U.S. patent application number 10/334661 was filed with the patent office on 2004-01-22 for vertical transformer.
Invention is credited to Hwu, Ruey-Jen, Ren, Jishi.
Application Number | 20040012474 10/334661 |
Document ID | / |
Family ID | 22589362 |
Filed Date | 2004-01-22 |
United States Patent
Application |
20040012474 |
Kind Code |
A1 |
Hwu, Ruey-Jen ; et
al. |
January 22, 2004 |
Vertical transformer
Abstract
A vertical transformer that comprises a primary and a secondary
winding, wherein one winding is positioned on a first plane, and
the other winding is positioned on a second plane. The primary and
secondary windings are separated by a dielectric substrate. In one
embodiment, the primary and secondary windings are configured to
use the same ground reference, and terminals in the center of each
winding are connected to the ground reference by a via hole to form
an in-phase transformer. In a second embodiment, a center terminal
of one winding and an outbound terminal of the other winding are
connected to the ground reference to form an opposite-phase
transformer. In the second embodiment, a dielectric substrate is
positioned between one of the windings and a ground plane.
Inventors: |
Hwu, Ruey-Jen; (Salt Lake
City, UT) ; Ren, Jishi; (Kanata, CA) |
Correspondence
Address: |
TRASK BRITT
P.O. BOX 2550
SALT LAKE CITY
UT
84110
US
|
Family ID: |
22589362 |
Appl. No.: |
10/334661 |
Filed: |
December 30, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10334661 |
Dec 30, 2002 |
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09706328 |
Nov 3, 2000 |
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6501363 |
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60163294 |
Nov 3, 1999 |
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Current U.S.
Class: |
336/200 |
Current CPC
Class: |
Y10T 29/4902 20150115;
H01L 23/645 20130101; H01L 2924/0002 20130101; H01P 5/02 20130101;
H01L 2924/00 20130101; H01F 27/2804 20130101; H01L 2924/0002
20130101; H01L 2924/3011 20130101 |
Class at
Publication: |
336/200 |
International
Class: |
H01F 005/00 |
Claims
What is claimed is:
1. A circuit assembly, comprising: a primary winding having a first
conductive strip, wherein the primary winding is positioned in a
first plane; a secondary winding having a second conductive strip,
wherein the secondary winding is positioned in a second plane,
wherein second plane is substantially parallel to the first plane;
a dielectric material positioned between the primary and secondary
windings; and a conductive material positioned and formed to
provide electrical communication between an interior of the primary
winding and an interior of the secondary winding.
2. The circuit assembly of claim 1, wherein the conductive material
is also configured to function as a common ground node between the
primary and secondary winding.
3. The circuit assembly of claim 1, wherein the first and second
conductive strips are substantially vertically aligned.
4. The circuit assembly of claim 1, wherein the primary and
secondary windings are positioned at a distance of less than 8
microns from each other.
5. The circuit assembly of claim 1, wherein the primary and
secondary windings are constructed of copper.
6. The circuit assembly of claim 1, wherein the conductive material
is formed from a single via.
7. A circuit assembly, comprising: a primary winding having a first
conductive strip, wherein the primary winding is positioned in a
first plane; a secondary winding having a second conductive strip,
wherein the secondary winding is positioned in a second plane,
wherein second plane is substantially parallel to the first plane;
a dielectric material positioned between the primary and secondary
winding; a first conductive material positioned to provide
electrical communication between an interior section of the primary
winding and a common conductor; and a second conductive material
positioned to provide electrical communication between an exterior
section of the secondary winding and the common conductor.
8. The circuit assembly of claim 7, wherein the primary and
secondary windings are positioned at a distance less than 8 microns
from each other.
9. The circuit assembly of claim 7, wherein the first and second
conductive strips are substantially vertically aligned.
10. The circuit assembly of claim 7, wherein the primary and
secondary windings are constructed of copper.
11. The circuit assembly of claim 7, wherein the first conductive
material is formed from a single via.
