ES2396773A1 - Device comprising differential transmission lines with common-mode suppression - Google Patents

Abstract

The invention relates to a device comprising differential transmission lines with common-mode suppression. The device comprises: a planar differential transmission medium including two conductive transmission lines (L1, L2), a metal earth plane (M) and a dielectric substrate and a filter formed by one or more open-ring resonators (R) etched in the earth plane (M) and configured, dimensioned and arranged symmetrically in order to suppress the propagation of signals in common mode in one or more pre-determined frequencies and to allow the transmission of signals in differential mode at said one ore more pre-determined frequencies.

Description

Device of differential transmission lines with common mode suppression

Technical sector

The present invention concerns, in general, a device of differential transmission lines with common mode suppression, which includes a filter formed by one or more resonators recorded in the ground plane to suppress the propagation of common mode signals, and more particularly to a device where said resonator is a complementary open ring resonator (CSRR). This resonator does not significantly disturb the differential mode

Prior art

It is well known that complementary open ring resonators (CSRRs) recorded in the ground plane of a micro-tape transmission line, below the conductive strip, are capable of inhibiting the propagation of electromagnetic signals in said transmission line. This is a consequence of the fact that such complementary open ring resonators introduce transmission zeros due to the electrical coupling between such resonators and the transmission line, preventing the propagation of signals at frequencies around the resonator resonance frequency. Thus, by recording a chain of complementary open ring resonators in the ground plane, below the conductive strip, it is possible to achieve a band of rejection frequencies of controllable width, by engraving resonators with different resonance frequency, by coupling the resonators by approximation thereof, designing the resonators to have a significant bandwidth, or a combination of the above.

The CSRRs were first presented in [1], where it was demonstrated that these elements are useful for the design of negative permittivity structures in micro-tape technology.

The complementary open ring resonators recorded in the mass plane of a micro-tape line, below the conductive strip, efficiently suppress signal transmission in the vicinity of their resonance frequencies. This result can be interpreted as due to the negative effective permittivity of the line, but it can also be explained in terms of circuit theory, as a result of the capacitive coupling between the line and the CSRR.

In Fig. 1 (a) the topology and circuit model of a micro tape line loaded with a CSRR is shown.

As indicated in [2], L models the inductance of the line, C the electrical coupling

between the line and the resonator, and the CSRR is modeled by the parallel resonant tank,

Le-Ce.

Application EP1855348A 1 proposes a band pass filter formed by a line

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transmission and one or more filter cells, each consisting of one or more

complementary open ring resonators, an inductive element and an element

capacitive

Application EP1675212A 1 describes a microwave and wave filter

millimeter comprising a planar means of transmission with a conductive strip, a

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metallic plane of mass and a dielectric substrate, and that also includes a resonator

open rings

On the other hand, differential transmission lines are well known.

consisting of a pair of lines coupled on a mass plane, separated from the

lines through a dielectric substrate. These differential lines have, like

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key features, high noise immunity, a level of mutual interference

low and low electromagnetic interference, which makes them very interesting

for high speed digital circuits.

In applications of such differential lines it is necessary to eliminate noise in

common mode at those frequencies in which the line must transmit the signals in the

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differential mode However, the presence of common mode noise in the lines

Differentials are inevitable in practical circuits. This unwanted noise is caused

mainly due to an imbalance in amplitude or a time lag of the signals

differentials and should be reduced as much as possible to avoid radiation in mode

common that causes electromagnetic interference (EMI).

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Therefore, the design of differential lines capable of suppressing noise in

common mode, maintaining the integrity of the differential signals is of utmost

importance.

Structures with grooves in the ground plane (DGS) consist of

practice a defect, either one or several symmetric geometric figures or

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asymmetric, on the ground plane just below the micro tape line.

In [3], periodic dumbbell patterns engraved on the

mass plane, in the form of a DGS structure, below the lines

differentials, in order to suppress even mode by opening the path of

current return through the ground plane. This provision has an effect

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   small in differential signals (odd mode) since, for such signals, a

current density

In [4], the authors achieve a wide elimination band for the common mode

through the use of symmetrically coupled U-shaped and H-shaped resonators

recorded in the mass plane, also implementing a DGS structure.

