Posting a question for a customer using the PCM4222...
I have a question about the PCM4222 low group delay decimation/anti-alias filter. I took a look through the data sheet and can see the filter is specified up to about 4*Fs. In this case, I’m not sure exactly WHICH Fs it’s talking about. The part has several modes of operation. The mode we are operating in is Quad mode, so the oversampling is stuck at 32x Fs/2 (An assumption on my part). This also means that we must provide a clock to the ADC, the master clock, at 64xFs. And then there is the sample output rate, which I am only guessing IS DEFINED AS Fs.
So my question is, which of these clock rates is the low group delay filter response referring to? The output sample rate? The 32x oversample clock?
My end goal is to determine the amount of attenuation this filter would provide over a very wide bandwidth. It sure looks like a digital filter response to me, so it should repeat every Fs…but which one? Normally, this is handled by a rather simple analog anti-alias filter on the input of the ADC, but in my particular case I am concerned with noise (supply noise) that can bypass that type of filter.