EP3391537A1 - Composite power amplifier - Google Patents

Composite power amplifier

Info

Publication number
EP3391537A1
EP3391537A1 EP16700217.9A EP16700217A EP3391537A1 EP 3391537 A1 EP3391537 A1 EP 3391537A1 EP 16700217 A EP16700217 A EP 16700217A EP 3391537 A1 EP3391537 A1 EP 3391537A1
Authority
EP
European Patent Office
Prior art keywords
power amplifier
output
driving signal
composite
power
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP16700217.9A
Other languages
German (de)
French (fr)
Inventor
Francesc Purroy MARTIN
Zhixiong Zeng
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Huawei Technologies Co Ltd
Original Assignee
Huawei Technologies Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Huawei Technologies Co Ltd filed Critical Huawei Technologies Co Ltd
Publication of EP3391537A1 publication Critical patent/EP3391537A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/20—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers
    • H03F3/24—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers of transmitter output stages
    • H03F3/245—Power amplifiers, e.g. Class B amplifiers, Class C amplifiers of transmitter output stages with semiconductor devices only
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/02—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
    • H03F1/0205—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers
    • H03F1/0288—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers using a main and one or several auxiliary peaking amplifiers whereby the load is connected to the main amplifier using an impedance inverter, e.g. Doherty amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/02—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
    • H03F1/0205—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers
    • H03F1/0294—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in transistor amplifiers using vector summing of two or more constant amplitude phase-modulated signals
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/189—High-frequency amplifiers, e.g. radio frequency amplifiers
    • H03F3/19—High-frequency amplifiers, e.g. radio frequency amplifiers with semiconductor devices only

