46
Tin hieu qua do tai cac nhiet do khac nhau
M i i e t do
Hirih 3. 6 - Ciia so t o e do v a pho TLTS tiiong urig.
Ky t h u a t ELTS da b i e n tiiong quan 3 c h i e u C ( t , T) tharih tiiong quan 2
chieii R(T) de eo t h i de dang do dae xii l y t r e n h i dọ
'Rjilc c h a t eua qua t r i n h thiic nghiem l a cho rihiet do cua mau t h a y
doi v a dirih trxioc eno ^ b ^ i g cac v i t r i t j , t 2 o Boxcar). Dirih ciic d a i
cua pho IM^TS cho t a xac d i n h diioe rihiet do Tno* Tut (5.5) eo:
2
eno= ATno exp(E>r/KTno) (3. 14) L 5 P l a i phep do v o l eni» l a i xac dirih dlioc Tni . Khi do :
-47-
Tai Ian do trai i t a cung xac dirih diiac êj. va T ^ va cung co
a
eni= ATni exptBp/KTmJ (3. 16) Co t h e Viet (3. 16) duai dang:
2
L n ( e n i / T n i ) = Ln A + Bp/KTni (3. 17)
Bang cap g i a t r i e m i Tm xac dirih diioc tii phep do , co t h e l a p do
2 - - - - ,
-ní -^ni
thi Ln(eni/Tni ) ham theo (l/KT^) voi cac gia tri Khac nhau cua eni ( thiic te thiiong phai do vol i >=4 ). Diiong bieu dien se la mot diong thang ma do doc bieu dien nang liiong ion hoa Bp, diem ciiong thang cat true tung eho thong tin ve tiet dien bat hat taị
Nong do cac tam c6 t h e t i n h diioc t r u e t i e p tii sii t h a y doi d i e n dung ling v d i sii l a p day hoan t o a n cac tam bang xung t i e m bao hoa ( o t n i o n g hop tam h a t t a i Khong co ban) h a y bang xung h a t t a i co ban rong n h i t eo t h e co diioc (tniong hop tam h a t t a i co ban).
Thi du v o l cau t r u e N -P , b i e u thiic nong do t i m b a t d i e n tii r a t don g i a n [63, 6 8 ] :
^.
NT = 2 (NA - Nr,) (3. 16)
C
O day : N^- % l a nong do a c c e p t o r tong cong a p h i a P eua t i e p
g i a p ( n o i t a quan s a t cac tam s a u ) .
C - d i e n dung cua d i o t o d i e u Kien p h i n ciic ngiioc tirih. ^ - sii t h a y doi d i e n dung t a i t = 0 gay boi xung t i e m bao h o a Hinh 3. 7 mirih h o a phep do DLTS v a i 5 eiia so t o e do Khac rihau v a e a c h xac d i n h nang liiong i o n hoa cua tam saụ
46 -
Nhiet d6 1/kT
Hirih 3. 7 - Rio IX-TS va e a c h xac dirih EJp.
S a i só cua cac thong so xac dirih bang phiiong phap IXTS thiiong Khong qua lOX . Mot d i i u dang liiu y cua phiiong phap nay l a can xac
d i n h v i t r i dirih cua t i n h i e u ( de b i e t T^QX* " ^ Khong e i n quan tam d a i b i i n <^ cua t i n h i e u . Vi t h e hang so t n i y e n t r e n h e d i e n tii Khong h e arih hiiong den phep do [49].
Nhin x e t : Bang v i i c d a t cac ciia só t l . t 2 (thiic c h a t l a dkt t n i o c
e n ) , ptiep do da chuyen quan h i h a i b i e n so C ( t , T ) sang quan h e n o t b i e n so A C ( T ) n o t each t i i dong. Phep do rihii v i y co t h e x i y diing diioc t r e n h e analog dung tut ghị
- 49 -
2. 2. So do cac khoi cJnic nang.
Dlia t r e n nguyin l y do DLTS dung cong Boxcar Kep, chung t o i da
t h i e t Ke va lap r a p h e do voi cac Khoi cfnic nang dutoe rihii hirih dutoi :
Phat (1) 5,6 MHz i Cau 0D(2) 1 1 L —*" QP(4) KDLL (5) — > > Voltke r y TH{6) Chuan 1 TSNP C7) — J •1 r- Đky KV,(9) KO (8) B • _ A B • ' -^ f z ^V2 Y X TL/ ghi -f Hirih 3. 8
So do cac Khoi chute nang cua he do dien dung
DLTS.
