10 W Class AB Power Amplifier Design for UMTS Applications Using

26th NATIONAL RADIO SCIENCE CONFERENCE (NRSC2009)

~ !D04 [J]March 17-19,2009, Faculty of Engineering, Future Univ., Egypt

10 W Class AB Power Amplifier Design for UMTS Applications Using GaNHEMT

Ahmed Sajjad, Ahmed Sayed, Ahmed Al Tanany, Georg Boeck

Microwave Engineering, Berlin University oJTechnology

EinsteinuJer 25, 10587 Berlin, GermanySajjad.giki @gmail.com, [email protected] .de

ABSTRACT

This paper exhibits a 10 W class AB highly linear power amplifier (PA) for a frequency of2.14 GHz using GaNHEMT. Power and linearity measurements and simulations illustrate stupendous correspondence. An outputpower of II W (41 dBm) with maximum drain efficiency (T]) of 72 % (PAE 56 %) is achieved. Linearitymeasurements were made with a frequency spacing of 100 KHz and output third-order and second-orderintercept points (GIP3 and GIP2) were observed to be 48 dBm and 80 dBm respectively.

1. INTRODUCTION

In the ever growing world of advance communication standards, Power amplifiers (PAs) playa vital role inperformance and cost factor of a communication system. In the digital modulated wireless communicationsystems (W-CDMA, GFDM) there has been an intensive challenge to improve the efficiency, linearity andthermal characteristic of the PA. Among PA design to achieve all the conflicting goals an advanced transistor isthe primary necessity . GaN HEMT has made itself a strong contender in the application of the microwavefrequency systems due to its wide bandgap features of high electric breakdown field strength, hence high powerdensity, high electron saturation velocity and high operating temperature [1]-[3]. It is a very useful device forwide band applications due to its high power density and it also attains high input and output impedancecomparing to other devices which in-tum makes matching easier [3]. Linearity is also one of the key issues inmulti carrier communication system where the carrier signals are closely spaced in frequency and it's suggestedthat GaN HEMT address this requirement significantly [4].

For the last few years wide-band devices has been implemented using several classes and with differentperformances. In [5] a 43 dBm output power with 13 dB power gain and 73 % PAE class EPA. In another worka PAE of 74 % with 11.4 W output power and 12.6 dB power gain using class E [6]. Finally, class AlAB PAusing SiC achieved maximum PAE 66 % at 500 MHz and 24.9 dB power gain, with 44.15 dBm output power(26 W) [7].

This paper introduces a class AB power amplifier at 2.14 GHz with Max. output power of 10 W, drainefficiency (T]) of 72 % and output IP3 (GIP3) of 48 dBm.

Section 2 introduces the design parameters of this class in details. Measured and simulated small signal aswell as large signal performance are depicted in details in section 3. Finally, section 4 concludes the figure ofmerits of this work.

2. DESIGN

This work is done using the Advanced Design System (ADS) from Agilent and 10 watts transistor modelfrom Eudyna.The first step in designing a power amplifier is determining the bias points which ultimatelydetermine the class of operation. In this work class AB bias points are chosen as shown in table I to achieve highgain, high efficiency and linearity. The drain voltage Vos is set to 48 volts and the quiescent current los is set as240 mA.

As it a narrow band design so for biasing a lambda quarter transmission line is used which gives completeisolation at RF frequency. The large signal model for Eudyna transistor was used to extract the load and sourceimpedances as shown in Fig. 2 using the load/source-pull technique while shorting all the harmonics. Transistorwas made unconditionally stable by fulfilling the Rollet's stability criterion [8] (K>1) and this was achieved byusing a combination of resistance and capacitance at the input. Conjugate matching for maximum transfer ofpower was implemented using open shunt stub solution .

26"' NATIONAL RADIOSCIENCECONFERENCE, NRSC'2009Future University, 5"'Compound, New Cairo, Egypt, March 17- 19,2009


~ ID041~~ March 17-19,2009, Faculty of Engineering, Future Univ., Egypt

3. EXPERIMENTAL RESULTS

Comparison of simulations and measurements for small signal performance, power performance and linearityof the power amplifier is discussed in this section. All these simulations and measurements were made at2.14 GHz. Fig. 3 shows a prototype for the designed PA based on Rogers material R04003 with a dielectricconstant e, of 3.48 and thickness of 0.51 mm.

A. Small signal performance

Fig. 4 and Fig. 5 represent a comparison between simulated and measured small signal return loss and gainand stability factor (K), respectively. Both diagrams show a strong agreement between the simulations andmeasurements and table II concludes the achieved performances at 2.14 GHz.

