U.S. patent application number 15/026336 was filed with the patent office on 2016-08-18 for power amplifier for amplification of an input signal into an output signal.
This patent application is currently assigned to Telefonaktiebolaget LM Ericsson (publ). The applicant listed for this patent is TELEFONAKTIEBOLAGET L M ERICSSON (PUBL). Invention is credited to Richard HELLBERG.
Application Number | 20160241201 15/026336 |
Document ID | / |
Family ID | 52828440 |
Filed Date | 2016-08-18 |
United States Patent
Application |
20160241201 |
Kind Code |
A1 |
HELLBERG; Richard |
August 18, 2016 |
POWER AMPLIFIER FOR AMPLIFICATION OF AN INPUT SIGNAL INTO AN OUTPUT
SIGNAL
Abstract
A power amplifier comprising a first, second and third
sub-amplifier for amplification of an input signal into an output
signal is disclosed. The sub-amplifiers are connected to an input
network and an output network. The output network comprises a
first, second and third transmission line connected to the first,
second and third sub-amplifier, respectively. A difference in
electrical length between the first, second and third transmission
lines is an integer number of quarter-wavelengths of a center
frequency of the power amplifier. A first, second and third
electrical length includes the first, second and third transmission
line, respectively. A longest one of the electrical lengths is at
least a multiple of quarter-wavelengths of the center frequency.
Furthermore, a radio network node, comprising the power amplifier,
and a user equipment, comprising the power amplifier, are
disclosed.
Inventors: |
HELLBERG; Richard;
(Huddinge, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TELEFONAKTIEBOLAGET L M ERICSSON (PUBL) |
Stockholm |
|
SE |
|
|
Assignee: |
Telefonaktiebolaget LM Ericsson
(publ)
|
Family ID: |
52828440 |
Appl. No.: |
15/026336 |
Filed: |
October 18, 2013 |
PCT Filed: |
October 18, 2013 |
PCT NO: |
PCT/SE2013/051217 |
371 Date: |
March 31, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H03F 2200/451 20130101;
H03F 3/72 20130101; H04W 88/08 20130101; H03F 1/0277 20130101; H04W
88/02 20130101; H03F 2203/7209 20130101; H03F 1/0294 20130101; H03F
2200/423 20130101; H03F 3/602 20130101; H03F 2200/111 20130101;
H03F 2200/408 20130101; H03F 3/19 20130101; H03F 3/211 20130101;
H03F 1/0288 20130101 |
International
Class: |
H03F 1/02 20060101
H03F001/02; H04W 88/02 20060101 H04W088/02; H03F 3/21 20060101
H03F003/21; H04W 88/08 20060101 H04W088/08; H03F 3/60 20060101
H03F003/60; H03F 3/19 20060101 H03F003/19 |
Claims
1. A power amplifier comprising a first and a second sub-amplifier
for amplification of an input signal into an output signal, wherein
the first and second sub-amplifiers are connected to an input
network for receiving the input signal at an input port of the
input network, and the first and second sub-amplifiers are
connected to an output network for providing the output signal at
an output port of the output network, wherein the output network
comprises a first transmission line and a second transmission line
connected to the first sub-amplifier and the second sub-amplifier,
respectively, wherein a difference in electrical length between the
first and second transmission lines is an integer number of
quarter-wavelengths of a center frequency of the power amplifier,
wherein the power amplifier is characterized by further comprising:
a third sub-amplifier for amplification of the input signal into
the output signal, wherein the third sub-amplifier is connected to
the input network and the output network, wherein the output
network further comprises a third transmission line connected to
the third sub-amplifier, wherein a first electrical length includes
the first transmission line, a second electrical length includes
the second transmission line, and a third electrical length
includes the third transmission line, and wherein a longest one of
the first, second and third electrical lengths is at least a
multiple of quarter-wavelengths of the center frequency.
2. The power amplifier according to claim 1, wherein the power
amplifier is operable down to the center frequency divided by the
multiple.
3. The power amplifier according to claim 1, wherein the first and
second transmission lines are connected to a first common
transmission line, included in the output network, wherein the
first common transmission line is common to the first and second
sub-amplifiers.
4. The power amplifier according to claim 1, further comprising a
fourth sub-amplifier, wherein the fourth sub-amplifier is connected
to the input network and the output network, wherein the output
network further comprises a fourth transmission line.
5. The power amplifier according to claim 4, wherein the third and
fourth sub-amplifier are connected to a second common transmission
line, included in the output network, wherein the second common
transmission line is common to the third and fourth
sub-amplifiers.
6. The power amplifier according to claim 1, wherein the power
amplifier is operable to: provide the output signal mainly supplied
by the first sub-amplifier in a first mode; provide the output
signal mainly supplied by the second sub-amplifier in a second
mode; and provide the output signal mainly supplied by the third
sub-amplifier in a third mode.
7. The power amplifier according to claim 1, wherein the power
amplifier is a composite power amplifier.
8. A radio network node comprising: a power amplifier comprising a
first and a second sub-amplifier for amplification of an input
signal into an output signal, wherein the first and second
sub-amplifiers are connected to an input network for receiving the
input signal at an input port of the input network, and the first
and second sub-amplifiers are connected to an output network for
providing the output signal at an output port of the output
network, wherein the output network comprises a first transmission
line and a second transmission line connected to the first
sub-amplifier and the second sub-amplifier, respectively, wherein a
difference in electrical length between the first and second
transmission lines is an integer number of quarter-wavelengths of a
center frequency of the power amplifier, wherein the power
amplifier is characterized by further comprising: a third
sub-amplifier for amplification of the input signal into the output
signal, wherein the third sub-amplifier is connected to the input
network and the output network, wherein the output network further
comprises a third transmission line connected to the third
sub-amplifier, wherein a first electrical length includes the first
transmission line, a second electrical length includes the second
transmission line, and a third electrical length includes the third
transmission line, and wherein a longest one of the first, second
and third electrical lengths is at least a multiple of
quarter-wavelengths of the center frequency.
9. A user equipment comprising: a power amplifier comprising a
first and a second sub-amplifier for amplification of an input
signal into an output signal, wherein the first and second
sub-amplifiers are connected to an input network for receiving the
input signal at an input port of the input network, and the first
and second sub-amplifiers are connected to an output network for
providing the output signal at an output port of the output
network, wherein the output network comprises a first transmission
line and a second transmission line connected to the first
sub-amplifier and the second sub-amplifier, respectively, wherein a
difference in electrical length between the first and second
transmission lines is an integer number of quarter-wavelengths of a
center frequency of the power amplifier, wherein the power
amplifier is characterized by further comprising: a third
sub-amplifier for amplification of the input signal into the output
signal, wherein the third sub-amplifier is connected to the input
network and the output network, wherein the output network further
comprises a third transmission line connected to the third
sub-amplifier, wherein a first electrical length includes the first
transmission line, a second electrical length includes the second
transmission line, and a third electrical length includes the third
transmission line, and wherein a longest one of the first, second
and third electrical lengths is at least a multiple of
quarter-wavelengths of the center frequency.
