S/H really necessary with AC input on ADC?

[JimRayden]

I love titles that say it all.


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Jimbo

[JimRayden]

By that I mean, is it necessary to present a constant sampled voltage into the converter or does it handle the sloped piece of an AC signal.

Also, what difference would it make at different frequencies, for example with heavy aliasing going on (with the AC frequency being rediculously higher than the clock freq.)

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Jimbo

[octfrank]

Well, you really want a stable value during the conversion process. Most modern ADCs have the s/h built into them so no need to have an external one. Without a s/h in the path you would be doing what is called "impulse sampling" which has its own problems.

[JimRayden]

Thanks for the reply.

If the ADC datasheet calls for an external S/H, I guess that means it hasn't got one built in.

Well, the project doesn't really need too much precision, the it's the most basic digital effect there is - a variable bit and sample rate processor. I'm wondering if the difference will be audible enough to make the S/H switchable...


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Jimbo

[octfrank]

My guess is that if the sample rate is MUCH greater than the signal you may be able to get by without a s/h. I say give it a try, I've never done it but would like to hear your results.

[JimRayden]

Oh joy, the chips are here: one AD, one DA, one 555 for adjustable clock, one 7805, and an op-amp. Now let's see....

My exams are coming up next week, so this might take a while.

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Jimbo