Power combiner/splitter

Abstract

A distributed combiner/splitter having a first line formed of a first planar winding in a first conductive level and of a second planar winding in a second conductive level, and a second line formed of a third planar winding interdigited with the first winding in the first level, and of a fourth planar winding interdigited with the second winding in the second level, the windings having an increasing width from the outside to the inside.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, previously described, is a block diagram illustrating a combiner/splitter of the type to which an embodiment of the present invention applies;

FIG. 2 is a schematic block diagram illustrating an example of an electronic circuit using a combiner of the type to which an embodiment of the present invention applies;

FIG. 3 shows a conventional example of coupled-line combiner/splitter;

FIG. 4 shows the equivalent electric diagram of a combiner/splitter according to an embodiment of the present invention;

FIGS. 5A and 5B are top views of conductive levels taking part in an integrated embodiment of the coupled lines of the combiner/splitter of FIG. 4;

FIG. 6 is a top view of the coupled lines of the combiner/splitter according to an embodiment of the present invention; and

FIG. 7 is a cross-section view along line I-I of FIG. 6.

DETAILED DESCRIPTION

For clarity, the same elements have been designated with the same reference numerals in the different drawings and, further, as usual in the representation of integrated circuits, the various drawings are not to scale.

Further, only those elements which are useful to the understanding of the present invention have been shown and will be described. In particular, the applications of a combiner/ splitter of the present invention have not all been detailed, it being possible for such a combiner/splitter to be used to replace a conventional device in any application applying a 90° phase shift. Similarly, methods for forming thin layers by using integrated circuit manufacturing technologies have not been detailed, the present invention being compatible with conventional techniques.

FIG. 4 shows the equivalent electric diagram of a combiner/splitter according to an embodiment of the present invention.

As previously, a first line defines a first inductive element L1 while a second line defines a second inductive element L2 coupled to the first one. The ends of the first inductive element respectively define combined access IN and one OUT1 of the distributed accesses. The ends of inductive element L2 respectively define second distributed access OUT2, phase shifted by 90° with respect to the signals of accesses IN and OUT1, and a terminal ISO generally loaded with a 50-ohm impedance or other according to the application. The ends defining accesses IN and OUT2 are connected by a first capacitive element C1 while the ends defining accesses OUT1 and ISO are connected by a second capacitive element C2.

Capacitive elements C1 and C2 enable, without modifying the line impedance, increasing the coupling between them, and accordingly the combiner/splitter performances. Elements C1 and C2 also enable shifting the operating band towards lower frequencies and ensuring the phase quadrature between accesses OUT1 and OUT2. Another effect of capacitive elements is that they enable setting the operating frequency band of the combiner.

Another effect of capacitive elements provided on the two sides is to make the structure symmetrical.

FIGS. 5A, 5B, 6 and 7 illustrate an embodiment of inductive elements L1 and L2 in the form of planar conductive windings to form a combiner/splitter according to an embodiment of the present invention. FIGS. 5A and 5B are simplified top views of two conductive levels used for this embodiment. FIG. 6 is a top view illustrating the stacked levels of FIGS. 5A and 5B. FIG. 7 is a cross-section view along line I-I of FIG. 6.

A feature of this embodiment is to form the coupled lines of the combiner/splitter in the form of planar conductive windings in two stacked levels, each level comprising two interdigited windings. Another feature is to provide an increasing width of the tracks from the outside of each winding to the center.

The present invention takes advantage from the current density distribution in a conductive winding, which is greater at the center of the winding than at its periphery. This amounts to taking into account the fact that a combiner is a structure poorly adapted to carrying off the power that it dissipates by Joule effect both due to its compactness and to the low heat conductivity of currently-used dielectrics. Increasing the track width at the center locally increases the exchange surface area between the heat sources and their environment, and thus favors the heat dissipation.

Further, the fact that the combiner conducts variable currents generates a variable orthogonal magnetic field. This results in the occurrence of eddy currents which oppose the general current on the external portion of the spirals and add thereto on the internal portion. The localization of the current at the internal border of the spirals results in that only part of the conduction section is used, which increases resistive losses.

Thus, by providing an increasing width towards the center of the winding, an embodiment of the present invention enables sizing a combiner/splitter of reduced bulk for a given current with respect to an embodiment with a constant track width.

Embodiments of the present invention use tracks of variable width such that the conductive windings are wider at their center than at their periphery.

