Nghiên cứu phương pháp cải thiện snr của các hệ đo vật lý

DAI HOC QUOC GIA HA NOI TRirClNG DAI HOC KHOA HOC TlT NHIEN NGHIEN CtJU PHl/ONG PHAP CAITHIEN SNR CUA CAC HE DO VAT LY MA SO: QT-07-59 CHl) TRi D £ TAI: PGS TS P H A M QUOC TRIEU DAI HOC Q U O C GIA HA NQI iRUNG TAV THQNG TIN THiJ VIEN nuLiiZi V ^ HA NOI - 2008 + Pham Qu6c Tridu, Nguyen Anh Due Nghien curu che tao he Lock-in so umg dung phep tin hieu nho b) Dao tao: 01 Thac sy - Hoc vien cao hoc: Nguyen Huu Lam - T6n Luan van cao hoc: Nghien cihi giai phap nang cao ty so S/N mot so he vat ly Nam bao ve: 2007 c) K^t qua ciia D^ tai duac s^ dung mot ph^n Bai giang: Pham Quoc Trieu - Phuomg phap thirc nghiem VM ly Dung cho sinh vi^n nam thu ba Khoa Val ly, Truong Dai hoc KHTN Tinh hmh su dung kinh phi 25.000.000 d {hai muai lam trieu dong) Tong kinh phi duac cap: Cdc khodn da chi Muc 114: Thu6 khoan chuy^n mon Muc 119: Vattu Quan ly phi va dong gop khac % 25.000.000 d {hai mum lam trieu dong) Tong cong: yJ^Q NHAN CUA BCN KHOA CHU TRI DE TAI / PGS TS Nguyen The Binh Pham Quoc Trieu XAC NHAN CUA NHA T R U I N G oc: DAI HOC x: i • • I KHOA HOC a NMfEN \ : ^ \ \ It- b) Training: 01 MSc ( Year to uphold thesis: 2007) - Name of Master Student: Nguyen Huu Lam - Title of Thesis: Study of the method to increase S/N in physical measurement systems c) The results of project have participated into the lecture; Pham Quoc Trieu - Experimental Methods in Physics MODAU Trong cac ht Ihu phat, he tin hieu vat ly, chat lugng ciia tin hieu la mot yeu cSu ra'l dugc quan tarn Sof di nhu vay la vi yeu cau quyel dinh den nhay, d6 chinh xac, tin cay, on dinh cua thiet hi Ddi vdi cac hang che tao may, chat lugng tin hi6u cang cao, gia may cang \dn De cai thien chat lugng cua tin hieu cac he thiet hi, nbidu phuong phap cai thien chat lugng linh kien, phuong phap ap dung nguyen ly phu hgp, phuong phap tang cucmg ty so tin hieu iren lap am Tren Ihuc le, khdng c6 tin hieu nao khong kem theo tap nhi6u Viec tang cudng tin hieu m6l each don gian dong ihdi lam tang cucmg tap nhilu, ket qua la la khong ihu dugc tin hieu ro ret hon Chi nao ta lam lang cucmg dugc tin hieu can thiet dong thai vdi viec lam suy giam vai tro cLia tap nbi^u kem theo tin hieu, liic chat lugng ciia tin hieu thuc su mdi dugc cai thien Noi each khac, chat lugng cua tin hieu dugc nang cao neu ly so tin hieu tren tap am (S/N) dugc nang cao D6 tai nghien cuii vi cac giai phap nang cao ty so S/N mot so phep vat ly, nghien cuu anh huang cua cac tap nhi^u len he va xii ly tin hieu vat ly, giiip cho viec lua chgn phuong phap va ihiel bi Ihuc nghiem hieu qua Ngi dung cua bao cao de tai dugc trinh b^y bon chuong: Chuong 1: Tin hieu Chuong 2: Mot so giai phap nang cao ty so S/N Chuong 3: Xii ly tin hieu qua dien dung ciia cac tarn sau ban dan DLTS Chuong 4: Nghien cihi xu ly nhi^u tren tin hieu pbd qua dien dung cac tam sau (DLTS) Ggi tin hieu cSn ihu lijr dai phat ihanh la Sg, ta c6 the bieu diln tin hidu Ihu dugc lai may thu S dang: S = So.A(t).B(/) ^ ^ Trong do: fO Oh ^ 6h re 6/7 - 24/1 A=i [l [1 le f = fo (May chi Ihu dugc tin hieu chinh / = /o) Nhu vay, nhd biet tru6c mot so thong tin ve tin hieu ma la thu dugc tin hi^u ro rang dam lap am L2 Tap nhi^u 1.2.1 Nhi^u Nhi6u la nhiing thang giang tCr ben ngoai anh hucmg vao he thu Khac vdi tin hieu, dac trung cua nhi6u ph^n Idn khong biet lru6c vi chiing la nhung thang giang, bien