Integrated segmented and interdigitated broadside- and edge-coupled transmission lines

#The present invention relates to impedance transforming elements, and in particular to segmented and interdigitated integrated coupled transmission line elements.

#The use of twisted pairs of copper wires to form coupled transmission line elements is well known. These transmission line elements may be used to create balanced and unbalanced transmission lines, balanced-unbalanced (balun) transmission lines, and current and voltage inverters. Examples of the use of conventional transmission line elements are presented in C. L. Ruthroff, “Some Broad-Band Transformers,” Proceedings of the IRE (Institute for Radio Engineers), vol. 47, pp. 1337-1342 (August 1959), which is incorporated herein by reference. These transmission line elements are typically found in forms that are useful in frequency bands through UHF.

#The use of such transmission line elements in integrated circuits such as RF power amplifiers and low noise amplifiers that operate at higher than UHF frequencies is desirable. However, the incorporation of these conventional transmission line elements into RF devices such as cellular telephones is not competitively feasible due to size and cost. Moreover, conventional coupled transmission line elements are not suitable for use in the desired frequency range.

#For a more complete understanding of the present invention and for further features and advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

#FIG. 1 is a top view of an bifilar broadside- and edge-coupled transmission line element according to the invention.

#FIG. 2A is a view of the top metal layer in the crossover region of the transmission line element of FIG. 1.

#FIG. 1 shows a general view of a bifilar transmission line element 10 in accordance with the invention. Bifilar element 10 includes two pairs of broadside- and edge-coupled transmission lines formed in two metal layers separated by a dielectric layer. FIG. 4 illustrates the relative positions of the transmission line pairs. Lines 104A and 102A are formed in a top metal layer TM, and lines 102B and 104B are formed in a bottom metal layer BM. The top and bottom metal layers TM and BM are separated by a dielectric layer 103. This structure is fabricated using conventional semiconductor processes that are well-known to those skilled in the art and will not be detailed here. Metal layers TM and BM may be formed, for example, of aluminum, gold, or another conductive material.

#As shown in FIG. 1, the transmission line pairs extend from a first terminus 106 to a second terminus 108. While the transmission lines in FIG. 1 are laid out in the pattern of a square spiral, many other geometries may be used. For example, other spiral shapes (circular, rectangular, etc.) can be used, or the transmission lines can be linear or variety of other shapes. This invention is not limited to any particular shape of transmission lines.

#Transmission lines 102A, 102B, 104A, 104B are “segmented” in the sense that at predetermined intervals line 102A is connected to line 102B, and line 104A is connected to line 104B. Lines 102A, 102B thus together constitute a first conductor 102 and lines 104A 104B together constitute a second conductor 104. The intervals between such connections are referred to as “segments”. Referring to FIG. 1, the connections are made at interconnects 112, 114, 116, 118,120, 122, 124, 126, 128, 130, 132 and 134. The length between interconnects 112, 114 (terminus 106) and interconnects 116, 118 constitutes a first segment, the length between interconnects 120, 122 and interconnects 124, 126 constitutes a second segment, and the length between interconnects 128, 130 and interconnects 132, 134 (terminus 108) constitutes a third segment. Preferably, the interconnects are spaced such that, at the operating frequency of the transformer, the segments are less than 30 degrees long.