KR20120125191A - Band-stop filter - Google Patents

Abstract

PURPOSE: A band-stop filter is provided to determine a cut-off frequency with two or more self-inductances which is serial to a second channel and one or more capacities which are mounted between the self-inductances and a ground point. CONSTITUTION: A band stop filter includes a filter input(1) and a filter output(2). The band stop filter includes a signal transmission channel(3) corresponding to a direct channel and a signal transmission channel(4) corresponding to a second channel. The two channels are located between the filter input and the filter output. The channels are generated with microstrip lines which are printed on a dielectric substrate. The channels are together combined in the filter input and the filter output. A low-pass filter(5) comprises two inductances or self-inductances(5a,5b) and a capacity(5c) mounted between a junction of two inductances and a ground point.

Description

Band Stop Filter {BAND-STOP FILTER}

FIELD OF THE INVENTION The present invention relates to band-rejection or band reject filter improvement, and more particularly to band reject filter improvement having two cutoff frequencies simultaneously. The invention particularly relates to multi-standard multi-mode user terminals and to transmission and / or compliance with the Digital Video Broadcasting-Handheld (DVB-H) or Digital Video Broadcasting Terrestrial (DVB-T) standard. Or applies to receiving systems.

User terminals incorporating several wireless communication systems inherently interfere because of congestion of the frequency spectrum by systems operating in frequency bands that are getting closer to each other, or because these terminals become smaller and smaller. Are affected, which means that the wireless antennas used for transmission, in particular for wireless communication, are getting closer and closer physically, resulting in harmful interference coupling to the system. To overcome these disadvantages, ultra selective filters are used, which allow the systems to withstand interference.

As such, to filter out interfering signals, a suitable band cut filter such as, for example, the filter discussed in the document entitled " Exact Synthesis of Microwave Filters with Non-uniform Dissipation " of IEEE-IMS-2007, C. Guyette et al. Or it has already been proposed to use a band stop filter. In addition, in a French patent application published under number 2947683 in the name of Thomson Licensing, a band cut filter improvement first described in a paper by Guyette et al. Was also proposed. This type of filter is shown in FIG. 1. The filter comprises a first signal transmission channel 3 called a direct channel, between the filter input 1 and the filter output 2, to which a second signal transmission channel 4 called a second channel is coupled. do. These two channels 3 and 4 are created through transmission lines called micro-strip lines printed on the substrate. This second path 4 forms a resonant line whose length lr is a function of [lambda] / 2 and gives a resonant frequency corresponding to the frequency for the signals to be blocked. The direct path 3 and the second path 4 are coupled together along the line length ls to the input 1 and output 2 of the filter. The topology of the filter is that the signal from the direct channel 3 and the signal from the second channel 4 at the resonant frequency are added to opposite phases at the filter output, resulting in a relatively narrow band around the resonant frequency. Is defined to produce theoretically infinite attenuation. Thus, this structure can achieve a significant blocking level, but at the cost of an increase in insertion losses, the level of these losses depends on the quality factor of the resonant element.

The band cut filter described above was simulated taking into account the micro strip type line technique with the following parameters.

The substrate selected was an Fr 4 substrate with a thickness of 0.25 mm and Er = 4.5.

The width of the microstrip line is W = 0.44 with a characteristic impedance of 50Ω.

The lines joined by the length ls are chosen such that s = 100 μm and ls = 18.2 mm, where s represents the distance between the two lines.

The length of the main line 3 is 2 x ls + lp, where lp = 72 mm and the length 4 of the resonant line is 2 ^* x ls + lr.

In Fig. 2, the response at the transmission of the filter for three values of lr, lr = 44 mm, 60 mm and 80 mm, is shown. This simulation shows, in particular, that a significant attenuation is obtained over a relatively wide frequency band using this filter structure. Thus, it can be inferred that the level of attenuation is not very sensitive to variations in the phase difference between the main channel and the second channel.

The present invention is directed to a filter structure which can have two band cut response types, i.e. two cutoff frequencies simultaneously, using the properties of both Guetette type band cut filters, both compact and lossless. It is to calculate.

In short, an object of the present invention is a band cut filter comprising a filter input and a filter output,

A first signal transmission channel called a direct channel and a second signal transmission channel called a second channel, which channels are arranged between the filter input and the filter output and are coupled between the filter input and the filter output therebetween. ,

Each of the direct channel and the second channel comprises at least one transmission line,

The second channel comprises a resonant element whose resonance frequency is equal to the frequency to be cut off called the first cut-off frequency,

The direct channel and the second channel are designed to introduce a phase difference of 180 ° between the signal circulating through the direct channel and the signal circulating through the second channel at the cutoff frequency,

The second channel may further include a filtering element having a cutoff frequency different from the first cutoff frequency as a method for generating a second cutoff frequency.

Band cut filter.

Thus, the possibility of simultaneously blocking two interfering signals located close to the useful frequency band is obtained with a single filter.

According to a first embodiment, the filtering element is a low pass filter whose cutoff frequency is greater than the first cutoff frequency of the filter. The low pass filter preferably consists of at least two self inductances in series with the second channel and at least one capacitor mounted between its inductances and the ground point, the value of its inductances and the value of the capacitor being the cutoff frequency of the filter. Determine.