12. The circuit assembly of claim 7, wherein the second conductive
material is formed from a via.
13. A transformer for use in an integrated circuit, comprising: a
primary winding disposed in a first layer of the integrated
circuit; a secondary winding disposed in a second layer of the
integrated circuit, the second layer being separated from the first
layer by a dielectric layer; wherein the primary and secondary
windings are positioned such that the windings are inductively
coupled.
14. The transformer of claim 13, wherein the primary and secondary
windings are substantially vertically aligned in the integrated
circuit.
15. The transformer of claim 13, further comprising one or more
additional windings disposed in separate layers of the integrated
circuit and positioned to be inductively coupled to the primary or
secondary windings of the transformer.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of application Ser. No.
09/706,328, filed Nov. 3, 2000, now U.S. Pat. No. ______, issued
______, which is a nonprovisional application claiming the benefit
under 35 U.S.C. .sctn. 119(e) of U.S. Provisional Application No.
60/163,294 filed on Nov. 3, 1999, and titled "3-D VERTICAL MMIC
STRUCTURES AND SOFTWARE FOR CAPACITORS, TRANSFORMERS, RESONATORS
AND OTHER COMPONENTS," the subject matter of which is specifically
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to the integrated circuits,
and in particular, to transformers and a system and method for
analyzing the same.
[0004] 2. State of the Art
[0005] Transformers are widely used in electrical and electronic
engineering for the purpose of voltage, signal or impedance
transformation. In high frequency integrated circuits or microwave
monolithic integrated circuits (MMICs), transformers are usually
used in low-noise amplifiers (LNA), doubly-balanced mixers, or
voltage-controlled oscillators (VCO). More particularly, coplanar
microstrip, stripline couplers, or coplanar transformers are
commonly used in applications where signals need to be coupled at
different voltage or phase levels or the impedance of a terminator
needs to be transformed to another level. Typical designs for such
applications involve transformers having primary and secondary
windings that are configured on the same plane. Although operable,
these typical designs of coplanar transformers are found to occupy
a large area of a chip on which they are fabricated, thus, leading
to an inefficient manufacturing process.
BRIEF SUMMARY OF THE INVENTION
[0006] The present invention provides a vertical transformer that
comprises a primary and a secondary winding, wherein one winding is
positioned on a first plane, and the other winding is positioned on
a second plane. The primary and secondary windings are separated by
a dielectric substrate. In one embodiment, the primary and
secondary windings are configured to use the same ground reference,
and terminals in the center of each winding are connected to the
ground reference by a via hole to form an in-phase transformer. In
a second embodiment, a center terminal of one winding and an
outbound terminal of the other winding are connected to the ground
reference to form an opposite-phase transformer. In the second
embodiment, a dielectric substrate is positioned between one of the
windings and a ground plane.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated as the same
become better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
[0008] FIG. 1A is a perspective view showing an in-phase
transformer in accordance with one embodiment of the present
invention;
[0009] FIG. 1B is circuit diagram that may be used to model the
in-phase transformer depicted in FIG. 1A;
[0010] FIG. 2A is a perspective view showing an opposite-phase
transformer in accordance with one embodiment of the present
invention;
[0011] FIG. 2B is circuit diagram that may be used to model the
opposite-phase transformer depicted in FIG. 2A;
[0012] FIG. 3 is a sectional view of the transformer depicted in
FIG. 1A illustrating each layer of the structure;
[0013] FIG. 4 is a top view of one plane of the transformer
depicted in FIG. 1A;
[0014] FIGS. 5-9 illustrate graphs of the transformed impedance of
a transformer in accordance with one embodiment of the present
invention;
[0015] FIG. 10 illustrates a flow diagram of a modeling and
analysis routine for modeling and analyzing a vertical
transformer;
[0016] FIG. 11 illustrates a flow diagram of a FDTD calculation
routine utilized in the modeling and analysis routine shown in FIG.