Definitions

  • the present invention relates to a composite power amplifier system for amplification of electric signals. Furthermore, the present invention also relates to a transmitter comprising such a composite power amplifier.
  • the amplifier size should be eight times bigger than what is needed for the power that the power amplifier (PA) will in average deliver to the antenna load. This makes it difficult to implement a high efficiency, low power consumption, power amplifiers.
  • PA architectures have been proposed to improve efficiency at low power level (i.e. Back Off power levels). Basically, these architectures are based on two main techniques: Voltage modulation and Load modulation.
  • Voltage modulation techniques are mainly limited by the modulator signal bandwidth capability and by modulator efficiency: both at maximum power and at back off power.
  • Load modulation techniques are limited by Efficiency vs Bandwidth trade-off for high load pull ratio requirements.
  • An objective of the present invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions.
  • a further objective of the present invention is to provide a composite power amplifier system for amplifying an electric signal to be fed to an antenna, and a transmitter device comprising such an amplifier system, which amplifier system provides a better efficiency at low power levels compared to power amplifiers according to conventional technologies.
  • Another objective of the present invention is to provide a composite power amplifier system for amplifying an electric signal to be fed to an antenna, and a transmitter device comprising such an amplifier system, which amplifier system provides at least one of an improved efficiency versus bandwidth, an improved efficiency at back-off power levels, and an improved average efficiency of the amplifier system transmitting Rayleigh distributed signals with limited peak to average ratio.
  • Embodiments of the present invention focus on the group of techniques based on load modulation and improves the efficiency vs bandwidth trade off by reducing the demand of load pull ratio of the devices used in the power amplifier implementation.
  • the above objectives are fulfilled by the subject matter of the independent claims. Further advantageous implementation forms of the present invention can be found in the dependent claims.
  • an IQ data signal is to be understood as a data signal comprising an in-phase data signal or an I data signal and a quadrature data signal or a Q data signal.
  • a composite power amplifier system comprising an input node configured to receive an input signal, an output node configured to output an output signal, and at least a first power amplifier, a second power amplifier, a third power amplifier, and a fourth power amplifier together configured in a multi way Doherty structure connected between the input node and the output node.
  • the first power amplifier and the second power amplifier are configured as a Chireix pair of power amplifiers and configured to operate as a main power amplifier in the multi way Doherty structure.
  • the third power amplifier is configured to operate as a first auxiliary power amplifier (preferably a first peak amplifier) in the multi way Doherty structure
  • the fourth power amplifier is configured to operate as a second auxiliary power amplifier (preferably a second peak amplifier) in the multi way Doherty structure.
  • the efficiency of the power amplifier may be kept high over a wide range of back-off power levels. Furthermore, the efficiency may be kept almost constant from a first peak in efficiency at a back-off power level up to the maximum output power of the composite power amplifier system.
  • the composite power amplifier system further comprises a driving signal device configured to provide a first driving signal to the first power amplifier, a second driving signal to the second power amplifier, a third driving signal to the third power amplifier, and a fourth driving signal to the fourth power amplifier.
  • the driving signal device is configured to provide the first driving signal to the first power amplifier so as to operate the first power amplifier for all amplitude levels of the input signal, and provide the second driving signal to the second power amplifier so as to operate the second power amplifier for all amplitude levels of the input signal.
  • the amplitude of the input signals may be a voltage level and/or a current level.
  • the efficiency of the composite power amplifier system may be optimized at the same time as the full power range of all power amplifiers are used optimally.
  • the driving signal device comprises digital hardware.
  • the driving signal device is configured to provide the first driving signal so that the amplitude of the first driving signal, up to the output voltage for a maximum voltage swing of the first power amplifier, is linear with the output voltage of the output signal, provide the second driving signal so that the amplitude of the second driving signal, up to the output voltage for a maximum voltage swing of the second power amplifier, is linear with the output voltage of the output signal, and wherein the phase difference between the first driving signal and the second driving signal is constant up to the output voltage for a maximum voltage swing of at least one of the first power amplifier and the second power amplifier.
  • the amplitude may be a voltage amplitude and/or a current amplitude in dependence of how the first power amplifier and the second power amplifier are driven.
  • the provision of such driving signals provides a desired high efficiency of the composite power amplifier.
  • the desired peaks of efficiency of the composite power amplifier are achieved by appropriate changes in phase difference between the first driving signal and the second driving and appropriate changes in amplitude of the first and second driving signals.
  • the driving signal device is configured to provide the first driving signal and the second driving signal so that at least one of the amplitude of the first driving signal, the amplitude of the second driving signal and the phase difference between the first driving signal and the second driving signal, changes in a nonlinear way for output voltages above the output voltage for the maximum voltage swing of the first power amplifier and the output voltage for the maximum voltage swing of the second power amplifier.
  • the driving signal device is configured to provide a third driving signal to activate the third power amplifier for voltage levels of the output signal exceeding a first predetermined threshold level.
  • the driving signal device is configured to provide a fourth driving signal to activate the fourth power amplifier for voltage levels of the output signal exceeding a second predetermined threshold level which is higher than the first predetermined threshold level. By activating the fourth power amplifier in this way a high efficiency of the composite power amplifier may be provided.
  • the first predetermined threshold level and the second predetermined threshold level are determined based on the peak in efficiency of the composite power amplifier system being closest to zero output voltage and the ratio between the peak output power of the third power amplifier or the peak output power of the fourth power amplifier and the sum of the peak output powers of the first power amplifier and the second power amplifier.
  • the dimensioning of the composite power amplifier is started with the dimensioning of the first power amplifier and the second power amplifier and the position of the first peak in efficiency of the composite power amplifier.
  • This first peak in efficiency is the peak that is closest to zero output voltage of the peaks in the efficiency curve of the composite power amplifier.
  • the first power amplifier and the second power amplifier are usually chosen to have the same maximum output power.
  • the second peak is then given by the above mentioned design parameters. When maximizing the efficiency of the composite power amplifier the first predetermined threshold level and the second predetermined threshold level are thus determined by the given parameters.
  • the driving signal device is configured to provide the third driving signal and the fourth driving signal with an amplitude which varies in a nonlinear way with the voltage of the output signal and with a phase which is constant.
  • the amplitude may be a voltage amplitude and/or a current amplitude in dependence of how the third power amplifier and the fourth power amplifier are driven.
  • the efficiency of the composite power amplifier system may be optimized.
  • the composite power amplifier system further comprises a first adapting network and a second adapting network, wherein the first adapting network is connected between an output of the first power amplifier and a common node and the second adapting network is connected between an output of the second power amplifier and the common node so as to provide the Chireix pair of power amplifiers.
  • the composite power amplifier system according to the ninth possible implementation form is advantageous in that it is easy to implement and optimize.
  • the composite power amplifier system further comprises a third adapting network, wherein the common node is connected to the output node via the third adapting network.
  • an output of the third power amplifier is connected to the output node via the third adapting network.
  • an output of the fourth power amplifier is directly connected to the output node.
  • the composite power amplifier system according to the tenth, eleventh or twelfth possible implementation form is advantageous in that it is easy to implement and optimize. It is of course possible to have the composite power amplifier system arranged in a different way but the described arrangement is advantageous.
  • a thirteenth possible implementation form of a composite power amplifier system according to any one of the preceding implementation forms of the first aspect or to the first aspect as such the ratio between, the peak output power of the third power amplifier or the peak output power of the fourth power amplifier and the sum of the peak output powers of the first power amplifier and the second power amplifier is in the interval 1 -2.
  • the ratio it is possible to choose the ratio to be outside said interval, but a ratio in said interval provides a high efficiency of the composite power amplifier system over a broad interval of back of power. In usual telecommunications applications it is desirable to maintain a high efficiency up to approximately 9 dB back-off power.
  • the third power amplifier and the fourth power amplifier are configured to have equal peak output power. This, makes the composite power amplifier system more easily implemented.
  • a transmitter device for a wireless communication system comprises a composite power amplifier system according to any one of the implementation forms of the first aspect or to the first aspect as such.