According to a second embodiment, the filtering element is a high pass filter whose cutoff frequency is smaller than the first cutoff frequency of the filter. The high pass filter is preferably constituted by at least two capacitors in series with the second channel and at least one self inductance mounted between the capacitors and the ground point, the value of the self inductances and the value of the capacitors being the cutoff frequency of the filter. Determine.

According to another feature of the invention, the first and / or second cutoff frequencies can be modified by modifying the value of the self inductances and / or capacities of the filtering elements. Thus, by operating on one of the components of the filtering element, it is possible to dynamically specify the cutoff frequency without interfering with another frequency. It is also possible to dynamically adjust two cutoff frequencies simultaneously by operating on the values of different components of the filtering elements.

Other features and advantages of the present invention will become apparent upon reading the following description with reference to the accompanying drawings,
Figure 1 already described shows the structure of a band cut filter according to the prior art.
FIG. 2 shows a diagram illustrating the response of the filter of FIG. 1 to different resonant line lengths. FIG.
3 shows a first embodiment of a band cut filter with two cutoff frequencies according to the present invention;
4A and 4B show diagrams presenting a response to the transmission of the filter of FIG. 3 for two different values of capacity.
FIG. 5 shows a diagram showing the response of the filter of FIG. 3 to values of different self inductances. FIG.
Figure 6 shows a second embodiment of a band cut filter with two cutoff frequencies according to the present invention.
7A and 7B each show a diagram presenting a response to the transmission of the filter of FIG. 6 for two different values of its inductances.
In the drawings, the same elements have the same reference numerals for simplicity of explanation.

It will first be described with reference to Figs. 3 to 5 of the first embodiment of the band cut filter according to the present invention. As in FIG. 3, the band cut filter includes a filter input 1 and a filter output 2. It also includes a signal transmission channel 3 called a direct channel and a signal transmission channel 4 called a second channel. These two channels are located between the filter input 1 and the filter output 2. In the embodiment shown, the channels 3 and 4 are created by micro strip lines printed on the dielectric substrate. Moreover, as in the case of the filter shown in FIG. 1, the direct channel 3 and the second channel 4 are combined together at the input and output of the filter. To this end, part of the line 3 'of the direct channel and part of the line 4 of the second channel are adapted to generate electromagnetic coupling between the direct channel 3 and the second channel 4 at the input of the filter. Are arranged in parallel with each other and in close proximity to each other. Similarly, part of the line 3 '' of the direct channel 3 and part of the line 4 '' of the second channel are between the direct channel 3 and the second channel 4 at the output of the filter. Arranged in parallel and close to each other in a manner to create a bond. In the example of FIG. 3, the dimensions of the line portions 4 ′, 3 ′, 4 ″, 3 ″ are the same, and the line at the input and output so that the combination at the input and output of the filter is the same. The distance between the parts is the same.

The length of the line elements constituting the direct channel 3 and the second channel 4 blocks the phase difference 180 ° between the signal circulating through the direct channel 3 and the signal circulating through the second channel 4. Is determined to introduce into the frequency.

According to the invention, on the second channel 4, a filtering element 5 which is constituted by a low pass filter in this embodiment is integrated. More specifically, and as shown in FIG. 3, the low pass filter 5 has two inductances or self inductances 5a, 5b of value La mounted in series in the second channel 4, and two. It consists of the capacitance 5c of the value Ca mounted between the junction point of the inductances 5a and 5b and the ground point. This relates to the third-order low pass filter, which is calculated with separate components. It is apparent to those skilled in the art that the low pass filter may be calculated using known techniques, such as transmission lines, and / or that the filter may be of higher order.

The filter of FIG. 3 was simulated using the elements used for the simulation of the filter of FIG. 1 as a substrate and as dimensions for transmission lines. Moreover, the following parameters were considered:

This simulation consisted of the value lr = 44 mm. The two inductances 5a and 5b have a value La = 5nH, and the capacitor 5c has a value Ca = 4pF for FIG. 4A and 6pF for FIG. 4B. Moreover, further simulations were performed with its own inductance value La = 4nH and capacity value Ca = 6pF, and the results of the simulations are shown in FIG. 5.

In FIG. 4A, the response of the filter to the inductance value La = 5nH and the capacity Ca = 4pF is shown. The curve shown shows the presence of two cutoff frequencies, one near 730 MHz and one near 1270 MHz.

Comparing the curves of FIG. 5 with the curves of FIG. 2, it is noted that the low pass filter integrated in the second channel 4 introduces a positive phase difference which causes a shift in the resonant frequency of the initial filter shown in FIG. 1. Able to know. Thus, the initial frequency, which was near 1010 MHz, passed at 730 MHz, which corresponds to the first cutoff frequency.

