents
Low group delay fluctuation and high inhibition filter and implementation method thereof Download PDFInfo
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Abstract
The invention discloses a low group delay fluctuation and high inhibition filter and an implementation method thereof, wherein the filter comprises a 15-order Butterworth band rejection filter circuit and a 7-order elliptic function low-pass filter circuit. The 15-order Butterworth band elimination filter circuit comprises 7 LC parallel units I which are sequentially connected in series, wherein the output end of the previous LC parallel unit I is connected with the input end of the next LC parallel unit I, and the input end of each LC parallel unit I is connected with the ground through an LC series unit; the 7-order elliptic function low-pass filter circuit comprises 3 LC parallel units II which are sequentially connected in series, the output end of the previous LC parallel unit II is connected with the input end of the next LC parallel unit II, and the input end of each LC parallel unit II is connected with the ground through a capacitor unit. The passband within DC-800 MHz is realized, the suppression at the position of 1.25GHZ of an interference signal is more than 140dBc, the requirement that the group delay fluctuation in the passband is within 3ns is met, and the filtering functions of low group delay fluctuation and high suppression degree are realized.
Description
Technical Field
The invention relates to the technical field of filters, in particular to a low-group delay fluctuation and high-inhibition filter and an implementation method thereof.
Background
In a communication system, group delay fluctuation of a receiving system can cause aliasing of signals, distortion of received signals is brought, and extraction of useful signals and suppression of interference signals are key technologies for guaranteeing communication quality.
With the increase of the functions of the communication system, the sources and the intensities of the interference signals are also increased, and the suppression degree of the interference signals is improved by increasing the circuit order in the resonance filter circuit formed by the inductance and capacitance LC. In the aspect of reducing group delay fluctuation, an attenuation network formed by resistance inductance and capacitance (RLC) is generally loaded at the front end of a filter, or an all-passband filter is loaded at the rear end of the filter, and in addition, a capacitor is connected in series with each LC parallel circuit, so that the parallel circuit is converted into a BVD (Butterworth-Van Dyke) equivalent circuit model, and the fluctuation and group delay compensation are realized. No matter the order of the filter circuit is increased or the additional circuit is loaded, the size is increased, the manufacturing difficulty, the process and the cost are increased, and the like, which is contrary to the miniaturization trend of the device, the process quality control and the commercial cost control target.
More importantly, a pair of contradictory indexes is provided between low group delay fluctuation and high suppression degree. The high out-of-band rejection will bring about the increase of passband fluctuation, and the general solution is to load a delay equalizer, which will also increase the device volume, process flow, cost, etc., especially when the useful signal is a weak signal and the interference signal is a strong signal, it is important to improve the rejection of the interference signal. Under the trends of complexity of a receiving system, diversification of application scenes and miniaturization of microwave devices, the traditional method cannot meet the requirement of simultaneously considering both group delay fluctuation and suppression degree.
Disclosure of Invention
In order to solve the defects of the prior art, the invention provides a low-group delay fluctuation and high-inhibition filter and an implementation method thereof, which realize a passband within DC-800 MHz, inhibit at 1.25GHz of an interference signal is more than 140dBc, meet the requirement that the group delay fluctuation in the passband is within 3ns, simultaneously realize the filtering functions of low-group delay fluctuation and high inhibition, ensure the voltage standing-wave ratio of an input port and an output port to be less than 1.5, and also consider the miniaturization characteristic.
In order to realize the purpose of the invention, the following scheme is adopted:
a low group delay fluctuation and high suppression filter comprises a 15 th-order Butterworth band rejection filter circuit and a 7 th-order elliptic function low-pass filter circuit which are connected in series.
The 15-order Butterworth band rejection filter circuit comprises 7 LC parallel units I which are sequentially connected in series, wherein the output end of the previous LC parallel unit I is connected with the input end of the next LC parallel unit I, the input end of each LC parallel unit I is connected with the ground through an LC series unit, and the output end of the last LC parallel unit I is also connected with the ground through an LC series unit;
the 7-order elliptic function low-pass filter circuit comprises 3 LC parallel units II which are sequentially connected in series, the output end of the previous LC parallel unit II is connected with the input end of the next LC parallel unit II, the input end of each LC parallel unit II is connected with the ground through a capacitor unit, and the output end of the last LC parallel unit II is also connected with the ground through a capacitor unit;
the input end of the first LC parallel unit I is the input end of a low group delay fluctuation and high inhibition filter;
the output end of the last LC parallel unit I is connected with the input end of the first LC parallel unit II;
and the output end of the last LC parallel unit II is the output end of the low group delay fluctuation and high suppression filter.