As illustrated in FIGS. 5A and 5B, inductive element L1 is formed of two planar windings 31 and 32 formed in first (FIG. 5A) and second (FIG. 5B) conductive levels (for example, two metallization levels of an integrated circuit) which are superposed and separated by an insulator 38 (FIG. 7). Inductive element L2 is also formed of two planar windings 33 and 34, respectively in the first and second conductive windings. Winding 33 is interdigited (interlaced) with winding 31 while winding 34 is interdigited with winding 32. The external ends of windings 31, 32, 33, and 34 respectively define accesses IN, OUT1, OUT2, and ISO. Internal ends 31′ and 32′ of windings 31 and 32 are connected by a conductive via 35 (FIG. 7 and in dotted lines in FIGS. 5A and 5B). Internal ends 33′ and 34′ of windings 33 and 34 are interconnected by a conductive via 36. The stacking order of the conductive levels doesn't matter. Other conductive and/or insulating levels not shown in FIG. 7 may be provided according to the application.

In the shown example and once the structure is finished (FIG. 6), windings 31 and 33 wind, in top view and as seen from the outside, clockwise, while windings 32 and 34 wind in the reverse direction. The opposite is of course possible, provided for the windings forming a same line to wind in reverse directions (from the outside) so that the current of a same line winds in the same direction along the entire line.

The fact of stacking up and interdigiting different windings enables a first coupling effect of the first winding on itself due to the second winding formed in the lower or upper level, and a second coupling effect by the fact that the winding is interdigited with a winding of the other line. This increase in the coupling coefficient with respect to conventional techniques enables, among others, for developed lengths of the lines forming the windings to be lower than one quarter of the wavelength of the work frequency of the coupler.

The fact of providing increasing lengths of conductive lines between the line access (width W1, FIG. 5B) and its inner end (width W2) enables, without increasing the combiner size, having wider tracks at the center, where the current is greater.

The line widths are preferably the same at all accesses and the same at all internal ends.

According to an embodiment of the present invention, capacitive elements C1 and C2 (FIGS. 4 and 6) are made in the form of lumped non-distributed elements.

In the preferred embodiment illustrated in FIGS. 4 to 7, the number of turns of each conductive level differs by one quarter of a turn. This enables making the external ends of the winding defining the combiner/splitter accesses close to one another. It is then possible to connect capacitive elements C1 and C2 to these ends, as illustrated in FIG. 6, without lengthening the coupled lines. An advantage is that this enables not having long connections to connect the capacitances and thus decreases the risk of deterioration of the combiner performances.

The passband of the combiner/splitter depends on the number of turns of the windings (and thus on the inductance value) as well as on the value of the capacitive elements.

For a given work frequency (central frequency of the passband of the combiner/splitter), the shorter the windings, the greater the values of the associated capacitive elements. In applications at high frequency (greater than 100 MHz) more specifically aimed at by embodiments of the present invention, the capacitive elements will have values ranging between 0.1 and 10 picofarads.

According to a first embodiment of the variable-width windings, pattern definition software usual in integrated and printed circuit technology is used, defining the different characteristic points required by the software.

According to another embodiment, the variable-width windings are formed by rectilinear segments placed end-to-end and having their parameters determined as follows.

A segment S_i (with i ranging from 1 to N*T, where N represents the number of segments per turn and T the number of turns of the concerned winding) is defined by an end point P_i and a width W_i, the other end being defined by point P_i−1 of the preceding segment S_i−1.

The polar coordinates of a point P_i of a segment S_i of a winding in a reference frame, with origin O representing the center of the structure, are obtained from width W_i−N of segment S_i−N of same angle θ_i (θ_i=θ_i−N) at the preceding turn of this winding and from width W_i−N/2 at the preceding half-turn. Embodiment of the present invention take advantage of the fact that the width of a segment S_i−N/2 at the preceding half-turn corresponds to the width of the segment of the other winding located between current segments S_i and the segment of the preceding winding S_i−N (that is, of segment S_i−3N/2 of the other winding).

Modulus R_i in polar coordinates of point P_i is obtained from the modulus of point P_i−N of same angle θ_i−N at the preceding turn:

R _i =R _i−N +W _i−N +W _i−N/2+2*D,   (equation 1)

where D shows the constant interval between windings.

Width W_i of current segment S_i is obtained from that W_i−1 of the previous segment S_i−1:

W _i =W _i−1+(Wmin−Wmax)/(N(T−1)+1),   (equation 2)

where Wmax designates the maximum width (W2, FIG. 5B) and Wmin designates the minimum width (W1).

