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LOGO
II : CC MCH VNG KHA PHA (PLL)
1: Tng quan PLL ( Phase-Locked Loop )
- L h thng vng kn hi tip
- Tn hiu vo c th c dng tng t hnh sine hoc dng s.
- ng dng rng ri trong cc mch lc, tng hp tn s, iu ch v gii iu ch, iu khin t ng . . .
- C rt nhiu kiu mch PLL v phc v cho nhiu mc ch
LOGO 2: S khi
LOGO 2: S khi
Tch sng pha: So snh tn hiu vo v tn hiu ra ca VCO to ra tn hiu sai lch Vd(t).
Lc thng thp: Lc gn ca in p Vd(t)
Khuch i mt chiu: Khuch i in p mt chiu Vdk(t).
VCO(Voltage Controled Oscillator): B dao ng m tn s ra c iu khin bng in p a vo.
LOGO 3: Hot ng ca mch
Nguyn l hot ng
Cc thnh phn ca PLL
VCO (Voltage controlled oscillator )
Hot ng ca mch
Khuch i mt chiu
LOGO 3: Hot ng ca mch
1: Nguyn l hot ng
- Hot ng theo nguyn tc vng iu khin m i lng vo v ra l tn s, chng c so snh vi nhau v pha.
LOGO 3: Hot ng ca mch
Di bt Bc (Cature range): Bc = f2 f1
- Di tn s m tn hiu vo ban u phi lt vo PLL thit lp ch ng b.
- Bc ph thuc vo bng thng LPF.
LOGO 3: Hot ng ca mch
Di kha Bl: K hiu Bl = fmax fmin.
- Gii tn s m PLL ng nht c tn s f0 vi f1.
- Ph thuc hm truyn t ca b tch sng pha, khuch i, VCO.
- Khng ph thuc vo p tuyn b lc LPF v PLL (khi PLL kha pha f1 - f0 = 0).
- ch kha pha, dao ng f0 ca VCO bn ng b theo f1 (Bl > Bc).
LOGO 3: Hot ng ca mch
LOGO 3: Hot ng ca mch
LOGO 3: Hot ng ca mch
Cc thnh phn ca PLL
- B tch sng pha: C 3 loi
- Tng ng dng mch chn
- S thc hin bi mch s EX-OR,RS FlipFlop
- Tch sng pha ly mu
- B tch sng pha tng t
LOGO 3: Hot ng ca mch
Ng ra ca in p c:
LOGO 3: Hot ng ca mch
B tch sng pha s:
- Dng mch s EX-OR, R-S Flip Flopc p tuyn so snh pha dng:
LOGO 3: Hot ng ca mch
Lc thng thp LPF:
- Mch lc bc 1, c th dng th ng hoc tch cc
- Ng ra gm nhiu thnh phn f0,f1,f1-f0,...
- Hot ng chnh xc khi f0,f1 thp.
LOGO 3: Hot ng ca mch
Khuch i mt chiu
- Khuch i tn hiu bin i chm (DC) sau b lc thng thp LPF. li Ka
LOGO 3: Hot ng ca mch
VCO (Voltage controlled oscillator)
- Mch dao ng c tn s c kim sot bng in p.
- Quan h in p iu kin Vdk(t) v tn s ra f0(t) phi tuyn tnh.
- V nguyn tc c th dng mi mch dao ng. Tuy nhin cc b dao ng to xung ch nht c s dng rng ri v loi ny c th lm vic t 1MHz 100MHz
LOGO 3: Hot ng ca mch
VCO (Voltage controlled oscillator)
- T 1MHz 50MHz thng dng mch dao ng a hi.
LOGO 3: Hot ng ca mch
LOGO 3: Hot ng ca mch
LOGO 4: ng dng ca vng kha pha PLL
ng dng ca vng kha pha PLL
S Dng Trong
FM
Stereo
Gii iu Ch AM
ng B Tn S Ngang
V Dc Trong
TV
Gii iu Ch FSK
Gii iu Ch FM
B Tng Hp Tn S n
LOGO 4: ng dng ca vng kha pha PLL
B tng hp tn s n
- S dng cc b tng hp tn s da trn nguyn l vng kha pha PLL
- u im nh gn, khng yu cu chnh xc c kh cao, ng dng cc thnh qu cng ngh sn xut vi mch. . .
- ng thi khi kt hp vi thch anh, n c kh nng to ra di rng, chnh xc cao, gi thnh thp. . .
LOGO 4: ng dng ca vng kha pha PLL
- Khi PLL thc hin kha pha, th ta c:
fref =fvco / N => fvco = N*fref = f0
B iu khin tn s ny c th c iu khin d dng nh my tnh, t xa. Gim gi thnh v phc tp so vi trc y
LOGO 4: ng dng ca vng kha pha PLL
- Khuyt im l n ch to ra cc tn s bng bi s ca tn s chun f0= N*fref
- Khc phc bng cch chia nh t/s chun
LOGO 4: ng dng ca vng kha pha PLL
Gii iu ch FM
- Thc hin bng cch ci t tn s dao ng t do fn bng tn s trung tm tn hiu FM ng vo c bin khng i
- Trong nhiu ng dng c th, trc tch sng pha PLL c mch khuch i hn bin
LOGO 4: ng dng ca vng kha pha PLL
Gii iu ch FSK
- Dng c bit ca FM, ch c 2 tn s iu tn. Lin quan n tch (gii m) tn hiu quay s in thoi nt nhn v truyn tn hiu s FSK
- Ng ra ca PLL dng 2 mc in p
LOGO 4: ng dng ca vng kha pha PLL
ng b tn s ngang dc trong TV
LOGO 4: ng dng ca vng kha pha PLL
Gii iu ch AM
LOGO 4: ng dng ca vng kha pha PLL
Gii iu ch AM
- Vo(t) t l vi m(t) tc l t l vi tn hiu gii iu ch AM
- L kiu tch sng trc tip khng cn i tn, c u im khng dng trung tn, khng chn lc tn s nh.
- bin tn hiu ra ln nht ta dng b tch sng ng b
LOGO 4: ng dng ca vng kha pha PLL
Gii iu ch AM
- Tch sng ng b c cht lng tch sng khng ng b khi t s S/N nh
LOGO 4: ng dng ca vng kha pha PLL
S dng trong FM Stereo
- S khi my pht FM Stereo
LOGO 4: ng dng ca vng kha pha PLL
S dng trong FM Stereo
- Ph ca tn hiu FM Stereo
LOGO 4: ng dng ca vng kha pha PLL
S dng trong FM Stereo
- S khi my thu FM Stereo
LOGO 4: ng dng ca vng kha pha PLL
S dng trong FM Stereo
- ng dng PLL trong vic gii m FM Stereo