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ADS8699: Internal LPF characteristics

Part Number: ADS8699

Tool/software:

Hi,

For our application we want to sample signals from 0Hz to 10kHz with a sample-rate of 25600Hz.

As anti-alias filter we want to use a 4th order butterworth filter at 10kHz.

We found the ADS8699, which would fit very well for our application.

Since it has already an integrated LPF 2nd order, it could minimize our design effort.

Our idea is to use an additional active 2nd order LPF in front of the ADS8699, so the combination of internal and external filter should result in our required filter characteristics.

To calculate the coefficients of the external filter, we need the coefficients of the internal filter.

I found a digram of the filter transfer function in the datasheet in chapter 7.3.5 Second-Order, Low-Pass Filter (LPF).
www.ti.com/.../ads8699.pdf
But it is very hard to get the filter coefficients out of this diagram.

Can you give us more details (especiallly the filter coefficients) about the ADC's internal LPF?