It always makes me vaguely uneasy when people start asking questions
about the use of op-amps...I worry that I don't know as much as I
thought I did...So as a check on myself, let me propose this as a
solution to the gain < 1 non-inverting op-amp:

Unity gain voltage follower into a high impedence voltage divider, with
another voltage follower lowering the output impedence of said
divider.  If the output impedence of the signal source is low enough,
the first voltage follower can be omitted.

Choose resistor values based on input bias current of op-amp; with a
good FET input op-amp and resistors in the 10's of kOhms, the input
current can be ignored (hundreds of uA of signal current vs. 10's of
pA of input bias current).

Now...does anyone have anything to say about my solution?
Preferably not too abusive, but enlightening me as to any...
shortcomings in my understanding of op-amps?

Mike H.

>Regarding "straining the op amp" in the non-inverting mode, I believe the
>writer was refering to the fact that in non-inverting mode, there is a
>large common mode voltage on the input in non-inverting mode, while the
>common mode voltage in inverting mode is zero.
>
>For some notes on using what I call "the theory of the happy op amp"
>(differential input voltage ideally zero), see
>http://kauko.hallikainen.org/cuesta/et113/InstrumentationAmpAnalysis.pdf .
>This is an analysis of an instrumentation amplifier using this approach.
>
>Harold

_________________________________________________________________
Stop worrying about overloading your inbox - get MSN Hotmail Extra Storage!
http://join.msn.click-url.com/go/onm00200362ave/direct/01/

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics