The Nyquist sample rate of Fs/2 is the minimum rate at which you can
sample and theoretically recover the exact original signal. It's only
theoretical, though, because recovery of the signal from the samples
would require a perfect, "brick-wall" frequency response, flat phase
response, low pass filter. Because we're stuck with using real filters,
we have to sample at a considerably higher rate if we want to recover
the original signal. Just how fast you have to sample depends on how
good a filter you're willing to construct and how much distortion in the
reconstructed signal you're willing to tolerate.

The bandwidth of an ADC can be limited by things other than the sampling
characteristics, such as internal circuitry and packaging. For that
matter, the distortion can also greatly exceed the amount determined
only by quantization error.

Roy Lewallen, W7EL

wrote:
Hello All,
I was going through an ADC tutorial and realized that they use the term
input bandwidth more frequently as one of the important factors to be
considered before choosing an ADC.

Based on my search, I found out that "the input bandwidth is something
that determines the maximum bandwidth of an input signal that can be
accurately sampled, regardless of the stated sample rate".

http://www.diamondsystems.com/slides...utorial&page=4

I am not sure why is this input bandwidth different from Fs/2. From the
above link, one of the example has Fs/4. Is it just because to increase
more precision that we use a sampling frequency 4 times the bandwidth
of the signal?

I assume for practical reasons, we oversample it but that is for more
precision (correct me) but the Nyquist criteria still holds good for
sampling the frequencies upto Fs/2. That means I can still get the
original signal. I am not sure about the accuracy though.


Also, can I say that if an ADC is oversampled 4 times the Nyquist rate
(Fs = 4*BW), then is my input frequency given by Fs/4? Assume single
channel case.
Correct me if I am wrong.

Thanks for your responses.