Bao Cao Hoan Chinh

i

LI CM N

Em xin gi li cm n n tt c thy c trong trng cung cp cho em nhng

kin thc v gi gip em chun b hnh trang trn con ng lp nghip sau ny.

Em cng xin cm n n cha m, nhng ngi nui dy em nn ngi v

nhng ngi than gip em rt nhiu trong thi gian hc v thc hin ti.

Em cng xin chn thnh cm n thy Nguyn Tn Nhn trc tip hng dn

em thc hin ti, gip em t ti liu cho n phng php nghin cu. t cch

vit lun vn cho n cch thi cng mch, gip em nhng kinh nghim qu bu cng

nh tnh cm ca thy dnh cho em.

Em cng xin cm n n bn b, cc anh ch kha trc gip v to iu

kin cho em trong sut thi gian hc.

Vi trnh v kh nng cn hn ch v vy lun vn hon thnh khng trnh

khi nhng thiu st v c ni dung v hnh thc. Em rt mong nhn c s ch bo

v nh gi qu bu ca cc qu thy c, y l nhng kinh nghim qu bu cho cng

vic ca em sau ny.

Xin chn thnh cm n!

Sinh vin: H nh ng

ii

MC LC

LI NI U ................................................................................................................ 1

........................................... 2

1.1 Tng quan .......................................................................................................... 2

1.1.1 Pha pht ...................................................................................................... 2

1.1.2. Pha thu: .......................................................................................................... 3

1.2 Ph tn sng in t: .......................................................................................... 4

1.3 Cc tham s h thng: ........................................................................................ 4

1.3.1 My pht ...................................................................................................... 4

1.3.1a Cng sut my pht .................................................................................... 5

1.3.1b Nhiu my pht: ......................................................................................... 5

1.3.1c T s cng sut knh ln cn: ..................................................................... 6

1.3.2 My thu: ...................................................................................................... 6

1.3.2a H s nhiu my thu: .................................................................................. 6

1.3.2b Di rng, im nn 1dB v tn hiu c th tch c nh nht ................. 7

1.3.2c im chn bc 3 v mo iu ch tng h IMD ...................................... 8

......................................................................................... 9

2.1 Gii thiu: .............................................................................................................. 9

2.2 Cc ng trn trong th ................................................................................... 9

2.2.1 ng trn h s phn x ngoi cng ............................................................. 9

2.2.2 H ng trn ng r: ................................................................................... 11

2.2.3 H ng trng ng x .................................................................................. 13

2.3 M t th smith ................................................................................................ 14

2.4 Dn np trn th smith ..................................................................................... 18

2.5 Cch c th Smith .......................................................................................... 20

2.6 ng dng c bn ca th Smith ...................................................................... 24

2.6.1 Tnh h s sng ng, h s phn x v tr khng ng dy...................... 24

2.6.2 Tnh tr khng mch phc hp ..................................................................... 24

2.6.3 Phi hp tr khng ......................................................................................... 26

....................................................................... 27

3.1 Phi hp tr khng bng cc phn t tp trung (cc mng hnh L) ..................... 27

3.1.1 Phng php gii tch .................................................................................... 28

3.1.2 gii php dng th Smith ........................................................................... 29

........................................................................................... 32

iii

4.1 Gii thiu ng truyn vi di - Microstrip line .................................................. 32

4.2 Phi hp tr khng trn ng truyn vi di ....................................................... 33

4.3 Thit k on truyn sng dng Microstrip Line ................................................. 36

........................................ 37

...................................................................... 39

................................................................. 42

...................... 43

.................................................................................................... 43

..................................................................................... 43

...................................................................................... 43

-31122 ............................................................................... 44

................................................................................................. 45

6.3.1 .......................................................................... 45

6.3.2 n L , S .............................................. 46

6.3.3 .................................................................... 47

6.3.4 ....................................................................... 52

6.3.5 ................................................................ 53

................................................................................................................... 55

............................................................................................. 58

iv

DANH MC HNH

Hnh 1.1 : Cc phn t c bn trong thu pht v tuyn ................................................... 2

Hnh 2.1 mt phng phc .......................................................................................... 10

Hnh 2.2: Tr khng ti khi xem xt h s phn x ...................................................... 10

Hnh 2.3 H ng trn ng r ..................................................................................... 12

Hnh 2.4 H ng ng x ............................................................................................ 13

Hnh 2.5 th smith .................................................................................................... 15

Hnh 2.6. th Smith hn hp .................................................................................... 19

Hnh 2.7 : ly i xng qua gc ta ...................................................................... 19

Hnh 2.8 Mch in minh ha v d trn ...................................................................... 25

Hnh 2.9 th Smith minh ha v d trn. .................................................................. 26

Hnh 3.1: Mng phi hp hnh L(a) Mng c dng khi zL nm trong vng trn 1+

jx (b) Mng c dng khi zL nm ngoi vng trn 1 + jx ........................................... 27

Hnh 3.2: Li gii cho v d trn. th Smith cho cc mch phi hp L .................. 30

Hnh 3.3 Hai kh nng cho mch phi hp L ................................................................ 30

Hnh 4.1: Dng hnh hc v mt ct ngang ng truyn vi di .................................. 32

Hnh 4.2: Cc ng sc t trng v in trng ..................................................... 32

Hnh 4.3. V d v phi hp tr khng cho ng vo khi s dng ng truyn vi di

....................................................................................................................................... 34

Hnh 4.4 V d v phi hp tr khng cho ng ra khi s dng ng truyn vi di .... 35

Hnh 4.6 Mch khuch i thc hin phi hp tr khng v d trn. ........................ 35

Hnh 4.7 Mch khuch i phi hp tr khng ...................................................... 36

Hnh 5.1 (a) m t vic phn loi cc mch khuch i cng sut. .............................. 38

Hnh 5.1 (b) m t vic phn loi cc mch khuch i cng sut. .............................. 38

Hnh 5.2 ......................................................................................................................... 39

Hnh 5.3 Tn hiu nh ................................................................................................... 40

Hnh 5.4. Tn hiu ln .................................................................................................. 40

Hnh 5.5 M t mch khuch i cng sut loi B ........................................................ 42

.......................................................... 43

..................................................................... 44

v

-0C ....................................................................... 44

-31122 ............................................................................ 45

-31122 ............................................................ 45

.......................................................................... 48

......................................................................... 48

............................................................................. 49

............................................................................. 49

................. 50

-31122 .......................................................... 50

ALM-31122 .......................................................... 51

-31122 ........................................................... 51

-31122 ........................................................... 52

-21122........ 52

C ....................................................... 53

................................ 54

-31122 trong datasheet ....................... 54

....................................................... 54

LI NI U

SVTH: H NH NG LP: D10CQVT01-N 1

LI NI U

Hin nay, mng vin thng Vit Nam a vo s dng cc thit b vi ba s

hin i, dung lng cao. Vic kho st nghin cu nguyn l hot ng ca thit b vi

ba l c s ban u kim chng kin thc c hc, thy c s ng dng t l

thuyt ti thc t cng nh l nn tng tm hiu khng ch cc h thng v tuyn

khc ang ph bin nh thng tin di ng v thng tin v tinh.

c s phn cng ca nh trng, trong thi gian qua em thit k v thi

cng phn cng cho ti thit k v thi cng b khuch i cng sut cao tn vi

s hng dn ca thy Nguyn Tn Nhn.

Ni dung ti g chng c th chia nh sau. nm chng u ni v c

s l thuyt vi ba s, l thuyt v cc khi trong mt h thng vi ba s, l thuyt v

mng phi hp tr khng, l thuyt v mch khuch i v cc c s l thuyt mch

b sung lm nn tng cho vic xy dng.

Chng cui l phn thit k mch khch i cng sut.


Chng 1:

1.1 Tng quan

Hnh 1.1 th hin cc phn t c bn ca h thng thu pht v tuyn. mi phn c

mt vai tr quan trng nht nh.

Hnh 1.1 : Cc phn t c bn trong thu pht v tuyn

1.1.1 Pha pht

Khi K v giao din ng s c cc chc nng sau:

Phi khng vi ng s

Khuych i v cn bng cp ng truyn s

Bin i m ng vo m my

Ti sinh tn hiu s

Khi phc xung ng h

Khi x l s bng gc pht:

Ghp thm cc thng tin iu khin v qun l ng truyn

Mt m ho cc thng tin quan trng

M ho knh chng li

Ngu nhin ho tn hiu s trc khi a ln iu ch

Khi iu ch v bin i nng tn:


iu ch sng mang bng tn hiu s chuyn i tn hiu s ny vo vng

tn s cao thun tin cho vic truyn dn

i vi cc my pht i tn vi iu ch thc hin trung tn khi bin i

nng tn cho php chuyn tn hiu trung tn pht vo tn s v tuyn trc khi

pht.

Khi khuych i cng sut:

Khuych i cng sut pht n mc cn thit trc khi a pht vo khng

trung.

