|
Mobile Phone Patent Abstract
To achieve an improved matching of a power amplifier to transmission
line impedances of different transmission branches in a dual band
mobile phone there is proposed a new power amplifier output circuit
for such a dual band mobile phone. This power amplifier output circuit
comprises a transmission branch change over unit being connected
to an output terminal of the power amplifier. Further, there is
provided a second impedance matching means in at least one transmission
branch and the transmission branch change over unit comprises at
least two switching elements between the first impedance matching
unit and the second impedance matching unit. Therefore, the disturbing
influence of parasitic elements in the switching elements may be
reduced significantly.
Mobile Phone Patent Claims
What is claimed is:
1. A power amplifier output circuit for a dual band mobile radio
unit, comprising:
a first transmitter/receiver change over unit for transmitting/receiving
a first transmitting/receiving signal, said first transmitter/receiver
change over unit being provided with an input terminal receiving
said first transmitting signal to which a first impedance matching
unit is connected,
a second transmitter/receiver change over unit for transmitting/receiving
a second transmitting/receiving signal,
a transmission branch change over unit to selectively connect said
first transmitter/receiver change over unit or said second transmitter/receiver
change over unit to a power amplifier outputting transmitting signals
in two frequency bands, wherein
a second impedance matching unit is provided between an output
terminal of said power amplifier and said transmission branch change
over unit,
the transmission branch change over unit comprises at least two
switching elements being connected in parallel in a first transmission
branch which connects said power amplifier with said first transmitter/receiver
change over unit,
a third impedance matching unit is provided at an input terminal
of said second transmitter/receiver change over means, and
a switchable band stop filter is provided downstream said third
impedance matching means that filters harmonics of said first transmitting
signal in said second transmission branch during the transmission
of said first transmitting signal.
2. A power amplifier output circuit for a dual band mobile radio
unit, comprising:
a first transmitter/receiver change over unit for transmitting/receiving
a first transmitting/receiving signal, said first transmitter/receiver
change over unit being provided with an input terminal receiving
said first transmitting signal to which a first impedance matching
unit is connected,
a second transmitter/receiver change over unit for transmitting/receiving
a second transmitting/receiving signal,
a transmission branch change over unit to selectively connect said
first transmitter/receiver change over unit or said second transmitter/receiver
change over unit to a power amplifier outputting transmitting signals
in two frequency bands, wherein
a second impedance matching unit is provided between an output
terminal of said power amplifier and said transmission branch change
over unit,
the transmission branch change over unit comprises at least two
switching elements being connected in parallel in a first transmission
branch which connects said power amplifier with said first transmitter/receiver
change over unit,
a third impedance matching unit is provided at an input terminal
of said second transmitter/receiver change over means, and
said transmission branch change over unit is realized with a third
diode of said PIN-type between said second impedance matching unit
and said third impedance matching unit.
3. The power amplifier output circuit of claim 2, wherein said
first impedance matching unit is provided with a first capacitor
at an input thereof, said first capacitor being connected in Shunt-configuration.
4. The power amplifier output circuit of claim 3, wherein a second
capacitor is connected in series between said input of said first
impedance matching unit and an output of said first impedance matching
unit.
5. The power amplifier output circuit of claim 4, wherein an inductivity
is connected across said second capacitor.
6. A power amplifier output circuit for a dual band mobile radio
unit, comprising:
a first transmitter/receiver change over unit for transmitting/receiving
a first transmitting/receiving signal, said first transmitter/receiver
change over unit being provided with an input terminal receiving
said first transmitting signal to which a first impedance matching
unit is connected,
a second transmitter/receiver change over unit for transmitting/receiving
a second transmitting/receiving signal,
a transmission branch change over unit to selectively connect said
first transmitter/receiver change over unit or said second transmitter/receiver
change over unit to a power amplifier outputting transmitting signals
in two frequency bands, wherein
a second impedance matching unit is provided between an output
terminal of said power amplifier and said transmission branch change
over unit,
the transmission branch change over unit comprises at least two
switching elements being connected in parallel in a first transmission
branch which connects said power amplifier with said first transmitter/receiver
change over unit,
a third impedance matching unit is provided at an input terminal
of said second transmitter/receiver change over unit, and
a second line element is provided between an input and an output
of said third impedance matching means and a third line element
is connected in series to said second line element in said third
impedance matching unit.
