U.S. patent application number 15/130900 was filed with the patent office on 2017-10-19 for ultra-broad bandwidth matching technique.
This patent application is currently assigned to MACOM Technology Solutions Holdings, Inc.. The applicant listed for this patent is M/A-COM Technology Solutions Holdings, Inc.. Invention is credited to David Runton, Robert Sadler.
Application Number | 20170302245 15/130900 |
Document ID | / |
Family ID | 58428358 |
Filed Date | 2017-10-19 |
United States Patent
Application |
20170302245 |
Kind Code |
A1 |
Sadler; Robert ; et
al. |
October 19, 2017 |
ULTRA-BROAD BANDWIDTH MATCHING TECHNIQUE
Abstract
A multicomponent network may be added to a transmission line in
a high-frequency circuit to transform a first impedance of a
downstream circuit element to second impedance that better matches
the impedance of an upstream circuit element. The multicomponent
network may be added at a distance more than one-quarter wavelength
from the downstream circuit element, and can tighten a frequency
response of the impedance-transforming circuit to maintain low Q
values and low VSWR values over a broad range of frequencies.
Inventors: |
Sadler; Robert; (Raleigh,
NC) ; Runton; David; (Cary, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
M/A-COM Technology Solutions Holdings, Inc. |
Lowell |
MA |
US |
|
|
Assignee: |
MACOM Technology Solutions
Holdings, Inc.
Lowell
MA
|
Family ID: |
58428358 |
Appl. No.: |
15/130900 |
Filed: |
April 15, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H03H 7/38 20130101; H03H
7/383 20130101 |
International
Class: |
H03H 7/38 20060101
H03H007/38 |
Claims
1. An impedance-transforming circuit that is configured to operate
at frequencies between 500 MHz and 6 GHz, the
impedance-transforming circuit comprising: a multicomponent network
comprising passive circuit elements integrated on a substrate; and
at least one transmission line configured to connect between the
multicomponent network and a circuit element such that the
multicomponent network is at least one-quarter wavelength from the
circuit element, wherein the multicomponent network and the at
least one transmission line transform an input impedance of the
circuit element to provide a reduced voltage-to-standing-wave-ratio
(VSWR) over a bandwidth that lies at least partly within the
frequencies.
2. The impedance-transforming circuit of claim 1, wherein the
substrate comprises a printed circuit board or pallet.
3. The impedance-transforming circuit of claim 1, wherein the
substrate comprises one or more semiconductor chips.
4. The impedance-transforming circuit of claim 1, wherein the
reduced VSWR is less than or approximately equal to 2.
5. The impedance-transforming circuit of claim 1, wherein the
multicomponent network comprises at least two passive circuit
elements.
6. The impedance-transforming circuit of claim 1, further
comprising a source having a second impedance at an output that is
connected to the impedance-transforming circuit, wherein the
reduced VSWR is less than or approximately equal to 2 and the
bandwidth is greater than 800 MHz.
7. The impedance-transforming circuit of claim 1, wherein the
reduced VSWR is less than or approximately equal to 2 and the
bandwidth is between 1 GHz and 2 GHz.
8. The impedance-transforming circuit of claim 1, wherein the
multicomponent network comprises a three-element .pi. network.
9. The impedance-transforming circuit of claim 1, wherein the
multicomponent network comprises a T network.
10. The impedance-transforming circuit of claim 1, wherein the
multicomponent network comprises an LCC network.
11. The impedance-transforming circuit of claim 1, wherein the at
least one transmission line comprises two transmission line
sections having different impedances.
12. The impedance-transforming circuit of claim 1, further
comprising a source connected to the multicomponent network,
wherein the source comprises a gallium-nitride amplifier.
13. The impedance-transforming circuit of claim 1, further
comprising a source connected to the multicomponent network,
wherein the source is included in a wireless communication
device.
14. The impedance-transforming circuit of claim 1, wherein the
reduced VSWR is less than or approximately equal to 2 and the
bandwidth is centered at approximately 750 MHz and has a width
between approximately 325 MHz and approximately 750 MHz.
15. The impedance-transforming circuit of claim 1, wherein the
reduced VSWR is less than or approximately equal to 2 and the
bandwidth is centered at approximately 2.2 GHz and has a width
between approximately 1.1 GHz and approximately 2.2 GHz.
16. The impedance-transforming circuit of claim 1, wherein the
reduced VSWR is less than or approximately equal to 2 and the
bandwidth is centered at approximately 2.7 GHz and has a width
between approximately 1.3 GHz and approximately 2.7 GHz.