Description
TECHNICAL FIELD
[0001] Embodiments herein relate to wireless communication systems,
such as telecommunication systems. In particular, a power amplifier
for amplification of an input signal into an output signal is
disclosed. Furthermore, a radio network node, comprising the power
amplifier, and a user equipment, comprising the power amplifier,
are disclosed.
BACKGROUND
[0002] Power amplifiers are widely used in communication systems,
for example in radio base stations and cellular phones of a
cellular radio network. In such cellular radio network, power
amplifiers typically amplify signals of high frequencies for
providing a radio transmission signal. A consideration in the
design of power amplifiers is the efficiency thereof. High
efficiency is generally desirable so as to reduce the amount of
power that is dissipated as heat. Moreover, in many applications,
such as in a satellite or a cellular phone, the amount of power
that is available may be limited due to powering by a battery,
included in e.g. the satellite. An increase in efficiency of the
power amplifier would allow an increase of operational time between
charging of the battery.
[0003] A conventional Power Amplifier (PA), such as class B, AB, F,
has a fixed Radio Frequency (RF) load resistance and a fixed
voltage supply. Class B or AB bias causes the output current to
have a form close to that of a pulse train of half wave rectified
sinusoid current pulses. The Direct Current (DC), and hence DC
power, is largely proportional to the RF output current amplitude,
and voltage. The output power, however, is proportional to the RF
output current squared. An efficiency of the conventional power
amplifier, i.e. output power divided by DC power, is therefore also
proportional to the output amplitude. The average efficiency is
consequentially low when amplifying signals that on average have a
low output amplitude, or power, compared to the maximum required
output amplitude.
[0004] Known RF power amplifiers include both Doherty and Chireix
type power amplifiers. These kinds of RF PAs are generally more
efficient than the conventional amplifier described above for
amplitude-modulated signals with high Peak-to-Average Ratio (PAR),
since they have a lower average sum of output currents from the
transistors. Reduced average output current means high average
efficiency.
[0005] The reduced average output current is obtained by using two
transistors that influence each other's output voltages and
currents through a reactive output network, which is coupled to a
load. By driving the constituent transistors with the right
amplitudes and phases, the sum of RF output currents is reduced at
all levels except the maximum. Also for these amplifiers the RF
voltage at one or both transistor outputs is increased.
[0006] Generally, RF power amplifier can be driven in a so called
backed off operation. This means that the power amplifier is
operated a certain number level, e.g. expressed as a number of
decibels (dBs), under its maximum output power. Backed off
operation may also refer to that an instantaneous output power is
relatively low.
[0007] Referring to FIG. 1, WO03/06111 discloses a composite power
amplifier 10 including a first and a second power amplifier 11, 12
connected to an input signal over an input network and to a load
R.sub.LOAD over an output network 13. The output network 13
includes a longer and a shorter transmission line 14, 15 for
generating different phase shifts from each power amplifier output
to the load R.sub.LOAD). Each of the longer and shorter
transmission lines 14, 15 connects each of the first and second
amplifiers 11, 12 to a common output at the load R.sub.LOAD). In
order to achieve, for this composite power amplifier 10, a widest
wideband operation, lengths of the longer and shorter transmission
lines 14, 15 are chosen such that the longer transmission line 14
has an electrical length of half a wavelength at a center frequency
of the composite amplifier 10, while the shorter transmission line
15 is a quarter wavelength long at the center frequency. The
composite power amplifier may be operated, typically over a 3 to 1
bandwidth, in Doherty mode, in Chireix mode or in other
intermediate modes between the Doherty and Chireix modes. Thus, the
3 to 1 bandwidth of high efficiency is achieved by devising an
output network 13 that has both suitable impedance transformation
characteristics and full power output capacity over the bandwidth.
A continuous band of high efficiency amplification is thus
achieved.
[0008] In FIG. 2, a simplified structure of the composite amplifier
of FIG. 1 is shown. The shorter and longer transmission lines are
shown as branches 21, 22 and the first and second amplifiers 11, 12
are connected to a respective branch 21, 22. The branches 21, 22
are connected to the load R.sub.LOAD.
[0009] A drawback of the above mentioned composite power amplifier
is that the bandwidth in which high efficiency is achieved may for
some applications not be sufficient.
[0010] Moreover, the above mentioned composite power amplifier may
not always achieve high efficiency for signals with high PAR, e.g.
10 dB.
SUMMARY
[0011] An object is to improve a power amplifier, such as the
composite power amplifier of the above mentioned kind.
[0012] According to an aspect, the object is achieved by a power
amplifier, comprising a first and a second sub-amplifier, for
amplification of an input signal into an output signal. The first
and second sub-amplifiers are connected to an input network for
receiving the input signal at an input port of the input network,
and the first and second sub-amplifiers are connected to an output
network for providing the output signal at an output port of the
output network. The output network comprises a first transmission
line and a second transmission line connected to the first
sub-amplifier and the second sub-amplifier, respectively. A
difference in electrical length between the first and second
transmission lines is an integer number of quarter-wavelengths of a
center frequency of the power amplifier.
[0013] The power amplifier further comprises a third sub-amplifier
for amplification of the input signal into the output signal. The
third sub-amplifier is connected to the input network and the
output network. The output network further comprises a third
transmission line connected to the third sub-amplifier. A first
electrical length includes the first transmission line, a second
electrical length includes the second transmission line, and a
third electrical length includes the third transmission line. A
longest one of the first, second and third electrical lengths is at
least a multiple of quarter-wavelengths of the center
frequency.
[0014] According to another aspect, the object is achieved by a
radio network node, comprising the power amplifier.
[0015] According to a further aspect, the object is achieved by a
user equipment, comprising the power amplifier.
[0016] Hence, according to some exemplifying embodiments herein,
multistage amplifiers with high efficiency operation in much wider
bandwidths than the prior art solutions are provided.
[0017] The much wider bandwidths are obtained by the output
network, e.g. comprising the above mentioned first, second and
third sub-amplifiers. The output network may provide multiple
frequency regions, e.g. modes of operation, thanks to combinations
of electrical length asymmetries among the first, second and third
transmission lines.
[0018] Asymmetries in electrical length between the first, second
and third transmission lines, also referred to as branches, that
connect to the same point may give rise to impedance transformation
in the output network. As a consequence, maintained or increased
average efficiency is achieved in backed off operation.
[0019] As a result, the above mentioned object is achieved in that
wider bandwidths in back off operation may be obtained.
[0020] Advantageously, some embodiments herein provide universal,
very wideband, high efficiency power amplifiers. The amplifier
according to some embodiments herein may also be used without
redesign or trimming for many different bands of operation.
