WO2019072400A1

WO2019072400A1 - A power amplifier

Info

Publication number: WO2019072400A1
Application number: PCT/EP2017/076215
Authority: WO
Inventors: Suo HAILEI; Francesc Purroy MARTIN
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2017-10-13
Filing date: 2017-10-13
Publication date: 2019-04-18

Abstract

The invention relates to a power amplifier (100). In particular the invention relates to devices system and arrangements related to a power amplifier operating as a 3-way Doherty amplifier and for driving thereof. The power amplifier comprises a 90° Quadrature Hybrid combiner (112), a main amplifier (102); a first pair of amplifiers (104, 106) and a second pair of amplifiers (108, 110). The main amplifier is operatively connected to a first port of the 90° Quadrature Hybrid combiner. The ports are selected such that the first port is isolated from a fourth port of the 90° Quadrature Hybrid combiner. The fourth port is operatively connected to an output port of the power amplifier. Further, the first pair of amplifiers are connected to work together as a first balanced peak amplifier. A first amplifier of the first balanced peak amplifier is operatively connected to a second port of the 90° Quadrature Hybrid combiner via a first electrical length and a second amplifier of the first balanced peak amplifier is operatively connected to a third port of said 90° Quadrature Hybrid combiner via an equal first electrical length. Also, the second pair of amplifiers work together as a second balanced peak amplifier. A first amplifier of the second balanced peak amplifier is operatively connected to the second port of said 90° Quadrature Hybrid combiner via a second electrical length and a second amplifier of the second balanced peak amplifier is operatively connected to the third port of said 90° Quadrature Hybrid combiner via an equal second electrical length.

Description

A Power Amplifier

TECHNICAL FIELD

The invention relates to a power amplifier. In particular the invention relates to devices system and arrangements related to a power amplifier operating as a 3-way Doherty amplifier and for methods driving thereof.

BACKGROUND

Power amplifiers are used to amplify input signals to output signals having increased power. One type of power amplifier is known as a Doherty amplifier.

A multistage Doherty power amplifier, 3-way Doherty, is described in F.H. Raab "Efficiency of Doherty RF Power Amplifiers Systems", IEEE Trans. Broadcasting, vol. BC-33, no 3, pp. 77-83, September 1987. The advantage of the 3-way Doherty architecture compared with pre-existing 2-way Doherty amplifiers is that it allows to extend the Back-off range where the efficiency is maximum. As consequence there will be an improved average efficiency when amplifying signals with a non-zero Peak-to Average Ratio (PAR).

The 3-way Doherty structure is depicted in Fig. 1 and uses a main amplifier and two peak amplifiers.

Further, US 8,022,760 describes another 3-way Doherty structure aiming to simplify the driving signals and to allow an improved efficiency at high back-off values.

There is a constant desire to improve power amplifiers. Hence, there is a need for an improved power amplifier.

SUMMARY It is an object of the present invention to provide an improved power amplifier. This object and/or others are obtained by the devices as set out in the appended claims.

In some applications the power amplifier size needs to be high to provide high power levels. Also, the high peak to average ratio in some mobile telecom standards such as long-term evolution (LTE), is close to 9dB. In such an application, the amplifier size should be about eight times bigger than the average power that the power amplifier will deliver to the antenna load. This makes it difficult to implement a high efficiency, low power consuming, power amplifier (PA). To meet this need, a new power amplifier structure is provided.

In accordance with a first aspect of the invention a power amplifier is provided. The power amplifier comprises a 90° Quadrature Hybrid combiner, a main amplifier; a first pair of amplifiers and a second pair of amplifiers. The main amplifier is operatively connected (i.e. directly connected or connected via some other component(s)) to a first port of the 90° Quadrature Hybrid combiner. The ports are selected such that the first port is isolated from a fourth port of the 90° Quadrature Hybrid combiner. The fourth port is operatively connected to the output port of the power amplifier. Further, the first pair of amplifiers are connected to work together as a first balanced peak amplifier. A first amplifier of the first balanced peak amplifier is operatively connected to a second port of the 90° Quadrature Hybrid combiner via a first electrical length and a second amplifier of the first balanced peak amplifier is operatively connected to a third port of said 90° Quadrature Hybrid combiner via an equal first electrical length. Also, the second pair of amplifiers work together as a second balanced peak amplifier. A first amplifier of the second balanced peak amplifier is operatively connected to the second port of said 90° Quadrature Hybrid combiner via a second electrical length and a second amplifier of the second balanced peak amplifier is operatively connected to the third port of said 90° Quadrature Hybrid combiner via an equal second electrical length.

Hereby a power amplifier that can eliminate the load pull ratio of the main amplifier is provided that can keep the same Back-Off values as in the existing power amplifiers described above. Also, the power amplifier allows a design of matching networks having a high bandwidth as compared to the existing power amplifiers. In accordance with a first implementation of the first aspect, a matching network is interconnected between the main amplifier and the Quadrature Hybrid combiner to match to the characteristic impedance of the 90° Quadrature Hybrid combiner. Hereby an efficient driving of the main amplifier can be obtained in that the main power amplifier can be configured to operate at an optimal impedance.

