250W宽带100-450MHz功放.pdf

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1、100 450 MHz 250 W PowerAmplifier with the BLF548MOSFETAPPLICATION NOTEAN980211998 Mar 232Philips Semiconductors100 450 MHz 250 W Power Amplifierwith the BLF548 MOSFETApplication NoteAN98021CONTENTS1INTRODUCTION2DESIGN CONSIDERATIONS3AMPLIFIER CONCEPT4INPUT CIRCUITRY5ADJUSTMENT OF THE AMPLIFIER5.1Tun

2、ing the outputnetwork5.2Testing the unit under RF conditions5.3Tuning the units inputnetwork5.4Combining the units6CONCLUSIONS7REFERENCES8APPENDIX A9APPENDIX B10APPENDIX C1998 Mar 233Philips Semiconductors100 450 MHz 250 W Power Amplifierwith the BLF548 MOSFETApplication NoteAN980211INTRODUCTIONIn t

3、his report the design procedures and measurement results are given of a two octave wideband amplifier(coveringboth the civil and military airbands between 100 and 450 MHz),equiped with two MOSFET devices,which is capable ofgenerating 250 W of output power.In order to achieve a good broadband capabil

4、ity one has to use devices with the output capacitance reduced to theutmost minimum.While applying PHILIPS BLF548 MOSFETs it was possible to obtain a respectable powergain of morethan 10 dB,throughout the whole band.The BLF548 is a balanced N-channel enhancement mode vertical D-MOS transistor in a S

5、OT262 package,especiallydesigned for use in wideband amplifiers up to 500 MHz.The transistor is capable to deliver 150 W nominal outputpowerat a supply voltage of 28 Volts.Due to the low output capacitance the attainable bandwidth will exceed 300 MHz.2DESIGN CONSIDERATIONSWhile designing broadband a

6、mplifiers,one has to take several things into account:To select the right manufacturer,able to supply the products with a good reliability,gives a good support and offers acomplete range of transistors e.g.for driverstages.To select the right active components,capable to fulfill the desired wishes,s

7、uch as;high reliability,high powergain,high efficiency,excellent mismatch capabilities,right loadpower,good long-life properties and last but not least;goodbroadband capability.To terminate the transistor with the right load impedance,with other words,to determinate the right output matchingnetwork.

8、To eliminate the 6 dB/octave gain slope throughout the band of operation,in order to achieve an acceptablegainflatness.To find the right input matching network;the input VSWR has to be low in order to achieve a good termination for thedriverstage.To design the matching networks in such a way that th

9、ey are capable to handle the,at some points very high,R.F.currents.A balanced transistor was chosen in order to reduce the second harmonic(due to the push-pull effect)and to reduce thenumber of required components.The criteria for chosen MOSFETs over bipolar transistors are;high powergain,high load

10、mismatch capabilities,low noiseand easy biasing.Nowadays three major MOSFET suppliers are involved when Pl=150 W is needed at f=500 MHz and Vds=28 V.Available are;BLF548,industry type A and industry type B.Table 1 gives an overview of the characteristics of these3 types.Table 1BLF548TYPE ATYPE BUNIT

11、f500400500MHzGp10108dBd505055%Ciss105180140pFCoss90200100pFCrss252032pFBW300133266MHz1998 Mar 234Philips Semiconductors100 450 MHz 250 W Power Amplifierwith the BLF548 MOSFETApplication NoteAN98021With:BW=1/(2*Rload*Co);Rload=Vds2/(2*Pl)and Co=1.15*Coss.BW=bandwidth,Rload=loadresistance,Co=outputcap

12、acitance.In order to achieve the best possible broadband results,the BLF548 is a very good choice.Other Philips MOSFETs in the 500 MHz series are,followed by nominal loadpower:12.5 Volts single ended28 Volts single ended28 Volts push-pull3AMPLIFIER CONCEPTThe amplifier concept described in this pape

13、r is based upon two identical modular units,each containing one BLF548MOSFET.Both units are combined by means of two 3 dB 90 hybrid couplers,which is shown in Fig.1.The mainadvantage is that the input VSWR will be very good;since it is independent of the mismatch introduced by the units,the50 termin

