Azuther,
Thanks for the advice. In fact, I didn't know that! I suppose this is what the other posters meant when they told me to "compensate my probe."
So, I got a 10x oscilloscope probe. Is that what you mean? My scope manual instructed me how to output a square wave and make adjustments to the probe to make sure it looked square. I didn't have to make any adjustments...it looked ok.
Anyway, using this probe to test my circuit didnt help. I had the same problem. Am I doing what you suggested or have I misinterpreted something?
Thanks,
--Jeremy
Added after 1 hours 22 minutes:
So I talked to the op-amp chip manufacturers again, and they suggested that it might be an impedance matching problem.
I am using a 55 ohm resistor at the output. This goes into the 50 ohm BNC cable. I WAS using a 1 M-ohm scope impedance, but now I changed it to a 50 ohm impedance. This DOES get rid of the node at 45 MHz.
However, using a 50 ohm scope impedance, I don't get the full output. It's drawn down by a factor of 2 or 3 since its impedance is no longer much greater than the other output components.
I plugged in a 10x scope probe to try that out. Using this (combined with the 50 ohm scope impedance) seems to work. I don't understand this. Isn't the impedance of the 10x probe pretty high? If we're supposed to match impedances, why is this seeming to work?
On the other hand, using the 10x probe, the phase shift changes a lot. It's already 90 degrees by the time I get out to 45 MHz. Any explanation for that?
Thanks for helping me with this. As you might have been able to tell, this is my first real project involving electronics...at all...so the hand-holding is much appreciated.
--jeremy