7. The power amplifier output circuit of claim 6, wherein a fourth
capacitor branches off to ground at a connection point between said
second line element and said third line element.
8. A power amplifier output circuit for a dual band mobile radio
unit, comprising:
a first transmitter/receiver change over unit for transmitting/receiving
a first transmitting/receiving signal, said first transmitter/receiver
change over unit being provided with an input terminal receiving
said first transmitting signal to which a first impedance matching
unit is connected,
a second transmitter/receiver change over unit for transmitting/receiving
a second transmitting/receiving signal,
a transmission branch change over unit to selectively connect said
first transmitter/receiver change over unit or said second transmitter/receiver
change over unit to a power amplifier outputting transmitting signals
in two frequency bands, wherein
a second impedance matching unit is provided between an output
terminal of said power amplifier and said transmission branch change
over unit,
the transmission branch change over unit comprises at least two
switching elements being connected in parallel in a first transmission
branch which connects said power amplifier with said first transmitter/receiver
change over unit, and
said transmission branch change over unit is realized with a first
diode of the PIN-type and a second diode of the PIN-type between
said first impedance matching unit and said second impedance matching
unit such that first diode of the PIN-type and said second of the
PIN-type are connected in parallel.
9. The power amplifier output circuit of claim 8, wherein said
first diode of the PIN-type and said second diode of said PIN-type
(46) are accommodated in a single package.
10. A power amplifier output circuit for a dual band mobile radio
unit, comprising:
a first transmitter/receiver change over unit for transmitting/receiving
a first transmitting/receiving signal, said first transmitter/receiver
change over unit being provided with an input terminal receiving
said first transmitting signal to which a first impedance matching
unit is connected,
a second transmitter/receiver change over unit for transmitting/receiving
a second transmitting/receiving signal,
a transmission branch change over unit to selectively connect said
first transmitter/receiver change over unit or said second transmitter/receiver
change over unit to a power amplifier outputting transmitting signals
in two frequency bands, wherein
a second impedance matching unit is provided between an output
terminal of said power amplifier and said transmission branch change
over unit,
the transmission branch change over unit comprises at least two
switching elements being connected in parallel in a first transmission
branch which connects said power amplifier with said first transmitter/receiver
change over unit, and
a low pass filter is provided between said first impedance matching
unit and said first transmitter/receiver change over unit for the
filtering harmonics of said first transmitting signal.
11. A power amplifier output circuit for a dual band mobile radio
unit, comprising:
a first transmitter/receiver change over unit for transmitting/receiving
a first transmitting/receiving signal, said first transmitter/receiver
change over unit being provided with an input terminal receiving
said first transmitting signal to which a first impedance matching
unit is connected,
a second transmitter/receiver change over unit for transmitting/receiving
a second transmitting/receiving signal,
a transmission branch change over unit to selectively connect said
first transmitter/receiver change over unit or said second transmitter/receiver
change over unit to a power amplifier outputting transmitting signals
in two frequency bands, wherein
a second impedance matching unit is provided between an output
terminal of said power amplifier and said transmission branch change
over unit, and
the transmission branch change over unit comprises at least two
switching elements being connected in parallel in a first transmission
branch which connects said power amplifier with said first transmitter/receiver
change over unit, wherein
a first line element is provided at an input of said second impedance
matching unit.
12. The power amplifier output circuit of claim 11, wherein at
an end of said first line element lying at an output side a third
capacitor is connected to ground.
13. A power amplifier output circuit for a dual band mobile radio
unit, comprising:
a first transmitter/receiver change over unit for transmitting/receiving
a first transmitting/receiving signal, said first transmitter/receiver
change over unit being provided with an input terminal receiving
said first transmitting signal to which a first impedance matching
unit is connected,
a second transmitter/receiver change over unit for transmitting/receiving
a second transmitting/receiving signal,
a transmission branch change over unit to selectively connect said
first transmitter/receiver change over unit or said second transmitter/receiver
change over unit to a power amplifier outputting transmitting signals
in two frequency bands, wherein
a second impedance matching unit is provided between an output
terminal of said power amplifier and said transmission branch change
over unit, and
the transmission branch change over unit comprises at least two
switching elements being connected in parallel in a first transmission
branch which connects said power amplifier with said first transmitter/receiver
change over unit.