  • the transmitter device according to the second aspect may operate in radio frequencies. In this application radio frequency may mean the frequency range from 1 MHz to 300 GHz.
  • a transmitter device according to the second aspect of the present invention provides the same benefits and advantages as the first aspect of the invention and the different implementation forms of the first aspect.
  • Fig. 1 shows schematically in block form a composite power amplifier system according to an embodiment of the present invention.
  • Fig. 2 shows schematically a composite power amplifier system according to an embodiment of the present invention.
  • Fig. 3 shows the efficiency as a function of the normalized output voltage of a composite power amplifier system according to the embodiment in Fig. 2.
  • Fig. 4a shows the amplitude of the different driving signals as a function of the output power in dB from the maximum output power.
  • Fig. 4b shows the phase of the different driving signals as a function of the output power in dB from the maximum output power.
  • Fig. 5a shows the drain voltage swing over different power amplifiers in the composite power amplifier system according to the embodiment of the present invention shown in Fig. 2, as a function of the output power in dB from the maximum power.
  • Fig. 5b shows the phase of the drain voltage as a function of the output power in dB from the maximum output power.
  • Fig. 6a shows the amplitude of the drain impedance as a function of the output power in dB from the maximum output power.
  • Fig. 6b shows the phase of the drain impedance as a function of the output voltage in dB from the maximum output power.
  • Fig. 7 shows schematically a composite power amplifier system according to an embodiment of the present invention.
  • Fig. 8 shows schematically a transmitter device for a wireless communication system comprising a composite power amplifier system according to Fig. 2 or Fig. 3. DETAILED DESCRIPTION
  • Fig. 1 shows schematically in block form a composite power amplifier system 100 according to an embodiment of the present invention.
  • the composite power amplifier system 100 comprises an input node 102 configured to receive an input signal, an output node 104 configured to output an output signal.
  • the composite power amplifier system 100 comprises a first power amplifier 106, a second power amplifier 108, a third power amplifier 1 10, and a fourth power amplifier 1 12, together configured in a multi way Doherty structure and connected between the input node 102 and the output node 104.
  • the first power amplifier 106 and the second power amplifier 108 are arranged as a Chireix pair of power amplifiers and configured to operate as a main power amplifier in the multi way Doherty structure.
  • the third power amplifier 1 10 is configured to operate as a first auxiliary power amplifier in the multi way Doherty structure
  • the fourth power amplifier 1 12 is configured to operate as a second auxiliary power amplifier in the multi way Doherty structure.
  • Fig. 2 shows schematically a composite power amplifier system 100 according to an embodiment of the present invention.
  • the embodiment shown in Fig. 2 is a possible implementation of the embodiment shown in Fig. 1 .
  • the composite power amplifier system 100 comprises an input node 102 configured to receive an input signal, an output node 104 configured to output an output signal.
  • the output node 104 can be connected to an antenna 1 18 in this particular embodiment.
  • the composite power amplifier system 100 comprises a first power amplifier 106, a second power amplifier 108, a third power amplifier 1 10, and a fourth power amplifier 1 12.
  • the 4 power amplifiers 106, 108, 1 10 and 1 12 are together configured in a multi way Doherty structure and connected between the input node 102 and the output node 104.
  • the first power amplifier 106 and the second power amplifier 108 are arranged as a Chireix pair of power amplifiers and configured to operate as a main power amplifier in the multi way Doherty structure.
  • the third power amplifier 1 10 is configured to operate as a first auxiliary power amplifier in the multi way Doherty structure
  • the fourth power amplifier 1 12 is configured to operate as a second auxiliary power amplifier in the multi way Doherty structure.
  • the composite power amplifier system 100 further comprises a driving signal device 1 14 configured to provide a first driving signal to the first power amplifier 106, a second driving signal to the second power amplifier 108, a third driving signal to the third power amplifier 1 10, and a fourth driving signal to the fourth power amplifier 1 12.
  • the driving signal device 1 14 is configured to provide the first driving signal to the first power amplifier 106 so as to operate the first power amplifier 106 for all voltage levels of the input signal, and to provide the second driving signal to the second power amplifier 108 so as to operate the second power amplifier 108 for all voltage levels of the input signal.
  • the driving signal device 1 14 may comprise digital hardware. Part of the driving signal device may be implemented in a computer. Alternatively, the driving signal device 1 14 may be purely analogue.
  • the first power amplifier 106 comprises a first input 120 connected to the driving signal unit 104 and a first output 122.
  • the second power amplifier 108 comprises a second input 124 connected to the driving signal unit 104 and a second output 126.
  • the third power amplifier 1 10 comprises a third input 128 connected to the driving signal unit 104 and a third output 130.
  • the fourth power amplifier 1 12 comprises a fourth input 132 connected to the driving signal unit 1 14 and a fourth output 134.
  • the fourth output 134 is connected directly to the output node 104.
  • the composite power amplifier system 100 also comprises a first quasi impedance transformer 136 connected to the first output 122 and a second quasi impedance transformer 138 connected to the second output 126.
  • the first quasi impedance transformer 136 constitutes a first adapting network and the second quasi impedance transformer 138 constitutes a second adapting network.
  • the first quasi impedance transformer 136 transforms the signal on the first output 122 by phase shifting it with an amount of 90° minus a correction angle ⁇ .
  • the second quasi impedance transformer 138 transforms the signal on the second output 126 by phase shifting it with an amount of 90° plus the correction angle ⁇ .
  • the first quasi impedance transformer 136, the second quasi impedance transformer 138 and the third output 130 are all connected to a common node 140.
  • the composite power amplifier system 100 also comprises a third impedance transformer 142 connected between the common node 140 and the output node 104.
  • the third impedance transformer 142 constitutes a third adapting network.
  • the third impedance transformer 142 shifts the signal on the common node with an angle of 90°.
  • the fourth power amplifier 1 12 is directly connected to the output node 104.
  • Fig. 3 shows the efficiency as a function of the normalized output voltage from a composite power amplifier system according to the embodiment in Fig. 2.
  • first maximum in efficiency is shown at Ti at which the output voltage amplitude is about 20 % of the maximum output voltage.
  • a second maximum in efficiency is shown at T2 at which the output voltage is about 35 % of the maximum output voltage.
  • a third point T3 is shown at an output voltage of 40 % of the maximum output voltage.
  • a fourth point T 4 is shown at an output voltage of about 63 % of the maximum output voltage.
  • the Load Pull Ratio (LPR) levels are kept low.
  • the LPR of the main device is 6.9 dB.
  • the BO is -9 dB as is shown at T2 the LPR of the main device is 2.9 dB.
  • the LPR at the peak T 4 when the BO is -4 dB, is 4.2 dB.
  • Table 1 shows a comparison of LPR values for a composite power amplifier system according to the embodiment of the present invention and a power amplifier according to conventional technology. There is no value for peak at T 4 for the power amplifier according to conventional technology.
  • the drain efficiency in a composite power amplifier system according to an embodiment of the present invention can be kept almost constant in a wide range of power levels such as from -13 dB to -9 dB, i.e., from 0.
  • the range of constant efficiency can be controlled by the proper choice of elements in the composite power amplifier system as will be explained later.
  • the composite power amplifier system may be optimized to maximize the average efficiency with modulated signals of a given statistics.
  • the driving signal unit 1 14 may be implemented in many different ways. It may be implemented using analogue components or digital components. The driving signal unit 1 14 may also be implemented using digital hardware, such as a computer.
  • Fig. 4a shows the amplitude of the different driving signals as a function of the output power in dB from the maximum output power.
  • Fig. 4b shows the phase of the different driving signals as a function of the output power in dB from the maximum output power.
  • the curve 144 in Fig. 4a depicts the amplitude of the driving signal(s) to the first power amplifier 106 and to the second power amplifier 108.
  • the amplitude of the driving signals 144 to the first power amplifier 106 and to the second power amplifier 108, respectively, are equal.
  • the curve 146 depicts the amplitude of the driving signal to the third power amplifier 1 10.
  • the curve 148 depicts the amplitude of the driving signal to the fourth power amplifier 1 12.
  • the curve depicts the phase of the first driving signal to the first power amplifier 106 and the second driving signal to the second power amplifier 108
  • the curve 152 depicts the phase of the third driving signal to the third power amplifier 1 10
  • the curve 154 depicts the phase of the fourth driving signal to the fourth power amplifier 1 12.
  • the first driving signal and the second driving signal, up to a first maximum in efficiency Ti of the first power amplifier 106 and the second power amplifier 108, respectively, are linear with the output power on the output node 104, and wherein the phase difference between the first driving signal and the second driving signal is constant up to said first maximum in efficiency.
  • the amplitude of the driving signal to the third power amplifier 1 10 starts to rise at an output power of -8 dB from the maximum output power. This output power corresponds to T3.
  • the third driving signal is provided to activate the third power amplifier 1 10 for voltage levels of the output signal exceeding a first predetermined threshold level corresponding to T3.
  • T3 is chosen to maximize the efficiency of the composite power amplifier system 100 in dependence of the positions of Ti and T2.
  • the amplitude of the driving signal to the first power amplifier 106 and the amplitude of the driving signal to the second power amplifier 108 have a first discontinuity d1 .
