5.1.1 Ideal Frequency-Selective Filters Ideal bandstop filter h,e）+,e(e-8 01@Kw2 others hos n]=n] sinan sinaan ，-0<n<0 πn πn .Noncausal,not computationally realizable ◆no phase distortion 1H(el) -π-02 一0%0 0c2 8
◆Ideal bandstop filter − 0 ( ) H ej 1 −c2 −c1 c1 c2 5.1.1 Ideal Frequency-Selective Filters 8 ◆Noncausal, not computationally realizable ◆no phase distortion 2 1 sin [ ] sin , bs c n c n n n n n n h = + − − ( ) ( ) ( ) 0, | | 1 2 1, j c c b j hp j lp H es oth r H H e e s e + = =
Stages of Filter Design 1.Determine the specification of the desired properties of the system(filter). 2.The approximation of the specifications using(designing)a causal discrete-time system. 3.The realization of the system. ◆Our focus is on second step.(实验侧重3) Specifications are typically given in the frequency domain. 9
9 Stages of Filter Design ◆1. Determine the specification of the desired properties of the system(filter). ◆2.The approximation of the specifications using(designing) a causal discrete-time system. ◆3. The realization of the system. ◆Our focus is on second step.(实验侧重3) ◆Specifications are typically given in the frequency domain
7.1 Filter Specifications THe figure depicts the typical representation of tolerance limits associated with approximating a discrete-time ideal lowpass filter. H(ej)l 容差极限 In passband, tolerance scheme容限图 1+δp H(may vary symmetrically around1,δp1=δp2 1 1-823H(elo)3Hp,laop 1- or1-ozH(e/lls0δ1=0 Passband Transition Stopband In stopband,H(eo)l≤δs,wzo cutoff frequency edge frequency 0 T 10通带边界（截止）频率 阻带边界（截止）频率
10 7.1 Filter Specifications tolerance scheme 容限图 ◆The figure depicts the typical representation of tolerance limits associated with approximating a discrete-time ideal lowpass filter. edge frequency |H(e j)| may vary symmetrically around 1, δp1=δp2 or ,δp1=0 cutoff frequency 1 c 容差极限 通带边界(截止)频率 阻带边界(截止)频率 P S 1- 1 p2 ( ) H j e ， p 1- 1+ p p 2 1 ( ) H j e ， p In passband, In stopband, |H(e j)|≤δs , ||≥s
7.1 Filter Specifications nd constraints on phase response other than implicit requirements of stability and causality for IIR filter. The constraint for FIR filters:linear phase. H(ej)l 容差极限 In passband, tolerance scheme容限图 1+δp H()may vary symmetrically around 1,1=p2 1 1- 1-82H(el@)31+p,laop P2 or1-o2H(eoKl,osδ1=0 Passband Transition Stopband In stopband,lH(eo)l≤δs,ozos cutoff frequency edge frequency 0 W T 1通带边界（截止）频率 阻带边界（截止）频率
11 7.1 Filter Specifications tolerance scheme 容限图 edge frequency |H(e j)| may vary symmetrically around 1, δp1=δp2 or ,δp1=0 cutoff frequency 1 c 容差极限 通带边界(截止)频率 阻带边界(截止)频率 P S 1- 1 p2 ( ) H j e ， p 1- 1+ p p 2 1 ( ) H j e ， p In passband, In stopband, |H(e j)|≤δs , ||≥s ◆no constraints on phase response other than implicit requirements of stability and causality for IIR filter. ◆The constraint for FIR filters: linear phase
Ex.7.1 Determine Specifications for a Discrete- Time Filter H(ei). given: Specifications of the continuous-time filter: ◆1.passband1-0.01<He(/2kl+0.01,for02≤2π(2000) ◆2.stopband m(2<0.001,for2π(3000)≤2 f®-47 CID H(ej) DIC xa(t) x(n] y[n] T=104s 2=27=2x00000) T For bandlimited input,aliasing avoided when sampling frequency is high enough 12
12 ◆Specifications of the continuous-time filter: ◆1. passband ◆2. stopband 1 0.01 1 0. − + H j for eff( ) 01, 0 2 20 ( 00) H j for eff( ) 0.001, 2 3000 ( ) 4 T s 10− = ( ) 2 S 2 10000 T = = ( ) ( ) , , 0, j T eff H e H T j T = For bandlimited input, aliasing avoided when sampling frequency is high enough Ex. 7.1 Determine Specifications for a DiscreteTime Filter H(e j) . given: If 可作为