Further, the LC parallel unit I and the LC series unit are basic units of a 15 th-order Butterworth band elimination filter circuit and are used for providing attenuation peaks in band elimination, and the inherent attenuation of the 15 th-order Butterworth band elimination filter circuit is equal to the sum of the attenuation peaks in all band elimination.
Furthermore, the LC parallel unit I comprises a parallel circuit formed by an inductor and a capacitor, the LC series unit comprises a series circuit formed by an inductor and a capacitor, the inductor end of the LC series unit is connected with the LC parallel unit I, and the capacitor end is connected with the ground.
Further, the LC parallel unit II and the capacitor unit are used as basic units of a 7 th-order elliptic function low-pass filter circuit and are used for providing attenuation peaks in low-pass, and the inherent attenuation of the 7 th-order elliptic function low-pass filter circuit is equal to the sum of the attenuation peaks in all low-pass.
Further, the LC parallel unit II includes a parallel circuit formed by an inductor and a capacitor, and the capacitor unit includes a capacitor.
A method for implementing a low group delay ripple and high rejection filter as described above, comprising the steps of:
constructing a 15-order Butterworth band elimination filter circuit;
constructing a 7-order elliptic function low-pass filter circuit, and calculating to obtain the inductance value and the capacitance value of the 7-order elliptic function low-pass filter circuit according to the design indexes of low group delay fluctuation and a high-inhibition filter;
a 15-order Butterworth band elimination filter circuit and a 7-order elliptic function low-pass filter circuit are connected in series;
wherein, construct 15 grades of butterworth bandstop filter circuit, include:
constructing a 15-order Butterworth low-pass filter circuit;
calculating and obtaining the inductance value and the capacitance value of a 15-order Butterworth low-pass filter circuit according to the design indexes of the low-group delay fluctuation and the high-rejection filter;
and converting the 15 th order Butterworth low-pass filter circuit into a 15 th order Butterworth band elimination filter circuit through frequency domain transformation.
Further, the following formula is adopted to convert the 15 th order butterworth low-pass filter circuit into the 15 th order butterworth band-stop filter circuit through frequency domain transformation:
wherein
Is the center frequency of the band-stop,sfor low-pass prototype Laplace variables
， 
Is the real part of the low-pass complex frequency,
for the imaginary part of the low-pass complex frequency,
the imaginary-part symbol mark is represented,Pfor Laplace variable of band-stop prototype
，
Is the real part of the bandstop complex frequency,
the imaginary part of the complex frequency of the band stop.
Further, the inductance and capacitance values of the 7 th order elliptic function low-pass filter circuit are calculated by the following steps:
wherein the reference filter has a cut-off frequency of
The impedance of the reference filter is 1 ohm by default,
and
is the latest value converted by the inductance and the capacitance in the elliptic function low-pass filter circuit,
and
as initial values before conversion of the inductance and capacitance in the circuit,M、K、L(new 0 )、C(new 0 )the transition value in circuit conversion has no practical significance.
The invention has the beneficial effects that:
1. the filtering function of low ripple jitter and high out-of-band rejection degree is realized by adopting a mixed filtering algorithm of Butterworth and an elliptic function, the Butterworth filtering algorithm ensures low ripple jitter, and the elliptic function filtering algorithm can realize rapid attenuation of out-of-band rejection frequency point amplitude and realize better interference signal rejection degree;
2. on the premise of only considering the realization of a filtering index, the passband within DC-800 MHz can be realized without increasing the order and adding an additional circuit, the passband has lower group delay fluctuation which is less than 3ns, the high suppression degree of 1.25GHz interference signals is realized, and the suppression is more than 140 dBc;
3. different filter pass band and out-of-band rejection indexes are realized by increasing and decreasing the orders of the Butterworth filter circuit and the elliptic function filter circuit respectively and changing the values of the inductance and the capacitance in the two filter circuits, and relatively low in-band group delay fluctuation and high out-of-band rejection can be realized by adopting a hybrid filter algorithm formed by the two modes.
Drawings
FIG. 1 is a circuit diagram of a low group delay ripple and high rejection filter according to an embodiment of the present invention;
FIG. 2 is a circuit diagram of a 15 th order Butterworth bandstop filter circuit according to an embodiment of the present invention;
FIG. 3 is a circuit diagram of a 7 th order elliptic function low-pass filter according to an embodiment of the present invention;
FIG. 4 is a signal output of a Butterworth, elliptic function hybrid filter algorithm according to an embodiment of the present invention;
FIG. 5 is a graph of the group delay of the Butterworth, elliptic function hybrid filter algorithm of an embodiment of the present invention;
FIG. 6 is the signal output of the series low pass elliptic function filtering algorithm;
fig. 7 is a group delay of the series low-pass elliptic function filtering algorithm.