14. The power amplifier output circuit of claim 13, which comprises
a third impedance matching unit at an input terminal of said second
transmitter/receiver change over unit.
15. The power amplifier output circuit of claim 14, wherein said
transmission branch change over unit comprises at least one switching
element between said second impedance matching unit and said third
impedance matching unit.
Mobile Phone Patent Description
FIELD OF INVENTION
The present invention relates to an improved power amplifier matching
in dual band mobile phones, in particular to a power amplifier output
circuit for a dual band mobile radio unit according to the preamble
of claim 1.
BACKGROUND OF INVENTION
Currently, mobile phones are operated predominantly with a single
operating frequency. FIG. 7 shows a realization of such a transmitter/receiver
operation in a mobile phone being operated with a single operating
frequency, e.g., with approximately 900 MHz for GSM, approximately
1800 MHz for DCS or approximately 1900 MHz for PCS. An antenna 100
being used to transmit signals and to receive signals is connected
to a transmitter/receiver change over unit 102. The transmitter/receiver
change over unit 102 comprises a transmitter switch TX and a receiver
switch RX. In the receiving mode, the transmitter switch TX is opened
and the receiver switch RX is closed. To the contrary, in a transmitting
mode the transmitter switch TX is closed and the receiver switch
RX is opened.
In the transmitter mode, a power amplifier 104 outputs a transmitting
signal in the pre-specified frequency band. Here, an impedance matching
is carried out through an impedance matching circuit 106 such that
the output of the power amplifier sees an impedance which in most
cases is lower than the impedance of the following transmission
branch, e.g., 50 .OMEGA..
However, the circuit design shown in FIG. 7 more and more limits
the increasing use of digital mobile telephony since the number
of subscribers is continuously increasing while the number of transmitting
frequencies and related transmission channels is limited. Although
an increased transmitting frequency of, e.g., approximately 1800
MHz for DCS or approximately 1900 MHz for PCS in comparison to approximately
900 MHz for GSM enables an increased number of transmission channels,
this is only possible at the expense of reduced working ranges for
the transmitter stations.
Nevertheless, a combination of different technical advantages for
the different approaches through provision of cellular dual band
networks and dual band mobile phones adapted thereto seems to be
promising, e.g., a combination of the GSM-frequency band with the
DCS- or PCS-frequency band.
Heretofore, in U.S. Pat. No. 5,774,017 there is proposed a dual-band
amplifier for wireless communication, in particular for operation
at either the 800 MHz or the 1900 MHz band. The described dual band
amplifier provides desired gain and input/output impedance. Switching
impedance networks are used at the input and output of a power amplifier
to provide matching input impedance and a desired output impedance
for operation in two bands.
FIG. 8 shows another option of a corresponding power amplifier
output circuit designed for the necessary transmission/receiving
operation in a dual band mobile phone. This approach directly relies
on the circuit design shown in FIG. 7.
Here, the antenna 200 is connected to two transmitter/receiver
change over units 202 and 204. The sending/receiving change over
unit 202 comprises a transmitter switch TXa and a receiver switch
RXa for a first transmitter frequency. Further, the transmission/receiving
change over unit 204 comprises a transmitter switch TXb and a receiver
switch RXb for a second transmitter frequency. The different switches
TXa, RXa, TXb, and RXb are operated in accordance with the different
operation frequencies, respectively, as outlined above with respect
to FIG. 7. Further, a diplexer 206 is necessary to join the two
transmission paths to the antenna 200 without losses. For the amplification
of the transmitting signals in the frequency bands, there are provided
related power amplifiers 214 and 216. For these power amplifiers
214 and 216 an impedance matching is realized through impedance
matching circuits 218 and 220 provided in each of the two transmission
branches. Alternatively, the two power amplifiers 214 and 216 for
the two transmitting frequencies can be substituted through a single
power amplifier with two output terminals and a downstream impedance
matching circuit.
