Getting to know simulation - Part9 - Fixing oscillation

  

1.       There are plenty of ways to resolve this, one way is to add a capacitor in parallel with feedback resistor R2. Let’s do this in the schematic and re-do the AC simulation. At this point of time, the value of C2 is arbitrary chosen to be 1nF, we will talk more about this in next session – any way the latest schematic becomes:  

2.       Re-do the simulation for AC with simulation frequency up to 10MHz to see the new closure- you can see now that the rate of closure becomes 20dB / decade – indicating stability has achieved, let’s modify the schematic to re-do the transient

3.       To look at the end result of the fix in time domain, insert 1nF for the transient simulation file:

4.       Re-run of transient simulation shows that so we have solved the problem of oscillation – but the problem is that the output of the buffer takes 4ms to settle to the right value – too slow for our liking – this we will try to solve in next session.