A5191HRTNGEVB
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Figure 16. Group Delay of the Total Filter
First Stage
The first stage of the filter is implemented as a modified
third−order high pass active filter.
Consider the circuit shown in Figure 17. This resembles
the implemented filter except for the coupling capacitor on
the operational amplifier, and the removal of R
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. The filter
is a variation on the Sallen−Key topology with three poles.
The AREF voltage serves here as a biasing voltage, but can
for ac frequencies be regarded as ground. For a complete
analysis of this filter type, see the Appendix on Page 17.
Figure 17. Simplified First Filter Stage Schematic