WO2014075735A1

WO2014075735A1 - High efficiency high peak-to-average ratio broadband 3-way power amplifier

Info

Publication number: WO2014075735A1
Application number: PCT/EP2012/072886
Authority: WO
Inventors: Karlheinz Borst
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2012-11-16
Filing date: 2012-11-16
Publication date: 2014-05-22

Abstract

The present invention addresses an apparatus and method for achieving a broadband, high efficient amplifier design to handle communication signals with high peak-to-average ratios. The amplifier comprises a main amplifier circuit, two auxiliary amplifier circuits, each of the two auxiliary amplifier circuits being selectively interacting in a load modulation operation with the main amplifier circuit for boosting the output signal at high power output levels, and a coupler circuit having an output port and coupled to combine output signals of the amplifiers at the coupler output port, wherein the coupler circuit is a two-section coupling structure comprising feeding ports for the amplifier stages of the main amplifier and each of the auxiliary amplifiers.

Description

Title

HIGH EFFICIENCY HIGH PEAK-TO-AVERAGE RATIO BROADBAND 3-WAY POWER AMPLIFIER

Field of the invention

The present invention generally relates to a broadband 3-way power amplifier which may be used in wired or wireless communication networks, and more specifically relates to an apparatus and method for achieving a broadband, high efficient amplifier design using load modulation principle to handle communication signals with high peak-to-average ratios.

Background

High power amplifier designs for multistandard (MS), multicarrier (MC) and even multiband (MB) communication systems show a challenging task when also high efficiency is required. Several well proven design ideas exist like Doherty amplifier, envelope tracking, outphasing and so on.

Due to the technical limits in the past, efficient multiband (MB) broadband applications have not been in the design development focus. But with increasing demands for shrinked size and effective use of resources together with the implementation of broadband high capability digital predistortion systems the need for corresponding high power stages becomes evident. One possible solution is published in patent No. WO2004/088837. However, according to this solution, different parallel combining principles of amplifier stages are used in order to achieve higher powers.

All of the above mentioned amplifier concepts suffer more or less from the ability to generate very high power levels in a very power efficient way over a significantly large range of frequency.

Summary of the Invention

In order to overcome the drawbacks of the prior art, it is an object underlying the present invention to provide an improved broadband 3-way power amplifier. In particular, it is an object of the present invention to provide an apparatus and method for enabling improved high efficiency high power peak-to-average ratio broadband 3-way power amplification.

According to a first aspect of the present invention, there is provided an apparatus, comprising a main amplifier circuit, two auxiliary amplifier circuits, each of the two auxiliary amplifier circuits being selectively interacting in a load modulation operation with the main amplifier circuit for boosting the output signal at high power output levels, and a coupler circuit having an output port and coupled to combine output signals of the amplifiers at the coupler output port, wherein the coupler circuit is a two-section coupling structure comprising feeding ports for the amplifier stages of the main amplifier and each of the auxiliary amplifiers.

According to a second aspect of the present invention, there is provided a method, which comprises combining output signals of a main amplifier circuit and of two auxiliary amplifier circuits with a coupler circuit having an output port providing an output, each of the two auxiliary amplifier circuits interacts selectively with the main amplifier in a load modulation operation for boosting the output signal at high power output levels, wherein the coupler circuit is a two-section coupling structure comprising feeding ports for the amplifier stages of the main amplifier and each of the auxiliary amplifiers.

According to certain embodiments, the characteristics of each of the coupling sections are defined by f₀ and corresponding Z_eVen, Z₀dd, wherein : f0 = low f high' _f ZOcPLsect = Z even Z odd' · _{a nc}j

ZOcPLsect = ZOi l, Z0iN2, ZOAUX, ZOoUT

flow is the lowest frequency of operation

f_high is the highest frequency of operation;

Zeven is the even mode impedance of the corresponding coupler section; and

Zodd is the odd mode impedance of the corresponding coupler section

During design phase, the coupling and isolation with respect to the characteristic impedance of each coupler section is defined by: coupling =

odd

POUT = ^PINI ^" ^AUX = O coupling ² ) P, N1 isolation= 0

Advantageous further developments or modifications of the aforementioned exemplary aspects of the present invention are set out in the dependent claims.

