Ex.7.1 Determining Specifications for a Discrete-Time Filter Specifications of the continuous-time filter: ◆1.passband1-0.01<He(J2<l+0.01,for0≤2≤2π(2000) ◆2.stopband(2l<0.001,for2π(3000)≤2 He(j)川 近似地认为H(2)=0,2π/T=2π5000 δp1=0p21+dp 可作为fmax 离散时间系统 hin]=Th (nT) =0.01 1-62 aliasing avoided nearly 近似满足采样定理 Passband i Transition Stopband T=104s 只需变换频率 2.=2m(10000) 6,=0.0016s2。=2t2000) 由变换公式： =T 0 n.2、=2π(3000) π T下 CT系统频率响应→=DT系统频率响应，当低于Nyquist频率时 1414 Ex. 7.1 Determining Specifications for a Discrete-Time Filter ◆Specifications of the continuous-time filter: ◆1. passband ◆2. stopband 1 2 0.01 P P   = = 0.001 S  = 2 (2000)  = p  2 (3000)  = s  2 (10000)  =s  1+ P1 1− P2  S aliasing avoided nearly 4 T s 10− = H j T c (  =  ) 0, =2 5000   近似满足采样定理 CT系统频率响应→ =DT系统频率响应, 当低于Nyquist频率时 = T 只需变换频率, 由变换公式: 近似地认为 T  1 0.01 1 0. −    + H j for eff( ) 01, 0 2 20  ( 00) H j for eff(  ) 0.001, 2 3000 ( ) [ ] ( ) c h n Th nT = 可作为 max f 离散时间系统