DAI HOC QUOC
GIA
HA
NOI
TRITCING
DAI HOC KHOA HOC
TU^NHIEN
DE
TAI
:
NGHIEN
Ciru Xir
LY TIN
HIEU
NHO
PHUC Vy
DO
LUCING
MA SO: QT-06-45
CHU TRl
DE TAI : PGS. TS.
PHAM QLOC TRIEL
CAC
CAN
BO
THAM
GIA: ThS. Nguyen Anh
Due
HVCH.
N"uv6n
Huu
HVCH.
Nguyen
Huu Lam
Muc
tieu
nghicn ciiu
- Nghien
cuu
cac
phuong
phap xu
ly
tin
hieu
nho, lay
vf
du tin
hieu
DLTS
ling dung vao do
luang
cac
dai lugng
vat ly, nhan manh phuang phap
Fourier, Tach song dong bo. Boxcar va Lock-in.
- Nghien cuu van
di
tang cuang
tin
hieu dong
Hudng dSn
Luan van cao hoc va viet bai bao khoa hoc
Cac ket qua dat
diroc
- Nghien cuu
tinh
chat
ciia
tin hieu nho tren ca sa moi tuang quan giua tin hieu
va tap
nhi^u
tac dong vao he do vat ly.
- Nghien cuu tap hop va khai quat boa mot so phuang phap xu ly tin hieu nho
nhu phuang phap Fourier, phuang phap Tach song dong bo, phuang phap
Boxcar, phuang phap Lock-in. Tin hieu nho duac dan chung
la
tin hieu
DLTS.
Tuy
nhien,
hoan toan c6
the
su dung cac phuang phap noi tren
dd
do
dac,
xu ly cac
tin
hieu nho khac trong he do.
- Huang
XAC NHAN
CLA
NHA TRtONG
S.TS.^W^/J^
\y^/rh/(^^juci,
fotui/'
BRIEF REPORT
Project title:
STUDY ON TREATMENT WEEK SIGNAL FOR IMPROVING
MEASURED SYSTEMS
Project code: QT-06-45
COORDINATOR: ASSOC. PROF. DR. PHAM QUOC TRIEU
KEY IMPLEMENTORS: MSc. Nguyen Anh Due
Nguyen Huu Lam
Project purpose
- Study on signal transformation methods for applicadon in measurement
the physical quantities, focusing on methods for week signal processing
such as Fourier. Synch Rectifier, Boxcar. Lock-in.
- Study on problems of increase signals and decreace the noises
- Summarise the theories in order to apply
into
measued systems
Project content
- Review of the theories for the week signal proccessing (for example
DLTS signal)
- Study of the methods for improvement of the measured quality
- Study of the effects concerning the signal proccessing
- Orientate to build measured systems of MSc Thesis
-
Full fill
Xac dinh nong do muc
Np
4
1.2.2
Xac dinh tiet
dicn
bat 5
1.2.3 Xac dinh
miic
sau 5
CHUDNG
2- CAC PHUONG
PHy\P
XU' LY TIN
HIEU
DLTS 6
2.1 Phuang phap Fourier 6
2.1.1
Co
soTy thuyet 6
2.1.2
Tinh
Uu
viel ciia phucmg
phap 7
2.1.3 So do
khoi
va
nguyen
tac boat dong 8
3.2 Cac khai niem
co"
ban 17
3.3 Bo phat hien nhay pha (Phase-sensitive
deicclion)
22
3.3.1 Gioi
thieu
22
3.3.2 Nguyen ly boat dong 22
3.3.3 Cac khai niem lien quan den
bp
PSD 26
3.4 Khuech dai lock-in hai pha
(fwo-phase
Lock-in amplifier) 27
3.5 Cac nguon nhieu 28
Ket luan 33
MODAU
Trong thuc nghiem vat
ly,
phep do tin hieu nho la mot thach thuc thudng xuyen
doi
vdi ngudi
nghien cuu. So
dT
nhu vay
la
bai vi
tin
loai
bo, boc tach toi da anh huang
ciia
tap nhieu vao
tin
hieu do, phat hien ro rang
nhat tin hieu vat ly
c^n
quan tam.
De tai nay nghien cuu ve mot so phuang phap
xii'
ly
tin
hieu nho trong phep do
dai luang dien nhu phuo'ng phap Fourier, phuong phap tach song dong bo, phuang
phap
Boxcar,
phuang phap Lock-in. Day
chi
la mot so phuo'ng phap thong
dung,
mot
so cong doan trong qua trinh het
sue
da dang, phong
phii
cua thuc nghiem vat ly.
