Integrated circuit transformer

Details Integrated circuit transformer Integrated circuit transformer

2003-03-24

2004-09-28

Mai, Anh (Department: 2832)

Inductor devices

Coil or coil turn supports or spacers

Printed circuit-type coil

C336S223000, C336S232000

Reexamination Certificate

active

06798327

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an integrated circuit transformer, and more particularly,to an integrated circuit transformer having two symmetrical conductive coils respectively disposed inside two insulating layers.
2. Description of the Prior Art
Owing to the dramatic development of semiconductors and the growing demand for wireless communications chips, conventional passive components such as transformers are usually integrated into a chip to meet the requirements of small size and low cost for a modern wireless communications chip.
In wireless communications integrated circuits, an integrated circuit transformer is capable of changing impedances for signal ends. To effectively reduce common mode interference, increasingly wireless communications integrated circuits adopt a differential approach to transform single-ended unbalanced signals into differential-ended balanced signals and vise versa. For example, a balance-to-unbalance (BALUN) transformer can transform single-ended unbalanced signals into differential-ended balanced signals.
Please refer to
FIG. 1A
to FIG.
1
D.
FIG. 1A
is a schematic diagram of a BALUN integrated circuit transformer
10
according to the prior art. FIG.
1
B and
FIG. 1C
are equivalent circuit diagrams of the transformer
10
shown in FIG.
1
A.
FIG. 1B
shows an equivalent circuit diagram of the transformer
10
having two pairs of differential-ended signal ends.
FIG. 1C
shows an equivalent circuit diagram of the transformer
10
having one single-ended signal end and one pair of differential-ended signal ends.
FIG. 1D
corresponds to a cross section of the transformer
10
along a cross plane
11
shown in FIG.
1
A.
The transformer
10
comprises a primary conductive coil
12
and a secondary conductive coil
14
, both disposed above an insulating layer
16
(shown in FIG.
1
D). The primary conductive coil
12
comprises a pair of differential-ended signal ends P
+
and P
−
. The secondary conductive coil
14
also comprises a pair of differential-ended signal ends S
+
and S
−
.
The primary conductive coil
12
and the secondary conductive coil
14
of the transformer
10
shown in
FIG. 1A
are interlaced with but not connected to each other. As the secondary conductive coil
14
crosses the primary conductive coil
12
or the primary conductive coil
12
and the secondary conductive coil
14
crosses themselves (as indicated by arrows shown in FIG.
1
A), the primary conductive coil
12
or the secondary conductive coil
14
takes a bypass to another insulating layer first through a via plug and then returns to the original layer. Additionally, the primary conductive coil
12
and the secondary conductive coil
14
are symmetrical to a symmetry line
18
. That is, both the primary conductive coil
12
and the secondary conductive coil
14
can be divided into two totally identical coils and these two pairs of identical coils are symmetrical to the symmetry line
18
. Such a layout for the conductive coils of the transformer
10
can effectively reduce common mode interference. A first single-ended single end
17
of the transformer
10
is located at an intersection of an innermost coil of the primary conductive coil
12
and the symmetry line
18
. Likewise, a second single-ended single end
19
of the transformer
10
is located at an intersection of an innermost coil of the secondary conductive coil
14
and the symmetry line
18
. An impedance ratio for the pair of differential-ended signal ends P
+
and P
−
and the pair of differential-ended signal ends S
+
and S
−
is determined by the number of coils of the primary conductive coil
12
and that of the secondary conductive coil
14
.
The above-described single-insulating-layer symmetrical transformer
10
is immune from the common mode interference. However, because the primary conductive coil
12
and the secondary conductive coil
14
are both disposed on the same insulating layer
16
, the transformer
10
needs a large area to accommodate the primary conductive coil
12
and the secondary conductive coil
14
.
Please refer to
FIG. 2A
to FIG.
2
C.
FIG. 2A
is a schematic diagram of a dual-layer integrated circuit transformer
20
according to the prior art.
FIG. 2B
is an equivalent circuit diagram of the transformer
20
.
FIG. 2C
corresponds to a cross section of the transformer
20
along a cross plane
21
shown in FIG.
2
A. Note that the transformer
20
does not provide single-ended signals to differential-ended signals transformation. The transformer
20
also comprises a primary conductive coil
22
and a secondary conductive coil
24
. The primary conductive coil
22
and the secondary conductive coil
24
respectively comprise a pair of differential-ended signal ends P
+
, P
−
and S
+
, S
−
. An impedance ratio for the transformer
20
is determined by the number of coils of the primary conductive coil
22
and that of the secondary conductive coil
24
.
Contrary to the transformer
10
shown in
FIG. 1A
, the transformer
20
comprises two insulating layers. As shown in
FIG. 2C
, the primary conductive coil
22
is disposed inside a primary insulating layer
26
and the secondary conductive coil
24
is disposed inside a secondary insulating layer
28
. Such a disposition of the primary conductive coil
22
and the secondary conductive coil
24
has the advantage to reduce the area of the integrated circuit transformer
20
. However, because the primary conductive coil
22
and the secondary conductive coil
24
are lacking symmetry, the transformer
20
is vulnerable to common mode interference.
SUMMARY OF INVENTION
It is therefore a primary object of the claimed invention to provide a double-insulating-layer symmetrical integrated circuit transformer to solve the drawbacks of the prior art integrated circuit transformers.
According to the claimed invention, the multi-layer symmetrical integrated circuit transformer includes a first insulating layer, a first conductive segment formed inside the first insulating layer and disposed on a first side of a first line, and a second conductive segment formed inside the first insulating layer and disposed on a second side of the first line. The second conductive segment and the first conductive segment are symmetrical to the first line. A first end of the first conductive segment and a first end of the second conductive segment are connected to a point located on the first line. The transformer further includes a second insulating layer disposed on the first insulating layer, a third conductive segment formed inside the second insulating layer and disposed on a first side of a second line, and a fourth conductive segment formed inside the second insulating layer. The fourth conductive segment and the third conductive segment are symmetrical to the second line. A first end of the third conductive segment and a first end of the fourth conductive segment are connected to a point located on the second line.
The transformer further comprises a fifth conductive segment formed inside the first insulating layer and disposed on the first side of the first line, a sixth conductive segment formed inside the first insulating layer and disposed on the second side of the first line. The sixth conductive segment and the fifth conductive segment are symmetrical to the first line.
The transformer further includes a first connection conductive segment and a second connection conductive segment. A first end of the first connection conductive segment is connected to an end of the fifth conductive segment and a second end of the first connection conductive segment is connected to a second end of the second conductive segment. A first end of the second connection conductive segment is connected to an end of the sixth conductive segment and a second end of the second connection conductive segment is connected to a second end of the first conductive segment.
It is an advantage of the claimed invention that an

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