Neu c h i su! dung cac Khoi tut (1) den (9), t a eo h e do d i i n dung riho, c h i t h i bang dong ho n ^ t c h i e u [22]. Diy thiic c h a t l a mot c i u do d i e n dung t i i l a p t r o n g d i e u Kien Khong eo may cong nghlep. Neu sii dung t o a n bo cac Khoi t r e n Hirih 3. 8, t a s e c6 h i do d i e n dung DLTS dung Ky t h u i t xii l y t i c h p h i n Boxcar Kep.
Qiutc nang hoat d ^ i g cua cac Khoi nhii sau:
Khoi p h a t t i n h i i u hirih s i n cao tan ( l ) lam v i i c o t a n só 5 , 6
MHz. Macih p h a t dung bo dao dong t h a c h arih v o i cae cong NAND ciia v i mach SN7400 [7]. Sau Khi qua cac t a n g loc liia, t i n h i e u hirih s i n 5, 6MHz dutoe dlia vao cau (2) v a Khói quay pha (4). Khoi cau d i i n dung (2) dlioc mo t a t r e n Hirih 3. 9. Cau gom 4 riharih. t r o n g do h a i riharih l a
- 50 -
h a i d i e n t r o Rj, R2. n » t rihanh l a d i e n dung t h a y doi {gom CQ va C mac
song song), n o t riharih l a mau do ( d i o t ) . Cau diioc n u o i b o i dao dong t ^ so 5, 6 MHz t a i h a i d i a n E, F riho b i e n t h e cao t a n Diem H l a diem
l^y t i n h i i u r a (so v o i Q). Tren cau con mac h a i t u ngan each h a i
d i a n G v a H ve phiiong d i e n not c h i e u rihiing ve phiiong d i e n xoay c h i e u
Chung v m thong mach. Hai t u nay cho phep thiic h i i n t r e n mau do cae d i e n ap p h i n ciic ngiioc v a xung Kich mau Kieu g a l v a n i c .
+ 10V J l C I €n U H: D l C H R2 5,6 M & Hirih 3 . 9 c i u do d i i n dung Ra Co
Mau do dlioc d a t t r o n g birih chiic mau (Dewar) co t h e h a rihiit do
•». A - )
xuong toi 77 K, co ciia so quang de dung arih sang Kich thich mau neu ein. Cung mot luc, mau do c6 the chiu rihieu tac dong cua:
- Dong cao tin 5, 6 MHz.
- Dien ap p h i n ciic ngiioc (thay doi dbiqc tut 0-10 V do R Hirih 3, 9) - Xung d i e n ap p h i n cute ngiioc tren d i e n tii r (tut bo Boxcar diia
t o i ) . Xung nay co b i e n do t h a y d o i ciioc tut 0-5V v a t a n só l a p l a i tuC 10C«z-20KHz. Dien t r o r l a d i i n t r o r a t riho (r=15S2), co t h e bo qua so v o l d i i n t r o ngiioc cua mau, song no c6 t a c dung bom xung p h i n cute ngiioc Kieh t h i c h mau dọ
-51-
Khoi Khuech dai loc lua (KDLL) (5) (Hirih 3. 6j diioc xay dung bang Vl mach SC2929 [41.53] va cae Khung cong Prolong o tan so 5, 6HHz, dam bao cho do tniyen qua cua ea Khoi dat 0, 5 MHz. Khoi nay co nriiem vu
loc ra duong qua do dien dung (dutong bao bien do) tu song cao tin (song mang J. Dac diem ciia Khoi TSNP la duoc dieu chinh sao cho rihay rihat vol bien doi tren cau gay ra do thanh phan dien dung va "tro" vai bien doi do thanh phan dien trọ
Chinh vi dieu nay na bo quay pha (4) tnioc Khoi tin hieu chuan giu vai tro rat quan trong trong giaa doan tien xut ly cua he dọ
Do trung thiic ciia diiong qua do thu diioc sau Khoi TSNP diioc quyet dinh bai do don sac cua tin hieu cao tin hinh sin 5, 6 MHz.