Tuy nhien
chiing
cung
2 trinh bay ve cac phuo'ng phap xu ly tin
hieu
nho DLTS. Chuong nay
chii
yeu dua ra cac nguyen ly va
each
thuc hien
de
co
the xan
dung vao cac he do tin
hieu nho khac.
Chuong 3 trinh bay ve phuang phap Lock-in
xii'
ly
tin hieu nho rat hieu qua trong
cac phep do thuc nghiem
vdi
nguyen ly va each ap dung do tin hieu nho.
Hy vong
rang,
nhieu nguyen ly do,
nhi(!u
giai phap thuc nghiem nham nang cao
chat luang phep do se duac nghien cuu tiep
luc irong
thoi
^ian
tai.
CHUONG 1
tii*
va
16
trong
Cp,
e„
:
la
toe
dp
phat hat tai bang nhiet tuong ung vai
16
trong
\a
dien
tii.
kp
,
kn
la cac hang so lien quan den ban chat dan dien.
Nj
la nong dp tam.
Co the thay doi dp lap day dien
tii'
ciia
tam sau bang chuyen tiep P - N hoac
bang hang rao Schottky.
Gia su
CO
mot
(N^+N-,)-n-,
^ ^ _ _
(1.3)
Tir cong
thiic
(1.2) va
(1.3)
ta thay dien dung cua lop chuyen tiep
the
hien
miic
dp lap day dien tu
ciia
tam sau.
Neu
e^
»ep do la truang hop tam sau bat dien tu thi cong thuc
(1.1)
tra thanh
dn
dl
n,(
e„
-
nCj +
Nr.n.Cn,
(1.4)
Truang hop phan
cue
thuan cho chuyen tiep. Nong dp dien tu trong
duge
giai phong khoi tam sau.
Ta
CO
np=N-|-
e\p(
-e,^.T
).
C(t)-
qX^'.^^'i)
S
A-,
+
A
,
-exp(-c^^/)
2(f^.+rj
Trong
truc^ng
hop
NY«N^
CO dang gan
diing
(1.5)
C(t)=
?>(^,;+'V,y
_ 2{V,+V,<)
_
C(t)
=Cf
toe
dp
phat xa nhiet
c^.
1.2 Xac dinh mot
so
thong so
tu
tin hieu nho DLTS.
1.2.1 Xac dinh nong dp
miic
Nj.
Trong truang hop dien dung thay doi nho do qua trinh lap
d^y
hoan toan tam
bat
N[
trong vung ngheo va dp pha tap la deu theo kh6ng gian vai ban dan loai N ta
co:
N,=2(N,-N,).
\(
C la dien dung lop ngheo.
Neu tap phan bo khong dong nhat trong kh6ng gian thi nong dp tam sau duac
tinh theo cong thuc chinh xac
hon
la:
AC
<>( ) =
AC
Tron>i
dien dung theo thai gian ta
tinh
tiet dien
bdt
:
e^^cr,,
.0',
.n
doi
\oi
hat tai
co'
ban. Phuong phap
na>
cho ket qua chinh xac ma don
gian.
Doi voi qua trinh
bai
hat tai khong co' ban
ihi phiic
tap vi no phu thuoc vao co
che tiem.
De
xac dinh tiet dien bat
nguoi
ta con co
each
khac la tinh tu toe dp phat xa
trong vung ngheo
e,^
duang phu thupc chinh
la nang lugng kich boat phat hat lai.
Tuy nhien nang lugng kich boat khong phai
liic
nao cung triing vai nang lugng
do duge.
Di^u
nay co
the
do cac nguyen nhan sau:
1/
Trong c6ng thuc (1.12) phan truac
ciia
ham exp phu thupc nhiet dp.
-Tiet dien bat
a ,
phu thuoc vao nhiet do
thuanu
la
khoniz biel
truoc.
-Thanh phan
(r,,
A;
phu thupc bac 2
ciia
nhiet dp
(-
J-}.
2/
su
so hoa dien dung,
thai gian qua
do va
xac dinh
he
so roi
rac
Fourier. Ket qua
do
duge dieu khien
tu
dong cho dp chinh xac cao. Phuang phap nay g6m
4
dac trung co ban sau:
1-
Dat
N gia tri do
lam
mSu
tu
pho dien dung qua dp. Khai trien theo chu6i
Fourier de tim
ra
cac he so roi rac.
