AMC1210_14 Datasheet, PDF (18/54 Pages) Texas Instruments – Quad Digital Filter for 2nd-Order Delta-Sigma Modulator

AMC1210
SBAS372D – APRIL 2006 – REVISED MAY 2009.............................................................................................................................................................. www.ti.com
The comparator filter unit and the sinc filter unit differ in the way they handle input data. The comparator filter unit
translates a low input signal to a '0' and a high input signal to a '1', whereas the sinc filter unit uses '–1' and '1'.
The resulting calculations give only positive values for the output of the comparator filter. The data representation
is straight binary. Table 9 and Figure 14 show the different full-scale values that the comparator filter can store
using different oversampling ratios.
OSR
x
4
8
16
32
Table 9. Peak Data Values for Different OSR/Filter Combinations
Sinc¹
0 to x
Sinc²
0 to x²
Sinc³
0 to x³
0 to 4
0 to 16
0 to 64
0 to 8
0 to 64
0 to 512
0 to 16
0 to 256
0 to 4096
0 to 32
0 to 1024
0 to 32,768
Sincfast
0 to 2x²
0 to 32
0 to 128
0 to 512
0 to 2048
100000
10000
1000
100
10
3
Sinc
Sincfast
2
Sinc
1
Sinc
1
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
Oversampling Ratio
Figure 14. Comparator Filter Resolution
The maximum resolution yields the peak values in Table 9 (15 bits binary, 32,768 decimal). Note that in order to
achieve the maximum value, the delta-sigma modulator is operated at absolute maximum positive or negative
full-scale, which is outside of the recommended full-scale range of 80% of most delta-sigma modulators.
Sinc Filter Unit
The AMC1210 utilizes a standard integration/decimation/differentiation scheme to achieve the sinc filter. It can be
configured as a Sinc¹, Sinc², Sinc³ or Sincfast filter with oversampling ratios (OSRs) continuously between 1 and
256. Figure 15 illustrates the frequency response of each type of filter.
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