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[time-freq] After staring at te TADD-1 schematic for a while ....

Christopher Hoover ch at murgatroid.com
Fri Sep 8 01:52:01 UTC 2006

Some more thoughts on the TADD-1 design ....
(I should preface this by saying my analog skills are not strong ... I'm
a digital guy and I'm out of my element in the analog world.  I might be
way off base ...)
It seems the design might be better, given the single-sided supply and
the need for a virtual ground, if the first and final stage were
inverting, resulting in ultimately the same non-inverted output.
IIRC, an inverting amplifer config is preferred when a virtual ground is
needed as the current into the non-inverting input from the virtual
ground node is (approx.) zero.  This makes practical the use of a
resistive divider to produce the potential for the virtual ground node.
The other issue is that performance of  an opamp is better when any
common mode is held constant.  That falls out of the inverting case with
a virtual ground on the non-inverting input.
Here's what I am suggesting (the x1 and x2 stages could be swapped):

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