ADC Channel Design Overview
 The ADC Channel Design process selects and assembles elements in the signal path, from the signal being acquired to the analog to digital converter. The input signal is representative of a sensor output signal that has been amplified or otherwise adjusted using appropriate signal conditioning.
An anti-aliasing filter is included, to prevent out-of-bandwidth signal or noise from being aliased into the signal being acquired. The filter uses the multiple-feedback topology, which holds a steady common-mode voltage, minimizing linearity errors from the amplifier. Gain is added in the filter to increase the input signal to a level matching the ADC input range.
Following the filter is a simple R-C combination to decouple the filter circuit from the ADC. The value of the capacitor is selected to make the effects of changing ADC input capacitance negligible. The resistor is set to 22ohms.
Designer News! The anti-aliasing filter is now 2nd order, and is designed separately from the R-C input to the ADC. This generally gives smaller component values for the R-C network, while still taking advantage of the anti-aliasing filter function.
The anti-aliasing filter will be tested to see that its attenuation at the Nyquist frequency (= Sample Rate/2) meets your requirements. All components in the schematic above will be selected. System performance will be presented, and adjustments to the design will be suggested to improve yield over temperature and component tolerance variations.
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