2-
Tinh
duge
true tiep tren ph6 qua
dp
thuong
duac tinh toan doi vai cac
he so
a nhiJng
bac
dau tien.
Phuang phap qua
dp
tam
sau
Fourier
vdn
dua tren moi tuang quan giua
cac
thong
so ban
dSn
nhu trong c6ng thuc (1.10)
va
(1.12). Tuy nhien duge phan tich
duoi dang chu6i Fourier.
f(t)='-^
- ^./,
cos(noji)
^
J^h
sminfot]
(2.1)
Vai
CO
ph6
suy ra
tinh
duge
nong
d6
tam
sau.
A=^h^
exp
+
n'co'
1
-
-
^^p\
-
V
T ]]
- —
T
J]
(2.4)
nco
Va
h^ng
so thai gian co cong thiic:
"^/r ••
cf,
-a,
ghi
nhan rat nhieu
giii
tri (
N-512.
1024, )trong khoang thoi gian
T,,
bang pho
ki
thuat
so.
Vi \ay
CO
N cap gia
Iri
r va
l
nen co
the
ap dung
luy \
cac phuong phap de
tinh cac thong so tam sau. Song
sii"
dung phuo'ng phap nay cac thong so ban dan duge
rut ra true tiep tu cac he so Fourier th6ng qua cac
dinh ciia
chiing.
2,1.2
Tinh uu viet
Kha nang loai nhieu cao.
6. Dt dieu chinh
b^ng
cac th6ng so nhu bien dp, dp rpng chu ky.
7.
Van hanh dan gian.
Son"
CO
han che la chi
dumz
duoc
trons
he do tu
d6n^.
7
2.1.3
Sa do khoi va nguyen tac hoat dong.
•
So
do khoi:
Mdudo
Dat nhiet
do
A
-^-
Chua
Ket thuc
phep do
Roi
^
cpid
do tam
sdii
Fourier.
• Nguyen
tie
hoat dong:
Dal
mSu
do vao trong buong
miu,
buong
m5u duge hiit
chan khong thong qua
may bom, sau do dat gioi ban nhiet dp cho phep do. Tac dung xung vao
mSu
do. Co
the
la xung anh sang hoac the xung. Cho qua thiet bi do dien
dung,
diing
ph6
ki
thuat
so ghi nhan va \ e d6 thi pho.
May tu dong khai trien pho dien dung theo chu6i Fourier roi tinh ra cac he so
de tii do danh gia nhom qua dp.
Neu nhom qua dp da xac dinh thi
buoc
nhay nhiet dp la 0.5K. con kh6ng xac
Cho
t|
tang dan thi AC dat
cue
dai
a
thai diem
t,,,,
nao do.
Dt
xac dinh t
^,,
tii
dieu kien:
dAC ^ ^
ln(r)
,0-7,
=
0 Suy ra
i ^
(2.7)
dl
"""
(/•
-
1).L:^
Do
vay
e =
'I'iLL.
CS.At,
CS =
l,2,3 m
va A/
^ -^,
m
Tgla
thai gian do dien dung qua dp.
May tinh se tu dong tinh hieu AC - C(t) - C(r.l)
a
nhu'ng thoi diem t lien tiep
nhau de ve
len
d6 thi su phu thupc C(t) tai vai
gia Iri
nhiet dp khac nhau.
Gpi phuang phap dich
ciia
la do viec quet thoi gian
duge
thuc
hien
nha may
tinh
b^ng
each dich dan cac
cii'a
Sampling.
2.2.2.
iTu
hgp so lieu khong
chiia
tap.
- Tai mot so nhiet do chua xuat ro bieu hien tam sau.
2.3.
Phuang phap tach song dong
bp
A -
B.
Du6i su tac dong
ciia
the phan cue mot chieu gay nen mot vung dien tich qua
dp tai
mi^n
chuyen tiep. Su thay doi trang thai
tinh
dien
ciia
vung qua dp
duge
coi la
su thay doi dien dung
ciia
mot tu dien hoac dong dicn
ciia
mot mach kin
chiia viing
dien tich khong gian phd. Ghi nhan su thay doi
ciia
dong dien la pho dong qua dp.
~
const.
