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1 MOTOOLA Orer this oument y AN749/D SEMICONDUCTO APPLICATION NOTE BOADBAND TANSFOMES AND POWE COMBINING TECHNIQUES FO F Prepre y: H. Grnerg F Ciruits Engineering ACHIVE INFOMATION.. INTODUCTION The following isussion fouses on ron trnsformers for F power pplitions with prtil exmples of vrious types given with performne t. Detile esign formul re ville in the eferene setion. Power omining tehniques useful in esigning high power mplifiers re isusse in etil. BOADBAND TANSFOMES The input n output trnsformers re mong the most ritil omponents in the esign of multi-otve mplifier. The totl performne of the mplifier (linerity, effiieny, VSW, gin fltness) will epen on their qulity. Trnsformers with high impene rtios n for low impenes re more iffiult to esign in generl. In the trnsmission line trnsformers very low line impenes re require, whih mkes them imprtil for higher thn 16:1 impene rtios in 50-Ohm system. Other type trnsformers require tight oupling oeffiients etween the primry n seonry, or exessive lekge inutnes will reue the effetive nwith. Twiste line trnsformers (Figure 1C, D, F, G) re esrie in eferenes 1, 2, n 4. Experiments hve shown tht the ieletri losses in ertin types of mgnet wire, employe for the twiste lines, n limit the power hnling pility of suh trnsformers. This ppers s het generte within the trnsformer t higher frequenies, lthough prt of this my e use y the losses in the mgneti ore employe to improve the low frequeny response. At low frequenies, mgneti oupling etween the primry n seonry is preominnt. At higher frequenies the lekge inutne inreses n the permeility of the mgneti mteril ereses, limiting the nwith unless tight pitive oupling is provie. In trnsmission line trnsformer this oupling n e lerly efine in the form of line impene. The require minimum inutne on the low impene sie is: L= 4 2πf where L = Inutne in µh = Impene in Ohms f = Frequeny in MHz This pplies to ll trnsformers esrie here. Figure 1. HF Bron Trnsformers F Applition eports Motorol, In For More Informtion On This Prout, 1 PODUCT TANSFEED TO M/A COM AN749

2 Freesle Semionutor, I ACHIVE INFOMATION Some trnsformers, whih exhiit goo ro n performne n re esy to uplite re shown in Figure 1. Trnsformers E n F re intene for input pplitions, lthough A in smller physil form is lso suitle. In E, the winings re photo ethe on oule sie opper-kpton* (or opper-fierglss) lminte. The ieletri thikness is 3 mils, n the wining re is 0.25 in 2. Ferrite pltes (µ r = 2000 to 3000) re emente on eh sie to improve the low frequeny response. This type trnsformer in the size shown, n hnle power levels to 10 W. Figure 2 shows urves for lminte thikness versus wining re for vrious impene rtios. Ω Ω Ω Ω Ω Ω Figure 2. Lminte Thikness versus Wining Are Impene rtios of this trnsformer re not limite to integers s 1:1, 4:1 N:L, n the isolte primry n seonry hve n vntge in ertin iruit onfigurtions. This esign will fin its pplitions in high volume proution or where the smll physil size is of min onern. Tle 1 shows the wining onfigurtion n mesure t of the trnsformer shown in Figure 3. Ω Tle 1. Impene t Terminls BB Trnsformer Terminte s Shown f (MHz) p (Ohms) X p (Ohms) j j j j j j 30 Soler Are 70 Plsti Insultion Strip 58 Copper Strip 56 Ferrite Mteril 82 Fierglss Mteril Soler Are 68 Copper Strip 38 Plsti Insultion Mteril 40 Soler Are 62 Ptent Applie for. Figure 3. Detile Struture of Trnsformer Shown in Figure 1E In the trnsformer shown in Figure 1F n Tle 2, regulr ntenn lun ore is employe (Inin Generl F684-1 or equivlent). Lines A n B eh onsist of two twiste pirs of AWG #30 enmele wire. The line impenes re mesure s 32 Ohms, whih is suffiiently lose to the optimum 25 Ohms lulte for 4:1 impene rtio. (Z o = in L ). Winings n re woun one on top of the other, roun the enter setion of the lun ore. Line shoul hve n optimum Z o of 50 Ohms. It onsists of one pir of AWG #32 twiste enmele wire with the Z o mesure s 62 Ohms. The lun ore hs two mgnetilly isolte torois on whih is woun, ivie eqully etween eh. The inutne of shoul pproh the omine inutne of Lines n (eferene 4, 6). *Tremrk of E. I. DuPont, De Nemours n Co., In. PODUCT TANSFEED TO M/A COM 2 For More Informtion On This Prout, F Applition eports

