High frequency class F and inverse class F power

amplifiers obtain high efficiency of dc to ac power conversion, by reducing the overlap of voltage and current waveforms at the output of the active device, to ensure that the power dissipated in the resistance Ron of the active device is minimised. In this paper the active device is modelled as a switch in series with resistance Ron 0 to 5Ω. For ideal switch voltage / current waveforms and equal dc input power for both amplifiers the efficiency of power conversion is compared. To confirm the predicted results ideal lossless load harmonic networks using lumped elements were designed to meet all frequency conditions of the two amplifiers. These networks were done used in Advanced Design System (ADS) software for Ron=0, 2 and 4 Ω. The predicted efficiency for 2Ω and 4 Ω were 80% and 60% and the obtained simulation efficiency were 83.2% and 65.5% for class F amplifier. For the inverse class F amplifier the predicted efficiency was 87.3% and 74.5% and for the simulation results it was 87.26% and 74.4%. Above predicted and simulated results show that the resistance Ron has less effect on the efficiency of inverse class F than for class F amplifier. As lumped elements can not be used at high frequencies they were replaced initially with lossless transmission lines and then by microstrip lines to also investigate also how copper and dielectric losses affect the efficiency of power conversion

Danaher, Sean

Ghassemlooy, Zabih

Korolkiewicz, Edward

Liu, Lei

Lu, Qing

Sambell, Alistair

English

Northumbria Research Link

Effect of Losses in an Active Device and Harmonic Network on the Efficiency ofClass F and Inverse Class F Power AmplifiersL. Liu, Student Member, IEEE, E. Korolkiewicz, Fellow, IET, Z. Ghassemlooy, Senior Member, IEEE, A.Sambell, Member, IEEE, S. Danaher, Member, IEEE, and Q. Lu, Student Member, IEEEEmail: lei.liu@northumbria.ac.ukAbstract- High frequency class F and inverse class F poweramplifiers obtain high efficiency of dc to ac power conversion,by reducing the overlap of voltage and current waveforms atthe output of the active device, to ensure that the powerdissipated in the resistance Ron of the active device isminimised. In this paper the active device is modelled as aswitch in series with resistance Ron 0 to 5Ω. For ideal switchvoltage / current waveforms and equal dc input power for bothamplifiers the efficiency of power conversion is compared. Toconfirm the predicted results ideal lossless load harmonicnetworks using lumped elements were designed to meet allfrequency conditions of the two amplifiers. These networkswere done used in Advanced Design System (ADS) software forRon=0, 2 and 4 Ω. The predicted efficiency for 2Ω and 4 Ω were 80% and 60% and the obtained simulation efficiency were83.2% and 65.5% for class F amplifier. For the inverse class Famplifier the predicted efficiency was 87.3% and 74.5% andfor the simulation results it was 87.26% and 74.4%. Abovepredicted and simulated results show that the resistance Ronhas less effect on the efficiency of inverse class F than for classF amplifier. As lumped elements can not be used at highfrequencies they were replaced initially with losslesstransmission lines and then by microstrip lines to alsoinvestigate also how copper and dielectric losses affect theefficiency of power conversion.Key words-high efficiency power amplifier, class F andinverse class F power amplifier, harmonic matchingI. INTRODUCTIONThere is an increasing demand for low cost mobilecommunication systems and battery operated radio receiverswhere high efficient power amplifiers are used. The mainobjective in the design of these amplifiers is to produce highefficiency conversion of dc energy supplied by the batteryto ac energy that is used in the transmitter part of the abovesystems. If high efficiency is obtained there is considerablereduction of dissipated power consumption which becomesincreasing important as the use of these systems isincreasing not only in developed, but also in emergingcountries. This increase in efficiency also addresses thecurrent the problem of saving global energy. For an idealclass F amplifier [1]-[3] load harmonic network ensures thatonly odd harmonics are present in the voltage and only