B. Large signal performance

Large signal measurements were done using an RF signal generator in combination with high gain amplifieras power source and a 1 dB compression point output power of37.2 dBm (max Pout = 41 dBm) and power gainof 14.8 dBm along with drain efficiency 42.3 % (PAE 40.2 %) was achieved. Also we see in Fig. 6 thatmaximum drain efficiency (11) of 72 % and PAE of 56 % comparing to that of simulation i.e. maximum drainefficiency 74 % and PAE 59 %, it is observed that a good match between simulated and measured result hasbeen achieved. Fig 6 represents the PAE and output power over the frequency range of2.0 GHz to 2.24 GHz at adrive input power of 29 dBm. The output power of 40 dBm (10 watts) at this point is noticed to be constantalong with the PAE (50 %). From these results it's concluded that an output power of 41 dBm (11 watts), powergain of 14.3 dB, 72 % drain efficiency (11) at 35 dBm input power with a PAE of 56 % has been achieved.

Linearity which is also an integral characteristic for a power amplifier was also measured with conventionaltwo tones set up which includes a multi tone signal generator and a spectrum analyzer. Two signals of equalamplitude with a frequency spacing of 100 KHz were applied to the power amplifier with input power sweepranging from of -20 dBm to 16 dBm. The fundamental second and third order components were detected on aspectrum analyzer and the second and third order intercept points (OIP2 and OIP3) were calculated using theequation [3-5].

OIPn =Pout + (harmonic suppression)/n-l (4)

where n is the harmonic order. From Fig. 9 we observe that an OlP3 and OlP2 of 48 dBm and 80 dBmrespectively have been achieved.

4. CONCLUSIONS

This paper presents a 10 W GaN HEMT amplifier for frequency of 2.14 GHz. Load pull measurements toretrieve optimum load and source impedance for maximum output power and drain efficiency was performedusing customized model for GaN on ADS and microstrip open shunt stub matching network was implemented.Small signal and larger signal performance over a frequency range of 2.04 GHz to 2.24 GHz has been presentedand discussed. Small signal gain of 14.2 dB and output return loss of -15 dB has been achieved. An outputpower of 41 dBm (11 W) with a maximum efficiency (11) of 72 % (PAE = 56 %) is measured. Linearitymeasurements were also carried out using conventional two tone signal at the input and OlP3 and OlP2 werefound to be 48 dBm and 80 dBm respectively.

REFERENCES

[1] A. Sayed, and G. Boeck, "5 W Highly Linear GaN Power Amplifier with 3.4 GHz Bandwidth," in Proc. 37thEuropean Microwave Conf., Germany, Munich, Oct. 2007.

26fuNATIONAL RADIO SCIENCE CONFERENCE, NRSC'2009Future University, 5th Compound, NewCairo, Egypt, March 17-19,2009


~ !n04 OJMarch 17-19,2009, Faculty of Engineering, Future Univ., Egypt

[2] A. Sayed , and G. Boeck, "Two stage ultra wideband 5 W power amplifier using SiC MESFET ," in IEEETrans. on Microwave Theory Tech., vol. 53, pp. 2441-2449, July 2005.

[3] A. Zhang, L. Rowland, E. Kaminsky, 1. Kretchmer, V. Ti1ak, A. Allen, and B. Edward, "Performance ofAIGaN/GaN HEMTs for 2.8 GHz and 10 GHz power amplifier applications," in IEEE MTT-S Int.Microwave Symp. Dig., vol. 1, June 2003, pp. 251-254.

[4] N. Ceylan, 1. Mueller, T. Pittorino, and R. Weigel, "Mobile phone power amplifier linearity and efficiencyenhancement using digital predistortion," 33rd European Microwave Conf., Munich, Germany, vol. I ,Oct. 2003, pp. 269-272.

[5] Y-S. Lee, Y-H. Jeong; "A High- Efficiency Class- E GaN HEMT Power Amplifi er for WCDMAApplications" IEEE Microwave and wireless component lett., vol. 17, NO.8, Aug 2007.

[6] H. G. Bae, R. Negra, S. Boumaiza, F. M. Ghannouchi; "High-efficiency GaN class- E power amplifier withcompact harmonic-suppression network" IEEE European Microwave Conference, 2007.