17. The impedance-transforming circuit of claim 1, wherein the
reduced VSWR is less than or approximately equal to 2 and the
bandwidth is centered at approximately 3.8 GHz and has a width
between approximately 1.9 GHz and approximately 3.8 GHz.
18. A method for transforming an impedance of a circuit element in
a high-frequency circuit, the method comprising: receiving a signal
having a frequency component between 500 MHz and 6 GHz at a
multicomponent network comprising passive circuit elements;
providing the signal from the multicomponent network to at least
one transmission line; providing the signal from the at least one
transmission line to the circuit element, wherein the
multicomponent network is at least one-quarter wavelength from the
circuit element; and transforming, by the multicomponent network
and the at least one transmission line, the input impedance of the
circuit element to provide a reduced VSWR over a bandwidth.
19. The method of claim 18, wherein the reduced VSWR is less than
or approximately equal to 2.
20. The method of claim 18, wherein the multicomponent network
comprises at least two passive circuit elements.
21. The method of claim 18, wherein the multicomponent network
comprises a .pi. network.
22. The method of claim 18, further comprising reflecting a voltage
amount from the multicomponent network less than or equal to
one-half of an incident voltage over a bandwidth greater than 800
MHz.
23. The method of claim 18, wherein the reduced VSWR is less than
or approximately equal to 2 and the and the bandwidth is centered
at approximately 750 MHz and has a width between approximately 325
MHz and approximately 750 MHz.
24. The method of claim 18, wherein the reduced VSWR is less than
or approximately equal to 2 and the bandwidth is centered at
approximately 2.2 GHz and has a width between approximately 1.1 GHz
and approximately 2.2 GHz.
25. The method of claim 18, wherein the reduced VSWR is less than
or approximately equal to 2 and the bandwidth is centered at
approximately 2.7 GHz and has a width between approximately 1.3 GHz
and approximately 2.7 GHz.
26. The method of claim 18, wherein the reduced VSWR is less than
or approximately equal to 2 and the bandwidth is centered at
approximately 3.8 GHz and has a width between approximately 1.9 GHz
and approximately 3.8 GHz.
27. The method of claim 18, wherein the multicomponent network
comprises a T network.
28. The method of claim 18, wherein the multicomponent network
comprises an LCC network.
29. The method of claim 18, further comprising generating the
signal that is received at the multicomponent network with a
gallium-nitride amplifier.
30. The method of claim 29, further comprising transmitting the
signal wirelessly.
Description
BACKGROUND
Technical Field
[0001] The technology relates to impedance-matching networks for
high-frequency and ultra-broad bandwidth devices.
Discussion of the Related Art
[0002] Impedance matching is carried out for high-speed circuits to
improve power transfer between circuit components, improve circuit
performance, and reduce unwanted power reflections. Often,
impedance matching involves a process of transforming an impedance
at a first location in a circuit to a different value that matches
an impedance at a second location in a circuit. For example, a load
(e.g., an antenna) may have a first impedance that is different
from an output impedance of a source (e.g., a signal generator). A
circuit designer may add elements (e.g., capacitors, inductors,
transmission line, or other components) between the load and
source, so as to "transform" the impedance of the load. The added
elements present a different impedance to the source that, when
selected properly, match an output impedance of the source.
SUMMARY
[0003] Circuits and methods for transforming impedances in
high-frequency circuits are described. The techniques may be used
to match impedances over ultra-broad bandwidths (e.g., bandwidths
greater than about 800 MHz). Lumped elements may be added to a
circuit at distances greater than approximately one-quarter
wavelength from the element for which an impedance is being
transformed to obtain impedance matching over an ultra-broad
bandwidth. The lumped elements may include passive components such
as inductors and capacitors arranged in a network. The
impedance-matching techniques may improve a matched bandwidth by
more than 40% compared to conventional techniques.
[0004] According to some embodiments, an impedance-transforming
circuit may be configured to operate at frequencies between 500 MHz
and 6 GHz. An impedance-transforming circuit may comprise a
multicomponent network integrated on a substrate and at least one
transmission line configured to connect between the multicomponent
network and a circuit element such that the multicomponent network
is at least one-quarter wavelength from the circuit element. The
multicomponent network and the at least one transmission line may
be configured to transform an input impedance of the circuit
element, so that a reduced voltage-to-standing-wave ratio (VSWR)
(compared to a circuit that does not include the
impedance-transforming circuit) is provided over a bandwidth that
lies at least partly within the frequencies.
[0005] In some implementations, the substrate may comprise a
printed circuit board or pallet. In other implementations, the
substrate may comprise one or more semiconductor chips (e.g., chips
of a multi-chip module). In some aspects, the reduced VSWR is less
than or approximately equal to 2. In some cases, the reduced VSWR
is less than or approximately equal to 2 and the bandwidth is
between 1 GHz and 2 GHz.