Detailed Description
The filter algorithm is generally a Butterworth (Butterworth), Bessel (Bessel), Chebyshev (Chebyshev) or Elliptic (eliptic) function. Wherein, the ripple of the frequency response curve in the Butterworth frequency band is minimum and is not influenced by the order; bessel has the largest flat group delay, but requires more orders under the same out-of-band rejection conditions; the frequency response of Chebyshev on the pass band or stop band shows equal ripple wave fluctuation, and the Chebyshev has higher external rejection degree than Butterworth but larger ripple wave jitter under the same order; the elliptic function has the minimum pass band and stop band fluctuation under the condition of the same order, so the invention adopts a mixed filtering algorithm mode of Butterworth and the elliptic function to realize the filtering function of low ripple jitter and high out-of-band rejection degree.
Example 1
As shown in fig. 1, the low group delay ripple and high rejection filter provided for this embodiment includes a 15 th order butterworth bandstop filter circuit and a 7 th order elliptic function lowpass filter circuit connected in series.
Specifically, as shown in fig. 2, the 15-step butterworth band rejection filter circuit includes 7 LC parallel units I connected in series in sequence, an output end of a previous LC parallel unit I is connected to an input end of a next LC parallel unit I, an input end of each LC parallel unit I is connected to ground through an LC series unit, and an output end of a last LC parallel unit I is also connected to ground through an LC series unit.
Specifically, as shown in fig. 3, the 7 th-order elliptic function low-pass filter circuit includes 3 LC parallel units II connected in series in sequence, an output terminal of a previous LC parallel unit II is connected to an input terminal of a next LC parallel unit II, an input terminal of each LC parallel unit II is connected to ground through a capacitor unit, and an output terminal of a last LC parallel unit II is also connected to ground through a capacitor unit.
Specifically, the input end of the first LC parallel unit I is the input end of the low group delay fluctuation and high rejection filter, the output end of the last LC parallel unit I is connected to the input end of the first LC parallel unit II, and the output end of the last LC parallel unit II is the output end of the low group delay fluctuation and high rejection filter.
More specifically, the LC parallel unit I and the LC series unit are each basic units of a 15 th order butterworth bandstop filter circuit for providing an attenuation peak in the bandstop, the intrinsic attenuation of the 15 th order butterworth bandstop filter circuit being equal to the sum of the attenuation peaks in all bandstops.
More specifically, the LC parallel unit I includes a parallel circuit formed by an inductor and a capacitor, and the LC series unit includes a series circuit formed by an inductor and a capacitor, the inductor end of the LC series unit is connected to the LC parallel unit I, and the capacitor end is connected to ground.
More specifically, the LC parallel unit II and the capacitor unit each serve as a basic unit of a 7 th order elliptic function low-pass filter circuit for providing an attenuation peak in a low-pass, and the inherent attenuation of the 7 th order elliptic function low-pass filter circuit is equal to the sum of the attenuation peaks in all low-passes.
More specifically, the LC parallel unit II includes a parallel circuit of an inductor and a capacitor, and the capacitor unit includes a capacitor.
The circuit is finally designed to be a parallel circuit which is formed by connecting an inductor L1 and a capacitor C1 in series, then grounding the series circuit and then connecting an inductor L2 and a capacitor C2 in parallel; then, an inductor L3 and a capacitor C3 are connected in series and then are grounded, and then a parallel circuit consisting of an inductor L4 and a capacitor C4 is connected in parallel; then, an inductor L5 and a capacitor C5 are connected in series and then are grounded, and then a parallel circuit consisting of an inductor L6 and a capacitor C6 is connected in parallel; then, an inductor L7 and a capacitor C7 are connected in series and then are grounded, and then a parallel circuit consisting of an inductor L8 and a capacitor C8 is connected in parallel; then, an inductor L9 and a capacitor C9 are connected in series and then are grounded, and then a parallel circuit consisting of an inductor L10 and a capacitor C10 is connected in parallel; then, an inductor L11 and a capacitor C11 are connected in series and then are grounded, and then a parallel circuit consisting of an inductor L12 and a capacitor C12 is connected in parallel; then, an inductor L13 and a capacitor C13 are connected in series and then are grounded, and then a parallel circuit consisting of an inductor L14 and a capacitor C14 is connected in parallel; and finally, connecting an inductor L15 and a capacitor C15 in parallel and then grounding the circuit to form a 15-order Butterworth band-stop filter circuit.
