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516 Chapter 9 SAMPLING RATE CONVERSION<br />

Input Signal: x(n) = cos(πn8)<br />

Amplitude Response<br />

1<br />

1<br />

Amplitude<br />

0<br />

Amplitude<br />

−1<br />

1<br />

0 8 16 24 32<br />

n<br />

Output Signal y(n): D = 2<br />

0<br />

0 0.125 0.5 1<br />

Frequency in π units<br />

Log–magnitude Response<br />

0<br />

Amplitude<br />

0<br />

Decibels<br />

−1<br />

−51<br />

0 4 8 12 16<br />

−60<br />

0 0.125 0.5 1<br />

m<br />

Frequency in π units<br />

FIGURE 9.27 Signal plots and filter design plots in Example 9.14<br />

9.5.5 FIR RATIONAL-FACTOR RATE CONVERSION<br />

Replacing the ideal filter of the system given on page 494 with an FIR<br />

filter H(ω), we obtain the system shown in Figure 9.28. In this case the<br />

relevant ideal lowpass filter is given by (9.36), which is repeated here for<br />

convenience.<br />

{<br />

I, 0 ≤|ω| ≤min(π/D, π/I)<br />

H(ω) =<br />

(9.58)<br />

0, otherwise<br />

For the signal x(n) wedefine<br />

• ω x,p as the signal bandwidth that should be preserved<br />

• ω x,s1 as the overall signal bandwidth<br />

• ω x,s2 as the signal bandwidth that is required to be free of aliasing error<br />

after resampling<br />

Then we have<br />

0

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