1CC KHI NIM L THUYT THC HNHBi 1 Thnh phn v cc im l thuyt c bn ca PLLBi 2 Cc chc nng ca m un T10L\EVBi 3 Tng hp tn sBi 4 B gii m m tnBi 5 iu binBi 6 iu tnBi 7 H thng truyn dn AM/DBS & FMBI 1VNG BM PHA PLL V NG DNG2A. CC KHI NIM L THUYTI. PLLPhn ny bao gm: m t s b hot ng ca mt h thng PLL v m t gii tch cc tnh cht ca n.1.1. HOT NG CA PLLHnh 2.1, mt cch nh tnh, c th c coi l mt im khi u trong chui ng thi ca mt vng kho pha.Ccdngsngtrongqutrnhhotngcahthngcgislsng vung cho n gin.Nhim v cavng baogm c nhimv gicho tn hiu (xungnhpcc b) to bi b to giao ng cc b (VCO) khp v mt pha v tn s vi xung nhp ti li vo ca h thng (xung nhp ti-incoming clock).M t di y cp ti trng thi n nh (steady state)ca PLL, l ng thi ca vng bm pha sau mt thi gian di vi s tc ng ca cc nhiu v d nh mt thng ging t ngt ca tn s li vo; nhng nhiu ny to ra cc dao ng thit lp (settling oscillations) cho cc i lng c trng ca h thng, n cng c bit n nh l cc gi tr chuyn tip (transition values).Nu h thng ny l n nh, cc ga tr chuyn tip ca qu trnh thit lp pha ny (the settling phase), c gi l trng thi chuyn tip (transient state), rt ngn li khi h thng t c mt trng thi n nh mi.CcthnhphncabPLL,cngnhchcnngcachngtronghthng c ch ra trong hnh 2.1 v c gii thch nh di y.1.1- 1. B tch phase (Phase Detector)B tch pha lin tc o s sai khc v pha gia xung nhp ti v xung nhp cc b (VCO).Nh trong v d ch ra trong hnh 2.1, b tchpha to ra cc xungdng hoc cc xung m tu thuc hoc l cc gi tr chuyn tip ca xung nhp sp ti n trc cc gi tr ca xung nhp cc b (VCO), hoc ngc li.diccxungnytngngvithigiantchbitgiacctrngthi chuyn tip ca hai xung nhp ny.3Hnh 2.1:Gitrtrungbnhcaxungmttrncbiudinbngngntt trn hnh 2.1: N biu din khuynh hng khc bit v pha ca hai tn hiu li vo ca b tch pha ny.Min l nhng s khc bit v pha ny c gi tr nh, khuynh hng ny l cn bngctorabixlhaisngsincngtnsvkhcpha,dovy btchpha thng thng c m t nh mt b nhn (hnh 2.1).Thct, ccbxcinhphakiutngtl cc btrnthcthchinnhn hai tn hiu li vo ca b.1.1- 2. B lc vng (Loop filter)Tnhiuracabtchphacgitiblcthngthpcavngbmpha (hnh 2.1); b lc ny rtgi tr trung bnh ca tn hiu thu c t cc php o pha v c gng loi b nhiu ca tn hiu li vo.Tn hiu c lc bin iu tn s ca b to dao ng cc b (VCO).Nh nhim v ca b lc thng thp, n b i tt c cc thnh phn tn s cao tccxungtnhiucabtchphagilitnhchtcassaikhcvpha(trong khongthigianngn),dovytnhiucabtodaongccbciuchnh da trn pha ca tn hiu vo.1.1- 3. B to dao ng iu khin bng in p (VCO)B to dao ng cc b (VCO) c iu khin bng in p ca tn hiu li ra ca b lc thng thp.4Khi tn hiu iu khin bng khng, tn s VCO lc ny cn c gi l tn s trung tm (centerfrequency), s tngngvi tn s trung bnh ca tn hiu vo ca PLL.Trong trng thi n dnh,tn hiu qua b lc datrn sso snh v pha, s iu chnh tn s VCO sao cho s sai khc pha ca tn hiu vo tn s cc b (VCO) c gim xung.Mc d vy, mt s lng nht nh n hoc can nhiu pht sinh trong b tch