Thuc hien
vice chia
chu ky xung kich mau lam bon phan bang nhau
a
bp
xii
ly. Tin hieu J(t) chi duge th6ng
6
hai khoang thoi gian.
T,
T,
.
37;
— <
I
< — va
—
<
I
< T,
4 2 4
Gpi tin hieu J(t)
a
khoang dau la A va khoang sau la B.
Sii
dung bp tach song
so sanh hai dien tich A va B.
Neu gpi R - R(l) la ham
/
<
4
T
neu
T.
T,
neu — < / < —
2 4
(2.12)
T.
=
-2/
neu
37;
4
<
/ <
r,
Vai
T,
la chu ky
lap
lai
ciia
xung kich
mSu.
Ham
truydn
Qua trinh thuc nghiem la dinh truo'c
e,,^,
( bang tan so f), do nhiet dp
ciia mlu
thay doi. Dinh
cue
dai pho DLTS cho ta xac dinh nhiet dp
T^^,.
Thuc hien phep do vai
cac
e^j
khac nhau, do tuang
ling
T,^,.
Tu cac cap gia tri do duoc ve do thi su phu thupc
Ln
T:
theo
KT.
Duong bieu dien cho biet nang lugng ion boa
Ej,
tiet dien
b4t
hat tiii
ciia
cac
mii'c
sau. Vay vai phuang phap nay phep do da chuyen quan he hai
bien so
J(t,T)
=
C, -
c;.exp(-
e
I
(2.15)
11
Neu khong quan tam den thanh phan khong doi
C^
va de y
r^ng
V„ -
T~;
V^
«
T~
thi
(T,,
coi nhu khong doi theo nhiet dp va cong thiic (2.14),
(2.15)
co the viet
dang:
E,
KT
^„ =
AJ^\
exp
an
=
C,.cxp{-e,,.t)
Trong c6ng thiic
(2.16)
va (2.17) chiia cac thong tin
chii
yeu can thiet ve tam
sau hu nang lugng ion hoa
E,.
toe
dp phat xa dien
tii
e,^,
tiei dien bat dien
tii
a^
(
n^m
trong A), nong dp tam sau
.N-,
( nam trong
e^,).
Tii cac phuong trinh (2.16) va (2.17) cho ta thay
duong
dien dung qua dp phu
thupc vao hai bien so la nhiet dp va
thoi
gian. Ta \iei: C
=
C(t.T).
ky thuat
xii
t
DoC
L(t)
D
Cil
1
Cl
>
Tu
ghi
Hinh 2.2: Mo td ky thuat Boxear kep
Tin hieu di qua m6i bp
xii
ly
duge
dac trung boi ham truyen:
R{t)
=
\C(t).F{i).dt
(2.18)
12
F(t):
La ham
loc
dac trung cho bp
xii
ly;
Tf:
La chu ky lap lai
ciia
(::.[exp(-
e,,./,
) - exp( -
.',./
)]
(2.21)
(2.22)
Do
(2.16)
ta thay toe dp phat dien
tiie^
lai phu thupc vao nhiet dp:
e^
-
e,/T).
Khi do R theo su thay doi nhiet dp
ciia miu
( co nghla
e„
thay doi ) thi R se di qua
cue
tri thoa man
di6u
kien:
dR
de
cj-
/,
. e
xp(-
-/.
Vay ghi nhan tai hai thoi diem
tj,
t-,
thong qua he Boxcar kep va thay doi nhiet
dp
m3u
thi ham truyen R se dat gia tri cue dai.
Toe
dp phat xa dien
tii
tinh
duge
tu
gia tri cue dai do la
e,^.
Neu dinh san hai thoi diem
t,, t.
co
nghia
la an dinh mot gia
tri
to'c
dp
phai
xa. Ghi nhan ham truyen R theo su thay doi nhiet dp
ciia mSu
thi se
xac dinh
duge
Khi do ham truyen R dat
cue
dai, ky thuat DLTS co tinh uu viet
a
dac diem nay. No
da bien su phu thupc C(t,T) ba chieu thanh R(T) hai
chi^u
cho ta
xii
ly
di.
dang ban.
- Trong qua
trinh
thuc nghiem cho nhiet dp
ciia m3u
thay doi va gia tri
e^
dinh
trudc
( cac vi tri
t,,
t2
dinh truac ).
Tir
pho DLTS xac dinh duge nhiet dp
T^^
a cue dai
pho.