This direct generalization of the single band transmitting/receiving
circuit shown in FIG. 7 leads to the advantage that the different
transmission branches for both transmitting frequency bands are
completely decoupled. However, while suitable impedance matching
of the different transmitting frequency bands is achieved through
the separated and fully decoupled provision of the impedance matching
circuits this is only achieved with a high circuit complexity. On
the one hand this leads to an increase in the production costs and
on the other hand also the space requirements necessary for such
a dual band transmitting/receiving change over unit constitute a
barrier for the implementation thereof.
In view of the above, the object of the present invention is to
achieve an improved matching of a power amplifier outputting transmitting
signals in different transmitting frequency bands over a single
output terminal to impedances of the different transmission branches
in a dual band mobile phone.
According to the invention, this object is achieved through a power
amplifier output circuit for a dual band mobile radio unit according
to claim 1. The power amplifier output circuit comprises a first
transmitter/receiver change over means for transmitting/receiving
a first transmitting/receiving signal, the transmitter/receiver
change over means being provided with an input terminal to which
a first impedance matching means is connected, a second transmitter/receiver
change over means for transmitting/receiving a second transmitting/receiving
signal, a transmission branch change over means to selectively connect
the first transmitter/receiver change over means or the second transmitter/receiver
change over means to a power amplifier outputting transmitting signals
in two frequency bands such that a second impedance matching means
is provided between an output terminal of the power amplifier and
the transmission branch change over means and the transmission branch
change over means comprises at least two switching elements being
connected in parallel in a branch connecting the power amplifier
with the first transmitter/receiver change over means.
Therefore, for the present invention the stepwise approach to impedance
matching in at least one transmission branch of the power amplifier
output circuit is of importance as well as the simultaneous use
of a plurality of switching elements connected in parallel. Both
measures in functional relationship lead to a significant minimization
of parasitic disturbances in the power amplifier output circuit.
At the same time, there is also achieved a suitable impedance matching
for the respective frequency bands and transmitting powers in both
transmission branches.
Further, while the use of only a single impedance matching at the
output of the power amplifier will not lead to an optimum impedance
matching for both transmission branches according to the present
invention this is achieved, firstly, through the first common impedance
matching at the output of the power amplifier and, secondly, through
a further impedance matching optimized for each transmitting frequency
band, respectively. Further, since the common impedance matching
is used for both. frequency bands the circuit complexity may be
reduced significantly.
Still further, the present invention takes into account that the
power absorption in parasitic elements of the transmission branch
change over means increases when the disturbing real part of the
impedance of the transmission branch change over means lies close
to the output impedance of the power amplifier. E.g., the real part
of output impedances of practically used power amplifiers lies in
the range from approximately 5 to 6 .OMEGA. while typical connecting
resistances of different switching elements lie in the range of
approximately 1 .OMEGA.. In case switching elements are inserted
in the transmission branch change over unit only after a first impedance
transformation, e.g., to approximately 20 .OMEGA. at 900 MHz for
GSM or 50 .OMEGA. for 1800 MHz for DCS, the power absorption in
the parasitic elements is significantly reduced due to a smaller
ratio between switching element connecting resistance and impedance
level at the input terminal to the switching element, e.g., the
ratio being smaller by an order of magnitude.
According to the present invention the power absorption through
the parasitic elements may be further significantly reduced by providing
at least two switching elements in at least one transmission branch
of the transmission branch change over means. Through the parallel
connection the parasitic resistance and the parasitic inductance
due to the necessary switching between the first and the second
impedance matching are reduced by a factor corresponding essentially
to the number of switching elements connected in parallel.
Besides the minimization of the absorbed power the switching elements
connected in parallel also contribute to an improved impedance matching.
Due to the decreased overall connecting resistance and the decreased
overall parasitic inductance between the first and second impedance
matching stage, respectively, the overall impedance matching gets
less sensitive towards the disturbing influence of the switching
elements.
According to a preferred embodiment of the invention there is provided
a third impedance matching means at an input terminal of the second
transmitter/receiver change over means.
Thus, there is provided an optimized matching in the single transmission
branches specifically adapted to the respective transmitting frequency
and transmitting power, e.g., 3 W for approximately 900 MHz and
1.5 W for approximately 1800 MHz. However, since part of the impedance
matching for the different transmission branches is achieved through
the common impedance matching circuit connected to the output terminal
of the power amplifier the circuit complexity specifically necessary
for the different transmission branches is minimized.