phadntissailchtrongqutrnhiukhintnsVCOtoramttnslch (offset) gia hai tn hiu a vo b xc nh pha.Sdchnytoramtstchlusaikhcphatheothigian,nhtrungbnh theo thi gian ca gi tr lch (offset) gia hai tn s, v tng s bin ng ca th iu khinbVCO;sbinngnynhanhchnghiuchnhlchtnscabdao ng cc b.QutrnhvamtchophpVCOgicgitrtnstrungtmmong mun, nhng n s to ra nhng bin ng khng th trnh khi v tn s v pha ca b to dao ng cc b.1.2. GII TCH TUYN TNH CA PLLPhptnhtuyntnhvihthngcthcthchinkhittcccthnh phn ca b PLL c tnh cht tuyn tnh.Trong trng hp tng qut, iu ny ch ng khi di bin ng ca pha gia haitnhiucnhncabxcnhlnh,khnglnhnxpxnaqungt 2 / +ti - 2 / .Mt iu kin rng buc khc l h thng phi ang trong trng thi n nh v xu hng bin ng ca cc i lng nh hng n hot ng ca PLL l mt sng sin,cnghaltrngthicahthnglmttrngthidngsinthngtrc(a permanent sinusoidal state).HotngcaPLLcthcmtvirngbucnythngquabiudin trong min thi gian v tn s; mc d vy, cc biu din ny khng th a ra bt k p n no cho trng thi chuyn tip ca h thng.Tt c cc iu kin hot ng ca PLL c th c tnh ton v nh gi bng s dng bin i Laplace: n biu din p ng theo thi gian ca mt h thng trong mtminbinphcj s + = vcungcpcpncatrngthichuyntipv trng thi n nh.5Hnh nh ca mt PLL trong tp cc iu kin nh c ch ra trong hnh 2.2.Tn hiu li vo ca h thng n t ngoi v ti u vo ca b xc nh pha, xc nhtng ng vi cng thc sau:; ) t sin( Pi i i+trong Pi l cng sut trung bnh ca tn hiu, il tn s v i l pha ca tn hiu sin li vo.Tn hiu li ra to bi VCO v gi ti li vo th hai ca b tch pha.Trong cc iu kin hot ng ny, tn hiu ny s l mt sng sin vi tn s bng vi tn s ca tn hiu vo:; ) t cos( A0 0 0+trong i 0 = v 0 l pha ca tn hiu li ra.B tch pha nhn hai tn hiu ny v a ra s sai khc:) sin( K ) sin( K A P0 i d 0 i p 0 i = Cc thnh phn cha tn s gp i khc c th c b qua bi v chng c loi tr khi i qua b lc thng thp v bi vng lp ca chnh n, s c gii thch k hn sau ny.Hs p 0 i dK A P K =lhskhuchicabtchphavcbiudin bng n v V/rad.; gi tr ca n ph thuc vo cng sut trung bnh ca tn hiu vo.K tip, b tch pha to ra mt th da trn:); ( K v0 i d d ~Nu s sai khc pha gia tn hiu vo v tn hiu VCO l kh nh; in p ny s cung cp iu kin ca s tuyn tnh trong PLL.Nu(t) 0l pha ca tn hiu VCO, kt qu thu c s l:;dtd (t)dt(t) d000+ = O =trong l 0 l mt hngss bi v n tngng vi tn s trung tm cto bi VCOkhiinpravdcabtchphabngkhng,cnghalkhissaikhcpha ) (0 i bng khng.6Kt qu in p vd t l vi sin ca ) (0 i cho php coi rng tnh cht ca b tch pha l tuyn tnh xung quanh gi tr khng, nhng n ngm yu cu mt (gi tr lch)offset2 / trongtnhiuctorabiVCOtngngvitnhiulivo, hin din trong tch sin.cos ca hai tn hiu vo b xc nh pha.HotngcabPLLdatrnlnskhcbitsovi 0 ,ilng dtd0= s c iu ch bi in th v2 (hnh 2.2). Khi :; v Kdtd2 00=Trong K0 l h s khuch i (gain) ca VCO v c biu din bng n v rad/s V.Gi s trong trng hp vng bm pha khng gm b lc thng thp; kt qa s l v2 = vd; v khi :); ( K K v Kdtd0 i d 0 2 00 = =suy ra:; K K K Kdtdi d 0 