5

REFERENCES

[1] F. Falcone, T. Lopetegi, J.D. Baena, R. Marqués, F. Martín and M. Sorolla,

"Effective negative-E stop-band of micro tape lines based on complementary split

ring resonators ", IEEE Microwave and Wireless Components Letters, vol. 14, pp.

280-282, June 2004.

1O

[2] J.D. Baena, J. Bonache, F. Martín, R. Marqués, F. Falcone, T. Lopetegi, M.A.G.

Laso, J. García, 1 Gil, M. Flores-Portillo and M. Sorolla, "Equivalent circuit models

for split ring resonators and complementary split rings resonators coupled to

planar transmission lines ", IEEE Transactions on Microwave Theory and

Techniques, vol. 53, pp. 1451-1461, April 2005.

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[3] W.T. Liu, C-H. Tsai, T-W. Han, T-L. Wu, "An embedded common-mode

suppression filter for GHz differential signals using periodic defected ground

plane ", IEEE Microw. Wireless Comp. Lett., vol. 18, no. 4, pp. 248-250, April2008.

[4] S-J. Wu, C-H. Tsai, T-L. Wu, T. ltoh, "A novel wideband common-mode

suppression filter for gigahertz differential signals using coupled patterned ground

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structure ", IEEE Trans. Microw. Theory Techn., vol. 57, no.4, pp. 848-855, April

2009

[5] F. Falcone, T. Lopetegi, M.A.G. Laso, J.D. Baena, J. Bonache, R. Marqués, F.

Martín, M. Sorolla, "Babinet principie applied to the design of metasurfaces and

metamaterials ", Phys. Rev. Lett., vol. 93, paper 197401, November 2004.

25

[6] F. Aznar, M. Gil, J. Bonache and F. Martín, "On the effects of resonator's

electrical size on bandwidth in resonant-type metamaterial transmission lines ",

Microwave and Optical Technology Letters, vol. 52, no.?, Pp. 1526-1530, July

2010

[7] J. Bonache, M. Gil, l. Gil, J. García-García and F. Martín, "On the electrical

30

characteristics of complementary metamaterial resonators ", IEEE Microwave and

Wireless Components Letters, vol. 16, pp. 543.545, October 2006.

[8] C-H. Tsai, T-L. Wu, "A broadband and miniaturized commonmode filter for

gigahertz differential signals based on negative permittivity metamaterials ", IEEE

   Trans. Microw. Theory Techn., Vol. 58, no.1, pp. 195-202, Jan. 201 O.

[9] B.C. Tseng, L. K. Wu, "Design of miniaturized common-mode filter by multilayer

low-temperature co-fired ceramic ", IEEE Trans. Electromagn. Compat., vol. 46,

no.4, pp. 571-579, Nov. 2004.

5

Explanation of the invention.

The present invention constitutes an alternative to the proposals made in [3]

and [4], offering another approach to the design of differential lines with suppression of

common mode

For this, the present invention concerns a device of lines of

1 o

transmission differential with common mode suppression, which comprises

itself known:

-a differential planar transmission medium that includes at least two lines

transmission conductors, a metal mass plane, and a dielectric substrate,

Y

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- a filter formed by at least one resonator recorded in said mass plane

to suppress the propagation of signals in common mode.

Unlike the known proposals, in the device of the present

invention the resonator is an open ring resonator configured, sized and

arranged to suppress the propagation of signals in common mode in at least

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a certain frequency and allow the transmission of signals in differential mode to

said determined frequency.

For an exemplary embodiment, said open ring resonator is found

engraved in said metal mass plane, such as in the form of a DGS structure.

The resonator is, according to a preferred embodiment, a resonator of

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complementary open rings, or CSRR.

The openings of each complementary open ring resonator ring,

they are arranged in the plane of longitudinal symmetry of the two conductive lines of

differential transmission.

Depending on the exemplary embodiment, each ring resonator ring

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Complementary openings have a circular, square, rectangular or polyhedral shape.