According to yet another preferred embodiment of the present invention
the transmission branch change over means between the second impedance
matching means and the third impedance matching means comprises
at least one switching element.
Usually, the transmission branches are provided to output transmitting
signals with a lower transmitting frequency, e.g., approximately
900 MHz for GSM, and a higher transmitting frequency, e.g., approximately
1800 MHz for DCS and approximately 1900 MHz for PCS. Here, it should
be noted that the impedance matching at the output of the power
amplifier leads to different results for the different frequency
bands. In particular, in the transmission branch for the higher
frequency band there is achieved an almost complete matching to
the necessary impedance level through the impedance matching means
at the output terminal of the power amplifier such that parasitic
elements in the related branch of the transmission branch change
over means only have a minor influence. According to this preferred
embodiment of the invention, the object is to provide measures against
parasitic effects via frequency selective way only for the lower
frequency band while minimizing the additional costs for switching
elements. In other words, switching elements are only inserted to
an extent necessary for the selected transmitting frequency.
According to yet another preferred embodiment of the present invention,
there is provided a switchable band stop filter between the second
impedance matching means and the third impedance matching means
to filter the harmonics of the first transmitting signal during
the transmission of the first transmitting signal in the second
transmission path.
The power amplifier is usually operated near saturation. This leads
to the generation of harmonics, e.g., at approximately 1800 MHz,
approximately 2700 MHz, . . . in the GSM-transmitting mode and also
to the generation of harmonics at approximately 3600 MHz, etc. in
the DCS-transmitting mode. Usually, harmonics of first order are
dominating.
Although in the GSM-transmitting mode the harmonics at approximately
1800 MHz, approximately 2700 MHz, . . . are low pass filtered in
the first transmission branch, the first harmonic at approximately
1800 MHz of the GSM transmitting mode is not suppressed through
a low pass filter in the second transmission branch being only adapted
to harmonics of the second transmitting signal at approximately
3600 MHz, etc. The same holds true for a combination of the transmitting
frequencies for GSM and PCS with a transmitting frequency of approximately
1900 MHz. Generally speaking, this problem arises for power amplifier
outputting transmitting signals in a plurality of transmitting frequency
bands in case harmonics of the first, lower transmitting frequency
lie below the second, higher transmitting frequency or are identical
thereto.
To solve this problem the second transmission branch is advantageously
provided with a switchable band stop filter being adapted to suppress
specifically during the transmission of the first lower transmitting
frequency the first harmonic thereof in the second transmission
branch. This allows for an optimum decoupling of the different operation
modes.
According to yet another preferred embodiment of the invention
the transmission change over means between the first impedance matching
means and the second impedance matching circuit consists of a first
diode of a PIN-type and a second diode of the PIN-type such that
the first diode of the PIN-type and the second diode of the PIN-type
are connected in parallel. Preferably, the first diode of the PIN-type
and the second diode of the PIN-type are comprised in a single package
or housing.
Thus, during fabrication and operation of the power amplifier output
circuit according to the present invention only a single component
must be handled and supplied with power. During fabrication placement
of components is essentially unchanged so that approved circuit
layouts and fabrication processes may be maintained essentially
without any modification.
According to yet another preferred embodiment of the present invention
the first impedance matching means has a first capacitor connected
in shunt configuration at its input. Further, the first impedance
matching circuit comprises a second capacitor in series between
the input and the output thereof.
Usually, the impedance matching is achieved in the single transmission
branches through a sequence of capacitors and inductivities. Also
different line elements for the connection of the components and
parasitic inductivities of the switching elements are considered.
According to the present invention, it is taken into account that
capacitors usually are only available with capacitances lying in
a prespecified basic grid, e.g., according to 3.3 pF, 3.9 pF, 4.7
pF, 5.6 pF, etc. The increased number of capacitances in the first
impedance matching circuit results in a finer gradation for the
impedance transformation and thus in an improved impedance matching.
This is a particular advantage for transmission branches carrying
the transmitting signal in the lower transmitting frequency range.