In accordance with a second implementation of the first aspect, a matching network, in particular one per amplifier, is interconnected between the first balanced peak amplifier and the Quadrature Hybrid combiner to match to the characteristic impedance of the 90° Quadrature Hybrid combiner. Hereby it is obtained that the first balanced peak power amplifier can be configured to operate at an optimal impedance.

In accordance with a third implementation of the first aspect, a matching network, in particular one per amplifier, is interconnected between the second balanced peak amplifier and the Quadrature Hybrid combiner to match to the characteristic impedance of the 90° Quadrature Hybrid combiner. Hereby it is obtained that the second balanced peak power amplifier can be configured to operate at an optimal impedance.

In accordance with a fourth implementation of the first aspect, the first electrical length is configured to provide a phase off-set of 90°. This will provide a phase off-set which added to the phase offset of other components, such as a matching network, will be 90°. Hereby the signal from the first balanced peak amplifier can be given a phase that will make the power amplifier operate at high efficiency when the second balanced peak amplifier is in an off state.

In accordance with a fifth implementation of the first aspect, the second electrical length is configured to provide a phase off-set of 0° or 180°. This will provide a phase off-set which added to the phase offset of other components, such as a matching network, will be 0° or 180°. Hereby the signal from the second balanced peak amplifier can be given a phase that will make the power amplifier operate at high efficiency at maximum power.

In accordance with a sixth implementation of the first aspect, a transformer is provided operatively interconnected between the fourth port of the Quadrature Hybrid combiner and the output port of the power amplifier. Hereby it is possible to transform the characteristic impedance of the 90° Quadrature Hybrid combiner to match the system impedance.

In accordance with a second aspect of the invention, a power amplifier arrangement is provided that comprises a power amplifier in accordance with the first aspect. The power amplifier arrangement further comprises a driving circuitry that has one single input port and five output ports. The output ports are operatively connected to drive each of the main amplifier, the first pair of amplifiers and the second pair of amplifiers, respectively. Hereby an arrangement that can drive a power amplifier and which only requires one input port is provided. In accordance with a third aspect of the invention, a power amplifier arrangement is provided that comprises a power amplifier in accordance with the first aspect. The power amplifier arrangement further comprises a driving circuitry that has two input ports and five output ports. The output ports are operatively connected to drive each of the main amplifier, the first pair of amplifiers and the second pair of amplifiers, respectively.

Hereby an arrangement that only requires two input signals is provided but which gives some more flexibility of the driving of the power amplifier than the arrangement of the second aspect.

In accordance with a first implementation of the third aspect, a first input port of the driving circuitry is operatively connected to drive the main amplifier. Further, a second input port of the driving circuitry is operatively connected to drive the first pair of amplifiers and also to drive the second pair of amplifiers. Hereby, an efficient driving arrangement for a power amplifier that can provide a good control of the power amplifier is obtained.

In accordance with a fourth aspect of the invention, a power amplifier arrangement is provided that comprises a power amplifier in accordance with the first aspect. The power amplifier arrangement further comprises a driving circuitry that has three input ports and five output ports. The output ports are operatively connected to drive each of the main amplifier, the first pair of amplifiers and the second pair of amplifiers. Hereby an arrangement that only requires three input signals is provided but which gives full flexibility of the driving of the power amplifier. In accordance with a first implementation of the fourth aspect, a first input port of the driving circuitry is operatively connected to drive the main amplifier. Further, a second port of the driving circuitry is operatively connected to drive the first pair of amplifiers. Also, a third port of the driving circuitry is operatively connected to drive the second pair of amplifiers. Hereby, the power amplifier can be efficiently controlled by providing an individual control of the main amplifier and the respective balanced peak amplifiers.

In accordance with a fifth aspect of the invention, a driving circuit for driving a power amplifier is provided. The driving circuit is configured to provide a main driving signal for driving a main amplifier, to provide a first peak signal for driving a first pair of amplifiers and to provide a second peak signal for driving a second pair of amplifiers. The driving circuit is configured to provide the main driving signal until a maximum current amplitude for the main driving signal is reached. Further, when the maximum current amplitude for the main driving signal is reached, the driving circuit is configured to start providing the first peak signal while maintaining the maximum current amplitude for the main driving signal. Hereby, an efficient driving of a power amplifier having a main amplifier and two pairs of amplifiers is provided that only uses the main amplifier when the main amplifier is capable of providing the demanded output power alone.

In accordance with a first implementation of the fifth aspect, the driving circuit further being configured to, when the first peak signal has reached a pre-determined level, start providing the second peak signal while maintaining providing (and eventually increasing) the first peak signal and while maintaining the maximum current amplitude for the main driving signal. Hereby, the power amplifier can be efficiently driven using two peak signals.

