AMC1210 Datasheet, PDF (42/47 Pages) Burr-Brown (TI) – Quad Digital Filter for 2nd-Order Delta-Sigma Modulator

AMC1210
SBAS372A – APRIL 2006 – REVISED OCTOBER 2006
APPLICATION INFORMATION (continued)
www.ti.com
10
ADS1203
9
8
7
6
5
4
3
2
1
0
0
2
3
Sinc
2
Sinc
4
6
Settling Time (ms)
Sincfast
1
Sinc
8
10
Figure 27. Effective Number of Bits vs Settling Time (ADS1203)
The user should choose a digital filter that gives the maximum ENOB for the desired settling time. If a 3.2µs
settling time is assumed, the user should select a Sinc² filter. For any delay greater than 4µs, the user should
choose a Sinc³ filter.
The total delay can be represented by Equation 12:
Group_Delay
+
Order_of_Filter
@
OSR
f_MODULATOR
(12)
We can then calculate what OSR is necessary to achieve a delay time of 3.2µs by using Equation 13.
OSR
+
Group_Delay @ f_MODULATOR
Order_of_Filter
+
3.2ms
@ 10MHz
2
+
16
(13)
A Sinc² comparator filter with an OSR of 16 satisfies the settling time requirements for this example system. A
high and low comparator value can be chosen by referring to Table 9. For the present example, the comparator
filter is capable of a span of 256 codes (from 0 to 256). If an over-current situation is defined at ±25% of the
modulator full-scale range, the High Level Threshold level (HLT15–0) and Low Level Threshold level (LLT15–0)
should be set to a maximum value of 64 from the full-scale values, or 64 to 192. It may also be necessary to
lower this value to avoid an accidental over-current situation. If a 5% guardband is presumed, the threshold
levels should be set to 60 and 196.
Hall Sensor Measurement
The AMC1210 can be used directly with the ADS120x family of modulators to interface with Hall sensors in
order to provide magnetic field strength measurements. The ADS1208 is a 16-bit, second order, delta-sigma
modulator with Hall element biasing circuitry. By connecting the MCLK and MDATA lines of the ADS1208 to the
INx and CLKx lines, the AMC1210 needs only a system clock to provide filtered data from the modulator.
42
Submit Documentation Feedback