Cirrus Logic CRD5381 - Manual (Page 7)

DS563RD1 7
CRD5381
1.3 Filter Response
The transition-band response of the CRD5381 is due to the combination of the digital filtering performed by both the
CS5381 and the CS8421. Due to the superior stop-band rejection of the CS8421, the combination of the two parts
yields a better stop-band rejection then the CS5381 alone. When the output sample rate is close to that of the
CS5381, signals that fall within the transition-band spectrum will already have been aliased down into the pass-band
prior to the CS8421’s output filter. This can be seen in
Figure 3 on page 8 , where the signals above the notch at
approximately 97.5 kHz represent signals that have been aliased downward prior to the action of the CS8421 output
filter.
Figure 1. Transitional Band, 48 kHz Out
-120
+0
-115
-110
-105
-100
-95
-90
-85
-80
-75
-70
-65
-60
-55
-50
-45
-40
-35
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-25
-20
-15
-10
-5
d
B
F
S
20k 26k 20.5k 21k 21.5k 22k 22.5k 23k 23.5k 24k 24.5k 25k 25.5k
Hz