Preferred embodiments of the invention will be described in the
following under reference to the drawing in which:
FIG. 1 shows the basic structure of a power amplifier output circuit
for a dual band mobile phone where a single output amplifier outputs
transmitting signals in different frequency bands via a single output
terminal;
FIG. 2 shows an equivalent circuit diagram for the switches shown
in FIG. 1 according to the opened and closed state thereof;
FIG. 3 shows a schematic diagram of the power amplifier output
circuit according to the present invention;
FIG. 4 shows a circuit diagram of the power amplifier output circuit
according to the present invention;
FIG. 5 illustrates the functionality of the components and line
elements shown in FIG. 4 and also the impact of parasitic elements
onto the impedance matching in a GSM-transmission branch;
FIG. 6 illustrates the functionality of the components and line
elements shown in FIG. 4 as well as the impact of parasitic elements
onto the impedance matching in a DCS-transmission branch;
FIG. 7 shows a schematic diagram for a power amplifier output circuit
for a single band mobile phone; and
FIG. 8 shows a schematic diagram for a power amplifier output circuit
for a dual band mobile phone with two power amplifiers and related
impedance matchings.
FIG. 1 shows the basic structure of a power amplifier output circuit
for a dual band mobile phone according to the present invention.
As shown in FIG. 1, a power amplifier 10 is connected at its output
terminal 12 to a first impedance matching circuit 14. At the output
terminal of the first impedance matching circuit 14 there is connected
a first switch 16 connecting the first impedance matching circuit
14 to a first transmission branch.
The first transmission branch comprises a series connection with
a second impedance matching circuit 18, a first low pass filter
20 and a first transmitter/receiver change over unit 22 and is operated
in a first frequency band. To switch between the transmitter and
receiver operation mode, the first transmitter/receiver change over
unit 22 comprises a first transmitter switch 24 and a first receiver
switch 26.
As also shown in FIG. 1, at the output of the first impedance matching
circuit 14 there is also connected a second switch 28 connecting
the first impedance matching circuit 14 to a second transmission
branch.
The second transmission branch comprises a series connection with
a third impedance matching circuit 30 and a switchable band stop
filter 32 being operated to suppress the first harmonic of the transmitting
signal carried on the first transmission branch in the second transmission
branch during transmission of the first transmitting signal. Further,
a second low pass filter 33 is provided to suppress the harmonics
of the transmitting signal carried on the second transmission branch.
To switch between the transmitter and the receiver operation mode
the second transmitter/receiver change over unit 34 comprises a
second transmitter switch 36 and a second receiver switch 38.
The center tap between the first transmitter switch 24 and the
first receiver switch 26 and the center tap between the second transmitter
switch 36 and the second receiver switch 38 are connected to a diplexer
40, respectively, being provided to join the single transmission/receiving
paths without loss to an antenna 42.
In a first operative mode where the power amplifier 10 outputs
a transmitting signal in a first frequency band with a first transmitting
frequency f1 the first switch 16 is closed and the second switch
28 is opened. The first impedance matching circuit 14 and the second
impedance matching circuit 18 achieve an optimum matching of the
output impedance of the power amplifier 10 to the load impedance
necessary for the first transmitting frequency and power.
Since the power amplifier 10 is operated near saturation the output
thereof comprises not only the transmitting signal itself with the
frequency f1 but also harmonics thereof at the frequencies 2*f1,
3*f1, . . . . These undesired harmonics are suppressed in the first
transmission branch through the first low pass filter 20 and the
filtered transmitting signal is outputted to the antenna 42 via
the first transmitter switch 24.
While this enables the filtering of harmonics of the first transmitting
signal in the first operative mode for the reason of non-ideal behaviour
of the first switch 16 and the second switch 28 further measures
are necessary to avoid the undesired transmission of these harmonics
via the second transmission branch. E.g., when considering a combination
of the transmitting frequency for GSM at approximately 900 MHz and
for DCS at approximately 1800 MHz the first harmonic of the GSM
transmitting signal is not suppressed through the second low pass
filter 33 lying in the second transmission branch for DCS at approximately
1800 MHz being only adapted to harmonics of the second transmitting
signal at approximately 3600 MHz. Generally, this problem arises
for each power amplifier outputting transmitting signals with a
plurality of transmitting frequencies in case harmonics of the first,
lower transmitting frequency lie below the second, higher transmitting
frequency or are identical thereto.