[0021] Moreover, the amplifier according to some embodiments herein
may be designed to have high efficiency, especially in backed off
operation or for high PAR input signals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The various aspects of embodiments disclosed herein,
including particular features and advantages thereof, will be
readily understood from the following detailed description and the
accompanying drawings, in which:
[0023] FIG. 1 is a schematic overview of a power amplifier
according to prior art,
[0024] FIG. 2 is a schematic simplified overview of the power
amplifier according to FIG. 1,
[0025] FIG. 3 is a schematic overview of the power amplifier
according to embodiments herein,
[0026] FIG. 4 is a schematic simplified overview of the power
amplifier according to embodiments herein,
[0027] FIGS. 5a-5d illustrate currents, voltages, and corresponding
phases as well as amplitude for each of the sub-amplifiers for
input signals at respective portion of the center frequency for an
exemplifying power amplifier,
[0028] FIG. 6 illustrates average efficiency of the power
amplifiers according to some embodiments over a 10 to 1
bandwidth,
[0029] FIG. 7 illustrates a realization of a transmission line,
[0030] FIGS. 8a-8i illustrate exemplifying power amplifiers with
three sub-amplifiers,
[0031] FIGS. 9a-9c illustrate efficiency versus frequency for some
embodiments of the power amplifier in FIG. 3,
[0032] FIG. 10 illustrates theoretical minimum efficiency for
different bandwidths for some exemplifying power amplifiers,
[0033] FIG. 11 illustrates another exemplifying embodiment of the
power amplifier,
[0034] FIGS. 12a-12d illustrate currents, voltages, and
corresponding phases as well as amplitude for each of the
sub-amplifiers for input signals at respective portion of the
center frequency for another exemplifying power amplifier,
[0035] FIGS. 13a-13d illustrate currents, voltages, and
corresponding phases as well as amplitude for each of the
sub-amplifiers for input signals at respective portion of the
center frequency for a further exemplifying power amplifier,
[0036] FIGS. 14a-14k illustrate further exemplifying power
amplifiers,
[0037] FIGS. 15a-15h illustrate efficiency versus frequency for
exemplifying power amplifiers according to some embodiments,
[0038] FIG. 16 illustrates theoretical minimum efficiency for
different bandwidths for some exemplifying power amplifiers,
[0039] FIGS. 17a-17d illustrate currents, voltages, and
corresponding phases as well as amplitude for each of the
sub-amplifiers for input signals at respective portion of the
center frequency for a further exemplifying power amplifier,
[0040] FIGS. 18a and 18b illustrate efficiency versus frequency for
exemplifying power amplifiers according to some embodiments,
[0041] FIG. 19 illustrates efficiency versus frequency for
exemplifying power amplifiers according to some embodiments,
[0042] FIG. 20 illustrates an exemplifying radio network node
according to embodiments herein, and
[0043] FIG. 21 illustrates an exemplifying user equipment according
to embodiments herein.
DETAILED DESCRIPTION
[0044] Throughout the following description similar reference
numerals have been used to denote similar elements, units, modules,
circuits, nodes, parts, items or features, when applicable. In the
Figures, features that appear in some embodiments are indicated by
dashed lines.
[0045] In some of the Figures, ".lamda./4" denotes a quarter
wavelength at a center frequency of a power amplifier according to
some embodiment. This may mean that--at the center frequency--the
".lamda./4" is a quarter wavelength of the center frequency.
".lamda./4" denotes a physical length that has an electrical length
of a quarter wavelength at a center frequency.
[0046] FIG. 3 depicts an exemplifying power amplifier 100 according
to embodiments herein. The power amplifier 100 comprises a first, a
second and a third sub-amplifier 111, 112, 113 which are operated
to amplify an input signal into an output signal.
[0047] The first, second and third sub-amplifiers 111, 112, 113 are
connected to an input network 120 for receiving the input signal at
an input port 150 of the input network 120. As an example, the
input network 120 may include connections (not shown) for driving
of each of the first, second and third sub-amplifiers 111, 112,
113.
[0048] Moreover, the first, second and third sub-amplifiers 111,
112, 113 are connected to an output network 130 for providing the
output signal at an output port 140 of the output network 130. The
output network 130 comprises a first transmission line 131, a
second transmission line 132 and a third transmission line 133
connected to the first sub-amplifier 111, the second sub-amplifier
112 and the third sub-amplifier 113, respectively. A difference in
electrical length between the first and second transmission lines
131, 132 is an integer number of quarter-wavelengths of a center
frequency of the power amplifier 100. Moreover, a further
difference in electrical length between the first and/or second
transmission lines 131, 132 may be a further integer number of
quarter-wavelengths of the center frequency of the power amplifier
100.
[0049] Hence, a first electrical length includes the first
transmission line 131, a second electrical length includes the
second transmission line 132, and a third electrical length
includes the third transmission line 133. A longest one of the
first, second and third electrical lengths is at least a multiple
of quarter-wavelengths of the center frequency.
[0050] The power amplifier 100 may be operable, e.g. efficiency of
the power amplifier 100 may be above a threshold value, down to,
e.g. approximately, the center frequency divided by the multiple.
In some examples, the power amplifier 100 may be operable over a
continuous bandwidth, e.g. range of frequencies, down to the center
frequency. However, in some examples, the power amplifier 100 may
be operable over two or more relatively narrow bandwidths, e.g.
ranges of frequencies, where the two or more relatively narrow
bandwidths may or may not include a lowest frequency defined as the
center frequency divided by the multiple.
[0051] In more detail, in some examples, the power amplifier 100
may be operable somewhat lower than the center frequency divided by
the multiple. Yet, it may be that in some other examples, the power
amplifier 100 is only operable down to somewhat higher than the
center frequency divided by the multiple. Therefore, the expression
"operable down to the center frequency divided by the multiple"
shall be understood as having a margin. The margin will for example
depend on threshold value for when the efficiency may be considered
to be good.
[0052] The threshold value, e.g. for when to consider the
efficiency good, may be 60%. The threshold value is usually in the
range from 30% to about 70%. The lower the threshold value is set,
the wider the operational bandwidth may typically be. In further
embodiments, the threshold value may even be outside the above
mentioned range. This will be explained for some embodiment with
reference to FIGS. 15a-15f.
[0053] In order to maintain, for example compared to WO03/06111,
efficiency of the power amplifier 100 at maximum output power, i.e.
available output power, the first, second and third sub-amplifier
111, 112, 113 are driven, across the operational bandwidth, such
that the output signal is obtained by in-phase combining of
respective output signals from the first, second and third
sub-amplifier 111, 112, 113, respectively. The maximum output power
refers to maximum output power from each respective
sub-amplifier.
[0054] In some embodiments, which will be further explained with
reference to FIG. 4 and FIGS. 5a-5d, the first and second
transmission lines 131, 132 may be connected to a first common
transmission line 135, included in the output network 130. The
first common transmission line 135 may be common to the first and
second sub-amplifiers 131, 132. In these embodiments, the first and
second electrical lengths may further include electrical length of
the first common transmission line 135. The first common
transmission line 135 may be referred to as a trunk, or a first
trunk, herein. Obviously, in embodiments in which the first common
transmission line 135 is not present, the lines that end to the
right and left of the first common transmission line 135 are
connected to each other, i.e. no break in the circuit shall
occur.