Brief description of drawings For a more complete understanding of example embodiments of the present invention, reference is now made to the following descriptions taken in connection with the accompanying drawings in which :

Fig. 1 schematically illustrates a standard 3-way Doherty amplifier according to the prior art;

Fig. 2 illustrates definitions of operating points of load-modulation type power amplifiers exemplified by a standard 3-way Doherty amplifier according to the prior art;

Fig . 3 shows graphs indicating deviations from target values towards band edges exemplified by a standard 3-way Doherty amplifier according to the prior art;

Fig. 4 shows a principle configuration of an example for a method according to certain embodiments of the present invention;

Fig. 5 shows a principle flowchart of an example for an apparatus according to certain embodiments of the present invention;

Fig. 6 schematically illustrates a 3-way load-modulation power amplifier according to certain embodiments of the present invention;

Fig. 7 illustrates definitions of operating points of a load-modulation type power amplifier according to certain embodiments of the present invention;

Fig. 8 schematically shows a coupler sections design definition according to certain embodiments of the present invention;

Fig. 9 schematically shows a real feeding port design definition according to certain embodiments of the present invention; Fig. 10 schematically shows a final design according to certain embodiments of the present invention; and

Fig. 11 shows graphs indicating deviations from target values towards band edges according to certain embodiments of the present invention.

Description of exemplary embodiments

Exemplary aspects of the present invention will be described herein below. More specifically, exemplary aspects of the present invention are described hereinafter with reference to particular non-limiting examples and to what are presently considered to be conceivable embodiments of the present invention. A person skilled in the art will appreciate that the invention is by no means limited to these examples, and may be more broadly applied.

It is to be noted that the following description of the present invention and its embodiments mainly refers to specifications being used as non-limiting examples for certain exemplary network configurations and deployments. Namely, the present invention and its embodiments are mainly described in relation to 3GPP specifications being used as non-limiting examples for certain exemplary network configurations and deployments. In particular, a UMTS/HSDPA communication system is used as a non-limiting example for the applicability of thus described exemplary embodiments. As such, the description of exemplary embodiments given herein specifically refers to terminology which is directly related thereto. Such terminology is only used in the context of the presented non-limiting examples, and does naturally not limit the invention in any way. Rather, any other network configuration or system deployment, etc. may also be utilized as long as compliant with the features described herein.

Hereinafter, various embodiments and implementations of the present invention and its aspects or embodiments are described using several alternatives. It is generally noted that, according to certain needs and constraints, all of the described alternatives may be provided alone or in any conceivable combination (also including combinations of individual features of the various alternatives).

Fig. 1 schematically illustrates a standard 3-way Doherty amplifier according to the prior art. The 3-way Doherty amplifier is comprised of a load modulation type amplifier with λ/4 combiners, wherein the structure also includes output transformation to Z_LOAD. In Fig. 1, PI denotes the output of the main amplifier, and P2 and P3 denote an output of a peak 1 amplifier and a peak 2 amplifier, respectively, which are connectable via a switch. It is to be noted that the switches are only shown for schematically illustration, wherein the open/close condition is automatically controlled by signal level and matching structure of peakl/2 amplifiers. Reference sign P4 denotes an output to a load. Further, λ corresponds to center frequency of amplifier, and Z0_xxx corresponds to characteristic impedance of the transmission line.

Fig. 2 illustrates definitions of operating points of load-modulation type power amplifiers exemplified by a standard 3-way Doherty amplifier according to the prior art as shown in Fig. 2. In the upper scheme, peak 1 amplifier and peak 2 amplifier are OFF, in the middle scheme, peak 1 amplifier is ON and peak 2 amplifier is OFF, and in the lower scheme, peak 1 amplifier and peak 2 amplifier are switched ON.

Fig . 3 shows graphs indicating deviations from target values towards band edges exemplified by a standard 3-way Doherty amplifier according to the prior art according to an example, with the following settings: Example:

1 :2:2 MAIN:PEAK1 :PEAK2 Power Contribution

Frequency Range= 791 - 960 MHz (~ 20 % BW)

Z_LOAD= 50 Ohm

Ideal transmission lines

Optimized characteristic impedance values for given frequency range:

Z0_MAIN= 48.34 Ohm / Z0_PEAK12= 16.78 Ohm / Z_OUT= 22.81 Ohm

Port 1 (= MAIN-Port) :