1.1.2. Pha thu:

Khuych i tp m nh:

Khuych i tn hiu thu yu trong khi khuych i rt t tp m

Bin i h tn, khuych i trung tn v gii iu ch :

i vi my thu i tn trc khi gii iu ch tn hiu thu c bin i vo

trung tn thu nh khi bin i h tn. Trong qu trnh bin i h tn do sut

hin tn s nh gng nn khi bin i h tn thng lm thm nhim v trit

tn s nh gng.

i vi cc my thu i tn sau bin i h tn l khuych i trung tn.

Nhim v ca khi chc nng ny l khuych i, lc nhiu knh ln cn v cn

bng thch ng vng tn s cng nh cn bng tr nhm cc phn t ca

knh truyn dn .

Gii iu ch tn hiu thu phc hi tn hiu s

X l s bng tn gc thu: Thc hin cc chc nng ngc vi khi x l s bng

gc pht nh:

Gii ghp xen

Gii m knh

Gii ngu nhin

Phn lung cho lung s chnh v lung s iu khin qun l ng truyn

Cn bng thch ng vng thi gian gim thiu nh hng ca fallding

Khuych i v giao in ng s:

Khuych tn hiu s n mc cn thit trc khi a ra ngoi my

Bin i m my vo m ng

Phi khng vi ng s


1.2 Ph tn sng in t:

Tn s Bc sng Di tn

3Hz 30KHz 108 - 104 Very low frequency (VLF)

30 300 KHz 104 103 Low frequency (LF)

300KHz 3MHz 103 102 Medium frequency (MF)

3 30 MHz 102 - 10 High frequency (HF)

30 300 MHz 10 - 1 Very high frequency (VHF)

300MHz 3GHz 1 - 10-1 Utrahigh frequency (UHF)

3 30 GHz 10-1 10-2 Superhigh frequency (SHF)

30 300 GHz 10-2 10-3 Extremely high frequency (EHF)

103 106 GHz 3.10-4 3.10-7 Infrared, visible light, ultra violet

B khuch i ang thi cng c tn s 900 MHz nn nm trong di tn UHF.

1.3 Cc tham s h thng:

1.3.1 My pht

Mt my pht ni chung gm mt b dao ng, mt b iu ch, mt b nng tn,

cc b lc v b khuch i cng sut. my pht n gin ch c mt b giao ng v

nu phc tp, my pht c th bao gm mt b giao ng kha pha hay b tng hp

tn s v cc thnh phn nh trn. Hnh 1.2 ch s khi my pht in hnh. Thng

tin s iu ch dao dng thng qua phng thc iu ch AM, FM, PM hay iu ch

s. khuch i cng sut tng cng sut pht trc khi pht i bi anten. c nhiu

pha thp, b dao ng c th c kha pha vi dao dng thch anh tn s thp. b

giao ng cng c th c thay th bi b tng hp tn s t ngun dao ng thch

anh n nh cao.

Mt s c tnh my pht cn quan tm l:

- Cng sut ng ra v tn s hot ng: mc cng sut RF ng ra bi my pht ti

mt tn s xc nh hay mt di tn.

- Hiu sut: hiu sut chuyn i DC-to-RF ca my pht. Hiu sut ny c xc

nh bng 100%RF

dc

P

P i vi mch khch i cng sut ln, hiu sut cng sut


c thm vo (PAE) c xc nh bng 100%out in

dc

P P

P Vi outP v inP ln

lt l cng sut RF ra vo tng ng.

- S bin i cng sut ng ra: s bin i cng sut ng ra i vi di tn hot

ng

- Di tn hot ng: di tn ny ph thuc vo linh kin v mch.

- n nh tn s: kh nng ca b dao ng ( my pht) tr v hot ng ti

im lm vic ban u sau khi chu tc dng ca nhiu t hay nhiu in.

- Nhiu : nhiu AM, FM, hay nhiu pha. Nhiu AM l s bin i bin khng

mong mun ca tn hiu ng ra. Nhiu FM l s bin i tn s khng mong mun,

cn nhiu pha l s bin i v pha khng mong mun.

- T s cng sut knh ln cn: nh gi theo mo IMD ca b khch i cng sut

c thit k cho h thng thng tin v tuyn s.

1.3.1a Cng sut my pht

Cng sut my pht l mt trong nhng ch tiu thit k h thng, vi yu cu

cng sut ra v hiu sut my pht cc i do mch khuch i cng sut c thit

k v hot ng ti vn nn hoc vng bo ha nhm tng di ng mch v t s tn

hiu trn nhiu ca my thu. Tuy nhin cc vng ny l cc vng phi tuyn nn sinh ra

si dng nh si dng AM sang AM v AM sang PM.

Vic thit k cc mch khuch i cng sut tuyn tnh thng c chn ti im nn

1dB, y l gii php tha hip gia yu cu cng sut, hiu sut ti a v si dng ti

thiu. v vi cc linh kin cng sut siu cao tn di tn 2GHz hin nay, cng sut ti

im nsn 1dB ti u t cc ch tiu k thut cng nh kinh t trong thit k h thong

nm trong khong +30 dBm n +40dBm.

1.3.1b Nhiu my pht:

Khi b dao ng l mt thit b khng tuyn tnh, in p v dng in nhiu c

to ra. Nhiu c chia lm 3 loi: nhiu AM, FM v nhiu pha.

Nhiu AM gy ra s bin i bin ca tn hiu ng ra. Nhiu FM c ch nh

bng tri rng ca ph tn s.

Thng thng ngi ta nh gi nhiu bng t s:

( )fm =

Thng s trn chnh l s phc bit v cng sut gia sng mang ti tn s f0

V nhiu ti fm . n c n v l dBc/Hz . dBc ngha l dB di cng sut sng

mang.


Phn ln nhiu ca giao ng l nhiu FM hay nhiu pha. Nhiu ny i din cho

dch pha hay n nh ca b giao ng. cng sut b dao ng khng tp trung

ti mt tn s n m phn b xung quanh tn s .

1.3.1c T s cng sut knh ln cn:

S pht trin nhanh chng ca thng tin v tuyn s yu cu my pht r hn v

vn ti u v cng sut ng ra, PAE, v tuyn tnh. ACPR c dng nh mt hnh

c gi tr nh gi b khuch i cng sut v tnh tuyn tnh ca chng:

ACPR = V cng c o bng dBc

1.3.2 My thu:

My thu c dng x l tn hiu vo thnh thng tin c ch vi mo nh

nht. s thc thi ny ca my thu ph thuc vo vic thit k h thng, thit k mch

v mi trng lm vic. mc mo hay nhiu c th chp nhn c ph thuc vo

tng ng dng.

Cc tham s ca my thu bao gm:

- nhy: nhy my thu xc nh kh nng p ng ti mt tn hiu yu. c th

l yu cu v SNR i vi h thng tng t hay BER i vi h thng s.

- chn lc: chn lc my thu l kh nng loi b cc tn hiu khng mong

mun trn cc knh ln cn hot ng ng thi trn cng h thng co hay trn

cng nhiu min a l.

- Nhiu spur: kh nng trit cc p ng knh khng mong mun th quan trng

trong vic gim s giao thoa. iu ny c th thc hin c bng cch chn v

dng cc b lc.

- Mo iu ch tng h IMD: my thu c khuynh hng t to ra s giao thoa

trong knh t tn hiu RF. Cc tn hiu giao thoa ny gi l mo iu ch tng h

IMD.

- S n nh tn s: s n nh ca ngun LO th nh ng n qu trnh iu ch,

nht l trong iu ch FM v iu ch pha. Cc bin php n nh thng dng l

k thut vng kha pha hay tng hp tn s.

- S bc x: tn hiu LO c th r r qua b trn n anten v bc x ngoi. S bc

x ny hay ra s giao thoa v cn phi tun theo quy nh FCC.

1.3.2a H s nhiu my thu:

H s nhiu l mt tham s nh gi mc nhiu m mt linh kin hay mt h

thng c. H s nhiu ca mt h thng ph thuc vo nhiu yu t nh suy hao trong

mch. Loi thit b, loi thit b, loi phn cc v vic khuch i.


H s nhiu c nh ngha nh sau:

0 0

/

/

i iS NFS N

Vi m hnh ca mt mng 2 ca c li l G v mc nhiu u vo l

Ni = kTB th

0GFGkTB

0K)

Vi h thng nhiu tng ta c cng thc sau:

1 1 1

3 1 12 11

2 2

.......

n

n

F F F FF FF F

G G G G G G

Nh vy nu h thng gm nhiu tng khch i th h s nhiu ca h thng s do

tng u tin quyt nh.