[0055] In some embodiments, the power amplifier 100 may further
comprise a fourth sub-amplifier 114. The fourth sub-amplifier 114
may be connected to the input network 120 and the output network
130. The output network 130 may further comprise a fourth
transmission line 134. These embodiments, a second common
transmission line 136, may be devised as described in more detail
with reference to FIGS. 11a and 11b below.
[0056] In some embodiments, the power amplifier 100 may be operable
to provide the output signal mainly supplied by the first
sub-amplifier 111 in a first mode. As an example, the first mode
may be that the first sub-amplifier 111 acts, e.g. at a first
frequency, as a primary sub-amplifier. Hence, the expression
"primary sub-amplifier" is used to indicate that a specific
sub-amplifier makes a larger contribution to the output signal,
e.g. at the first frequency for a specific amplitude, than any
other sub-amplifier make at the first frequency for the specific
amplitude. At some other amplitude, but still at the first
frequency, any one of said any other sub-amplifier may act as
primary sub-amplifier. In an example, the specific sub-amplifier
may be the first sub-amplifier and said any other sub-amplifier may
be one of the second and third sub.
[0057] Moreover, the power amplifier 100 may be operable to provide
the output signal mainly supplied by the second sub-amplifier 112
in a second mode. As an example, the second mode may be that the
second sub-amplifier 112 acts, e.g. at a second frequency, the
primary sub-amplifier.
[0058] Furthermore, the power amplifier 100 may be operable to
provide the output signal mainly supplied by the third
sub-amplifier 113 in a third mode.
[0059] As an example, the third mode may be that the third
sub-amplifier 113 acts, e.g. at a third frequency, the primary
sub-amplifier. In further examples, each of the first, second and
third modes may be a pure or detuned Doherty, Chireix, combined
Doherty/Chireix or combined Chireix/Doherty mode.
[0060] Therefore, the power amplifier 100 may said to be a
composite power amplifier. The term composite power amplifier is
herein defined as referring to power amplifiers which may be
operated in at least two different modes, such as a pure or detuned
Doherty, Chireix, combined Doherty/Chireix or combined
Chireix/Doherty mode.
[0061] Continuing with the example with the first, second and third
frequencies for each of the first, second and third mode, the power
amplifier may be configured to be driven in the first mode at the
first frequency, in the second mode at the second frequency and in
the third mode at the third frequency. In some examples, when the
first frequency is close to the center frequency divided by the
multiple, the one of the first, second and third sub-amplifiers
111, 112, 113, that is associated to the longest one of the first,
second and third electrical lengths may act as a primary amplifier.
Notably, the second and third frequencies are greater than the
first frequency.
[0062] The descriptive text after FIG. 5 also explains the general
behaviour, or mode of operation for different frequencies, of the
power amplifier 100 disclosed herein.
[0063] FIG. 4 depicts an exemplifying power amplifier 101 according
embodiments herein, in which a three-transistor amplifier is
employed. This means that the power amplifier 101 includes the
first, second and third sub-amplifiers 111, 112, 113. The
exemplifying power amplifier has a 10-to-1 bandwidth of high
average efficiency. In this embodiment, the first and second
transmission lines 131, 132 are connected to the first common
transmission line 135, included in the output network 130. The
first common transmission line 135 is common to the first and
second sub-amplifiers 131, 132.
[0064] In this embodiment, the output network 130 is configured as
follows. The first transmission line 131 is 2 quarter wavelengths,
i.e. an electrical length of the first transmission line 131 is 2
quarter wavelengths of the center frequency of the power amplifier
101. The second transmission line 132 is 1 quarter wavelength. The
third transmission line 133 is 3 quarter wavelengths and the first
common transmission line 135, aka the first trunk, is 5 quarter
wavelengths
[0065] Since an electrical length of any transmission line shown
here is proportional to frequency and physical length, the physical
lengths of the transmission lines are given as electrical length at
center frequency.
[0066] The small triangles, in FIG. 4, represent sub-amplifiers,
e.g. power transistors, with accompanying wideband input match,
bias and output match. The electrical length of the output match is
included in the electrical lengths of the transmission lines 131,
132, 133 from respective sub-amplifier.
[0067] In this example, as mentioned above but now expressed
somewhat differently, the first and second sub-amplifiers 111, 112
are connected to the first common transmission line 135 by a half
and a quarter wavelength at center frequency, respectively. This
means that the first and second transmission lines have electrical
lengths of a half and a quarter wavelength, respectively. The first
common transmission line 135 has an electrical length of five
quarter wavelengths at center frequency. The first common
transmission line 135 is connected to the output port 140. The
third sub-amplifier 113 is directly connected to the output port by
the third transmission line 133, which is three quarter-wavelengths
at center frequency.
[0068] According to embodiments herein, the output network 130 may
be built up entirely of (non-dispersive) transmission lines that
are multiples of a quarter wavelength long at center frequency. In
this manner, a symmetric frequency response around center frequency
may be obtained. Thanks to the transmission lines of quarter
wavelengths at center frequency the power amplifier may be operated
over a very wide bandwidth, such as 6 to 1 or greater. The
operation around center frequency may be a pure 2-stage or
multistage Doherty mode of some kind. Since the transmission lines
131, 132, 133 are generally longer than they would be in a
dedicated conventional Doherty amplifier, the Doherty mode region
at center frequency may usually be narrower in bandwidth in the
power amplifiers according to embodiments herein, even though the
total high-efficiency bandwidth is far greater than that of a
conventional Doherty amplifier.
[0069] The wideband operation, i.e. amplifying a relatively
narrowband signal at any frequency in a wide band, instead relies
on using many other modes of operation. The operation modes vary
across the bandwidth, or operational bandwidth, and may include
pure or detuned Chireix-Doherty, Doherty-Chireix and Doherty modes
and transitional modes between these modes. The different modes of
operation at different frequencies usually require differently
shaped drive signals as is exemplified by FIGS. 5a-5c and other
similar sets of Figures.
[0070] FIGS. 5a-5c show operation of the exemplary power amplifier
101 of FIG. 4 at various frequencies within one half of the 10-to-1
bandwidth. The other half is a mirror image; even symmetry for the
amplitudes and odd for the phases. For the 10-to-1 bandwidth to be
centered at 1, it must go from about 0.18 to 2-0.18 (=1.8), so the
lowest frequency supported is 0.18 times the center frequency. In
these Figures, the first sub-amplifier 111 is represented by a
dotted line, the second sub-amplifier 112 is represented by a solid
line and the third sub-amplifier 113 is represented by a dashed
line.