10; and
[0017] FIGS. 12-14 illustrate the results of the modeling and
analysis routine shown in FIG. 10 in the form of transformed
impedance and frequency response graphs.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] One aspect of the present invention relates to a transformer
for performing impedance or coupling transformation. More
specifically, the present invention provides a vertical transformer
that comprises a primary and a secondary winding, wherein one
winding is positioned on a first plane, and the other winding is
positioned on a second plane. The primary and secondary windings
are separated by a dielectric or non-conducting substrate. In one
embodiment, the primary and secondary windings are configured to
use the same ground reference, and terminals in the center of each
winding are connected to the ground reference by a via hole to form
an in-phase transformer. In a second embodiment, a center terminal
of one winding and an outbound terminal of the other winding are
connected to the ground reference to form an opposite-phase
transformer. In addition, a dielectric substrate may be positioned
between one of the windings and a ground plane.
[0019] In one embodiment of the present invention, the
above-identified circuit may be constructed from an integrated
circuit chip or a printed circuit board. In general, an integrated
circuit chip, module substrates and printed circuit boards
generally comprise a number of laminated layers. These layers are
made up of conductive material that are, in turn, separated by
insulating layers of appropriate thickness. The conductive layers
or planes may be voltage supply planes or ground planes. External
or interplanar connections are made to various planes of the
multi-layered structure by via pins, also referred to as "via
holes." Via holes are either electrically connected to a particular
plane, or they may pass through a plane, being insulated therefrom
by a hole therein, which is of sufficient diameter to provide the
necessary electrical properties to electronically connect one plane
to another.
[0020] Referring now to FIG. 1A, one exemplary embodiment of an
in-phase transformer 100 will now be described. The in-phase
transformer 100 comprises a primary winding 102 positioned on a
first plane, and a secondary winding 104 positioned on a second
plane. The primary and secondary winding 102 and 104 are positioned
such that the planes of each winding are substantially parallel to
one another. In addition, the in-phase transformer 100 comprises a
conductive surface 105 that forms a plane that is parallel to the
planes of the primary and second windings 102 and 104. In this
embodiment, the conductive surface 105 functions as a ground for
the electrical connections associated with the in-phase transformer
100.
[0021] The windings 102 and 104 are formed into flat conductive
strips each formed of rigid metal, preferably, such as copper or
copper alloy. In one embodiment, the conductive strips have a
rectangular cross section and can be formed with a thickness
approximate to the range of 1-5 microns. The conductive strips have
a multi-turn configuration in which a series of straight segments
wind inwardly about an axis of the winding elements. The primary
winding 102 winds inwardly in a clockwise direction from a terminal
112 at an outer edge of primary winding 102 to a center terminal
106. The secondary winding 102 winds in a clockwise direction
inwardly from a terminal 114 at an outer edge of secondary winding
104 to a center terminal 108. The direction of each winding can be
in a clockwise or counter-clockwise direction.
[0022] The primary and secondary windings 102 and 104 also comprise
terminals in the center of each winding, 106 and 108, respectively.
In the embodiment of FIG. 1A, the center terminals 106 and 108 are
vertically aligned with one another such that a single via hole 110
can pass from the terminal 106 of the primary winding, through the
terminal 108 of the secondary winding, to the conductive surface
105. The primary and secondary winding 102 and 104 also comprise
terminals at the exterior ends of the windings, 112 and 114
respectively. Hence, a first port (port 1) is formed between the
exterior terminal 112 of the primary winding 102 and the conductive
surface 105, and a second port (port 2) is formed between the
exterior terminal 114 of the secondary winding 104 and the
conductive surface 105.