Tu cong
Ln\
~ \
theo
'
Du6n2
bieu dien se la duang
thdng
ma dp doc la nang lugng ion hoa
E,
va giao
dicm ciia
duong thang voi true
tung cho ta thong so
\'6
tiet dien bat
hai
tai.
- N6ng dp cac tam co
the'
tinh true tiep tu su thay d6i dien dung
ling
vai su lap day
hoan toan cac tam
b^ng
xung tiem bao hoa doi vai truang hgp hat tai khong ca ban
hoac
bing
xung hat tai co' ban rpng nhat co the co doi voi truang hgp tam hat tai ca
ban.
-
giap.
14
Ln(e/r2)
C(t,)-C(t,)
KT
•>
Nhiet
do
Hinh
2.3:
Minh
hoa
phep
do
DLTS
vdi nam
ci'ra
so toe do
kluic
nhau
vd
edeli
xde
dinh
ndnq
luang
ion hod cua tam sau.
Bang
phucmg
phap DLTS
bao
nhieu
nen anh
huang
ciia
hang
so
truyen tren
he
dien
tii
den
phep
do la
khong
he co.
Vay viec
dat cac
ciia
s6
t|, t.
(co
nghla
dat
truoc e„
) da
chuyen quan
he 2
bien
AC{LT)
1
TH
chuan(6)
^Vi(9) ^^
Boxcar
Hinh
2.4 Sa do
khoi
ehue
nang
ei'ia
he do
dien dung DLTS.
15
Neu chi
sir
dung cac khoi tii (l)den (9) cho he do dien dung DLTS thi ta co he
do dien dung nho
duge
chi thi
b^ng
dong ho mot chieu . Hinh tren
la
sa do khoi
chiic
nang
ciia
he do dien dung DLTS dung ky thuat
xii
ly Boxcar kep.
(5). Khoi nay duge xay
dung
b^ng
vi mach SC2929 va cac khung cong huang lam viec a
tdn
so' 5.6MHz sao
cho dp truyen qua
ciia
khoi dat 0.5 MHz. Khoi co nhiem vu
Ipc
ra duang dien dung
tii song cao tan hay noi
each
khac
Ipc
duang bao bien dp tii song mang.
Khoi TSNP (7) duge dieu
chinh
de nhay nhat voi bien doi do thanh phan dien
tra. Vi
ly
do nay ma bp quay pha (4) nam truac khoi tin hieu
chuain
co vai tro quan
trpng trong giai doan
tit^n
xu ly
ciia
he do.
Tin hieu thu
16
CHl/ONG
3
PHiroNG
PHAP
KHUECH
DAI
LOCK-IN
3.1 Gioi thieu chung
Khuech dai Lock-in (Lock-in amplifier) duoc dung de phat hien va khuech dai
nhirng
tin hieu AC cue nho, co the dat toi ca vai nanovolt. No co the do chinh xac
nhirng
tin hieu nho ban nhieu nhieu
Ian
Khuech dai Lock-in
sii
dung ky thuat phat hien nhay pha, no
chi
giii lai
nhimg
thanh
phan tin hieu co
ciing
tan so voi tin hieu chuan, con nhung thanh phan tan so khac
vai tan so tin hieu chuan se bi loai nen khong anh
hucrng
gi den phep do
Xet vi du sau:
Gia
x/lOO
kHz x 1000). Nhu vay chiing ta se khong thuc hien duge phep do
neu nhu khong tach duge thanh phan tan so quan tam ra khoi nhieu
Neu chiing ta dung mot bp
Ipc
dai voi dp pham chat Q
^ 100
(day la thong so
ciia
bp
Ipc cue
tot),
tan so trung tam la 10 kHz thi tin hieu nam trong dai tan 100 Hz (10
kHz/Q) se duge truyen qua. Nhieu trong truang hgp
na\
se la 50
j.iV
(5 nV/vHz x
VlOO
Hz x
1000)
va dp
Ion ciia
tin hieu van la
10
)_iV.
