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Sampling Bandwidth vs. Bandwidth in Tracking Mode of a Sample/Track and Hold

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Puppet123

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What is the difference between the Sampling Bandwidth vs. Bandwidth in Tracking Mode of a Sample/Track and Hold Amplifier ?

Is Bandwidth in tracking mode different then the sampling bandwidth ?
 

Depends how you like to define bandwidth.

Small signal bandwidth as -3dB from flat-top, is not
a very useful descriptor of a T/H amp's performance
when what you care about is a settled-to-N-bits
time window. And T/H amp intra-cycle performance
is neither continuous-time nor small signal - it's
clocked, discontinuous and dealing with switch charge
injection on top of natural amplifier settling.

I'm no ADC specialist but you need way more BW
to get decent THA - ADC lineup performance than
your sampling clock frequency. Off the cuff I'd call
it fClk*2^N or something like that - figuring T/H amp
is a capacitor burdened unity gain follower, and you
want about 1/2^N gain error @ freq.
 

Sampling bandwidth is defined by the Nyquist criteria, i.e. the sampling frequency must be greater than twice the highest signal frequency of interest to reconstruct the waveform (in practice a significantly higher sample frequency than the minimum is usually used to allow analog low-pass filtering of the signal to minimize aliased noise).

In the track mode you want a bandwidth sufficient so that it can settle to the desired precision within the sample acquisition time.
That bandwidth is usually higher than the sampling bandwidth.
 

Crutschow,

Thank you for your answer.

So the sampling bandwidth is the max sinuosoidal bandwidth that can be sampled while the tracking bandwidth is the maximum sinuosidal bandwidth that can be acquired and tracked to the desired precision. But why would you want a higher tracking bandwidth if you can''t sample it ? You just would just a higher clock frequency to increase the sampling bandwidth since it can acquire and track the signal ?
 

Hi,

But why would you want a higher tracking bandwidth if you can''t sample it
Undersampling...

Many RF systems use undersampling technique.
If interested: do an internet search.

Klaus
 

I doubt that both terms have clearly commonly understood definitions. The original post is apparently referring to a paper or datasheet. If so, why don't you quote the definition therin.

tracking bandwidth is the maximum sinuosidal bandwidth that can be acquired and tracked to the desired precision
It's more commonly understood as -3dB bandwidth in tracking mode, I think. Small and large signal behavior has to distinguished.

I agree that sampling bandwidth can be reasonably read as Nyquist frequency, as suggested by crutschow. But the term could also describe the aperture bandwidth of a sampler. For clarity, I suggest to desribe a test setup and how the respective parameters are derived.
 

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