[sdiy] Buffer feedback loop vs. PCB layout

[Neil Johnson]

Justin,

> http://www.sdiy.org/juz/feedback_loop_01.png
>
> 1) This simplified diagram represents the physical layout. A buffer output on PCB1 connects to an inverting op-amp input on PCB2 via an inter-board connector (the blue trace).

Do this, but put a small series resistor after the buffer op-amp, say
22 Ohms, to isolate the op-amp from any capacitance that the long
trace might have.

> 2) Is essentially what the circuit 'sees' - a long trace from the output of the buffer to the input of the inverting op-amp.

No, the circuit includes lots of parasitic elements that you have not
included, including capacitance, inductance and resistance.  You
haven't included those.

> 3) This is what I'm worried about though - as far as the circuit is concerned - it's not just one trace from output to input - it's also - potentially(?) -  a long, extended feedback path/loop that travels all the way from PCB1 to PCB2 and back again.

Umm, no.

> My original idea was to put some sort of small value resistor after the output of the buffer - is that a contender?

Yep, that's the way.

Neil
--
http://www.njohnson.co.uk