Slide 1

FILTER DESIGN

Mt s nh ngha min tn s:

Bandwidth = f2-f1 Riple Q factor = fc/(f2-f1) Shape factor = (f4-f3)/(f2-f1)

Cc loi mch lc: Lc thng thp, lc thng cao, lc thng di, lc chn di

Cc p ng ca mch lc hin nay c th l: Butterworth, Chebysev, Belssel

on Quang Hng RF TeamFILTER DESIGN Mt s nh ngha min thi gian:

Rise time: 90% gi tr tn hiu Overshoot Settling time: t thi im t 90% n gi tr n nh

Cc mch lc: Butterworth, Chebysev, Belssel c c trng p ng min thi gian v tn s khc nhau.

FILTER DESIGN Butterworth Filter: c thit k cho ra p ng phng nht c th

Trong : A suy gim tnh ti tn s c- Tn s ct -3 dBn S phn t trong mch LC cu trc Butterworth.FILTER DESIGN Nhn xt: Bit c dc cn thit k, t xc nh c s phn t ti thiu

V d 1: Tnh s phn t LC ti thiu mch lc thng thp p ng Butterworth c dc 36 dB tn s f=3.fc

Li gii: T gin hnh bn, ng vi f/fc=3 , dc t 36 dB, suy ra N>=4. Vy s phn t ti thiu N min=4.

Vn : lm sao c gin hnh bn?FILTER DESIGN

Nu ngun v ti c cng tr khng, cc phn t trong mch c xc nh nh sau:

Ak: phn t th k trong n phn t (c th l t hoc cun cm) Phn t Ak v Ak+1 khng cng tnh cht S dng cng thc xy dng vi n=8, 9,10 .FILTER DESIGN

V d 2: Vi s phn t N=4, tnh cc gi tr chun ha ca mch lc bit tr khng ngun v ti bng nhau.

Li gii:

FILTER DESIGN Cc mch lc chun ha c tr khng ngun v ti l 1, tn s ct -3 dB bng 1 rad/s. Do khi gii quyt cc bi ton thc t cn nhn theo t lV d 3: Thit k mch lc thng thp Butterworth, c tr khng ngun v ti 75, tn s ct fc=65 Mhz, ti tn s f=3fc suy gim ln hn 36 dB.

Li gii:Da vo v d 1: s phn t ti thiu Nmin=4.Vy cu trc mch lc nh v d 2. tnh ton cc gi tr L,C ta s dng cng thc:

FILTER DESIGN Vn :Nu tr khng ngun v ti khng bng nhau?M phng ADS:

FILTER DESIGN Chebysev Filter: c h s Q ln hn mch lc kiu Butterworth, dc c tnh ln hn.

Trong :

RdB: Riple in bandFILTER DESIGN R rng l suy gim tn s f ph thuc vo phng trong di, do s c mt ca

Vi phng trong di 0.01 dBVi phng trong di 0.1 dBFILTER DESIGN

Vi phng trong di 0.01 dBV d 1: Tnh s phn t LC ti thiu mch lc thng thp p ng Chebysev c dc ln hn 24 dB tn s f=3.fc

Li gii: T gin hnh bn, ng vi f/fc=3 , dc t 24 dB, suy ra N>=3. Vy s phn t ti thiu N min=3.

FILTER DESIGN V d 2: Vi s phn t N=3, tnh cc gi tr chun ha ca mch lc bit tr khng ngun v ti bng nhau.

Li gii:

L1= 1.181C2=1.821L3=1.181

FILTER DESIGN V d 3: Thit k mch lc thng thp Chebysev, c tr khng ngun v ti 75, tn s ct fc=65 Mhz, ti tn s f=3fc suy gim ln hn 24 dB. Ripple trong di t 0.01 dB

Li gii:Da vo v d 1: s phn t ti thiu Nmin=3.Vy cu trc mch lc nh v d 2. tnh ton cc gi tr L,C ta s dng cng thc:

FILTER DESIGN

M phng ADSFILTER DESIGN Bessel Filter: c thit k min thi gian c rise time khng ph thuc vo cao xung 1(t) u vo

Trong : A suy gim tnh ti tn s c- Tn s ct -3 dBn S phn t trong mch LC cu trc Bessel.