AMC1210_14 Datasheet, PDF (19/54 Pages) Texas Instruments – Quad Digital Filter for 2nd-Order Delta-Sigma Modulator

AMC1210
www.ti.com.............................................................................................................................................................. SBAS372D – APRIL 2006 – REVISED MAY 2009
1
(1)
SINC FILTER RESPONSE
0
-20
-40
-60
-80
-100
-120
0
0
312.5k
625k
937.5k
Frequency (Hz)
3
(1)
SINC FILTER RESPONSE
-20
-40
-60
-80
-100
-120
0
312.5k
625k
937.5k
Frequency (Hz)
NOTE:
(1)
f_DATA
=
312.5kHz
=
f_CLK
OSR
=
10MHz
32
0
-20
-40
-60
-80
-100
1562.5k
-120
0
0
-20
-40
-60
-80
-100
1562.5k
-120
0
2
(1)
SINC FILTER RESPONSE
312.5k
625k
937.5k
Frequency (Hz)
(1)
SINCFAST FILTER RESPONSE
312.5k
625k
937.5k
Frequency (Hz)
Figure 15. AMC1210 Frequency Responses with Various Sinc Filters
1562.5k
1562.5k
These figures show the digital filter frequency response for one oversampling ratio (SOSR = 32) and a modulator
rate of 10MHz.
The general purpose of the digital filter is to average the input modulator data. Achieving higher resolution
requires additional samples for averaging, thereby increasing the total samples necessary to accurately
represent an abrupt change. It also requires additional clock cycles to complete a single sample. The ratio of
clock cycles to output samples is controlled by the SOSR value (the oversampling ratio for the sinc filter unit) in
the Sinc Filter Parameter Register. Table 10 and Figure 16 show the maximum resolution given different filter
structures and SOSR values.
SOSR
x
4
8
16
32
64
128
256
Table 10. Peak Data Values for Different SOSR/Filter Combinations
Sinc¹
x
Sinc²
x²
Sinc³
x³
Sincfast
2x²
–4 to 4
–16 to 16
–64 to 64
–32 to 32
–8 to 8
–64 to 64
–512 to 512
–128 to 128
–16 to 16
–256 to 256
–4096 to 4096
–512 to 512
–32 to 32
–1024 to 1024
–32,768 to 32,768
–2048 to 2048
–64 to 64
–4096 to 4096
–262,144 to 262,144
–8192 to 8192
–128 to 128
–16,384 to 16, 384
–2,097,152 to 2,097,152
–32,768 to 32,768
–256 to 256
–65,536 to 65,536
–16,777,216 to 16,777,216
–131,072 to 131,072
Copyright © 2006–2009, Texas Instruments Incorporated
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