[0023] Referring now to FIG. 2A, one exemplary embodiment of an
opposite-phase transformer 400 will now be described. The structure
of the opposite-phase transformer 400 is similar to the structure
of the in-phase transformer 100, except a second via hole 420 is
configured to electronically connect an external terminal 415 of
the secondary winding 104 to the conductive surface 105. Also
unique to the opposite-phase transformer 400, a center terminal 422
of the secondary winding 104 is electronically connected to a
terminal conductor 424 which, in conjunction with the conductive
surface 105, forms a second port (port 2). The via hole 110
connected to the center terminal 106 of the primary winding 102
electronically couples the center terminal 106 to the conductive
surface 105, however, in this embodiment, the via hole 110 is not
electronically coupled to the secondary winding 104.
[0024] The opposite-phase transformer 400 comprises primary and
secondary windings 102 and 104, and a dielectric substrate
positioned between the windings. The windings 102 and 104 are
formed into flat conductive strips each formed of rigid metal,
preferably, such as copper or copper alloy. In one embodiment, the
conductive strips have a rectangular cross section and can be
formed with a thickness approximate to the range of 1-5 microns.
The conductive strips have a multi-turn configuration in which a
series of straight segments wind inwardly about an axis of the
winding elements. The primary winding 102 winds inwardly in a
clockwise direction from a terminal 112 at an outer edge primary
winding 102 to a center terminal 106. The secondary winding 102
winds in a clockwise direction inwardly from a terminal 415 at an
outer edge of secondary winding 104 to a center terminal 422. The
direction of each winding can be in a clockwise or
counter-clockwise direction. The top winding is referred to the
primary winding for illustrative purposes, as it is known in the
art that either winding of a transformer can be interchangeably
used as a primary or secondary winding.
[0025] The primary winding 102 is positioned on a first plane and
the secondary winding 104 positioned on a second plane. The primary
and secondary winding 102 and 104 are positioned such that the
planes of each winding are substantially parallel to one another.
In addition, the opposite-phase transformer 400 comprises a
conductive surface 105 that forms a plane that is parallel to the
plane of the primary and second windings 102 and 104.
[0026] The opposite-phase transformer 400 also comprises a
conductive device, such as a via hole 110, to electronically couple
the center terminal 106 to a conductive surface 105. A first port
(port 1) is formed between the exterior terminal 112 of the primary
winding 102 and the conductive surface 105. A center terminal 422
of the secondary winding is electronically coupled with a
conductive device 424, which can be formed from a series of
interconnections or a plurality of via holes. An exterior terminal
415 of the secondary winding 104 is coupled to the conductive
surface 105 by a conductive device, such as a via hole 420.
Accordingly, a second port (port 2) is formed between the
conductive device 424 and the conductive surface 105.
[0027] FIG. 3 is a sectional view of the in-phase transformer 100
illustrating each layer of the three-dimensional structure.
Although the sectional view of FIG. 3 illustrates the embodiment of
the in-phase transformer, the general structure and dimensions
shown in this illustration also apply to the opposite-phase
transformer 400. In one embodiment, the primary and secondary
windings 102 and 104 can be configured to form a winding having an
overall width of 168 micrometers, as indicated by points (a) and
(b). The conductive strips of the primary and secondary windings
102 and 104 are formed from copper or any other conductive
material. In this embodiment, the conductive strips have a width of
8.0 micrometers, as indicated by points (c) and (d), and the gap
between each wind is also 8.0 micrometers, as indicated by points
(e) and (f). Although these dimensions are described herein, the
transformer design of the present invention can be made to conform
to many other sizes depending on the application.
[0028] As shown in FIG. 3, the conductive strips of the primary and
secondary windings 102 and 104 are positioned such that they are
capable or receiving flux emissions from one another. In one
embodiment, the conductive strips of the primary winding 102 are
positioned above or below the conductive strips of the secondary
winding 104. The conductive strips of the primary winding 102 may
be vertically aligned with the conductive strips of the secondary
winding 104, or they may be positioned in a staggered
configuration. In addition, for the in-phase transformer 100, the
center terminals of the primary and secondary windings 102 and 104
are vertically aligned to allow a via hole 110 to contact the
conductive strips of each winding 102 and 104. The via hole 110 is
configured to such that it provides electrical communication
between the primary winding 102, secondary winding 104 and the
conductive surface 105. In this embodiment, the conductive surface
105 functions as the common ground node for the primary and
secondary winding 102 and 104. Also shown, the dielectric material
124 is positioned between the primary and secondary windings 102
and 104 and can be formed from any substrate material with a
dielectric characteristic. In one embodiment, the dielectric
material 124 is formed from a material with a dielectric constant
of three. One such suitable substrate for the dielectric material
124 is polyimide.
