I am attempting to address the following recurring situation in the optics lab I work in:
1) Our Amplified Photodiodes output at 0-10V.
2) The ADCs we use are generally 14 to 16 bits, with -10 to +10 Volt Ranges.
3) The sampling rate of the ADCs varies depending on application (Samps/sec split among input channels) (the NI USB-6009 as an example). Therefore, the filter cut-off needs to be adjustable as well.
4) The gain between the Photodiode and the ADC sometimes needs to be varied automatically.
5) We digitize spectroscopy signals, which need to retain their shape (linear phase).
6) My experience with circuit design is limited, and I need a design I can't easily screw up.
On bouncing around the web, I ran across the
Linear Technologies 1064-7, an 8th order, monolithic, switched capacitor low-pass filter with some kind of enhanced Bessel response (linear phase, compromise in roll-off). I'd like to cascade these together (to sharpen up the roll-off). I've attached an image of the overall circuit idea.
Question: What trade-offs, or potential disasters, am I overlooking here? Is this design worth pursuing?
Thanks in advance to anyone willing to weigh in here.
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Sorry guys, I'm having trouble uploading the image. I'll try again tomorrow.