Targerl : Zin_Port1 = 90 Ohm @ B02 (PEAK1-Amp.= OFF / PEAK2-Amp.= OFF) Target2: Zin_Port1 = 50 Ohm @ B01 (PEAK1-Amp.= ON / PEAK2-Amp.= OFF) Target3: Zin_Port1= 50 Ohm @ PMAX (PEAK1-Amp.= ON / PEAK2-Amp.= ON)

Port 2 (= PEAK1-Port) :

Target4: Zin_Port2= 62.5 Ohm @ B01 (PEAK1-Amp.= ON / PEAK2-Amp.= OFF) Target5: Zin_Port2= 25.0 Ohm @ PMAX (PEAK1-Amp.= ON / PEAK2-Amp.= ON)

Port 3 (= PEAK2-Port) :

Target6: Zin_Port3= 25.0 Ohm @ PMAX (PEAK1-Amp.= ON / PEAK2-Amp.= ON)

As becomes apparent from this example, significant deviations from target values towards band edges are present. Therefore, the prior art amplifier is not well suited for broadband applications.

The present invention shows a novel design method for output combining a 3- way very high power amplifier structure to achieve a broadband, high efficient amplifier design to handle communication signals with high peak-to-average ratios (PAR). The core of the invention is a two-section coupling structure which has feeding ports for three amplifier stages. One of the stages is called MAIN- amplifier stage the others are PEAK-amplifier stages which are boosting the output signal at high output power levels. The power capability of that peak amplifiers are defined by the factors a i and α ₂ relative to the main amplifier power contribution. If we consider a graph output power versus input power we have two characteristic points where peakl and peak2 amplifier starts to support the main amplifier. The operating points where the peak amplifiers become active are called the backoff (BO) points. These points depend on on and a ₂. All three amplifier paths are subjected to impedance variations during signal amplitude changes. This is the basic feature of the load modulation principle. These impedances can be specified at the BO-points and are also a function of on and a ₂- Knowing these conditions it is possible to design a double section coupler structure that fulfils the constraints exactly for one frequency point and to a remarkable extent for a wide range of frequency.

Fig. 4 shows a principle configuration of an example for an apparatus according to certain embodiments of the present invention. The apparatus 40 comprises a main amplifier circuit 41, two auxiliary amplifier circuits 42; 43, each of the two auxiliary amplifier circuits 42; 43 being selectively interacting in a load modulation operation with the main amplifier circuit 41 for boosting the output signal at high power output levels, and a coupler circuit 44 having an output port 45 and coupled to combine output signals of the amplifiers 41; 42; 43 at the coupler output port 45, wherein the coupler circuit 44 is a two-section coupling structure comprising feeding ports 46a, 46b, 46c for the amplifier stages of the main amplifier 41 and each of the auxiliary amplifiers 42; 43.

Fig. 5 shows a principle flowchart of an example for a method according to certain embodiments of the present invention.

In Step S51, output signals of a main amplifier circuit and of two auxiliary amplifier circuits are combined with a coupler circuit having an output port providing an output, each of the two auxiliary amplifier circuits being selectively interacting in a load modulation operation with the main amplifier circuit for boosting the output signal at high power output levels, wherein the coupler circuit is a two-section coupling structure comprising feeding ports for the amplifier stages of the main amplifier and each of the auxiliary amplifiers.

The invention can be realized by several implementation structures. Lossless transformers, discrete or distributed branchline couplers, Lange couplers or coupled line structures can be used. The most favorite design is the coupled transmission line coupler structure which combines power capability, broadband, very low losses as well as possible small size in one component. There are several vendors in the market that can produce a compact component that fulfill the task. The most important use cases are the high power multiband application where a 3-way amplifier is needed to achieve the requested power levels. The currently available transistors are of course limited in power but the requirements for power grow up. So one of the most suitable design methods is a kind of parallelization of stages. Therefore the invention is best suited for solving that problem.

Fig. 6 schematically illustrates a 3-way load-modulation power amplifier according to certain embodiments of the present invention. Reference sign 1 denotes the output of the main amplifier, and reference signs 2 and 3 denote an output of a peak 1 amplifier and a peak 2 amplifier, respectively, which are connectable via a switch. Reference sign 4 denotes the output to a load . It is to be noted that the switches are only shown for schematically illustration, wherein the open/close condition is automatically controlled by signal level and matching structure of peakl/2 amplifiers. CPL sectl and CPL sect2 define a two-section coupling structure which has feeding ports for three amplifier stages.