0 d 00= +PhngtrnhviphnnyxcnhthigianpngcahthngPLLkhi khng c b lc thng thp.HngsK0*Kd=Kcnhnghanhlhskhuchidngmtchiuca vng bm pha (direct-current gain of the loop) v c biu din bng 1/t.7Hnh 2.2: p ng xung tuyn tnh ca h thng PLLKho st trng thi sin thng trc ca PLL, gi s rng tn hiu vo gm mt sngmangsinvibinlhngsvtnsciuchbimtsngsinl tng tn s m.Khi tn hiu u vo l:); t sin( Pi i i+vi phn pha, dtdii +, s c dng:t); mcos( i i +thu c:t) sin(mdt t) os( c m mmmt0i= = }khi biu din sin ca is l mt biu din phc:2) / t j(i ime z =Tn hiu VCO s c c tnh ging ca tn hiu li vo nu cho rng trng thi ca PLL l trng thi sin thng trc; mt cch chi tit vi phn pha s c dng nh sau:t); mcos( t) mcos( dtdm i m 000+ = + = +khi :) t j(0 00 me z =;8ch xt n cc gi tr quan trng, n c th dc biu din li nh sau:; jdtd0 m0=khi phng trnh vi phn ca p ng ca PLL s l:; K Kdtdi 0 00= +; K K ji 0 0 m= +mi 0j KK +=khi p ng tn s ca PLL l:;K) / j( 11m i0+=cng thc ny ch r dng p ng ca lc thng nh cp trc o khi vng bm pha c m t c kh nng loi b cc thnh phn tn s gp i to bi b xc nh pha/php nhn, ngay c khi khng c b lc thng thp.H thng kiu ny c gi l bc mt (first order) bi v p ng tn s c duy nhtmtcc(uniquepole);nkhngcsdngthngxuyntrongthct;tr khi h thng thc s yu cu di rng.Mt cch tng qut, mt PLL bao gm mt b lc thng thp.Quaytrlihnh2.2;Nu( ) j F lpngtnscablc,ktqusl ( ) j F v vd 2 = ; t thu c:( ); j F ) ( K K F(j( v K v K jdtd0 i d 0 d 0 2 0 0 m0 = = = =( ) j KF ) ( j 0 i 0 m =;do p ng tn s ca PLL tr thnh:( )( )( );jj KF1jj KFKF(jF jj KFi0+=+=9 ( )jj KFlhskhuchicahthngvngm(gainofopenloopsystem), ging nh trong bt k h thng c hi tip khc.Khi khuch i dng mt chiu ca PLL s l: K F(0)Mt tnh cht quan trng khc ca PLL l p ng li (error response):( )( )( )( );j KF jjj Ej KF jj KF1) (i i0 i+= =+ = =eDovy,pngblcnylmtphntchhpcapngcavngbm pha, n cho php xc nh c tnh ca PLL.Mttrongccblcthngcsdnglmtblcthng(passive filter) ch ra trong hnh 2.3.Hnh 2.3: B lc vng th ngp ng tn s ca b lc ny l:( )( ); j 1j 1j F2 12+ + += C; R 1 1 = vC; R 2 2 =Mt kiu b lc tng ng khc l dng b lc tch cc ch ra trong hnh 2.4.Hnh 2.4: B lc vng tch ccTrong trng hp ny p ng ca b lc l:( ) ;j 1j 1j F12++=10B lc tch cc cho php nhiu bc t do thay i thu cd liu thit k bivcchngsthigiancaccvkhnglhontonclp;hnthna khuch i ca vng c th c thay i nh c s dng b lc tch cc.Thay hm ( ) j Fca b lc ny vo trong cng thc p ng tn s ca PLL s thu c cng thc sau:( )( )( ); K K 1j j j 1 Kj H2 1 2 1222 12+++++++=i vi b lc th ng( )( )( );KK 1j jj 1 Kj H1 12212++++= i vi b lc tch ccdng chun ho ca cc cng thc ny, s dng trong cc h thng iu khin t dng, s c dng nh sau:( )( )( ); 2 j j /K 2 jj H2n n22n n n+ ++ = i vi b lc th ng( )( ); 2 j j 2 jj H2n n22n n+ ++= i vi b lc tch cc cc i lng sau y c th c nh ngha nh l:( )2 1n K+=; v ( );K11 K212 1|.|