[0006] In some implementations, the reduced VSWR is less than or
approximately equal to 2 and the bandwidth is centered at
approximately 750 MHz and has a width between approximately 325 MHz
and approximately 750 MHz. In some implementations, the reduced
VSWR is less than or approximately equal to 2 and the bandwidth is
centered at approximately 2.2 GHz and has a width between
approximately 1.1 GHz and approximately 2.2 GHz. According to some
aspects, the reduced VSWR is less than or approximately equal to 2
and the bandwidth is centered at approximately 2.7 GHz and has a
width between approximately 1.3 GHz and approximately 2.7 GHz. Yet,
in other implementations, the reduced VSWR is less than or
approximately equal to 2 and the bandwidth is centered at
approximately 3.8 GHz and has a width between approximately 1.9 GHz
and approximately 3.8 GHz.
[0007] In some implementations of an impedance-transforming
circuit, a multicomponent network comprises at least two passive
circuit elements. In some aspects, a multicomponent network
comprises a three-element .pi. network. According to some
implementations, a multicomponent network comprises a T network. In
some implementations, a multicomponent network comprises an LCC
network. In yet other aspects, the at least one transmission line
of an impedance-transforming circuit comprises two transmission
line sections having different impedances.
[0008] Some implementations may further include a source having an
output impedance at an output that is connected to the
impedance-transforming circuit, wherein the reduced VSWR is less
than or approximately equal to 2 and the bandwidth is greater than
800 MHz. Some implementations may further comprise a source
connected to the multicomponent network, wherein the source
comprises a gallium-nitride amplifier. Some implementations may
further comprise a source connected to the multicomponent network,
wherein the source is included in a wireless communication
device.
[0009] Some embodiments relate to methods of operating a device
having an impedance-transforming circuit. The
impedance-transforming circuit may include any of the foregoing
aspects and implementation. In some embodiments, a method for
transforming an impedance of a circuit element in a high-frequency
circuit may comprise acts of receiving a signal having a frequency
component between 500 MHz and 6 GHz at a multicomponent network;
providing the signal from the multicomponent network to at least
one transmission line; providing the signal from the at least one
transmission line to the circuit element, wherein the
multicomponent network is at least one-quarter wavelength from the
circuit element; and transforming, by the multicomponent network
and the at least one transmission line, the input impedance of the
circuit element to provide a reduced VSWR over a bandwidth.
[0010] In some aspects, a method for transforming an impedance may
comprise reflecting a voltage amount from the multicomponent
network less than or equal to one-half of an incident voltage over
a bandwidth greater than 800 MHz. In some implementations, a method
may comprise reflecting a voltage amount from the multicomponent
network less than or equal to one-half of an incident voltage over
a bandwidth that is between about 1 GHz and about 2 GHz. Some
method implementations may further include generating a signal that
is received at the multicomponent network with a gallium-nitride
amplifier. Some implementations may include using the
impedance-transforming circuit to transmit a signal wirelessly.
[0011] The foregoing apparatus and method embodiments may be
included in any suitable combination with aspects, features, and
acts described above or in further detail below. These and other
aspects, embodiments, and features of the present teachings can be
more fully understood from the following description in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The skilled artisan will understand that the figures,
described herein, are for illustration purposes only. It is to be
understood that in some instances various aspects of the
embodiments may be shown exaggerated or enlarged to facilitate an
understanding of the embodiments. The drawings are not necessarily
to scale, emphasis instead being placed upon illustrating the
principles of the teachings. In the drawings, like reference
characters generally refer to like features, functionally similar
and/or structurally similar elements throughout the various
figures. Where the drawings relate to microfabricated circuits,
only one device and/or circuit may be shown to simplify the
drawings. In practice, a large number of devices or circuits may be
fabricated in parallel across a large area of a substrate or entire
substrate. Additionally, a depicted device or circuit may be
integrated within a larger circuit.
[0013] When referring to the drawings in the following detailed
description, spatial references "top," "bottom," "upper," "lower,"
"vertical," "horizontal," "above," "below" and the like may be
used. Such references are used for teaching purposes, and are not
intended as absolute references for embodied devices. An embodied
device may be oriented spatially in any suitable manner that may be
different from the orientations shown in the drawings. The drawings
are not intended to limit the scope of the present teachings in any
way.
