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TRANSMISSION-LINE MICROWAVE CLASS-E AMPLIFIER

Vladimir A. Printsovskii, Vladimir G. Krizhanovd

Abstract: The new technique of construction of microwave class-E power amplifier oulput net- work was proposed. The amplifer was designed, fabricated and tested. AtJ+equency of 820 MHz, out- put power of 410 m W with power-added efjiciency 70 % and input DC voltage 5 V was demonstrated. No post-production tuning of output marching network was applied.

1. Introduction Operation modes known as classes E and F are necessary for increasing the efficiency of microwave

power amplifiers. Realization of class-E switching amplifier assumes several conditions: on a given frequency, the transistor should he able to work as a switch while having low resistance RON in "ON" condition, the output capacity of the transistor should not exceed some defined value for the given frequency and output power, the output network should create a defined impedance on the fundamental frequency while presenting impedance close to infinity on frequencies of higher harmonics.

The realization of class-E microwave amplifiers utilizing microstrip lines is described in [ I]-[6]. The output networks implemented in these amplifiers differ by schematic and design methods, that testifies continu- ing search for optimum configuration. In the given work, new technique of construction of an output matching circuit is offered, the simulation and experimental research of the class-E amplifier with the proposed output network is performed.

2. Design Methodology The equivalent lumped element circuit of class-E amplifier is shown in fig. 1. In microwave amplifiers,

an impedance transformer must he added to output network with series resonant circuit, since for power amplifi- ers the situation is typical when load impedance RL (usually 50 Ohm) is not equal to resistance R found from conditions ofrequired output power and supply voltage [I], [3], [SI, [7].

Thus, the output circuit should create input impedance

Z = R ( I + jtan49.052') On a fundamental frequency and (1) Z - t j m On harmonics, (2)

at a standard load on its output (for optimum idealize class-E operation).

and the line segments I, implement the shaping of required input impedance-versus-frequency dependence. The equivalent circuit of proposed output circuit of the class-E amplifier is shown in fig.2. Stubs Is,

JVdC

R

Fig. 2. Equivalent circuit transmission-line amplifiei Fig. 1. Lumped-element class-E amplifier

The stubs Is, ,Is, ,___, Is, and lines I , , I 2 ,..., I , realize control of impedance on harmonics N, N - 1 ,..., I accordingly, and elements Is,+, ,I,+, control impedance on fundamental frequency.

of harmonics. The electrical lengths of stubs on a fundamental frequency are found from expression: For topology shown in fig.2, it is technologically possible to satisfy condition (2) only for finite number

(3) 1

Is, =90°.- N - n

* Donetsk National University, Radio Physics Department, ul. Universitetskaya 24, Donetsk 83055, Ukraine. Phone: +380 622 91 92 61, e-mail: apex@dongu.donetsk.ua

39

Length of line I , for n E [I ... N] is selected such that electrical length of a preceding equivalent circuit on appropriate harmonics is equal:

0 2 . k - 1 /NA/S ,A /N- I ... AIS,+lAI, =Yo .-,

n where k E [1,2 ,..,, (n + l)/2].

quency are determined by expression: In order to satisfy condition ( l ) , electrical lengths of transmission-lines lNtl , / s ~ + ~ on fundamental fre-

I, A ... A I , A Is,,, A I , = 180' . k + 49,0524' (4) For the real transistor it is necessaly to take into account transistor parasitic inductance, it will reduce in

a modification of length first segment of a transmission-line. Simulation of an output circuit. Following described technique, the output circuit with impedance

control on two harmonics was calculated and simulated. The parameters of lines are shown in Table 1. Simula- tion results for the case of lossless lines are given in fig. 3 and fig. 4.

1 .O Ghz

5 Frequency (GHz)

Fig. 3. Simulated parameter S2, output matching circuits

From fig. 4 it is apparent that the impedance on harmonic frequencies has large reactive value in a wide band of frequencies. At the same time, the impedance angle on fundamental frequency varies in narrow limits. This fact says about wide bandwidth of output circuit on transmission lines class-E amplifiers.

circuit was applied to a realization the class-E ampli- fier with central frequency of 820 MHz with use Siemens CLY5 MESFET. 100 15.0

The simulation of the amplifier was per- formed with the aid of model provided in [3]. Har-

voltage waveform to correspond class-E power am- plifiers with 50 % duty cycle. Fig. 5 present current

network. The difference hetween this form and clas- sical waveform caused drain inductance transistor

Simulation of the amplifier. The calculated ti, 20.0

Vd M

monic-balance simulation show, that current and 200 10.0

and voltage waveform on input transmission-line o 5.0

package. On the transistors chip waveforms corre- .ZOO 0

spond class-E conditions. Tlme ("sec) 0.0 0.5 1.0 1.5 2.0 2.5

Fig. 5. Current and voltage waveform at output of tran- sistors package.