Fig. 7 illustrates definitions of operating points of load-modulation type power amplifier according to certain embodiments of the present invention as shown in Fig. 6. In the upper scheme, peak 1 amplifier and peak 2 amplifier are OFF, in the middle scheme, peak 1 amplifier is ON and peak 2 amplifier is OFF, and in the lower scheme, peak 1 amplifier and peak 2 amplifier are switched ON .;

Fig. 8 schematically shows a coupler sections design definition according to certain embodiments of the present invention. It is to be noted that the coupler sections design definition is identical to both coupler sections.

In the coupler sections design definition as shown in Fig . 8, auxiliary port and sketched feeding lines are only for coupling section design definition phase, and are not present in real layout. In Fig.8, the following characteristics apply: f_!ow lowest frequency of operation

frequency of operation

Zeven(i.2) even mode impedance of coupler

Zodd(i.2) odd mode impedance of coupler

_7Π -i/ — ~ — i characteristic impedance

^CPLsect(1,2) - V Zeven Zodd _{Qf co p}|_{er sectjon}

Z0|_N1 ,Z0|_N2, Z0_AUX, ZOQUT ~ Z0_Cp_Lsect(-| 2)

Coupling & isolation definition with respect to

characteristic impedance (= termination impedance)

ZO CPLsect(1,2)

coupling =

^P = ^ρ _ΐΝΓ^ΡΑυχ ⁼ coupling ² )P_IN1

Fig. 9 schematically shows a real feeding port design definition according to certain embodiments of the present invention. According to the real feeding port design of Fig. 9, for a given frequency range of at least 20% of relative bandwidth solutions for the design parameter of CPLsectl and CPLsect2 can be found that approximately fulfill the given target values. An optimizer program will find one result set for the four parameters Zevenl, Zoddl, Zeven2, Zodd2.

In Fig.9, the following characteristics apply: LENO should be short

ZO QUT ^~ 50 Ohm for example

LEN1 «< lamda/4 of f _high

Z0,_N1 = Z0_main

LEN2 << lamda/4 of f _high

Z0_|N2 = Z0_peak1

LEN3 << lamda/4 of f _high

Z0|_N3= Z0_peak2

Z0_main, Z0_peak1 , Z0_peak2=

external feedline impedances

Fig. 10 schematically shows a final design according to certain embodiments of the present invention, wherein the lower scheme is a schematically side view.

Fig. 11 shows graphs indicating deviations from target values towards band edges according to certain embodiments of the present invention in comparison with a standard 3-way Doherty amplifier (dashed traces), with the following settings:

Example:

1 :2:2 MAIN:PEAK1 :PEAK2 Power Contribution

Frequency Range= 791 - 960 MHz (~ 20 % BW)

f0= 871 MHz

Z_LOAD= 50 Ohm

Ideal transmission line couplers

Optimized characteristic impedance values for given frequency range:

Zeven1= 1 17.9 Ohm / Zodd1= 17.50 Ohm

Zeven2= 73.67 Ohm / Zodd2= 27.51 Ohm

Port 1 (= MAIN-Port) :

Targetl : Zin_Port1 = 90 Ohm @ B02 (PEAK1-Amp.= OFF / PEAK2-Amp.= OFF) Target2: Zin_Port1 = 50 Ohm @ B01 (PEAK1-Amp.= ON / PEAK2-Amp.= OFF) Target3: Zin_Port1 = 50 Ohm @ PMAX (PEAK1-Amp.= ON / PEAK2-Amp.= ON)

Port 2 (= PEAK1-Port) :

Port 3 (= PEAK2-Port) :

Target6: Zin_Port3= 25.0 Ohm @ PMAX (PEAK1-Amp.= ON / PEAK2-Amp.= ON)

As becomes apparent from this example, all target values are reasonable approached also towards band edges. Therefore, the amplifier according to the present invention is well suited for broadband applications.

In the foregoing exemplary description of the apparatus, only the units that are relevant for understanding the principles of the invention have been described using functional blocks. The apparatuses may comprise further units that are necessary for its respective function. However, a description of these units is omitted in this specification. The arrangement of the functional blocks of the apparatuses is not construed to limit the invention, and the functions may be performed by one block or further split into sub-blocks.