evenharmonics are present in the current waveforms at theoutput terminals of the active deice. For the aboveconditions square voltage and half-sinusoidal currentwaveforms are obtained at the active device. For Ron equalto zero these ideal waveforms do not overlap and hence100% dc to ac power conversion can theoretically beobtained. Similarly for the ideal inverse class F amplifier[4]-[6] the harmonic network produces square current andhalf-sinusoid voltage waveforms and again 100% dc to acpower conversion can also be obtained if Ron is equal tozero.In [7] the losses in Ron were investigated where it wasassumed that the output powers were the same for the twoamplifiers and to solve the obtained complex equationsrequired the use of MachCAD software. In this paper thesolution of the derived equations is considerably simplifiedby assuming that the input power to the two amplifiers is thesame. The theoretical derived equations were then used tocompare the efficiency of power conversion for the twoamplifiers. The theoretically predicted results for Ron equalto0, 2 and 4 Ω were compared with results obtained bysimulation using ADS software where ideal losslesstransmission lines were used. Then the ideal transmissionlines were replaced by microstrip lines so that the effect ofsubstrate and copper losses on the efficiency of powerconversion for both amplifiers could also be compared.II. EFFECT RON ON THE EFFICIENCY OF POWERCONVERSION FOR CLASS F AND INVERSE CLASSF POWER AMPLIFIERSFor the two amplifiers the ideal voltage and currentwaveforms at the output terminals of the active device areshown below.In deriving the below equation it was assumed same dcvoltage vDD is used in both amplifiers. For the class Famplifier using Fourier series expansion for the abovewaveforms equations for dc input power PdcF, output powerPoF at design frequency, impedance RLF at the designfrequency (see Fig. 2) and efficiency of power conversionηF shown below were derived. In the below equations vk isthe knee voltage of the output characteristics of the activedevice and given by ݒ௞ = ௣݅ி ∗ ܴ௢௡(a) (b)Fig. 1 Ideal voltage and current wave forms at the output of the activedevice (a) Class F (b) Inverse class Fௗܲ௖ி = ௏ವವ௜೛ಷగ(1a)௢ܲி = (௏ವವି௩ೖ)௜೛ಷగ(1b)ܴ௅ி = (଼௏ವವି௩ೖ)గ௜೛ಷ(1c)ߟி = ௏ವವି௩ೖ௏ವವ(1d)The corresponding equations for the inverse class Famplifier are shown below.ܲௗ௖ிᇲ = ௏ವವ௜೛ಷᇲଶ (2a)ܲ௢ிᇲ = (௏ವವି௩ೖᇲ)௜೛ಷᇲଶ (2b)ܴ௅ிᇲ = గమ(௏ವವି௩ೖᇲ)ସ௜೛ಷᇲ (2c)ߟிᇲ = ௏ವವି௩ೖᇲ௏ವವ (2d)The performance of the two amplifiers can be comparedby deriving equations for the inverse class F amplifier interms of the design parameters of the class F amplifier. Thisis obtained by ensuring that the dc input power for bothamplifiers is the same so that the current ipF’ can beexpressed in terms of ipF. as shown in equation (3) by usingequation equations 1(a) and 2(a).௣݅ிᇱ= ଶ௜೛ಷగ(3a)The knee voltage vk’ for the inverse class F is obtained interms of ipF as shown in equation 3(b) and as can be seen vkis less than vk’ݒ௞ᇱ= ௣݅ிᇱܴ ௢௡ = ଶ௜೛ಷగܴ௢௡ (3b)Similarly RLF’ in equation 2(c) is given by equation (4)below.ܴ௅ிᇲ = గయ(௏ವವିమ೔೛ಷഏ ோ೚೙)଼௜೛ಷ (4)For the derived equations 1(c), (3b) and (4) the outputcharacteristic of an active device are shown in Fig. 2.Fig. 2 Output characteristic of the active deviceTo compare the efficiencies of the two amplifiers thefollowing modified equations for inverse class F amplifiercan be obtained by using equations (3a), in equations (2c)and (2d).ܲ௢ிᇲ = (௏ವವିమ೔೛ಷഏ ோ೚೙)௜೛ಷగ (5a)ߟி' = ௏ವವିమ೔೛ಷഏ ோ೚೙௏ವವ(5b)Assuming that for VDD =5V and ipF =0.5 A, the input dcpower given by equation 1(a) is 0.796 watts and the effectof Ron (0 to 5ohms) on the out output power for the twoamplifiers using equations (1b) and (2b )are shown Fig.3(a) below. Fig. 3(b) shows how the load resistances RL andRLF’ and Fig. 3(c) shows how the efficiencies of the twoamplifiers are affected by Ron.(a)(b)(c)Fig. 3 Effect of Ron on (a) Power output (b) Dc to ac power conversionefficiency (c) Load resistanceFig. 3 (b) shows that the efficiency reduces as a functionof Ron but this reduction is larger for class F amplifier than itis for the inverse class F amplifier. For Ron = 2Ω the powerthe conversion efficiency is 87.3% for inverse class F and80% for class F amplifier. The resistances shown on Fig.3(c) will be used to design the load harmonic networks forthe two amplifiers as discussed in the next section.III. INVESTIGATION OF THE WAVEFORMS ANDEFFICIENCY OF POWER CONVERSION OF THETWO AMPLIFIERS USING ADS SOFTWAREThe block diagram of the above amplifiers is shown inFig. 