On Fri, 30 Jan 2009 00:07:55 -0800 (PST), " snipped-for-privacy@gmail.com" put finger to keyboard and composed:
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The voltage at U4A-1 = SI/2 since R1 and R2 form a potential divider.
The voltage at U4C-9 = voltage at U4C-10 (if op-amp is operating in linear region).
Therefore voltage at U4C-8 = SI.
So it would seem that U4A and U4C are functioning as a unity gain buffer with a 10K input impedance, in which case I don't understand why they are needed, either.
They reduce the gain of the high frequency components in the signal.
- Franc Zabkar
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