According to exemplarily embodiments of the present invention, a system may comprise any conceivable combination of the thus depicted devices/apparatuses and other network elements, which are arranged to cooperate as described above. Embodiments of the present invention may be implemented as circuitry, in software, hardware, application logic or a combination of software, hardware and application logic.

As used in this application, the term "circuitry" refers to all of the following : (a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and (b) to combinations of circuits and software (and/or firmware), such as (as applicable) : (i) to a combination of processor(s) or (ii) to portions of processor(s)/software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and (c) to circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. This definition of 'circuitry' applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term "circuitry" would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and/or firmware. The term "circuitry" would also cover, for example and if applicable to the particular claim element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in server, a cellular network device, or other network device.

The present invention relates in particular but without limitation to mobile communications, for example to environments under GSM, HSDPA, UMTS, LTE, WCDMA, WIMAX and WLAN and can advantageously be implemented also in controllers, base stations, user equipments or smart phones, or personal computers connectable to such networks. That is, it can be implemented as/in chipsets to connected devices, and/or modems thereof. If desired, the different functions discussed herein may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the above-described functions may be optional or may be combined .

Although various aspects of the invention are set out in the independent claims, other aspects of the invention comprise other combinations of features from the described embodiments and/or the dependent claims with the features of the independent claims, and not solely the combinations explicitly set out in the claims.

It is also noted herein that while the above describes example embodiments of the invention, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention as defined in the appended claims.

The following meanings for the abbreviations used in this specification apply:

MC Multi Carrier

MS Multi Standard

MB Multi Band

DPD Digital Predistortion

PA Power Amplifier

PAR Peak to Average Ratio

BO Backoff

(Xi , a₂ PowerFactor for Peak Amplifier Stages

Claims

What is claimed is:

1. An apparatus, comprising :

a main amplifier circuit;

two auxiliary amplifier circuits, each of the two auxiliary amplifier circuits being selectively interacting in a load modulation operation with the main amplifier circuit for boosting an output signal at high power output levels; and a coupler circuit having an output port and coupled to combine output signals of the amplifiers at the coupler output port,

wherein the coupler circuit is a two-section coupling structure comprising feeding ports for the amplifier stages of the main amplifier and each of the auxiliary amplifiers.

2. The apparatus according to claim 1, wherein the characteristics of each of the coupling sections is defined by f₀ and Z_eVen, Z₀dd, wherein : fO = low f high' _r f_low is the lowest frequency of operation and f_high is the highest frequency of operation;

Zeven is the even mode impedance of the corresponding coupler section; and

Zodd is the odd mode impedance of the corresponding coupler section.

3. The apparatus according to claim 1 or 2, wherein the characteristic impedance of each coupler section is defined by:

ZOcPLsect = Z even Z odd' ^■ _{a n c}J

ZOcPLsect ⁼ ZOi l, Z0iN2, ZO , ZOoUT■

4. The apparatus according to any of claims 1 to 3, wherein the coupling and isolation with respect to the characteristic impedance of each coupler section is defined by:

P = ^ΡΙΝΓ ^PAUX = (1- coupling ² ) IN1

5. A method, comprising :

combining output signals of a main amplifier circuit and of two auxiliary amplifier circuits with a coupler circuit having an output port providing an output signal of the coupler circuit, each of the two auxiliary amplifier circuits being selectively interacting in a load modulation operation with the main amplifier circuit for boosting the output signal at high power output levels;

6. The method according to claim 5, wherein the characteristics of each of the coupling sections is defined by f₀ and Z_eVen, Z₀dd, wherein : f0 = » ^ low f high _t

flow is the lowest frequency of operation and

fnign is the highest frequency of operation;

Zeven is the even mode impedance of the corresponding coupler section; and

Zodd is the odd mode impedance of the corresponding coupler section .

7. The method according to claim 5 or 6, wherein the characteristic impedance of each coupler section is defined by:

^ Lsect - Z even Z odd ^■ _{a nc}J

ZOcPLsect = ZOi l, Z0iN2, ZOAUX, ZOQUT ^■

8. The method according to any of claims 5 to 7, wherein the coupling and isolation with respect to the characteristic impedance of each coupler section is defined by: coupling =

^POUT = ^P!N - ^PAUX = 0 - coupling ² ) P_IN1 isolation=