[sdiy] Taming an oscillating unity-gain voltage follower

[Tim Stinchcombe]

> >Having done so I was both dismayed and delighted at the same time to 
> >discover that the *buffer* could easily be made to oscillate 
> at around 
> >760kHz.
> 
> That's to be expected.
> 
> If you don't need zero output impedance, there's an easy 
> cure: Put a 470 Ohm 
> resistor between opamp output and the cable.

Now why is that one can get so embroiled in a problem one misses the
absolutely obvious? Of the handful of simulations I had run, plotting loop
gain and phase, I had tried this and realised that the resistor effectively
isolates the cap from the buffer, giving loads of phase margin back, yet had
completely failed to recognise that this was probably the easiest solution?!
Damn! Many thanks Juergen! (Still, at least I know a little more about
'noise gain' now, and its difference to 'signal gain'!)

Tim
__________________________________________________________
Tim Stinchcombe 

Cheltenham, Glos, UK
email: tim102 at tstinchcombe.freeserve.co.uk
www.timstinchcombe.co.uk