c6 ngSu nhien liir ben ngoai dua vao he ihu ciia ta (chang han nhu: nhilu cac dai phat song, cac thiet bi diing cong nghiep va sinh boat, nhi6u chdp, set quyen va cac buc xa tir vu tru ) Vi the, neu nhilu c6 dac trung giong tin hieu thi la khong biet dugc la nhilu Nhilu irucmg hgp khong phan biet dugc nen ngudi phai cha'p nhan nhilu la tin hieu Chi nao la biet dugc su khac giiJa tin hieu va nhilu thi mdi CO the lim each lach nhilu khoi tin hieu 1.2.2 Nhi^u phep thifc nghiem Xet mot he thu tin hieu ba'l ky: + Tin hieu nho la tin hieu ma cuomg ciia no tuong duong nhu cucfng cua nhilu va tap + Do Idn hay nho ciia tin hieu chi la luong doi Nhu vay, nhilu tin hieu chi c6 bien co vai chuc micro von cung dugc xem la 16n, irong c6 tin hieu co hang von cung bi xem la nho Va'n da la ch6 so sanh tuong quan giua tin hieu va tap nhilu Vi the, ta cung co the noi : + Tin hieu dugc ggi la nho cong suat tin hieu tuong duong vdi cong sua't ciia nhilu, tap + Thu tin hieu co dat chat lugng cao hay khong phii thugc vao cong sua't toi thieu ma ta thu dugc, khong bi Ian vdi tap nhilu 1.1.2 Dac trung cua tin hieu Thucmg thi ta biet irudc mgl so thong tin chu d6ng vl tin hieu: + Thong tin vl toa khong gian: Mot tin hieu co the dugc phat ti^ mot diem nao khong gian Ta CO the' du doan mot so thong so cua diem toa cSu nhu khoang each ( r ), cac goc ( (p,0) + Thong tin vl miln tan so cua tin hieu ( / ) + Thong tin vl thoi gian xay tin hieu (t) Vi dii: Mot dai phat co tan so song mang f^ nao Dai chi phat song ILT 6h sang den mia dem, nghi tieng Ggi tin hieu c^n Ihu iix dai phat la So, ta co the bieu diln tin hi6u thu dugc lai may Ihu S b dang: S = So.A(t).B(/) ^ ^ Trong do: ^ fO t€ Oh ^ 6h te 6h ^ 24// A=< \\ (May chi Ihu dugc tin hieu chinh f = fo) Nhu vay, nho bill irudc mot so thong tin vl tin hieu ma la thu dugc tin hi6u ro rang Irong dam lap am 7.2 Tap nhilu 1.2.1 Nhilu Nhilu la nhiJng thang giang tir ben ngoai anh hudng vao he thu Khac vdi tin hieu, dac inmg cua nhilu phan Idn kh6ng biet irudc vi chiing la nbOng thang giang, bien co ngSu nhi6n tijr ben ngoai dua vao he Ihu ciia ta (chang han nhu: nhilu cac dai phat song, cac thiet bi diing cong nghiep va sinh boat, nhilu chdp, set Irong quyen va cac buc xa lir vu Iru ) Vi the, neu nhilu cd dac trung gidng tin hieu thi ta khong biet dugc la nhilu Nhilu trudng hgp khong phan biet dugc nen ngudi phai chap nhan nhilu la tin hieu Chi nao ta biet dugc su khac giiia tin hieu va nhilu thi mdi cd the tim each lach nhilu khoi tin hieu 1.2.2 Nhilu phep thuc nghiem 4- Dai bg phan nhilu thudng cd dac Irung khdng biet irudc Tuy nhien, co mot vai loai nhilu la biet trudc qui lual, nguon gdc va phuong hudng Idi ciia no Viec xir ly tot he de' tranh cac loai nhilu cung bet sue quan trong, gdp phan nang cao ty so tin hieu (Signal) tren tap nhilu (Noise) ky hieu la: Cd the phan loai nhu sau : Nhieu dien : - Nhilu 50 Hz ( mang dien cong nghiep) - Nhilu v6 tuyen (song dien tir) nhu : dai phat thanh, truyin binh, bo dam, bg danh lua iCr ben ngoai lac dong den he Khi lam thuc nghiem , can de y phat bien mot so qui luat dac trung ctia nhilu de phong tranh XLT ly: Nhilu 50 Hz, can xir ly mach Igc that tot, each dien giira v6 may vdi xung quanh lot, noi da'l thai lot (neu khong dl bi phan lac dung: day dat co the trd anten thu song dien tir ciia moi trudng ben ngoai dua vao h6 thu) Xu ly cac loai sdng dien