VHF COMMUNICATIONS 4/95

Harald Fleckner, De8UG

A 10 Watt Power Amplifier forthe 13cm Band using GaAsTechnology

Developed with the help of PUFFCAD Software

1.CHOICE OFSEMICONDUCTOR

The transistor s used in the amplifier arcMitsubishi GaAsrETs from the 0900range. The 0905 type is used in thedriver stage. with two type 0906's inthe parallel high-level stage .

The following performance data werethe targets aimed for in the develop­ment work:

The two-stage power amplifier intro­duced in issue 3/1994 [11 of VHFCommunications supplies an outputpower of S Watts in the l3em hand inlinear operation (class A) with 23 dBampuncauon.

The aruclc below introduces a newamplifier in this development range,which yields an oulput power of 10Walls with a linear amplification of20 dR.

The circuit and layout have onceagain been set up using purr CADsoftware [4J. on the basis of theresults from the development workon the 5 wen.amputter. As 8 resultof this. a parallel circuit with two 5Waft stages has been inserted in thehigh-level stage of this amplifier unit.

Amplification:Output power:

Band width.Zin = Zout:

>20dBatK >1Min. 10 W at max,1 dB compression100 MHz= 50n withreturn loss> = 20 dB

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Arguments in favour of using a para llelhigh-level stage consisting of two5 Watt transistor; (as opposed to :I

singfc stage with a 10 Wall transistor)arc the higher efficiency and the higher(in total ) power loss of the para llel­switc hed high-level stage transistorsand the, at presen t. rather more favour­able cost/performance rat io of the 0906GaAsmT. as against the 10 Wall 0907type.

According to the Mitsubishi data sheet,in the given frequency range the 0906attains an output power of 5.0 Watts =37 dBm at Uds = 10 V, Ids = 1.1 A,with an amplification of 11 dB at 40%efficiency .

In comparison with the {)l}(17 type(40 dBm output power 1 10 an 1 37%).there is a lower power adva ntage infavour of the two parallel-Wired ()l)()6stages .

The 0905 type com fortably supp lies thenecessary drive power of app . I Wallfor the para llel stage with an ampli fica­tion of approximately 10 dB. lts typicalpower is given by Mitsuhishi as app.34 dBm = 2.5 Walt s at 8 V 10.8 A,

The S-parameters for the selec ted tran­sistors required for the circuit develop­ment are taken from the Mitsuhishi da tahank and are valid for the DC voltageconditions referred to above.

218

frequency. the ga in slope obtained(S.2 I) clearly shows the influence of tile710 1./4 coupler between the twohigh-level transistors. This type of cou­piing pre -supposes a transforma tion ofall individua l stages with a son impcd­anrc, and is well known from aerialengineering. It is relatively loss-freeand is parti cularly effective when eachindividual stage is transformed heforethe hook-up on the calculator to Zin =Zout = 500:. The better this transfo rma­tion is carried out, the "smoother" thegain slope actually obtained is, plottedagainst the frequency.

The calc ulated input impedance (S I t)is more strongly depe ndent on thefrequency than the output impedance(S::!:2). and here the typica l broad­bandcdn css of parall el stages shows toadvantage. The val ues shown in l-ig. Igive the following performance valuesfor the simulated circuit at all operatingfrequency of 2.320 MIll'.:

VHF COMMU NICATIONS 4/95

In operation. there is a OC input powerexceedi ng 30 Watts. so the heat sinkmust have IH.·nc·rous d imensions. inorder to guarantee that the maximumpermissible temperature for the transis­tors. of 175" is never reached.

2.SIM ULATION ANDA:-;ALYSIS OF AMPLIFIERCIRCUIT USING CADSOFT WARE

The functio ning of the Puff Cl\Dsoftware is comprehensively descri bedin [21 13J f41 . so only the resultsobtained are presented and ana lysedhere . Fig. I shows the screen print -ourfrom Pu ff with the draft layout of thecirc uit, the associated Smith diagram,the parts list and the scatter parametercurve over the selected frequency range(1.5 - 3.0 Gllz).

From the calculated scatter parameters,the stability factor. K. of the amplifiercircuit can be subsequently determinedfor the operating frequency (2.3216GHz) [51. When plotted aga inst the

Return loss input:Return loss output :Ampl ification:Feedback:K factor at 2.320 MHz:Power band width (-3 db).