The capacitor C16 is grounded and then connected with a parallel circuit consisting of an inductor L16 and a capacitor C17 in parallel; the capacitor C18 is grounded and then connected with a parallel circuit consisting of an inductor L17 and a capacitor C19 in parallel; the capacitor C20 is grounded and then connected with a parallel circuit consisting of an inductor L18 and a capacitor C21 in parallel; and then the parallel connection C22 is grounded to form an elliptic function low-pass filter circuit with 7 th order.
And finally, a 15-order Butterworth band elimination filter circuit and a 7-order elliptic function low-pass filter circuit are connected in series to realize the filter function of low group delay fluctuation and high inhibition degree.
Example 2
In the prior art, a passband within DC-800 MHz is realized, and the suppression of an interference signal at 1.25GHz reaches 140dBc, and the suppression is generally realized by adopting a method of serially connecting low-pass filters. As shown in FIGS. 6 and 7, three elliptic function low-pass filters with the minimum group delay fluctuation are adopted to be connected in series, the passband of each low-pass filter is DC-800 MHz, and the suppression degree of 1.25GHz interference signals is 47 dBc.
The input end of the 15-order Butterworth band elimination filter circuit is the input end of a low group delay fluctuation and high inhibition filter, the output end of the 15-order Butterworth band elimination filter circuit is connected with the input end of the 7-order elliptic function low-pass filter circuit, and the output end of the 7-order elliptic function low-pass filter circuit is the output end of the low group delay fluctuation and high inhibition filter.
The present embodiment provides a method for implementing a low group delay ripple and high rejection filter in embodiment 1, including the steps of:
constructing a 15-order Butterworth band elimination filter circuit;
constructing a 7-order elliptic function low-pass filter circuit, and calculating to obtain the inductance value and the capacitance value of the 7-order elliptic function low-pass filter circuit according to the design indexes of low group delay fluctuation and a high-inhibition filter;
a 15-order Butterworth band elimination filter circuit and a 7-order elliptic function low-pass filter circuit are connected in series;
wherein, construct 15 grades of butterworth bandstop filter circuit, include:
constructing a 15-order Butterworth low-pass filter circuit;
calculating and obtaining the inductance value and the capacitance value of a 15-order Butterworth low-pass filter circuit according to the design indexes of the low-group delay fluctuation and the high-rejection filter;
and converting the 15 th order Butterworth low-pass filter circuit into a 15 th order Butterworth band elimination filter circuit through frequency domain transformation.
More specifically, the following formula is adopted to convert the 15 th order butterworth low-pass filter circuit into the 15 th order butterworth band-stop filter circuit through frequency domain transformation:
wherein
Is the center frequency of the band-stop,sfor low-pass prototype Laplace variables
， 
Is the real part of the low-pass complex frequency,
for the imaginary part of the low-pass complex frequency,
the imaginary-part symbol mark is represented,Pfor Laplace variable of band-stop prototype
，
Is the real part of the bandstop complex frequency,
the imaginary part of the complex frequency of the band stop.
More specifically, the inductance and capacitance values of the 7 th-order elliptic function low-pass filter circuit are calculated by the following steps:
wherein the reference filter has a cut-off frequency of
The impedance of the reference filter is 1 ohm by default,
and
is the latest value converted by the inductance and the capacitance in the elliptic function low-pass filter circuit,
and
as initial values before conversion of the inductance and capacitance in the circuit,M、K、L(new 0 )、C(new 0 )the transition value in circuit conversion has no practical significance.
In summary, the invention adopts a mixed filtering algorithm of butterworth and elliptic functions to realize the filtering functions of low ripple jitter and high out-of-band rejection degree, the butterworth filtering algorithm ensures the low ripple jitter and realizes the rejection of 1.25GHz interference signals, the rejection degree is 50dBc, and the group delay at 800MHz of the circuit is 0.9 ns; the elliptic function filtering algorithm can realize the rapid attenuation of the out-of-band rejection frequency point amplitude, realize the passband within DC-800 MHz, and the rejection of 1.25GHz interference signals, the rejection degree is 65dBc, the group delay at 800MHz of the circuit is 1.75ns, as shown in fig. 4 and 5, the whole circuit of the embodiment can realize the passband within DC-800 MHz, the rejection degree of 1.25GHz interference signals is more than 140dBc, and the group delay at 800MHz is about 2.69 ns.
The comparison shows that the method used by the invention not only can achieve the indexes of the method in the prior art in the aspects of passband and interference signal suppression, but also has the group delay of about 4.24ns at 800MHz, and the group delay is 57.6% higher than that of the method in the prior art, which shows that the method of the invention has better low group delay effect.