tCr bang each che chan bang cac long Faraday, bgc kirn, Igc tan, may cd lap nhilu tang triet nhilu bang cac tu dien dung nho (shoch killer), noi dat tot Nhieu quang : - Nhilu anh sang tu nhien - Nhilu anh sang nhan tao Xu ly : che chan anh sang tac dong vao be bang cac Idp giay, man vai mau l6i - 5- Nhiiu ca: • Nhilu nhOng rung ddng ndi lai va ben ngoai anh hudng ddh ket qua Vi du : Cac thiel bi quang hgc chinh xac khong nen dai b tr6n tang cao vi bi anh hucmg ciia rung dong co hgc manh Xtr 15^: Sir dung day treo dan h6i, lAiSn each biei lap, dat thie'l bi IrSn de' nang Nhiiu moi trudng - anh hudng ciia khong khi quang (khdi ihudc, bui ) - anh hudng ciia nhi6t do, dd ^m Irong he quang, dien Xix ly: giu mdi trudng d dilu ki&i tuong dol on dinh (dd sach, nhiel do, dd &i ) 1,2.3 Tap ngi Tap ngi dugc gay bdi cac bien tugng thang giang ciia cac qua trinh vat ly x^y d ben irong ban than cac linh kien Loai tap khd khac phuc vi nd xua'l phat tir tinh chat ciia vat lieu va linh ki6n Tuy nhien ngudi la cd the han che anh hudng ciia nd n6'u biet dac linh va nguyen nhan gay nd Dua vao nguon gdc gay lap, den ngudi la da phat hien dugc tren 10 loai lap ngi khac nhu: tap nhiel (thermal noise), tap nd (short noise), tap 1/f hay ggi la tap nha'p nhay (flicker noise), lap phat sinh - tai hgp (generation ~ recombination noise), tap bap bung (burst noise), tap ihac lu (avanlanche noise), tap cam ling (induced noise), lap phan chia (partition noise), lap phai xa Ihur ca'p (secondary emission noise), tap du gay cac kich Ihich xoay chilu (excess noise due to a.c excitation), lap hiil - nha (absorption - desortion noise) Tuy Ihugc vao ban cha'l ciia val lieu, cau tnic, cong nghe che tao va nguyen ly boat dong ciia linh 6- kien ma mdi loai vat lieu, linh kien thudng chi cd mgl so loai tap lieu bilu nhft dinh noi irgi Van dl dat de cd the Ihu dugc tin hieu can ta phai tang ty so tin hieu tren tap nhilu (S/N) bang dudng, tang tin hieu hoac giam lap nhilu Trong nhilu irudng hgp van dl giam lap nhilu cd y nghia bet siic quan Irgng Sau day la mot so nhimg phan tich cac lap nhieu 1.2.4 Phan loai mot so tap noi cac linh kien cam bien Theo A.Van Der Ziel thi tat ca cac dai lugng dac trung cua mdi loai v|t lieu hoac linh kien diu thang giang mot each ngSu nhien xung quanh gia tri tmng binh (ngay ca trudng hgp can bang nhiet) va su thang giang ngSu nhien dugc ggi la tap ngi Theo linh chat cua nd, loai lap dugc mgl so tac gia ggi la nhilu thang giang ngi tai bay ggi la nhilu ngi vi nd xay b^n ban than v$t lieu va linh kien - Tap nhiet (thermal noise) Nguon gdc tap nhiel la chuyen dong Brown ciia cac bat lai dien htn vat dan gay nen d mgl nhiet dd nha'l dinh mat ph6 ciia dien ap lap nhidt dugc xac dinh bang bieu Ihiic: 5'^(f) = 4kTR (1.1) Trong dd k = 3,18.10 "J/K la hang so Bollzmann, T la nhiet dd tuyet ddi, R la dien trd cua vat din Tap nhiet la nguon lap pbd bien nha'l cac linh kien va thie'l bi dien tir - Tap nd (shot noise) thdng ke ;c bang thong ke p(e) 93 phd phat xa Nd cung cd the' dugc sir dung tdl Irong cac phuong phap tuong quan dua tren phan lich Laplace [Provencher, 1982; Dobaczewski & Peaker, 1997] do nhay ciia cac phuong phap phu thudc qua nhilu vao nhilu Viec tach biet dugc nhilu khoi tin hieu la budc diu lien dd tien ldi xay dung he cd d6 nhay cao hoat ddng dugc mdi trudng nhilu loan vk thang giang ldn thudng xuit hien irong vai ly