According to an embodiment example, the distance between internal edges of the strip

conductor that forms each ring of the complementary open ring resonator

(i.e. the inside diameter when the shape is circular or the inside width when it is

square) is greater than the separation distance between the two conductive lines of

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   differential transmission, plus the width of each of the two conductive lines of

differential transmission, that is, so that the resonator protrudes to the region

occupied by the lines

The complementary open ring resonator rings are located

arranged centered, below the differential transmission conductive lines

5

so that its common geometric center is located in said plane of symmetry

longitudinal, which allows to reject the common mode without affecting the differential mode.

For more elaborate embodiments, the device filter

proposed by the present invention comprises a plurality of resonators of

open rings configured, sized, arranged and related to each other to

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suppress common mode broadcast in a required rejection frequency band.

Said plurality of open ring resonators have, for one of said

embodiments, dimensions slightly different from each other and are

highly coupled, to expand the rejection frequency band.

As regards the dimensions referred to in said dimensioning, these

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They are relative to: width of each ring, distance between rings, distance between edges

internal of the conductive strip that forms each ring and separation between resonators

individual.

According to another example of embodiment, said filter of the device of the

invention comprises, in combination with open ring resonators, one or

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more electric resonators of another type.

By means of the symmetrical engraving of the CSRRs in the mass plane, the

an efficient common mode suppression over broadband. In comparison with

other approaches, the common mode suppression strategy followed by the

device of the invention is technologically simple (only two are used

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metal levels), the resulting common mode filters are electrically small,

They provide wide and high rejection removal bands, and their design is simple.

Brief description of the drawings

The above and other advantages and features will be understood more

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fully from the following detailed description of some examples of

realization with reference to the attached drawings, which should be taken for illustrative purposes and

non-limiting, in which:

Fig. 1 (a) represents the topology and circuit model of a line of

micro tape loaded with a CSRR;

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   Fig. 1 (b) represents the topology and circuit model of the proposed device

by the present invention, formed by a differential line loaded with a CSRR;

Fig. 2 shows the circuit models related to the even mode (a) and the mode

odd (b) of the device proposed by the invention;

Fig. 3 is a graph that represents the result of simulations

made with the structure illustrated in Fig. 3, with the

5

CSRR without turning and turned 90 °, in the form of insertion losses in common mode

1Scc211 and insertion losses in differential mode 1Sdd211, for some

dimensions of c = 0.2mm, d = 0.2mm, rex1 = 5mm, W = 1mm and S = 2.5mm;

Fig. 4 is a graph that represents the result of simulations

electromagnetic and circuitry corresponding to the structure illustrated in Fig.

1 o

4, in the form of insertion losses in common mode 1Scc211, where

CSRR dimensions are c = 0.2mm, d = 0.2mm, W = 1mm, S = 2.5mm, and length

7.6mm side, for circuit parameters of L '= 4.93nH, C = 1, 06pF,

Cc = 2.68pF and Lc = 3.36nH;

Fig. 5 is another graph illustrating simulated insertion losses in mode

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common and in differential mode for a third order structure that results from

cascade three unit cells as illustrated in Fig. 4;

Fig. 6 illustrates two photographs of the differential line with wide rejection of the

common mode of the device proposed by the invention, for an exemplary embodiment

for which the filter comprises three square-shaped CSRRs, where (a) corresponds

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to a top view that illustrates the two differential lines and (b) to a bottom view

which shows the three CSRRs recorded in the mass plane; Y

Fig. 7 illustrates, by means of a graph, the insertion losses in common mode

1Scc211 and in differential mode i1Sdd211 for the structure of Fig. 6.

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Detailed description of some embodiments

The unit cell structure of the differential line of the proposed device

is shown in Fig. 1 (b), for an exemplary embodiment for which the rings of the

CSRR have a circular shape. It consists of a pair of coupled lines L 1, L2 with a

R resonator of the CSRR type engraved in the mass plane M. The circuit model of this

30

structure is also represented in Fig. 1 (b), where Cm and Lm model,

respectively, the capacitance and mutual inductance between the coupled lines.