14、ation will cause a good load for the driver stage,e.g.equipped with BLF544.BLF5212 WBLF5225 WBLF5425 WBLF54310 WBLF54420 WBLF544B20 WBLF54540 WBLF54680 WBLF547100 WBLF548150 W1998 Mar 235Philips Semiconductors100 450 MHz 250 W Power Amplifierwith the BLF548 MOSFETApplication NoteAN98021The following

15、 seven steps have been followed in order to develop a first prototype of one unit.1.Determine the BLF548s 150 W output power load impedance between 100 and 500 MHz(50 MHz interval steps)by measurement techniques or simulations.At the moment of writing it was not possible to perform full automaticmea

16、surements at frequencies lower than 500 MHz with transistors build in a balanced SOT262 header.Thereforethe load impedances have been calculated by means of the electrical equivalent diagram shown in Fig.2.2.Find the correct output matching network which transforms the 50 termination to the required

17、 load impedance forthe frequency range 100-500 MHz.3.Optimize the outputmatching network of step 2 with help of linear simulation software,such as Touchstone(EESOF).4.Since the matching network will not have an ideal behaviour,it is necessary to determine the actual load impedanceof the selected out

18、put matching network,again in 50 MHz steps between 100-500 MHz.5.Calculate(or even better,determine by means of load-pull measurements)both the powergain and input impedanceof the transistor by presenting the load impedences,found at step 4,to it.This is very important to investigate thebehaviour of

19、 the transistor while terminating it with the selected output matching network.6.Choose the right input matching network which has a minimum returnloss(Rl)at the highest frequency(450 MHz)and a declining Rl for lower frequencies in a way that the gain increase effect for lower frequencies is equaliz

20、ed.Other possibilities,as feedback or frequency dependent damping at the gate side(by means of low Rgs),can betaken into consideration.7.Optimize the input network for gainflatness by means of linear simulation software(Touchstone,EESOF).Remember the input VSWR throughout the band is taken care of b

21、y the use of 90 hybrids,which combine the twomodular units.Fig.1 Schematical representation of the concept of the eventual amplifier.handbook,full pagewidthMGH7841:41:41:41:4BALUNBALUN3 dB90HYBRIDBLF548UNIT 11:41:41:41:4BALUNBALUNBLF548UNIT 250 input3 dB90HYBRID50 output1998 Mar 236Philips Semicondu

22、ctors100 450 MHz 250 W Power Amplifierwith the BLF548 MOSFETApplication NoteAN98021At the following pages the design steps are presented which were followed at PHILIPS laboratories in order to design a150 W unit.Using the diagram shown in Fig.2,powergain and impedances have been calculated first,usi

23、ng the datagiven in Table 2.Table 2Rg,Rd,Rs are derived from Rdson measurements,Gfs and Cs are measured,Cgs,Cds,Cgd derived from measuredCiss,Coss,Crss respectively.Lg,Ls and Ld are calculated.Some of the assumptions are based on empirical rules and have proven to be correct in the past.Gp and Zin c

24、an now be calculated:Lg0.58 nHLs0.11 nHLd0.50 nHRg0.09 Rs0.08 Rd0.19 Cgd29 pF1.15 CrssCgs120 pF1.5 (Ciss-Crss)Cds72 pF1.15 (Coss-Crss-Cs)Cs2.4 pF2.4 pFGfs1.6 S0.5 Gfs(for Class B)Fig.2 RF Power MOSFET equivalent diagram(one BLF548 section).handbook,full pagewidthMGH785CgsCsCdsCgdRgRgRdLgLdgatesource

25、LsRsGFSdrainsource1998 Mar 237Philips Semiconductors100 450 MHz 250 W Power Amplifierwith the BLF548 MOSFETApplication NoteAN98021Zin=Ri+jXiGp=10*10log(Gfs Rload/2 Ls Ci)with;Xi=Li 1/(Ci)Ri=(Gfs Ls)/CiLi=Lq+(Ls Cgs)/CiCi=Cgs+Cgd(1+Gfs Rload)w=2 fZload is chosen for maximum broadband capability.Table

26、 3Calculated powergain,Zin and required Zload(series components)The data is also given in datahandbook“RF power MOS transistors”Philips Components.It can be noticed that withoutany gaincompensation the powergain difference between 100 and 500 MHz will exceed 10 dB.To terminate the transistor with th