ban din cac Unh kien dien tir 94 K ^ T LUAN Sau thai gian thuc hien de tdi, chung toi dd nghien cuu vd thu duac mot sdket qua cu the nhu sau: Nghien ciiu idng quan khai niem tin hieu nhd, vai trd ciia tin hieu, lap nhilu va ly sd S/N mot sd he tin hieu vat ly Nghien ciiu cac giai phap nang cao ly sd S/N Tuy theo irudng hgp cu the, cd Ihe sir dung cac giai phap khac nham lang cudng tin hieu, giam ihieu lap nhilu hoac lach tin hieu khdi nln lap am Cac giai phap dugc dua nhu: Triing phung, Vi sai, Dilu bie'n, Ma hoa, Loc tan, Boxcar, Lock-in Phan lich phuong phap xir ly tin hieu DLTS dimg Boxcar kep de nang lugng kich hoal lam sau ban din Tin hieu DLTS thudng bao gdm anh hudng cua lap nhilu nhu tap du, tap phat sinh tai hgp, nhilu trang Viec lua chon cac cdng Boxcar thich hgp phin nao giam thieu vai trd tap nhilu xir ly tin hieu DLTS Nghien ciiu phuong phap loai irur nhilu tr^ng tren tin hieu DLTS dang luy Ihufa Phuong phap dua iren su khac biel cd tinh thdng ke giira tin hieu va tap am Tren co sd ly thuye'l, chu trinh lu ddng lach lgc nhilu khdi tin hieu da dugc trinh bay Kel qua md phdng cho thay su lach tinh te hai tam sau cd nang lugng kich hoat gin tren nln nhilu ty sd S/N - 10 Sir dung Ihich hgp giai phap thuc nghiem se cho phep he vat ly dat chat lugng cao nha'l ve phuong dien S/N Chung toi mong mudn co dieu kien tiep tuc nghien cuu cdc van de a miic sau han, vi du nhu nghien cUu xu ly sd tin hieu sU dung phuang phdp mc) phong tren may vi tinh nham muc tien loai trit tap nhieu, tdng cudng tv sd SIN cho cdc he 95 Tai lieu tham khao Tdi lieu tieng Viet: Tong Van On (2002), Ly thuyet vd bdi tap xu ly tin hieu so, Nha xuat ban Lao dong - Xa hoi Ho Van Sung (2003), Xu ly tin hieu s6 (su dung matlab), Nha xuat ban Giao due Pham Quoc Trieu (1994), Nghien cuu xay dung he tu dong cdc dai luang phu thuoc nhiet vat ly chat ran va icng dung, Luan an PTS Khoa hoc Toan Ly Pham Quoc Trieu, Phuang phdp thuc nghiem vat ly, Bai giang day tai khoa Vat ly Trudng Dai hoc Khoa hoc Tu nhien - Ha noi Nguyen Quoc Trung (1998), Xu ly tin hieu va loc s6, Nha xuat ban khoa hoc va ky thuat Tdi lieu tieng Anh: Coly L Crark (2005), Labview Digital Processing and Digital Communications, McGraw-Hill Publisher M.L Meade (1983), Lock-in amplifiers: Principles and Applications, Peter Peregrinus Ltd., London UK Monson H Hayes, Schaum's Outline of Theory and Problems of Digital Signal Processing, Mcgraw-Hill 1999 Narsser Kehtamavaz and Namjin Kim University of Texas at Dallas (2005), Digital signal processing system-level design using labview, ELSEVIER Publisher 10 T.S Rathore, Digital Measurement Techniques, Alpha S.I, UK, 2007 11 M.A Pai and others, Small Signal Analysis of Power systems, Narosa, New Delhi, 2007 12 S.V Narasimhan, Signal Processing (principle and implimentation) Harrow, UK, 2005 V ^ DAI HOC QUOC GIA HA NOI TRirdNG DAI HOC KHOA HOC TlT NHIEN Nguyln Huru Lam NGHIEN Ciru GIAI PHAP NANG CAO TY SO S/N TRONG MOT SO HE DO VAT LY Chuyen nganh: Vat ly v6 tuyen Ma so: 1.02.05 LUAN VAN THAC SI KHOA HOC Ngudi hirdmg d^n: PGS TS Pham Quoc Trieu HA NOI - Nam 2007 NGHIEN Ciru CHE TAO HE LOCK-IN SO ITNG DVNG TRONG PHEP DO TIN HIEU NHO Pham Quoc Trifu, Nguyen Anh Due Khoa Vgtly, Truong DHKHTN, DHQGHN T6in tat: Trong bai bao nay, cdc tdc gia nghien cuu xay dung he khuich dai Lock-in s6 SIC dung may tinh, toan bo thuat toan duac thuc hi$n