CS5532-BS 查看數據表（PDF） - Cirrus Logic
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CS5532-BS Datasheet PDF : 50 Pages
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CS5532/34-BS
2.9. Digital Filter
The CS5532/34 have linear phase digital filters
which are programmed to achieve a range of output
word rates (OWRs) as stated in the Channel-Setup
Register Descriptions section. The ADCs use a
Sinc5 digital filter to output word rates at 3200 Sps
and 3840 Sps (MCLK = 4.9152 MHz). Other out-
put word rates are achieved by using the Sinc5 filter
followed by a Sinc3 filter with a programmable
decimation rate. Figure 16 shows the magnitude re-
sponse of the 60 Sps filter, while Figures 17 and 18
show the magnitude and phase response of the filter
at 120 Sps. The Sinc3 is active for all output word
rates except for the 3200 Sps and 3840 Sps
( ) Sin x 3
x
0
-40
-80
-120
0
60 120 180 240 300
Frequency (Hz)
Figure 16. Digital Filter Response (WR = 60 Sps)
(MCLK = 4.9152 MHz) rate. The Z-transforms of
the two filters are shown in Figure 19. For the Sinc3
filter, “D” is the programmable decimation ratio,
which is equal to 3840/OWR when FRS = 0 and
3200/OWR when FRS = 1.
The converter’s digital filters scale with MCLK.
For example, with an output word rate of 120 Sps,
the filter’s corner frequency is at 31 Hz. If MCLK
is increased to 5.0 MHz, the OWR increases by
1.0175% and the filter’s corner frequency moves to
31.54 Hz. Note that the converter is not specified to
run at MCLK clock frequencies greater than
5 MHz.
0
-40
-80
-120
Flatness
Frequency dB
2
-0.01
4
-0.05
6
-0.11
8
-0.19
10
-0.30
12
-0.43
14
-0.59
16
-0.77
19
-1.09
32
-3.13
0
40
80
120
Frequency (Hz)
Figure 17. 120 Sps Filter Magnitude Plot to 120 Hz
180
90
0
-90
-180
0
30
60
90
120
Frequency (Hz)
Figure 18. 120 Sps Filter Phase Plot to 120 Hz
Sinc5
=
-(--1----–-----z---–--8--0---)--5-
(1 – z–16)5
×
-(--1----–-----z---–--1--6---)--3-
(1 – z–4)3
×
-(--1----–-----z---–--4---)--2-
(1 – z–2)2
×
-(--1----–-----z---–--2---)--3-
(1 – z–1)3
Sinc3 = -(--1----–-----z---–--D----)--3-
(1 – z–1)3
Note:
See the text regarding the Sinc3 filter’s
decimation ratio “D”.
Figure 19. Z-Transforms of Digital Filters
38
DS755F3
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