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ManualsBrandsTEXAS INSTRUMENTS ManualsData collecting ICsData acquisition IC - ADC 16 Bit SOIC 16
11121314151617181920
16
14
12
10
8
6
4
2
0
ENOB(Bits)
SettlingTime( s)m
1 2 3 4 5 6 7 8 90 13
sinc
2
sinc
1
sinc
3
sincfast
121110
16
14
12
10
8
6
4
2
0
ENOB(Bits)
OSR
1 10 100 1000
sinc
3
sinc
1
sinc
2
sincfast
H(z)=
1 z-
-OSR
1 z-
-1
2
(1+z )
-2OSR
SNR=1.76dB+6.02dB ENOB´
0
-10
-20
-30
-40
-50
-60
-70
-80
Gain(dB)
Frequency(kHz)
0 200 400 600 800 1000 1200 1400 1600
f
DATA
=20MHz/64=312.5kHz
-3dB:81.9kHz
OSR=64
30k
25k
20k
15k
10k
5k
0
OutputCode
NumberofOutputClocks
0 5 10 15 20 25 30 35 40
f =20MHz
MOD
OSR=64
FSR=32768
ENOB=12Bits
SettlingTime=
3 1/f´
DATA
=9.6 sm
AMC1204
AMC1204B
www.ti.com
SBAS512D –APRIL 2011–REVISED DECEMBER 2013
In a sinc
3
filter response (shown in Figure 46 and Figure 47), the location of the first notch occurs at the
frequency of output data rate f
DATA
= f
CLK
/OSR. The –3dB point is located at half the Nyquist frequency or f
DATA
/4.
For some applications, it may be necessary to use another filter type with different frequency response.
Performance can be improved, for example, by using a cascaded filter structure. The first decimation stage could
be built of a sinc
3
filter with a low OSR and the second stage using a high-order filter.
Figure 46. Frequency Response of the Sinc
3
Filter Figure 47. Pole Response of the Sinc
3
Filter
The effective number of bits (ENOB) is often used to compare the performance of ADCs and ΔΣ modulators.
Figure 48 illustrates the ENOB of the AMC1204 and AMC1204B with different oversampling ratios. In this data
sheet, this number is calculated from SNR using Equation 2:
(2)
In motor control applications, a very fast response time for overcurrent detection is required. The time for fully
settling the filter depends on its order; that is, a sinc
3
filter requires three data clocks for full settling (with f
DATA
=
f
CLK
/OSR). Therefore, for overcurrent protection, filter types other than sinc
3
might be a better choice; an
alternative is the sinc
2
filter. Figure 49 compares the settling times of different filter orders with sincfast being a
modified sinc
2
filter with behavior as shown in Equation 3.
(3)
Figure 48. Measured Effective Number of Bits Figure 49. Measured Effective Number of Bits
versus Oversampling Ratio versus Settling Time
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