Common results from superposition of dependent sources/feedback diagrams

Hey all,
So, I think this is probably one of the neatest analysis tools I've seen. Using superposition of dependent sources and drawing a feedback diagram, producing some common results. I've seen it used to determine the output resistance of a source degenerated FET/cascode which I included some simple diagrams for to see. Basically, if you simplify the feedback diagram using Black's formula you get output resistance of a cascode (ro1+ro2+(gm1+gmb1)ro1ro2). Has anyone seen any other particularly insightful uses of this method? I feel like it gives a lot more insight, but maybe I'm just a sucker for block diagrams.

Hi thutch,

I agree with you - it's a nice representation of the circuit and it gives a lot more insight in the feedback principle.
Such a block diagram representation is very useful - in particular, if the feedback loop can not be identified via visual inspection. More than that, it is the best method to derive an expression for the loop gain.
It's easy to produce a similar arrangement also for the simple case of a BJT with emitter degeneration.
In principle, such a block diagram is nothing else than a graphical representation of the corresponding formulas describing the voltage-current relationship within the circuit.

Hello.

This kinds of graphs are also well known as signal flow graphs.
There is an unified methodology to systematically build and analysis such graphs (driving-point impedance approach and Mason's gain formula).
I personally frequently use this method for analysis of some circuitries.

If you are interested in I can refer you to:
A systematic approach to the analysis of general and feedback circuits and systems using signal flow graphs and driving-point impedance
Ochoa, A., Jr.;
Circuits and Systems II: Analog and Digital Signal Processing, IEEE Transactions on
Volume: 45 , Issue: 2

Analysis of the modified MOS Wilson current mirror: a pedagogical exercise in signal flow graphs, Mason's gain rule, and driving-point impedance techniques
Spencer, R.G.;
Education, IEEE Transactions on
Volume: 44 , Issue: 4

Thanks for the papers DenisMark, this is exactly what sort of suggestions I was hoping for from this post! Looking forward to reading the papers.

Applying "signal flow graphs" to common oscillator topologies would be especially neat.
Thanks!