Nhit nhiu tng ng:

Nhit nhiu tng ng ca h thng c xc nh:

Te = (F 1).T0

Vi T0 = 290 0K

1.3.2b Di rng, im nn 1dB v tn hiu c th tch c nh nht

Trong mt b trn, mt b khch i hay mt my thu, vic hot ng thng c

thc hin trong vng m cng sut ng ta tuyn tnh vi cng sut ng vo. Min ny

gi l di rng Dr nh hnh bn di. nu tn hiu vo vt qu di rng ny th nhiu

tri hn. Di rng c xc nh l khong gia im nn 1dB v mc tn hiu c th

tch c nh nht MDS. Trong mt h thng chng ta cn mt di rng cao c th

hot ng mt di ln hn cc mc cng sut tn hiu vo.

MDS c xc nh nh l mc nhiu nn cng thm 3dB.

Hay

MDS = Ni + 3dB

Cn im nn 1dB c xc nh:

PD = Pout G +1 dB

Hay

PD = Pout Lc +1 dB

Vi G l li ca my thu

Lc suy hao chuyn i ca b trn th ng.

Nh vy di rng :


Dr = PD MDS

1.3.2c im chn bc 3 v mo iu ch tng h IMD

Khi hai hay nhiu tn hiu ti tn s f1 v f2 vo mt thit b khng tuyn tnh nh

b trn th chng to ra cc mo giao thoa IMD mf1 nf2 . bc ca tn hiu mo ny l

(m+n). trong thc t ngi ta thng quan tm n mo bc 3 v chng nm trong di

tn IF th nht.

V tn hiu ng ra c quan h bc nht tuyn tnh vi tn hiu ng vo trong khi

mo bc 3 c quan h bc 3. Tc l khi tn hiu vo tng 1dB th tn hiu ng ra cng

tng theo 1dB nhng mo IMD bc 3 tng 3dB. Nh vy n mt lc no mc mo

ng ra s ln hn mc tn hiu ng ra. Khi th khng th phn bit c gia tn

hiu v mo nn khng th thu c.

im chn bc 3 o c bng dBm l im m ti mc tn hiu ng ra v mc

mo IMD bc 3 bng nhau.

Gi tr im ny cho bit kh nng trit mo IMD bc tng ng. gi tr cng ln

th vic chn cng tt.

Chng 2: TH SMITH


Chng 2:

2.1 Gii thiu:

c pht trin nm 1939 bi Phillip Smith ti phng Lab Bell, n gin vic

tnh ton, gii cc h phng trnh di dng v phc tp trong k thut siu cao tn.

mc d kt qu cha c chnh xc cao nhng php gii bng th Smith c th ni

l cng c kh quan trng vi ngi thit k mch siu cao tn.

th Smith c xy dng trn mi quan h gia h s phn x ( )x v tr

khng ng dy Z(x) ti mt im x bt k trn ng dy truyn sng.

Ta c:

Tr khng ng dy:

0

1 ( )( )

1 ( )

xZ x Z

x (2.1)

Tr khng ng dy chun ha:

1 ( )z( )

1 ( )

xx

x (2.2)

H s phn x:

0

0

( ) Z( )

( ) Z

Z xx

Z x (2.3)

Hay

0

0

z( ) Z( )

z( ) Z

xx

x (2.4)

Vi 0

Z( )z( )

Z

xx

Ta c mi quan h trn l 1-1, ngha l ng vi mt gi tr z(x) ta ch tm c mt

gi tr ( )x m thi.

2.2 Cc ng trn trong th

2.2.1 ng trn h s phn x ngoi cng

y l ng trn tng ng vi h s phn x c bin bng 1. V h s phn

x c nh ngha l t s ca sng in o phn x trn sng in p ti, nn bin

ca h s phn x lun nh hn hoc bng 1. Min bn ngoi ng trn bng 1 ny

xem nh khng c ngha khi xem xt trong th Smith. y l ng trn c tm

(0,0) bn knh l 1.

Chng 2: TH SMITH


Hnh 2.1 sau minh ha mt mt phng phc :

Hnh 2.1 mt phng phc

Trc khi xt cc ng trn khc ta xem xt mt s tham s khc trn ng dy

truyn sng. Hnh 2.3 sau minh ha mt tr khng ti khi xem xt h s phn x.

Hnh 2.2: Tr khng ti khi xem xt h s phn x

Ta c biu thc ca h s phn x nh sau:

0

0

Z( )

Z

L

L

Zx

Z (2.5)

Hay

r ij (2.6)

Trong :

( )

( )

r

i

Re

Im (2.7)

Tr khng ng dy:

Z(x) = R(x) + jX(x) (2.8)

Hay vit ngn gn:

Chng 2: TH SMITH


Z = R + jX (2.9)

Trong :

R l in tr ng dy.

X l in khng ca ng dy.

Tr khng ng dy chun ha:

z(x) = r(x) + jx(x) (2.10)

hay

z r jx (2.11)

Trong :

0

Rr

Z l in tr ca ng dy chun ha.

0

Xx

Z l in khng ca ng dy chun ha.

2.2.2 H ng trn ng r:

Theo cc cng thc trn ta c quan h sau:

1 ( )z( )

1 ( )

xx

x (2.12)

Thay cc cng thc (2.6) v (2.11) vo (2.12) ta c:

1

1

r i

r i

jr jx

j (2.13)

Cn bng phn thc v phn o trn ta c:

2 2

2 2

1

1

i

i

r

r

jr

j (2.14)

2 2

2

1i

i

r

xj

(2.15)

By gi ta xt cc phng trnh (2.14) v (2.15). trong phng trnh (2.14) th r

c biu din theo r v i, do n c c trng bi mt h cc ng biu

din trong mt phng . Phng trnh ny ch ph thuc r m khng ph thuc x (

ngha l x bt k). ln lt cho r cc gi tr khc nhau ta c mt h cc ng biu

din, c gi l h cc ng ng r.

Tht vy, thc hin mt s php bin i phng trnh (2.14) ta c:

2 22 1

1 1r i

r

r r (2.16)

Chng 2: TH SMITH


Phng trnh (2.16) l phng trnh ng trn c tm l ;01

r

rbn knh bng

1

1r.

Cho cc gi tr r > 0 khc nhau ta s c mt h cc ng trn nh trong hnh

2.4:

Hnh 2.3 H ng trn ng r

- Khi r = 0, suy ra vng trn ng r = 0

Tm (0;0) bn knh bng 1

y l vng trn c tm gc ta ca mt phng phc

V bn knh bng 1 n v. tt c cc im h s phn x nm trn vng trn

ny u tng ng vi tr khng ng dy l thun khng, thnh phn in tr

trit tiu.

- Khi r = 1, suy ra vng trn ng r = 1.

Tm 1

;02

, bn knh 1

2.

y l vng trn c tm nm trn trc honh r , honh 1

2, bn knh

1

2.

ng trn ny i qua gc ta ca mt phng phc . Mi im nm trn

vng trn ny u tng ng vi tr khng ng dy, c thnh phn thc R

ng bng in tr chun ha 0R .

- Khi r tr thnh mt im trong mt phng phc . y l im tng ng

vi mt h mch.

Chng 2: TH SMITH


2.2.3 H ng trng ng x

Tng t ng trn ng r. ta thc hin mt s php bin i phng trnh (2.15),

ta c:

2 22 1 1

1r ix x (2.17)

Phng trnh (2.17) l phng trnh ca mt ng trn c tm l 1

1;x

v bn

knh bng 1

x.

Cc im tm ca cc ng trn ng x lun lun nm trn ng 1r . V

1r , nn trong mt phng phc ta ch xt cc im nm trong phm vi ca ng

trn n v.

Hnh 2.4 H ng ng x

- Khi x = 0 th vng trn ng x = 0 c:

Tm 1; bn knh

ng ng x = 0 bin thnh ng thng v trng vi trc honh r ca mt

phng phc . Nu tr khng ng dy l in tr thun th h s phn x

tr thnh s thc.

- Khi x vng trn ng x c :

Tm (1,0) bn knh 0

Chng 2: TH SMITH


ng x bin thnh mt im trng vi 1r . im ny tng ng vi tr

khng l mt h mch.

- Vi cc gi tr in khng x tri du, cc ng trn ng |x| tng ng s i

xng nhau qua trc honh.

2.3 M t th smith

th Smith l cng c c s dng rt nhiu trong phn tch v thit k cc mch

siu cao tn. Ta c th thc hin nhiu php tnh ton trc tip trn th Smith, n

gin ch bng cch v hnh v c tr s m khng cn dng cc cng c ton hc

khc. Hiu su sc v vn dng nhun nhuyn th Smith gip ngi thit k nm

c bn cht ca mch siu cao tn, ng thi on trc c kt qu thit k v

cc kh khn trong ch to mch.

th Smith ban u c to ra nh mt cng c h tr cho vic xc nh tr

khng u vo ca ng truyn, c xy dng da trn php biu din tr khng z

trong mt phng h s phn x trong bao gm cc ng trn ng r v ng x

nh tho lun phn trn. iu cn nhn mnh y l v bn cht ca th

Smith - l mt mt phng phc trn mi gi tr tr khng chun ha z = r + jx ti

mi im ch l cc gi tr gn ghp cho im () tng ng m thi. Do , cc

php ton v h s phn x c thc hin trc tip bng cc php cng (tr) vct,

trong khi cc php ton v tr khng chun ha z tr thnh cc php c v cng tr

s trn th Smith.

