for a precision weigh scale application I got into data sheets of 24 bit ADC (I am testing AD7195).
What I don't understand:
When I look data sheet AD7195, page 35, Figure 29, Figure 30 and Table 30:
1.) FS= 80 => output rate 15 Hz; Figure 29 shows approx. -3dB @ 15Hz
and almost no supression at nyquist frequency (of output rate)!
2.) FS= 480 => output rate 2.5 Hz; first filter-zero is at 10 Hz; almost no supression at 1,25 Hz.
Doesn't this behaviour create aliasing (Fin >= 1/2 Outputrate)??
Or is there a misunderstanding?
Why there is no modern ADC with a REAL digital filter (FIR), that have > -80dB at 1/2 output rate?
Do I need an anti-aliasing filter to cut off Fin <<1/2 output rate?