4 where the active device is modelled as an ideal switchin series with Ron and Zin is the input impedance of the loadharmonic network. For the class F amplifier the inputimpedance of the load harmonic at fundamental frequencyZin (f) = RLF, for even harmonic Zin (2nf) = 0, for oddharmonic Zin ((2n+1)f) = ∞, where n=1,2,3… For theinverse class F amplifier, the input impedance atfundamental frequency Zin (f) =RF’, for even harmonic Zin(2nf) = ∞, for odd harmonic Zin ((2n+1)f) = 0. Theseconditions ensure that the ideal voltage and currentwaveforms shown below are obtained.Fig. 4 Block diagram of a high efficiency amplifier(a)(b)Fig. 5 Ideal harmonic matching networks for all frequency (a) Class F(b) Inverse class FTo confirm the above predicted results the ideal loadharmonic networks for both amplifiers are shown in Fig. 5.The required input impedance of the two networks at 2 GHzusing equations 1(c) and (4) are RLF = 20.37Ω and RLF’ =33.82Ω. The networks also satisfy the required input impedance at all the harmonics that are required to obtainthe square and half sinusoidal waveforms.The above networks were used in ADS software and theobtained switch voltage and current waveforms for the twoamplifiers are shown in Fig. 6. For the inverse class Famplifier the predicted waveforms shown in Fig. 6(b) arevery similar to those predicted waveforms shown in Fig.1(b). However there is a small difference between thepredicted and obtained waveforms for the class F amplifier(see Fig.1(a)) and Fig. 6(a)) which due to the resistance Ron.(a)(b)Fig. 6 Voltage and current wave forms through ideal switch andinternal resistance Ron by ADS simulation for infinity number harmonic (a)Class F amplifier (b) Inverse class F amplifierFor high frequency power amplifier it is practically notpossible to use lumped reactive circuit element which mustbe replaced by transmission lines. For this reason it is notpossible nor is it desirable to design these load harmonicnetworks to satisfy the required conditions at all theharmonics. Such a network would require an infinitenumber of microstrip lines producing large losses whichwould cause the efficiency of power to conversion toreduce. Normally these networks are designed to obtain thedesired input impedances at the design frequency and at thenext two harmonics. The designed load harmonic networksup to the third harmonic are shown in Fig. 7 below for Ron =2Ω. The obtained simulated voltage and current waveformsfor the two amplifiers shown in Fig. 8.The effect of using load harmonic networks designed upto the third harmonic using lossless transmission lines(TLin) and microstrip lones (MLin) where there are copperand dielctric losses are compared with the infinity numberof harmonic results and shown in table 1 below for Ron = 0,2 and 4Ω.(a)(b)Fig. 7 Harmonic matching networks (a) Class F (b) Inverse class F(a)(b)Fig. 8 Voltage and current wave forms through ideal switch andinternal resistance Ron by ADS simulation up to 3rd harmonic (a) Class Famplifier (b) Inverse class F amplifier0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.0 1.00246810-2120100200300400500-100600time, nsects(vd),Vts(ipF.i),mA0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.0 1.024681012140160100200300-100400time, nsects(vd),Vts(ipF.i),mA0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.0 1.024680100100200300400500-100600time, nsects(vd),Vts(ipF.i),mA0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.0 1.0246810120140100200300-100400time, nsects(vd),Vts(ipF.i),mATable ITable 1 shows that for both amplifiers that the efficiencyreduces as Ron increases but however this reduction is largerfor class F amplifier than it is for the inverse class Famplifier. Microstrip line also causes the loss and efficiencydrops more than 5 % for both amplifiers and more effects onclass F as well.IV. CONCLUSIONSThe effect of losses on the efficiency of dc to ac powerconversion in Ron and in microstrip lines used in loadharmonic networks, are compared for class F and