[0014] FIG. 1 depicts sections of transmission line that may be
used to transform an impedance of a load;
[0015] FIG. 2 illustrates return loss calculated for the circuit of
FIG. 1 as a function of frequency;
[0016] FIG. 3 is a Smith chart that plots impedance values along
the sections of transmission line of FIG. 1 and impedance seen by
the generator as a function of frequency;
[0017] FIG. 4 depicts circuitry for transforming an impedance of a
load, according to some embodiments;
[0018] FIG. 5 is a Smith chart that plots impedance values along
the circuit of FIG. 4 and impedance seen by the generator as a
function of frequency, according to some embodiments;
[0019] FIG. 6 illustrates return loss calculated for the circuit of
FIG. 4 as a function of frequency, according to some
embodiments;
[0020] FIG. 7A depicts an alternate pi network that may be used to
transform impedance of a load, according to some embodiments;
[0021] FIG. 7B depicts a T network that may be used to transform
impedance of a load, according to some embodiments;
[0022] FIG. 7C depicts an LCC network that may be used to transform
impedance of a load, according to some embodiments; and
[0023] FIG. 8 depicts a method of operating a device that includes
an impedance-transforming circuit, according to some
embodiments.
[0024] Features and advantages of the illustrated embodiments will
become more apparent from the detailed description set forth below
when taken in conjunction with the drawings.
DETAILED DESCRIPTION
[0025] Impedance matching can be important in the area of
high-frequency electronics associated with signal communications
(e.g., radio-frequency (RF) communications), radar, and microwave
applications. In such applications, impedance matching can reduce
signal noise, increase power efficiency of battery-operated devices
(e.g., mobile communication devices), improve gain and/or linearity
of amplifiers, and reduce power reflections in high-power circuits
that might otherwise damage or interfere with signal generators.
Some of these applications may utilize gallium-nitride-based
transistors arranged in amplifier circuits, or other high-frequency
transistors that operate at multi-gigaHertz frequencies. Impedance
matching may be employed in these amplifier circuits to increase
their gain-bandwidth product and improve drain efficiency among
other figures-of-merit for high-frequency transistors arranged in
amplifier circuits.
[0026] Conventionally, there are a wide variety of ways to
transform an impedance at a node in a circuit to a different
impedance that may be a better match to an element or source
connected to the node. Some impedance-matching techniques employ
lumped elements, microstrip transmission lines, ferrite
transformers, and other devices that are added to the node in close
proximity to the node (e.g., less than about one-quarter wavelength
of a signal or carrier wave from the node). These elements can
transform the impedance of the node over a frequency bandwidth that
is limited by a resonance characteristic or Q of the resulting
circuit. Conventional wisdom has been that any elements added for
impedance transformation purposes to a node should be added within
one-quarter wavelength of the node. Beyond this distance, it was
thought that impedance transformation would be ineffective.
[0027] The inventor has recognized and appreciated that lumped
circuit elements may be added in a network at distances beyond
one-quarter wavelength and surprisingly improve impedance matching
over bandwidths broader than those achieved with conventional
techniques. In some practical applications, it may not be easy to
access a node and add lumped elements within a quarter wavelength
of the node to transform an impedance of the node. According to
some embodiments described herein, a three-component network
comprising passive circuit elements may be added at the end of a
transmission line that is coupled to a node to transform an
impedance of the node, and the transmission line may extend beyond
one-quarter wavelength from the node. Some embodiments may contain
fewer or more passive circuit elements. Impedance matching with a
voltage-to-standing-wave ratio (VSWR) of less than 2:1 over
bandwidths greater than 800 MHz and as wide as approximately 3 GHz,
or even wider, may be achieved using the techniques described
herein.
[0028] The phrases "impedance matching," "match the impedance," or
"match impedances reasonably well" may be used to refer to
instances where the impedances of two connected circuit elements
are matched to an extent that a VSWR at a connection between the
two elements is equal to or less than approximately 2:1. Circuit
elements with matched impedances may have approximately equal or
identical impedance values in some cases, but, in other cases, need
not have identical impedance values.
[0029] Impedance-matching circuits and techniques described herein
may be useful for high-frequency devices and circuits such as those
used in RF communications, radar, microwave applications as well as
lower frequency amplifiers. In these applications, amplifiers
comprising gallium-nitride transistors may be used to provide
signal amplification at frequencies from about 30 MHz up to about 6
GHz, although the impedance-transforming networks are not limited
to only these applications, gallium-nitride transistors, and
frequencies. In some implementations, the amplifiers may be
integrated into a circuit (e.g., a printed circuit board (PCB) or a
pallet), and an impedance-transforming network may be integrated
onto the PCB or pallet. For example, an impedance-transforming
network may be connected to a transmission line that is connected
to an input and/or output of a high-frequency amplifier. In some
implementations, an impedance-matching circuit of the present
embodiments may be connected between an amplifier and an antenna in
a signal transmitter of a wireless communication device, and may be
used to transmit a signal wirelessly. In some cases, an
impedance-transforming network may improve the drain efficiency and
bandwidth performance of an amplifier to which it is connected.