[0071] Now referring in detail to FIG. 5a, which comprises six
smaller FIGS. 5a:1-5a:6, each of these smaller Figures will be
described. In order to understand the context of these Figures,
FIG. 5a:6 is described first.
[0072] Thus, FIG. 5a:6 illustrates, beginning at the top of FIG.
5a:6, the third transmission line 133 with an electrical length of
0.14.lamda. at 0.18 times the center frequency f.sub.c., since
0.18*0.75=0.135=-0.14. Similarly, the first and second transmission
lines 131, 132 and the first common transmission line 135 have
electrical lengths of 0.045.lamda., 0.091.lamda. and 0.23.lamda.,
respectively for this frequency, i.e. at 0.18*f.sub.c.
[0073] From FIG. 5a:1, it may be seen that the second sub-amplifier
112 is operated as a primary sub-amplifier at this frequency and
for amplitudes up to about 0.5. This means that the second
sub-amplifier 112 outputs a current that is greater than any
respective currents from the first and third sub-amplifiers 111,
113. Moreover, it may also be seen that the third sub-amplifier 113
is not contributing at all up to about amplitudes of 0.6.
[0074] FIG. 5a:2 shows RF voltage as a function of amplitude when
operating the power amplifier 101 at 0.18*f.sub.c. This Figure
shows, e.g., that all sub-amplifiers 111, 112, 113 are saturated
for amplitudes above about 0.5. Moreover, the second sub-amplifier
112 increases voltage faster than the first and third
sub-amplifiers 111, 113.
[0075] FIG. 5a:3 shows total efficiency for all sub-amplifiers 111,
112, 113 as a function of amplitude when operating the power
amplifier 101 at 0.18*f.sub.c. This Figure shows, e.g., that total
efficiency increases linearly up to an amplitude of about 0.5.
[0076] FIG. 5a:4 shows RF current phase as a function of amplitude
when operating the power amplifier 101 at 0.18*f.sub.c. This Figure
shows, e.g., that the second sub-amplifier has the highest current
phase over all amplitudes. This depends on that the second
sub-amplifier has the longest electrical length towards the output
port and the phase of the current compensates for this. A positive
phase means ahead, or before, in time. If all phases are greater
than 2*pi (2*3.1415 . . . ), it can be reduced with 2*pi in a
narrowband perspective.
[0077] FIG. 5a:5 shows RF voltage phase as a function of amplitude
when operating the power amplifier 101 at 0.18*f.sub.c. This Figure
shows, e.g., that the second sub-amplifier has the highest voltage
phase over all amplitudes. Similarly to FIG. 5a:4, this depends on
that the second sub-amplifier has the longest electrical length
towards the output port and the phase of the voltage compensates
for this. A positive phase means ahead, or before, in time. If all
phases are greater than 2*pi (2*3.1415 . . . ), it can be reduced
with 2*pi in a narrowband perspective.
[0078] Similar observations may be made for each of the first,
second and third sub-amplifiers 111, 112, 113 while studying FIGS.
5b, 5c and 5d. As an example, with reference to FIG. 5b:1, the
second sub-amplifier 112 is operated as primary sub-amplifier at
frequency 0.39*f.sub.c for amplitudes above about 0.3. As another
example, with reference to FIG. 5c:2, saturation for each of the
second, first and third sub-amplifiers is reached at amplitudes of
about 0.2, 0.4 and 0.9, respectively, at frequency 0.59*f.sub.c. As
a further example, with reference to FIG. 5d:3, total efficiency
increases linearly up to an amplitude of about 0.35 for frequency
of 0.8*f.sub.c.
[0079] As can be observed above with reference to FIGS. 5a-5d, the
RF output currents of the transistors, referred to as
sub-amplifiers above, and the RF voltages are thus as follows, from
low to high amplitudes:
[0080] 1) One transistor delivers all RF current, linearly
increasing with amplitude and with a constant phase relative to the
output. All voltages are below saturation and breakdown limits.
Efficiency is in this region proportional to the amplitude and to
the trans-impedance from the driven transistor to the output. This
region continues until one transistor voltage reaches a limit.
[0081] 2) One transistor is voltage-limited. Two transistors
deliver RF current. Their phases relative to the output generally
change with amplitude. This continues until two transistors are
voltage limited.
[0082] 3) Two transistors are voltage limited, often similar to
what is called "outphasing" in a symmetric 2-transistor Chireix
amplifier, with increasing RF current amplitudes. This continues
until it is more efficient to start a third transistor, not
necessarily where the possibility of outphasing ends.
[0083] 4) Two transistors voltage limited with a third transistor
also delivering RF current, and not voltage limited.
[0084] 5), and so on . . .
[0085] In FIG. 6, a diagram over efficiency versus frequency is
illustrated. From about 0.18 to 1.8 relative to the center
frequency, i.e. from 0.5 to 5 GHz, a resulting average efficiency
with class B operation of the sub-amplifiers for use with a
narrowband signal with a 7 dB Rayleigh amplitude distribution is
plotted in the Figure. An average efficiency for a narrowband
signal of over 60% is achieved in the 10-to-1 bandwidth, i.e. from
0.5 GHz to 5 GHz in this example.
[0086] The electrical length of an output matching network for each
sub-amplifier may be different depending on the frequency range to
be covered. Each of the first, second and third transmission lines
131, 132, 133 of the output network includes a respective output
matching network for each sub-amplifier. For wideband operation
towards high frequencies, the output network is largely determined
by the capacitance of the output node, Cds (ds=drain-source), which
is "absorbed" into a suitable network. Although it is usually
called a "matching" network, impedance transformation is not the
primary objective, and usually more wideband operation is possible
if very little transformation is done in this part, instead
transforming the load to a value that is compatible with the
largely untransformed sum of admittances.
[0087] Now turning to FIG. 7, an arrangement of components called a
pi-network is shown. The arrangement of components has an
electrical length of about a quarter wavelength at the upper
frequency limit, and at center frequency about an eight of a
wavelength, and corresponds quite well to a fixed physical length.
The electrical lengths of the output network are deducted from the
transmission line lengths of the power amplifier 101 of FIG. 4. The
remaining of the transmission line length can be built from one or
more further pi-networks, transmission lines ("distributed"), or
semi-lumped varieties with both lumped and distributed elements.
For lower frequency operation, other pi-match dimensioning or a
simple L-match may be used, and sometimes no compensation at all is
needed
[0088] The class B assumption requires low-impedance termination of
harmonics two and higher at the output of a sub-amplifier, e.g.
drain or collector of a transisor. This is possible roughly above
center frequency, for the lower half the harmonics fall inside or
too close to the supported fundamental band. For wideband operation
including the lower frequency range operation similar to class B,
but without the harmonic termination can be used.
[0089] In some cases it is sufficient to simply terminate the
harmonics resistively for the lower part of the efficient
bandwidth. Resistive termination outside the band is achieved by
using a wideband isolator before the selected (or tuneable)
channel/band filter. All the power outside the band is reflected by
the filter and terminated in the backwards direction by the
isolator.