Angle θ_i in polar coordinates of point P_i is then obtained from that θ_i−1 of point P_i−1 of the previous segment S_i−1:

θ_i=θ_i−1+2π/N.   (equation 3)

If need be, the rectangular coordinates (abscissa X_i and ordinate Y_i) of point P_i can then be obtained:

X _i =R _i*cos θ_i; and

Y _i =R _i*sin θ_i.

In the above example, the case where point P_i is on the inner edge of the spiral is considered. If the segments are defined from outer points P_i, it is enough to add width W_i in equation 1 for obtaining modulus R_i.

Since the calculation of the point coordinates takes into account the preceding turn, the first turn of each winding preferentially is of constant width corresponding to maximum width Wmax. This amounts to considering that, for the first N segments, the calculation of modulus R_i is obtained from the modulus of the preceding point P_i−1:

R_i=R_i−1+(2*Wmax+2*D)/N, with R₀ being selected according to the desired internal radius, for example, according to a space required at the center by the application (for example, to form vias for transferring the internal end contacts of the windings to the outside). The turn of constant width may however be virtual and not be formed in the concerned conductive level.

Similarly, an identical number of segments N*T for the two windings, corresponding to a number of full turns, has been assumed. In practice, and as illustrated in the drawings, the pattern of each winding is stopped in the last turn, for a value of i ranging between 1+(N−1)*T and N*T, according to the needs of connection of the external ends of the windings.

As a specific example of embodiment, to form a combiner/splitter at a 2-GHz work frequency with windings of 2.25 turns each, each of the capacitive elements has a capacitance of 1 picofarad. The same combiner/splitter may be formed with windings of 2.75 turns and capacitive elements of 0.25 picofarad.

According to another specific example of embodiment applied to a 1-GHz work frequency, a combiner/splitter such as described in relation with the previous drawings may have the following characteristics:

developed length of each winding: 500 μm;

minimum width W1 of the lines: 10 μm;

maximum width W2 of the lines: 40 μm;

interval between the lines of the two interdigited windings on a same plane: 10 μm; and

line thickness: less than 10 μm.

Another advantage of embodiments of the present invention is that the lengths of the coupled lines need not be equal to one quarter of the wavelength of the working frequency.

Another advantage of embodiments of the present invention is that by the stacking up of the windings, the combiner bulk is further decreased.

Another advantage of embodiments of the present invention is that by the provision of lines of increasing width from the outside to the inside, the combiner bulk is further decreased for a given work current range.

Another advantage of embodiments of the present invention is that the phase and amplitude balance is ensured.

Another advantage of embodiments of the present invention is that the structure thus obtained is directional (no signal on terminal ISO).

Of course, the present invention is likely to have various alterations, modifications, and improvements which will readily occur to those skilled in the art. In particular, the dimensions to be given to the coupled lines (length, width, and section) depend on the application and are within the abilities of those skilled in the art according, in particular, to the desired line resistance and to the work frequency of the combiner/splitter as well as to the work current range.

Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The present invention is limited only as defined in the following claims and the equivalents thereto.

Claims

1. A distributed combiner/splitter comprising: a first line formed of a first planar winding in a first conductive level and of a second planar winding in a second conductive level; anda second line formed of a third planar winding interdigited with the first winding in the first level, and of a fourth planar winding interdigited with the second winding in the second level, said windings having an increasing width from the outside to the inside.

2. The combiner/splitter of claim 1, wherein: a first capacitive element connects the external ends of the first and third windings; anda second capacitive element connects the external ends of the second and fourth windings.

3. The combiner/splitter of claim 1, wherein the windings constitutive of a same line wind in reverse directions.

4. The combiner/splitter of claim 1, wherein the maximum width of the windings is selected according to the current acceptable by the combiner.

5. The combiner/splitter of claim 1, wherein: first and third windings have a length difference of one quarter of a turn; andthe second and fourth windings have a length difference of one quarter of a turn.

6. The combiner/splitter of claim 2, wherein the capacitive elements have values selected from a range between 0.1 and 10 picofarads.

7. The combiner/splitter of claim 6, wherein the capacitive elements are lumped elements.

8. A method for manufacturing a combiner/splitter with two coupled lines, wherein the lines are made in the form of planar conductive windings of increasing width from the outside to the inside in two levels stacked up on each other, each line comprising a winding in each level and the two windings of a same plane being interdigited with each other.

9. The method of claim 8, wherein: a first capacitive element is connected to connect first ends of the lines; anda second capacitive element is connected to connect second ends of the lines.

10. The method of claim 8, wherein the central ends of the windings of a same line are connected by a conductive via.