Impedance-transforming networks may also be used in multi-chip
modules to match impedances of devices on one or more chips.
[0030] Impedance-transforming circuits of the present embodiments
may be included in various types of electronic circuits and circuit
assemblies. For example, an impedance-transforming circuit may be
included in co-fired ceramic assemblies, such as low-temperature
co-fired ceramic (LTCC) assemblies, according to some embodiments.
Such an assembly may include LTCC passive elements (e.g.,
capacitors, inductors) as part of an impedance-transforming
circuit. Other embodiments of an impedance-transforming circuit may
include, but are not limited to, silicon substrates and/or passive
components, gallium-arsenide substrates and/or passive components,
and gallium-nitride substrates and/or passive components. An
impedance-transforming circuit of the present embodiments may be
included in an active die (e.g., a microwave monolithic integrated
circuit--MMIC), or may be included on a separate die coupled to an
active die in a multi-die or multi-chip module.
[0031] An example of an impedance-transforming circuit 100 is
depicted in FIG. 1, which illustrates sections of transmission
lines 110, 120, 130, 140 connected between a load 150 and a source
102. One way to transform the impedance of a load 150 so that it
matches an output impedance of a source is to connect a customized
transmission line between the two circuit components. In some
embodiments, the load may be an antenna and have a low impedance,
whereas the source may comprise an RF amplifier and have an output
impedance of approximately 50 ohms. Other types of loads and
sources having different impedances from these values may be used
in other embodiments.
[0032] The transmission line sections may be formed as microstrip
transmission lines (e.g., formed as conductive strips on a printed
circuit board) which have different impedance characteristics. In
this example, the four transmission line sections 110, 120, 130,
140 may have four different impedance characteristics, and be
connected at plural connection points 115, 125, 135. According to
some embodiments, the sections of transmission line may be formed
on a PCB that is approximately 25 mils thick and has a dielectric
constant E.sub.r of approximately 10.2.
[0033] A numerical simulation was carried out to evaluate impedance
transformation along transmission line sections, such as those
depicted in FIG. 1. For the simulation, a first transmission line
section 110 comprised a copper microstrip line having a length
L.sub.1 of approximately 6.5 mm and a width of approximately 0.5
mm. The second transmission line section 120 comprised a copper
microstrip line having a length L.sub.2 of approximately 15.1 mm
and a width of approximately 1.5 mm. The third transmission line
section 130 comprised a copper microstrip line having a length
L.sub.3 of approximately 12.7 mm and a width of approximately 5.3
mm. The fourth transmission line section 140 comprised a copper
microstrip line having a length L.sub.4 of approximately 9.1 mm and
a width of approximately 14.5 mm. Examples of simulations tools
that may be used to analyze the circuit include, but are not
limited to, Advanced Design System (ADS) available from Keysight
EEsof EDA of Santa Rosa, Calif., and Microwave Office (MWO)
available from National Instruments of El Segundo, Calif. Some
simulations may be done using a version of SMITH32, previously
available from Motorola of Schaumburg, Ill.
[0034] Values of return loss were computed as a function of
frequency for the impedance-transforming structure shown in FIG. 1
and having the PCB characteristics and transmission line dimensions
described above. A graph of return loss for the structure is
plotted in FIG. 2, and shows a resonance behavior with a peak at
about 1.8 GHz. The return loss represents an amount of power
provided from the signal generator 102 to the load 150 divided by
an amount of power reflected back from the impedance-transforming
circuit comprised of transmission lines. A high value of return
loss indicates that the source 102 is better matched to the
impedance-transforming circuit. From the graph of return loss,
values of voltage-to-standing-wave-ratio can be computed. It is
found that a bandwidth for which the VSWR is less than
approximately 2:1 extends from approximately 1.28 GHz to
approximately 2.08 GHz, a bandwidth of approximately 800 MHz with a
center at approximately 1.7 GHz.
[0035] Impedance values for the impedance-transforming circuit 100
were also calculated, and are plotted on the Smith chart of FIG. 3.
In a first set of calculations, illustrated as the dotted curve
310, impedance values were computed along the transmission line
sections between the load 150 and the source 102. The solid dots
indicate the locations of the nodes 105, 115, 125, 135, 145. These
values were computed for a fixed frequency of approximately 1.8
GHz. From these calculations, it can be seen that the impedance
value starts from a low value at the left side of the Smith chart
(corresponding to the load impedance) and increases to a value of
approximately 50 ohms at the center of the Smith chart, which
provides a better impedance match to the signal generator 102. The
impedance values of dotted curve 310 proceed through an inductive
region of the Smith chart.
