Fantastic P.I front end building block

[sharky]

High Sharky,

Yes to both of those, but also that the double correlated

sampling moves these external noise sources around in

frequency. particularly the movement into lower frequecies

like HZ and subHz.

Maxim.

Undersampling is a powerful tool that can be used effectively in selectedapplications. It allows an ADC to behave like a mixer in that it can takea modulated high-frequency carrier signal and create an image that islower in frequency . In this way it behaves like a downconverter.

One drawback of undersampling is that unwanted signals can appear in the desired band of interest and you cannot differentiate them from the desired signal.

http://www.maxim-ic.com/appnotes.cfm/an_pk/928

Here comes DSP chips , use fft,dft filtering . One nice approcah is not to use charge pumps,instead use 2 separate batteries, use optoisolators where ever necessary, keep a good low noise linear analog front end (dont use high feed back resistors), this should be in linear region, then follows adc then folows dsp chip.

[JC1]

moving

Hi Sharky,

My point is one of not being able to hit a moving target.

The internal/external noise will be in effect modulated by

the double correlated samping and will be all over the

passband of the detector. Filter all you want, analog or

digital, if you do you are filtering the signal of interest

at the same time. No dsp magic is going to make some

facts go away. Nor will DSP wishful thinking.

Thats my point. Now if someone has what they feel is

productive DSP approach then post it up and we can

debate the merits. This isn't happening and isn't going

to happen because either it is a "big million dollar secret"

or they got nothing.

I bet the later.