Nhu vay nhieu
o
loi ra van
Ian
Mot bp phat hien nhay pha PSD khong nhung co tac dong voi bien dp tin hieu cung
tan so vai tin hieu chuan ma con nhay voi su sai khac pha giiia tin hieu va tin hieu
chuan. Vi the nen mot he thong
dira
tren hoat dong cua bp PSD co the do duge ca ve
bien dp va pha cua tin hieu luan hoan tat nhien la co su hien dien cua nhieu. Cac he
thong dua tren nguyen ly boat dong cua bp PSD duge gpi la cac he Lock-in. Neu
trone
cac he khuech dai co su dung
nauven Iv
hoat
doim
cua bo PSD thi duoc
lioi
la
khuech dai lock-in [ |
3.2 Cac khai niem
co
ban
So do
klioi
CO ban cua mot he kbuech dai lock-in duge trinh bay tren hinh 1.1. Viec
chia chiing thanh cac khoi rieng biet
giiip ehiing
ta de hieu va co the tiep can mot
each CO
hieu qua va nhanh nhat.
u^.TU^Ouoc^^TT^'
RUNGTAV IHONG
IJ-
m
Fiher
Preanip
Kenh tin
hieu
Lowjiass
Fihcr
He so KD
Ref
input
OLllpUl
Kenh
Ref
Hinh 3.1 - Bp khuech dai lock-in co ban.
Nha tang tien kliuech dai ma chiing ta co the chpn duge he so khuech dai phu hgp.
Muc dich o day khong chi lam tang he so khuech dai ma con phai tang
duge
ti so tin
hieu tren tap. Voi
each
do thi chung ta se dam bao giam toi thieu nhung thanh phan
nhieu khong can thiet ra khoi tin hieu. Nhu
\'ay
doi voi cac he thi nghiem ta phai
chpn tang tien khuech dai
phii
hgp va co tap am thap
(lov\-noise).
3.2.2 Bo tach song dong bo
Hinh 1.2 la cau tao cua mot bp tach song dong bp (synchronous detector). No bao
la
Vs
va
V,.
Chiing duoc bieu dien boi cac phuong trinh:
18
j(0 =
V2V,cos[6?,/
+ ^J
r(0 =
V2V^cos[6i>,^
+ ^,]
d
loi ra
ciia
bp nhan chiing ta nhan duge tich
ciia
tin hieu s(t) va tin hieu chuan r(t)
CO
dang
la
tong
ciia
cac thanh phan tan so khac nhau:
V^(0
=
V,K,
COs[(a;,
+
W,
Aco ^
|(o,
-
O),!
thi o loi ra cua bp
Ipc
se chi
xuat hien nhiing thanh phan tan so
Aoj.
De tinh bien dp
ciia
thanh phan tin hieu do
thi chiing ta phai biet ham dap
ling
tan so cua bp
Ipc
HLO*^^)-
Dp Ion
bien dp loi ra
duge bieu dien bang phuong trinh:
khV,K,./i,(A^)
trong do
AI(CO)^\Hi(joj)\
Do
AL((O)
CO
tan so cat nho hon rat nhieu so voi
oj,-
nen chiing ta thay rang he chi co
the chap nhan nhCmg thanh phan tin hieu co tan so gan voi tan so tin hieu chuan.
truven
cua bp loc tan thap
\ai lan
so trung tam
oj^
• Giiii dieu che
vdi
tin hieu chuan dong bo (Demodulation with a
synchronous reference)
Xet so
d6 CO
dang nhu hinh 3.4. Bay gio chiing ta se khao sat y
nghia
thuc tien
ciia
phuang phap. Tin hieu dua vao he thi nghiem va tin hieu chuan duge lay tu mot
nguon.
Ta
CO
mot nguon tin hieu dang sin co tan so
cOr
duge diing lam nguon kich dong thi
nghiem va lam tin hieu chuan. Tin hieu loi ra
ciia
he tbi nghiem co cung tan so vai
19
nguon kich dong va
bj
dich pha di
^^.
He
thi
nghiem ^
.•*
(l)
/
v'"f/;
!
.(X)
vi^^
L'()S((0
/
^
0, )
Lou
-pas>
Filter
'
; \
r-
\
O
1
Synchronous detector
Hinh 3.4 - Detector dong bp vai bp dich pha
• Giai dieu che bien do (amplitude demodulation)
Khi chiing ta dieu chinh sao cho pha cua tin hieu chuan cung pha voi tin hieu thi loi
ra cua bp nhan se la:
Vo =
k,V,
day:
M(j(o)
la bien doi Fourier
ciia
tin hieu dieu che,
Hgifoj) = kJT^{jco)
la ham dap
ling
tan so
ciia
bp tach song
20
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