Furthermore, if the value of the capacity Ca is increased by 2pF, i.e., Ca = 6pF, Figure 4b, which shows the response of the filter, shows that the lowpass resonant frequency does not change even if the highpass resonant frequency passes at about 1137MHz. In addition, when the inductance value La is modified to 4nH for the capacity Ca = 6pF, as shown in FIG. 5, the two resonant frequencies, that is, the first cutoff frequency and the second cutoff frequency, are both offset to high frequencies. It can be seen that the first cutoff frequency is located at about 770 MHz and the second cutoff frequency is located at about 1190 MHz.

Thus, the filter structure shown in FIG. 3 has the following advantages.

The possibility of assigning a single resonant frequency only by changing the value Ca of the capacity,

The possibility of assigning two resonant frequencies by modifying their inductances and the values of the values La and Ca.

In practice, to calculate the dynamic allocation according to the interference situations that multiple wireless terminals must face, the low pass filter uses a varactor diode for capacitance and a transistor based active inductance for its own inductance. It can be prepared using.

A second embodiment of the cutoff filter according to the present invention will now be described with reference to Figs. 6, 7A and 7B. As shown in FIG. 6, the basic structure of the cutoff filter is the same as that of the cutoff filter of FIG. 3. Therefore, the basic structure will not be described again below. According to a second embodiment of the invention, the filtering element 6 constituted by the high pass filter is integrated into the second channel 4. More specifically, the high pass filter 6 comprises two capacitor elements 6a, 6b of value Ca mounted in series in a second channel, and an inductor element of value La mounted between the junction and ground points of the two capacitor elements. Or from its own inductance 6c.

The embodiment of FIG. 6 was simulated by taking the values of the cutoff filter shown in FIG. 1 as the values of the basic structure. Moreover, the second channel has a length Lr = 44 mm. The high pass filter was simulated with a capacitance value Ca = 11pF and its own inductance value La = 4nH or La = 2nH.

In this case, the high pass filter 6 introduces a negative phase difference, and its insertion into the second channel 4 offsets the resonant frequencies of the band cut filter to higher frequencies. As shown in FIGS. 7A and 7B showing the response of the filter of FIG. 6, the integration of the high pass filter 6 in the second channel causes two resonant frequencies to appear at the so-called first and second cutoff frequencies. It can be seen that.

As shown in FIGS. 7A and 7B, it can be seen that the change in the value of its inductance from 4nH (FIG. 7A) to 2nH (FIG. 7B) does not cause a change in the second cutoff frequency that remains constant at about 1.7 GHz. have.

This means that at high resonant frequencies its inductance has a strong impedance and small changes in this value do not change the condition of this resonance, while at low resonant frequencies its inductance is at 1.4 GHz for FIG. 7A, and for FIG. 7B. This can be explained by the fact that it participates in the resonant circuit checked by the value of the first cutoff frequency located at about 1.55 GHz.

In the embodiment of FIG. 6, high pass filter 6a has been described using individual elements. However, it will be apparent to those skilled in the art that this filter can be produced even with transmission line type elements. The high pass filter described is a third order filter. However, this filter can be of higher dimension.

Although the present invention has been described with respect to particular embodiments, it is by no means intended to be limiting and it is obvious that it includes both technical equivalents of the described means as well as combinations thereof, as long as they fall within the scope of the present invention.

Claims (8)

As a band cut filter,
Filter input (1) and filter output (2),
A first signal transmission channel 3 called a direct channel and a second signal transmission channel 4 called a second channel, which channels are located between the filter input and the filter output and are located between the filter input and the filter output. Coupled together to a filter output, each of the direct channel and the second channel including at least one transmission line,
The second channel comprises a resonant element whose resonant frequency is the same as the frequency to be cut off called the first cut-off frequency,
The direct channel and the second channel are designed to introduce a phase difference of 180 ° between the signal circulating through the direct channel and the signal circulating through the second channel at the cutoff frequency.
Including,
The second channel 4 is a method for generating a second cutoff frequency separate from the first cutoff frequency, and the filtering element 5 and 6 having a cut-off frequency different from the first cutoff frequency. Characterized in that it further comprises
Band cut filter. The method of claim 1,
And said filtering element is a low pass filter wherein said cutoff frequency is greater than said first cutoff frequency of said filter. The method of claim 2,
The low pass filter is constituted by at least two self inductances 5a, 5b in series with the second channel, and at least one capacitance 5c mounted between the self inductances and the ground point, the self inductance And the value of the capacity determines the cutoff frequency of the filter. The method of claim 1,
And said filtering element is a high pass filter wherein said cutoff frequency is less than said first cutoff frequency of said filter. 5. The method of claim 4,
The high pass filter is constituted by at least two capacitances 6a, 6b in series with the second channel and at least one self inductance 6c mounted between the capacitances and the ground point, the self inductances And the value of the capacity determines the cutoff frequency of the filter. In claim 3 or 5,
The first cutoff frequency and / or the second cutoff frequency may be modified by modifying the value of the self inductances and / or capacities of the filtering elements. 7. The method according to any one of claims 1 to 6,
And the resonant element of the second channel is constituted by a resonant line of length λ / 2, wherein λ is a wavelength of the resonant frequency. Multi-standard multi-mode terminal,
Multi-standard multi-mode terminal, characterized in that it comprises a band cut filter according to any one of claims 1 to 7.

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