bdngphdn mim H^ khuich dgi chi cdn mdt card thu thap du lieu (DAQ) thong thu&ng hoac co thi su dung card dm chat lucmg cao cua mdy tinh, mot bo tien khuich dgi tap nhiiu thdp co thi thay ddi he s6 khuech dgi Cdc ket qua thuc nghiem khao sat thi ldi theo tdn s6, pha vd tap nhiiu da chung to he co khd ndng loai trie tgp nhieu tot, co the ung dung mot s6 phep tin hieu nho, gid thdp, dac biet coy nghia dao tgo chuyen ngdnh LMdDAU Trong thuc te, phep tin hieu nho la mot phep tinh te nhung thudng gap r4t nhidu kho khan He chiu anh hudng bdi trang thai cua he, cac trang thai lai thay doi theo nhiet do, thdi gian, moi trudng dan den sir bat on djnh ciia ket qua Tin hieu nho la khai niem tuong doi, dugc danh gia thong qua ty so tin hieu tren tap nhieu (SNR) Cac loai nhilu thong thucmg nhu nhieu 50/60 Hz ciia mang dien ludi, nhieu 1/f ciia tang tien khuech dai, nhilu nhiet va dong ro cua sensor hoac su ket hgp cua cac loai nhieu tren luon luon ton tai doi vdi cac he [5] Khuech dai Lock-in sir dung ky thuat phat hien nhay pha PSD (phase-sensitive detection), chi giir lai nhiing phan tin hieu co ciing tan so vdi tin hieu chuan, nhung phan tan so khac vdi tan so tin hieu chuan se bi loai nen khong anh hudng gi den phep Mot bo phat hien nhay pha PSD khong nhung co tac dong vdi bien tin hieu cimg tan so vdi tin hieu chuan ma nhay vdi sir sai khac pha giira tin hieu va tin hieu chuan Vi the nen mot he thong dua tren hoat dong cua bo PSD co the dugc bien va pha cua tin hieu tuan hoan ca co su hien dien ciia nhieu Cac he thdng dua tren nguyen ly hoat dong cua bo PSD dugc goi la cac he Lock-in Nlu cac he khuech dai co sir dung nguyen ly hoat dong cua bo PSD thi dugc goi la khuech dai Lock-in [Ij NGHIEN c u t ] XAY DlTNG HE Khuich dai Lock-in dugc goi la khuich dai Lock-in s6 (Digital or DSP Lock-ir Amplifier) nlu bo phat hien nhay pha (phase-sensitive detector) ciia no dugc thuc hien bSng kj thuat s6 Khuich dai Lock-in co thi chia hai loai: khuich dai Lock-in sir dung mot bo pha hien nhay pha PSD, goi la khuich dai don pha (Single-phase Lock-in) va khuech dai Lock-in sij dung hai bo phat hien nhay pha, goi la khuech dai Lock-in hai pha (Two-phase Lock-in) [6] Voi bo khuech dai Lock-in don pha thi chung ta phai dieu chinh pha cua tin hieu chuar ciing pha voi tin hieu Khi bien tin hieu loi la cue dai va chinh la bien tin hiei] can Neu pha ciia tin hieu va tin hieu chuan lech thi bien dp loi giam Nhu vay de thuc hien phep voi khuech dai loai chung ta can co khoi dieu chinh pha ciia tin hieu chuan (quay pha) Doi voi bp khuech dai Lock-in hai pha thi bien dp loi cua tin hieu can khong phu thuoc vao dp lech pha giua tin hieu va tin hieu chuan Hon the nira, ta co the dugc dp lech pha giua lin hieu va tin hieu chuan [2] + Nguyen ly lam viec: Nguyen tac lam viec cua khuech dai Lock-in dua tren ky thuat tach song nhay pha PSD (Phasesensitive detection) Nguyen ly hoat dong cua bp PSD nhu sau: Reference Khuech dai Lock-in can phai co mot tin hieu chuan Thong thuong thi he thi nghiem se dugc kich thich a mot tan so co dinh (tir bp phat dao dong hoac may phat chirc nang) va khuech dai Lock-in se hoat ^ref dong tai dung tan so Trong gian duoi day, tin Lock-in Reference hieu chuan la song co dang xung vuong tan so cOrHinh 1- Gian song Tin hieu co the lay tir loi dong bp ciia may phat chuc nang Neu dimg tin hieu sine tir may phat chuc nang dl kich thich thi nghiem thi ta co the thu dugc tin hieu loi co dang nhu tren hinh Tin hieu co dang nhu sau [3]: Vs,gSin((Ort + 9s,g) Vsjg la dp Ion tin hieu Tin hieu chuan Lock-in co dang: VLSin((OLt + Gref) Tin hieu sau khuech dai se dirge nhan vai tin hieu chuAn Lock-in b4ng mot bp phat hien nhay pha (PSD) hoac mot bp nhan Tin hieu a I5i cua bp PSD co dang: Vpsd ^ Vs.gsin(a)rt + 0s.g) * VLsin(coLt + Gref) - B i —([COr - COjt + Os.g - Gref) - l/2Vsig VLCOS([C0r+ COLJI + Gsig+ G^f) Tin hi^u 161 sau PSD la cdc tin hieu AC bao gdm hai phJin tin s6: (cOp - COL) va (wr + COL) N^U dua tin hifiu vky qua bo loc tAn thip thi se loai dugc cac phan tin hieu AC Nhung nlu ©r = COL thi phSn thu nhit cua Vpsd tro tin hifu mpt chilu DC Trong trudng hgp tin hi$u loi sg c6 dang: Ta thay thi ldi cua bg PSD ty le thuan voi Vsjg cosG, G = Gsig - Gref la s\r sai khic pha gito tin hieu va tin hi^u chuSn lock-in (lock-in refference) BSng each dilu chinh Gref dl = 0, ta co thi Vsig (cosG = 1) Ngugc lai nlu G = 90° thi thi loi se bing khong Bg khuech dai Lock-in don pha (Single-phase lock-in) cho thi loi ra: psd[ K,//Cos(6')^K,^ 008(19) Nhu vay voi bg khuech dai don pha thi the loi phu thugc vao dp lech pha giua tin hi^u va tin hieu chuan Mu6n loai bo dugc sir phu thuoc pha chiing ta phai sir dung them mot bo PSD nUa CJ bg PSD thu hai tin hieu se dugc nhan voi tin hieu chuan da dich pha di nl2: VL = VLSin(C0Lt + 9ref+7r/2) Khi the loidangjcos dang: ^ =^n„f^.cos(^ -^./-^/2) Bay gia he se co hai l6i ra, I5i thir nhat cho the ty le thuan voi cosG loi thir hai cho thi ty le thuan voi sinG NIU gpi X la 16i thir nhat va Y la loi thir hai ta c6: X^V^,gCOS0 Hai dai lugng tren dai dien cho tin hieu va co lien quan den tin hieu chuan Lock-in X dugc gpi la phan ddng pha (in-phase) va Y dugc ggi la phdn pha vuong goc (quadrature) Khi G = 0, X dat gia tri cue dai Y = Binh phuang hai bilu thirc ciia X va Y r6i cong vai ta co: R = ^X'+Y' =V^^^ R chinh la bien dp ciia tin hieu Nhu vay ta se dugc bien dp ciia tin hieu ma khong phit thuoc va dp lech pha giira tin hieu va tin hieu chuan i Dp lech pha giixa tin hieu va tin hieu chuan Lock-in dugc tinh theo cong thiic: fY\ = arctan — + Thiet ke, xay dung he: Tren co so nguyen ly noi tren, chung toi da khao sat va xay dung he khuech dai Lock-in hai pha so Tat ca cac thuat toan dugc thuc hien bang may tinh dua tren ngon ngij lap trinh Labview So khoi cua khuech dai Lock-in hai pha dugc bieu dien tren hinh Hinh la giao dien ciia chuong trinh Tin hieu can (1) tir he thi nghiem dugc dua toi tang tien khuech dai (2) ta phai chon he so khuech dai phii hgp de tin hieu loi phii hgp voi dai bien doi ADC Tin hieu so tir bp bien doi ADC dugc dua toi hai bp nhan Tai bp nhan (5) tin hieu dugc nhan vai tin hieu chuan sin(a)rt + Gr), tai bp nhan (6) tin hieu dugc nhan vai tin hieu chuan sin(cort + Gr +7i/2) Tin hieu loi ciia cac bp nhan dugc dua qua cac bp Ipc tan thap Bp loc tin thap sS loai bo nhung phan xoay chieu va cho qua nhimg phan mot chieu DC Sau bp Ipc (7) ta thu dugc phan ciing pha sau bp loc (8) ta thu dugc phan vuong pha Hai phan ciing pha va vuong pha dugc dua qua khoi tinh toan (9), cr loi ta thu dugc bien dp tin hieu va dp lech pha Bien dp co the la bien dp cue dai Vo hoac la the hieu dung (Vrms) dp lech pha co the tinh theo radian hoac degree Tm hieu V.SirK.^U'O.) (1) Tang ticn KhuL-i-h Jii (2)T^ (7) -^ (5) X V- X V.Mri(0.-fl,) I iltei ( ) I Sin((,Hi R-[X- • V)' Ket (9) I'LL (4) I Sm(.^t'0rTi2) (6) 4.-tan'(Y/X) (8) Low-pass niter Y - V^os(0.-O,j Hinh - Sa khoi khuech dai Lock-in Dual-phase Hinh - Giao dien chucmg trinh KET QUA THUC NGHIEM + Khao sat sir phu thuoc cua the m9t chieu loi cua bQ PSD vao lech pha giua tin hieu va tin hieu chuan (Gs-Gr): -—-^ , ,,- r— ^hieu va tin hieu chuan (Gg-Gr), tiln hanh thi mot chilu l6i sau bp PSD thir nhat (X = VsSin(Gs-Gr)) chiing toi thu dugc sir phu thuoc cua thi mot chilu loi X vao dp lech pha co dang nhu hinh Tuong tu thay ddi dp lech pha giira tin hieu va tin hieu chuin (Gs-Gr), tiln hanh thi mot chilu ldi sau bp PSD thii hai (Y = VsCos(Gs-Gr)) chiing toi thu dugc sir phu thugc ciia thi mot chilu I6i Y vao dp lech pha co dang nhu hinh -1.00Oja 10.0 20.0 30D 40.0 SO^ 60.0 70J0 BOi) 95.0 D$ Ifch pha (degree) Hinh 4- X=- V,sin(Os-er) 0.0 lOJO 2DX} 30.0 40.0 50.0 60i) 70i) BOJ) l>9 l ^ b phu (def;re«) Hinh 5- Y= V^osOs-Or) + Khao sat sir phu thuoc the mot chieu loi cua b9 PSD vao tan so tin hieu; Dat tin hieu chuan co tan so IkHz Dat bien dp tin hieu VQ = IV Thay d6i tin s6 tin hieu tir khoang 980 Hz din 1020 Hz, thi mot chieu loi sau bp PSD tuong img, chiing toi thu dugc thj su phu thuoc ciia the mot chieu loi (R) ciia bp PSD vao tan so co dang nhu hinh Dua vao thi ta thay the loi se dat gia tri cue dai tan so tin hieu diing bang tan so tin hieu chuin (1000 Hz) Ngoai a cac tin s6 khac ta thiy ^ « ^ ^ Lhe ldi theo tdn sd CO cac hoa ba nhung co bien dp be Mot dieu quan doi vai khuech dai Lock-in la chi tan so tin hieu bang tan so tin hieu chuan thi phan tin hieu moi dugc khuech dai, nhimg ^hanh phan tin so khac co the la cac phan nhieu se bi suy hao Tom lai khuech dai Lock-in |c6 kha nang loai nhilu khac tan so rat cao + Khao sat sir phu thuoc cua bien dQ va dg Ifch pha loi theo Ion cua nhieu: Dat may phat chiic nang phat tan so chuan voi tan so I kHz, bien dp cue dai Vf = I V Tin hieu can co ciing tan so, lech pha (p so vai tin hieu chuan Dp Ion tin hieu can khong co nhieu la Vs = 0.495 V Hinh - Tin hieu cong nhieu (do l&n nhieu cue dgi 2.5 V) Sau trpn tin hieu va nhilu (white noise), voi bien dp cue dai cua nhieu la 2.5 V, chiin toi thu dugc tin hieu dang nhu hinh Tilp tuc khao sat su phu thuoc nay, chiing toi Iron nhieu vai tin hieu theo each tang di dp Ian ciia nhieu, ghi the mot chieu loi va thu dugc ket qua nhu tren hinh 60.0- 0.600 0.550- 55ili,1 0.500^ "1 * ^0.400- 10.350; J 0.300; ^0-250ô 0.200- - ã- - - ã - • - -1- t- + + "t f 50.0: Phase (degree) 0.450- -f- 45il: 40JD- 35.0^ 30il: 25i): 0.150204)^ 0.100- 15J0- 0.050ODOO00 D.5 i— 1.0 1.5 2.0 2.5 3.0 NCNse (V) 3.5 A-0 4.5 5.0 Hinh - Sir phu thuoc the mot chieu loi vao l&n cua nhieu 10.0 0.0 o!5 1.0 1.5 2.0 2.5 3.0 Notse(V) 3.5 4^0 4.5 5.0 Hinh - Sit phu thuoc cua lech pha vao l&n cua nhieu hinh ta thay bien dp cue dai ciia nhilu len den 5V nhung thi mpt chilu loi hai nhu khong doi, dat gia tri xung quanh Vj == 0.495 V Tuong tu tang bien dp nhieu chung toi thu dugc su phu thuoc ciia dp lech pha vao d( \an ciia nhieu c6 dang nhu hinh Bang each lay gia tri trung binh cac diem do, ta se thu dugc bien dp va dp lech pha mp each chinh xac hem KET LUAN He khuech dai Lock-in so hai pha (two-phase lock-in amplifier) chung toi xay dung ci gia thap (vi chi sir dung mot may tinh, card ghep nli hoac co thi sir dung luon card ar bp tien