In Figs. 1 (a) and 1 (b) are indicated a series of dimensions

dimensions relative to CSRR rings and conductive lines or strips. In

particular is indicated with the reference e the width of a CSRR ring, with d the

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   separation between both rings, with Rext the outer radius of the major ring of the CSRR,

with W the thickness of each conductive strip and with S the separation between the two strips

conductors that make up the two differential lines L 1, L2 of the proposed device

by the present invention, for the exemplary embodiment illustrated in Fig. 1 (b).

In said Figs. 1 (a) and 1 (b) an upper metallization layer is illustrated in black

in which the conductive strips L 1, L2 are defined and in gray a layer of

5

lower metallization corresponding to the plane of mass M, where it is defined,

by engraving, the CSRR. Between both layers of metallization there is a dielectric substrate,

That has not been illustrated.

The circuit model of Fig. 1 (b) explains that the differential signals are

insensitive to the presence of CSRRs, while these resonators prevent

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transmission of common mode signals at certain frequencies. The circuit model

equivalent of the structure of Fig. 1 (b) under common mode excitation is

represented in Fig. 2 (a), while for the odd mode it is represented in Fig.

2 (b). For odd mode, the resonator is shorted to ground, and the model

The result is that of a conventional transmission line. For even mode, you get

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the same circuit as that corresponding to a line loaded with CSRR (Fig. 1a), but

with modified parameters. Therefore, band behavior is expected from

Similar elimination for common mode.

As seen in said Fig. 1 (b) the rings of the open ring resonator

present the openings of each ring of the pair in the plane of symmetry of the lines

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differentials L 1, L2, and are sized so that such rings protrude to the

region occupied by lines L 1, L2. Advantageously, with this symmetric configuration,

a net electric field does not appear in the region inside the open ring resonator

complementary to the differential mode, these are not excited, and the signal in mode

differential can be propagated in the differential line. However, for common mode,

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a net electric field appears in the axial direction to the rings, so that the

Complementary open ring resonator is excited and the propagation of

signals for this mode, and therefore the noise in common mode, as intended.

In terms of field distributions, it is well known that the CSRR (first

resonance) can be excited by means of a variable axial electric field

30

temporarily [1, 5]. For common mode, there is a high density of lines of

electric field in the same direction below both lines. This causes arousal.

of the CSRR and therefore the generation of a disposal band. For mode

odd, the distribution of the electric field depends on the level of coupling between

both lines In highly coupled lines, the electric field lines are

35

   mainly concentrated in the (necessarily narrow) region of separation between

the lines. In weakly coupled lines, the electric field strength is higher

under the lines (similar to the even mode). However, the direction of the lines

Electric field is opposite on both strips of the differential line. If the structure is

symmetric, (i.e., the openings of the CSRRs are aligned with the plane of

symmetry of the differential lines), the opposite electric field vectors in

5

both lines cancel each other exactly and the CSRR is not activated.

To verify the integrity of the differential signals on these loaded lines

With CSRR, a differential line with weakly coupled lines (the

arrangement is illustrated in Fig. 3). The width and distance between the necessary lines

to obtain an odd mode impedance of 500 it has been determined by means of

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Transmission line calculator incorporated in the Agilent ADS commercial software

(Rogers R03010 microwave substrate parameters have been considered with

dielectric constant E, = 10.2 and a thickness h = 1.27mm). To analyze the effects of

Asymmetry in the circuit, the structure that results from rotating the CSRR 90 ° has been simulated.

Differential and common mode insertion losses simulated for both

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structures are illustrated in Fig. 3 (these simulations have been obtained by means of

commercial software Agi / ent Momentum). For even mode the results are

comparable (in the region of interest, at a frequency around 1.2GHz) and a zero

of transmission appears at the frequency where the shunt impedance (Fig. 2a)

is canceled:

(l)

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However, for the odd mode, while the insertion loss is less

of O, 1 dB (in the frequency range considered) for the symmetric structure,

A transmission zero appears in the structure with the CSRR rotated. Therefore these

results validate the principle of common mode suppression and point out the need for

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symmetrically record the CSRRs on the differential line in order to preserve the

Integrity of the differential signal in a broadband.

The following is an example of an embodiment related to a line design

differentials based on CSRR to form the device proposed here

invention.