[7] S. Azam 1, R. Jonsson2, Q. Wahab 1; "Single-Stage, High Efficiency, 26- Watt Power Amplifier Using SiCLE-M ESFET" IEEE Asia-Pacific Microwave Conference, 2006.

[8] D. Pozar, "Microwave Engineering", Third Edition, Danver MA, USA Wily, 2004.

Imax

o

2Vdd-Vknee

2 ~

a.: V dd Iq Co <D1S '-

'-C ::J

> o

o T/4 T/2 3T/4 T

Time

Fig. 1. IV curve for class AB.

26"' NATIONAL RADIO SCIENCECONFERENCE, NRSC'2009Future University. S"Compound, NewCairo, Egypt, March 17- 19,2009


~ In04 OJMarch 17-19,2009, Faculty of Engineering, Future Univ., Egypt

Fig. 2. Optimum impedance for output power and PAE efficiency.

Fig. 3. Prototype of the designed PA.

VDS [V] IDS [rnA] Zs[Q] ZL [Q]

48 240 3-i*9 6.201- i*4.8

Table.I. Quiescent point for optimum load and source impedances.

26mNATIONAL RADIO SCIENCE CONFERENCE, NRSC'2009Future University, Sib Compound, NewCairo, Egypt, March 17- 19,2009

26th NATIONAL RADIO SCIENCE CONFERENCE (NRSC2009)<g@> ID04 [JJMarch 17-19,2009, Faculty of Engineering, Future Univ., Egypt

S11rdBl S22rdBl Power Gain [dBl Stability factor (K)

Simulated -14 -8 16 1.5

Measured -17 -15 14.2 2.5

Table. II. Small signal gain and return losses with minimum stability factor.

0.-----.----.-----.-----.-----.------.----.----,--.---------,

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-15

--8 11 .stm

• 811meas

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o 822meas

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2.52.31.9 2.1f [GHz]

1.7-20 1---.-----.--------,..--------,..-------...-------.----.----.----.----1

1.5

Fig. 4. Measured (symbols) and simulated (solid lines) return losses of the designed PA.

26"'NATIONAL RADIOSCIENCE CONFERENCE, NRSC'2009Future University,5"'Compound,New Cairo, Egypt, March 17- 19,2009


~ In04 OJMarch 17-19,2009, Faculty of En gineering, Future Univ ., Egypt

20.--..~...........L-

a+-'

~ 15LL>-~

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C) 5 0 821meas

Cf)K .Cf) sun

0 Kmeas

01.5 1.7 1.9 2.1

f [GHz]2.3 2.5

Fig. 5. Measured (symbols) and simulated (solid lines) small signal gain and the stability factor (K) of thedesigned PA over the desired frequency band.

t-'OUlmeas

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Gainmeas

Poutsim

Gainsim

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403020Input Power [dBm]

10)-t---r-----,----r---r-----,----r---r-----t

o

Fig. 6. Output power and power gain over the swept input power: measurements (symbols),

26"'NATIONAL RADIO SCIENCE CONFERENCE, NRSC'2009Future University, 5"'Compound,NewCairo, Egypt, March 17- 19, 2009


~ !n04 OJMarch 17-19,2009, Faculty of En gineering, Future Univ., Egypt

simulations (solid lines).

80

Allmeas

D PAEmeas

60 -- lls im

........ PAEsim?fl.........>-oc 40Q)

'0~w

20

4020 30Input Power [dBm]

10o~~~~=;:::::"'--,.....--~--r-----r----r--~

o

Fig. 7. Measurements (symbols) and simulated (solid lines) results of the designed PA for drain efficiency (11)and PAE.

26mNATION/* RADIO SCIENCE CONFERENCE, NRSC'2009Future University, 5 Compound,NewCairo, Egypt, March 17- 19,2009


~ !n04 Q]March 17-19,2009, Faculty of Engineering, Future Univ., Egypt

-

-----~... T ...-

- • • • • • • • • • • • -

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2.1

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2.2 2.3f [G Hz]

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Fig. 8. Output power and PAE for a frequency range of200 MHz (2.04 GHz - 2.24 GHz).J

OlP3 - 48 dBm --------------m

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J-20

J

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Fig. 9. Second and third-order intercept points of the designed PA at 2.14 GHz with a frequency spacing of100 kHz: measurements (symbols) and simulations (solid lines).

26thNATIONAL RADIO SCIENCE CONFERENCE, NRSC'2009Future University, 5thCompound, NewCairo, Egypt, March 17- 19,2009

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10 W Class AB Power Amplifier Design for UMTS Applications Using