Khoi (8) tren Hirih 3. 6 la Khoi Khuech dai mot chieu eo loi dula ra dong ho chi thi mot chieu (9). Tai day ta co the quan sat duoc sii thay doi gia tri tuyet doi eua dien dung mau do theo cac tac rihan ben ngoaị Dang song cao tan dieu bien co the quan sat dutoe riha oscilloscope (0G2-23 tren Hirih 3. 8). Gia tri rihiet do cua mau do diiac c[uan sat tren von Ke hien so 4014a Cac dang song tai mot so diem Test dlioc mo ta tren Hirih 3. 11.
Khoi Boxcar tren Hirih 3. 6 la bo xii ly tin hieu hai cong, dilqc lap rap tu: cac lirih Kien roi rac. Khoi c6 ba ioi A, B, C trong do iói A
la lói phat xung phan ettc mau do trong Khoi cau do diin dung. Loi B la lói nhin tin hieu qua do diin dung sau Khoi Khuech daị Loi C la lói ra tii ghi, sau qua trinh xii ly tin hieu tii dong tai hai thai diem dat san. So do Khoi cua bo Boxcar Kep diiac tririh bay tren Hirih 3. 10. Nguyen tac hoat dong cua bo Boxcar rihu: sau:
52 ~» Xung nhip Xung t l Xung t2 > —e— J ' Tao xung 1 C6ng1 r~ Cong 2 > ) s KD CS KO KD B —^ A '—> Tien KD KDVS y-^ 1 n'l'l i 1 1 : \ S ( t 2 ) L o i A L o i r a Sau TSNP Khoa 1&2
Hirih 3. 10. Cae Khoi cua Boxcar Hirih 3. 11. Cac dang song t h u rihan
Tut Khoi p h a t xung rihip dung IC555, xung dao dong diioc diia sang bo t a o dang xung Kich t h i c h m^ụ Tai day, xung dao dong diioc qua Khoi Khuyech d a i cong s u a t de diia sang c i u do ( l o i A), dong t h o i xung n a y
dilqc dlia d i n cac Khoi t a o xung ma cong t j , t g . Cac Khoi t a o xung cong
sii dung IC74123 l a cac bo don h a i Kep. O l o i r a eua cac Khoi nay, t a
CO cac xung Kim, co t h e d i c h chuyen dilqc t r o n g s u o t Khoang t h a i g i a n
l a p l a i cua xung Kich t h i c h maa
Diiong cong qua <^ s a u bo TSNP (Hirih 3. 8) dufoe d i a vao l o i B cua Boxcar. Sau Khi qua Khoi t i e n Khuech d a i , t i n h i e u nay diiac p h i n r a
lam h a i Kirih t a i cac Khoi cong 1 v a cong 2 t r e n Hirih 3. 10, Tai d i y
t o a n bo diiong cong b i l o a i bo, c h i con l a i t i n h i e u t a i h a i v i t r i t\ v a t g cua cac xung mo cong diioc t r u y e n q u a CXiic nang nay diioc thiic
h i e n b o i cac Khoa dung t r a n s i s t o r t n i o n g v o i ciic D diioc n o i v o i ciiong
t i n h i e u , cilc G n o i v o l xung nh dutoe t a o r a b o i cac bo don h a i
[ 4 6 , 2 5 ] .
