Hi all, had a bit of a weird instrument amp oscillation today. (Oscillations were intermittent and triggered (sometimes) by the heat relay in my soldering iron switching on or off.) The int-amp (AD620) is looking at a voltage pulse on a 50 ohm resistor. Today I added a long (DB9) cable between the
50 ohm resistor and circuit board, and this resulted in the intermittent weirdness. Not a clean oscillation, but more of a rectified wave with AC coupling. Freq. 1 MHz (or 500 kHz depending on how you count.) Here's a 'scope shot.Anyway after much fussing I figured out it was the rather long coax cable I had hanging on the output of the int-amp* that was causing the problem. I added a 100 ohm series resistor and this cured the problem. But I'm wondering if there is some other (better) fix. (Short of adding a buffer amp to the output.) Is there some way to slow the int-amp down? A little resistance in the reference connection to ground?
Thanks
George H.
*just to be clear the coax is distinct from the long db9 cable added to what is the input to the int-amp. I needed both to have a problem