High Efficiency Frequency Tunable Inverse Class-E Amplifier in VHF Band

High Efficiency Frequency Tunable Inverse Class-E Amplifier in VHF Band Kumh Natinal Institute f Technlgy, 1 Yangh-Dng, Gumi, Gyungbuk, 730-701, Krea yungk@kumh.ac.kr Abstract This paper prpses the use f an inverse class-e amplifier with a tunable parallel resnatr at the utput prt in rder t btain a high pwer-added efficiency (PAE) and utput pwer in a wide frequency range. The tunable resnatr circuit has a cnstant Q factr in the perating frequency range, and since the circuit has a varactr dide, the inductr and capacitr values f the resnatr can be changed. Further, the inductance value fr zer-current switching (ZCS) is implemented a lumped element and the capacitance value is made a distributed element fr phase cmpensatin. The inverse class-e amplifier can deliver an utput pwer f 5dBm and can achieve a maximum a PAE f 75% in the frequency range 65-10MHz. 1. Intrductin High Efficiency Frequency Tunable Inverse Class-E Amplifier in VHF Band Keywrds: Inverse Class-E Amplifier, High Efficiency, Tunable Amplifier. In wireless cmmunicatin systems, the linearity and efficiency f pwer amplifier used in transmitter are imprtant factrs that decide system perfrmance. T imprve the efficiency f the amplifier, many techniques, including Envelpe Eliminatin and Restratin (EER), Envelpe Tracking (ET), and hybrid ET methd [1]-[3], have been develped. Further, the high-efficiency pwer amplifier may be a class-d, class-e, r class-f amplifier [4]-[7]. Althugh the class-d amplifier cnsists f tw active elements and has high efficiency, its large circuit size is a majr drawback. The class-f amplifier has high efficiency and can therefre cntrl higher harmnics; hwever, the circuit is very cmplex and cannt eliminate harmnic signals. The class-e amplifier with a shunt capacitance has fund widespread applicatin due t the simplicity f its design and high peratinal efficiency. Further, the inverse class-e amplifier with a series inductance has a lwer peaking switching vltage, lwer inductance values, and greater tlerance t variatins in the circuit cmpnent values as cmpared t the classical tplgy [8]. In this study, we investigate a tunable inverse class-e amplifier with zer-current switching t btain a high pwer-added efficiency (PAE) and a cnstant utput pwer in VHF range. Fr stable peratin in the presence f frequency variatin, the tunable resnatr includes a varactr dide t cntrl the capacitance and inductance values. Experimental results shw that the tunable inverse class- E amplifier can be perated in the frequency range 65 MHz~ 10 MHz.. Tunable inverse class E amplifier.1. Operatin thery Despite the cnventinal class-e amplifier being perated in the zer-vltage switching (ZVS), the inverse class-e amplifier is perated a zer-current switching (ZCS) mde, and the utput matching netwrks cnsist f a parallel LC resnatr and a series inductr t induce current. The blck-diagram f inverse class-e amplifier is shwn in Fig. 1. Internatinal Jurnal f Engineering and Industries(IJEI) Vlume, Number3, September 011 di : 10.4156/ijei.vl.issue3.4 31

Vcc RF in + v L - i s + v s L S RFC C p L p ΔC Rlad - Figure 1. Blck Diagram f Inverse Class E Amplifier. Nrmalized is, vs 5 4 3 1 v s i s 0 ZVS -1 0 144 88 43 576 70 wt (a) Class E (b) Inverse Class E Figure. Wavefrms f Switching Vltage and Current. The inverse class-e amplifier circuit cnsists f an active cmpnent, a parallel resnatr t cancel higher harmnics, and a parallel capacitr t cmpensate fr the current and vltage phase difference. The active cmpnent has an n-ff characteristic by reasn f current f inductance. When the active cmpnent is in the n state, the active cmpnent has zer internal resistance and zer vltage drp and current flws thrugh it. Further, if the active cmpnent perates in the ff state, it has infinite resistance and there is a vltage drp acrss it because f breaking current flw. The switching vltage and current wavefrms f class-e and inverse class-e amplifiers are presented in Fig.. It can be bserved that the class-e amplifier perates in the zer-vltage switching (ZVS) mde, while the inverse class-e amplifier perates in the zer-current switching (ZCS) mde. In ZCS wavefrm, if the inverse class-e amplifier has a 50% switching perid and 100% efficiency, the cmpnent values are calculated by using the fllwing equatins [9]. 5 4 3 1 0 ZCS v s i s -1 0 144 88 43 576 70 wt 4 VDC R (1) 8 P V L s fp () DC 4 C 4( 4) P fv DC (3) L p R fq (4) 3