Chng 2: TH SMITH


Hnh 2.5 th smith

th Smith chun c cho trn Hnh 2.6 . c th vn dng tt th ny

trong phn tch thit k mch siu cao tn chng ta cn phi hiu cn k v cu trc v

ngha ca cc k hiu, cc thang o tr s v cc php tnh, cc php bin i trn

th Smith. C th nh sau:

Trc ht cn lu rng tt c cc gi tr tr khng trn th Smith u l tr

khng chun ha theo mt gi tr tr khng chun ha (Z0) cho trc. Khi c c

gi tr ca z ta phi suy ra gi tr thc ca tr khng theo biu thc Z = z Z0.

th Smith nm trong phm vi vng trn n v v h s phn x l mt s

phc c module nh hn hoc bng 1. Ta s khng xt cc im nm ngoi phm vi

ca th Smith.

Cc ng ng r l h cc vng trn c phng trnh tham s r xc nh bi

(2.16), mi vng trn tng ng vi mt gi tr r duy nht. Trn th Smith, gi tr r

ca mi vng trn ng r c t tn l "Thnh phn in tr (R/ Z0) hoc thnh phn

in dn (G/ Y0 ) - RESISTANCE COMPONENT (R/Z0 ) OR CONDUCTANCE

Chng 2: TH SMITH


COMPONENT (G/ Y0 )" v tr s ca n c ghi dc theo trc honh ca th. Gi

tr ca r tng t 0 (ngn mch) n (h mch).

Cc ng ng x l h cc vng trn c phng trnh tham s x xc nh bi

(2.17), mi vng trn tng ng vi mt gi tr x duy nht v ch phn nm trong vng

trn ||=1 c v trn th Smith. C hai nhm vng trn ng x

Vi cc gi tr x dng (cm khng), cc ng trn ng x nm pha trn

trc honh ca th. Gi tr ca x tng t 0 n , c ghi dc theo chu vi ca vng

n v na trn ca trc honh v c t tn l "Thnh phn in khng cm

khng (+jX/ Z0 ) hoc in np dung khng (+jB/Y0 ) - INDUCTIVE REACTANCE

COMPONENT (+jX/ Z0 ) OR CAPACITIVE SUSCEPTANCE (+jB/ Y0 )".

Vi cc gi tr x m (dung khng), cc ng ng x nm pha di trc honh

ca th. Gi tr ca x gim dn t 0 n , c ghi dc theo chu vi ca vng trn

n v (ch ghi gi tr tuyt i |x|) na th pha di trc honh v c t tn l

"Thnh phn in khng dung khng (-jX/ Z0) hoc in np cm khng (-jB/ Y0 ) -

CAPACITIVE REACTANCE COMPONENT (-jX/ Z0) OR INDUCTIVE

SUSCEPTANCE (-jB/ Y0)".

Cc ng ng r v cc ng ng x hnh thnh h cc ng trn trc giao

vi nhau. Giao im ca mt ng ng r vi mt ng ng x bt k u tng

ng vi mt tr khng z = r + jx chun ha theo Z0.

Tm ca th Smith l giao im ca ng ng r = 1 v ng ng x = 0

(trc honh ca th). Do n tng ng vi tr khng chun ha z = 1 (tc Z = Z0

). im ny c bit quan trng v n i din cho trng hp ti hon ton phi hp

tr khng vi ng dy hoc mch thit k c phi hp tr khng (s cp n

cc phn sau). y cng l im c h s phn x = 0 (c phi hp tr khng).

im mt tri ca trc honh ca th Smith l giao im ca ng ng r = 0

v ng x = 0, do n tng ng vi tr khng chun ha z = 0 (hay Z = 0) v im

ny i din cho mt ngn mch. y cng l im c h s phn x = 1.

im mt bn phi ca trc honh ca th Smith l im c bit m tt c

cc ng ng r v ng x u i qua (mi gi tr ca r v x ). Ta coi im ny

tng ng vi tr khng chun ha z l mt h mch. y cng l im c h

s phn x = +1.

Chng ta bit h s phn x (x ) ti im z bt k trn ng truynsng

c th c suy ra t h s phn x (0) ti ti v khong cch t z ti ti

(z ) = (0).e-2 l (2.18)

Mt khc, mi im trn th Smith u tng ng vi mt h s phn x trn

ng dy. Do ta d dng suy ra im (z ) trn th Smith nu bit v tr ca im

Chng 2: TH SMITH


(0) bng cch xoay vng trn mt qu tch hnh xon c quanh gc ta (i vi ng

truyn khng tn hao th qu tch l mt ng trn c tm l tm ca th Smith). Biu

thc tng qut cho h s phn x ti im z c vit li nh sau:

2 20 . . jz e e (2.19)

Trong biu thc trn, l khong cch t im z ang kho st ti im ti z = 0.

Khi tng mt khong /2 th im h s phn x s quay ng mt vng quanh gc

ta ca th Smith. Trn th Smith, quanh vng trn chu vi c ghi thang chia t

1800 n +1800 tng ng vi gc quay ca khi di chuyn dc theo ng truyn sng.

Nh vy khi di chuyn khong cch bt k th s quay mt gc tng ng l

0 0360 . 720 ./ 2 (2.20)

Cng thc (3.18) thng c s dng ng vi k hong cch khi di chuyn t ti v

ngun. Tuy nhin n c th c m rng cho trng hp tng qut: im khi u v tr

bt k trn ng truyn sng v di chuyn v pha ngun ( tng) hoc v ti ( gim).

Vnh ai bao quanh chu vi ca th Smith ta cn thy c hai vng thang chia t 0,

0.01, 0.02, ... 0.49 trn :

Mt vng nh s theo chiu kim ng h t 0 n 0.49, tng ng vi "s ln bc

sng khi di chuyn v hng ngun" hay "WAVELENGTHS TOWARDS

GENERATOR".

Mt vng nh s theo chiu ngc chiu kim ng h t 0 n 0.49 tng ng vi

"s ln bc sng di chuyn v hng ti" hay "WAVELENGTH TOWARDS LOAD"

Nh vy gc quay ca h s phn x khi di chuyn trn ng truyn sng c th

c xc nh theo n v o gc () bin thin t 1800 n +1800 hoc theo s ln bc

sn g bin thin t 0 n 0.5 ln cho mi vng quay, ng thi ch v chiu quay:

V hng ngun: Thun chiu kim ng h

V hng ti: Ngc chiu kim ng h

iu ny c th cho php ngi thit k c th v, o c v tnh ton trc tip trn th

Smith.

i vi ng truyn ti c tn hao ( 0 ), khi di chuyn dc theo ng truyn sng

theo (2.19) th module ca h s phn x cng bin thin t l vi 2e . iu ny c ngha

khi di chuyn v hng ngun ( tng) th || gim dn v khi di chuyn v pha ti ( gim)

th || tng dn.

Module ca h s phn x || ti bt k im no cng c th c xc nh theo gi tr

"H s phn x - Reflection coefficient" phn di bn tri ca th Smith. Gi tr ny c

th c tnh theo

H s phn x in p |v | (RFL. COEFF, E or I), vi thang chia l tuyn tnh bin

thin t 0 n 1.0.

Chng 2: TH SMITH


H s phn x cng sut (RFL, COEFF, P) t l vi logarit ca |v|2 , vi thang chia

logarit t 0 n 1.0.

H s sng ng S trn ng truyn khng tn hao cng c th c xc nh theo

th Smith. Trong phn trc, chng ta bit rng vi ng truyn khng tn hao, gi tr ca

|| v S u l hng s trn sut chiu di ca ng truyn.

Nh vy, cc vng trn tm l gc ta trn th Smith c th c coi l cc ng

ng || hoc cc ng ng S, mi vng trn tng ng mt gi tr ca || v mt gi tr

duy nht ca S.

H cc ng ng S ny khng c v c th trn th Smith nhng chng ta c th

xc nh chng mt cch d dng nh thang gi tr "H s sng ng - Standing Wave Ratio

(SWR)" phn di bn tri ca th. Gi tr ny c th c tnh theo

H s sng ng (max

min

VS

V), vi thang gi tr t 1 n (T s in p)

H s sng ng tnh theo dB (dBS), vi thang gi tr t 0 dB n .