inverseclass F power amplifiers. Initially assuming ideal voltageand current waveforms design equations were derived forboth amplifiers. Then applying the condition that the dcinput power is the same for both amplifiers it was shownthat for the range of resistance Ron 0 to 5Ω, the obtainedefficiency of power conversion of the inverse class Famplifier is better than it is for the class F amplifier. Inpractice however such ideal voltage and current waveformscannot be practically obtained. A more realistic comparisoncan be made by using ADS software, where the activedevice is modelled as an ideal switch in series with Ron (0 to5Ω) and a suitable load harmonic network, to obtain thecurrent and voltage waveforms and efficiency of powerconversion for Ron 0 to 5Ω. In this modelling to ensure thatthe dc input power was the same for both amplifiers theinput impedance of both harmonic matching networks wasthe same as those derived by the design equations. Initiallythese load harmonic networks were designed using lumpedreactive elements to meet the required conditions at eachharmonic of the current and voltage waveforms. However inpractice the above lump elements cannot be used and hencethey were replaced by ideal lossless transmission lines andby microstrip lines to meet the required conditions at thedesign frequency and the first two harmonics. From theobtained results, for the above load harmonic networks, it isshown that the obtained efficiency is always better for theinverse class F amplifier than that of the class F amplifier.REFERENCES[1] S. F. Ooi, S. Gao, A. Sambell, D. Smith, and J. Butterworth,"High efficiency class-F power amplifier design," 2004 High FrequencyPostgraduate Student Colloquium, pp. 113-118 211, 2004.[2] H. C. Park, G. H. Ahn, S. C. Jung, C. S. Park, W. S. Nah, B. S.Kim, and Y. G. Yang, "High-efficiency class-F amplifier design in thepresence of internal parasitic components of transistors," 2006 EuropeanMicrowave Conference, Vols 1-4, pp. 1055-1058, 2006.[3] D. Schmelzer and S. I. Long, "A GaNHEMT Class F amplifierat 2 GHz with > 80 % PAE," IEEE Compound Semiconductor IntegratedCircuit Symposium - 2006 IEEE Csic Symposium, Technical Digest 2006,pp. 96-99, 2006.[4] Y. J. Xu, J. Q. Wang, and X. W. Zhu, "Analytical Design of anInverse Class F Power Amplifier for Linear Amplification," MicrowaveJournal, vol. 54, pp. 146-+, May 2011.[5] P. Aflaki, R. Negra, and F. M. Ghannouchi, "Design andimplementation of an inverse class-F power amplifier with 79 % efficiencyby using a switch-based active device model," 2008 IEEE Radio andWireless Symposium, Vols 1 and 2, pp. 423-426, 2008.[6] H. J. Kim, G. W. Choi, and J. J. Choi, "A high-efficiencyinverse class-F power amplifier using GaNHEMT," Microwave andOptical Technology Letters, vol. 50, pp. 2420-2422, Sep 2008.[7] Y. Y. Woo, Y. Yang, I. Kim, and B. Kim, "Efficiencycomparison between highly efficient class-F and inverse class-F poweramplifiers," IEEE Microwave Magazine, vol. 8, pp. 100-+, Jun 2007.Ron Class F Inverse class F Class F Inverse class F0 100% 100% 99.90% 99.90%2 80% 87.30% 83.20% 87.26%4 60% 74.50% 65.50% 74.40%Ron Class F Inverse class F Class F Inverse class F0 99.00% 99.10% 75.28% 88.31%2 81.70% 87.00% 62.70% 77.60%4 64.40% 73.10% 49.89% 67%Predicted resultsTLin ModelADS resultsMLin ModelInfinity number harmonicsUp to 3rd harmonics

A GaNHEMT Class F amplifier at 2 GHz with > 80 % PAE,&quot;

A high-efficiency inverse class-F power amplifier using GaNHEMT,&quot;

Analytical Design of an Inverse Class F Power Amplifier for Linear Amplification,&quot;

Design and implementation of an inverse class-F power amplifier with 79 % efficiency by using a switch-based active device model,&quot;

Efficiency comparison between highly efficient class-F and inverse class-F power amplifiers,&quot;

High efficiency class-F power amplifier design,&quot;

High-efficiency class-F amplifier design in the presence of internal parasitic components of transistors,&quot;

Effect of losses in an active device and harmonic network on the efficiency of Class F and inverse Class F power amplifiers

Effect of losses in an active device and harmonic network on the efficiency of Class F and inverse Class F power amplifiers

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