U.S. patent application number 13/609923 was filed with the patent office on 2013-01-03 for circuit for impedance matching.
This patent application is currently assigned to EPCOS AG. Invention is credited to Patrick Scheele, Matthias Schmidt.
Application Number | 20130005288 13/609923 |
Document ID | / |
Family ID | 41131671 |
Filed Date | 2013-01-03 |
United States Patent
Application |
20130005288 |
Kind Code |
A1 |
Scheele; Patrick ; et
al. |
January 3, 2013 |
Circuit for Impedance Matching
Abstract
A circuit provided for impedance matching includes an input, an
output and four impedance elements arranged between them. In this
case, two of the impedance elements are connected in series in a
main path and form a T configuration with a third component. In
addition, a fourth component is connected in parallel with the main
path of the circuit. By way of example, the components arranged in
the main path are variable capacitances and the further components
are inductances.
Inventors: |
Scheele; Patrick; (Ulm,
DE) ; Schmidt; Matthias; (Muenchen, DE) |
Assignee: |
EPCOS AG
Muenchen
DE
|
Family ID: |
41131671 |
Appl. No.: |
13/609923 |
Filed: |
September 11, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12950024 |
Nov 19, 2010 |
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13609923 |
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PCT/EP2009/056092 |
May 19, 2009 |
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12950024 |
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Current U.S.
Class: |
455/334 ;
333/32 |
Current CPC
Class: |
H03H 7/38 20130101; H03H
2007/386 20130101; H04B 1/0458 20130101 |
Class at
Publication: |
455/334 ;
333/32 |
International
Class: |
H03H 7/38 20060101
H03H007/38; H04B 1/16 20060101 H04B001/16 |
Foreign Application Data
Date |
Code |
Application Number |
May 21, 2008 |
DE |
10 2008 024 482.1 |
Claims
1. A circuit for impedance matching comprising: an input; an
output; a first component that has an effective impedance; a second
component that has an effective impedance and series-coupled with
the first component in a main path between the input and the
output; a third component that has an effective impedance and
forming a T configuration with the first component and the second
component; and a fourth component that has an effective impedance
and coupled in parallel with the main path, and wherein the first
component and/or the second component includes an adjustable
capacitance value to flexibly match an impedance connected to the
output with an impedance connected to the input.
2. The circuit for impedance matching as claimed in claim 1,
wherein the adjustable capacitance value is adjustable to at least
two different capacitance values between which it is possible to
select and switch to and from during operation of the circuit.
3. The circuit for impedance matching as claimed in claim 1,
wherein the first component and the second component both include
the adjustable capacitance value.
4. The circuit for impedance matching as claimed in claim 1,
wherein the adjustable capacitance value for the first component
and the second component have identical ranges.
5. The circuit for impedance matching as claimed in claim 1,
wherein the first component comprises an inductance, a capacitance
or a line, the second component comprises an inductance, a
capacitance or a line, the third component comprises an inductance,
a capacitance or a line, and the fourth component comprises an
inductance, a capacitance or a line.
6. The circuit for impedance matching as claimed in claim 1,
wherein the first and second components comprise capacitances and
wherein the third and fourth components comprise inductances.
7. A circuit arrangement for impedance matching comprising: an
input; an output; a first circuit that includes first, second,
third and fourth components that each have an effective impedance,
wherein the first and second components are coupled in series in a
first main path between the input and the output and form a T
configuration with the third component, and the fourth component is
coupled in parallel with the first main path, wherein the first
component and/or the second component includes an adjustable
capacitance value to flexibly match an impedance connected to the
output with an impedance connected to the input; and at least a
second circuit coupled to the first circuit and including fifth,
sixth, seventh and eighth components that each have an effective
impedance, wherein the fifth and sixth components are coupled in
series in a second main path between the input and the output and
form a T configuration with the seventh component, and the eighth
component coupled is coupled in parallel with the second main path,
wherein the fifth component and/or the sixth component includes an
adjustable capacitance value to flexibly match an impedance
connected to the output with an impedance connected to the
input.
8. The circuit arrangement for impedance matching as claimed in
claim 7,wherein the adjustable capacitance value of the first
component and/or the second component is adjustable to at least two
different capacitance values between which it is possible to select
and switch to and from during operation of the circuit.
9. The circuit arrangement for impedance matching as claimed in
claim 8, wherein the adjustable capacitance value of the fifth
component and/or the sixth component is adjustable to at least two
different capacitance values between which it is possible to select
and switch to and from during operation of the circuit.