27、e required loadimpedance,with respect to the broadband capability,the unbalanced50 load has to be transformed as close as possible to the loadimpedance as shown in Table 3.(Note:the impedancesshown are based on one section,since the transistor is of a balanced type,Zin and Zload are related to virtu

28、al ground).To reduce the number of components which would be needed in case of a lumped element solution,a coaxial semi-rigidbalun is used to transform the unbalanced 50 load into two 25 sections that are 180 apart in phase and 90 awayfrom virtual ground.This is followed by a coaxial 4:1 transformer

29、,with a characteristic impedance of 25.The result of this is:Rp=(25 25)/4=6.2,which is close to the required Rload of the transistor.In order to give a good description of the outputnetwork,it will be described as a 3-port:one port terminated with 50 unbalanced,the other two terminated with the tran

30、sistors outputimpedance(the complex conjugate of loadimpedance).A computer listing of the outputnetwork is given in“Appendix A”.After optimizing the network to minimum returnloss(S11),while checking S13,the optimized return loss(in dB)of this network has been determined,see Fig.3.As a nextstep now t

31、he difference between the required and the network related loadimpedance can be(re-)calculated.The resulton powergain(Gp)and imputimpedance(Zin)is given in Table 4.F(MHz)PL(W)Gp(dB)ZIN()ZLOAD()10078.826.70.43 j4.14.7+j1.515078.823.30.43 j2.54.0+j1.020078.820.80.42 j1.73.4+j2.025078.818.40.43 j1.12.8

32、+j1.930078.817.20.43 j0.72.3+j1.735078.815.80.43 j.0.31.9+j1.440078.814.50.44 j0.01.6+j1.145078.813.40.44+j0.21.3+j0.750078.812.40.45+j0.51.1+j0.41998 Mar 238Philips Semiconductors100 450 MHz 250 W Power Amplifierwith the BLF548 MOSFETApplication NoteAN98021Table 4Result on Zin and Gp as a result of

33、 the presented outputmatching network4INPUT CIRCUITRYSince Zin and Gp are now determined in a accurate way,the inputcircuitry can be determined.Special attention is givento the flatness of the gain as a function of frequency.The input network also consists of a coaxial balum,followed by a1:4 coaxial

34、 transformer,both made of semi-rigid coaxial cable.Since Zin is rather low the characteristic impedance ofthe 1:4 transformer was chosen to be 10.The result of this is:Rp=(25 10)/4=3.9.F(MHz)PL(W)Gp(dB)ZIN()ZLOAD()10078.632.70.11 j4.14.3+j1.015078.819.71.04 j2.94.1+j0.220078.817.31.02 j2.23.3+j0.125

35、078.816.00.87 j1.52.9+j0.130078.814.90.79 j0.92.8+j0.335078.813.50.80 j.0.42.8+j0.440078.812.40.79 j0.12.5+j0.245078.812.00.67+j0.11.9+j0.150072.012.40.43+j0.51.1+j0.6Fig.3 Simulated network response(output side).handbook,halfpage50150550frequency(MHz)0102030250350450MGH7861998 Mar 239Philips Semico

36、nductors100 450 MHz 250 W Power Amplifierwith the BLF548 MOSFETApplication NoteAN98021In order to compensate for the 6 dB/octave slope,matching to Zin is achieved at 450 MHz.At lower frequencies amismatch is created,resulting in a decrease of powergain inversely proportional to the increase of the g

37、ain related to thetransistors 6 dB/octave slope.The network listing of the input circuitry,again presented as a 3-port,is given in“Appendix B”.The network response(both input returnloss and predicted powergain)is given in Fig.4.Finally the schematic diagram and list of componentsare given in Fig.5.T

38、he units layout is given in Fig.6.Note:two toroidal cores around T2 and T3 are used to preventoscillations.5ADJUSTMENT OF THE AMPLIFIER5.1Tuning the outputnetworkIn order to terminate the transistor with the proper load impedance,first the output network has to be tuned.The transistor was replaced b

39、y a dummyload,representing the transistors output impedance under full power conditions.The dummyload was realized after fitting the data of Table 3.To the dummyload model(roughly Rload in parallel withCoss,in series with draininductance Ld).Later the model was compensated for parasitics of both SOT