2.4 Dn np trn th smith

Chng ta bit rng quan h c bn xy dng th Smith l quan h gia h s phn

x vi tr khng chun ha z c xc nh theo (2.2). T ta cng c th xy dng mi

quan h gia v dn np chun ha y nh sau:

nh ngha dn np chun l nghch o ca tr khng chun Z0

0

0

1Y

Z (2.21)

nh ngha dn np chun ha theo dn np chun

0 0 0

1/ 1 1

1/ /

Y Zy

Y Z Z Z z (2.22)

H s phn x c tnh theo (2.2) thnh

11

1 1

11 11

z yy

z y

y (2.23)

Hay

1

1y

(2.24)

Quan h gia v y theo (2.23) v (2.24) l quan h tng ng, hay ni cch khc,

mi im ca h s phn x trong mt phng phc tng ng vi mt v ch mt gi tr

ca dn np chun ha y. Do , ta cng c th gn cho mi im phc mt gi tr dn np

chun ha y tng ng (hon ton tng t nh php gn cho mi im mt gi tr chun

ha z nh trnh by phn trc), v ta c th xy dng th Smith theo dn np.

Chng 2: TH SMITH


Mt khc nu so snh (2.2) vi (2.23) v (2.24) ta cng nhn thy rng quan h gia v

z hon ton ging ht nh mi quan h gia (- ) vi y. iu ny c ngha th Smith xy

dng theo tr khng chun ha z v th Smith xy dng theo dn np chun ha y l i

xng nhau qua gc ta ca mt phng phc .

Ni cch khc, th Smith theo dn np chun ha y c suy ra t th Smith theo

tr khng chun ha z bng mt trong hai cch sau

Ly i xng ton b th Smith qua gc ta (Hnh 2.7)

Hnh 2.6. th Smith hn hp

Gi nguyn th Smith nhng ly i xng ca im h s phn x ang xt qua

gc ta thnh im h s phn x - (Hnh 2.8)

Hnh 2.7 : ly i xng qua gc ta

Trn Hnh 2.7, th Smith theo tr khng chun ha (ng mu ) c ly i xng

qua gc ta c th Smith theo dn np chun ha (ng mu xanh l cy). Mt

im trn th ny cng chnh l im trn th kia v ngc li. Trn Hnh 2.8, im

c ly i xng qua gc 0 thnh im (- ), cn cc thang o trn th Smith khng

thay i. C ngha l gi tr c c trn th Smith tr khng ti im s chnh l gi

tr ca dn np chun ha y(g,b ) vi y = g + j b , v y = 1/z .

Chng 2: TH SMITH


Ch nu tr khng chun ha z c th c vit

z = r + jx

th dn np chun ha y cng c vit tng t

y = g + jb

Trong :

g = G/Y0 - gi l in dn chun ha

b = B /Y0 - gi l in np chun ha

Nh vy, trn th Smith theo tr khn g chun ha ta c cc ng ng r v ng x th

trn th Smith theo dn np chun ha, cc th vng trn ging ht nh trn s tr thnh

cc ng ng g v ng b . Cc thang tr s trn th khng thay i (gi tr r gi tr g

; gi tr x gi tr b ).

2.5 Cch c th Smith

- Biu din trn th Smith:

- Cc c im s dng c:

Chng 2: TH SMITH


Chng 2: TH SMITH


- H s phn x:

- H s sng ng:

Chng 2: TH SMITH


- Dn np ng dy:

Chng 2: TH SMITH


- Bng sng v nt sng trn th Smith:

2.6 ng dng c bn ca th Smith

th Smith l mt cng c h tr c lc cho vic thit k, tnh ton v phn tch mch

in siu cao tn. Trong phn ny chng ta s xt mt vi ng dng c bn ca th Smith,

qua s cho thy mi vic tnh ton da trn cc cng thc u c thay th bng ng tc

v v o trc tip trn th Smith em li kt qu trc tip v nhanh chng bng vic c

cc tr s trn th. Cc ng dng trong trng hp c th s ty thuc vo s vn dng linh

hot ca ngi s dng.

2.6.1 Tnh h s sng ng, h s phn x v tr khng ng dy

Trn ng truyn sng (c tn hao hoc khng tn hao), nu bit gi tr tr khng ti

chun ha zL u cui dy (hoc tr khng ng dy chun ha z(z0) ti im z0 xc nh

trc), ta lun c th suy ra gi tr ca h s sng ng S, h s phn x (z) v tr khng

ng dy chun ha z(z) ti im z bt k trn ng dy, vi v tr ca z c xc nh

tng i so vi im ti (hoc im z0).

Tt c cc tnh ton trn u c thc hin trc tip trn th Smith m khng cn s

dng cc cng thc phc tp. chng ta s dng cch c th Smith ni trn xc

nh.

2.6.2 Tnh tr khng mch phc hp

Mch phc hp ny c hiu l mch in bao gm nhiu phn t th ng tuyn tnh

gm in tr R, in dung C v in cm L c ghp hn hp vi nhau. Ti mt tn s cho

Chng 2: TH SMITH


trc, tr khng hoc dn np ca mt mch phc hp c th c xc nh bng cc cng

thc ton hc ca nh lut m.

Php ton trn c th c thc hin trc tip trn th Smith ch bng cch v v o

m khng cn dng cng thc ton hc no. Tuy nhin, iu ny i hi ngi thc hin phi

s dng thnh tho th Smith.

Chng ta c th hiu r hn qua cc v d minh ha sau.

V d: Cho mch in phc hp trn Hnh 2.9. Cc tr s linh kin cho nh sau: R=50 ;

C1 = 10pF ; C2 = 12pF ; L = 22.5nH . Tn s lm vic = 109 rad/s . Tnh tr khng Z gia

hai u ca mch in.

Hnh 2.8 Mch in minh ha v d trn

Gii: Trc tin ta chn tr khng chun ha ca th Smith. Thng thng thun

tin ta chn tr khng chun ha Z0 = 50.

Tr khng gm R v C1 mc ni tip c tr s chun ha l:

1

9 121

0

1 150

10 10 10 1 250

RC

R jj C

z jR

Tr khng ny c biu din bng im A trn th Smith (Hnh 2.10). Do tr khng

zRC1 ny li mc song song vi t in C2 nn trn th Smith ta chuyn ton b gi tr tr

khng ca RC2 v C2 thnh gi tr dn np.

lm iu ny, ta ly i xng ca im A qua gc ta thnh im B . Ngay chnh

trn th ny, im B chnh l dn np ca zRC1 . c gi tr ca B ta c

yRC1 = 0.2 + j0.4. Dn np ca C2 c chun ha l :

9 12

22

0

10 12 100.6

1/ 1/ 50

j Cyc j j

Z

Khi in dung C2 c mc song song vi RC1 th dn np ca C2 s c cng vi dn

np ca RC1 . V yC2 = j0.6 (thun np ) nn in dn tng khng thay i v bng in dn

ca yRC1 nhng in np tng l tng ca in np 2 nhnh. Kt qu l trn th Smith, t

B ta di chuyn trn ng trn ng in dn g = 0. 2 theo hng tng ca in np mt

lng l b = +0.6 n im C c dn np yRC1C2 = 0.2 + j1.0

V L c mc ni tip vi (RC1C2) nn ta chuyn sang lm vic vi th Smith theo tr

khng tc chuyn ( RC1C2 ) thnh tr khng. lm iu ta ly i xng im C qua gc

ta c im D . c tr s ti im D ta c zRC1C2 = 0.2 j0.95.

Chng 2: TH SMITH


Tr khng chun ha ca L l:

9 9

0

10 22.5 100.45

50L

j Lz j j

Z

2.6.3 Phi hp tr khng

- Dng cc phn t th ng (R, L, C).

- Dng ng dy chm ( dy /4, chm ni tip, song song, mt si hay nhiu si)

Phn ny s ni r hn chng k tip

Hnh 2.9 th Smith minh ha v d trn.

V zL = j0.45 (thun cm khng) nn in tr tng khng thay i nhng in khng tng

l tng ca in khng ca zRC1C2 vi in khng ca zL . Kt qu, trn th Smith, t im

D , ta di chuyn dc theo vng trn ng r = 2 theo hng tng ca in khng (tc l gim

v gi tr tuyt i) mt lng l x = +j0.45 ta c im E . c gi tr tr khng ti E ta

c:

z = 0.2 j0.5

Lu thang gi tr ca in khng na di trc honh c ghi theo gi tr tuyt i,

du mang du m (-).

Nh vy tr khng thc ca mch l:

Z = z . Z0 = (0.2 j 0.5) 50 = 10 j25 ().


Chng 3

Mc ch khi phi hp tr khng:

- Cng sut ti a c pht i khi ti c phi hp vi ng truyn (gi thit l ngun

c phi hp), v tn hao cng sut trn ng cp (feed line) c gim ti a.

- Phi hp tr khng cc phn t nhy cm ca my thu (nh anten, b khuch i nhiu

thp vv ...) ci thin t s tn hiu trn nhiu ca h thng.

- Phi hp tr khng trong mt mng phn phi cng sut (nh mng cp cho mng

anten) s gim cc li v bin v pha.

