This op-amp buffer is oscillating and I can't figure out why
Chip suppliers are keen that their users avoid common design errors, shown by application examples in their data sheets. This one is addressed by Linear Technology in their data sheet for LTC6241. It also applies to many other opamps:


  The good noise performance of these op amps can be attributed to large
  input devices in the differential pair. Above several hundred
  kilohertz, the input capacitance rises and can cause ampliﬁer
  stability problems if left unchecked. When the feedback around the op
  amp is resistive (RF), a pole will be created with RF, the source
  resistance, source capacitance (RS, CS), and the ampliﬁer input
  capacitance. In low gain conﬁgurations and with RF and RS in even the
  kilohm range (Figure 4), this pole can create excess phase shift and
  possibly oscillation. A small capacitor CF in parallel with RF
  eliminates this problem.








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