[0090] Another method is to use a diplexed load for the harmonics.
In this case a high-pass path to a resistor (dummy load) is
provided. Since the second harmonic is quite far from the
fundamental band, this filter can be simple and cheap. Both these
methods terminate the harmonics outside the output network, so
reflections within the output network can still affect efficiency.
Tuneable tank circuits, or resonator, at the transistor outputs are
of course also possible.
[0091] A wideband method to get high efficiency and low harmonic
content directly at the sub-amplifier is to use a push-pull
arrangement of class B driven transistors. The term "push-pull" has
its conventional meaning that is known within the field of power
amplifiers. A single-ended, simpler but less efficient, wideband
alternative is to use class A with dynamically amplitude-following
gate bias to eliminate excess DC current.
[0092] FIGS. 8a-8i illustrate schematically a number of different
configurations of the output network 130 for the power amplifier
100 comprising three sub-amplifiers 111, 112, 113.
[0093] In these Figures, the following nomenclature is used.
Referring to FIG. 8a, the reference numerals 131, 132, 133 denote
the first, second and third transmission lines as is the case also
in FIG. 3. Also as in FIG. 3, the reference numeral 135 denotes the
first common transmission line. Additionally, a character `1` means
an electrical length is one quarter wavelength for the transmission
line at which an arrow next to the character points. Similarly, a
character `2` means an electrical length is one quarter wavelength
for the transmission line at which an arrow next to the character
points, etc.
[0094] Hence, as indicated for the configuration in FIG. 8a, the
four numbers indicate the electrical lengths at center frequency in
quarter wavelengths. The first three numbers are the lengths of the
transmission lines 131, 132, 133 originating from the three
sub-amplifiers 111, 112, 113, and the fourth number is the length
of the first common transmission line 135 from the junction of the
first and second transmission lines 131, 132 from sub-amplifiers
111, 112 to the output 140. Therefore, configuration of the output
network 130, shown in FIG. 8a, is denoted "1 2 2 1". The third
sub-amplifier's 113 third transmission line 133 is then connected
directly to the output port 140 as for all embodiments including
three sub-amplifiers.
[0095] In FIG. 8b, the first transmission line 131 has an
electrical length of one, 1, quarter wavelength, the second
transmission line 132 has an electrical length of two, 2, quarter
wavelengths, the third transmission line 133 has an electrical
length of one, 1, quarter wavelengths, and the first common
transmission line 135 has an electrical length of zero, 0, quarter
wavelengths. Thus, the nomenclature is "1 2 0 1".
[0096] In FIG. 8c, the first transmission line 131 has an
electrical length of 0 quarter wavelengths, the second transmission
line 132 has an electrical length of 1 quarter wavelengths, the
third transmission line 133 has an electrical length of 3 quarter
wavelengths, and the first common transmission line 135 has an
electrical length of 1 quarter wavelengths. Thus, the nomenclature
is "0 1 3 1".
[0097] In FIG. 8d, the first transmission line 131 has an
electrical length of 1 quarter wavelengths, the second transmission
line 132 has an electrical length of 4 quarter wavelengths, the
third transmission line 133 has an electrical length of 2 quarter
wavelengths, and the first common transmission line 135 has an
electrical length of 3 quarter wavelengths. Thus, the nomenclature
is "1 4 2 3".
[0098] In FIG. 8e, the first transmission line 131 has an
electrical length of 1 quarter wavelengths, the second transmission
line 132 has an electrical length of 2 quarter wavelengths, the
third transmission line 133 has an electrical length of 4 quarter
wavelengths, and the first common transmission line 135 has an
electrical length of 0 quarter wavelengths. Thus, the nomenclature
is "1 2 4 0".
[0099] In FIG. 8f, the first transmission line 131 has an
electrical length of 0 quarter wavelengths, the second transmission
line 132 has an electrical length of 1 quarter wavelengths, the
third transmission line 133 has an electrical length of 2 quarter
wavelengths, and the first common transmission line 135 has an
electrical length of 3 quarter wavelengths. Thus, the nomenclature
is "0 1 2 3".
[0100] In FIG. 8g, the first transmission line 131 has an
electrical length of 1 quarter wavelengths, the second transmission
line 132 has an electrical length of 2 quarter wavelengths, the
third transmission line 133 has an electrical length of 2 quarter
wavelengths, and the first common transmission line 135 has an
electrical length of 2 quarter wavelengths. Thus, the nomenclature
is "1 2 2 2".
[0101] In FIG. 8h, the first transmission line 131 has an
electrical length of 3 quarter wavelengths, the second transmission
line 132 has an electrical length of 4 quarter wavelengths, the
third transmission line 133 has an electrical length of 2 quarter
wavelengths, and the first common transmission line 135 has an
electrical length of 1 quarter wavelengths. Thus, the nomenclature
is "3 4 2 1".
[0102] In FIG. 8i, the first transmission line 131 has an
electrical length of 1 quarter wavelengths, the second transmission
line 132 has an electrical length of 2 quarter wavelengths, the
third transmission line 133 has an electrical length of 3 quarter
wavelengths, and the first common transmission line 135 has an
electrical length of 5 quarter wavelengths. Thus, the nomenclature
is "1 2 3 5".
[0103] FIG. 9a-9c illustrate diagrams in which efficiency versus
frequency for some exemplifying power amplifiers is plotted. The
configuration of the output network is noted--using the
nomenclature as above--in each diagram, directly above the axis of
frequency (horizontal axis). For these exemplifying power
amplifiers minimum average class B efficiency within the bandwidth
is relatively higher than other (not shown) tested configurations
of the output network. The power amplifier receives a signal with a
7 dB Rayleigh distributed amplitude as noted above each diagram.
Also above each diagram, an operational bandwidth of the power
amplifier is noted. Moreover, the threshold value for efficiency is
noted in each diagram, usually under the curve but in the upper
right corner of the plot area.
[0104] In FIG. 9a, efficiency for an exemplifying power amplifier
with an output network 130 configured as "1 2 3 5" is shown. In
this example, the efficiency is at least 62% for the operational
bandwidth of 6.1 to 1. Reference is made to FIG. 8i.
[0105] In FIG. 9b, efficiency for an exemplifying power amplifier
with an output network 130 configured as "1 4 2 3" is shown.
Reference is made to FIG. 8d.
[0106] In FIG. 9c, efficiency for an exemplifying power amplifier
with an output network 130 configured as "2 8 4 1" is shown.
Similarly to the examples of FIG. 8, this means that the first
transmission line 131 has an electrical length of 2 quarter
wavelengths, the second transmission line 132 has an electrical
length of 8 quarter wavelengths, the third transmission line 133
has an electrical length of 4 quarter wavelengths, and the first
common transmission line 135 has an electrical length of 1 quarter
wavelengths. Thus, the nomenclature is "2 8 4 1".