· 26.7 dB- 33.2 dB+ 20.7 dB· 38.3 an294 400 Mllz+ 100 ~Hz

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VHF COMMUN ICATIONS 4/95

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2.5pF2.5pF2.5pF2.5pF2.5pF2.5pF4.7pF4.7pF4.7pF4.7pFN-type or SMAN-type or SMAIO0(24mm Stripline65/23mm Siriplincl OO/24mm Stripline65(23mm Stripline100124mm Strlpline65123mm Stripline09050906090622/23mm Striplinc15/14mm Striplinc19/15mm Striplinc171l5 mm Stripline21116mm Striplinc17/15mm Striplinc2I /16mm Strip line71/24mm Srripline

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Mits ubishiMitsubishiMitsubishi

FigA: Paris List for the l Scm lOW PA

f ig.2 shows the layout gene rated by theCI\D software as a laser print-out. forTeflon-based materia l with a substratethickness of 0.79 r um..

The earth paths on the longitudi nal andtransvers e sides of the boards arcsurfaces which arc added later andwhich are through-hole plated to theunderside of the boards.

Tn the part s list in Fig .L we can also

recognise the necessary discrete compo ­nents of the circ uit. under the descrip­tion "lumped", lIere we arc dea lingwith capacito rs and resi stances whichare necessary for the circuit to operate.

Fig.3 shows the wiring diagram for the10 Watt paralle l high-level stage . Fig.4shows all components required in thepart s list

221

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F ig.5a : Side View of a fin ished unit Fig.5b: Component Layout

Veckel ;: Cover ; Gehause ;: Cover; RippenkatkiJrpu ;: Finn ed Cooling Rody;Mit de' Plat;" e & Folie VerliJtet ;: Soldered to Board and Foil;Weiflblechgehli" ,tt ;: Ti np late Housing; Kupfufolie e Copper Fo il;NUl ;: groove; Ma.ue,,;," ;: Solid Rivels; KlJhlklirper ::;. Cool i~ 8 ody;H ohl"iete, durchkonta1ctierf ::: Hollow rivet. through-hole pbttcd;Ntll1tilplotine. senkredu e;"gebauJ ;: PSU board, vertically Insert ed

222

VHF COMMUNICATIONS 4/95

3.AMPLIFIER ASSDlIlLY

The ampl ifier circuit is assembled on aTe no n board (er = 2.33) with "thed imen sions 146 mm. x 72 mm. x 0.79mm.. For its part , it is screwed to ana lum inium finn ed cooling. body withdim en sion s of 147 mm. x 100 rnm. x40 mm.• which acts as a fasten ing. and aheat sink for the power transistors andvoltage regulator (H g.Sa).

The lX: voltage supply is mounted on adouble-coated epox y board. measuring105 rnm. x 20 mrn. x 1.6 0101 .,internally soldered vert ically to thelon gi tudina l side of th e hou sing(Hg.Sb). Its circui t and structure corrc ­spond to the publications as pl'r (6) or[I] .

Fig..6 shows the wiring d iagram. Fig.7the components diagram. and Fig.S theparts list for this power supply. Th ecomponents are a ll mounted on the foilside. so that the earth surfaces have tobe throug h-bole plated.

Grooves are mi lled in the cooling body,so that the drain and gale connectionsof the transistors can be so ldered as natas possible to the board . The groovesarc laid out a litt le wide, to give agreater to lerance in the mounting of thctransistors.

'In c Tenon board has a recess of 4.5mm. x 17 mm . and two recesses of 6.5mm. x 22 mm.• into which the tran sis­tors are inserted and then screwed tothe cooling body (see Fig.S). Betweenthe board and the cooling body. there isalso some copper foil (dimensions

- Assemble and incorporate the powersupply hoard. The gale resistances(R4, R5) shou ld a lready he solderedto the power supply for a betterassem bly!

Tip: To avoid regenerative feedback.the gate power supply connection forthe transistor, n , Ihrouxh thi' resist­ance, R6, may not go straightacross theboard. but must be taken round outside,like the drain power supply (see Fig.5).

- Install and wire up the 8 feedthroughcapacitors (1 nF) and the blockingcapacitors, C9 - CI5. C I 7. C 19.

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VHF COMMUNICATIONS 4195

- Insu lated fastening and connect ingo f vo l tage re gu lator us in gfeedthrough capacitors.

- Insta ll and connect resistan ces (R7,R8, R9, RH, R1 2) on and tohigh-frequency board.

- Install trimmers (C I • C6)

Tip: Ceramic trimmers of the Johanson0.5 - 2.5 pF type are more suitable thanTeflon trimmers, as they still Rivestable capacity values, even after re­peated calibrations!

- Install chip capacitors (C7 - C IO)

Tip: You should definitely use the verylow 1().\·.~ A1C 100 porcelain type [romJohanson .

- De-bu gging the pow er supply(110 and UD)

- Insta ll GaAsl-ETs

- S e t zero signa l curren ts :0905 - ID = O.SA; 0906 - ID = l.IA

4.READINGS

After calibration at 2,320 MH7.. tileprototype attained an output power ofI I waus with a driving power of120 mW. The measurement was carriedcur using an lI P 432B Wattmeter and a30 dB + 10 dB aucnuator from Narda.

Fig.9 shows the amplifier's transfercharacteristic. The compression areabegins at an output power level ofapproximatel y 10.5 Watts - i.c . any

:ru le I I L T1 0 13 4 1 Ub .. r Ou oo<o

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Duko = Feedt hrough CapacitorUber Dukof = using "'fi"llhroll~h Ca paci tors

225

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VHF COMMUNICATIONS 4/95

InFIOIlFIOIJ.F22"F22" FIOJ.lFIOJlF10"FO. I"FO.lj.lFO.I).lF1OI-lPlOj.l.F10,,"100nfInflOOn} '

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CapacitorCapacitorCapacitorCapacitorCapacitorCa pacito rCa pacitorCa pacitorCapac itorCapac itorCapaci torCa pacitorCapacitorCapacitorCapacitorCapacitorCapacitorCapacitorCapaci torCapacitorniodeDiodeVoltage Regu latorVoltage Reg ulatorOC·OC ConverterPo te ntiometerPotentiometerPotentiometerRes istorResistorRes istorResistorResi storRe sistorRes istorResistorResistorRes istorRes istorResi storTransistor

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+5 InF Feed-Through Ca pacitors for PSU from UG3 and LTl084. (see Fig.S)

Fi~. 8: PSU Parts List226

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VHF COMMUNICATIONS 4/95

PA1 3·l0W0906 10Vf1,1A 0905 8V/O.8A

further increase in power leads to aconsiderable reduc tion i ll the inter­modulation interval and tim" \(l signaldistortion in linear mode ,

Hg.J u shows the gain slope measuredby means of an Il P ~l()()()H sweeperwith XCJ99B at all input power of 50mw and p lotted against the frequency .

Here curve A shows the stope measuredfor an amplifier tuned 10 2.320 MHz.Curve R shows the slope in u ..imula ­non of S21. as per H~. 1. The amplifier

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Transrer Charae tertsuetor lOW PA

consequently has a power hand widthof over 100 MIlz. Its amplificationdrop to the limit frequencies is. o fcourse. somewhat greater than in CurveB. The linear amplificati on of 20 dBattained dev iates on ly slightly from thecalculated values.

Thi s amplifier can be used in the"TVrange at 20380 Mltz - with rathe r lessamplification for the same outputpowe r. of course. The aut hor there foredeveloped an amplifier specia lly de-

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227

VHF COMMUNICATIONS 4/95(~ ~~~~~~);2

signed for the ATV range, with amaximum amplification level app. 80MHz higher. Another article in the ncarfuture will give details of the layoutand the readings obtained.

Note: The PUFF CAD software pack­age used in this project is availablef rom KM Publications at the usualaddress. The pric e of the software atthe rime of publication of (his article is£20 .00 plus shipping at cost.

5.LITERATURE

III Hcckncr, II.: /I.. Power Amplifierfor the l Scm nand using (TaA sTechnologyVHF Communications 3/1994,pr . 130-141

(2) Berte!smeier, R.: PUFF-DesignSoftwareDubus-Info, vel. 18 (1989), no. 4,pp. 30 - 33

[3] Lent z, R.E.: PUFF - a CADProgram for Microwave StriplineCircuitsVHF Communications 2/1991.pp. 66-68

[41 Wedge, S.W.• Compton, R. andRutledge, D.:PUH· ComputerAided Design for MicrowaveIntegrated CircuitsAvailable from KM Publications

L5] Unger I Harth: High-FrequencySemi-Conductor Ele ctronicsHirzel-Verlag StuttgartISBN 37776 0235 3

f61 Kuhn e. M,: High-PowerGaAs·rET Amplifier for 9 em.Dubus -lnfo , vo l. 20 (199 1). no. 2.pp. 7 - 16

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