AD6620
This table helps to calculate an upper bound on decimation,
CIC5, given the desired filter characteristics.
CIC5 Rejection
M
The table below illustrates the amount of bandwidth in percent-
age of the clock rate that can be protected with various decimation
rates and alias rejection specifications. The maximum input rate
into the CIC5 is 32.5 MHz. As in the previous table, these
are the 1/2 bandwidth characteristics of the CIC5. Note that
the CIC5 stage can protect a much wider band than the CIC2 for
any given rejection.
The plots following (Figure 38) represent the CIC5 transfer
function with respect to the CIC5 output rate for a decimation
of 4. The first plot is referenced to the input sample rate and
shows the complex spectrum from –fSAMP/2 to +fSAMP/2. The
second plot is referenced to the CIC5 output rate; the complex
spectrum ranges from –fSAMP5/2 to +fSAMP5/2. Aliased images in
CIC5 “fold back” toward the edge of the desired filter pass
band. It is the level of these aliases as they move into the desired
pass band that are of concern. The improved roll-off of CIC5
over CIC2 can be seen when these plots are compared to those
previously shown for CIC2.
Table IV. SSB CIC5 Alias Rejection Table (fSAMP2 = 1)
Bandwidth Shown in Percentage of fSAMP2
MCIC5 –50 dB –60 dB –70 dB –80 dB –90 dB –100 dB
2
3
4
5
6
7
8
9
10.227 8.078
6.393
5.11
5.066
4.107
3.271
2.687
2.27
1.962
1.726
1.54
4.008
3.297
2.636
2.17
1.836
1.588
1.397
1.247
1.125
1.025
0.941
0.87
0.809
0.755
0.708
0.667
0.63
0.597
0.568
0.541
0.516
0.494
0.474
0.455
0.437
0.421
0.406
0.392
0.379
0.367
0.355
3.183
2.642
2.121
1.748
1.48
1.281
1.128
1.007
0.909
0.828
0.76
0
–20
–40
7.924
6.213
5.068
4.267
3.68
3.233
2.881
2.598
2.365
2.17
6.367
5.022
4.107
3.463
2.989
2.627
2.342
2.113
1.924
1.765
1.631
1.516
1.416
1.328
1.25
1.181
1.119
1.064
1.013
0.967
0.925
0.887
0.852
0.819
0.789
0.761
0.734
0.71
4.057
3.326
2.808
2.425
2.133
1.902
1.716
1.563
1.435
1.326
1.232
1.151
1.079
1.016
0.96
–60
–80
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
1.39
1.266
1.162
1.074
0.998
0.932
0.874
0.823
0.778
0.737
0.701
0.667
0.637
0.61
2.005
1.863
1.74
0.703
0.653
0.61
–100
–120
1.632
1.536
1.451
1.375
1.307
1.245
1.188
1.137
1.09
1.046
1.006
0.969
0.934
0.902
0.872
0.844
0.818
0.572
0.539
0.509
0.483
0.459
0.437
0.417
0.399
0.383
0.367
0.353
0.34
0.328
0.317
0.306
0.297
0.287
–0.5 –0.4 –0.3 –0.2 –0.1
0
0.1 0.2
0.3
0.4
0.5
f/f
SAMP
0
0.91
0.865
0.824
0.786
0.752
0.721
0.692
0.666
0.641
0.618
0.597
0.577
0.559
0.541
–20
–40
–60
–80
0.584
0.561
0.54
0.52
0.501
0.484
0.468
0.453
0.439
–100
–120
0.687
0.666
–0.5 –0.4 –0.3 –0.2 –0.1
0
0.1 0.2
0.3
0.4
0.5
f/f
SAMP5
Figure 38. CIC5 Alias Rejection, MCIC5 = 4
REV. A
–24–
ADI [ ADI ]
