I'm studying signal processing and right now I'm going through types of sampling and how they apply, advantages and disadvantages. I have some questions about these concepts that I would like to clarify
Ideal periodic sampling: Can it be used in practice?
So my first question is regarding ideal sampling. Can it be used in practice? The notes I was reading told us that A/D conversion usually use this type of sampling. But how? One of the advantages I read about sampling with retention is that, unlike ideal sampling, it doesn't deal with ideal impulses (impossible to generate?) and therefore it can be realized with a circuit. So then I concluded that ideal sampling cannot be realized by a circuit and therefore cannot be used in practice, let alone with A/D converters. But apparently it can? How is that so? Or is this just done by a computer and therefore we can generate the ideal impulses and apply them? I'm confused about this.
A/D converters: What sampling process can be used?
As I said before reading my notes I read that: A/D conversion usually uses ideal periodic sample, while D/A conversion (signal reconstruction) usually uses the sampling with retention process.
Then I read this:
In a sampling system followed by analog to digital conversion using an A/D converter ideal sampling with retention must be used but the sampled signal spectrum is not distorted.
Err... how is this correct? Isn't the point of sampling with retention that the replicas come distorted? What am I missing here?
Another thing that I read was
The rectangular sampling type can not be used in a digital signal processing system because the analog to digital converter requires a finite, nonzero retention time.
I understand this but then I wonder why is the ideal sampling then used in A/D converters. Is there any retention when using ideal impulses? Or the problem here is that the A/D converter cannot "follow" a signal, but it is fine with either sampling and holding, or sampling with an impulse? Can someone clarify this to me?