\| ++=i vi b lc th ng;K1n = v21 *K21 =; i vi b lc tch ccn l tn s ring ca h thng (natural frequency of the system); l h s suy gim (damping factor).Mc d vy, nu t ti mt h s khuch i kh ln K, ko theo 2 /K n

Tmli,khicpntnskotrong(pull-infrequency),cthphtbiu rng, nu s sai khc khi to ban ul nh hn P ; khi , cng vi gi thit nhiu v nhng tc ng ph trong mch lkhng ng k,mt h thng bc hai vi gi tr trung bnh khuch i ln s c nhiu kh nng t ti trng thi kho trong, ngay c khi sut pht t mtln hn rt nhiu ln di ca vng bm.1.3- 3. Thi gian ko trong (Pull-in time)Thi gian ko trong TP c nh ngha l thi gian cn thit h thng t n trng thi kho trong k t lc lch khi to ban u (initial offset) thay i t P tiL .Cng v th gi tr ny khng th c tnh bi cng thc chnh xc nn cng thc xp x s dng l:( )3n2P 2T ~;Cngthcnyngvikhinm trongkhonggia P v L ;nbiu din thi gian cn thit h thng khi i vo tn s kho trong, sau khong thi gian ny, bin thin ca tn hiu li vo l ln.Trong trng hp mt h thng bc hai vi khuch i ln v0.707 = , thi gian ko trong l xp x bng:( )3L2PB 2 . 4Tf~;19 BL l di thng ca vng bm (loop band).Thi gian ko trong ny tr ln rt ln (thm ch mt vi gi) trong cc vng lp vi di thng BL rt hp.Trong cctrnghpny, tcngtrnPLLtheo ccphngphpnhtnh c th rt ngn rt nhiu ln thi gian ko trong t ti trng thi kho trong.II. B tng hp tn s2.1. TNG QUT V B TNG HP TN STng hp tn s l mt qu trnh cho php to ra mt gi tr tn s ln gp N ln ca mt tn s tham chiu, fr; tn s tham chiu ny thng c to vi mt gi tr c nh thu c t mt b to dao ng thch anh thng qua mt php chia. N thng l mt s thp phn n s hng, cn-1, cn-2, ...,c0, nhn gi tr thay i t 1 n 9. Khi gi tr N l : cn-110n-1+ cn-210n-2+....+ c0, do tn s thu c nh l mt php nhn thp phn ca tn s tham chiu, c th thay i bi cc bc n v, mi,..., m ca 10n-1ca gi tr tn s tham chiu.2.1- 1. phn gii ca s tng hp tn sBcthayinh nhtca tnsli ra,tngngvimt nvbin thin caN,ltnsthamchiu,cgilphnditncastnghptns (synthesis resolution).2.1- 2. Tng hp mt chiuKhi tng hp tn s din ra nh cm t trn, n cnh ngha nhl mt s tng hp mt chiu(direct synthesis).Mc chcamt b tnghptns l toramt chuicc gitrtn sri rc trong mt qung nht nh phn b xung quanh N/2.Nhng,trongtrnghptngqut,giihnhotngnocaccmch khngchophpsdngtonbdilthuyt,t1(N=1)n10n(N=0);iunycng khng cn thit trong thc t, v d, khi ch cn thit ph ht cc gi tr ca mt nhm FDM ca ccsngmang phn b trongmt khong nht nh xung quanhmt tn s trung tm.Khi cc gi tr ca tn s thu c ( biu din trong cc n v nht nh, v d MHz) cngcbiudin bisthpphn,so Nslmt snguyntobitt c ccsbiudinccgitrkhcnhauvphngiifr(tnsthamchiu)sc nh ngha sao cho N*fr c gi tr mong mun, theo n v ca fr.20ThastnghpNtrongcctnhhungnhtnhcdngM*m,;mlmt tha s c nh c chia thang sn (b nh thang), iu ny s c gii thch k hn sau ny.Trong trng hp ny, s thay i mt n v ca tha s M s thay i tn s thu cm*fr, do phn gii ca b tng r hp tn s khng cn l fr na m l m*fr.2.1- 3. Tng hp kt hp chuyn i tn sKhi cc gi tr tn s mong mun phi phn b xung bn trong