AD6622
–15–
REV. 0
–
150
–
2
–
1
d
0
1
2
–
130
–
110
–
90
–
70
–
50
–
30
–
10
10
Figure 16. Unfiltered CIC2 Interpolation Images
The CIC2 rejects each of the undesired images while passing
the image at baseband. The images of a pure tone at channel
center (dc) are nulled perfectly, but as the bandwidth increases
the rejection is diminished. The lower band edge of the
fi
rst
image always has the least rejection. In this example, the CIC2
is interpolating by a factor of
fi
ve and the input signal has a band-
width of 0.0033 of the CIC5 output sample rate. Figure 17
shows
–
110 dBc rejection of the lower band edge of the
fi
rst
image. All other image frequencies have better rejection.
–
150
–
2
–
1
d
0
1
2
–
130
–
110
–
90
–
70
–
50
–
30
–
10
10
Figure 17. Filtered CIC2 Interpolation Images
Table IV lists maximum bandwidth that will be rejected to various
levels for CIC2
interpolation factors from 1 to 32. The example
above corresponds to the listing in the
–
110 dB column and
the L
CIC2
= 5 row. It is worth noting that the rejection of the
CIC2 improves as the interpolation factor increases.
Table IV. CIC2 Alias Protection
–110 dB
–100 dB
–90 dB
–80 dB
–70 dB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Full
0.0023
0.0029
0.0032
0.0033
0.0034
0.0034
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
0.0035
Full
0.0040
0.0052
0.0057
0.0059
0.0060
0.0061
0.0062
0.0062
0.0062
0.0062
0.0062
0.0062
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
0.0063
Full
0.0072
0.0093
0.0101
0.0105
0.0107
0.0108
0.0109
0.0110
0.0110
0.0110
0.0111
0.0111
0.0111
0.0111
0.0111
0.0111
0.0111
0.0111
0.0111
0.0111
0.0111
0.0111
0.0112
0.0112
0.0112
0.0112
0.0112
0.0112
0.0112
0.0112
0.0112
Full
0.0127
0.0165
0.0179
0.0186
0.0189
0.0192
0.0193
0.0194
0.0195
0.0195
0.0196
0.0196
0.0196
0.0197
0.0197
0.0197
0.0197
0.0197
0.0197
0.0197
0.0197
0.0197
0.0197
0.0198
0.0198
0.0198
0.0198
0.0198
0.0198
0.0198
0.0198
Full
0.0226
0.0292
0.0316
0.0328
0.0334
0.0338
0.0341
0.0343
0.0344
0.0345
0.0346
0.0346
0.0347
0.0347
0.0347
0.0348
0.0348
0.0348
0.0348
0.0348
0.0348
0.0348
0.0348
0.0349
0.0349
0.0349
0.0349
0.0349
0.0349
0.0349
0.0349