3 Tle 2. Impene t Terminls BB Trnsformer Terminte s Shown of torois whih my e more reily ville, n e stke. Freesle Semionutor, I ACHIVE INFOMATION Ω f (MHz) p (Ohms) X p (Ohms) j j j j j j 3060 The retne in the 50 Ohm port (BB ) shoul mesure minimum of + j 200. To hieve this for 4:1 trnsformer, n shoul eh hve three turns, n for 9:1 trnsformer, four turns. When the winings re onnete s 9:1 onfigurtion, the optimum Z o is 16.6 Ohms, n lrger mount of high frequeny ompenstion will e neessry. Lower impene lines n e relize with hevier wires or y twisting more thn two pirs together. (e.g., four pirs of AWG #36 enmele wire woul result in the Z o of pproximtely 18 Ohms.) Detile informtion on the mnufture of twiste wire trnsmission lines n e foun in eferenes 2, 4, n 8. Figure 1A shows one of the most prtil esigns for higher impene rtios (16 n up). The low impene wining lwys onsists of one turn, whih limits the ville rtios to integers 1, 4, 9 N. Dt tken of this type of 16:1 trnsformer is shown in Tle 3, while Figure 4 illustrtes the physil onstrution. Two tues, 1.4 long n 1/4 in imeter opper or rss form the primry wining. The tues re eletrilly shorte on one en y piee of opper-l lminte with holes for the tues n the tue ens re solere to the opper foil. The hole sping shoul e lrger thn the outsie imeter of the ferrite sleeves. A similr piee of lminte is solere to the opposite ens of the tues, n the opper foil is ivie into two setions, thus isolting the ens where the primry onnetions re me. The seonry wining is forme y threing wire with goo F insulting properties through the tues for the require numer of turns. Although the mesurements inite negligile ifferenes in performne for vrious wire sizes n types (strne or soli), the lrgest possile imeter shoul e hosen for lower resistive losses. The initil permeility of the ferrite sleeves is etermine y the minimum inutne require for the lowest frequeny of opertion oring to the previous formul. Typil µ r s n vry from 800 to 3000 epening upon the ross setionl re n lowest operting frequeny. Inste of the ferrite sleeves, numer Tle 3. Impene t Terminls BB Trnsformer Terminte s Shown Ω Connetions to Tuings f (MHz) p (Ohms) X p (Ohms) j j j j j j 600 Ferrite Sleeves, Stkpole A, or Equivlent. Multi-Turn Wining Three Through Tuings Shorte Tue Ens Figure 4. Physil Constrution of 16:1 Trnsformer (Atul Numer of Turns Not Shown) The oupling oeffiient etween the primry n seonry is lmost logrithmi funtion of the tue imeter n length. This ftor eomes more importnt with very high impene rtios suh s 36:1 n up, where higher oupling oeffiients re require. The losses in the ferrite re etermine y the frequeny, permeility n flux ensity. The pproximte power hnling pility n e lulte s in eferene 4 n 6, ut the ferrite loss ftor shoul e tken into onsiertion. The µ r in ll mgneti mterils is inversely proportionl to the frequeny, lthough very few mnufturers give this t. Two other vritions of this trnsformer re shown in Figure 5. The smller version is suitle for input mthing, n n hnle power levels to 20 W. It employs stkpole ul lun ferrite ore B. The low impene wining is me of 1/8 opper ri. The portions of ri going through the ferrite re roune, n openings re me in the ens with pointe tool. The high impene wining is three through the roune portions of the ri, whih ws unovere in eh en of the ferrite ore. (See Figures 4 n 5.) PODUCT TANSFEED TO M/A COM F Applition eports For More Informtion On This Prout, 3