3. Experimental prototyping The experimental microstrip lines class-E amplifier was constructed according to topology based on

(3,4) (fig. 6). All lines have a characteristic impedances 50 Ohm; a substrate thickness - 1.00 mm with E =7.2, line width ~ 1.3 mm. Table 2 lists the basic parameters of the transistor operation mode and amplifier perform- ance on a series of fundamental frequencies.

In fig. 7 the amplifier experimental dependences of output power and drain efficiency versus frequency are shown. It can be seen that relative bandwidth of the amplifier is about 12 % for efficiency greater that 70 %. In fig. 8 and fig. 9 the output power and efficiency versus supply voltage dependences are shown.

Fig. 6 confirms the class-E operation of the amplifier, since observed behavior of dependencies of out- put power and drain efficiency are in full correspondence with those of RF class-E amplifiers [7].

Table 1 ine stubs

40

Table 2. Experimental parameters of amplifier

Pout Gain 12 dB 13 dB 13.4 dB

70 % 68 %

~~~~ 58 I D

68 rn e42 62 B f m ’. 8 0 -

58

58

54

s E m .‘ - - 52

50 100

740 780 180 800 820 840 880 880 m 9zD M O Frequency, MHz

Fig. 6. Prototype amplifier Fig. 7. Output power and drain efficiency versus frequency. Vdc=SV. The input power is 25 mW.

30

25

E g 20 i m

a 2 15

10

0 0 1 2 3 4 5 6Vdc.V

Fig. 8. Output power versus supply voltage

0.9 - -measurement ....... model ................................. 0.8 ......... -

frequency 820MHr

0 2 3 4 5 6 Voltage DC, V

Fig. 9. Power-added efficiency versus supply voltage

4. Conclusions The newly offered method of construction and analysis of output matched network for class-E micro-

wave amplifier was considered. The amplifier was simulated and fabricated for the case of two higher harmonic frequencies tuning, using Siemens CLY5 MESFET. Measurement data confirms the results of calculation and simulation. After manufacturing, the amplifier matching circuits were not exposed to tuning adjustment.

[I] T.B. Mader, 2.9. Popovic, “The transmission-line class-E amplifier” // IEEE Microwave Guided Wave Lett., References

V.5, pp. 290-292, Sept. 1995. [2] F.J. Ortega-Gonzalez, J.L. Jimenez-Martin, A. Asensio-Lopez, G. Torregrosa-Penalva, “High-efficiency

load-pull harmonic controlled class-E power amplifier”. // IEEE Microwave and Guided Wave Letters. - 1998. -Vol. 8, No. 10. - pp. 348-350.

[3] B. Mader, E. Bryerton, M. Markovic, M. Forman, Z. Popovic, “Switched-Mode High-Efficiency Microwave Power Amplifiers in a Free-Space Power-Combined Array” // IEEE Trans. on MTT, 1898, Vol. 46, No. 10, pp, 1391-1398.

[4] M. Markovic, A. Kain, Z. Popovic, “Nonlinear modeling of Class-E power Amplifiers” // Int. Journal RF and Microwave CAE.-V.9.-1999.- P.99-103.

[SI A.J. Wilkinson, J.K.A. Everard “Transmission-line load-network topology for class- E power amplifiers” // 2001 Transactions on Microwave Theory and Techniques.-V. 49, No 6, (Jun. 2001, Part 11), P. 1202-1210.

[6] A.V. Grebennikov, “Circuit Design Technique for high Efficiency Class F Amplifiers” // 2000 MTT- S In- ternational Microwave Symposium Digest, 2000.- Vol. 11.- P. 771-774.

[7] D.V. Chemov, M.K. Kazimierczuk, V.G. Krizhanovski, “Class-E MOSFET low-voltage power oscillator,” Proceedings of IEEE Int. Sym. on Circuits and Systems, vol. 5 , Phoenix, AZ, May 2002, pp. 509-512.