[0029] FIG. 4 is a top view of one plane of a transformer in
accordance with one aspect of the present invention. As shown in
FIG. 4, the conductive strip of the winding 102 is configured in a
spiral shape with a terminal 106 at the center of the winding and a
terminal 112 at the exterior portion of the winding. The via hole
110 is positioned within the terminal 106 at the center of the
winding allowing electrical communication with another winding
positioned in another plane and/or the conductive surface 105. In
the construction of the transformer 100, two layers having a shape
similar to the conductive strip shown in FIG. 4 are formed. As
described in more detail below, each layer of the transformer 100
is constructed by known fabrication methods.
[0030] In general, any type of substrate can be used as a
foundation (item 122 of FIG. 3), such as gallium arsenide. The
construction of the windings can be achieved by the use of a
technique known as sputtering, which is a copper seed-layer
deposition. Electrical plating techniques are used for a copper
strip thickness of 5 to 20 microns. Once a dielectric layer, such
as polyimide, is applied over the copper strip of the lower
winding, the dielectric is dry-etched using oxygen plasma. The
copper strip of the top winding is then applied using the
sputtering or electrical plating techniques. Although these
exemplary fabrication techniques are utilized, it is known to one
skilled in the art that copper strips and dielectric layers can be
applied using many other fabrication or circuit board construction
techniques.
[0031] Returning to FIGS. 1A-2B, one method of modeling the
transformers in the form of a circuit diagram will now be
described. As known in the art, the length, width, number of turns
of the windings, and the separation of the windings in a
transformer can be adjusted based on the application requirements,
such as a need for a specific center frequency, operation
bandwidth, transformation ratio, or phase or impedance
transformation. More specifically, the separation between the
primary and secondary windings impacts the operating bandwidth of
the transformer 100. When the windings are close together, the
bandwidth is significantly increased. Thus, a tightly coupled
transformer will have better performance for the impedance
transformation in the frequency domain. In one exemplary embodiment
of FIGS. 1A, 2A, and 3 the separation between the primary and
secondary windings 102 and 104 is approximately six micrometers,
and the separation between the secondary winding 104 and the
conductive ground plane 105 is approximately thirty micrometers. As
shown in the charts of FIGS. 5-9, these dimensions of the vertical
transformer provide characteristics similar to a traditional lumped
transformer.
[0032] Similarly, other adjustments can be made to configure a
transformer. For example, the ratio of turns for the windings can
be adjusted to improve the performance of the transformer if a
decreased transformation ratio is needed. As known in the art, the
range for the ratio of turns can be any value that is needed for
the application. For instance, the ratio of turns can be two to one
if such a coupling is desired. In addition, the length of the
conductive strips in the windings can be adjusted to configure the
transformer for various center frequencies.
[0033] FIGS. 1B and 2B illustrate circuit diagrams 150 and 160 that
model the in-phase transformer 100 and the opposite-phase
transformer 400, respectively. For illustrative purposes, the
symbols for each electronic parameter are shown. All equivalent
circuit parameters are the functions of the above-described
structure parameters. For example, the mutual inductance M depends
on the separation between upper and lower windings. Generally
described, the smaller the separation, the larger the mutual
inductance M. The inductance L1 and L2 depend on the length and
permeability, .mu., of each winding. For instance, when the length
of each winding increases, the inductance value increases. The
capacitance C1 and C2 largely depend on the permittivity, E, and
the distance from the plane, on which the winding is laid, to the
reference ground. As known to one of ordinary skill in the art, the
total combination of the equivalent circuit parameters determines
the resonance frequency and bandwidth. In addition, the choice of
large permeability, .mu., can significant improve the performance
of lower frequency range. These circuit models 150 and 160 and the
frequency response graphs shown in FIGS. 5-9 illustrate that the
transformers 100 and 400 of the present invention have performance
characteristics of a standard transformer.