In accordance with a sixth aspect of the invention, a system comprising a power amplifier according to the first aspect is provided. The system also comprises a driving circuit according to the fifth aspect. The main driving signal is then configured to drive the main amplifier, the first peak signal is configured to drive the first pair of amplifiers, and the second peak signal is configured to drive the second pair of amplifiers. Hereby an efficient system for driving the power amplifier of the first aspect is provided. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example, and with reference to the accompanying drawings, in which:

- Fig. 1 shows a conventional power amplifier implementing a 3-way Doherty amplifier.

- Fig. 2 shows the drain efficiency vs output power characteristics of a conventional power amplifier,

- Fig. 3 shows a first embodiment of a power amplifier,

- Figs. 4 and 5 illustrates driving signals for a power amplifier,

- Fig. 6 shows a second embodiment of a power amplifier,

- Fig. 7 shows a driving circuitry according to a first embodiment,

- Fig. 8 shows a driving circuitry according to a second embodiment,

- Fig. 9 shows a driving circuitry according to a third embodiment,

- Fig. 10a -10c are exemplary comparing views of required load-pulling of an embodiment of the invention compared to existing power amplifiers, and

- Fig. 1 1 is a comparing view illustrating the efficiency vs normalized output voltage for different amplifiers.

DETAILED DESCRIPTION The invention will now be described in detail hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the description.

In general, power amplifiers that are designed to improve the power amplifier efficiency at low power level are based on two main techniques: Voltage modulation and Load modulation. In voltage modulation techniques, the limitation is dominated 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 tradeoff for high load pull ratio requirements.

Further, as has been realized, conventional power amplifiers operating in the radio frequency domain will have practical limitations. Fig. 2 depicts the characteristics of such a conventional power amplifier. Thus, conventional power amplifiers have a limited output power range where the drain efficiency can be kept elevated. For example, the power amplifier depicted in Fig. 2 uses a load modulation technique. A change in power will then be achieved by actively load pulling the load. Because the available Load Pull Range (LPR) is limited, the best power amplifier architecture will then be one that achieves higher efficiency Back-off with a small LPR.

Further, a small LPR has another benefit, namely the radio frequency bandwidth. A smaller LPR will make it possible to implement broadband matching networks, capable of tracking the required loads for the different status of the different amplifiers of an overall power amplifier. However, the conventional 3-way Doherty architectures as set out above have been found to have a too high LPR which is limiting the tradeoff between bandwidth and efficiency.

By providing a power amplifier with a new architecture that is capable of having a reduced load pull ratio, it is made possible to improve the tradeoff between bandwidth and efficiency.

In Fig. 3 a power amplifier 100 according to a first embodiment is depicted. The power amplifier 100 comprises a main amplifier 102, a first pair of amplifiers 104, 106 and a second pair of amplifiers 108, 1 10. The first pair of amplifiers 104, 106 are provided to act as a first balanced peak amplifier to increase the output power when the main amplifier is saturated. Further, the second pair of amplifiers 108, 1 10 are provided to act as a second balanced peak amplifier to even further increase the output power when the main amplifier is saturated. The second pair of amplifiers 108, 1 10 are used as a supplement to the first pair of amplifiers 104, 106 to even further increase the overall amplifying of the power amplifier 100. The power amplifier 100 further comprises a 90° Quadrature Hybrid combiner 1 12. As is known, the 90° Quadrature Hybrid combiner 1 12 has four ports. One of the ports of the 90° Quadrature Hybrid combiner is used as an output port that is ultimately connected to a load 120 of the power amplifier. In other words, the output port can be operatively connected to the load 120 either directly or via some other component(s). Further, the main amplifier 102 is operatively connected to a first input port of the 90° Quadrature Hybrid combiner 1 12. In other words, the main amplifier is connected to the 90° Quadrature Hybrid combiner 1 12 either directly or via some other component(s). In the exemplary embodiment of Fig. 3 an electrical delay 1 14 (a phase shift) providing a 90° phase off-set is for example provided interconnected between the main amplifier 102 and the first input port of the 90° Quadrature Hybrid combiner 1 12. Hereby an electrical length is provided. The first input port and the output port of the 90° Quadrature Hybrid combiner 1 12 are selected as being isolated from each other. Apart from the restriction that the port operatively connected to the load 120 and the port operatively connected to the main amplifier of the 90° Quadrature Hybrid combiner are isolated from each other, the ports of the 90° Quadrature Hybrid combiner can be selected in any manner and is not restricted to the configuration depicted in Fig. 3.