4 Freesle Semionutor, I ACHIVE INFOMATION Figure 5. Vritions of Trnsformers in Figure 1A The onstrution tehnique of the lrger version trnsformer is similr, exept two seprte ferrite sleeves re employe. They n e emente together for esier hnling. This trnsformer is intene for output pplitions, with power hnling pility of W employing Stkpole A ferrites. For more etil, see eferene 7. The trnsformer shown in Figure 1B is superior in nwith n power hnling pility. Tle 4 shows t tken on 4:1 trnsformer of this type. The trnsmission lines ( n ) re me of 25-Ohm miniture o-xil le, Miroot or equivlent. Two 50 Ohm les n lso e onnete in prllel. Ω Tle 4. Impene t Terminls BB Trnsformer Terminte s Shown f (MHz) p (Ohms) X p (Ohms) j j j j j j 690 The lun, normlly require to provie the lne to unlne funtion is not neessry when the two trnsmission lines re woun on seprte mgneti ores, n the physil length of the lines is suffiient to provie the neessry isoltion etween AA n BB. The minimum line length require t 2.0 MHz employing Inin Generl F Q1 or equivlent ferrite torois is 4.2 inhes, n the mximum permissile length t 30 MHz woul e pproximtely 20 inhes, oring to formuls 9 n 10 presente in eferene 2. The 4.2 inhes woul mount to four turns on the toroi, n mesures 1.0 µh. This omplies with the results otine with the formul given erlier for minimum inutne lultions. Inresing the minimum require line length y ftor of 4 will provie the isoltion, n the totl length is still within the lulte limits. The power loss in this PTFE insulte o-xil le is 0.03 B/ft t 30 MHz in ontrst to 0.12 B/ft for twiste wire line. The totl line loss in the trnsformer will e out 0.1 B. The numer of turns on the torois hs een inrese eyon the point where the flux ensity of the mgneti ore is the power limiting ftor. The omine line n ore losses limit the power hnling pility to pproximtely 300 W, whih n e slightly inrese y employing lower loss mgneti mteril. Note the onnetion rrngement (Figure 6), where the ri of the le forms the high urrent pth of the primry. Torois-Inin Generl F Q1, or Equivlent. Cle, Miroot , or Equivlent. (16 Turns on Eh Toroi.) 4 Figure 6. Trnsformer Constrution (Figure 1B) HIGH-FEQUENCY POWE COMBINING TECHNIQUES EMPLOYING HYBID COUPLES The zero egree hyris esrie here re intene for ing the powers of multiple of soli-stte mplifiers, or to omine the outputs of groups of mplifiers, usully referre to s moules. With this tehnique, powers to the kw level t the high-frequeny ns n e relize. When reverse, the hyris n e use for splitting signls into two or more equl phse n mplitue ports. In ition, they provie the neessry isoltion etween the soures. The purpose of the isoltion is to keep the system opertive, even t reue power level uring possile filure in one mplifier or moule. The isoltion is espeilly importnt in output omining of liner mplifiers, where onstnt lo impene must e mintine. Sometimes the inputs n e simply prllele, n prtil system filure woul not hve tstrophi effets, ut will merely result in inrese input VSW. For very high frequenies n nrrow nwiths, the hyri ouplers my onsist of only lengths of trnsmission line, suh s o-xil le. The physil lengths of the lines shoul e negligile ompre to the highest operting frequeny to minimize the resistive losses, n to voi possile resonnes. To inrese the nwith n improve the isoltion hrteristis of the line, it is neessry to inrese the impene for non-trnsmission line urrents (prllel urrents) without effeting its physil length. This n e one y loing the line with mgneti mteril. Ielly, this mteril shoul hve liner BH urve, high PODUCT TANSFEED TO M/A COM 4 For More Informtion On This Prout, F Applition eports