[0034] FIGS. 5-9 illustrate the impedance graphs of the
above-described transformers. The graph lines referenced with an
"R" in each graph denotes the resistance, the real component of the
impedance, and the graph lines referenced with an "X" in each graph
denotes the reactance, the imaginary component of the impedance.
The resistance ("R") line shown in each chart represents the
resistance value when the imaginary component ("X") of the
impedance is at a zero value.
[0035] With reference to FIG. 5, the graph illustrates the
transformed impedance of a transformer in accordance with one
embodiment having a 200 Ohm impedance load connected to port 2. As
shown in FIG. 5, the input impedance of port 1 varies over a wide
range of frequencies. Also shown, the graph of FIG. 5 illustrates
two different sets of lines charting the transformed impedance when
the separation between the primary and secondary windings is 4
.mu.m (lines 501 and 507), 6 .mu.m (lines 502 and 508), and 8 .mu.m
(lines 503 and 508). As can be seen from the graph of FIG. 5, the
200 Ohm impedance load connected to port 2 is respectively
transformed into 1500, 1000 and 800 Ohms for the 4, 6, and 8 micron
separation. In addition, the input impedance of port 1 is more
uniform, i.e., having a broader bandwidth, when the separation
between the primary and secondary windings is smaller.
[0036] FIG. 6 illustrates a graph of the transformed impedance of a
transformer in accordance with another embodiment of the present
invention. The first line 601 graphs the resistance, the real
component of the impedance, of port 1 when port 2 is loaded with an
impedance of 150 Ohms. The second line 602 graphs the input
resistance of port 2 when port 1 is loaded with an impedance of
1000 Ohms. The third and forth lines 603 and 604 respectively graph
the input reactance, the imaginary component of the impedance, of
port 1 and port 2.
[0037] FIG. 7 illustrates a graph of the transformed impedance of a
transformer in accordance with yet another embodiment of the
present invention. The first line 701 graphs the resistance, the
real component of the impedance, of the input impedance of port 1
when port 2 is loaded with an impedance of 200 Ohms. The second
line 702 graphs the input resistance of port 2 when port 1 is
loaded with an impedance of 1300 Ohms. The third and forth lines
703 and 704 respectively graph the input reactance, the imaginary
component of the impedance, of port 1 and port 2.
[0038] FIG. 8 illustrates a graph of the transformed impedance of a
transformer in accordance with another embodiment of the present
invention. The first line 801 graphs the resistance of port 1 when
port 2 is loaded with an impedance of 250 Ohms. The second line 802
graphs the input impedance of port 2 when port 1 is loaded with an
impedance of 1600 Ohms. The third and forth lines 803 and 804
respectively graph the input reactance, the imaginary component of
the impedance, of port 1 and port 2. Similarly, FIG. 9 illustrates
a graph of the real (line 901) and imaginary (line 902) components
of the transformed impedance when the transformer is loaded at port
2 with a 200 Ohm impedance.
[0039] As shown by the various transformer configurations of FIGS.
5 and 9, the transformer can be configured to adapt to a wide range
of impedance transfer requirements. For example, the design of the
impedance transformer shown in FIGS. 1A and 2A meet the basic
requirement of transformation from 200 Ohms to 1000 Ohms operating
at a center frequency in the range of 20 to 40 GHz, and having a
bandwidth of about 10%, and with a component size within 500 .mu.m
by 500 .mu.m.
[0040] Although the above-described transformers 100 and 400 may be
analyzed with conventional electrical models such as those
illustrated in FIGS. 1B and 2B, it is also possible to utilize a
more sophisticated analysis tool such as a finite-difference
time-domain (FDTD) analysis algorithm. Disclosed herein, a FDTD
analysis algorithm is used to model and analyze the various
embodiments of the vertical transformer of the present invention.