A first peak amplifier 104 of the first pair of amplifiers 104, 106 ss operatively connected to a second input port (marked as ISO) of the 90° Quadrature Hybrid combiner 1 12. A second peak amplifier 106 of the first pair of amplifiers 104, 106 is operatively connected to a third input port (marked an IN) of the 90° Quadrature Hybrid combiner 1 12. In other words, the amplifiers 104, 106 are connected to the 90° Quadrature Hybrid combiner 1 12 either directly or via some other component(s). In the exemplary embodiment of Fig. 3 electrical delays 1 16, 1 18 (phase shifts) providing a phase off-set of 90° are for example provided interconnected between each amplifier 104, 106 and the second and third input port respectively of the 90° Quadrature Hybrid combiner 1 12. This provides for a first electrical length that is equal for the electrical delays 1 16, 1 18.

A first peak amplifier 108 of the second pair of amplifiers 108, 1 10 is operatively connected to the second input port of the 90° Quadrature Hybrid combiner 1 12. A second peak amplifier 1 10 of the second pair of amplifiers 108, 1 10 is operatively connected to the third input port of the 90° Quadrature Hybrid combiner 1 12. In other words, the amplifiers 108, 1 10 are connected to the 90° Quadrature Hybrid combiner 1 12 either directly or via some other component(s). In the exemplary embodiment of Fig. 3 no component is provided interconnected between each amplifier 108, 1 10 and the second and third input port respectively of the 90° Quadrature Hybrid combiner 1 12. However, some component/components can be interconnected between each amplifier 108, 1 10 and the second and third input port of the 90° Quadrature Hybrid combiner 1 12. For example, electrical delays (phase shifts) providing a phase off-set of 180° can for example be provided interconnected between each amplifier 108, 1 10 and the second and third input port respectively of the 90° Quadrature Hybrid combiner 1 12. This provides for a second electrical length that is equal for the signals output from the amplifiers 108, 1 10.

When the two pairs of amplifiers 104, 106 and 108, 1 10 respectively are driven with the same amplitude and 90° phase difference they will cancel at the port where the main amplifier is connected. As a result, the main amplifier 102 will see a constant load impedance equal to the impedance of the 90° Quadrature Hybrid combiner 1 12 in the whole power range of the power amplifier 100.

In Fig. 4 a diagram illustrating the operation of a power amplifier in accordance with some embodiments described herein is depicted. In Fig. 4, the solid line represents the driving signal characteristics of the main amplifier 102 of Fig. 3. Further the dashed line represents the driving signal characteristics of the first pair of amplifier 104, 106 of Fig. 3. Also, the dashed-dotted line represents the driving signal characteristics of the second pair of amplifiers 108, 1 10 of Fig. 3. Further, Fig. 5 shows a phase diagram for the driving signals of Fig. 4.

As can be seen in Fig. 4 and Fig. 5, at low output power only the main amplifier 102 is fed with a driving signal. When the main amplifier is saturated and cannot provide more output power, the first pair of amplifiers 104, 106 are fed with a driving signal to supplement the output from the main amplifier 102. The output from the first pair of amplifiers 104, 106 increases linearly with respect to the output voltage. Later, at some stage when the first pair of amplifiers are fed with an input driving signal, the second pair of amplifiers 108, 1 10 are also fed with an input driving signal to provide a linear output with regard to the output voltage. In accordance with some embodiments the second pair of amplifiers are fed with an input driving signal when the output voltage reaches a pre-determined value. The pre-determined value can be determined as set out below.

By selecting the size of the main amplifier 102 with respect to the total maximum power of the power amplifier 100 a first maximum of efficiency for the power amplifier 100 is selected. A second maximum of efficiency for the power amplifier 100 is selected by choosing the size of the first pair of amplifiers 104, 106. Then the size of the second pair of amplifiers 108, 1 10 will be determined by the overall power given to the power amplifier 100 to achieve the desired peak power. When the second pair of amplifiers are started to be driven by a drive signal, the second maximum of efficiency of the power amplifier 100 is reached. I.e. this is when the power amplifier 100 has its second maximum of efficiency. Depending on the probability density function of the modulated signal to transmit via the power amplifier 100, the values of the first and second maximums of efficiency of the power amplifier 100 can be optimized to maximize the average efficiency of the power amplifier 100. Therefore, in accordance with some embodiments, the second driving signal can be applied at an output voltage based on the probability density function of the modulated signal to transmit via the power amplifier 100. In particular, the second driving signal can be applied to set the second maximum of efficiency of the power amplifier 100 to a value maximizing the overall efficiency of the power amplifier 100 given a probability function of the input signal of the power amplifier 100.