Cc yu t quan trng trong vic la chn mt mng phi hp c bit bao gm:

- phc tp - Cng nh phn ln cc gii php k thut, thit k n gin nht tha

mn cc yu cu v c tnh k thut lun l gii php a chung nht. Mt mng phi

hp n gin hn thng r hn, tin cy cao hn v t tn hao hn mt thit k

phc tp.

- rng bng tn - Bt c mt loi mng phi hp no v l tng cng c th to ra

mt s phi hp hon ho (khng c phn x) ch mt tn s duy nht. Tuy nhin,

trong nhiu ng dng ngi ta mun phi hp ti trong mt di tn s. C mt s cch

khc nhau thc hin iu ny nhng tt nhin s lm tng phc tp thit k.

- Thc thi - Ty theo loi ng truyn hay ng dn sng c s dng, mt loi mng

phi hp c th c chung hn so vi loi mng khc. V d, cc dy chm iu

chnh thng d thc hin hn l cc b chuyn i mt phn t bc sng a on

(multi-section) bng ng dn sng.

- Kh nng iu chnh - Trong mt s ng dng, mng phi hp phi c kh nng iu

chnh c nhm phi hp vi mt ti c tr khng thay i. Trn quan im ny, mt

s loi mng phi hp d thc hin iu ny hn mt s mng khc.

C rt nhiu cch phi hp tr khng. Di y trnh by mt s cch nh sau:

3.1 Phi hp tr khng bng cc phn t tp trung (cc mng hnh L)

C l loi mch phi hp tr khng n gin nht l on mch hnh ch L s dng

hai phn t thun khng phi hp mt ti bt k vi ng truyn. C hai cu hnh cho

mng ny nh trnh by trn Hnh 3.1.

Hnh 3.1: Mng phi hp hnh L(a) Mng c dng khi zL nm trong vng trn

1+ jx (b) Mng c dng khi zL nm ngoi vng trn 1 + jx


Nu tr khng ti chun ha zL = ZL /Z0 nm bn trong vng trn 1 + j x trn th Smith

th mch in trn Hnh 3.1(a) c s dng. Cn nu tr khng ti chun ha nm ngoi

vng trn 1 + jx trn th Smith th mch in trn Hnh 3.1(b ) cn c s dng. Vng

trn 1 + jx l vng trn in tr trn th Smith c r = 1.

Trong c hai cu hnh trn Hnh 3.1, cc phn t thun khng c th l cc cun cm hay

t in ty thuc vo tr khng ti. V th, c tm kh nng khc nhau cho mch phi hp i

vi nhiu loi tr khng ti khc nhau. Nu tn s l thp v/hoc kch thc mch l

nh th cc phn t tp trung nh cun cm hay t in c th c s dng. Cu hnh ny

kh thi i vi cc tn s ln ti 1 GHz mc d cc mch tch hp cao tn hin i c th

nh cho cc phn t tp trung c th c s dng cc tn s cao hn. Tuy nhin c mt

phm vi rng cc tn s v kch thc mch cc phn t tp trung khng th thc hin

c. y l hn ch ca k thut phi hp tr khng s dng on mch L.

By gi chng ta s i tm biu thc gii tch cho cc phn t ca mng phi hp trong

hai trng hp trn Hnh 3.1, sau minh ha mt quy trnh thit k thay th s dng th

Smith.

3.1.1 Phng php gii tch

Trc ht xt mch in Hnh 3.1(a) v cho ZL = RL + jXL . Chng ta pht biu rng

mch in ny s c s dng khi zL = ZL /Z0 nm trong vng trn 1 + jx trn th Smith,

iu ny ng rng RL > Z0 cho trng hp ny.

Tr khng nhn vo mng phi hp ng trc ti phi bng Z0 , phi hp th

0

1

1/ ( )L LZ jX

jB R JX (3.1)

Sp xp li v phn tch thnh cc phn thc v o ta c hai phng trnh cho cc n s X

v B:

B(XRL XLZ0 ) = RL ZL (3.2)

0 BZ1 L L LRX B XX (3.3)

Gii (3.2) cho X v th vo (3.3) cho ta mt phng trnh bc hai cho B. Nghim ca

phng trnh ny l:

2 2

0

2

0

2

Z =

/B

L LL L L

L L

X Z R X

R X

R R

(3.4)

rng do RL > Z0 nn i s trong hm cn th hai lun dng. Khi in khng ni

tip c th tm c nh sau:

0 01 L

L L

X Z ZX

B R BR (3.5)

Phng trnh (3.4) ch ra rng hai li gii cho B v X l c th. C hai li gii ny v mt

vt l l c th thc hin c do c gi tr m v dng ca B v X u c th chp nhn


c (X dng ng l mt in cm, X m ng l mt t in, trong khi B dng ng l

mt t in cn B m ng l mt cun cm.) Tuy nhin, mt li gii c th dn ti cc tr s

nh hn ng k i vi cc phn t in khng v c th l gii php c quan tm nu

rng bng tn ca vic phi hp l cao hn hoc t s sng ng SWR trn ng dy gia

mng phi hp vi ti l nh hn.

By gi xt mch in trn Hnh 3.1(b). Mch in ny s c s dng khi zL nm ngoi

vng trn 1 + jx trn th Smith tng ng vi RL < Z0 . Dn np nhn vo mng phi hp

trc ti ZL = RL + jXL phi bng 1/Z0 , c phi hp

0

1 1

( )L LjB

Z R j X X (3.6)

Sp xp li v phn tch thnh cc phn thc v o chng ta nhn c hai phng trnh

hai n s l X v B:

0 0( )L LBZ X X Z R (3.7)

0( )L LX X BZ R (3.8)

Gii cho X v B ta c:

0( )L L LX R Z R X (3.9)

0

0

( ) /L LZ R RB

Z (3.10)

Do RL < Z0 nn cc i s trong cc cn bc hai u lun dng. Mt ln na, cn lu

rng hai li gii l kh thi.

phi hp mt ti phc bt k vi mt ng dy tr khng c tnh Z0 th phn thc

ca tr khng vo i vi mng phi hp phi l Z0 trong khi phn o phi l 0. iu ny

mun ni rng mng phi hp phi c t nht hai mc t do; trong mch phi hp L hai mc

t do ny c cho bi cc gi tr ca hai phn t in khng.

3.1.2 gii php dng th Smith

Thay v cc cng thc trn, th Smith c th c s dng thit kt mt cch nhanh

chng v chnh xc cc mng phi hp L. Sau y chng ta s xt mt v d minh ha quy

trnh thc hin.

V d: Thit k mt mng phi hp L phi hp mt ti RC ni tip c tr khng ZL =

200 j100 vi mt ng dy 100 ti tn s hot ng 500 MHz.

Gii: Tr khng ti chun ha l zL = 2 j1 c v trn th Smith Hnh 3.2. im ny

nm bn tro ng vng trn 1 + jx v vy chng ta s s d ng mch phi hp trn Hnh 3.1(a).

By gi, sau khi b sung in np song song ta c yt = yL + jb v chuyn v tr khng chng

ta mun tr khng n y nm trn vng trn 1 + jx chng ta c th b sung mt in khng

ni tip kh i thnh phn jx v phi hp ti.


Hnh 3.2: Li gii cho v d trn. th Smith cho cc mch phi hp L

Quy trnh thc hin c m t nh sau:

Bc 1: Xc nh im ti chun ha zL = 2 j1 trn th tr khng Smith.

Bc 2: Do phn t u tin t ti l mt in np song song (jb ) nn gi cho ta nn

chuyn i sang th dn np Smith bng cch v vng trn SWR qua ti v mt ng

thng t ti qua tm th nh trn Hnh 3.2. Khi ny dn np ti c c trn th l yL =

0.4 + j0.2. Do jb l thun np nn yt chnh l im di chuyn ca yL trn ng ng g = 0.4.

im yt l giao ca ng ng g = 0.4 (hay r = 0. 4 trn th tr khng) vi nh ca vng

trn ng r = 1 qua gc ta . Nh trn Hnh 3.21 ta thy c hai im yt1 v yt2 tng ng

vi hai li gii cho bi ton ny. Trn th Smith ta xc nh c

Hnh 3.3 Hai kh nng cho mch phi hp L

Phng n 1: yt1 = 0.4 + j0.5. Nh vy di chuyn yL ti yt1 ta cn c

jb1 = j0.5 j0.2 = j0.3 b1 = 0.3

Phng n 2: yt2 = 0.4 - j0.5. Nh vy di chuyn yL ti yt2 ta cn c


jb2 = -j0.5 j0.2 = -j0.7 b1 = 0.7

Bc 3: Do phn t ng trc yt l mt in khng mc ni tip nn n gin ta chuyn

ngc tr li sang tr khng. Khi ta c

Phng n 1: T im yt1 trn th k mt ng thng i qua tm th ct vng

trn 1 + jx ti zt1 (xem Hnh 3.2). Trn th xc nh c im ny c tr khng zt1 = 1

j1.2. a im ny v tm th ta cn mt in khng jx1 = j1.2 x1 = 1.2

Phng n 2: T im yt2 trn th k mt ng thng i qua tm th ct vng

trn 1 + jx ti zt2 . Trn th ta c c im ny c tr khng zt2 = 1 + j1.2. a

im ny v tm th ta cn mt in khng jx2 = j1.2 x2 = 1. 2

Bc 4: T Bc 2 v Bc 3 ta rt ra

Phng n 1: b1 = 0.3 v x1 = 1.2. By gi, t cc kt qu ny ta cn xc nh cc gi tr

in cm hay in dung cho mch in phi hp. Do b1 v x1 u c gi tr dng nn

chng i din ln lt cho cc t in v cun cm c cc tr s c xc nh nh sau:

1

6

0

0.30.95

2 2 500 10 .100

bC pF

fZ

V

1 0

6

. 1.2 10038.2

2 2 .500 10

x ZL nH

f

Mch phi hp cho phng n 1 c minh ha trn Hnh 3.3

Phng n 2: b2 = 0.7 v x2 = 1.2. Lu rng b2 c tr s m nn n i din cho mt

cun cm v x2 cng mang gi tr m nn n s i din cho mt t in. Tr s ca cc

phn t ny c xc nh nh sau:

0

6

2

10045.5

2 2 .500 10 0.7

ZL nH

fb

V

6

2 0

1 12.65

2 2 .500 10 1.2 100C pF

fx Z

Mch phi hp cho phng n 2 c minh ha trn Hnh 3.2.

Ngoi cch thng dng ny ra, chng ta cn c nhiu cch khc phi hp tr khng nh

dng ng dy chm ( dy l/4, chm ni tip, song song, mt si hay nhiu si),ng

truyn vi di, ng truyn ng phng coplanar-CPW

Chng 4 GII THIU NG TRUYN


Chng 4.

4.1 Gii thiu ng truyn vi di - Microstrip line

ng truyn vi di l mt trong nhng loi ng truyn phng ph bin nht, l do

chnh l v n c th c ch to nh cc qu trnh photolithography (quang khc) v d

dng c tch hp vi cc linh kin cao tn tch cc v th ng khc. Dng hnh hc ca

ng truyn vi di c minh ha trn Hnh 4.1. Mt di dn rng W c in trn mt

tm in mi c ni t c b dy h v hng s in mi tng i r .ng sc t

trng v in trng c v trn Hnh 4.2 .

Hnh 4.1: Dng hnh hc v mt ct ngang ng truyn vi di

Hnh 4.2: Cc ng sc t trng v in trng

Nu lp in mi khng c mt ( r = 1), chng ta c th coi ng truyn gm hai di dn

phng rng W , cch nhau mt khong 2h (mt phng t c th c b i theo l thuyt

nh). Trong trng hp ny ta c mt ng truyn TEM n gin vi p = c v

= k0 = 0 0

S c mt ca cht in mi v c bit l cht in mi khng ph kn vng khng kh

pha trn di dn (y>h), lm phc tp vic phn tch ng truyn vi di. Khng ging ng

truyn di, ton b trng u b giam trong vng in mi ng nht, ng truyn vi



di c phn ln ng sc trng nm trong vng in mi, tp trung gia di dn v mt

phng t, cn mt phn nm trong vng khng kh pha trn lp nn (substrate). V l do ny

ng truyn vi di kh ng th h tr mt sng TEM thun ty, do vn tc pha ca cc

trng TEM trong vng cht in mi l c/ r , cn vn tc pha ca cc trng TEM trong

vng khng kh l c. V vy, s bt phi hp v pha ti min tip gip in mi-khng kh s

khng th t c mt sng TEM.

Trong thc t, cc trng chnh xc ca ng truyn vi di hnh thnh mt sng TM-TE

hn hp, v i hi cc k thut phn tch cao hn m chng ta khng trnh by y. Tuy

nhin, trong hu ht cc ng dng thc t, lp in mi rt mnh v mt in (tc h ), v

v vy trng l cn TEM (quasi-TEM). Ni cch khc, cc thnh phn trng v c bn

ging nh trng trong trng hp tnh in. V vy, cc gi tr gn ng cho tc pha,

hng s truyn lan v tr khng c tnh c th t c t cc nghim tnh hoc cn tnh

in. Khi vn tc pha v hng s truyn lan c th c biu din bi

p

e

cv

0 ek

trong e l hng s in mi hiu dng ca ng truyn vi di. Do mt s ng sc

trng nm trong vng in mi v mt s trong khng kh nn hng s in mi tha mn

quan h,

1 e r

v ph thuc vo b dy ca lp in mi h , b rng ca di dn W.

4.2 Phi hp tr khng trn ng truyn vi di

tn s cao khi s dng t in v cun dy phi hp tr khng s d xut hin in

cm v in dung k sinh, nn trong khuch i cao tn thng dng phng php mch di

hoc mch vi di phi hp tr khng.

Phi hp s dng th Smith

V d cho 00.29 101s v

00.2 122L

Hnh di y s ch r cch phi hp



Hnh 4.3. V d v phi hp tr khng cho ng vo khi s dng ng truyn vi

di



Hnh 4.4 V d v phi hp tr khng cho ng ra khi s dng ng truyn vi di

Ta xc nh v jb sau xc nh dn np y tnh khong cch nh 2 hnh 4.4 v 4.5

Ta s c:

Hnh 4.6 Mch khuch i thc hin phi hp tr khng v d trn.



4.3 Thit k on truyn sng dng Microstrip Line

Thit k on truyn sng Z0 = 50 dng Microstrip Line, Substrate FR4 r = 4,6. Gi

s dy ca on truyn sng l h1, v rng l W1. Ta thc hin tm t s W1/h1, d on

W1/h1< 2

1

2

1

W 8

2

A

A

e

h e

Trong A = 1.5577

Vy 12

1

W 8

2

A

A

e

h e= 1.849 < 2

Ta chn h1 = 1 mm v W1 = 1.849 mm.

Kim tra li tnh ton vi phn mm APPCAD ta c kt qu nh sau:

T kt qu tnh ton trn APPCAD ta c cc thng s ca ng truyn sng nh sau

H = 1mm, W = 1.835mm, T = 0.01mm, Z0 = 50.01, = 179.386mm.

T kt qu trn ta c c mch phi hp tr khng nh sau:

Hnh 4.7 Mch khuch i phi hp tr khng

Chng 5. L THUYT KHUCH I CNG SUT


Chng 5

Mch khuch i cng sut c nhim v to ra mt cng sut ln kch thch

ti. Cng sut ra c th t vi trm mw n vi trm watt. Nh vy mch cng sut

lm vic vi bin tn hiu ln ng vo: do ta khng th dng mch tng

ng tn hiu nh kho st nh trong cc chng trc m thng dng phng

php th.

Ty theo ch lm vic ca transistor, ngi ta thng phn mch khuch i

cng sut ra thnh cc loi chnh nh sau:

- Khuch i cng sut loi A: Tn hiu c khuch i gn nh tuyn tnh,

ngha l tn hiu ng ra thay i tuyn tnh trong ton b chu k 360o ca tn hiu

ng vo (Transistor hot ng c hai bn k ca tn hiu ng vo).

- Khuch i cng sut loi AB: Transistor c phn cc gn vng ngng.

Tn hiu ng ra thay i hn mt na chu k ca tn hiu vo (Transistor hot ng

hn mt na chu k - dng hoc m - ca tn hiu ng vo).

- Khuch i cng sut loi B: Transistor c phn cc ti VBE =0 (vng

ngng). Ch mt na chu k m hoc dng - ca tn hiu ng vo c khuch

i.

- Khuch i cng sut loi C: Transistor c phn cc trong vng ngng

ch mt phn nh hn na chu k ca tn hiu ng vo c khuch i. Mch ny

thng c dng khuch i cng sut tn s cao vi ti cng hng v trong

cc ng dng c bit.

Hnh 5.1 m t vic phn loi cc mch khuch i cng sut.



Hnh 5.1 (a) m t vic phn loi cc mch khuch i cng sut.

Hnh 5.1 (b) m t vic phn loi cc mch khuch i cng sut.



5.1 A:

Mch phn cc c nh nh hnh 5.2 l m hnh ca mt mch khuch i cng sut

loi A n gin.

Hnh 5.2

Kho st phn cc

Ta c 0.7cc

B

B

V VI

R

V C BI I

V CE cc C CV V R I

Dng IC c gii hn ti a l cc

Csat

C

VI

R do khi c tn hiu vo, dng IC c

bin i ln nht v tt nht, im tnh Q phi c phn cc sao cho

2

ccCQ

C

VI

R tc / 2CEQ ccV V y l im phn cc mch cho hiu sut ln

nht.