40、262 header andnetwork components.Initial settings for each side of the dummyload are:Rload=Vds2/2 Pl=5.2 C=1.15 Coss=104 pFL=Ld=0.5 nHThe network listing is given in“Appendix C”.The final result,the dummyload lay-out,is given in Fig.7.Fig.4 Simulated network response of inputside(predicted Gp=f(f).h

41、andbook,halfpage100500frequency(MHz)201010200300400200MGH787(1)(2)(1)DB S12.(2)DB S22.1998 Mar 2310Philips Semiconductors100 450 MHz 250 W Power Amplifierwith the BLF548 MOSFETApplication NoteAN98021Fig.5 Schematical diagram and list of components of one unit.handbook,full pagewidthMGH788?C10C7C11C5

42、C6R4R3C8C9R5R5L9R7L1L2L3L4C13C4T5T4T3T2T1C19C16C14C15C16C15C3C250 output50 inputC12C17C18C1L10L11R8VdrainVBIASR1R2T6BLF548L5L6L7L81998 Mar 2311Philips Semiconductors100 450 MHz 250 W Power Amplifierwith the BLF548 MOSFETApplication NoteAN98021List of componentsNotes1.American Technical Ceramics type

43、 100B or capacitor of same quality.2.American Technical Ceramics type 175B or capacitor of same quality.3.The striplines are on a double copper-clad PCB with P.T.F.E.fibre-glass dielectric(r=2.2);thickness 1/32 inch.4.T2 and T3 are equipped with a Toroidal core,grade 4C6(cat.no.4322 020 97171).DESIG

44、NATIONDESCRIPTIONVALUEDIMENSIONSCATALOGUE NO.C1,C17multilayer ceramic chip capacitor100 nF2222 852 47104C2,C3multilayer ceramic chip capacitor(note 1)47 pFC4,C5,C8multilayer ceramic chip capacitor(note 1)820 pFC6,C9multilayer ceramic chip capacitor(note 1)300 pFC7film dielectric trimmer2-18 pF2222 8

45、09 09006C10,C14film dielectric trimmer2-9 pF2222 809 09005C11multilayer ceramic chip capacitor(note 2)39 pFC12capacitor22 nFC13capacitor100 nFC15,C16multilayer ceramic chip capacitor(note 1)120 pFC1863 V electorlytic capacitor1 F2222 685 78108C19film dielectric trimmer1-5 pF222 808 09004L1,L3stripli

46、ne(note 3)20 5 8 mmL2,L4stripline(note 3)20 2.5 8 mmL5,L7stripline(note 3)20 11.5 8 mmL6,L8stripline(note 3)20 4 8 mmL95 turns enamelled Cu wire on R61.4 mmL10,L11grade 3B Ferroxcube wideband RF choke4330 030 36642T1semi-rigid coax(note 4)50 length 54 mmT2,T3semi-rigid coax(note 4)10 length 44 mmT4,

47、T5semi-rigid coax25 length 53 mmT6semi-rigid coax50 length 74 mmR10.4 W metal film resistor19.6 k2322 151 11963R210 turn potentiometer5 k2122 362 00725R3,R4,R50.4 W metal film resistor2.05 k2322 151 12052R6,R7,R81.0 W metal film resistor10 2322 153 710091998 Mar 2312Philips Semiconductors100 450 MHz

48、 250 W Power Amplifierwith the BLF548 MOSFETApplication NoteAN98021Fig.6 Lay-out of one unit.handbook,full pagewidthMGH789drain voltagebias voltageRF outputRF input1998 Mar 2313Philips Semiconductors100 450 MHz 250 W Power Amplifierwith the BLF548 MOSFETApplication NoteAN98021By means of a RF-analyz

49、er the predicted frequency response of the network can be reproduced in practice,while tuningC10 and C14 for optimum R1.This is presented in Fig.8.A comparison with the simulated networkresponse(Fig.3)shows a high amount of common behaviour.Fig.7 Lay-out of BLF548 dummyload.handbook,full pagewidthC1

50、C1=C3=39 pFC2=C4=68 pFR1=R2=5.3 L=12 bonding wires per side(50 m),heigth 450 mC2R1C3 C4R2MGH790Fig.8 Measured network response of one unit after tuning C10 and C14.handbook,halfpage100Rl(dB)500frequency(MHz)016128420300400200MGH7911998 Mar 2314Philips Semiconductors100 450 MHz 250 W Power Amplifierw