Thus, the driving circuit is configured to provide the main driving signal until a maximum current amplitude for the main driving signal is reached. When the maximum current amplitude for the main driving signal is reached, the first peak signal is applied with a linear increase with respect to the output voltage while maintaining the maximum current amplitude for the main driving signal. Hereby an efficient driving of a power amplifier having a main amplifier and two pairs of amplifiers is provided that only uses the main amplifier when the main amplifier is capable of providing the demanded output power alone. The second driving signal is applied at an output voltage that can be set for example in accordance with the above. In Fig. 6 a second embodiment of a power amplifier is depicted. The second embodiment is similar to the first embodiment depicted in Fig. 3. However, in the second embodiment matching networks are provided interconnected between the amplifiers and the 90° Quadrature Hybrid combiner 1 12. Thus, a matching network 132 is provided interconnected between the main amplifier 102 and the 90° Quadrature Hybrid combiner 1 12. Also, matching networks 134, 136 are provided interconnected between the first pair of amplifiers 104. 106 and the 90° Quadrature Hybrid combiner 1 12. Matching networks 138, 140 are also provided interconnected between the second pair of amplifiers 108, 1 10 and the 90° Quadrature Hybrid combiner 1 12 The matching networks 132, 134, 136, 138 and 140 have the function to implement an impedance to match the amplifier impedance of the respective amplifiers 102, 104, 106,108 and 1 10 to the characteristic impedance of the 90° Quadrature Hybrid combiner 1 12. Also, the matching networks 132, 134, 136, 138 and 140 can be used to implement a corresponding phase off-set. There can be, at least, one matching network 132, 134, 136, 138 and 140 provided for each amplifier 102, 104, 106, 108 and 1 10 respectively.

A load 120 is connected to the output port of the 90° Quadrature Hybrid combiner 1 12. The load 120 forms the characteristic impedance of the output port of the 90° Quadrature Hybrid combiner 1 12. A transformer 150 can further be provided at the output port of the 90° Quadrature Hybrid combiner 1 12. In some scenarios, the characteristic impedance of the 90° Quadrature Hybrid combiner 1 12 is not equal to the system impedance that the power amplifier 100 drives (typically 50 Ohms). For this reason, it can be advantageous to add the transformer 150 to transform the characteristic impedance of the 90° Quadrature Hybrid combiner 1 12 to the system impedance. Further, the output from each pair of amplifiers 104, 106 and 108, 1 10 respectively are connected using cross joins 124 and 126 respectively. The cross joints are used to connect the output ports from the amplifiers 104, 106 and 108, 1 10 respectively. The cross joints can add to the electrical length of the outputs from the amplifiers. If the cross joints add an electrical length, it can be advantageous to take this electrical length into account when setting the phase off-set from the respective amplifier 104, 106, 108 and 1 10. For example, the implementation of the matching networks 134, 136, 138 and 140 can take the electrical lengths of the cross- joints 124, 126 into account so that the phase off-set from the amplifiers 104, 106 and the amplifiers 108, 1 10 amounts to a desired phase off-set when reaching the 90° Quadrature Hybrid combiner 1 12.

Since the power amplifier 100 has 5 amplifiers 102, 104, 106, 108 and 1 10, 5 driving signals are required, see Fig. 3. However, the 5 input signals can be reduced to 3 input signals by jointly driving each pair of amplifiers 104, 106 and 108, 1 10 as is shown in Fig. 6. It is possible to further reduce the number of input driving signals to further simplify the generation of the driving signal. However, this will require more complex driving circuitry.

In Fig. 7 a driving circuitry 200 that can be used to implement a power amplifier 100 with 3 driving input signals is shown. The arrangement in Fig. 7 has a driving circuitry 200 with three input ports and five output ports. The output ports are operatively connected to drive each of the main amplifier, the first pair of amplifiers and the second pair of amplifiers. In the embodiment shown in Fig. 7, a first input port of the driving circuitry is operatively connected to drive the main amplifier 102. A second port of the driving circuitry is operatively connected to drive the first pair of amplifiers 104, 106. Also, a third port of the driving circuitry is operatively connected to drive the second pair of amplifiers 108, 1 10. The implementation of Fig. 7 will provide full flexibility with the use of three driving input signals to the driving circuitry 200. In Fig. 7 the driving circuitry 200 comprises a main drive amplifier 210 for driving the main amplifier 102. The driving circuitry further comprises a first drive amplifier 220 for driving the first pair of amplifiers 104, 106 connect to different output ports of a first drive circuitry 90° Quadrature Hybrid combiner 230. Also, the driving circuitry comprises a second drive amplifier 240 for driving the second pair of amplifiers 108, 1 10 connect to different output ports of a second drive circuitry 90° Quadrature Hybrid combiner 250. In the embodiment of Fig. 7, one input signal is configured to drive the main driver amplifier directly. A second input signal drives directly the first drive amplifier 220. Switching ON of the first drive amplifier can be implemented in the digital domain. An implementation in the digital domain enables good control of magnitude and phase of the drive signal. A third input signal drives directly the second drive amplifier 240. Switching ON of the second drive amplifier can be implemented in the digital domain. An implementation in the digital domain enables good control of magnitude and phase of the drive signal. The first and second drive circuitry 90° Quadrature Hybrid combiners 230, 250 will drive the two branches of the pairs of amplifiers 104, 106, 108 and 1 10 forming the balanced peak amplifiers. Thus, the first drive circuitry 90° Quadrature Hybrid combiner 230 will split the signal equally to drive the two amplifiers 104, 106 in quadrature and in phase. Likewise, the second drive circuitry 90° Quadrature Hybrid combiner 250 will split the signal equally to drive the two amplifiers 108, 1 10 in quadrature and in phase.

