Datasheet

SNR=1.76dB+6.02dB ENOB´
16
14
12
10
8
6
4
2
0
ENOB(Bits)
OSR
1 10 100 1000
sinc
3
sinc
sinc
2
sincfast
H(z)=
1 z-
-OSR
1 z-
-1
2
(1+z )
-2OSR
10
9
8
7
6
5
4
3
2
1
0
ENOB(Bits)
SettlingTime( s)m
1 2 3 4 5 6 7 8 90 10
sinc
2
sinc
sinc
3
sincfast
AMC1203
SBAS427C –FEBRUARY 2008– REVISED JUNE 2011 www.ti.com
The effective number of bits (ENOB) is often used to
compare the performance of ADCs and delta-sigma
modulators. Figure 28 shows the ENOB of the
AMC1203 with different oversampling ratios. In this
data sheet, this number is calculated from the SNR
using following formula:
(2)
In motor-control applications, a very fast response
time for the over-current detection is required. The
time for full settling of the filter depends on its order
(that is, a sinc
3
filter requires three data clocks for full
settling (with f
DATA
= f
MOD
/OSR). Therefore, for
over-current protection, filter types other than sinc
3
might be a better choice; an alternative is the sinc
2
filter. Figure 29 compares the settling times of
Figure 28. Measured Effective Number of Bits vs
different filter orders (sincfast is a modified sinc
2
Oversampling Ratio
filter):
(3)
For more information, see application note SBAA094,
Combining the ADS1202 with an FPGA Digital Filter
for Current Measurement in Motor Control
Applications, available for download at www.ti.com.
Figure 29. Measured Effective Number of Bits vs
Settling Time
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