C p Q fr (5) where VDC is the cllectr r drain vltage, f is the center frequency, P is the utput pwer and Q is the quality factr f parallel resnatr. Using (1)-(5) equatins, we design an inverse class-e amplifier with cnstant Q that is capable f stable peratin in the presence f frequency variatins. Figure 3 shws a schematic f the prpsed amplifier. The parallel resnatr cmpnents have a variable parameter, which is cntrlled by the bias vltage. The Lp-Cp parallel resnatr circuit perates at the fundamental frequency in the pen circuit and at ther frequencies in the shrt-circuit cnfiguratin. Its functin is identical t the classical series resnatr f a class-e amplifier. C bypass V high V lw C bypass RFC RF ut RF in DCB IMN L S DCB C p L p ΔC. Variable parallel resnatr design Tunable Parallel Resnatr @ ƒ Figure 3. Tunable Inverse Class E Amplifier Schematic. In parallel resnatr shwn in Fig. 3, the tunable capacitr circuit cntains a varactr dide t cntrl the capacitance, which is carried ut by adjusting the reverse bias vltage in Fig. 4(a). Further, the tunable inductr circuit cnsists f a varactr dide and λ/4 transmissin line in Fig. 4(b). These cnnectin perate an inductance and its value is calculated the belw equatin. Z in Z j CZ (6) 1 j C The λ/4 transmissin line, which is used t implement the inductance, can help the π-type lumped equivalent circuit cmpensate fr lnger transmissin lines at lw frequency. The equivalent circuit is depicted in Fig. 5. Since the resnatr cnsists f the tunable capacitr and tunable inductr, the tunable characteristic f resnatr is satisfied t perate in 65 ~ 10 MHz tunable frequency by the bias vltage in case f cnstant Q. RFC V C RFC V L RF in RF in DCB (a) Z DCB(b) Figure 4. (a) Variable capacitr circuit (b) Variable inductr circuit. θ 33

L π θ C π / C π / Z Figure 5. π-type equivalent circuit f λ /4 transmissin line. 3. Simulatin and experiment results 3.1. Design and Simulatin In rder t cnfirm the variable characteristics f the parallel resnatr, we simulate the tunable capacitr and inductr using a 1T36 varactr dide manufactured by Sny Inc. The simulatin results are presented in Fig. 6; the simulatin is carried ut by using the ADS sftware develped by Agilent and by setting the center frequency t be 75 MHz. The graph gives the impedance values f tunable capacitr and tunable inductr circuits. The perating range f each cmpnent crrespnds t that fr an equivalent capacitance is.5 ~ 7 pf and an equivalent inductance f 180 ~ 680 nh when the reverse vltage f the dide is in the range 0 ~ 5 Vlts at 75 MHz. Fr Q=1.3, the variatin in the values f the elements f the inverse class-e amplifier with frequency change is shwn in Fig. 7. These data shw that the range f values f the tunable capacitance and inductance in the parallel resnatr crrespnds t that bserved in Fig. 6. In Fig. 7, the change f Ls and ΔC values cause a little effect in the circuit peratin. Figure 6. Impedance values f variable capacitr and inductr circuit 34

Figure 7. Characteristics f element value with frequency variatin in case f Q=1.3. Figure 8 shws the simulated utput pwer and PAE fr the inverse class-e amplifier with a tunable parallel resnatr. Despite variatins in the frequency, the utput pwer and PAE f the amplifier has a small variatin because the resnatr facilitates frequency adaptive peratin. The switching vltage and current wavefrms at a center frequency f 75 MHz and an utput pwer f 3 dbm are shwn in Fig. 9. It is apparent that the zer current and zer vltage pints d nt cincide. This indicated that the actual active cmpnents are nt perated as ideal switches. The internal capacitance f active cmpnent affects the n-ff nrmal peratin. Figure 8. Characteristics f utput pwer and PAE 35