In Fig. 8 a second embodiment of a driving circuitry 200 is shown. The driving circuitry 200 of Fig. 8 is similar to the driving circuitry in Fig. 7, but has only 2 input drive signals. Thus, in the embodiment of Fig. 8, two input signal ports provide drive signals to five output ports. The output ports are operatively connected to drive each of the main amplifier 102, the first pair of amplifiers 104, 106 and the second pair of amplifiers 108. 1 10, respectively. Further a first input port of the driving circuitry 200 is operatively connected to drive the main amplifier 102. The second input port of the driving circuitry 200 is operatively connected to drive the first pair of amplifiers 104, 106 and also to drive the second pair of amplifiers 108, 1 10. This can be obtained by letting one input signal drive the main driver amplifier 210 as in the implementation of Fig 7. A second input signal will drive both the first and the second drive amplifiers 220, 240 using a drive peak amplifier 260. The drive peak amplifier 260 will drive both the first and the second drive amplifiers 220, 240 via a peak drive circuitry 90° Quadrature Hybrid combiner 270 that is configured to divide the drive signal into two drive signals at different output ports of the peak drive circuitry 90° Quadrature Hybrid combiner 270. The first drive amplifier 220 is biased to allow the switch ON of the first drive amplifier 220 at a first predetermined output power level based on the received in-phase signal after the peak drive circuitry 90° Quadrature Hybrid combiner 270. The second drive amplifier 240 is biased to allow the switch ON of the second drive amplifier 240 at a second predetermined output power level based on the received in-quadrature signal after the peak drive circuitry 90° Quadrature Hybrid combiner 270. The second pre-determined output power level for the second drive amplifier 240 is higher than the first pre-determined output power level for the first drive amplifier 220. In Fig. 9 a third embodiment of a driving circuitry 200 is shown. The driving circuitry 200 of Fig. 9 is similar to the driving circuitry in Fig. 7 and Fig.8, but has only 1 input drive signal. Thus, in the embodiment of Fig. 9, one input signal port provides drive signals to five output ports. This is obtained by providing the single input signal to a combined amplifier 280 for amplifying the input signal. The output from the combined amplifier 280 is provided to a split 90° Quadrature Hybrid combiner 290 adapted to split the drive signal to a main drive signal and to a peak drive signal. The output from the split 90° Quadrature Hybrid combiner 290 will follow two different paths. One drive signal from one, in-phase, port of the split 90° Quadrature Hybrid combiner 290 will drive the main amplifier 102 in a first path. A second drive signal from a second port of the split 90° Quadrature Hybrid combiner 290 will drive the pairs of amplifiers 104,106, 108 and 1 10 as in Fig. 8. The in-phase signal is provided to drive the main drive amplifier driver 210 but can be made to go via a limiter circuit 295. The limiter circuit 295 is provided to limit the output power of the main amplifier 102 to its maximum value. The maximum value can be defined by a set input power level that can correspond to a maximum efficiency of the main amplifier 102.

Because the structure of the power amplifier 100 as described herein provides for an isolation between the main amplifier 102 and the pairs of amplifiers 104, 106 and 108, 1 10 forming the balanced peak amplifiers of the power amplifier 100, it is possible to drive the main amplifier 102 independently from the pairs of amplifiers. Hereby, the main amplifier is sequentially driven and its power is combined in phase, with the power generated by the pair of amplifiers at the load port of the 90° Quadrature Hybrid combiner 1 12. This structure allows for a more efficient driving of the power amplifier 100 compared to existing, conventional, power amplifiers such as the Raab amplifier and the power amplifier of US 8,022,760 set out above. Because the main amplifier 102 can be driven independently from the pairs of amplifiers 104, 106, 108 and 1 10, it is possible to achieve an efficiency vs. output voltage from the power amplifier 100 which is equal as the existing power amplifiers discussed above. However, the power amplifier as described herein can more easily achieve more back off because the non-existent load pull ratio provided by the power amplifier as described herein. Consider for example the Raab power amplifier. In the Raab power amplifier, the first peak drive signal is applied when the main amplifier has not reach the maximum output voltage. At the point when the first peak amplifier of the Raab power amplifier start to operate, the main amplifier is already working at its maximum efficiency, maximum voltage swing but not at its maximum power. This implies some load pull ratio. At this point, the Raab power amplifier will have its first maximum of efficiency and the first peak amplifier will not be active. On the other hand, in accordance with the power amplifier as described herein, the first maximum of efficiency of the power amplifier can be set to where the first pair of amplifiers will be off, but the main amplifier is at maximum power. Hence, there will be no load pull for the power amplifier as described herein in this scenario. As is depicted in Fig. 4, the driving signal to the main amplifier 102 should start and be used first until a first maximum of efficiency is reached where the main amplifier is at its maximum output power. After this power level, both the amplifiers 104, 106 of the first pair of amplifiers are also activated to supplement the main amplifier 102. The amplifiers 104, 106 are driven to have a linearly increasing (with respect to the output voltage) amplitude until a maximum current of the amplifiers 104, 106 is reached. At some stage, when the amplifiers 104, 106 are active, both the amplifiers 108, 1 10 of the second pair of amplifiers are activated to linearly increasing (with respect to the output voltage) the amplitude until a maximum current of the amplifiers 108, 1 10 is reached.