  • the amplitude of the driving signal to the fourth power amplifier 1 12 starts to rise at an output power of -4 dB from the maximum output power. This output power corresponds to T 4 as described above.
  • the fourth driving signal is provided to activate the fourth power amplifier 1 12 for voltage levels of the output signal exceeding a second predetermined threshold level corresponding to T 4 .
  • the position of this second predetermined threshold level is also chosen to maximize the efficiency of the composite power amplifier system 100 in dependence of the positions of Ti and T2.
  • the amplitude of the driving signal to the first power amplifier 106 and the amplitude of the driving signal to the second power amplifier 108 have a second discontinuity d2.
  • the driving signal device 1 14 is configured to provide the third driving signal and the fourth driving signal with an amplitude which varies in a nonlinear way with the voltage of the output signal and with a phase which is constant.
  • Fig. 5a shows the drain voltage swing over the different power amplifiers 106, 108, 1 10, 1 12, in the composite power amplifier system as a function of the output power in dB from the maximum output power.
  • the curve 156 depicts the voltage swing of the first power amplifier 106 and the second power amplifier 108.
  • the curve 158 depicts the voltage swing of the third power amplifier 1 10.
  • the curve 160 depicts the voltage swing of the fourth power amplifier 1 12.
  • Fig. 5b shows the phase of the drain voltage for the different power amplifiers 106, 108, 1 10, 1 12, as a function of the output power in dB from the maximum output power.
  • the curve 162 depicts the phase of the drain voltage of the first power amplifier 106.
  • the curve 164 depicts the phase of the drain voltage for the second power amplifier 108.
  • the curve 166 depicts the phase of the drain voltage for the third power amplifier 1 10.
  • the curve 168 depicts the phase of the drain voltage for the fourth power amplifier 1 12.
  • the driving signal device 1 14 is configured to provide the first driving signal 144 so that the amplitude of the first driving signal 144, up to the output voltage for a maximum voltage swing of the first power amplifier 106, is linear with the output voltage of the output signal.
  • the output power for the output voltage for a maximum voltage swing is depicted as MS in Fig. 4a and is at an output power of -15.6 dB from the maximum output power.
  • the amplitude of the second driving signal, up to the output voltage for a maximum voltage swing of the second power amplifier 108 is linear with the output voltage of the output signal. This output power is also shown in Fig. 4.
  • the phase difference between the first driving signal and the second driving signal is constant up to the output voltage for a maximum voltage swing MS.
  • the phase difference between the first driving signal and the second driving signal changes in a nonlinear way for output voltages above the output voltage for the maximum voltage swing MS of the first power amplifier and the output voltage for the maximum voltage swing of the second power amplifier MS.
  • Fig. 6a shows the drain impedance of the power amplifiers as a function of the output power in dB from the maximum output power.
  • the curve 170 depicts the magnitude of the impedance over the first power amplifier 106 and the second power amplifier 108.
  • the curve 172 depicts the magnitude of the impedance over the third power amplifier 1 10.
  • the curve 174 depicts the magnitude of the impedance over the fourth power amplifier 1 12.
  • Fig. 6b shows the phase of the impedance over the power amplifiers as a function of the output power in dB from the maximum output power.
  • the curve 176 depicts the phase of the impedance over the first power amplifier 106.
  • the curve 178 depicts the phase of the impedance over the second power amplifier 108.
  • the phase of the impedance over the third power amplifier 1 10 and the phase of the impedance over the fourth power amplifier 1 12 are at zero from their onset at T3 and T 4 .
  • Fig. 6b it is possible to see the positions where the impedance reaches real value corresponding to the maximum of efficiency. In contrast to conventional technology solutions it is noticeable that from T3 until Peak Envelop Power (PEP) it is possible to keep the impedance real for all four devices.
  • PEP Peak Envelop Power
  • the first predetermined threshold level and the second predetermined threshold level are determined based on the peak in efficiency of the composite power amplifier system 100 being closest to zero output voltage; and the ratio between the sum of the peak power of the first power amplifier 106 and the peak power of the second power amplifier 108, and the peak power of the third power amplifier 1 10 or the fourth power amplifier 1 12.
  • the first power amplifier 106 and the second power amplifier 108 are driven linearly with a constant phase difference between them.
  • the first peak in efficiency is at Ti when the phase of the impedance is at zero for both the first power amplifier and the second power amplifier.
  • the amplitude and phase of these two devices is changing in a non-linear way which can be theoretically calculated.
  • T4 and up to maximum power PEP these two devices should be driven with constant amplitude and constant phase as is shown in Figs. 4a and 4b.
  • the first peak device should start at T3 and should be driven non- linearly up to max power with a constant phase.
  • the second peak device should start at T4 and should be driven with non-linear amplitude and constant phase.
  • the first design parameter is the maximum peak power for the whole composite power amplifier system 100.
  • the third power amplifier 1 10 and the fourth power amplifier 1 12, which constitute the peak devices, are in this example of equal power size.
  • the second design parameter is defined as the ratio between the peak power size of one of the third power amplifier 1 10 and the fourth power amplifier 1 12 and two times the peak power size of one of the first power amplifier 106 and the second power amplifier 108 (which is in this case equal to the sum of powers of the first power amplifier 106 and the second power amplifier 108). Knowing these two parameters it is possible to calculate the peak power size (PEP) of the four power amplifiers 106, 108, 1 10, 1 12, that compose this composite power amplifier system.
  • PEP peak power size
  • the size of the main amplifier which comprises the first power amplifier 106 and the second power amplifier 108, is 150W PEP composed of two 75W PEP power amplifiers.
  • the third power amplifier 1 10 and the fourth power amplifier 1 12 which constitute the peak devices are both set to 225W PEP.
  • the third and last design parameter is Ti which will set up the maximum load pull ratio of the main transistors and the " ⁇ " or phase difference between the Chireix pair implemented with transmission lines (see Fig. 6).
  • the position of Ti determines the position of MS shown in Fig. 4.
  • the power level where the first peak device should start represented here as T3 can be calculated once the device sizes are known. The same applies for the power level where the second peak will start represented as T4.
  • the power level represented as T2 is the power level at which the impedance presented to both devices in the Chireix pair "enjoy" real impedance which guarantees a maximum of efficiency T2 can be calculated.
  • Table 2 Fig. 7 shows schematically a composite power amplifier system 100 according to a further embodiment of the present invention. Only the differences between the composite power amplifier system 100 in Fig. 2 and the composite power amplifier system 100 of Fig. 7 will be described.
  • the first quasi impedance transformer 136 and the second quasi impedance transformer 138 are connected directly to the output node 104.
  • the composite power amplifier system 100 also comprises a third impedance transformer 182 connected between the output 130 of the third power amplifier 1 10 and the output node 104.
  • the third impedance transformer 182 constitutes a third adapting network.
  • the third impedance transformer 182 shifts the signal on the common node with an angle of 90°.
  • the composite power amplifier system 100 also comprises a fourth impedance transformer 184 connected between the output 130 of the third power amplifier 1 10 and the output of the fourth power amplifier 1 12.
  • the fourth impedance transformer 184 constitutes a fourth adapting network.
  • the fourth impedance transformer 184 shifts the signal with an angle of 90°.
  • Fig. 8 shows schematically a transmitter device 300 for a wireless communication system 400 comprising a composite power amplifier system 100 according to any one of the embodiments described above.
  • the wireless communication system 400 also comprises a base station 500 which may also comprise a quadrature digital power amplifier system 100 according to any one of the embodiments described above.
  • the dotted arrow A1 represents transmissions from the transmitter device 300 to the base station 500.
  • the full arrow A2 represents transmissions from the base station 500 to the transmitter device 300.
  • the composite power amplifier system described above can be used to achieve optimum narrow/wideband designs in terms of drain efficiency.
  • Using GaN devices at 1 .8GHz it has been possible to demonstrate up to 3% higher drain efficiency, compared to conventional technology, when transmitting signals of 40MHz with Power to Average Ratio (PAR) of 8 dB, an output power of 80W and fulfilling all linearity requirements.
  • PAR Power to Average Ratio
  • the present transmitter device 300 may be any of a User Equipment (UE) in Long Term Evolution (LTE), mobile station (MS), wireless terminal or mobile terminal which is enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system.
  • the UE may further be referred to as mobile telephones, cellular telephones, computer tablets or laptops with wireless capability.
  • the UEs in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice or data, via the radio access network, with another entity, such as another receiver or a server.
  • the UE can be a Station (STA), which is any device that contains an IEEE 802.1 1 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM).
  • STA Station
  • MAC Media Access Control
  • PHY Physical Layer
  • the present transmitter device 300 may also be a base station a (radio) network node or an access node or an access point or a base station, e.g., a Radio Base Station (RBS), which in some networks may be referred to as transmitter, "eNB", “eNodeB”, “NodeB” or “B node”, depending on the technology and terminology used.
  • the radio network nodes may be of different classes such as, e.g., macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size.
  • the radio network node can be a Station (STA), which is any device that contains an IEEE 802.1 1 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM).
  • STA Station
  • MAC Media Access Control
  • PHY Physical Layer