The above embodiments are only for illustrating the technical ideas and features of the present invention, and are not meant to be exclusive or limiting of the present invention. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention.
Claims (8)
1. A low group delay fluctuation and high suppression filter is characterized by comprising a 15 th-order Butterworth band rejection filter circuit and a 7 th-order elliptic function low-pass filter circuit which are connected in series;
the 15-order Butterworth band rejection filter circuit comprises 7 LC parallel units I which are sequentially connected in series, wherein the output end of the previous LC parallel unit I is connected with the input end of the next LC parallel unit I, the input end of each LC parallel unit I is connected with the ground through an LC series unit, and the output end of the last LC parallel unit I is also connected with the ground through an LC series unit;
the 7-order elliptic function low-pass filter circuit comprises 3 LC parallel units II which are sequentially connected in series, the output end of the previous LC parallel unit II is connected with the input end of the next LC parallel unit II, the input end of each LC parallel unit II is connected with the ground through a capacitor unit, and the output end of the last LC parallel unit II is also connected with the ground through a capacitor unit;
the input end of the first LC parallel unit I is the input end of a low group delay fluctuation and high inhibition filter;
the output end of the last LC parallel unit I is connected with the input end of the first LC parallel unit II;
and the output end of the last LC parallel unit II is the output end of the low group delay fluctuation and high suppression filter.
2. The low group delay ripple and high rejection filter of claim 1, wherein the LC parallel unit I and the LC series unit are each basic units of a 15 th order butterworth bandstop filter circuit for providing attenuation peaks in bandstop, the intrinsic attenuation of the 15 th order butterworth bandstop filter circuit being equal to the sum of the attenuation peaks in all bandstops.
3. The low group delay ripple and high rejection filter of claim 2, wherein the LC parallel unit I comprises a parallel circuit of an inductor and a capacitor, the LC series unit comprises a series circuit of an inductor and a capacitor, the inductor terminal of the LC series unit is connected to the LC parallel unit I, and the capacitor terminal is connected to ground.
4. The low group delay ripple and high rejection filter of claim 1, wherein the LC parallel unit II and the capacitor unit are basic units of a 7 th order elliptic function low pass filter circuit for providing attenuation peaks in low pass, and the inherent attenuation of the 7 th order elliptic function low pass filter circuit is equal to the sum of the attenuation peaks in all low pass.
5. The low group delay ripple and high rejection filter of claim 4, wherein the LC parallel unit II comprises a parallel circuit of an inductor and a capacitor, and the capacitor unit comprises a capacitor.
6. A method for implementing a low group delay ripple and high rejection filter according to any of claims 1 to 5, comprising the steps of:
constructing a 15-order Butterworth band elimination filter circuit;
constructing a 7-order elliptic function low-pass filter circuit, and calculating to obtain the inductance value and the capacitance value of the 7-order elliptic function low-pass filter circuit according to the design indexes of low group delay fluctuation and a high-inhibition filter;
a 15-order Butterworth band elimination filter circuit and a 7-order elliptic function low-pass filter circuit are connected in series;
wherein, construct 15 grades of butterworth bandstop filter circuit, include:
constructing a 15-order Butterworth low-pass filter circuit;
calculating and obtaining the inductance value and the capacitance value of a 15-order Butterworth low-pass filter circuit according to the design indexes of the low-group delay fluctuation and the high-rejection filter;
and converting the 15 th order Butterworth low-pass filter circuit into a 15 th order Butterworth band elimination filter circuit through frequency domain transformation.
7. The method of claim 6, wherein the 15 th order Butterworth lowpass filtering circuit is converted into the 15 th order Butterworth bandstop filtering circuit by frequency domain transformation using the following formula:
wherein
Is the center frequency of the band-stop,sfor low-pass prototype Laplace variables
， 
Is the real part of the low-pass complex frequency,
for the imaginary part of the low-pass complex frequency,
the imaginary-part symbol mark is represented,Pfor Laplace variable of band-stop prototype
，
Is the real part of the bandstop complex frequency,
the imaginary part of the complex frequency of the band stop.
8. The method of claim 6, wherein the inductance and capacitance of the 7 th-order elliptic function low-pass filter circuit are calculated by:
wherein the reference filter has a cut-off frequency of
The impedance of the reference filter is 1 ohm by default,
and
is the latest value converted by the inductance and the capacitance in the elliptic function low-pass filter circuit,
and
as initial values before conversion of the inductance and capacitance in the circuit,M、K、L(new 0 )、C(new 0 )the transition value in circuit conversion has no practical significance.
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