The driving exemplified in Fig. 4 is different from the driving of conventional power amplifiers. Also, the power ratio between the main amplifier and the pairs of amplifiers forming the balanced peak amplifiers of the power amplifier is not the same for the power amplifier described herein compared to the existing power amplifiers set out above. In the below table, a comparison between the power levels for the power amplifier described herein with respect to the power levels of the Raab power amplifier and the power amplifier of US 8,022,760 is given. The table below thus shows a comparison of the power level size of the amplifiers used in the different power amplifiers. In the below table, the same output power level and the same Back-off levels are used for the different power amplifiers. Power Power Peak Power Peak Total Power

Main Amplifier No Amplifier No Power

Ratio:

Amplifier 1 2

Raab Power 0.16 W 0.33 W 0.5 W 1 W 1 : 2: 3 Amplifier

US 8,022,760 0.33 W 0.33 W 0.33 W 1 W 1 : 1 : 1

This Power 0.1 1 W 0.28 W x 0.165 W x 1 W 1 : 2.54: Amplifier 2=0.56 W 2= 0.33 1 .5

As can be seen in the table above, smaller devices can be used to achieve the same output power and the same instantaneous efficiency. The use of smaller devices can make it possible to achieve a wider signal bandwidth capability. However, the three different implementations of a power amplifier as exemplified in the table above, having different physical circuit implementation and different driving signals, will achieve exactly the same instantaneous efficiency vs output voltage. This is shown in Fig. 1 1 .

In Figs. 10a - 10c the load pulling required for the main amplifier and the peak amplifiers is compared for the different power amplifiers. In accordance with the teachings herein the main amplifier load pull ratio thanks to the 90° Quadrature Hybrid combiner is completely eliminated. This means that the main amplifier can be designed as a single ended amplifier working towards a constant load, this will improve the bandwidth that can be achieved. Fig. 10a shows the impedance for the main amplifier 102, the first pair of amplifiers 104, 106 and the second pair of amplifiers 108, 1 10 as function of the output voltage. As can be observed the main amplifier sees a constant load. The first pair of amplifiers forming the first balanced peak amplifier see a load modulated at the second maximum efficiency equal to conventional power amplifiers as can be seen in Fig. 10b which illustrates a Raab power amplifier and Fig. 10c which illustrates a power amplifier according to US 8,022,760. The size for the amplifiers used in the power amplifier 100 described herein can be selected as follows. The power of the main amplifier 102 can be selected as:

Pmain=PEP^*10^Λ(-ΒΟ1 dB/10)

Where PEP is the Peak Envelope Power and BO1 is the first Back-Off value. This size can be used since there is isolation between main amplifier and the pairs of amplifiers forming the peak amplifiers and knowing the desired total output power and the first Backoff value. The size of the first pair of amplifiers 104, 106 can be determined based on the second Back-Off value forcing the voltage of the of the first pair of amplifiers 104, 106 to be equal to the drain voltage (Vdd). For example, if

T1 =10^A(-BO1 dB/20); T2=10^A(-BO2dB/20;

where BO1 is the first Back-Off value and BO2 is the second Back-Off value. The power of each of the first pair of amplifiers can be determined as:

_. . . PEP*T2²-Pmain , . _,„_Λ

Ppeak1 = . (1 - 1)

r 2(T2-T1) ^J

The size of the second pair of amplifiers 108, 1 10 can be determined based on the size of the determined size of the main amplifier and the size of the first pair of amplifiers and the determined total power of the power amplifier 100 or the Peak Envelope Power (PEP) For example, a 1 kW power amplifier with a first Back Off at 9.54dB can be determined to have a main amplifier of 1 1 1 .2W in accordance with the above. If the second Back-Off value is 6dB then the first pair of amplifiers can be determined to be 278.2W each. Finally, since the total power is to be 1 kW the second pair of amplifiers can be determined to be 166.2W each.

The power amplifier as described herein can provide many advantages. In particular the efficiency of the power amplifier can be improved. The LPR of the main amplifier can be eliminated which in turn improve trade off Efficiency vs. Bandwidth. Also, the output power capability can be improved compared to existing power amplifiers by implementing the two peak amplifiers using two pairs of amplifiers instead two peak amplifiers with the same load pull ratio for the peaks. This allows to achieve more power with the same size of devices and having the same output Back-Off value. The power amplifiers as set out herein can advantageously be used in mobile communications base stations.