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Abstract

A composite power amplifier system (100) is described. The composite power amplifier system comprises an input node (102) configured to receive an input signal, an output node (104) configured to output an output signal, and at least a first power amplifier (106), a second power amplifier (108), a third power amplifier (110), and a fourth power amplifier (112) together configured in a multi way Doherty structure connected between the input node (102) and the output node (104). The first power amplifier (106) and the second power amplifier (108) are configured as a Chireix pair of power amplifiers and configured to operate as a main power amplifier in the multi way Doherty structure. The third power amplifier (110) is configured to operate as a first auxiliary power amplifier in the multi way Doherty structure, and the fourth power amplifier (112) is configured to operate as a second auxiliary power amplifier in the multi way Doherty structure. Furthermore, the present invention also relates to a transmitter comprising such a composite power amplifier.

Description

COMPOSITE POWER AMPLIFIER
TECHNICAL FIELD
The present invention relates to a composite power amplifier system for amplification of electric signals. Furthermore, the present invention also relates to a transmitter comprising such a composite power amplifier.
BACKGROUND
Due to a high peak to average ratio close to 9 dB in mobile telecom standards signals, i.e. long term evolution (LTE) signals, the amplifier size should be eight times bigger than what is needed for the power that the power amplifier (PA) will in average deliver to the antenna load. This makes it difficult to implement a high efficiency, low power consumption, power amplifiers.
Several PA architectures have been proposed to improve efficiency at low power level (i.e. Back Off power levels). Basically, these architectures are based on two main techniques: Voltage modulation and Load modulation.
Voltage modulation techniques are mainly limited by the modulator signal bandwidth capability and by modulator efficiency: both at maximum power and at back off power. Load modulation techniques are limited by Efficiency vs Bandwidth trade-off for high load pull ratio requirements.
SUMMARY
An objective of the present invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions.
A further objective of the present invention is to provide a composite power amplifier system for amplifying an electric signal to be fed to an antenna, and a transmitter device comprising such an amplifier system, which amplifier system provides a better efficiency at low power levels compared to power amplifiers according to conventional technologies. Another objective of the present invention is to provide a composite power amplifier system for amplifying an electric signal to be fed to an antenna, and a transmitter device comprising such an amplifier system, which amplifier system provides at least one of an improved efficiency versus bandwidth, an improved efficiency at back-off power levels, and an improved average efficiency of the amplifier system transmitting Rayleigh distributed signals with limited peak to average ratio.
Embodiments of the present invention focus on the group of techniques based on load modulation and improves the efficiency vs bandwidth trade off by reducing the demand of load pull ratio of the devices used in the power amplifier implementation. The above objectives are fulfilled by the subject matter of the independent claims. Further advantageous implementation forms of the present invention can be found in the dependent claims.
In the following, an IQ data signal is to be understood as a data signal comprising an in-phase data signal or an I data signal and a quadrature data signal or a Q data signal.
According to a first aspect of the present invention, a composite power amplifier system is provided. The composite power amplifier system comprises an input node configured to receive an input signal, an output node configured to output an output signal, and at least a first power amplifier, a second power amplifier, a third power amplifier, and a fourth power amplifier together configured in a multi way Doherty structure connected between the input node and the output node. The first power amplifier and the second power amplifier are configured as a Chireix pair of power amplifiers and configured to operate as a main power amplifier in the multi way Doherty structure. The third power amplifier is configured to operate as a first auxiliary power amplifier (preferably a first peak amplifier) in the multi way Doherty structure, and the fourth power amplifier is configured to operate as a second auxiliary power amplifier (preferably a second peak amplifier) in the multi way Doherty structure.
With a composite power amplifier system according to the first aspect of the present invention, the efficiency of the power amplifier may be kept high over a wide range of back-off power levels. Furthermore, the efficiency may be kept almost constant from a first peak in efficiency at a back-off power level up to the maximum output power of the composite power amplifier system. In a first possible implementation form of a composite power amplifier system according to the first aspect, the composite power amplifier system further comprises a driving signal device configured to provide a first driving signal to the first power amplifier, a second driving signal to the second power amplifier, a third driving signal to the third power amplifier, and a fourth driving signal to the fourth power amplifier. The driving signal device is configured to provide the first driving signal to the first power amplifier so as to operate the first power amplifier for all amplitude levels of the input signal, and provide the second driving signal to the second power amplifier so as to operate the second power amplifier for all amplitude levels of the input signal. Here and in the following application the amplitude of the input signals may be a voltage level and/or a current level.
By providing such a driving signal device the efficiency of the composite power amplifier system may be optimized at the same time as the full power range of all power amplifiers are used optimally. In a second possible implementation form of a composite power amplifier system according to the first implementation form of the first aspect, the driving signal device comprises digital hardware.
In a third possible implementation form of a composite power amplifier system according to the first or the second implementation form of the first aspect, the driving signal device is configured to provide the first driving signal so that the amplitude of the first driving signal, up to the output voltage for a maximum voltage swing of the first power amplifier, is linear with the output voltage of the output signal, provide the second driving signal so that the amplitude of the second driving signal, up to the output voltage for a maximum voltage swing of the second power amplifier, is linear with the output voltage of the output signal, and wherein the phase difference between the first driving signal and the second driving signal is constant up to the output voltage for a maximum voltage swing of at least one of the first power amplifier and the second power amplifier. The amplitude may be a voltage amplitude and/or a current amplitude in dependence of how the first power amplifier and the second power amplifier are driven.
The provision of such driving signals provides a desired high efficiency of the composite power amplifier. The desired peaks of efficiency of the composite power amplifier are achieved by appropriate changes in phase difference between the first driving signal and the second driving and appropriate changes in amplitude of the first and second driving signals.
In a fourth possible implementation form of a composite power amplifier system according to the third implementation form of the first aspect, the driving signal device is configured to provide the first driving signal and the second driving signal so that at least one of the amplitude of the first driving signal, the amplitude of the second driving signal and the phase difference between the first driving signal and the second driving signal, changes in a nonlinear way for output voltages above the output voltage for the maximum voltage swing of the first power amplifier and the output voltage for the maximum voltage swing of the second power amplifier.
It is advantageous to change the phase in a nonlinear way in order to get an optimized shape of the efficiency curve.
In a fifth possible implementation form of a composite power amplifier system according to anyone of the first to the fourth implementation forms of the first aspect, the driving signal device is configured to provide a third driving signal to activate the third power amplifier for voltage levels of the output signal exceeding a first predetermined threshold level.
By activating the third power amplifier in this way a high efficiency of the composite power amplifier may be provided. In a sixth possible implementation form of a composite power amplifier system according to the fifth implementation form of the first aspect, the driving signal device is configured to provide a fourth driving signal to activate the fourth power amplifier for voltage levels of the output signal exceeding a second predetermined threshold level which is higher than the first predetermined threshold level. By activating the fourth power amplifier in this way a high efficiency of the composite power amplifier may be provided.
In a seventh possible implementation form of a composite power amplifier system according to the sixth implementation form of the first aspect, the first predetermined threshold level and the second predetermined threshold level are determined based on the peak in efficiency of the composite power amplifier system being closest to zero output voltage and the ratio between the peak output power of the third power amplifier or the peak output power of the fourth power amplifier and the sum of the peak output powers of the first power amplifier and the second power amplifier. The dimensioning of the composite power amplifier is started with the dimensioning of the first power amplifier and the second power amplifier and the position of the first peak in efficiency of the composite power amplifier. This first peak in efficiency is the peak that is closest to zero output voltage of the peaks in the efficiency curve of the composite power amplifier. The first power amplifier and the second power amplifier are usually chosen to have the same maximum output power. The second peak is then given by the above mentioned design parameters. When maximizing the efficiency of the composite power amplifier the first predetermined threshold level and the second predetermined threshold level are thus determined by the given parameters.
In an eighth possible implementation form of a composite power amplifier system according to the sixth or seventh implementation form of the first aspect, the driving signal device is configured to provide the third driving signal and the fourth driving signal with an amplitude which varies in a nonlinear way with the voltage of the output signal and with a phase which is constant. The amplitude may be a voltage amplitude and/or a current amplitude in dependence of how the third power amplifier and the fourth power amplifier are driven.
By varying the voltage of the third driving signal and the fourth driving signal in a nonlinear way the efficiency of the composite power amplifier system may be optimized.
In a ninth possible implementation form of a composite power amplifier system according to any one of the preceding implementation forms of the first aspect or to the first aspect as such, the composite power amplifier system further comprises a first adapting network and a second adapting network, wherein the first adapting network is connected between an output of the first power amplifier and a common node and the second adapting network is connected between an output of the second power amplifier and the common node so as to provide the Chireix pair of power amplifiers.
The composite power amplifier system according to the ninth possible implementation form is advantageous in that it is easy to implement and optimize.
In tenth possible implementation form of a composite power amplifier system according to the ninth implementation form of the first aspect, the composite power amplifier system further comprises a third adapting network, wherein the common node is connected to the output node via the third adapting network. In an eleventh possible implementation form of a composite power amplifier system according to the ninth implementation form of the first aspect an output of the third power amplifier is connected to the output node via the third adapting network.