The FDTD algorithm is known to one of ordinary skill in the art and
is typically used to model various RF elements, such as resistors,
planar inductors, and capacitors. Details of such applications of
the FDTD algorithm is described in M. Picket-May and A. Taflove,
"FDTD Modeling of Digital Signal Propagation in 3-D Circuits With
Passive and Active Loads," IEEE Trans. MTT, Vol. 42, pp. 1514-1523,
August 1994, the subject matter of which is specifically
incorporated herein by reference. In addition, the FDTD algorithm
has been used to model more complicated MMIC elements such as via
holes. A detailed description of the application of the FDTD
algorithm to such MMIC elements is discussed in Dongsoo Koh,
Hong-Bae Lee and Tatsuo Itoh, "A Hybrid Full-Wave Analysis of
Via-Hole Grounds Using Finite-Difference and Finite-Element
Time-Domain Methods," IEEE Trans. MTT, Vol. 45, No. 12, pp.
2217-2222, December 1997, the subject matter of which is
specifically incorporated herein by reference.
[0041] Generally described, the method applies the FDTD algorithm
for performing computer-aided design of complex structures, such as
the above-described vertical transformer. In the application of
FDTD algorithm a user defines specific parameters of the complex
structure, such as the parameters of a vertical transformer. The
routine then calculates the magnetic and electrical field
distribution by the use of applicable Maxwell's equations and the
user specified parameters. The magnetic and electrical field
distributions are then treated on the boundaries of the code
through an absorbing boundary conditions (ABC) subroutine. As known
by those of ordinary skill in the art, the FDTD and absorbing
boundary condition routines model a three-dimensional structures by
dividing the three-dimensional structure into cubic cells and
iteratively performing the magnetic and electrical field analysis
on each cubic cell. Once all calculations are performed, the method
of the present invention provides data charts of the transformed
impedance and frequency response of the analyzed vertical
transformer. In addition, the electric and magnetic field
information is converted to circuit parameters such as voltage and
current, from which, circuit characteristics such as impedance,
transmission and reflection can be obtained.
[0042] Also known to those skilled in the art, the FDTD and
absorbing boundary condition routines can be implemented in a
software application running on a standalone or networked computing
device. Generally known programming methods utilizing C, C++,
Fortran, Pascal, or other commonly known programming languages can
be used to implement the FDTD and absorbing boundary condition
routines.
[0043] Referring now to FIG. 10, a general description for the FDTD
routine 1000 will now be described. The process starts at block
1001 where the system running the FDTD routine 1000 receives
parameter specifications. In this part of the process, the routine
1000 is configured to allow a user to enter the parameters in a
computing device for the FDTD calculations. More specifically, the
system is configured to receive the number of cells in the system,
the space steps in the three-dimensional directions, initial values
of the source specification, and the dimensions of the modeled
structure. The source specification defines the parameters of the
input signal, such as for instance a raised-cosine function. The
FDTD routine 1000 is also configured to receive the FDTD
coefficients and the absorbing boundary condition coefficients.
Also in block 1001, the FDTD routine 1000 is configured to receive
the absorbing boundary conditions, such as a first order, second
order, etc, to determine the level of accuracy of the calculations.
The above-described parameters are generally known to one of
ordinary skill in the art and, therefore, further explanation of
these parameters has not been provided herein.
[0044] After receiving the parameter specifications, the FDTD
routine 1000 continues at block 1003, where the FDTD calculations
are performed. In this part of the routine, variables may be
initialized. For instance, as mentioned above, values indicating
the initial electric and magnetic fields for the bottom, top, and
side surfaces of the modeled transformer may be provided. In one
embodiment, the absorbing boundary conditions can be initially set
to a zero value. As shown in the flow diagram of FIG. 11, the
routine of the FDTD calculations of block 1003 is described in more
detail. The flow diagram of FIG. 11 illustrates a general overview
of a FDTD calculation routine 1100.
[0045] The FDTD calculation routine 1100 starts at block 1101 where
the magnetic field calculations are executed. As known to one of
ordinary skill in the art, the magnetic field calculations
determine the field value of an individual cell of the modeled
transformer using Maxwell's models. This calculation is performed
for all of the cells in the same temporal space to obtain magnetic
field distribution at a given time and position. Next, at block
1103, the magnetic field treatments determined in the process of
block 1101 are applied to the absorbing boundary conditions. Then
at blocks 1105 and 1107, electronic field calculations are
preformed on the individual cell of the modeled transformer. As
shown by the loop of blocks 1101-1109, the electronic field
calculation is performed for all of the cells of the model to
determine the electric field distributions at a number of positions
and points in time. The results of the electronic field calculation
is then applied to the absorbing boundary conditions (block 1107).
As shown in block 1109, the FDTD calculation routine 1100 then
determines if it should proceed to the next section, e.g., a
section with a specific position at a specific time, of the modeled
transformer. At block 1109, if the routine determines that it
should proceed, the routine then returns to block 1101 where the
process of blocks 1101-1107 are repeated for another section.
Alternatively, at block 1107, if the FDTD calculation routine 1100
determines that the calculation is complete, the FDTD calculation
routine 1100 terminates.
[0046] Referring again to FIG. 10, the FDTD routine 1000 continues
at block 1104 where the routine then graphs the data calculated and
analyzed in block 1003. Several exemplary diagrams of the FDTD
routine 1000 output are illustrated in FIGS. 12-14. As shown in
FIGS. 12-14, the output diagrams can be configured to draft the
impedance transformation of the modeled transformer (FIG. 12), the
general frequency response (transmission parameter, S.sub.21, and
reflection parameter S.sub.11) of the modeled transformer (FIG.
13), or any other graph illustrating the calculated electric and
magnetic fields of the modeled transformer (FIG. 14). Although the
above example of the FDTD routine 1000 involves the modeling of a
transformer, the FDTD method of the present invention can be
applied to any other complex circuit structure.
[0047] The results of one exemplary analysis are shown in FIGS.
12-14. The transformer modeled and analyzed in this example of the
FDTD modeling contains a primary and secondary winding having a
structure similar to that of FIGS. 1A and 2A. The analyzed
transformer is made from a material having a dielectric constant of
12.96 for the GaAs substrate. The dielectric constant of the
separation layers 3.6 (polyimide), strip width 4.1 .mu.m, and gap
between strips 4.1 .mu.m. This modeled transformer, for example, if
configured in a coplanar configuration, having primary and
secondary windings on the same plane, would consume a total area of
13.111 .mu.m.sup.2. Conversely, if this modeled structure is
configured in a vertical structure such as the embodiments
illustrated in FIGS. 1A and 2A, where the primary and secondary are
separated into two layers with 3.0 .mu.m separation, the
transformer would only consume a total area of approximately 4,303
.mu.m.sup.2, approximately 1/3 of the area used by the coplanar
structure.
[0048] As described above, vertical MMIC transformers are disclosed
and modeled by the FDTD analysis method. The modeling results show
that the vertical transformer of the present invention, although it
may occupy a smaller area, maintains most of the original
properties of a traditional lumped transformer, i.e., impedance
transformation.
[0049] While the preferred embodiment of the invention has been
illustrated and described, it will be appreciated that various
changes can be made therein without departing from the scope of the
invention. For example, although the primary and secondary windings
are illustrated as being generally square, it will be appreciated
that other shapes such as round, oval or other polygon shapes
(hexagonal, pentagonal, octagonal, etc.) could also be used. In
addition, although the embodiments illustrated above utilize only a
primary and secondary winding it would be appreciated that the
structure could be continued to have more than two windings
arranged in different planes in an integrated circuit.
* * * * *