AMC1203 Datasheet, PDF (16/23 Pages) Texas Instruments – 1-Bit, 10MHz, 2nd-Order, Isolated Delta-Sigma Modulator

AMC1203
SBAS427 – FEBRUARY 2008
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:
SNR = 1.76dB + 6.02dB ´ ENOB
(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 sinc³ filter requires three data clocks for full
settling (with f_DATA = f_MOD/OSR). Therefore, for
over-current protection, filter types other than sinc³
might be a better choice; an alternative is the sinc²
filter. Figure 29 compares the settling times of
different filter orders (sincfast is a modified sinc²
filter):
2
H(z) =
1 - z^-OSR
1 - z^-1
(1 +
z ) ^-2OSR
(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.
www.ti.com
16
14
12
10
8
6
4
2
0
1
sinc³
sincfast
sinc²
sinc
10
100
OSR
1000
Figure 28. Measured Effective Number of Bits vs
Oversampling Ratio
10
sinc³
9
8
sincfast
7
sinc²
6
5
4
sinc
3
2
1
0
0 1 2 3 4 5 6 7 8 9 10
Settling Time (ms)
Figure 29. Measured Effective Number of Bits vs
Settling Time
16
Submit Documentation Feedback
Product Folder Link(s): AMC1203
Copyright © 2008, Texas Instruments Incorporated