Re: gEDA-user: Opamps et al...

[al davis <ad106@xxxxxxxxxxxxxxxx>]

On Monday 20 November 2006 15:04, Mark Rages wrote:
> This was posted a couple weeks ago.  Unused sections are
> discussed on page 8.
>
> http://encon.fke.utm.my/nikd/latest/sloa067.pdf

It can be misleading ..

I have often tied the inverting input to the output, and ground 
the noninverting input, perferably through a resistor.  The 
paper says "NO!" to this.

The paper is correct if you use a single supply.  With a single 
supply, grounding an input will force the output to a rail,as 
the paper says.  With a bipolar supply, grounding the 
noninverting input is equivalent to biasing it to the midpoint 
between the supplies.  It will put the output in the middle 
where it belongs.  Therefore, the "NO!" circuit is actually a 
good approach with a bipolar supply.

Since the original question mentioned an "instrumentation 
amplifier", and a concern about drift, it will probably use a 
bipolar supply.  Since there is a concern about drift, I am 
assuming that DC coupling is a requirement, with both positive 
and negative inputs.


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