10. The circuit arrangement for impedance matching as claimed in
claim 7, wherein the first component and the second component both
include the adjustable capacitance value, and the fifth component
and the sixth component both include the adjustable capacitance
value.
11. The circuit arrangement for impedance matching as claimed in
claim 7, wherein the adjustable capacitance value for the first
component and the second component have identical ranges, and the
adjustable capacitance value for the fifth component and the sixth
component have identical ranges.
12. The circuit arrangement for impedance matching as claimed in
claim 7, wherein the first circuit is suitable for impedance
matching in a first frequency band and is a passage element for a
second frequency band.
13. The circuit arrangement for impedance matching as claimed in
claim 12, wherein the second circuit is suitable for impedance
matching in the second frequency band and is a passage element for
the first frequency band.
14. The circuit arrangement for impedance matching as claimed in
claim 7, wherein the first and second circuits are connected in
series.
15. The circuit arrangement for impedance matching as claimed in
claim 7, wherein the first circuit and the second circuit are
connected in parallel with one another.
16. The circuit arrangement for impedance matching as claimed in
claim 15, wherein the first circuit is suitable for impedance
matching in a first frequency band and is a band rejection filter
for a second frequency band, and wherein the second circuit is
suitable for impedance matching in the second frequency band and is
a band rejection filter for the first frequency band.
17. An electrical circuit comprising: an input; an output; a first
component that has an effective impedance; a second component that
has an effective impedance and series-coupled with the first
component in a main path between the input and the output; a third
component that has an effective impedance and forming a T
configuration with the first component and the second component; a
fourth component that has an effective impedance and coupled in
parallel with the main path, wherein the first component and/or the
second component includes an adjustable capacitance value to
flexibly match an impedance connected to the output with an
impedance connected to the input; a generator coupled to the input;
and a load coupled to the output.
18. The electrical circuit as claimed in claim 17, wherein the
adjustable capacitance value is adjustable to at least two
different capacitance values between which it is possible to select
and switch to and from during operation of the electrical
circuit.
19. The electrical circuit as claimed in claim 17, wherein the
first component and the second component both include the
adjustable capacitance value.
20. The electrical circuit as claimed in claim 17, wherein the
adjustable capacitance value for the first component and the second
component have identical ranges.
21. The electrical circuit as claimed in claim 17, wherein the
first, second, third and fourth components are suitable for
impedance matching in a first frequency band and are a passage
element for a second frequency band.
22. The electrical circuit as claimed in claim 21, further
comprising: a fifth component that has an effective impedance; a
sixth component that has an effective impedance, wherein the fifth
and sixth components are coupled in series in a second main path
between the input and the output; a seventh component that has an
effective impedance, wherein fifth and sixth components form a T
configuration with the seventh component; and an eighth component
that has an effective impedance, the eighth component coupled in
parallel with the second main path, wherein the fifth, sixth,
seventh and eighth components are suitable for impedance matching
in the second frequency band and is a passage element for the first
frequency band.
23. The electrical circuit as claimed in claim 21, wherein at least
one of the first component and/or the second component is a
capacitance with an adjustable capacitance value, and wherein
capacitance values of the first and second components are chosen
such that in the first frequency band an input impedance of the
electrical circuit and the load matches an impedance of the
generator.
24. The electrical circuit as claimed in claim 23, wherein in the
first frequency band an output reflection factor (R.sub.OUT) is
less than -10 dB.
25. The electrical circuit as claimed in claim 23, wherein
capacitance values of the first and second components are chosen
such that in two frequency bands an input impedance matches an
impedance of the generator.
26. The electrical circuit as claimed in claim 23, wherein the
electrical circuit is part of a mobile radio and wherein the
generator comprises an output of a power amplifier and the load
comprises an antenna.
27. The electrical circuit as claimed in claim 23, wherein the
electrical circuit is part of a mobile radio and wherein the
generator comprises an antenna and the load comprises an input of a
receiver.
Description
[0001] This application is a continuation of application Ser. No.
12/950,024, filed Nov. 19, 2010, which is a continuation of
International Application No. PCT/EP2009/056092, filed May 19,
2009, which designated the United States and was not published in
English, and which claims priority to German Application No. 10
2008 024 482.1, filed May 21, 2008, all of which applications are
incorporated herein by reference.
BACKGROUND
[0002] The impedance of an antenna is dependent on the spatial
surroundings thereof. This impedance is therefore subject to severe
fluctuations, particularly in the case of mobile radios. However,
the radiated real power of a mobile radio is heavily dependent on
the extent to which the impedance of the antenna matches the
impedances of further electric components connected thereto, such
as a power amplifier. In addition, the impedance of electric
components is also dependent on the frequency of a transmitted
signal.
[0003] In the mobile radio sector, a plurality of frequency bands
is used for signal transmission. To attain a maximum radiated real
power, it is necessary to match the impedances in a plurality of
frequency bands which are used.
[0004] U.S. Pat. No. 7,202,747 B2 describes a circuit for impedance
matching.
SUMMARY
[0005] In one aspect, the present invention specifies a circuit
that can be used to match the impedance of a generator as flexibly
as possible to the impedance of a load.
[0006] Embodiments of the invention specify a circuit for impedance
matching. The circuit has an input, which can be connected to a
generator, for example, and an output, which can be connected to a
load, for example. In a mobile radio, this may correspond to a
power amplifier as a generator and to an antenna as a load.
However, the antenna can also be used as a generator and the load
can correspond to the input of a receiver.
[0007] The circuit has a plurality of components that can each be
described by an effective impedance. In this case, each of the
components may be made up of one or more electric units. The
interaction of the impedances of the electric units results in an
effective impedance for the component. Such a component is
subsequently also called an impedance element.
[0008] A main path between the input and the output of the circuit
contains two impedance elements connected in series with one
another. A third impedance element is connected thereto such that a
T configuration is obtained. In addition, the circuit comprises a
further impedance element which is connected in parallel with the
main path of the circuit.
[0009] This configuration allows a flexible layout for a circuit
for impedance matching and optimization and, in particular,
expansion of the usable frequency range.
[0010] Preferably, each of the impedance elements is chosen
independently of the other impedance elements from the set of
inductances, capacitances and lines or is made up of a plurality of
such electric units.
[0011] In one preferred embodiment, the impedance elements arranged
in the main path are embodied as capacitances and the third and
further impedance elements are embodied as inductances.
[0012] Preferably, at least one impedance element is adjustable. By
way of example, at least one of the capacitances can have the
capacitance value adjusted, In this case, adjustability is intended
to mean at least two different capacitance values between which it
is possible to select and switch to and fro during operation of the
circuit. Advantageously, the adjustability covers a multiplicity of
possible capacitance values. In one embodiment, the capacitance
values of both capacitances are variable steplessly in a particular
adjustment range.
[0013] Variable capacitances of this kind can be used to match the
impedance of a load flexibly to the impedance of a generator. By
way of example, it is thus possible to optimize the real power
within the largest possible tuning range for the load impedances.
In particular, it is possible for alteration of the impedance of
the load or of the generator to involve attainment of tuning for
the impedances without needing to connect or disconnect individual
circuit elements. In this case, a particularly inexpensive and
space-saving circuit for impedance matching may result.
[0014] The tuning range for the circuit can be optimized by means
of suitable selection of the capacitances and of the inductances.
In particular, it is determined by the magnitude of the adjustment
ranges for the capacitances and by the fineness of the stepping
between the adjustable capacitance values. A variable capacitance
may be in the form of a switched capacitor in which the capacitance
values can be adjusted, for example, using binary stepping, between
a maximum value and a minimum value. An example of a switched
capacitance is a MEMS capacitance. In a further embodiment, a
capacitance is used in which the capacitance value can be varied
steplessly within an adjustment range. By way of example, this is
possible in the case of a varactor based on semiconductors or
ferroelectrics, which can be used in a circuit as a steplessly
variable capacitance.
[0015] In one embodiment, the two capacitances of the main path
have identical adjustment ranges. The use of identical units
reduces the complexity of the circuit and the costs of
production.
[0016] Alternatively, the capacitances may have different
adjustment ranges.
[0017] In one preferred embodiment, the capacitances and the
inductances are chosen such that the impedances can be matched
within a plurality of frequency bands simultaneously. This is
advantageous particularly in the case of mobile radios, in which a
plurality of frequency bands are used.
[0018] In addition, a circuit arrangement is specified which
comprises a plurality of circuits for impedance matching.
[0019] In one embodiment, the circuit arrangement has at least two
circuits for impedance matching which are connected in series with
one another.
[0020] This is advantageous particularly if the impedance needs to
be matched within a plurality of, e.g., two frequency bands. In the
case of two frequency bands, the circuit arrangement comprises two
circuits for impedance matching, for example, which are connected
in series with one another. In this context, a first circuit is
dimensioned such that it can be used for matching the impedance in
the first frequency band. One suitable instance of circuit
dimensioning involves the circuit prompting no significant change
in the impedances for a second frequency band. This circuit is
therefore a passage element for the second frequency band. A
suitably dimensioned second circuit can be used to attain matching
impedance in the second frequency band. This further circuit is
designed such that it has no significant effect on the impedance
matching in the first frequency band and is therefore a passage
element for the first frequency band.
[0021] In a further embodiment, the circuit arrangement has at
least two circuits for impedance matching which are connected in
parallel with one another.
[0022] Such a circuit arrangement can likewise be used for the
simultaneous matching of the impedance in two frequency ranges. By
way of example, the impedance elements of the first circuit are
chosen such that it can be used for matching the impedance in a
first frequency band but is a band rejection filter for the second
frequency band. To this end, the input and output impedances of the
circuit are chosen such that their real parts are very much larger
than the real parts of the generator and load impedances. A second
circuit connected in parallel therewith is dimensioned such that it
is a band rejection filter for the first frequency band and can be
used for impedance matching for the second frequency band.
[0023] Such a circuit arrangement can therefore be used to attain
simultaneous impedance matching within a plurality of frequency
bands.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The text below explains the specified circuits for impedance
matching and the advantageous embodiments thereof with reference to
schematic figures, which are not to scale, in which:
[0025] FIG. 1 schematically shows the arrangement of a circuit for
impedance matching between a generator and a load;
[0026] FIG. 2 shows a circuit for impedance matching with four
impedance elements;
[0027] FIG. 3 shows a circuit for impedance matching with two
capacitances and two inductances;
[0028] FIG. 4A uses a Smith diagram and a Cartesian coordinate
system to show the optimum load impedances for a circuit for
impedance matching as shown in FIG. 3 for a first frequency;
[0029] FIG. 4B uses a Smith diagram and a Cartesian coordinate
system to show the optimum load impedances for a circuit for
impedance matching as shown in FIG. 3 for a second frequency;
[0030] FIGS. 5A and 5B use a Smith diagram and a Cartesian
coordinate system to show the optimum load impedances for a circuit
comprising a T configuration for the frequencies shown in FIGS. 4A
and 4B;
[0031] FIGS. 6A and 6B use a Smith diagram and a Cartesian
coordinate system to show the optimum load impedances for a further
circuit for impedance matching as shown in FIG. 3 for two
frequencies;
[0032] FIGS. 7A and 7B use a Smith diagram and a Cartesian
coordinate system to show the optimum load impedances for a further
circuit for impedance matching as shown in FIG. 3 for two
frequencies; and
[0033] FIGS. 8A to 8G show the optimum load impedances for a
circuit for impedance matching as shown in FIG. 3 for various
frequencies.
[0034] The following list of reference symbols may be used in
conjunction with the drawings:
[0035] A Circuit for impedance matching
[0036] IN Input
[0037] OUT Output
[0038] Z1, Z2, Z3, Z4 Impedance elements
[0039] L1, L2 Inductances
[0040] C1, C2 Capacitances
[0041] G Generator
[0042] L Load
[0043] Z.sub.G Generator impedance
[0044] Z.sub.L Load impedance
[0045] Z.sub.IN Input impedance
[0046] Z.sub.OUT Output impedance
[0047] R.sub.IN Input reflection factor
[0048] R.sub.OUT Output reflection factor
[0049] VSWR Voltage Standing Wave Ratio
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0050] FIG. 1 schematically shows a generator G which is connected
to a load L via a circuit for impedance matching A. The circuit for
impedance matching A is also called a matching network. In a mobile
radio, the generator G corresponds to the output of a power
amplifier and the load L corresponds to an antenna, for example.
The generator G delivers an AC voltage u.sub.G and can be described
by the complex generator impedance Z.sub.G. The load L is described
by its complex load impedance Z.sub.L. The generator outputs a
first real power P.sub.1 to the matching network via the input IN.
The matching network outputs a second real power P.sub.2 to load L
via the output OUT. The circuit for impedance matching is intended
to be used to maximize the real power P.sub.2 which is output to
the load and hence to minimize the reflected power.
[0051] The reflected power can be described by an input reflection
factor R.sub.IN and an output reflection factor R.sub.OUT. On the
generator side, there is a whole circuit with the input impedance
Z.sub.IN and a normalized input reflection factor R.sub.IN. In this
case, the input reflection factor R.sub.IN is normalized to the
generator impedance Z.sub.G. On the load side, there is accordingly
an output impedance Z.sub.OUT and a whole circuit with an output
reflection factor R.sub.OUT. In this case, the output reflection
factor R.sub.OUT is usually based on the output impedance
Z.sub.OUT. The reflection factor R.sub.IN is defined as
R.sub.IN=(Z.sub.IN-Z.sub.G*)/(Z.sub.IN+Z.sub.G). Similarly, the
output reflection factor is defined as
R.sub.OUT=(Z.sub.OUT-Z.sub.L*)/(Z.sub.OUT+Z.sub.L).
[0052] In the case of an ideal, lossless matching network A, the
conditions to be satisfied simultaneously for reflectionless
matching of the input and output are Z.sub.IN (A, Z.sub.L)=Z.sub.G*
and Z.sub.OUT (A, Z.sub.G)=Z.sub.L*. In this case, the generator G
outputs its maximum possible real power P.sub.1 to the matching
network, which in turn output the maximum possible real power
P.sub.2 to the load. An ideal, lossless matching network of this
kind is technical infeasible, however.
[0053] In the case of a not completely lossless matching network,
only one of the two conditions can be satisfied. This means that
either reflectionless matching of the impedance between the
generator and the input of the matching network or reflectionless
matching between the output of the matching network and the load is
feasible.
[0054] To ascertain the tuning range for a matching network A, it
is possible to require reflectionless matching at the input of the
matching network, for example. For the purpose of calculation, it
is assumed that the generator impedance Z.sub.G and hence also the
input impedance Z.sub.IN are constant. These can be used to
ascertain those load impedances for which reflectionless matching
between the generator and the matching network is fulfilled, i.e.,
for which R.sub.IN=0 is true. These load impedances are
subsequently also called optimum load impedances Z.sub.L, OPT.
[0055] Alternatively, reflectionless matching at the output of the
matching network can be required. In this case, it is assumed for
the calculation of the tuning range that the load impedance Z.sub.L
and hence the output impedance Z.sub.OUT are constant. These can be
used to ascertain optimum generator impedances, which result in
reflectionless matching between the output of the matching network
and the load, i.e., in R.sub.OUT=0.
[0056] FIG. 2 shows a circuit for impedance matching A, in which an
input IN and an output OUT have two impedance elements Z1 and Z2
connected in series between them in a main path. These impedance
elements form a T configuration together with a third impedance
element Z3. A fourth impedance element Z4 is connected in parallel
with the main path between the input IN and the output OUT.
[0057] By way of example, the impedance elements Z1, Z2, Z3, Z4 are
capacitances, inductances or lines. Each impedance element may also
be made up of a plurality of such elements which can be described
by an effective total impedance.
[0058] FIG. 3 shows a circuit for impedance matching A in which the
impedance elements Z1, Z2 connected in series in the main path are
embodied as capacitances C1, C2. The third and further impedance
elements are inductances L1 and L2.
[0059] In one advantageous embodiment, the capacitances C1 and C2
are elements with adjustable capacitance values. The use of
variable impedance elements allows the properties of the matching
network A and particularly the tuning range thereof to be
altered.
[0060] By way of example, the input of the matching network A has a
generator with a generator impedance Z.sub.G=50.OMEGA. applied to
it. Complex generator impedances are also possible. The output has
a load with a load impedance Z.sub.L applied to it, for example.
The tuning range of such a matching network A is obtained, by way
of example, from the requirement of reflectionless matching at the
input, i.e., the following shall apply: Z.sub.IN*=Z.sub.G=50.OMEGA.
and R.sub.IN=0.
[0061] FIGS. 4A, 4B, 6A, 6B, 7A, 7B and 8A-8G have optimum load
impedances Z.sub.L, OPT, at which reflectionless matching appears
at the input, plotted for differently dimensioned matching networks
as shown in FIG. 3. For comparison therewith, FIGS. 5A and 5B have
optimum load impedances Z.sub.L, OPT plotted which arise for a
circuit which only comprises a T configuration without a further
parallel impedance element.
[0062] In FIGS. 4A to 8G, the optimum load impedances Z.sub.L, OPT
are respectively plotted in a Smith diagram and in a Cartesian
coordinate system. From the presentation of an optimum load
impedance Z.sub.L, OPT in the Smith diagram, it is possible to
ascertain the associated reflection factor and the standing wave
ratio VSWR (Voltage Standing Wave Ratio). In this case, the optimum
load impedances Z.sub.L, OPT are respectively normalized to a
reference impedance of 50.OMEGA., which may correspond to the
generator impedance Z.sub.G, for example. In a Cartesian coordinate
system, the imaginary part I(Z.sub.L, OPT) of an optimum load
impedance Z.sub.L, OPT is plotted against the real part R(Z.sub.L,
OPT) thereof.
[0063] FIGS. 4A and 4B are based on a circuit for impedance
matching as shown in FIG. 3, wherein the capacitances C1 and C2
have an adjustment range of between 0.125 pF and 2 pF. The
capacitance values have each been adjusted in sixteen steps in this
range. The inductance L1 has an inductance value of 4.9 nH and the
inductance L2 has an inductance value of 12.3 nH.
[0064] Optimum load impedances Z.sub.L, OPT have been ascertained
for two frequency bands of the mobile radio range. The calculations
have respectively been based on the center frequency of the uplink
range.
[0065] In FIG. 4A, optimum load impedances Z.sub.L, OPT have been
ascertained for UMTS band I, in which the center frequency is 1950
MHz. In this case, a broad distribution for the optimum load
impedances and hence a large matchable impedance range are
obtained.
[0066] In FIG. 4B, optimum load impedances Z.sub.L, OPT have been
ascertained for the GSM 900 frequency band, in which the center
frequency is 897.5 MHz. The ratio of the center frequencies of the
UMTS-band and of the GSM 900 band is 2.17. As shown by FIG. 4B,
impedances around 50.OMEGA. are easily matched in the GSM 900 band.
The matching network can also be used as a passage element for this
frequency band without impedance matching.
[0067] FIGS. 5A and 5B have the optimum load impedances Z.sub.L,
OPT plotted which are obtained for a circuit with a T
configuration, i.e., without the inductance L2. In this case, the
capacitances C1 and C2 are designed like the capacitances shown in
FIGS. 4A and 4B and are varied in the same range. The inductance L1
has an inductance value of 7.35 nH.
[0068] In FIG. 5A, the optimum load impedances Z.sub.L, OPT are
again plotted for the center frequency of UMTS band I. As can be
seen from the presentation in the Cartesian coordinate system, the
present choice of inductance L1 allows a large tuning range to be
attained in this case too.
[0069] FIG. 5B has the optimum load impedances plotted for the
center frequency of the GMS 900 band. In this case, generator
impedances around 50.OMEGA. can no longer be matched in
reflectionless fashion. Therefore, this matching network cannot be
used as a passage element in this frequency range.
[0070] FIGS. 6A and 6B have optimum load impedances plotted for the
frequency bands GSM 900 and GSM 1800. The capacitances C1 and C2
and the inductances L1 and L2 are chosen such that the largest
possible tuning range is obtained in both frequency bands. The
capacitances C1 and C2 have been adjusted in sixteen steps between
0.125 pF and 2 pF. The inductance L1 has an inductance value of 5.5
nH and the inductance L2 has an inductance value of 10.9 nH.
[0071] The center frequency in the uplink range is 1747.5 MHz for
the GSM 1800 band and 897.5 MHz for the GSM 900 band. This gives a
ratio for the center frequencies of 1.95.
[0072] FIG. 6A has the optimum load impedances Z.sub.L, OPT plotted
for the GSM 1800 band. As can be seen from the presentation in the
Cartesian coordinate system, a large matchable impedance range is
obtained.
[0073] FIG. 6B has the optimum load impedances Z.sub.L, OPT plotted
for the center frequency of the GSM 900 band. With this circuit
dimensioning, generator impedances around 50.OMEGA. are easily
matched. Alternatively, this matching network can be used as a
passage element in the 897.5 MHZ range without impedance
transformation.
[0074] The subsequent Smith diagrams show circles with a constant
VSWR. In each case, the VSWR=2, VSWR=4 and VSWR=8 circles are
shown. These circles have also been transferred to the Cartesian
coordinate system.
