sampling and quantization

[rameshbalan]

i have one doubt.
when A and B system are cascade, then if the system is linear time invariant system even A and B are interchanged, no change in result.
quantizer is a nonlinear system. but even the sampling and quantization is interchanged the entire result is unchanged and same result get like sampling and quantization.

 

[crutschow]

How can you interchange sampling and quantization? If you quantize a signal then you have sampled it by definition.

So what is your doubt?

 

[rameshbalan]

my doubt is if the system is LTI then only the output is not change even we interchange the order of the system.
here if we sample and quantize or quantize first and sample next will give a same result.
so that means the combination of sampling and quantization is LTI system.
reference:Y. Tsividis, ICASSP 2004
refer the paper.
but quantization is a nonlinear system. how the non Linear system satisfy the condition.

 

[yuvan]

You are correct, sampling & quantization are interchangeable theoretically. But practically you have lot more issues by interchanging them. Let say you do Quantization first, a completely non-linear block, then the sampler would relatively see very large frequency at its input & making them to have very low distortion would require a lot of power --> too much of constraint on Sampler. And also to characterizing the sampler on its own would be a nightmare.
also have a look at this lecture: **broken link removed**