Claims

1. A power amplifier (100) comprising:

- a 90° Quadrature Hybrid combiner (1 12); - a main amplifier (102);

- a first pair of amplifiers (104, 106); and

- a second pair of amplifiers (108, 1 10);

- wherein the main amplifier is operatively connected to a first port of the 90° Quadrature Hybrid combiner, the first port being isolated from a fourth port of the 90° Quadrature Hybrid combiner, the fourth port being operatively connected to an output port of the power amplifier,

- wherein the first pair of amplifiers work together as a first balanced peak amplifier;

- wherein a first amplifier of the first balanced peak amplifier is operatively connected to a second port of said 90° Quadrature Hybrid combiner via a first electrical length; - wherein a second amplifier of the first balanced peak amplifier is operatively connected to a third port of said 90° Quadrature Hybrid combiner via an equal first electrical length;

- wherein the second pair of amplifiers work together as a second balanced peak amplifier;

- wherein a first amplifier of the second balanced peak amplifier is operatively connected to the second port of said 90° Quadrature Hybrid combiner via a second electrical length;

- wherein a second amplifier of the second balanced peak amplifier is operatively connected to the third port of said 90° Quadrature Hybrid combiner via an equal second electrical length.

2. The power amplifier (100) according to claim 1 , further comprising a matching network (132) interconnected between the main amplifier and the Quadrature Hybrid combiner to match to the characteristic impedance of the 90° Quadrature Hybrid combiner.

3. The power amplifier (100) according to claim 1 or 2, further comprising a matching network (134, 136) interconnected between the first balanced peak amplifier and the

Quadrature Hybrid combiner to match to the characteristic impedance of the 90°

Quadrature Hybrid combiner.

4. The power amplifier (100) according to any one of claims 1 - 3, further comprising a matching network (138.140) interconnected between the second balanced peak amplifier and the Quadrature Hybrid combiner to match to the characteristic impedance of the 90° Quadrature Hybrid combiner.

5. The power amplifier (100) according to any one of claims 1 - 4, wherein the first electrical length is configured to provide a phase off-set of 90°.

6. The power amplifier (100) according to any one of claims 1 - 5, wherein the second electrical length is configured to provide a phase off-set of 0° or 180°.

7. The power amplifier (100) according to any one of claims 1 - 6, further comprising a transformer (150) operatively interconnected between the fourth port of the Quadrature Hybrid combiner and the output port of the power amplifier.

8. A power amplifier arrangement comprising the power amplifier (100) according to any one of claims 1 - 7, the power amplifier arrangement further comprising a driving circuitry (200) having one single input port and five output ports, the output ports being operatively connected to drive each of the main amplifier, the first pair of amplifiers and the second pair of amplifiers, respectively.

9. A power amplifier arrangement comprising the power amplifier (100) according to any one of claims 1 - 7, the power amplifier arrangement further comprising a driving circuitry (200) having two input ports and five output ports, the output ports being operatively connected to drive each of the main amplifier, the first pair of amplifiers and the second pair of amplifiers, respectively.

10. The power amplifier arrangement according to claim 9, wherein a first input port of the driving circuitry is operatively connected to drive the main amplifier, and wherein a second input port of the driving circuitry is operatively connected to drive the first pair of amplifiers and also to drive the second pair of amplifiers.

1 1 . A power amplifier arrangement comprising the power amplifier (100) according to any one of claims 1 - 7, the power amplifier arrangement further comprising a driving circuitry (200) having three input ports and five output ports, the output ports being operatively connected to drive each of the main amplifier, the first pair of amplifiers and the second pair of amplifiers.

12. The power amplifier arrangement according to claim 1 1 , wherein a first input port of the driving circuitry is operatively connected to drive the main amplifier, wherein a second port of the driving circuitry is operatively connected to drive the first pair of amplifiers and wherein a third port of the driving circuitry is operatively connected to drive the second pair of amplifiers.

13. A driving circuit (200) for driving a power amplifier configured to provide a main driving signal for driving a main amplifier, to provide a first peak signal for driving a first pair of amplifiers and to provide a second peak signal for driving a second pair of amplifiers, wherein the driving circuit is configured to:

- provide the main driving signal until a maximum current amplitude for the main driving signal is reached, and to

- when the maximum current amplitude for the main driving signal is reached, start providing the first peak signal while maintaining the maximum current amplitude for the main driving signal.

14. The driving circuit (200) according to claim 13, the driving circuit further being configured to:

- when the first peak signal has reached a pre-determined level, start providing the second peak signal while maintaining providing the first peak signal and while maintaining the maximum current amplitude for the main driving signal.

15. A system comprising a power amplifier (100) according to any one of claims 1 - 7, the system further comprising a driving circuit (200) according to any one of claims 13 or 14, wherein the main driving signal is configured to drive the main amplifier, the first peak signal is configured to drive the first pair of amplifiers, and the second peak signal is configured to drive the second pair of amplifiers.