5 Freesle Semionutor, I ACHIVE INFOMATION permeility n low losses over wie frequeny rnge. For high-frequeny pplitions, some ferrites offer stisftory hrteristis, mking nwiths of four or more otves possile. Depening upon the lne n phse ifferenes etween the soures, the urrents shoul e mostly nelle in the lun lines. In lne onition, very little power is issipte in the ferrite ores, n most ourring losses will e resistive. Thus, stright piee of trnsmission line loe with high permeility ferrite sleeve, will give etter results thn multiturn toroi rrngement with its inherent higher istriute wining pitne. It is ustomry to esign the iniviul mplifiers for 50 Ohm input n output impenes for testing purposes n stnriztion. 50- n 25-Ohm o-xil le n then e employe for the trnsmission lines. Twiste wire lines shoul not e use t power levels higher thn 100 Wtts verge, ue to their higher ieletri losses. Vritions of the si hyri re shown in Figure 7A n B where oth re suitle for power iviing or omining. Figure 7A Figure 7B Figure 7. Vritions of Bsi Hyri The lning resistors re neessry to mintin low VSW in se one of the 50-Ohm points rehes high impene s result of trnsistor filure. As n input power splitter, neither 50-Ohm port will ever e sujete to short ue to the se ompenstion networks, shoul se-emitter juntion short our. An open juntion will result in hlf of the input power eing issipte y the lning resistor, the other hlf still eing elivere to the mplifier in opertion. The opertion is reverse when the hyri is use s n output ominer. A trnsistor filure will prtilly lwys use n inrese in the mplifier output impene. Compre to the 50-Ohm lo impene it n e regre s n open iruit. When only one mplifier is opertive, hlf of its output power will e issipte y, the other hlf eing elivere to the lo. The remining tive soure will still see the orret lo impene, whih is si requirement in omining liner mplifiers. The resistors () shoul e of noninutive type, n rte for 25% of the totl power, unless some type of utomti shutoff system is inorporte. The egree of isoltion otinle epens upon the frequeny, n the overll esign of the hyri. Typil figures for 2 to 30 MHz opertion re B. Figures 8A n B show 4 port totem pole strutures erive from Figures 7A n 7B. Both n e use with even numer of soures only, e.g. 4, 8, 16, et. For type 8B, it is more prtil to employ toroil multi-turn lines, rther thn the stright line lterntives, isusse erlier. The power output with vrious numers of inopertive soures n e lulte s follows, if the phse ifferenes re negligile: (eferene 2) P out = P N N 1 where: P = Totl power of opertive soures N = Totl numer of soures N 1 = Numer of opertive soures Assuming the most ommon sitution where one out of four mplifiers will fil, 75% of the totl power of the remining tive soures will e elivere to the lo. Another type of multiport hyri erive from Figure 7A is shown in Figure 9. It hs the vntge of eing ple of interfing with n o numer of soures or los. In ft, this hyri n e esigne for ny numer of ports. The optimum vlues of the lning resistors will vry oring to this n lso with the numer of ports ssume to e isle t one time. Two other power omining rrngements re shown in Figures 10 n 11. The isoltion hrteristis of the four-port output ominer were mesure, the t eing shown in Tle 5. The ferrite sleeves re Stkpole A, n the trnsmission lines re me of G-142/U o-xil le. The input power iviers esrie here, employ Stkpole B ferrites, n the o-xil le is Miroot PODUCT TANSFEED TO M/A COM F Applition eports For More Informtion On This Prout, 5

6 Freesle Semionutor, I ACHIVE INFOMATION Z o (,,, ) = Z o (e, f, g) = 100 Ω Ω C1 C2 1 2 Figure 8A Line impenes:, =, = Figure 8B 3 g 12.5 Ω T1 = 4: Ω C1 Figure 8. Four Port Totem Pole Struture + e f C3 1: Ω 3 Input Output T1 = 3:1 C1 T2 = 1:3 C2 e = 22.2, 16.6 Ohms + + PODUCT TANSFEED TO M/A COM Z o (,, ) = Z o (, e) = (optimum 28.9Ω) Figure 9. Three-Port Hyri Arrngement 6 For More Informtion On This Prout, F Applition eports

7 + + Freesle Semionutor, I ACHIVE INFOMATION Input C1 Z o (, ) = Z o (, ) = (optimum 35.4Ω) Input C1 T1 = 4:1 1 POT INOPEATIVE. Optimum = 28.3 Ohms P out = (P1+P2+P3) (P + P 3 ) e T1 = 2:1 T2 = 1:2 Figure 10. Two-Port Hyri System 2 POTS INOPEATIVE. Optimum = 25 Ohms P out = (P1+P2) (P + P 2 ) P1, P2, P3 = Power t ny opertive port, P = Power issipte in, exluing L. V = MS voltge t ny 50 Ohm point. (The phse ifferenes re ssume negligile.) Z o (,,,) = Z o (e,f) = (optimum) V L = 12.5 Ohms Figure 11. Four-Port Hyri System f C2 T2 = 1:4 C2 Output 3 POTS INOPEATIVE. Optimum = Ohms P out = P1 (P + P 1 ) Output PODUCT TANSFEED TO M/A COM F Applition eports For More Informtion On This Prout, 7

