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

["John Luciani" <jluciani@xxxxxxxxx>]

On 11/20/06, Peter Clifton <pcjc2@xxxxxxxxx> wrote:

> My intention was to use an AD8230 precision zero drift instrumentation
> amplifier (basically with the datasheet input circuit), then follow it
> with an unity (or 2x) gain op-amp buffer to drive a cable. (Probably in
> series with a 50 Ohm resistor (assuming a 50 Ohm load), however I may
> opt just to drive low-impedance, since I'm working with low frequencies,
> and transmission line effects to the 'scope or control circuit intended
> won't be severe.

You didn't say how low a frequency you are working with. Since the AD8230
appears to be specified in the 10Hz-10KHz you shouldn't need series or
parallel termination.

> If I have an op-amp left over unused in a package, what is the
> recommended way of tying its inputs to avoid noise / power consumption?
> I figured connecting the inverting input to the O/P, then the
> non-inverting input to GND.

On the unused op-amps you want to avoid output oscillation. I have seen unused
amps connected as 0V buffers (like you mentioned). I have also seen the +In tied
to one power supply rail and the -In tied to the opposite rail. What
you want to avoid
is connecting the +In and -In together since a change in input offset
voltage could
change the output.

(* jcl *)

--
http://www.luciani.org


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