Cac g i a t r i C ( t i ) v a C(t2) diioc l^y t r u n g birih s a u n » t só chu Ky t h a n h niic mot chieu, diioc diia vao bo Khuech d a l so sarih (sau Khi qua
5."=i-
cac Khoi dem phói hop tra Khang), cuoi ciing eho tin hieu ra a loi C diioi dang mic n^t chieụ Do ion eua mic mot chieu tai C trong dieu Kien he so Khuyech dai cua toan he Khong doi phu thuoc vao trang thai Kieh thich mau do rihii: nhiet do, xung phin cue, anh sang. . . va phep dat eiia so toe do thong qua vi tri cac cong t^, tg cua Boxcar. Tren tii ghi se ghi duac pho lâTS phu thuoc rihiet do vai true Y diiac noi vai C tu Boxcar, true X la loi ra cua cap rihiet do nhiet do m a n
Sa do chi tiet cua Khoi Boxcar Kep diioe tririh bay tren Hirih 3. 12. Hirih 3. 13 la gian do thai gian eua mot so Khoi ehiie nang trong Boxcar. Khoi phat xung Kich thich mau do gom co 2 mach: mach tren (Al) dung cho phep do dien dung qua do, mach diioi (A2) dung cho phep do dong qua dọ
t
74123
- 54
(I Jl
Xung nhip 555 Tao xung Kich mau
Tao silon t a i t^ Jl Jl Xung cong t^ Jl Jl Tao siion t a i t 2 Xvmg cong t 2 Lay mau t i n h i e u
Hirih 3. 1 3 - Gian do t h o i g i a n t r o n g Khoi Boxcar Kep
Mach p h a t xung sut dung IC555 eo so do rihii t r e n Hirih 3. 14. T r i n
l o i r a 3 t a t h u dlioc cac xung Kim v o l do rong t^^ v a t i n so f v o l quan h i :
t i = 0. 7(Ri+R2)Ci
55 -
-^ t-
Hirih 3. 14. Mach phat xung 555
Hinh 3. 15 tririh bay mach don hai sii dung IC74121. Chin vao (3) lay xung Kim tut IC555, chin ra Q(6) va Q(l) co xung tan so f nhiing do rong thay doi dutoẹ Xung o chin 1 diioc diia den Kich thich mau o he do qua do dien dung, xung o chin 6 Kich thich mau o he do qua do dong dien.
^
m
<?
t — f — t *-
14 4 5 11 10
Hirih 3. 15. Mach don h a i dung 74121
Q
1
u
Xu, ::: 0, 52 RC 'W
rf.
IC74123 cung l a mach don h a i rihiing l a mach Kep, v i v i y no r i t t i e n l o i t r o n g mach t a T eac xung coiig t j , t ^ (Hirih 3. 13).
Hinh 3. 16 t r i r i h bay mach t a o xung cong bang IC don h a i Kep SK74123.
^ in in 1 = CT- R n 74123(1/2) C 1 10 -—11 1 74123(1/2) T " •^ r c 5 56 - 1 r S~L I T " Do npng xung t^ tjC=0. 52RC
Hinh 3. 16. Tao xung cong bang don h a i Kep SN74123.
Ntui v i y , b a i g v i i c d i e u chirih c h i i t ap R o niia t r e n cua IC74123, t a CO t h e lam silon xung d i c h chuyin ( c h i n 4 ) , tute l a lam d i c h chuyen cong t j , t g . Tiiong tii rihii o niia t r e n , c h i i t ap R o mia diioi cho phep t h a y d o i do rong t ^ cua xung cong. Dieu chirih t a n so l a p l a i cua xung Kich nau dlioc thiic h i e n b o i c h i i t ap Rg thuoc Khoi p h a t 555. Dieu chirih do rong xung Kich mau d i c e thiic h i i n b o i c h i i t ap R t r e n Khoi
t a o xung dung don h a i SN74121. Do l a cac tiiong só co ban can diioc d i e u
chirih doi v o l phep do xii l y bang Boxcar Kep.
Tren so do Hinh 3. 8, t n i eac n a y c h i t h i l a : Dao dong Ky 0G2-23,
M i e r o D i g i t a l V o l t m e t e r 4014a, t i i Ky h a i t r u e Endim 2200/1, dong ho
mot chieu, cac Khoi con l a i do chung t o i l a p r a p , x i y durig tii rihiing
- 57 -
1 9 A
2. 3. Chuan va h i e u chinh he
a ) . G i a i phap d i a xung k i c h t h i c h vac mau dọ
Fhep do ELTS diioe thiic h i e n t r i n vung chuyin t i e p P-N hoac d i o t SchottKy p h i n ciic ngiioc, dong t h o i co xung Kich t h i c h . Mni viy, cung
mSt luc p h a i dcit t r i n n&i do mot h i f u d i e n t h e mot chieu, dong t h a i
CO mot xung Kich t h i c h de mmi dot n g o t b i diia vao t i r i h t r a n g l i i i n ciic n ^ o c i t h e n (thu riho mien n^heo) sau do l a i t r o v i t r a n g t h a i p h i n ciic ban dau de cac h a t t a i b i b a t vao cac t i m t r o n g mien neiheo g i a i phong r a
Hon t h e niia, nau do p h a i dblqc d a t t r o n g c i u do d i e n dung cao t i n rihii mot rihanh cua cau d^ do dac qua t r i n h g i a i phong do,
De thiic h i i n d i e u t r e n , ban d i u chung t o i da l a p r a p c i u do co
dang rihii Hirih 3. 17, t r o n g do Tj l a b i i n t h e cao t a n , dlia t i n h i e u 5, 6 MHz vao nuoi ciu- Tai riharih GF n a c mmi do, co d a t mot bién t h e xung Tg c^ dlia xung Kich t h i c h vao mail. I h e p h i n ciic ngiioc mot c h i e u
d a t l i n m£i c6 t h e chirih d i o c riho c h i e t ap R. Cau do diioc n u o i cao tan
t r e n h a i n u t E, F va t i n h i e u l a y r a t r e n h a i n u t G, H, t r o n g do H dlioc n o i d a t .