[0107] Turning to FIG. 10 theoretical minimum efficiency for
different bandwidths in class B mode of the power amplifier for a
number of different structures, illustrating that the output
networks which include the first common transmission line 135 are
generally more efficient, but a configuration of the output network
according to "1 2 4" (without trunk) to the common output is
relatively good up to a 7:1 bandwidth.
[0108] In some embodiments, higher order configurations of the
output network 130 are employed. Due to the higher number of
electrical length combinations in these embodiments, longer
transmission lines may be used. In this manner, wider bandwidth
with high efficiency may be obtained. Alternatively or
additionally, the output network may be configured to obtain high
efficiency over a somewhat smaller bandwidth but for signals with
larger PAR values.
[0109] In FIG. 11a, an embodiment of the power amplifier 100 is
shown. In this example, the power amplifier 100 further comprises
the fourth sub-amplifier 114. The fourth sub-amplifier 114 is
connected to the input network 120 and the output network 130. The
output network 130 further comprises the fourth transmission line
134.
[0110] In some examples, the fourth transmission line 134 may be
connected directly to the output port 140, as illustrated in FIG.
11a and by connector 160 in FIG. 3. Moreover, a fourth electrical
length may include electrical length of the fourth transmission
line 134. Since the lines to the sub-amplifiers branch out from a
single trunk line, e.g. the second common transmission line 136, at
different points this configuration of the output network is
referred as "serial branched", denoted S in the FIG. 11a. In
contrast, the configuration of the output network 130, as shown in
FIG. 11b below, is referred to as "parallel branched", denoted P in
FIG. 11b.
[0111] In these embodiments, the third and fourth sub-amplifier
133, 134 may be connected to the second common transmission line
136, included in the output network 130. Obviously, in embodiments
in which the second common transmission line 136 is not present,
the lines that end to the right and left of the second common
transmission line 136 are connected to each other, i.e. no break in
the circuit shall occur. The second common transmission line 136,
or a second trunk, may be common to the third and fourth
sub-amplifiers 133, 134, as shown in FIG. 11b. However, it shall be
noted that in some examples the second common transmission line 136
is connected the third transmission line 133, but not to the fourth
transmission line 134, as already shown in FIG. 11a. The notion
`common` is due to that the first common transmission line 135 is
connected to the second common transmission line 136, which make
the second common transmission line 136 indirectly common to the
first, second and third sub-amplifiers 111, 112, 113. Therefore,
the third electrical length may include electrical length of the
second common transmission line 136. For the fourth electrical
length it may be that electrical length of the second common
transmission line is not includes as in FIG. 11a, while in other
examples as in FIG. 11b the fourth electrical length includes
electrical length of the second common transmission line 136.
[0112] With reference to FIGS. 12a-12d, the power amplifier of FIG.
11a is shown to have high average efficiency in a 12-to-1
bandwidth. As mentioned, the electrical lengths of the transmission
lines from the sub-amplifiers at center frequency are (from the top
down) 1, 2, 5, and 7 quarter wavelengths, and the lengths of the
trunk line segments between the connection points are one quarter
wavelength each.
[0113] FIGS. 12a-12c show operation of the power amplifier of FIG.
11a at various frequencies within one half of the 12-to-1
bandwidth, starting at 0.15 of the center frequency. As with the
previous example of a 3-stage amplifier, i.e. the power amplifier
comprises three sub-amplifiers, this 4-stage amplifier uses
different combinations of operating modes at different frequencies,
and achieves good efficiency curves over the whole bandwidth.
Similar observations as for FIGS. 5a-5d may be made here without
further elaboration in detail.
[0114] Referring to FIGS. 13a-13d, operation of another 4-stage
power amplifier is illustrated. In this example, the 4-stage power
amplifier, comprising the first, second, third and fourth
sub-amplifiers 111, 112, 113, 114, employs an output network, which
has a configuration that is shown to have high average efficiency
in an 8-to-1 bandwidth.
[0115] In this exemplifying output network 130, also shown in FIG.
11b, the electrical lengths of the transmission lines from the
sub-amplifiers at center frequency are (from the top down) 2, 3, 1
and 2 quarter wavelengths, and the lengths of the two trunk lines,
e.g. the first and second common transmission lines 135, 136, that
both connect directly to the load, that are 1 and 4 quarter
wavelengths each. Since the first and second trunk lines branch out
from (or, looking in the other direction, come together to) the
same point (the load), this type of configuration is referred to as
"parallel branched" herein. Reference is made to the schematic
configurations shown in the sixth smaller Figure of FIGS. 13a-d,
e.g 13a:6, 13b:6, etc, for each respective frequency.
[0116] Similar observations as for FIGS. 5a-5d may be made here
without further elaboration in detail.
[0117] In FIGS. 14a-14k, further exemplifying output networks 130
are illustrated schematically. In these exemplifying power
amplifiers are also referred to as 4-stage amplifiers since the
power amplifiers include four sub-amplifiers. The output networks
may be configured in serial or parallel manners of branching.
[0118] For some of the power amplifiers of FIGS. 14a-14k efficiency
versus frequency is plotted in FIGS. 15a-15h. Similarly to FIGS.
9a-9c, configuration of the output network, operational bandwidth,
PAR of signal and efficiency is shown in the diagrams. Therefore,
reference is made to the diagrams themselves in order to make
observations. FIGS. 15a-g show diagrams for 7 dB PAR Rayleigh
distributed amplitude, while FIGS. 15e-h show diagrams for 10 dB
PAR Rayleigh distributed amplitude.
[0119] This means that some embodiments of the power amplifier may
have increased backed off operation, e.g. higher number of dBs,
i.e. 3 dBs (10-7) as in the examples above, with high
efficiency.
[0120] FIG. 16 shows theoretical minimum efficiency within
different bandwidths in class B mode for some configurations of the
output network 130. The branched output networks (serial, parallel
and single trunk) perform best. The un-branched network with 1, 2,
4, and 8 quarter wavelengths to the common output at center
frequency is relatively good for the widest bandwidths, but far
behind the branched configurations at the lower bandwidths.
[0121] Networks using only line lengths that are multiples of a
quarter wavelength have a periodically repeating frequency response
pattern. The first instance of a higher mode, i.e. a mode with
higher efficiency, occurs at three times the first mode center
frequency. The bandwidth of the wideband amplifiers described above
goes very close to twice the center frequency, so the repeating
pattern will have just a small unsupported region before the higher
mode starts. Using the first and second modes of the 12-to-1
bandwidth example, the unsupported region is 2*0.15 in the original
frequency scale, with the total bandwidth going from 0.15 to
4-0.15. This gives a 25-to-1 bandwidth with a 15% relative
bandwidth around center frequency (now at two times the original
center frequency) unsupported.