30

To efficiently suppress common mode noise it is necessary to achieve

Wide elimination bands for even mode. To this end, the strategy consists of

expand the elimination band of the individual resonators, couple them as much as

possible, or record CSRRs with slightly modified dimensions in order to

   get different frequencies of zero transmission in the elimination band

35

desired, or a combination of all these effects. To expand bandwidth

of rejection of an individual CSRR (which is relevant to achieve wide bands of

elimination), it is necessary to increase the coupling capacity, C, and reduce the

inductance, Le, and capacitance, Ce of the CSRR as much as possible [6]. Agree

with this strategy, weakly coupled lines have been considered, since the

5

width of the lines needed to achieve an oddly impedance of 500 is

greater, and improves the coupling capacity of even mode. To reduce inductance

and capacitance of the CSRR, while maintaining the coupling level, it is necessary to increase

the width of the rings, e, and the separation, d. Obviously, this results in a CSRR of

larger size (for a given zero transmission frequency), but bandwidth

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attainable is also greater.

In the present invention, the bandwidth is reinforced by the

coupling of identical CSRRs. Two different structures have been considered: in

one of them, the rings of the CSRRs are wide and are visibly separated, in

the other, the rings are narrow and with a small separation between them. In both

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cases, in order to improve the coupling between CSRRs, rings have been considered

square shaped.

In the first design, the objective has been to reduce the size of the structure both

as possible. For this reason, it has been considered a unitary CSRR cell with

narrow and slightly separated rings (e = 0.2 mm and d = 0.2 mm). These values are

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near the limit of available technology. With these values, the CSRR model

reported in [2], and the capacitance per unit length of the coupled lines (mode

common), the side of the CSRR has been estimated in order to obtain a frequency of zero

transmission at fz = 1.4GHz (obviously, it has been necessary to perform a

corresponding optimization since the model reported in [2] is valid in

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conditions that are not met exactly in the structure).

The simulation of the insertion loss in common mode is represented in the

Fig. 4. The simulation of the structure circuit with the parameters extracted from

according to the procedure reported in [7] it is also represented in Fig. 4.

There is a good match between circuit simulation and simulation

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electromagnetic In order to improve rejection bandwidth, it has been

implemented a third order structure with closely coupled CSRRs.

Bandwidth is closely related to the level of coupling

between resonators. Therefore, the CSRR has been separated by O, 15 mm in order to

Increase bandwidth as much as possible. The simulation of the structure

35

   resulting is shown in Fig. 5, where for comparison purposes it has also been

Circuit simulation included. The simulated circuit is the one that results from connecting in

cascade the elementary cells, but with the addition of coupling capacitances

between adjacent resonators. The coupling capacitance has been considered

it is an adjustable parameter, and it has been found that the capacitance that provides a

Best adaptation is Ccoup = O, 11 pF. The dimensions of the structure are

5

23mmx7.6mm, that is 0.28A x 0.09A (where A is the wavelength guided to the

center frequency). The device is therefore very small, although the bandwidth

It has not been optimized in this structure. It is clear that the differential signal is not

altered by the presence of CSRRs (see also Fig. 5).

To increase bandwidth, CSRRs with rings and

1 o

wider inter-ring spaces. The goal is to achieve a common mode rejection of

at least 20 dB in the frequency range between 1.2GHz and 1.8GHz. The model of

CSRR is not so simple in this case because the element cannot be

considered as electrically small, so the

design level optimization. It has been found that three square-shaped CSRRs

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0.2 mm apart, with a side length of 1 0.8 mm and e = 1.2 mm and d = 0.8 mm, is

enough to reach the target specifications. The structure has been manufactured

by means of a milling machine LPKF H1 OO. The access lines have been

added in order to solder the connectors.

The photograph of the entire structure is represented in Fig. 6. Fig. 7 shows

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differential and common mode simulated insertion losses of the structure, as well

as the frequency response measured for even and odd mode. Dimensions

of the active region of the structure are 32.8mm x 1 0.8mm, that is 0.43A x O, 14A. Is

Note that the measured insertion loss for the differential signal is less than

0.5 dB in the range considered, the substrate loss tangent being 0.0023.