According to the present invention it is therefore proposed to
provide a switchable band stop filter 32 in the second transmission
branch being adapted to specifically suppress the first harmonic
of the first, lower transmitting frequency signal in the second
transmission branch during transmission of the first transmitting
signal. This allows for an optimum decoupling of the different operative
modes.
As also shown in FIG. 1, in a second operation mode where the power
amplifier 10 outputs a transmitting signal in a second frequency
band or with a second transmitting frequency, respectively, the
first switch 16 is opened and the second switch 28 is closed.
In this case, the first impedance matching circuit 14 and the third
impedance matching circuit 30 achieve an optimum matching of the
output impedance of the power amplifier 10 onto the load impedance
necessary for the second transmitting frequency and power.
Again, harmonics are generated at 2*f2, 3*f2, . . . . These harmonics
are suppressed in the second low pass filter 33 before the output
of the transmitting signal to the antenna 42 via the second transmitter
switch 36.
The basic structure of a power amplifier output circuit according
to the present invention shown in FIG. 1 allows to consider the
fact that an optimum impedance matching for transmission branches
through only a single impedance matching circuit at the output of
the power amplifier may not be achieved. To the contrary, on the
one hand this may only be achieved through the stepwise impedance
matching using a common impedance matching circuit at the output
of the power amplifier and on the other hand through an additional
impedance matching circuit optimized for each transmitting frequency
band. Due to the impedance matching provided in common for both
transmission branches the circuit complexity may be significantly
decreased.
In case of an ideal switching behaviour of the first switch 16
and the second switch 28, respectively, the output of the transmitting
signals in both frequency bands through the power amplifier 10 with
only a single output would be completely realized.
However, as is shown in FIG. 2 with equivalent circuit diagrams
for switches in the opened and closed state, switches used in practice,
e.g., diodes of the PIN-type exhibit a non-ideal behavior. The damping
for an opened switch is limited and gets increasingly lower for
higher frequencies. For diodes of the PIN-type the damping lies
in the range of 25 dB for 900 MHz and 10 dB for 1800 MHz.
FIG. 3 shows the solution according to the present invention for
a power amplifier output circuit. Here, circuit components having
the same functionality as the circuit components shown in FIG. 1
are denoted by the same reference numerals.
As shown in FIG. 3, the first switch 16 of the transmission branch
of the change-over unit comprises at least two first switching elements
S11, . . . , S1N. Further, the second switch 28 of the transmission
branch change-over unit comprises at least one second switching
element S21, . . . , S2N.
Operatively, all first switching elements S11, . . . , S1N are
closed during the transmission of the first transmitting signal
with the first transmitting frequency and therefore connected in
parallel. Further, during transmission of the second transmitting
signal with the second transmitting frequency all second switching
elements S21, . . . , S2N are closed and thus connected in parallel.
Operatively, through the parallel connection of the first switching
elements S11, . . . , S1N and the second switching elements S21,
. . . , S2N there is achieved a decrease in the connecting resistance
and parasitic inductance of the first and second switch 16 and 28,
respectively. Here, the factor for the decrease essentially corresponds
to the number of first switching elements S11, . . . , S1N and second
switching elements S21, . . . , S2N connected in parallel.
For the functionality of the power amplifier output circuit according
to the present invention shown in FIG. 3 it is also of importance
that the first switching elements S11, . . . , S1N and the second
switching elements S21, . . . , S2N are provided downstream the
common impedance matching circuit 14, respectively. The reason for
this is that the power absorption in the parasitic elements of the
first switching elements S11, . . . , S1N and S21, . . . , S2N respectively,
increases when the disturbing real part of the impedance of the
related transmission branch is closed to the output impedance of
the power amplifier. In case the first switching elements S11, .
. . , S1N and the second switching elements S21, . . . , S2N are
provided downstream a first impedance matching circuit implementing
an impedance transformation to approximately 20 .OMEGA. at approximately
900 MHz for GSM or approximately 50 .OMEGA. at approximately 1800
MHz for DCS the power absorption in the parasitic elements is significantly
decreased due to the increased impedance level at the respective
input terminals.
For the functionality of the power amplifier output circuit according
to the present invention shown in FIG. 3, it is also of importance
that due to a decreased overall connecting resistance and a decreased
overall parasitic inductance of the first switch 16 and the second
switch 28 the impedance matching is less sensitive towards disturbances
caused by the switching elements.