Kho st xoay chiu:

Khi a tn hiu vi vo ng vo (hnh 5.2), dng IC v in th VCE (tn hiu

ra) s thay i quanh im iu hnh Q. Vi tn hiu ng vo nh (hnh 5.4), v

dng in cc nn thay i rt t nn dng in IC v in th VCE ng ra

cng thay i t quanh im iu hnh.

Khi tn hiu ng vo ln, ng ra s thay i rt ln quanh im tnh iu hnh.

Dng IC s thay i quanh gii hn 0mA v VC /RC . in th VCE thay i

gia hai gii hn 0V v ngun VCC (hnh 5.3,5.4).



Hnh 5.3 Tn hiu nh

Hnh 5.4. Tn hiu ln

Kho st cng sut

- Cng sut cung cp c nh ngha:

Pi(dc) = VCC . ICQ (5.1)

- Cng sut ng ra ly trn ti, trong trng hp ny l RC, c nh ngha:

0(ac) ( ) ( ).CE rms C rmsP V I (5.2)

2

0(ac) ( ).C C rmsP R I (5.3)

2

( )

0(ac)

CE ms

C

VP

R (5.4)

Nu tnh theo in th nh v dng in nh: 2

2

( ) ( )2

0(ac) ( ). .R .22

C p C p

C C rms C C

I IP R I R (5.5)



Hoc 2

( )

0(ac)2

CE p

C

VP

R (5.6)

Hoc ( ) ( )0(ac).

2

CE p C pV IP (5.7)

Nu tnh theo in th v dng in nh i nh:

( ) ( ) ( ) ( )

0(ac)

/ 2 / 2 .

2 8

CE p p C p p CE p p C p pV I V I

P (5.8)

Hoc 2

(p p)

0(ac) .R8

C

C

IP (5.9)

Hoc 2

(p p)

0(ac)8

CE

C

VP

R (5.10)

Hiu sut:

Hiu sut mch khuch i c tnh theo cng thc:

0(ac)

i(dc)

%P

P (5.11)

. Hiu sut ti a:

Ta thy trong mch cng sut loi A, VCE c th thay i ti a:

VCE(p-p) max = VCC

Dng IC thay i ti a:

IC(p-p) max = VCC/RC

Cng sut ra ti a:

2

0(ac) max8

cc

C

VP

R

Cng sut cung cp ti a:

2

i(dc) max2

cc

C

VP

R

Hiu sut ti a ca mch:

2

0(ac)

2

i(dc)

max 8% .100% .100% 25%

max

2

cc

C

cc

C

V

P R

VP

R



5.2 :

- mch khuch i cng sut loi B

Trong mch khuch i cng sut loi B, ngi ta phn cc vi VB =0V nn bnh

thng transistor khng dn in v ch dn in khi c tn hiu ln a vo. Do

phn cc nh th nn transistor ch dn in c mt bn k ca tn hiu (bn k

dng hay m ty thuc vo transistor NPN hay PNP). Do mun nhn c c chu

k ca tn hiu ng ra ngi ta phi dng 2 transistor, mi transistor dn in mt

na chu k ca tn hiu. Mch ny gi l mch cng sut y ko (push-pull).

Hnh 5.5 M t mch khuch i cng sut loi B

Tnh ton tng t phn trn ta c thng s sau:

Hiu sut ti a:

% 78.54%

Hiu sut ca mch khuch i loi B cao hn nhiu so vi loi A. thm vo loi

B s khng tiu hao cng sut khi khng c cng sut tn hiu ng vo. y l u

im ln nht trong nhiu ng dng.

- Mch khuch i cng sut loi C

c im: + phi tuyn

+ hiu sut cao, thng c dng trong mch tn s cao

+ Mch khch i loi C c th t c hiu sut 100% khi gim

gc ti 0. V trong khong 0-900 hiu sut l 78.5%.

+ d t c hiu sut cao hn cc loi A,B nhng ng thi n

cng to ra mo nhiu hn 2 loi .

+ mch khuch i lp C thng s dng thm mch cng hng

lc hi tn hiu ng ra.

N


-31122

6.1 C

5V

6.2 T

6.2.1 T

BG13D l

N


6 LM-31122

-31122:

900 MHz; 5V, 394mA (typical)

15.6 dB Gain

47.6 dBm Output IP3

31.6 dBm Output Power at 1dB gain compression

52.5% PAE at P1dB

2 dB Noise Figure

-0C

A = 25 C, Vdd =5V, Vctrl 900MHz

N


-31122

- -31122

5 -31122

- dd = 5V, T = 250C,

f = 900MHz

IC S11 S22 S12 S21

BG13D 0.148 79.53 0.314 90.77 0.032 23.22 17.28 96.74

ALM-31122 0.183 105.8 0.235 176.4 0.077 65.3 6.124 87.6

6.3.1

BG13D

N


2 2 2

11 22 12 21 11 22

21 12

11.167

2. .

S S S S S SK

S S

ALM-31122 2 2 2

11 22 12 21 11 22

21 12

11.227

2. .

S S S S S SK

S S

-

6.3.2 L , S

BG13D

11 22 12 21 0.575 110.64sD S S S S

2 2 2

1 11 221 0.922sB S S D

221

12

10log 10log 1 24.85S

MAG K K dBS

2 22 11 0.28 105.93sC S D S

2 2 2

2 22 111 0.746sB S S D

22

2 2 2

2

40.452

2L

B B C

C

L 2

0.452 105.93L

12 2111

22

0.305 149.391 .S

LS

L

S SS

ALM-31122

11 22 12 21 0.5 30.9sD S S S S

2 2 2

1 11 221 0.728sB S S D

N


221

12

10log 10log 1 16.1S

MAG K K dBS

2 22 11 0.185 155.2sC S D S

2 2 2

2 22 111 0.772sB S S D

22

2 2 2

2

40.43

2L

B B C

C

L 2

0.43 155.2L

12 2111

22

0.077 142.11 .S

LS

L

S SS

IC L S

BG13D 0.452 105.93 0.305 149.39

ALM-31122 0.43 155.2 0.077 142.1

6.3.3

xut hin in cm v in dung k sinh, nn ta dng phng php mch vi d

phi hp tr khng.

BG13D

-

N


6

6

N


-

7

7

N


8

ALM-31122

- i

9 -31122

N


9 -31122

-

10 -31122

N


10 -31122

1 -21122

6.3.4

Thit k on truyn sng Z0 = 50 dng Microstrip Line, Substrate FR4 r = 4,6. Gi

s dy ca on truyn sng l h1, v rng l W1. Ta thc hin tm t s W1/h1, d on

W1/h1< 2

1

2

1

W 8

2

A

A

e

h e

Trong A = 1.5577

Vy 12

1

W 8

2

A

A

e

h e= 1.849 < 2

Ta chn h1 = 1 mm v W1 = 1.849 mm.

Kim tra li tnh ton vi phn mm APPCAD ta c kt qu nh sau:

N


T kt qu tnh ton trn APPCAD ta c cc thng s ca ng truyn sng nh sau

H = 1mm, W = 1.835mm, T = 0.01mm, Z0 = 50.01, = 179.386mm.

T kt qu trn ta c c mch phi hp tr khng 2 IC nh sau:

2

6.3.5

-

BG13D

N


3

ALM-31122

4 ch ALM-31122 trong datasheet

-

5.

KT LUN


HNG M CA TI


T VIT TT


AM : Amplitude modulation

ASK : Amplitude shift keying

BER : Bit Error rate

CPM : Continous Phase Modulation

FM : Frequency modulation

FSK : Frequency shift keying

IF : Intermodulation Frequency

IMD : Intermodulation distoertion

IMR : Intermodulation distoertion ratio

IP : Intercept point

ISI : Intersymbol interfering

LNA : Low noise amplifier

LO : Local oscillator

MDS : Minimum detecable signal

NF : Noise figure

PCM : Phase coding modulation

OOK : On-off keying

RF : Radio frequency

PM : Phase modulation

PSK : Phase shift keying

SNR : signal-to-noise ratio

VSWR : VOLAGE standing wave ratio

TI LIU THAM KHO


[1] TS. Hunh Ph Minh Cng, MICROWAVE INTERGRATED CIRCUITS,

Chapter 4, Microwave Amplifier, Ho Chi Minh city University of Technology, 2014.

[2] Ahmed Sedek Mahmoud Sayed, ULTRA WIDEBAND 5W HYBRID

POWER AMPLIFIER DESIGN USING SILICON CARBIDE FESFETS, Master

of Engineering, Elektrotechnik und Informatik der Technischen Universitt

Berlin, 2005.

[3] Guillermo Gonzalez, MICROWAVE TRANSISTOR AMPLIFIER

Analysis and Design, Second Edition, Prentice Hall.

[4] Marian K.Kazimierczuk, RF POWER AMPLIFIERS, First Edition, A

John Wiley and Sons, Ltd., Publication, 2008.

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Bao Cao Hoan Chinh