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

[al davis <ad106@xxxxxxxxxxxxxxxx>]

On Monday 20 November 2006 13:36, Peter Clifton 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.

There probably is no need for a unity gain op-amp stage, except 
for current drive capability.  Very few IC op-amps can properly 
drive 50 ohms directly.  Most are speced for 2K.

If you need to drive a low impedance load like 50 ohms, add a 
class AB complementary pair emitter follower, and put it inside 
the feedback loop, making believe it is part of the op-amp.


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