In a twelfth possible implementation form of a composite power amplifier system according to the ninth, tenth or eleventh implementation form of the first aspect an output of the fourth power amplifier is directly connected to the output node.
The composite power amplifier system according to the tenth, eleventh or twelfth possible implementation form is advantageous in that it is easy to implement and optimize. It is of course possible to have the composite power amplifier system arranged in a different way but the described arrangement is advantageous.
In a thirteenth possible implementation form of a composite power amplifier system according to any one of the preceding implementation forms of the first aspect or to the first aspect as such the ratio between, the peak output power of the third power amplifier or the peak output power of the fourth power amplifier and the sum of the peak output powers of the first power amplifier and the second power amplifier is in the interval 1 -2.
It is possible to choose the ratio to be outside said interval, but a ratio in said interval provides a high efficiency of the composite power amplifier system over a broad interval of back of power. In usual telecommunications applications it is desirable to maintain a high efficiency up to approximately 9 dB back-off power.
In a fourteenth possible implementation form of a composite power amplifier system according to the thirteenth implementation form of the first aspect, the third power amplifier and the fourth power amplifier are configured to have equal peak output power. This, makes the composite power amplifier system more easily implemented.
According to a second aspect of the present invention a transmitter device for a wireless communication system is provided. The transmitter device according to the second aspect comprises a composite power amplifier system according to any one of the implementation forms of the first aspect or to the first aspect as such. The transmitter device according to the second aspect may operate in radio frequencies. In this application radio frequency may mean the frequency range from 1 MHz to 300 GHz. A transmitter device according to the second aspect of the present invention provides the same benefits and advantages as the first aspect of the invention and the different implementation forms of the first aspect.
SHORT DESCRIPTION OF THE DRAWINGS
Fig. 1 shows schematically in block form a composite power amplifier system according to an embodiment of the present invention.
Fig. 2 shows schematically a composite power amplifier system according to an embodiment of the present invention. Fig. 3 shows the efficiency as a function of the normalized output voltage of a composite power amplifier system according to the embodiment in Fig. 2.
Fig. 4a shows the amplitude of the different driving signals as a function of the output power in dB from the maximum output power.
Fig. 4b shows the phase of the different driving signals as a function of the output power in dB from the maximum output power.
Fig. 5a shows the drain voltage swing over different power amplifiers in the composite power amplifier system according to the embodiment of the present invention shown in Fig. 2, as a function of the output power in dB from the maximum power. Fig. 5b shows the phase of the drain voltage as a function of the output power in dB from the maximum output power.
Fig. 6a shows the amplitude of the drain impedance as a function of the output power in dB from the maximum output power.
Fig. 6b shows the phase of the drain impedance as a function of the output voltage in dB from the maximum output power.
Fig. 7 shows schematically a composite power amplifier system according to an embodiment of the present invention.
Fig. 8 shows schematically a transmitter device for a wireless communication system comprising a composite power amplifier system according to Fig. 2 or Fig. 3. DETAILED DESCRIPTION
In the following detailed description of embodiments of the invention, the same reference numeral will be used for the corresponding feature in the different drawings. Fig. 1 shows schematically in block form a composite power amplifier system 100 according to an embodiment of the present invention. The composite power amplifier system 100 comprises an input node 102 configured to receive an input signal, an output node 104 configured to output an output signal. The composite power amplifier system 100 comprises a first power amplifier 106, a second power amplifier 108, a third power amplifier 1 10, and a fourth power amplifier 1 12, together configured in a multi way Doherty structure and connected between the input node 102 and the output node 104. The first power amplifier 106 and the second power amplifier 108 are arranged as a Chireix pair of power amplifiers and configured to operate as a main power amplifier in the multi way Doherty structure. The third power amplifier 1 10 is configured to operate as a first auxiliary power amplifier in the multi way Doherty structure, and the fourth power amplifier 1 12 is configured to operate as a second auxiliary power amplifier in the multi way Doherty structure.
Fig. 2 shows schematically a composite power amplifier system 100 according to an embodiment of the present invention. The embodiment shown in Fig. 2 is a possible implementation of the embodiment shown in Fig. 1 . The composite power amplifier system 100 comprises an input node 102 configured to receive an input signal, an output node 104 configured to output an output signal. The output node 104 can be connected to an antenna 1 18 in this particular embodiment. The composite power amplifier system 100 comprises a first power amplifier 106, a second power amplifier 108, a third power amplifier 1 10, and a fourth power amplifier 1 12. The 4 power amplifiers 106, 108, 1 10 and 1 12 are together configured in a multi way Doherty structure and connected between the input node 102 and the output node 104. The first power amplifier 106 and the second power amplifier 108 are arranged as a Chireix pair of power amplifiers and configured to operate as a main power amplifier in the multi way Doherty structure. The third power amplifier 1 10 is configured to operate as a first auxiliary power amplifier in the multi way Doherty structure, and the fourth power amplifier 1 12 is configured to operate as a second auxiliary power amplifier in the multi way Doherty structure.
The composite power amplifier system 100 further comprises a driving signal device 1 14 configured to provide a first driving signal to the first power amplifier 106, a second driving signal to the second power amplifier 108, a third driving signal to the third power amplifier 1 10, and a fourth driving signal to the fourth power amplifier 1 12. The driving signal device 1 14 is configured to provide the first driving signal to the first power amplifier 106 so as to operate the first power amplifier 106 for all voltage levels of the input signal, and to provide the second driving signal to the second power amplifier 108 so as to operate the second power amplifier 108 for all voltage levels of the input signal.
The driving signal device 1 14 may comprise digital hardware. Part of the driving signal device may be implemented in a computer. Alternatively, the driving signal device 1 14 may be purely analogue.
Moreover, the first power amplifier 106 comprises a first input 120 connected to the driving signal unit 104 and a first output 122. The second power amplifier 108 comprises a second input 124 connected to the driving signal unit 104 and a second output 126. The third power amplifier 1 10 comprises a third input 128 connected to the driving signal unit 104 and a third output 130. The fourth power amplifier 1 12 comprises a fourth input 132 connected to the driving signal unit 1 14 and a fourth output 134. The fourth output 134 is connected directly to the output node 104.
The composite power amplifier system 100 also comprises a first quasi impedance transformer 136 connected to the first output 122 and a second quasi impedance transformer 138 connected to the second output 126. The first quasi impedance transformer 136 constitutes a first adapting network and the second quasi impedance transformer 138 constitutes a second adapting network. The first quasi impedance transformer 136 transforms the signal on the first output 122 by phase shifting it with an amount of 90° minus a correction angle δ. The second quasi impedance transformer 138 transforms the signal on the second output 126 by phase shifting it with an amount of 90° plus the correction angle δ. The first quasi impedance transformer 136, the second quasi impedance transformer 138 and the third output 130 are all connected to a common node 140. The composite power amplifier system 100 also comprises a third impedance transformer 142 connected between the common node 140 and the output node 104. The third impedance transformer 142 constitutes a third adapting network. The third impedance transformer 142 shifts the signal on the common node with an angle of 90°. The fourth power amplifier 1 12 is directly connected to the output node 104.
Fig. 3 shows the efficiency as a function of the normalized output voltage from a composite power amplifier system according to the embodiment in Fig. 2. In Fig. 3 a, first maximum in efficiency is shown at Ti at which the output voltage amplitude is about 20 % of the maximum output voltage. A second maximum in efficiency is shown at T2 at which the output voltage is about 35 % of the maximum output voltage. A third point T3 is shown at an output voltage of 40 % of the maximum output voltage. A fourth point T4 is shown at an output voltage of about 63 % of the maximum output voltage.
As described in the summary of the invention, the main advantages of this invention are the following. The Load Pull Ratio (LPR) levels are kept low. For the embodiment shown in Fig. 2, when the Back Off (BO) is -13 dB as shown at Ti the LPR of the main device is 6.9 dB. When the BO is -9 dB as is shown at T2 the LPR of the main device is 2.9 dB. Furthermore, the LPR at the peak T4, when the BO is -4 dB, is 4.2 dB. Table 1 below shows a comparison of LPR values for a composite power amplifier system according to the embodiment of the present invention and a power amplifier according to conventional technology. There is no value for peak at T4 for the power amplifier according to conventional technology.
Table 1 The lower level of LPR will improve the efficiency that can be achieved with a real device and will also improve the bandwidth for the composite power amplifier system according to the embodiment of Fig. 2 in comparison with the bandwidth of a power amplifier according to the conventional technology.
It can be observed that the drain efficiency in a composite power amplifier system according to an embodiment of the present invention can be kept almost constant in a wide range of power levels such as from -13 dB to -9 dB, i.e., from 0. The range of constant efficiency can be controlled by the proper choice of elements in the composite power amplifier system as will be explained later. Also the composite power amplifier system may be optimized to maximize the average efficiency with modulated signals of a given statistics. The driving signal unit 1 14 may be implemented in many different ways. It may be implemented using analogue components or digital components. The driving signal unit 1 14 may also be implemented using digital hardware, such as a computer.
Fig. 4a shows the amplitude of the different driving signals as a function of the output power in dB from the maximum output power. Fig. 4b shows the phase of the different driving signals as a function of the output power in dB from the maximum output power.
The curve 144 in Fig. 4a depicts the amplitude of the driving signal(s) to the first power amplifier 106 and to the second power amplifier 108. Thus, the amplitude of the driving signals 144 to the first power amplifier 106 and to the second power amplifier 108, respectively, are equal. The curve 146 depicts the amplitude of the driving signal to the third power amplifier 1 10. Finally, the curve 148 depicts the amplitude of the driving signal to the fourth power amplifier 1 12.
Correspondingly, in Fig. 4b, the curve depicts the phase of the first driving signal to the first power amplifier 106 and the second driving signal to the second power amplifier 108, the curve 152 depicts the phase of the third driving signal to the third power amplifier 1 10, and the curve 154 depicts the phase of the fourth driving signal to the fourth power amplifier 1 12.
As can be seen in Fig. 4a, the first driving signal and the second driving signal, up to a first maximum in efficiency Ti of the first power amplifier 106 and the second power amplifier 108, respectively, are linear with the output power on the output node 104, and wherein the phase difference between the first driving signal and the second driving signal is constant up to said first maximum in efficiency. As can be seen in Fig. 4a the amplitude of the driving signal to the third power amplifier 1 10 starts to rise at an output power of -8 dB from the maximum output power. This output power corresponds to T3. Thus, the third driving signal is provided to activate the third power amplifier 1 10 for voltage levels of the output signal exceeding a first predetermined threshold level corresponding to T3. T3 is chosen to maximize the efficiency of the composite power amplifier system 100 in dependence of the positions of Ti and T2. At this output power the amplitude of the driving signal to the first power amplifier 106 and the amplitude of the driving signal to the second power amplifier 108 have a first discontinuity d1 . The amplitude of the driving signal to the fourth power amplifier 1 12 starts to rise at an output power of -4 dB from the maximum output power. This output power corresponds to T4 as described above. Thus, the fourth driving signal is provided to activate the fourth power amplifier 1 12 for voltage levels of the output signal exceeding a second predetermined threshold level corresponding to T4. The position of this second predetermined threshold level is also chosen to maximize the efficiency of the composite power amplifier system 100 in dependence of the positions of Ti and T2. At the output power corresponding to T4 the amplitude of the driving signal to the first power amplifier 106 and the amplitude of the driving signal to the second power amplifier 108 have a second discontinuity d2.
As is evident from Fig. 4, the driving signal device 1 14 is configured to provide the third driving signal and the fourth driving signal with an amplitude which varies in a nonlinear way with the voltage of the output signal and with a phase which is constant.
The dimensioning of the amplifiers and the positioning of Ti , T2, T3, and T4, will be described in more detail below.
Fig. 5a shows the drain voltage swing over the different power amplifiers 106, 108, 1 10, 1 12, in the composite power amplifier system as a function of the output power in dB from the maximum output power. The curve 156 depicts the voltage swing of the first power amplifier 106 and the second power amplifier 108. The curve 158 depicts the voltage swing of the third power amplifier 1 10. The curve 160 depicts the voltage swing of the fourth power amplifier 1 12.
Fig. 5b shows the phase of the drain voltage for the different power amplifiers 106, 108, 1 10, 1 12, as a function of the output power in dB from the maximum output power. The curve 162 depicts the phase of the drain voltage of the first power amplifier 106. The curve 164 depicts the phase of the drain voltage for the second power amplifier 108. The curve 166 depicts the phase of the drain voltage for the third power amplifier 1 10. The curve 168 depicts the phase of the drain voltage for the fourth power amplifier 1 12.
The driving signal device 1 14 is configured to provide the first driving signal 144 so that the amplitude of the first driving signal 144, up to the output voltage for a maximum voltage swing of the first power amplifier 106, is linear with the output voltage of the output signal. The output power for the output voltage for a maximum voltage swing is depicted as MS in Fig. 4a and is at an output power of -15.6 dB from the maximum output power. Similarly, the amplitude of the second driving signal, up to the output voltage for a maximum voltage swing of the second power amplifier 108, is linear with the output voltage of the output signal. This output power is also shown in Fig. 4. The phase difference between the first driving signal and the second driving signal is constant up to the output voltage for a maximum voltage swing MS. The phase difference between the first driving signal and the second driving signal changes in a nonlinear way for output voltages above the output voltage for the maximum voltage swing MS of the first power amplifier and the output voltage for the maximum voltage swing of the second power amplifier MS.
Fig. 6a shows the drain impedance of the power amplifiers as a function of the output power in dB from the maximum output power. The curve 170 depicts the magnitude of the impedance over the first power amplifier 106 and the second power amplifier 108. The curve 172 depicts the magnitude of the impedance over the third power amplifier 1 10. The curve 174 depicts the magnitude of the impedance over the fourth power amplifier 1 12.
Fig. 6b shows the phase of the impedance over the power amplifiers as a function of the output power in dB from the maximum output power. The curve 176 depicts the phase of the impedance over the first power amplifier 106. The curve 178 depicts the phase of the impedance over the second power amplifier 108. The phase of the impedance over the third power amplifier 1 10 and the phase of the impedance over the fourth power amplifier 1 12 are at zero from their onset at T3 and T4. In Fig. 6b it is possible to see the positions where the impedance reaches real value corresponding to the maximum of efficiency. In contrast to conventional technology solutions it is noticeable that from T3 until Peak Envelop Power (PEP) it is possible to keep the impedance real for all four devices. This is thanks to a non-linear driving of the third power amplifier 1 10 and the fourth power amplifier 1 12. After T3 the phase of the impedance over all four power amplifiers 106, 108, 1 10, 1 12, is zero which is shown by the solid line 180. The first predetermined threshold level and the second predetermined threshold level are determined based on the peak in efficiency of the composite power amplifier system 100 being closest to zero output voltage; and the ratio between the sum of the peak power of the first power amplifier 106 and the peak power of the second power amplifier 108, and the peak power of the third power amplifier 1 10 or the fourth power amplifier 1 12.
Up to the maximum swing of the voltage, designated as MS in Fig. 6, the first power amplifier 106 and the second power amplifier 108, constituting the Chireix pair, are driven linearly with a constant phase difference between them. As can be seen in Fig. 6b the first peak in efficiency is at Ti when the phase of the impedance is at zero for both the first power amplifier and the second power amplifier. After MS and up to T4 the amplitude and phase of these two devices is changing in a non-linear way which can be theoretically calculated. After T4 and up to maximum power PEP these two devices should be driven with constant amplitude and constant phase as is shown in Figs. 4a and 4b. The first peak device should start at T3 and should be driven non- linearly up to max power with a constant phase. The second peak device should start at T4 and should be driven with non-linear amplitude and constant phase.
The first design parameter is the maximum peak power for the whole composite power amplifier system 100. The third power amplifier 1 10 and the fourth power amplifier 1 12, which constitute the peak devices, are in this example of equal power size. The second design parameter is defined as the ratio between the peak power size of one of the third power amplifier 1 10 and the fourth power amplifier 1 12 and two times the peak power size of one of the first power amplifier 106 and the second power amplifier 108 (which is in this case equal to the sum of powers of the first power amplifier 106 and the second power amplifier 108). Knowing these two parameters it is possible to calculate the peak power size (PEP) of the four power amplifiers 106, 108, 1 10, 1 12, that compose this composite power amplifier system. If we want to design a 600W PEP PA with a ratio equal to 1 .5 the size of the main amplifier, which comprises the first power amplifier 106 and the second power amplifier 108, is 150W PEP composed of two 75W PEP power amplifiers. The third power amplifier 1 10 and the fourth power amplifier 1 12 which constitute the peak devices are both set to 225W PEP. The ratio "r" will then be: r=225/150 =1 .5. It is possible to have the ratio r in the interval 1 -2.
The third and last design parameter is Ti which will set up the maximum load pull ratio of the main transistors and the "δ" or phase difference between the Chireix pair implemented with transmission lines (see Fig. 6). The position of Ti determines the position of MS shown in Fig. 4.
The power level where the first peak device should start represented here as T3 can be calculated once the device sizes are known. The same applies for the power level where the second peak will start represented as T4. The power level represented as T2 is the power level at which the impedance presented to both devices in the Chireix pair "enjoy" real impedance which guarantees a maximum of efficiency T2 can be calculated. Example design:
Table 2 Fig. 7 shows schematically a composite power amplifier system 100 according to a further embodiment of the present invention. Only the differences between the composite power amplifier system 100 in Fig. 2 and the composite power amplifier system 100 of Fig. 7 will be described. The first quasi impedance transformer 136 and the second quasi impedance transformer 138 are connected directly to the output node 104. The composite power amplifier system 100 also comprises a third impedance transformer 182 connected between the output 130 of the third power amplifier 1 10 and the output node 104. The third impedance transformer 182 constitutes a third adapting network. The third impedance transformer 182 shifts the signal on the common node with an angle of 90°. The composite power amplifier system 100 also comprises a fourth impedance transformer 184 connected between the output 130 of the third power amplifier 1 10 and the output of the fourth power amplifier 1 12. The fourth impedance transformer 184 constitutes a fourth adapting network. The fourth impedance transformer 184 shifts the signal with an angle of 90°.
Fig. 8 shows schematically a transmitter device 300 for a wireless communication system 400 comprising a composite power amplifier system 100 according to any one of the embodiments described above. The wireless communication system 400 also comprises a base station 500 which may also comprise a quadrature digital power amplifier system 100 according to any one of the embodiments described above. The dotted arrow A1 represents transmissions from the transmitter device 300 to the base station 500. The full arrow A2 represents transmissions from the base station 500 to the transmitter device 300.
The composite power amplifier system described above can be used to achieve optimum narrow/wideband designs in terms of drain efficiency. Using GaN devices at 1 .8GHz it has been possible to demonstrate up to 3% higher drain efficiency, compared to conventional technology, when transmitting signals of 40MHz with Power to Average Ratio (PAR) of 8 dB, an output power of 80W and fulfilling all linearity requirements.
The present transmitter device 300 may be any of a User Equipment (UE) in Long Term Evolution (LTE), mobile station (MS), wireless terminal or mobile terminal which is enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The UE may further be referred to as mobile telephones, cellular telephones, computer tablets or laptops with wireless capability. The UEs in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice or data, via the radio access network, with another entity, such as another receiver or a server. The UE can be a Station (STA), which is any device that contains an IEEE 802.1 1 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM).
The present transmitter device 300 may also be a base station a (radio) network node or an access node or an access point or a base station, e.g., a Radio Base Station (RBS), which in some networks may be referred to as transmitter, "eNB", "eNodeB", "NodeB" or "B node", depending on the technology and terminology used. The radio network nodes may be of different classes such as, e.g., macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. The radio network node can be a Station (STA), which is any device that contains an IEEE 802.1 1 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM).

