vn KythuatTanSoTrucTiep DDS

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<p>TM TT NI DUNG</p> <p> ti hng ti mt ci nhn tng quan v k thut tng hp tn s trc tip (DDS). Trong phn u, ni dung cp ti s cu to v gii thch nguyn l hot ng ca mt h thng DDS (Direct Digital Syntherizer). Khi xem xt ton b h thng DDS th mi quan h gia ph u ra ca h thng v nhiu do nh hng ca ly mu, ti to tn hiu, v do cc hn ch phi chp nhn khi trin khai thc t l vn u tin c quan tm tm hiu. Tip l vn sai s, cc ngun gy sai s v nh hng ca sai s ti hiu nng tn hiu k sinh, vn iu ch tn hiu,b lc trit mo, b lc FIR, b lc IIR, b lc polyphase..Nhng ng dng iu ch l mt phn khng th thiu khi nghin cu k thut DDS, v vy phn sau ti trnh by mt s vn v iu ch FSK, PSK, QAM dng DDS. Ngoi nhng vn l thuyt trn, ti cng dnh mt s trang minh ha nhng u im ni bt ca k thut DDS, nhng xu th pht trin nhm hon thin cng ngh DDS v nhng tin b t c ca mt h thng tch hp cng ngh DDS.</p> <p>i</p> <p>MC LCM U...............................................................................................................1 CHNG 1: NHNG IU C BN V K THUT DDS.......................21.1Nhng u im ca DDS..........................................................................................2 1.2L thuyt hot ng..................................................................................................2 1.3Xu hng tch hp chc nng...................................................................................5</p> <p>CHNG 2: LY MU U RA V KH NNG CHUYN PHA V TN S CA THIT B DDS...........................................................................72.1Ly mu u ra thit b DDS.....................................................................................7 2.2Kh nng chuyn pha v tn s ca DDS.................................................................8 3.1Xc nh tc iu chnh ti a..........................................................................9 3.2Giao tip iu khin DDS.....................................................................................9</p> <p>CHNG 3: VN NHIU TRONG H DDS.........................................113.1Tc ng ca phn gii DAC ln hiu nng nhiu vt (spurious performance)..11 3.2Tc ng ca oversampling) ln hiu nng nhiu vt.............................................12 3.3Tc ng ca ct gim trong b tch ly pha ln hiu nng vt (spur)....................13 3.3.1Bin cc vt.................................................................................................14 3.3.2Phn b cc vt to bi s ct pha....................................................................15 3.3.3Tm tt v ct b phase....................................................................................18 3.4Cc ngun gy ra cc vt khc ca DDS.................................................................19 3.5Hiu nng vt gii rng...........................................................................................20 3.6Hiu nng vt gii hp............................................................................................21 3.7D bo v khi thc vt sweet spots trong di iu chnh ca DDS....................21 3.8Xem xt s bin ng (Jitter) v n pha trong h thng DDS.................................21 3.9Xem xt b lc u ra.............................................................................................24 3.9.1p ng ca h Chebyshev..............................................................................27 3.9.2p ng ca b lc h Gauss...........................................................................28 3.9.3p ng ca h Legendre.................................................................................29</p> <p>CHNG 4: NG DNG IU CH S CA DDS..................................314.1L thuyt iu ch s c bn...................................................................................31 4.1.1Cc khi nim c bn.......................................................................................31 4.1.2iu ch...........................................................................................................33 4.2Kin trc h thng v yu cu.................................................................................35</p> <p>ii</p> <p>4.3B lc s.................................................................................................................36 4.3.1B Lc FIR.......................................................................................................36 4.3.2B lc IIR.........................................................................................................38 4.4DSP a tc..............................................................................................................39 4.4.1Tng tc............................................................................................................40 4.4.2Gim tc...........................................................................................................41 4.4.3Chuyn i tc vi t s n/m.......................................................................43 4.4.4B lc s...........................................................................................................43 4.5Xem xt ng b d liu vo v xung.....................................................................47 4.6Cc phng thc m ha d liu v trin khai DDS...............................................49 4.6.1M ha FSK.....................................................................................................49 4.6.2M ha PSK.....................................................................................................50 4.6.3M ha QAM...................................................................................................51 4.6.4Quadrature up-conversion................................................................................52</p> <p>CHNG 5: MT S KT QU THC NGHIM...................................545.1Gii thiu chip DDS AD9835.................................................................................54 5.2.1L thuyt hot ng..........................................................................................54 5.2.2Giao tip vi vi iu khin...............................................................................55 5.2.1S nguyn l................................................................................................56</p> <p>KT LUN........................................................................................................60</p> <p>DANH SCH CC HNH V</p> <p>iii</p> <p>HNH 1: S MT B TNG HP TN S TRC TIP N GIN ...............................................................................................................................3 HNH 2: H THNG DDS C TH IU CHNH TN S.......................3 HNH 3: TN HIU CHUYN QUA MT H DDS......................................4 HNH 4: KIN TRC DDS 12 BT VI CC CHC NNG PH.............5 HNH 5: PHN TCH PH U RA CA DDS............................................7 HNH 6: TC NG CA PHN GII DAC.......................................11 HNH 7: TC NG CA OVERSAMPLING LN SQR.........................12 HNH 8: SAI S DO CT BT V BNH PHA.......................................13 HNH 9: MU T IU CHNH C MC VT CC I......................14 HNH 10: MU T IU CHNH KHNG GY RA PHASE TRUNCATION SPUR......................................................................................15 HNH 11: DY TCH LY PHA....................................................................15 HNH 12: HOT NG CA T CT B..................................................17 HNH 13: PH CA DY T B CT B...................................................18 HNH 14: VNG NYQUIST V NH XA CA CC TN S BN NGOI BNG NYQUIST................................................................................19 HNH 15: TC NG CA S BIN NG XUNG H THNG..........23 HNH 16: PH U RA DDS.........................................................................24 HNH 17: B LC ANTI-ALIAS...................................................................25 HNH 18: P NG MIN THI GIAN......................................................25 HNH 19: P NG MIN TN S.............................................................26</p> <p>iv</p> <p>HNH 20: P NG CA CC B LC H CHEBYSHEV....................27 HNH 21: P NG B LC H GAUSSIAN...........................................29 HNH 22: P NG H LEGENDRE..........................................................29 HNH 23: PH BNG THNG C S MT PHA...................................32 HNH 24: PH BNG THNG C S HAI PHA.....................................32 HNH 25: PH BNG C S PHC............................................................32 HNH 26: PH BNG THNG DI..............................................................33 HNH 27: CU TRC IU CH C BN.................................................34 HNH 28: CU TRC IU CH S C BN...........................................34 HNH 29: CU TRC IU CH DDS C BN........................................35 HNH 30: B IU CH DDS........................................................................35 HNH 31: B LC FIR DNG N GIN..................................................36 HNH 32: P NG TN S B LC FIR CHO A0 = A1 = 0.5..............37 HNH 33: B LC FIR N-TAPS....................................................................37 HNH 34: B LC IIR N GIN...............................................................38 HNH 35: B LC IIR NHIU TAP..............................................................39 HNH 36: B TNG TC N GIN..........................................................40 HNH 37: S TNG TC BIU DIN TRONG MIN TN S..............40 HNH 38: B GIM TC N GIN..........................................................41 HNH 39: QU TRNH TNG TC XEM TRONG MIN TN S........42</p> <p>v</p> <p>HNH 40: B CHUYN I TC N/M.................................................43 HNH 41: B TCH PHN V B COMP C BN...................................44 HNH 42: P NG TN S CA B LC CIC C BN......................45 HNH 43: TNG TC V H TC DNG CIC.........................................45 HNH 44: P NG TN S CA B LC CIC C BN......................46 HNH 45: B TNG TC TRIPLE CASCADE CIC...................................46 HNH 46: B GIM TC CIC TR GP HAI............................................47 HNH 47: SO SCH P NG B LC CIC SAU KHI SA I..........47 HNH 48: S KHI IU CH CHUNG..............................................48 HNH 49: B M HA FSK DNG DDS.....................................................49 HNH 50: B M HA RAMPED FSK DNG DDS..................................49 HNH 51: CHM SAO 16QAM......................................................................51 HNH 52: QUADRATURE UP-CONVERTER.............................................52 HNH 53. SNG COS.......................................................................................54 HNH 54: NGUN V MCH DAO NG.................................................56 HNH 55: S MC AT89C2051...............................................................57 HNH 56: S GHP NI MY TNH QUA CNG COM..................57 HNH 57: S MC AD9835.....................................................................58 HNH 58: S MCH IN............................................................................58 HNH 59: MCH NG DNG CHIP DDS AD9835....................................59</p> <p>vi</p> <p>M UThc t, k thut DDS trc y ch yu dnh ring cho cc ng dng qun s, v n t, kh trin khai v yu cu b chuyn i s - tng t tc cao. V s tin b ca cng ngh mch tch hp, DDS tr thnh s la chn khc bn cnh cng ngh vng kha pha to ra tn s u ra nhanh trong cc ng dng dng tng hp tn s. V c xy dng bng phng php x l s nn DDS cho php thc hin iu ch d dng. Gn y, nhng tin b trong cng ngh sn xut IC, c bit l CMOS, cng vi s pht trin ca cc thut ton DSP cung cp gii php chip DDS cho cc h thng con x l tn hiu s v truyn thng phc tp nh l iu ch, gii iu ch, to dao ng ni, my pht xung kh trnh, my pht chirp1). Phm vi ng dng DDS ngy cng m rng, bao gm cable modems, cc thit b o, cc my to sng ty , trm t bo c s v nhiu ng dng khc na. Mc ch ca ti ny l tip cn cng ngh DDS, trn c s tm hiu cu to, nguyn l hot ng, cc ngun sai s trong mt h thng DDS v nhng kh nng ng dng rng ln ca DDS. Trn c s gip cho trong tng lai c th trin khai c mt h thng DDS trn FPGA, hay xa hn c th dng DDS tch hp vo cc h thng khc nh l vng kha pha, cc ng dng iu ch v gii iu ch Em xin gi li cm n chn thnh nht n PGS.TS Ng Din Tp, ngi tn tnh hng dn v gip em rt nhiu trong qu trnh lm lun vn. Em cng xin gi li cm n ti ton th cc thy c gio trong Khoa in t - Vin thng gip em hon thnh lun vn ny.</p> <p>----------------------------------------------</p> <p>1)</p> <p>chirp l qu trnh chuyn tn s t mt tn s ny ti tn s khc.</p> <p>1</p> <p>CHNG 1: NHNG IU C BN V K THUT DDSTng hp tn s l mt k thut s dng cc khi x l tn hiu s to ra mt tn hiu u ra c th iu chnh c v tn s v pha tham chiu t mt ngun xung c nh, c chnh xc cao. V bn cht, tn s tham chiu c chia xung trong khi DDS bng h s t l t trc trong mt t nh phn lp trnh c.T nh ny c chiu di t 24 n 48 bits, cho php khi DDS trin khai c kh nng cung cp phn gii tn s cc cao. Sn phm DDS ngy nay c ng trong cc khi nh, tch hp nhiu chc nng hiu sut cao v gi c cnh tranh, nhanh chng dn tr thnh mt la chn bn cnh gii php tng hp tn s truyn thng tng t. S tch hp b chuyn i s tng t hiu sut- tc cao v kin trc DDS vo trong mt chp n cho php cng ngh ny t ti phm vi ng dng rng hn v cung cp mt s la chn hp dn khc vi b tng hp tn s tng t da trn PLL. Trong nhiu ng dng, gii php DDS gi mt vi u im khc bit so vi b tng hp tn s tng t dng mch PLL.</p> <p>1.1 Nhng u im ca DDS- Tn s u ra phn gii c micro Hz, kh nng iu chnh gc pha, tt c</p> <p>u c thc hin bng iu khin s.- Tc bc nhy cc k cao trong qu trnh iu chnh pha v tn s, bc</p> <p>nhy tn s c pha lin tc.- Kin trc DDS s loi b vic tinh chnh bng tay lin quan n nhng vn </p> <p>v tui th linh kin v tc ng ca nhit nh xy ra trong tng hp tng t.- Giao tip iu khin s ca DDS to ra mt mi trng ni chng ta c th thc</p> <p>hin iu khin t xa, ti u bng vi iu khin.- Khi c s dng nh mt b tng hp vung pha, DDS cho hai tn hiu li ra</p> <p>I v Q cc k khp vi nhau.</p> <p>1.2 L thuyt hot ngTrong dng n gin nht, mt b tng hp tn s c th c trin khai t mt xung tham chiu chnh xc, mt b m a ch, mt b nh ch c lp trnh c, v mt b chuyn i D/A.</p> <p>2</p> <p>Hnh 1: S mt b tng hp tn s trc tip n gin</p> <p>Trong trng hp ny, thng tin bin s ci tng ng vi mt chu k y ca sng sin c lu trong PROM. PROM do c chc nng ging nh mt bng tra cu hm sin. B m a ch nhy ti tng v tr nh, v ni dung v bin sng sin c a ti b chuyn i D/A tc cao. Khi ny to ra tn hiu hnh sin tng t, tng ng vi t li vo s t PROM. Tn s u ra ca DDS trin khai theo m hnh ny ph thuc vo:- Tn s ca xung ng h tham chiu. - Kch c bc nhy sng sin, ci c lp trnh vo trong PROM.</p> <p> chnh xc, mn v cng sut AC ca u ra ca kin trc n gin ny l kh tt, song n thiu s iu chnh linh hot. Tn s u ra ch c th thay i nu thay i tn s xung tham chiu hoc lp trnh li PROM. Nu ta a vo b tch ly pha, kin trc ny tr thnh mt my pht dao dng iu khin s, l li ca thit b DDS mm do, linh ng.</p> <p>Hnh 2: H thng DDS c th iu chnh tn s</p> <p> y mt b m bin N bt v thanh ghi pha thay th b m a ch, chc nng nh lm cho khi ny ging nh mt vng pha trong kin trc DDS. hiu chc nng c bn ny, ta xem dao ng sng sin ging nh mt vc-t quay quanh</p> <p>3</p> <p>mt vng pha. Mi im trn vng pha tng ng vi nhng im trn dng sng sin. Khi vc-t quay quanh bnh xe, dng sng sin c to ra. Mt vng quay ca vc-t xung quanh bnh xe dn ti mt...</p>