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The broadband structure manufactured in accordance with the

present invention (Fig. 6) with other structures reported in the references, and the

Results of such comparison are shown in the following table, in terms of

Bandwidth fraction!

Ref.

Length (A) Width (A) Surface (A2) FBW (%)

-10 dB

-30 dB

[8]

0.26 0.16 0.04 60 24

[3]

0.76 0.47 0.36 53 40

[4]

0.44 0.44 0.19 87 -----

   Present invention

0.43 0.14 0.06 54 24

The combination of size, and rejection bandwidth is competitive. The structure in [8] exhibits small dimensions and a relatively wide bandwidth, but requires three levels of metal. In summary, an alternative and promising proposal for the design of the lines has been presented

5 differentials with common mode suppression.

In conclusion, it has been shown that CSRRs are useful elements for the suppression of even mode in differential micro-tape lines. The structure circuit models for both modes, differential and common have been reported and validated.

10 The manufactured device prototype exhibits a rejection bandwidth for the common mode that extends from 1.18 GHz to 1.74 GHz with more than 20 dB rejection. The measured insertion loss for differential mode is better than 0.5 dB from DC to at least 2.5 GHz. Therefore, the presence of CSRRs has little influence on differential signals. Since CSRRs are resonators

15 compact, a small space of the differential line is required to achieve efficient common mode suppression. Therefore, this proposal is of interest for its application in structures based on differential lines.

A person skilled in the art could introduce changes and modifications in the described embodiments without departing from the scope of the invention as defined in the appended claims.

Claims (11)

 Claims 1.-Device of differential transmission lines with common mode suppression, of the type comprising:

-

a differential planar transmission means that includes at least two conductive transmission lines (L 1, L2), a metal mass plane (M), and a dielectric substrate,

Y

-

a filter formed by at least one resonator (R) recorded in said metal mass plane (M) to suppress the propagation of signals in common mode;

wherein the device is characterized in that said resonator (R), which is at least one, is an open ring resonator configured, dimensioned and arranged symmetrically to suppress the propagation of signals in common mode on at least a certain frequency and allow the differential signal transmission at said determined frequency, which is at least one. 2. Device according to claim 1, characterized in that said resonator (R), which is at least one, is a complementary open ring resonator. 3. Device according to claim 2, characterized in that the openings of each ring of said complementary open ring resonator (R), which is at least one, are arranged in the longitudinal symmetry plane of said differential transmission conductive lines (L 1, L2), which are at least two. Device according to claim 3, characterized in that the distance between internal edges of the conductive strip that forms each ring of said complementary open ring resonator (R), which is at least one, is greater than the separation distance (S ) between said differential transmission conductive lines (L 1, L2), which are at least two, plus the width (W) of each of the two differential transmission conductive lines (L 1, L2). 5. Device according to claim 4, characterized in that the rings of the complementary open ring resonator (R), which is at least one, are arranged centered, below the differential transmission conductive lines (L1, L2), which they are at least two, so that their common geometric center is located in said plane of longitudinal symmetry. 6. Device according to any one of the preceding claims, characterized in that each ring of said complementary open ring resonator (R), which is at least one, has a circular shape.

7. Device according to any one of claims 1 to 5, characterized

because each ring of said complementary open ring resonator (R), which is

At least one, has a square, rectangular or polyhedral shape.

8.-Device

according a anyone from the claims previous

5

characterized in that said filter comprises a plurality of said resonators of

open rings (R) configured, sized, arranged and related to each other

to suppress common mode broadcast in a rejection frequency band.

9. Device according to claim 8, characterized in that said plurality

of open ring resonators (R) have slightly different dimensions

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each other and are highly coupled, to expand the rejection frequency band

of the individual resonators.

10. Device according to claim 8, characterized in that the dimensions

referred to in said dimensioning are relative to: width of each ring, distance between

rings, distance between inner edges of the conductive strip that makes up each ring and

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separation between individual resonators.

eleven.-

Device according the claim 8, characterized why said filter

comprises, in combination with said open ring resonators (R), at least

an electric resonator of another type.