Claims

1 . A composite power amplifier system (100) comprising:
an input node (102) configured to receive an input signal,
an output node (104) configured to output an output signal, and
at least a first power amplifier (106), a second power amplifier (108), a third power amplifier (1 10), and a fourth power amplifier (1 12) together configured in a multi way Doherty structure connected between the input node (102) and the output node (104), wherein the first power amplifier (106) and the second power amplifier (108) are configured as a Chireix pair of power amplifiers and configured to operate as a main power amplifier in the multi way Doherty structure, wherein the third power amplifier (1 10) is configured to operate as a first auxiliary power amplifier in the multi way Doherty structure, and wherein the fourth power amplifier (1 12) is configured to operate as a second auxiliary power amplifier in the multi way Doherty structure.
2. The composite power amplifier system (100) according to claim 1 , further comprising a driving signal device (1 14) configured to provide a first driving signal to the first power amplifier (106), a second driving signal to the second power amplifier (108), a third driving signal to the third power amplifier (1 10), and a fourth driving signal to the fourth power amplifier (1 12), wherein the driving signal device (1 14) is configured to
provide the first driving signal to the first power amplifier (106) so as to operate the first power amplifier (106) for all voltage levels of the input signal, and
provide the second driving signal to the second power amplifier (108) so as to operate the second power amplifier (108) for all voltage levels of the input signal.
3. The composite power amplifier system (100) according to claim 2, wherein the driving signal device (1 14) comprises digital hardware.
4. The composite power amplifier system (100) according to claim 2 or 3, wherein the driving signal device (1 14) is configured to provide the first driving signal so that the voltage of the first driving signal, up to the output voltage for a maximum voltage swing of the first power amplifier (106), is linear with the output voltage of the output signal,
provide the second driving signal so that the amplitude of the second driving signal, up to the output voltage for a maximum voltage swing of the second power amplifier (108), is linear with the output voltage of the output signal, and
wherein the phase difference between the first driving signal and the second driving signal is constant up to the output voltage for a maximum voltage swing of at least one of the first power amplifier (106) and the second power amplifier (108).
5. The composite power amplifier system (100) according to claim 4, wherein the driving signal device (1 14) is configured to provide the first driving signal and the second driving signal so that at least one of the amplitude of the first driving signal, the amplitude of the second driving signal, and the phase difference between the first driving signal and the second driving signal, changes in a nonlinear way for output voltages above the output voltage for the maximum voltage swing of the first power amplifier and the output voltage for the maximum voltage swing of the second power amplifier.
6. The composite power amplifier system (100) according to any of claims 2-5, wherein the driving signal device (1 14) is configured to provide a third driving signal to activate the third power amplifier (1 10) for voltage levels of the output signal exceeding a first predetermined threshold level.
7. The composite power amplifier system (100) according to claim 6, wherein the driving signal device (1 14) is configured to provide a fourth driving signal to activate the fourth power amplifier (1 12) for voltage levels of the output signal exceeding a second predetermined threshold level which is higher than the first predetermined threshold level.
8. The composite power amplifier system (100) according to claim 7, wherein the first predetermined threshold level and the second predetermined threshold level are determined based on the peak in efficiency of the composite power amplifier system (100) being closest to zero output voltage and the ratio between the peak output power of the third power amplifier (1 10) or the peak output power of the fourth power amplifier (1 12) and the sum of the peak output powers of the first power amplifier (106) and the second power amplifier (108).
9. The composite power amplifier system (100) according to claim 7 or 8, wherein the driving signal device (1 14) is configured to provide the third driving signal and the fourth driving signal with an amplitude which varies in a nonlinear way with the voltage of the output signal and with a phase which is constant.
10. The composite power amplifier system (100) according to any one of the preceding claims, further comprising a first adapting network (136) and a second adapting network (138), wherein the first adapting network (136) is connected between an output of the first power amplifier (106) and a common node (140) and the second adapting network (138) is connected between an output of the second power amplifier (108) and the common node (140) so as to provide the Chireix pair of power amplifiers.
1 1 . The composite power amplifier system (100) according to claim 10, further comprising a third adapting network (142), and wherein the common node (140) is connected to the output node (104) via the third adapting network (142).
12. The composite power amplifier system (100) according to claim 10, wherein an output of the third power amplifier (1 10) is connected to the output node (104) via the third adapting network (142).
13. The composite power amplifier system (100) according to claim 10, 1 1 or 12, wherein an output of the fourth power amplifier (1 12) is directly connected to the output node (104).
14. The composite power amplifier system (100) according to any one of the preceding claims, wherein the ratio (r) between the peak output power of the third power amplifier (1 10) or the peak output power of the fourth power amplifier (1 12) and the sum of the peak output powers of the first power amplifier (106) and the second power amplifier (108) is in the interval 1 -2.
15. The composite power amplifier system (100) according to claim 14, wherein the third power amplifier (1 10) and the fourth power amplifier (1 12) are configured to have equal peak output power.
16. A transmitter device (300) for a wireless communication system (400) comprising a composite power amplifier system (100) according to any one of the preceding claims.
EP16700217.9A 2016-01-11 2016-01-11 Composite power amplifier Withdrawn EP3391537A1 (en)

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PCT/EP2016/050367 WO2017121455A1 (en) 2016-01-11 2016-01-11 Composite power amplifier

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CN112771778A (en) * 2018-11-30 2021-05-07 华为技术有限公司 Power amplifier circuit
JP7281932B2 (en) * 2019-03-22 2023-05-26 古河電気工業株式会社 amplifier

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ATE422108T1 (en) * 2002-12-19 2009-02-15 Ericsson Telefon Ab L M COMPOSITE AMPLIFIER STRUCTURE
SE0302586D0 (en) * 2003-09-26 2003-09-26 Ericsson Telefon Ab L M Composite power amplifier
US8022760B2 (en) * 2007-12-21 2011-09-20 Nxp B.V. 3-way Doherty amplifier with minimum output network
CN103178786A (en) * 2011-12-26 2013-06-26 瑞典爱立信有限公司 Multiway Doherty amplifier

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