khuech dai), dl dang thuc hien dieu kien phong thi nghiem Chuc nang hoa dong cua thiet bi linh hoat, co thi ap dung cho cac he tin hieu c6 ty s6 S/N rit nh6 Chung t CO thi thay ddi cac thong so thilt kl ciing nhu hinh thuc thi hien d l he phii hgp vai cac tli nghiem khac Du lieu dugc thu thap va xir ly rit thuan tien, co thi lim trii tren dla cim^ Mot img dung quan trpng khac la sir dung he nhu mot cong cu giang day He sir dung ngon ngi lap trinh Labview (ngon ngu lap trinh dang hinh tugng) nen de dang kilm tra, khao sat dang ti: hieu tai bat ky mot khoi nao giiip nguoi sir dung de dang hinh dung va nim vijng nguyen tic lar viec cua bo khuech dai Lock-in so Cong trinh dugc hodn fhdnh khuon kho de tdi cap DHQGHN md so QT-07-59 Tai lieu tham khao M.L Meade (1983), Lock-in amplifiers: Principles and Applications, Peter Peregrinus Ltd., London UK LlA-150 Dual Phase Lock-in Amplifier (1999), Becker & Hickl GmbH Nahmitzer Damm Berlin MODEL SR830 DSP Lock-In Amplifier (R2.2 2005), Stanford Research Systems Inc NI Lock-in Amplifier Start-Up Kit User Manual (8-2002), National Instruments Philip Kromer, Ralph Robinett, Roger Bengtson, Charles Hays Department of Physics, University of Texas at Austin, PC-Based Digital Lock-In Detection of Small Signals in the Presence of Noise The Digital Lock-in Amplifier Technical Note TNI003, PerkinElmer Instruments Inc 2000 UTiLIA: A PC-Based Lock-in Amplifier (Using Labview), At http://mrflip.com/papers/LlA^ Coly L Crark (2005), Labview Digital Processing and Digital Communications, McGrawHill Publisher Labview Measurement Manual (2000 Edition), National Instruments Corporation Part Number 322661A-01 PHIEU D A N G KY KET QUA NGHIEN CLfU KH-CN Ten d^ tai; Nghien cuu phuong phap cai thien SNR cua cac he vat ly Mas6: QT-07-59 Co quan chu tri di tai: Dia chi: Telephone; Truomg Dai hoc Khoa hoc Tu nhien Dai hpc QuO'c gia Ha Npi 334 Nguyen Trai, Thanh Xu^n, Ha N6i 858-5277 Co quan quan ly 66 tai: Dia chi; Telephone; Dai hoc Quoc gia Ha Noi 144 Ducmg Xuan Thiiy, Ciu Gia'y, Ha Noi 04-8340569 long kinh phi thuc chi: 25.000.000 (hai muoi lam trieu dong) Trong do: - Tir ngan sach nha nuac : 25.000.000 d - Kinh phi nha truong ; khong - Vay tin dung ; khong - VO'n tu CO : khOng - V6'n thu h6i : khong Thcfi gian nghidn cihi: 12 thang Thcfi gian bat d^u: 1/2007 Thdi gian ke't thiic; 1/2008 Ten can bp phoi hgp nghien cuu: ThS Nguyen Huu Lam ThS Nguyen Anh Due SO' dang ky de tai Ngay: S6 chimg nhan dang ky ket qua nghien cim Bao mat: a) Ph6 biefn rOng rai b) Pho bie'n han che c) Bao mat T o m t^t k^'t q u a nghien cdru: - N g h i e n cihi 1^ thuyet t6ng quan v^ ti s6' tin hieu tren tap a m - D a d l xuflft m d t s p h u o n g p h a p nang c a o S N R h e d o vat ly - Nghien cihi xir ly tach nhieu trang khoi tin hieu DLTS nghien cuu vat ly ban din, nang cao kha nang phan giai cac tam sau - D a CO bai b a o giii dang T a p c h i Khoa hpc D H Q G H N - D a h u d n g d i n m d t luan van Thac si K h o a hpc ciia hoc vien N g u y e n H u u L a m bao ve thang 12/2007 Ki^'n nghi: - Di nghi d u g c tie'p tuc nghien cim d m u c dO c a o hon C h u n h i e m d e tai Ho ten Hpc h a m Hoc vi Pham Qu6'c Trieu Thu truong co quan chu tri de tai Chu tich hoi dong danh gia chinh thurc ji^mM^ld-i^ i\%iM^T(i( (iS.U^tl p^s.n Thu truong co quan quan ly de tai ^1^-^ TL.G'Ar/, BANKhDA DC-CONG NGHE f!{li H J/MUHf-^n :iy^lfi 4i