mt khong bao gm mtditnsrtcao,sltthnkhi cctnsliracabtnghptnsc h tn (down-converted)mt di c cc gi tr thp hn. Trong trng hp ny, cctnschuyni(conversionfrequencies)sduytrquanhvitnstham chiu, c nh bi tha s N. Nh c h thng ny, phn gii cng nh, s tch bit gia ccgi tr ca tn s tng hp khng thay i vi tng hp trc tip, nhngcc tn s c s dng s c dch chuyn theo mt tn s offsettng ng vi gi trca b to dao ng cc b s dng trong qu trnh chuyn i. Cc loi tng hp tn scptrnscbnchitittrongcconsau. Thitbcbnthngsdng cho tng hp tn s l PLL.2.2. TNG HP TN S TRC TIPS dng PLL trong tng hp tn smt chiu c ch ra trong hnh 4.1. Nh cchratrnhnhny,livocabtchphanhntnsthamchiufr. Tns VCOcatrlibxcnhpha,khngmtchiumthngquamtbchia modul N (N modulo divider). PLL bm tn s tham chiu thng qua li ra ca b chia, do vy tn s VCO s ln gp N ln gi tr tn s tham chiu.21Hnh 4.1: S ca tng hp mt chiu s dng mt PLLPhn t chia N c th c c nh s dng thit b ging nh mt b nhn tn.Mc d vy, php chia modul N thng kh trnh v c th thit lp tn s li ra caVCOtheoccgitrrircphnbxungquanhmtgitrtnstrunggian F0=N0*fr, v c phn bit bi phn gii da trn gi tr tham chiu fr.TnstrungtmcaVCO(tnsVCOkhigitrcathiukhinlbng khng) s tng ng vi tn s trung tm F0.Nhtrnhbytronghnh4.1,vngtnghpcthgmmtngtrctip (direct path).( ) ( ) ( ) j / K * j F * K j G0 d=;trongshng( ) j / 1 btngunttchphntnslitoraphalira; vmt ng phn hi (feedback path):( ) ;N1j =trong N l phn t chia ca b chia nm gia b VCO v ng phn hi tr v b xc nh pha.Gingnhmihthngcphnhikhac,hmtruynvoracavngbm tun theo cng thc sau:( )( )( ) ( );j * j G 1j Gj H+=trong ( ) ( ) j * j Gl hm truyn ca vng h;22Thay cc gi tr ca( ) j G v ( ) j ta thu c: ( )( )( )( )( );N jK * j F * K1N jK * j F * KNjK * j F * K1jK * j F * Kj H0 d0 d0 d0 di0+=+= =Nu gi tr N0 ca tn s trung gian F0 c xem nh l nhn t chia, n c th vit li l:( )( )( );N jK * j F * K1N jK * j F * K Nj H00 d00 di 00 I+= =cng thc ( ) j HIch ra rng khuch i ca PLL, nhn t b tch pha vi pha li ra 0c thay bng 0 0/N nh c b chia, l 0 d 0/N K * Kthay v d 0K * K.Thct, pht biu ny ckhng nhli bnghm truynli (errortransfer function) nh sau:( )( ) ( )( );N jK * j F * K11j * j G 11/N j E00 di0 0 iie+=+== =Khi li phacabtch phas cxemnhlmt ssaikhctngi gia pha li vo v pha li ra c chuyn i bi b chia, tc l php chia cho N0.Khi , vng hot ng ca vng bm (dynamics of the loop), vi cc gi tr c th ca n v (tn s ring, l di thng, v h s tt (damping factor)) ph thuc vo khuch i 0 d 0/N K * K thay v ph thuc d 0K * K .S la chn PLL tham chiu gi tr phn hi 1/N0 ph thuc vo iu l tn s tng hp trung gian F0c to ra trong cu hnh ny; tn s trung tm 0 ca VCO c b tr da trn gi tr trung gian ny sao cho PLL thng thnggi ng gi tr khuch i 0 d 0/N K * K .Thc t, gi tr khuch i ny ca vng bm c th thu c ngay c khi PLL c xem nh l khng da trn tr tn s tham chiu fr, bi v khuch i K0 ca 23VCO l lun lun t l vi tn s 0 ; do vy, ton hng 