[0122] The equivalent of placing the center frequency at two times
the original center frequency is to build the output network only
from lines that are multiples of a half wavelength. This can be
advantageous if there is no need for operation in a middle region,
since the efficiency in the two supported regions is higher for the
same total (lowest to highest) bandwidth. The technique can
trivially be extended to responses having three (using only
multiples of three quarter wavelengths at center frequency), four
or more regions. The only requirement is that the lines are built
only from multiples of some specific line length.
[0123] In the previous examples, very wideband operation is
achieved. In those cases, a symmetric or close to symmetric
frequency response, obtained by using lines with lengths that are
multiples of a quarter wavelength at center frequency, generally
gives the best results. For less wideband operation, higher
efficiency can sometimes be achieved by using other transmission
line lengths than multiples of quarter-wavelengths of the center
frequency. As an example, operation of a 3-stage power amplifier
that achieves high average efficiency for signals with large PAR in
a 2.5 to 1 bandwidth is shown in FIGS. 17a-17d. The line lengths
are in this case about 0.21, 0.32 and 0.52 wavelengths at center
frequency, and are all connected directly to the output, i.e. no
first common transmission line is employed. Similar observations as
for FIGS. 5a-5d may be made here without further elaboration in
detail.
[0124] The class B efficiency for a signal with 7 dB PAR Rayleigh
distributed amplitude is 70% or higher in the 2.5-to-1 frequency
range, as shown in FIG. 18a.
[0125] The class B efficiency for a signal with 10 dB PAR Rayleigh
distributed amplitude is 62% or higher in the 2.5-to-1 frequency
range, as shown in FIG. 18b.
[0126] Hence, these embodiments of the power amplifier have
increased efficiency, but not increased bandwidth, in backed off
operation.
[0127] In the embodiments described above, the sub-amplifiers 111,
112, 113, 114 may have the same size.
[0128] However, in some embodiments different sizes for the
different amplifiers may be used. For example, one sub-amplifier
may have twice the size of the two other sub-amplifiers in case of
a 3-stage power amplifier. It is also possible to make a
configuration with a trunk line from the connection point of two of
the lines from the sub-amplifiers to the output. An example of both
these features is a power amplifier in which sub-amplifiers 1 and 3
have half the size of amplifier 2 (and the lines from
sub-amplifiers 1 and 3 consequentially having twice the
characteristic impedance of the line from sub-amplifier 2).
Sub-amplifiers 1 and 2 are connected via lines of length 0.22 and
0.49 wavelengths (at center frequency) to a trunk line of 0.05
wavelengths, which trunk line is connected to the output.
Sub-amplifier 3 is coupled via a line that is 0.32 wavelengths at
center frequency. The efficiency in class B mode is better than 63%
over a frequency range of 2.5 (or even 2.6) to 1 (0.56 to 1.44), as
shown in FIG. 19.
[0129] Hence, expressed somewhat differently, each of the first and
third sub-amplifier 111, 113 may have half of a size of the second
sub-amplifier 112. Moreover, the first and second transmission
lines 131, 132 have electrical lengths of 0.22 wavelengths and 0.49
wavelengths, respectively and the first common transmission line
135 has electrical length of 0.05 wavelengths. The third
transmission line 133 has electrical length of 0.32 wavelengths.
All wavelengths here are relative the center frequency of the power
amplifier.
[0130] FIG. 20 shows an exemplifying radio network node 200.
[0131] As used herein, the term "radio network node" may refer to
is a piece of equipment that facilitates wireless communication
between user equipment (UE) and a network. Accordingly, the term
"radio network node" may refer to a Base Station (BS), a Base
Transceiver Station (BTS), a Radio Base Station (RBS), a NodeB in
so called Third Generation (3G) networks, evolved Node B, eNodeB or
eNB in Long Term Evolution (LTE) networks, or the like. In UMTS
Terrestrial Radio Access Network (UTRAN) networks, where UTMS is
short for Universal Mobile Telecommunications System, the term
"radio network node" may also refer to a Radio Network Controller.
Furthermore, in Global System for Mobile Communications (GSM) EDGE
Radio Access Network (GERAN), where EDGE is short for Enhanced Data
rates for GSM Evolution, the term "radio network node" may also
refer to a Base Station Controller (BSC).
[0132] The radio network node 200 comprises a power amplifier 210
according to the embodiments described above.
[0133] Furthermore, the radio network node 200 may comprise a
processing circuit 220 and/or a memory 230.
[0134] As used herein, the term "processing circuit" may be a
processing unit, a processor, an application specific integrated
circuit (ASIC), a field-programmable gate array (FPGA) or the like.
As an example, a processor, an ASIC, an FPGA or the like may
comprise one or more processor kernels. In some examples, the
processing circuit may be embodied by a software or hardware
module. Any such module may be a determining means, estimating
means, capturing means, associating means, comparing means,
identification means, selecting means, receiving means,
transmitting means or the like as disclosed herein. As an example,
the expression "means" may be a unit, such as a determining unit,
selecting unit, etc.
[0135] As used herein, the term "memory" may refer to a hard disk,
a magnetic storage medium, a portable computer diskette or disc,
flash memory, random access memory (RAM) or the like. Furthermore,
the term "memory" may refer to an internal register memory of a
processor or the like.
[0136] The radio network node 200 may further comprise additional
transceiver circuitry (not shown) for facilitating transmission and
reception of data, e.g. in the form of radio signals.
[0137] FIG. 21 shows an exemplifying user equipment 300.
[0138] As used herein, the term "user equipment" may refer to a
mobile phone, a cellular phone, a Personal Digital Assistant (PDA)
equipped with radio communication capabilities, a smartphone, a
laptop or personal computer (PC) equipped with an internal or
external mobile broadband modem, a tablet PC with radio
communication capabilities, a portable electronic radio
communication device, a sensor device equipped with radio
communication capabilities or the like. The sensor may be any kind
of weather sensor, such as wind, temperature, air pressure,
humidity etc. As further examples, the sensor may be a light
sensor, an electronic switch, a microphone, a loudspeaker, a camera
sensor etc.
[0139] The user equipment 300 comprises a power amplifier 310
according to the embodiments described above.
[0140] Furthermore, the user equipment 300 may comprise a
processing circuit 320 and/or a memory 330. The means of the terms
"processing circuit" and "memory" as explained above applies also
for the user equipment 300.
[0141] The user equipment 300 may further comprise additional
transceiver circuitry (not shown) for facilitating transmission and
reception of data, e.g. in the form of radio signals.
[0142] As used herein, the terms "number", "value" may be any kind
of digit, such as binary, real, imaginary or rational number or the
like. Moreover, "number", "value" may be one or more characters,
such as a letter or a string of letters. "number", "value" may also
be represented by a bit string.
[0143] As used herein, the expression "in some embodiments" has
been used to indicate that the features of the embodiment described
may be combined with any other embodiment disclosed herein.
[0144] Even though embodiments of the various aspects have been
described, many different alterations, modifications and the like
thereof will become apparent for those skilled in the art. The
described embodiments are therefore not intended to limit the scope
of the present disclosure.
* * * * *