FIG. 4 shows a circuit diagram for the realization of the power
amplifier output circuit according to the present invention.
As shown in FIG. 4, the first switch 16 comprises a first diode
of the PIN-type 44 and a second diode of the PIN-type connected
across thereto. Preferably, the first diode of the PIN-type 44 and
the second diode of the PIN-type 46 are accommodated in a single
housing and are supplied with power through the same power supply.
As also shown in FIG. 4, the second switch 28 comprises only a
single diode of the PIN-type 47. Without restricting the scope of
the present invention it is assumed here that the transmitting signal
with the first lower transmitting frequency is transmitted by the
first switch 16 and that the transmitting signal with the second
higher transmitting frequency is transmitted via the second switch
28. The reason why the second switch 28 comprises only a single
diode of the PIN-type 47 is that here the impedance matching for
the higher frequency band is almost fully accomplished, e.g., to
50 .OMEGA. for DCS at approximately 1800 MHz. Therefore, the influence
of the parasitic resistance (approximately 1 .OMEGA.) of the connecting
diode of the PIN-type 47 is so low that measures against parasitic
elements become obsolete.
As also shown in FIG. 4, the impedance matching circuit 14 connected
to the output of the power amplifier 10 comprises a first line element
50 at the input thereof, wherefrom a first capacitor 48 branches
off to ground before the output terminal of the impedance matching
circuit 14. The first line element 50 functions as serial inductivity
for the impedance matching. In FIG. 4, further line elements 52
and 51 are shown which reflect different geometrical layout configurations
for the connection of the different transmission branches to the
power amplifier 10.
As also shown in FIG. 4, the impedance matching circuit 30 in the
second transmission branch comprises two serially connected line
elements with an intermediate connecting point wherefrom a second
capacitor 54 branches off to ground.
As also shown in FIG. 4, the impedance matching circuit 18 in the
first transmission branch comprises a third capacitor 60 connected
in shunt configuration at the input thereof and further a fourth
capacitor 62 serially connected between the input and output thereof.
The fourth capacitor 62 is bridged with an inductivity 64.
FIG. 5 shows as an example the functionality of the components
and line elements shown in FIG. 4 as well as the influence of parasitic
elements onto the impedance matching in a GSM-transmission branch.
As shown in FIG. 5, the impedance matching is achieved starting
from the output impedance Za of the power amplifier 10 with a sequence
of transformation steps shown in a Smith chart diagram. The transmission
from the output impedance Za of the power amplifier 10 to the matching
point shown in FIG. 5 is achieved in the first transmission branch
via partial transformation steps realized according to the sequence
line element 50, first capacitor 48, line elements 52, parasitic
inductivity of the first switch 16, parasitic resistance of the
first switch 16, third capacitor 60 and fourth capacitor 62.
The fourth capacitor 62 of the impedance matching circuit in the
first transmission branch is provided since capacitances are normally
only available according to discrete grid-like capacitance values,
e.g., 3.3 pF, 3.9 pF, 4.7 pF, 5.6 pF, etc. The fourth capacitor
62 allows for a finer tuning of the impedance transformation and
thus for a more precise impedance matching. The inductivity 64 serves
for a DC-decoupling.
FIG. 6 shows as an example the functionality of the circuit components
and line elements shown in FIG. 4 as well as the influence of parasitic
elements onto the impedance matching in a DCS-transmission branch.
As shown in FIG. 6, also in the second transmission branch the
impedance matching is achieved starting from the output impedance
Za of the power amplifier 10 via a sequence of transformation steps
implemented through the sequence of line element 50, first capacitor
48, line element 51 and parasitic inductivity of the second switch
28 and second capacitor 54. In FIG. 6 the line elements 56 and 58
have been neglected.
As already outlined above with reference to FIG. 4 the parasitic
resistance of the second switch 28, e.g., the third diode of the
PIN-type 47 only plays a minor role in the second transmission branch
due to the higher frequency band such that the corresponding partial
transformation step in the Smith chart diagram shown in FIG. 6 is
omitted. Further, a capacitor comparable to the fourth capacitor
62 can be omitted due to the higher frequency band therefore reducing
the circuit complexity in the second transmission branch.
|