Getting to know simulation - Part7 - Bode Plot from a buffer circuit (that oscillate)

Continue from last post, to solve the problem, we need to acknowledge that the buffer circuit is in fact a feedback loop

To identify which components belong to with block – refer to the blog

http://electroniccircuitdesignsharing.blogspot.com/2012/05/feedback-loop-element-identification_23.html

Let’s modify the schematic to perform bode plot analysis

1.       Ground non-inverting input – since op-amp input is already high impedance – any voltage source with series resistance is pretty much behaving just like a pure voltage source – for DC voltage source, it is always a AC ground.

2.       Place large inductor, infinite AC coupling capacitor and AC source, configure the AC source as below:

3.       Choose AC analysis:

4.       Your schematic should becomes:

5.       After simulation, you get

6.       But, how to interpret the plot?