0 0/N m gi tr K0/N0 ph thucvo,sakhuchicaVCOtimtkhuchithamchiumt chiuti gi tr ca fr (0 r 0N * f 2 =).Mcdvy,khikimtrahotngcaPLL,iuquantrnglxemxtdi ng (variation range)ca tham s Nm s thay i ca cc thngs vng bm ph thuc thng qua gi tr tham chiu; do vy, n m bo rng d liu hot ng ca PLL l chnh xc trong ton di hot ng.Thct, nhngthayinh hngn thams vngbm khimodulo N thay i, s gii hn ln kh d ca vng cc tn s c tng hp.B chia kh trnh c t trc cc thng s c sn nh g tr chia c nh m trong cc trng hp nht nh.Khi cp ti tng s tng hp, cc ga tr quan trng nht l modulo tng th v tn s tham chiu fr; b nh thang ch dch phn gii t fr ti m*fr to ra mt t s khc bit gia phn gii v tn s tham chiu.Hot ng ca b Bnh thang clin kt ti cc hot ng cth ca s tng hp bi v n gim tn s VCO trc khi a vo b chia kh trn; v d n c s dng lm ph hp gi tr ca phn gii v di tng hp tng ng vi mt tn s tham chiu cho sn.2.3. TNG HP C CHUYN I TN SBtnghptnscthbaogmmtbhtnthngthng(atypical frequencydownconverter)btrgiaVCOvbchiakhtrnh. Skhicab tng hp loi ny c ch ra trong hnh 4.2. Trong trng hp ny, kho st t li vo ca b chia kh trnh, vng tng hp hot ng vi cc gi tr khc bit gia cc tn s c to bi VCO v tn s ca b chuyn i cc b (local conversion oscilator). 24Hnh 4.2: S ca b tng hp s dng mt PLL v chuyn i tn sStchphnbit(hayphngii-resolution)vkhongtnskhdtili vo ca b chia kh trnh c cc gi tr ging nh c xc nh ti li ra VCO, nhng chng cha trong mt di tn s c gim xung (downward) mt lng bng vi tn s to bi b dao ng cc b.Nu khuch i K0khng ph thuc vo tn s trung tm ca VCO, b PLL skhngkhcsovicuhnhthitlptrongtnghpmtchiukhikhngcb chuyn i tn s.Ngc li, thng thng khuch i K0 lun tng t l vi gi tr tn s trung tm ca VCO, do vy PLL s nh dng theo cc gi tr tn s c to ra bi VCO.Mt thun li ca tng hp tn s kt hp vi chuyn i s thu c cc tn s tng hp cao ti li ra ca VCO m khng cn cc thnh phn khc ca vng bm phi hot ng ti tc ny.Hn th na, ln ca khong tn s tng hp khng nh hng ti vng hot ng ca PLL (dynamics), trong di tn s cao.Trong bt k tnh hung no, loi thit b ny c bit hu ch trong cc chuyn i tn s m l c s ca ht ng trong cc my thu v tuyn.III. B gii m m tn PLLBPLLcthcsdngnhlmtbgiimmtnnhcbathnh phn chnh sau:25- PLL hot ng vi tn s m thanh c gii m;- mtb xc nh vungpha i vi tn hiubo hiu trng thi khotrong ca PLL;- Mt mch li ra cha b lc lm iu kin cho tn hiu gii m v gi ti trng thi kho trong.S khi ca ton b n v c ch ra trong hnh 5.1Hnh 5.1: S khi ca mt b PLL gii m m tnB PLL s kho m tn khi tn s ca tn hiu li vo nm trong khong tn s kho trong ca n. ln ca tn s kho trong xc nh phn gii (resolution) ca b gii m. Gi tr ny thng c th hin di dng phn trm ca tn s danh nh(nominalfrequency)camtnvnthngnhnghanhldixcnh (detectionbandwidth). Thay iindungcablcPLLsquytnhkchcca di xc nh ny (kt qu ny th hin trn s khi v trn m t thnh phn NE567 s dng trong m un T10L). Khi tc ng thng qua gi tr n , tc l thng qua gii