Sau mot qua t r i r i h van harih may chung t o i rihin t h a y sii t r e cac siion xung Kich t h i c h mau arih hiiong dang Ke den do chirih xac cua cac Ket qua dọ Nguyin rihin l a do chít liiong ciia b i e n t h e xung Tg o vung t a n so cao b i h a n che g i y n i n sii Kem t r u n g thiic cua dutong d i i n dung qua dọ
56
Hirih 3. 17. Phin ciic m ^ g i a n t i e p Hirih 3. 16. P h i n cOc miu t n i c t i e p
De Khac Fhue t i r i h t r a n g t r e n , ehung t o i da t h i e t Ke l a i c i u do de CO t h e dila xung Kich t h i c h nau mot e a c h t n i c t i e p . So do c i u do
t h e o g i a i phap nay dniqc t r i r i h bay t r i n Hinh 3. 18. V i i c duta xung Kich t h i c h t r o n g so do nay dblqc thute h i i n thong qua d i e n t r o r co t r i so
riho (r=15ft) n o i t i e p v o l mau do t r e n mot rihanh c a a Gia t r i cua d i e n t r o r CO t h e bo qua b i n carih t r o Khang ciia l o p chuyen t i i ' p PN p h i n
5
ciic ngaoc (~10 ^). D i i n t r o r dong t h a i l a d i e n t r o emito ciia n » t
mach Khuech dai cong s u a t dong. caiiet ap R^ cho phep t h a y doi b i i n c^ xung Kich t h i c h mau con c h i e t ap R^ t h a y doi d i e n ap phan cute ngiioc m&t c h i e u t r e n maụ
Ket qua sii dung da cho t h i y , g i a i phap diia xung p h i n cute Kich t h i c h n a u t n i c t i e p dam bao siion xung r a t dóc, Khong b i neo Khi t a n g b i e n do cung rihii do rong, v i v i y da gop p h ^ quan t r o n g giii cho dutong d i e n dung qua do (dutong bao song cao t a n ) t r u n g thiic t n i o c Khi xut lỵ
59
b | Mach tii dong c h ^ g bao hoa caụ
Phep do ILTS d i i n dung sii dung phiiong phap t i c h p h i n Boxcar da
qui v i e e Khao s a t cac dutong qua do d i i n dung ve dang ghi niic d i e n ap
t y l e v o l h i e u so ^ = C ( t i ) - C ( t 2 ) . Mute d i e n ap do phu thuoc rihiet do
dang V = V(T) v a do chinh l a pho DLTS t h u diioc.
Mat Khac, t r o n g qwa t r i r i h t h a y doi rihiet do mau do, d i e n dung cua l o p chuyin t i e p PN p h i n ciic ngutoc mot c h i e u ciang t h a y doị Vol mSt nutc p h i n ciic ngiioc n o t c h i i u , d i e n dung cua mau Ion o rihiet do cao v a riho o rihiet do thap. Qiirih d i e u nay lam c i u d i i n dung b i l e c h r ^ t rihieu t r o n g qua t r i r i h q u i t rihiet do ciia phep do v a day cimg l a l y
do t o n t a i cua t u d i e u chirih C t r i n can (Hirih 3. 9 ) .
Tu C cho Kha nang bu trut sut l e c h c i u sirih r a do d i i n dung mot