[0075] FIGS. 7A and 7B have optimum load impedances Z.sub.L, OPT
plotted for the frequency bands GSM 900 and GSM 1800. in this case,
the basis is a circuit for impedance matching as shown in FIG. 3,
wherein the capacitances C1 and C2 have different adjustment
ranges. The capacitance C1 can be adjusted in the range from 0.176
pF to 2.82 pF and the capacitance C2 can be adjusted in the range
from 0.125 pF to 2 pF. Both capacitances can be varied in sixteen
steps. The inductance L1 has a value of 6.8 nH and the inductance
L2 has a value of 13.7 nH.
[0076] FIG. 7A has the load impedances plotted for the center
frequency of the GSM 1800 band, which is 1747.5 MHz. It can be seen
that in this case no reflectionless matching to 50 .OMEGA. is
possible. The reason for this is that the capacitances can only be
switched in steps. However, there are two optimum load impedances
within the VSWR=2 circle, which results in matching with a
reflection factor <-10 dB. Within the VSWR=8 circle, a large
tuning range is obtained, however. The use of capacitances with
finer stepping of the adjustable capacitance values allows the
tuning range to be improved further.
[0077] FIG. 7B has the optimum load impedances plotted for the
center frequency of the GSM 900 band. It is clear from the
presentation in the Cartesian coordinate system that the matchable
impedance range of this circuit is significantly increased in
comparison with the circuit on which FIG. 6B is based. In
particular, the impedances are largely covered in the VSWR=4
circle.
[0078] FIGS. 8A to 8G show the broadband properties of this
matching network.
[0079] FIG. 8A has optimum load impedances plotted for a frequency
of 824 MHz. This corresponds to the lower frequency limit of the
GSM 850 uplink band and to the lowest operating frequency of UMTS
bands I to X.
[0080] FIG. 8B has optimum load impedances plotted for a frequency
of 880 MHz. This frequency is the lower frequency limit of the GSM
900 uplink band.
[0081] FIG. 8C has optimum load impedances plotted for a frequency
of 960 MHz. This corresponds to the upper frequency limit of the
GSM 900 downlink band.
[0082] As can be seen from FIGS. 8A to 8C, the matching network can
be used in the whole frequency range from 824 to 960 MHz for
impedance transformation to a generator impedance of 50.OMEGA..
Similarly, this matching network can also be used as a passage
element in this case. If the generator impedances differ from
50.OMEGA., an optimum tuning range can be attained by virtue of
another choice of capacitances C1 and C2 and of inductances L1 and
L2.
[0083] FIG. 8D has optimum load impedances plotted for a frequency
of 1710 MHz. This corresponds to a lower frequency limit of the GSM
1800 uplink band.
[0084] FIG. 8E has optimum load impedances plotted for a frequency
of 1880 MHz. This corresponds to the upper frequency limit of the
GSM 1800 downlink band and is at the same time the center frequency
of the GSM 1900 uplink band.
[0085] FIG. 8F has optimum load impedances plotted for a frequency
of 1980 MHz. This corresponds to the upper frequency limit of the
UMTS I uplink band and is 10 MHz below the upper frequency limit of
the GSM 1900 downlink band.
[0086] FIG. 8G has optimum load impedances plotted for a frequency
of 2170 MHz. This corresponds to the upper frequency limit of the
UMTS I downlink band and is at the same time the highest operating
frequency of UMTS bands I to VI and VIII to X.
[0087] As can be seen from FIGS. 8D to 8G, there is always the
assurance that a load impedance of 50.OMEGA. with a reflection
factor <-10 dB can be matched to a generator impedance of
50.OMEGA.. In addition, a large tuning range is obtained within the
VSWR=8 circle. There are few optimum load impedances in the region
of the VSWR=2 and VSWR=4 circles. Towards relatively large
frequency values, the number of optimum load impedances in this
range decreases. However, it is possible to compensate for this by
selecting capacitances with finer stepping of the capacitance
values.
[0088] In one preferred embodiment, variable capacitances are used
which can be altered continuously in an adjustment range. By way of
example, these are ferroelectric varactors or semiconductor
varactors.
[0089] The invention is not limited to the exemplary embodiments by
virtue of the description thereof but rather comprises any new
feature and any combination of features. This includes particularly
any combination of features in the patent claims, even if this
feature or this combination is itself not explicitly specified in
the patent claims or exemplary embodiments.
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