[0036] Also shown on the Smith chart in FIG. 3 are impedance values
calculated as a function of frequency for the
impedance-transforming circuit 100. These values are shown as the
solid line 320 in the drawing. This curve shows that the impedance
generally follows a spiral path from a low-frequency of 100 MHz at
the left side of the Smith chart to a high-frequency of 2200 MHz.
Near the resonance frequency, the impedance of the
impedance-transforming circuit nearly matches the impedance of the
source 102.
[0037] Although the impedance-transforming circuit 100 depicted in
FIG. 1 can provide impedance transformation and reasonable
impedance matching over a range of frequencies, the inventor has
recognized and appreciated that the addition of a lumped element
network at the end of the transmission line can improve the
bandwidth over which impedances can be matched, even if the lumped
element is more than one-quarter wavelength from the circuit
element for which impedance is to be transformed. An example of an
improved impedance-transforming circuit is depicted in FIG. 4.
According to some embodiments, an impedance-transforming circuit
400 may comprise two or more sections of transmission line T1, T2,
T3, T4 and a multicomponent impedance-matching network 405. The
sections of the transmission line may be different from each other
in some embodiments, or may be identical sections in other
embodiments. The sections of transmission line may be connected
electrically at nodes 412, 413, 414. The transmission line sections
may extend more than one-quarter wavelength beyond a node 411 at
which an impedance is to be transformed to a matching impedance at
a desired frequency.
[0038] A multicomponent network 405 may include passive components,
such as inductors, capacitors, resistors, diodes, and ferrite
transformers. According to some implementations, a multicomponent
network 405 may comprise a pi network (.pi. network) that includes
a first shunt capacitor C1 connected in parallel with a second
shunt capacitor C2 and an inductor L1 connected between the first
and second capacitors C1, C2. The inductor may be connected in
series with the transmission line sections. According to some
embodiments, a multicomponent network 405 may be located at a
distance from a load 150 or other element that is greater than
one-quarter wavelength of a frequency for which impedance matching
is desired. In some embodiments, the multicomponent network 405 may
be located between approximately 1/4 wavelength and approximately
3/4 wavelength from a load or other element for which impedance
matching is desired.
[0039] Numerical simulations were carried out for the
impedance-transforming circuit 400 of FIG. 4. For the simulations
the sections of the transmission line T1, T2, T3, T4 comprised
microstrip transmission lines. The first section T1 had a length of
approximately 12.3 millimeters and a width of approximately 14.6
millimeters. The second section T2 had a length of approximately
19.1 millimeters and a width of approximately 7.7 millimeters. The
third section T3 had a length of approximately 18.8 millimeters and
a width of approximately 3.2 millimeters. The fourth section T4 had
a length of approximately 5.4 millimeters and a width of
approximately 0.5 millimeters. The PCB had a thickness of
approximately 0.63 mm and a dielectric constant E.sub.r of
approximately 10.2. A capacitance of the first capacitor C1 was
approximately 2.7 pF and a capacitance of the second capacitor C2
was approximately 1.4 pF. The value of the inductor L1 was
approximately 2.6 nH. In some embodiments, a capacitance of the
first capacitor C1 may be between approximately 0.5 pF and
approximately 10 pF. In some embodiments, a capacitance of the
second capacitor C2 may be between approximately 0.5 pF and
approximately 5 pF. A value of the inductor L1 may be between
approximately 0.5 nH and approximately 10 nH.
[0040] Impedance values were computed for the
impedance-transforming circuit of FIG. 4, and are plotted in the
Smith chart of FIG. 5. In a first set of calculations, impedance
values were calculated at a fixed frequency of approximately 1.8
GHz along the impedance-transforming circuit 400, beginning at the
load and working toward the generator. These impedance values are
shown as the dashed line 510 in the Smith chart. The locations of
the nodes 411, 412, 413, 414, 415, 416, 417, 418 are indicated as
solid dots on the curve. The impedance values at the load end (low
impedance) begin on the left side of the Smith chart, and the
impedance increases to less than about 50 ohms. Unlike the case for
the four transmission line sections plotted in FIG. 3, the
impedance values along the impedance-transforming circuit 400
traverse a similar region of the Smith chart, but now oscillate
between inductive and capacitive impedances along the circuit.
[0041] Also plotted on the Smith chart, as solid line 520, are the
impedance values seen at the generator for the
impedance-transforming circuit 400 as a function of frequency. For
this calculation the frequency was stepped from approximately 100
MHz to 2.2 GHz in increments of approximately 19 MHz. The impedance
trajectory as a function of frequency begins at a low impedance
value toward the left side of the Smith chart and spirals in to a
value that reasonably well matches the impedance of the generator.
Also plotted in FIG. 5 is a circle 560 for which the magnitude of
the reflection coefficient is constant. According to some
embodiments, circle 560 represents a region for which the VSWR for
the impedance-transforming circuit 400 is less than or equal to
2.
[0042] In comparison with the Smith chart of FIG. 3, it can be seen
that the addition of the multicomponent network 405 tightens the
frequency response (spiral trajectory) of the
impedance-transforming circuit 400 over a range of high
frequencies. Although the impedance trajectory traverses a similar
impedance zone on the Smith chart to that of FIG. 3, the impedance
values at the higher frequencies stay within the reflection
coefficient circle 560 over a larger range of frequencies.
Therefore, the VSWR remains below 2 over a broader bandwidth than
can be achieved with the transmission-line impedance-transforming
circuit 100 of FIG. 1.
[0043] Also plotted in FIG. 5 are the Q=1 lines 550. The impedance
trajectory of the impedance-transforming circuit 400 stays within
the Q=1 line over a larger range of frequencies. This indicates
that the multicomponent network 405 helps maintain a low-Q value
for the impedance-transforming circuit. By extending a low-Q value
over a larger range of frequencies, it is possible to provide
better impedance matching over a broader bandwidth. In some
implementations, discrete transistors may have high-Q values and
high reactive impedances, which can limit the bandwidth of
conventional impedance-matching networks added to the transistor at
its input and/or output. According to some embodiments, a
multicomponent network 405 may be added to a transmission line
connected to the transistor, more than a quarter wavelength from
the transistor, and improve the bandwidth over which impedances are
reasonably well matched to within an acceptable level (e.g., a VSWR
less than about 2).
[0044] In some implementations, a multicomponent network 405 and at
least one transmission line may be used to transform a first
impedance of a downstream circuit element (e.g., a load) to match a
second predetermined impedance of an upstream circuit element
(e.g., a signal source). The multicomponent network and at least
one transmission line may be configured to operate at one or more
frequencies of at least 1 GHz, according to some embodiments. In
some embodiments, a predetermined impedance of an upstream circuit
element may be between approximately 25 ohms and 100 ohms. In some
cases, a predetermined impedance of an upstream circuit element may
be approximately 50 ohms or approximately 75 ohms. In some
implementations, the matching may further extend over a range of
frequencies, such that the transformed impedances provide a VSWR
less than approximately 2 between the source and
impedance-transforming circuit.
[0045] Return loss values were also computed for the
impedance-transforming circuit 400 of FIG. 4, and the results are
shown in FIG. 6. The plot shows several resonant peaks of lower
amplitude and broader width than was the case for the
impedance-transforming circuit 100 of FIG. 1. As a result, the
bandwidth over which the impedance is reasonably well matched to
the source extends from approximately 750 MHz to over 2.2 GHz, over
a bandwidth of approximately 1.5 GHz. The bandwidth over which the
impedance is reasonable well matched has a center frequency at
approximately 1.5 GHz. The bandwidth over which impedances are
reasonably well matched is approximately .+-.50% of the center
frequency. The addition of the multicomponent network 405 increases
the impedance-matched bandwidth (compare FIG. 2) by more than 80%
compared to a transmission line impedance-transforming circuit 100,
as in FIG. 1.
[0046] The impedance-matching techniques may be used for other or
specific frequency ranges and other impedance values. For example,
the lengths and impedance of transmission line sections and values
of capacitive and inductive components in a multicomponent network
may be selected to match impedances reasonable well over broad
bandwidths at frequencies as low as 30 MHz and as high as 6 GHz.
Impedances that are matched reasonable well may provide a VSWR less
than or approximately equal to 2. In some implementations,
transmission line sections and values of capacitive and inductive
components may be selected to match impedances reasonably well over
a bandwidth centered at approximately 750 MHz. In some
implementations, transmission line sections and values of
capacitive and inductive components may be selected to match
impedances reasonably well over a bandwidth centered at
approximately 2.2 GHz. In some embodiments, transmission line
sections and values of capacitive and inductive components may be
selected to match impedances reasonably well over a bandwidth
centered at approximately 2.7 GHz. In some embodiments,
transmission line sections and values of capacitive and inductive
components may be selected to match impedances reasonably well over
a bandwidth centered at approximately 3.8 GHz. For each of these
center frequencies, the bandwidth over which the impedance provides
a VSWR less than or about equal to 2 may be between approximately
.+-.25% and approximately .+-.50% of the center frequency.
