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Technical question about anti aliasing filter

Dear All,

I want to use the ADC ( 16 Ch., 80 nS conversion rate ) of TMS320F28335.

It is required only 5 Ch. and 3.5 kHz per Ch. rate, designed for 350 Hz analog signal.

For converting analog to digital, I have tow methods:

- To place a 3.3 nF-56 Ohm anti aliasing filter, sampling by 80 nS rate and to down-sample in the program. ( The 3.3 nF-56 Ohm network is provided in the experimenter kit of the MCU ).

- To place an anti aliasing filter, designed for 350 Hz, and sampling by 3.5 kHz ( 1 Ch. ).

Important constraint: Negligible phase error.

Probably the first method is better choice, as in low frequencies, designing a filter having small phase error is a hard work.

Which of the tow methods is better?

Best Regards,

Ras Sharif