[sTaTIx]

Let's take, for instance, an opamp that is running with 15mhz bandwidth, and a current buffer that's rated at 40mhz inside the feedback loop. I've heard somewhere that the general rule of thumb is that the buffer should be at least ten times the speed of the opamp; anything less, and the likelihood of instability increases. Would I encounter any issues with stability with the above (hypothetical) config?

 

[jeffreyj]

Stability is only mildly related to the ratio between buffer GBW and op-amp GBW, though it is true that using a slower op-amp will improve your odds. The most important criteria are pc board layout, power supply bypassing and rolling off the gain well before the unity gain frequency is reached (adding a few pF capacitor across each feedback resistor).