[0047] Although FIG. 4 shows one embodiment of a multicomponent
network 405 that can be used in an impedance-transforming circuit
400, other networks are contemplated. Some multicomponent networks
may include fewer or more elements than are depicted in FIG. 4. For
example some multicomponent networks may include only an inductor
and a capacitor. In some embodiments, the multicomponent network
405 may include additional inductors and capacitors and other
elements so that the total number of components may be between 3
and 10.
[0048] FIG. 7A depicts an alternative embodiment of a
multicomponent network 710, which may be used in an
impedance-transforming circuit. The embodiment shown in
[0049] FIG. 7A may be referred to as a high-pass .pi. network. This
network may include a first inductor L1 and a second inductor L2
connected in a parallel shunt arrangement. The network may further
include a capacitor C1 connected between ends of the first and
second inductors and in series with a transmission line (not
shown). In some embodiments, a capacitance of the first capacitor
C1 may be between approximately 0.5 pF and approximately 10 pF. A
value of the first inductor L1 may be between approximately 0.5 nH
and approximately 10 nH. A value of the second inductor L2 may be
between approximately 0.5 nH and approximately 10 nH.
[0050] FIG. 7B depicts an alternative embodiment of a
multicomponent network 720, which may be used in an
impedance-transforming circuit. The embodiment shown in FIG. 7B may
be referred to as a T network. According to some embodiments, a T
network may include a first inductor L1 connected in series with a
second inductor L2. The two inductors may be connected in series
with a transmission line (not shown). The network may further
include a shunt capacitor C1 connected to a node between the first
inductor and second inductor, and further connected to a ground
plane or ground conductor. In some embodiments, a capacitance of
the shunt capacitor C1 may be between approximately 0.5 pF and
approximately 10 pF. A value of the first inductor L1 may be
between approximately 0.5 nH and approximately 10 nH. A value of
the second inductor L2 may be between approximately 0.5 nH and
approximately 10 nH.
[0051] FIG. 7C depicts another embodiment of the multicomponent
network 730, which may be used in an impedance-transforming
circuit. The embodiment shown in FIG. 7C may be referred to as an
LCC network. An LCC network 730 may include a first inductor L1
connected in series with a first capacitor C1. The first inductor
and first capacitor may be connected in series with a transmission
line (not shown). The network may further include a second
capacitor C2 connected in a shunt arrangement to a node between the
first inductor and the first capacitor and further connected to a
ground conductor or ground plane. In some embodiments, a
capacitance of the first capacitor C1 may be between approximately
0.5 pF and approximately 10 pF, and a value of the second capacitor
C2 may be between approximately 0.5 pF and approximately 10 pF. A
value of the first inductor L1 may be between approximately 0.5 nH
and approximately 10 nH.
[0052] Methods of operating devices with impedance-transforming
circuits integrated in the devices are also contemplated by the
inventor. According to some embodiments, a method 800 depicted in
FIG. 8 may comprise transforming an impedance of an element in a
high-frequency circuit that is configured to operate at a frequency
between 500 MHz and 6 GHz. A method may comprise acts of receiving
a signal (act 810) having a frequency component between 500 MHz and
6 GHz at a multicomponent network of an impedance-transforming
circuit. A method may further include providing the signal (act
820) from the multicomponent network to at least one transmission
line, and providing the signal (act 830) from the at least one
transmission line to a circuit element. The received signal may be
from any suitable signal source (e.g., a signal generator) that is
connected to the multicomponent network. The multicomponent network
and at least one transmission line may be connected to the circuit
element, for which impedance matching to the source is desired over
a range of frequencies. In various embodiments of the method 800,
the multicomponent network may be at least one-quarter wavelength
from the circuit element.
CONCLUSION
[0053] The terms "approximately" and "about" may be used to mean
within .+-.20% of a target value in some embodiments, within
.+-.10% of a target value in some embodiments, within .+-.5% of a
target value in some embodiments, and yet within .+-.2% of a target
value in some embodiments. The terms "approximately" and "about"
may include the target value.
[0054] The technology described herein may be embodied as a method,
of which at least some acts have been described. The acts performed
as part of the method may be ordered in any suitable way.
Accordingly, embodiments may be constructed in which acts are
performed in an order different than described, which may include
performing some acts simultaneously, even though described as
sequential acts in illustrative embodiments. Additionally, a method
may include more acts than those described, in some embodiments,
and fewer acts than those described in other embodiments.
[0055] Having thus described at least one illustrative embodiment
of the invention, various alterations, modifications, and
improvements will readily occur to those skilled in the art. Such
alterations, modifications, and improvements are intended to be
within the spirit and scope of the invention. Accordingly, the
foregoing description is by way of example only and is not intended
as limiting. The invention is limited only as defined in the
following claims and the equivalents thereto.
* * * * *