Figure 9. Wavefrms f switching vltage and current 3. Fabricatin and Measurement Results A measurement data f variable capacitr circuit is shwn in Fig. 10. It is presented that the simulatin and measurement data is almst cincide. Cmpared the simulatin with the measurement results, because the internal resistance f varactr dide cntribute the insertin lss f tunable circuit, the result is sme different. Als, cmpare t the simulatin results, the variable inductr peratin is almst the same. The characteristic f tunable resnatr is shwn in Fig. 11 in the frequency range 65 ~ 10 MHz. Because f resistance f varactr dide, the tunable resnatr has a lss. A phtgraph f the implemented tunable inverse class-e amplifier is shwn in Fig. 1. The amplifier was implemented using micrstrip technlgy n a Tefln substrate with εr=3.55 and height (h) f 0.815 mm; the design frequency was f=75 MHz. The active cmpnent used was an NE85634 transistr f NEC Crp., with 3.5V bias vltages. The amplifier requires a large-sized PCB since the cntrlling circuit f parallel resnatr, cnsisting f a tunable inductr and capacitr, is t be accmmdate. The fabricated ΔC has a large electrical length, which is the capacitance value f 4.7pF. Als, the value f inductr Ls is 10nH. Fig. 13 shws a plt f the utput pwer versus PAE fr the tunable inverse class-e amplifier at a center frequency f 75 MHz. A PAE f 7% is btained at an utput pwer f.5 dbm. Since the internal resistance f dide cntributed the lss f utput pwer, the PAE f measurement data is reduced at high pwer regin especially. Fig. 14 shws the measurement data in the frequency range 65 MHz ~ 10 MHz. This graph shws that the utput pwer is 0.5 ~ 6.5 dbm at a PAE f 4 ~ 75 %. The maximum pwer and PAE f the prpsed amplifier are 5 dbm and 75%. At 10 MHz, the perfrmance is degraded because f abnrmal peratin f the parallel tunable resnatr. 36

[db] High Efficiency Frequency Tunable Inverse Class-E Amplifier in VHF Band Figure 10. Characteristics f simulated and measured capacitance impedance values. 5 0 15 10 5 0 0 10 0 30 40 50 60 70 80 90 100 110 10 130 Frequency [MHz] Figure 11. Tunable characteristic f the resnatr in case f cnstant Q. Figure 1. Fabricated tunable inverse class E amplifier 37

Figure 13. Characteristics f utput pwer verse PAE f the prpsed amplifier in case f 75 MHz. 4. Cnclusin Figure 14. Measured data f utput pwer and PAE This paper presents experimental validatin f the peratin f a tunable inverse class-e amplifier with a tunable parallel resnatr; the amplifier can prvide a cnstant high pwer and pwer-added efficiency. The prpsed amplifier has a 40 ~ 75% pwer-added efficiency and a 5 dbm utput pwer in the frequency range 65 MHz ~ 10 MHz. In the presence f frequency variatins, the prpsed amplifier shws high efficiency in a wide perating frequency range. The size f the prpsed amplifier can be reduced by using MMIC technlgy. 5. Reference [1] Kahn, L.R., "Single Sideband Transmissin by Envelpe Eliminatin and Restratin," Prc. IRE, vl.40, pp.803-806, July 195. [] J. Jeng, D. F. Kimball, M. Kwak, P. Draxler, and P. M. Asbeck, "Envelpe Tracking Pwer Amplifiers with Reduced Peak-t-Average Pwer Rati RF Input Signals," IEEE Radi and Wireless Sympsium, pp.11-115, January 010. 38

[3] D. Kim, D. Kim, J. Chi, and B. Kim, "LTE Pwer Amplifier fr Envelpe Tracking Plar Transmitters," Prceedings f the 40the Eurpean Micrwave Cnference, pp.68-631, September 010. [4] Steve C. Cripps, RF Pwer Amplifiers fr Wireless Cmmunicatins, Nrwd, MA, New Yrk, 1999. [5] Skal, N.O., and A.D.Scal, "Class E-A New Class f High Efficiency Tuned Single-Ended Pwer Amplifiers", IEEE J. Slid State Circuits, SC-10, n.3, pp.168-176, June 1975. [6] F. H. Raab, "Class-F Pwer Amplifiers with Maximally Flat Wavefrms," IEEE Trans. Micrw. Thery Tech., vl.45, n.11, pp.007-01, Nvember 1997. [7] R. Miyahara, H. Sekiya, M.K. Kazimierczuk, "Nvel Design Prcedure fr Class-E Pwer Amplifiers," IEEE Trans. Micrwave Thery Tech., vl.58, n.1, pp.3607-3616,dec, 010. [8] Thian Mury, Vincent F. Fusc, "Inverse Class-E Amplifier with Transmissin-Line Harmnic Suppressin," IEEE Trans. n Circuits and Systems, vl.54, n.7, pp.1555-1561, July 007. 39