Get Fast Stable Response From Im

　　In many applications， a unity-gain follower （e.g. any operational amplifier with tight feedback to the inverting input） may oscillate or exhibit bad ringing when required to drive heavy load capacitance. For example， the LM110 follower will normally drive a 50 pF load capacitor， but will not drive 500 pF， because the open-loop outout impedance is lagged by such a large capacitive load. The frequency at which this lag occurs is comparable to the gain-bandwidth product of the amplifier， and when the phase margin is decreased to zero， oscillation occurs.

　　While the solution to this problem is not widely known， an analysis of the general problem shown in Figure 2 can lead to a useful approach. It is generally known that increasing the noise gain of an op amp’s feedback network will improve tolerance of capacitive load. In Figure 2， adding a resistor R2 j RF/10 will do this. （A moderate capacitor C2 is usually inserted in series with R2， to prevent the DC noise gain from increasing alsoÐto avoid degrading DC offset， drift and inaccuracy.） If the op amp has a 1 MHz gain bandwidth product， and R1 e RF， the closed-loop frequency response will be （/2 MHz. Adding R2 e RF/10 will drop the closed-loop frequency response to 90 kHz， where the amplifier can usually tolerate a much larger CL;