Stopping an op-amp from oscillating

lion-mclionheadlion mclionhead wrote 03/30/2018 at 22:25 • 1 min read • Like

How quickly 1 project to make an op-amp oscillate turned to another project to stop an op-amp from oscillating. The internet says op-amp oscillations are caused by very high frequency op-amps with slight delays between the output & feedback. Capacitance on the output & feedback terminals & higher feedback resistors cause delays just like an RC circuit. They recommend lower feedback resistors & a resistive load for the output.

100 & 200 were the lowest reasonable feedback resistors, but this caused the ADA4817 to oscillate at 80Mhz. Increasing to 1k & 2k actually seemed to eliminate the oscillation. The output of each op-amp is very noisy, but when combined in a difference amplifier, it's relatively clean.  The only explanation is if physics experiments never work, pick what doesn't work to make them work.  Perhaps having the output impedance too low slowed down its response rate & caused it to oscillate.