thng PLL m tn s kho trong ph thuc vo (n L 2 =i vi h thng bc hai), s xc nh di tn s mongmun). Mc dvy, di thngPLL phthuc khng ch vo in dung ca b lc m cn ph thuc vo khuch i vng bm KdK0, trong 26khuchiKdcabtchphabtcngbimc(P1/2)catnhiulivo (iu kin thng thng ca cc mch tng t hot ng vi cc sng sin). Do , khi nhkchcdithngcngcnquantmtiinthhiudngcatnhiulivo (khi cp n thnhphn NE567, cc bngv cc biu thch hp cho cc gi tr ny ccung cpbinh sn xut). D nhin,tn s trungtm cavng bm VCO (CCO = b to dao ng iu khin c ang xt (current controlled Oscillator), khi s dng NE567) s c sp t vi gi tr chun ho ca tn s m thanh (m tn): gi trnycthitlptrnmunl50kHz. BCCO(NE567)storamttns tham chiu vung pha2 / so vi tn hiu li vo khi PLL c kch hot. Sng tham chiu ny cng vi tnhiu li vo c gi ti mt b tch pha vungm li ra ca b tch pha ny, sau khi c lc thch hp, to ra mt c tnh th hin mi lin h datrn ssai khcphaso vi2 / . Trongtrnghp ny,svungpha to ramt gitrnhnhnhtvgitrnyphthucvogitrhiudngcalivo(xem thm phn ccctnhkthut (specifications). lncagitrnycsosnh (thng qua mt b quyt nh) vi mt ngng quyt nh da trn mt gi tr hp l, cho php xc nh s vung pha ca b gii m (decoder) v ko theo trng thi kho trongcaPLLvilivomtn. Liracabtchphacsdngchras hin din ca m tn v bt LED bo hiu (DET.) trn m un T10L. in dung ca b lc li ra trong b gii m s c mt gi tr tng quan vi gi tr in dung ca b lc trong vng bm: gi tr ny tng ln khi tr s hng s thi gian ca PLL tng. S ph thuc ny c th c gii thch da trn iu l khi gim di thng ca PLL (n ) s gim h s tt (damping factor); do mt vi p ng khng mong mun c th xut hin d dng hn (tng hng s thi gian ca b lc li ra s trit cc p ng khng mong mun ny).M un T10L cho php chn hai gi tr ca di thng b quyt nh thng qua b chn di BANDSELECTION;hai gi tr ny l: NARROW(hp)% 4 ~ v WIDE (rng) % 14 12 = .IV. iu tn FM4.1. L THUYT CHUNGMtsngsinloi:| |; (t) Acos t) . cos( . A (t) v = =ccgilsng mang, thng qua mt kiu iu ch tn s gc, pha) (t ca n ph thuc vo mt tn hiu x(t) gi l tn hiu iu ch.27Nu) (t ph thuc vo x(t) nh sau:x(t); . k t . (t) + = y l iu ch pha.Ngc li, nu ; dt x(t). . k t . (t)}+ =y l iu tn.Thc t, trong trng hp th hai, tn s gc tc thi(t) ca tn hiu iu ch l:x(t); . k ) ((t) + = =dtt ddo dng ca tn hiu iu ch, cn gi l tn hiu mang tin, thay i tn s gc ca tn hiu iu ch. Ol tn s gc ca tn hiu sng mang; k l nhy iu chTrong trng hp c th khi tn hiu iu ch l mt sng sin:t); . cos( . B (t) v x(t)m= =trong O f:t) . sin(2 . (t) v F Ac=Nu bin ca tn hiu vc(t) l thay i bng tng ca tn hiu vm(t) v A, tn hiu thu c vM(t) s c dng sau:35| | | | ); . 2 sin( . ) . 2 sin( . 1 . ) . 2 sin( . ) . 2 sin( . . ) ( t F t f m A t F t f B k A t vM + = + =trong k l mt hng s t l.TnhiuvM(t)giltnhiuiubin(amplitudemodulatedsingal)haytn hiu AM (AM signal).Tn hiu vm(t) c gi l tn hiu c iu ch hay tn hiu mang tin;Tn hiu vc(t) gi l sng mang (carrier).Hs:AB km.= cgitr0