How to analyse a circuit with multiple feedback loops?

[efun]

There are several feedback loops in my circuit: except a main feedback loop, there are some other internal feedback loops.

Although the main loop is stable, but the circuit still oscillates due to another internal feedback loop. But the problem is that I am not able to discover which internal loop causes the unstability, because some paths of different loops overlap, which makes this problem quite confusing.

Could someone can give me some tipps, how can I analyze this problem of facing a circuit with multiple feeback loops which are not easy to seperate?

 

[FvM]

Obviously, if the loops "overlap", you can't identify a single loop that causes the instability.

I would start to visualize each loop gain, e.g. by bode diagrams.

See also this contribution:

 

[LvW]

.................
Although the main loop is stable, but the circuit still oscillates due to another internal feedback loop.
............

Are you sure that the problem is an internal loop? That means: The system oscillates when the main loop is open?

 

[love_analog]

There is no easy way out of this. Don't make a circuit with so many loops. Can you share what you're trying to do. We could suggest alternate ways to get there.