8 AN749 Freesle Semionutor, In. f (MHz) Isoltion, Port-to-Port (B) The input n output mthing trnsformers (T1 T2) will e somewht iffiult to implement for suh impene rtios s 2:1 n 3:1. One solution is multi-turn toroi woun with o-xil le, suh s Miroot A tp n e me to the ri t ny point, ut sine this is 25-Ohm le, the Zo is optimum for 4:1 impene rtio only. Lower impene rtios will normlly require inrese vlues for the lekge inutne ompenstion pitnes (C1 C2). For power levels ove W, lrger imeter o-xil le is esirle, n it my e neessry to prllel two higher impene les. The require ross setionl re of the toroi n e lulte oring to the Bmx formuls presente in eferenes 4 n 6. The 2 to 30 MHz liner mplifier (shown in Figure 13) onsists of two 300 W moules (8). This omine mplifier n eliver 600 W pek envelope power. The CW power output is limite to pproximtely 400 W y the hetsink n the output trnsformer esign. Figure 12. Two-Four Port Hyris The one t the lower left is intene for power ivier pplitions with levels to W. The lrger one ws esigne for mplifier output power omining, n n hnle levels to kw. The lning resistors re not shown with this unit.) The power ominer (Figure 13A) n the 2:1 step-up trnsformer (Figure 13B) n e seen in the upper right orner. The input splitter is lote ehin the rket (Figure 13C). The eletril onfigurtion of the hyris is shown in Figures 7A n 10. Note the loops equlizing the lengths of the o-xil les in the input n output to ssure minimum phse ifferene etween the two moules. Figure to 30 MHz Liner Amplifier Lyout 8 For More Informtion On This Prout, F Applition eports PODUCT TANSFEED TO M/A COM ACHIVE INFOMATION.. Tle 5. Isoltion Chrteristis of Four Port Output Cominer

9 Freesle Semionutor, I ACHIVE INFOMATION EFEENCES 1. uthroff: Some Bro Bn Trnsformers, IE, Volume 47, August Pizlis-Couse: Bron Trnsformer Design for F Trnsistor Amplifiers, ECOM-2989, U.S. Army Eletronis Commn, Fort Monmouth, New Jersey, July Lewis: Notes on Low Impene H.F. Bro Bn Trnsformer Tehniques, Collins io Compny, Novemer Hilers: Design of H. F. Wien Power Trnsformers, Philips Applition Informtion # Philips Teleommunition eview, Volume 30, No. 4, pp , Novemer Grnerg, H.: Bron Liner Power Amplifiers Using Push-Pull Trnsistors, AN-593, Motorol Semionutor Prouts In. 7. Grnerg, H.: Get 300 Wtts PEP Liner Aross 2 to 30 MHz From This Push-Pull Amplifier, EB-27, Motorol Semionutor Prouts In. 8. Lefferson: Twiste Wire Trnsmission Line, IEEE Trnstions on Prts, Hyris n Pkging, Vol. PHP-7, No. 4, Deemer Kruss-Allen: Designing Toroil Trnsformers to Optimize Wien Performne, Eletronis, August PODUCT TANSFEED TO M/A COM F Applition eports For More Informtion On This Prout, 9

10 Freesle Semionutor, I ACHIVE INFOMATION Motorol reserves the right to mke hnges without further notie to ny prouts herein. Motorol mkes no wrrnty, representtion or gurntee regring the suitility of its prouts for ny prtiulr purpose, nor oes Motorol ssume ny liility rising out of the pplition or use of ny prout or iruit, n speifilly islims ny n ll liility, inluing without limittion onsequentil or inientl mges. Typil prmeters n n o vry in ifferent pplitions. All operting prmeters, inluing Typils must e vlite for eh ustomer pplition y ustomer s tehnil experts. Motorol oes not onvey ny liense uner its ptent rights nor the rights of others. Motorol prouts re not esigne, intene, or uthorize for use s omponents in systems intene for surgil implnt into the oy, or other pplitions intene to support or sustin life, or for ny other pplition in whih the filure of the Motorol prout oul rete sitution where personl injury or eth my our. Shoul Buyer purhse or use Motorol prouts for ny suh unintene or unuthorize pplition, Buyer shll inemnify n hol Motorol n its offiers, employees, susiiries, ffilites, n istriutors hrmless ginst ll lims, osts, mges, n expenses, n resonle ttorney fees rising out of, iretly or iniretly, ny lim of personl injury or eth ssoite with suh unintene or unuthorize use, even if suh lim lleges tht Motorol ws negligent regring the esign or mnufture of the prt. Motorol n re registere tremrks of Motorol, In. Motorol, In. is n Equl Opportunity/Affirmtive Ation Employer. PODUCT TANSFEED TO M/A COM Literture Distriution Centers: USA: Motorol Literture Distriution; P.O. Box 20912; Phoenix, Arizon EUOPE: Motorol Lt.; Europen Literture Centre; 88 Tnners Drive, Blkelns, Milton Keynes, MK14 5BP, Engln. JAPAN: Nippon Motorol Lt.; , Nishi-Gotn, Shingw-ku, Tokyo 141, Jpn. ASIA PACIFIC: Motorol Semionutors H.K. Lt.; Silion Hrour Center, No. 2 Di King Street, Ti Po Inustril Estte, Ti Po, N.T., Hong Kong. 10 For More Informtion On This Prout, F Applition eports AN749/D