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Block diagram from circuit diagram

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CAMALEAO

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Hi everyone,

Can someone give a source about how to build a block diagram from a circuit diagram? Any good references even if it is an online references?
Regards.
 

There is no general rule, looking from the point of view of the signal to be processed, the system is subdivided into functional parts, each one performing its task. The level of detail will depend on the purpose of this diagram. Needless to say, being skilled in the application area of this equipment helps in the use of common terminology
 

Hi andre_teprom,

I want to know basically if you think about an electronics schematic, how to go from a circuit schematic to a block diagram like the ones that we got in a control class.

For example, if you have an opamp followed by a pmos transistor, a resistor string and a feedback like this one:

123.gif

How one could draw it?
 

Hi,

It really depends on the complexity needed.

I think a good approach is to look for existing examples of things like voltage regulator control theory block diagram maybe, maybe because I don't know how your circuit works. Then when you figure out the blocks and the degree of sophistication you wish to convey, hopefully fit them together. The link is just to Google images search and as you can see, there's K, E and so on style, more literally-worded (control element).
 

For example, if you have an opamp followed by a pmos transistor, a resistor string and a feedback like this one:
The feedback part is solved directly by writing v+=v-, you do not need to draw its block diagram for that. Then, solve the rest of the circuit, Vin/R=gm*(AAVD-Vout)
 

For example, if you have an opamp followed by a pmos transistor, a resistor string and a feedback like this one:

Figures like the one above should not properly be considered as a block diagram at all, but rather as a simplified representation of the circuit, omitting elements that do not impact the intelligibility of the whole, or replacing well-known topologies with symbols. Note that the operational amplifier you mentioned is in short a differential arrangement of transistors along with its biasing and interfacing circuitry (actually, the above `OpAmp` is being used as a comparator), and the bandgap reference may contain several components. If the circuit in question is in the context of an ASIC design or not, we should even take a slightly different approach, but essentially the look would be pretty similar. In other words, a block diagram, as suggested in the thread title, is something more abstract in general.
 

BJT_emitter_feedback.jpg

Here is a simple example how to convert a circuit diagram (more correct: all the equations describing the current-voltage relations) into a block diagram (simple common emitter gain stage with Re-feedback).
The collector current is determined by the voltage Vbe - hence, we need a subtractor for Vbe=Vb-Ve. This voltage is multiplied with the transconductance gm resulting in a collector current Ic.
For simplicity, I have assumed here Ic=Ie.
 


Hi,

A block diagram should give an overview of any complex circuit / regulation loop / device /apparatus ...
It should hide all confusing complex things in one or a couple of black boxes in a way that the operation becomes more obvious.

It may also be split: unecessary things are hidden in a black box, where the important things may be more detailed.

Example:
blockdiag.png
Here you see they hid how the UVLO or the THERMAL_SHUTOWN works, but they show in detail how the resistors are arranged.
Mind: even the OPAMP is just a symbol (block) for a complex circuit.

For the same circuit you could draw a block diagram where the resitors are hidden, but the THERMAL SHUTDOWN is shown in detail.
Do this when you want to explain how the thermal shutdown works.

As already said: You need to decide on which parts to go in detail and what parts to hide.

Klaus
 

Sorry for this. Because I was not able to edit the post, I was not able to delete the content.

Getting back to the question: Ok, I understand. Probably calling it block diagram was not the best thing. So they are called circuit diagrams.

Now, rectifying this (which makes sense BTW) the questions remain. Can you please explain?
 

Link in discussion

Basically, my understanding is that you can represent a circuit using the normal schematic approach, small-signal approach and sort of block diagram representing the several gm or amplifier stages.

For example, if you look at link 1, it is easier to understand and derive the equations. How can we go from a symbol schematic view to this kind of "circuit diagram"?

We can also see some signs inside each of the blocks on the "circuit diagram". Where do they come from? Why one is plus and others minus?
 

How can you say "it's easier to derive the equations" although you don't even understand the meaning of the gm symbol sign? It's just a shortcut for an OTA with differential input having either the + or - input connected to the input signal and the other to the reference potential, e.g. vdd/2.
 

Ok, I understand you. But why the author then presents two different type of "schematic diagram"? And how to you derive one from the other? And above all, what those signs inside the what so the author call amplifier?

For example, in this paper: Paper 1 the author only uses a "schematic block diagram" (don't know how to call this thing. In there you can see some blocks with a sign inside it. What does that mean?
Now, some of the configurations represent a possible "circuit schematic" which it is not shown anywhere in the paper with the exception of a very small blocks, don't know why. Now what those more complex diagrams might represent? Can you go from that diagram to a circuit schematic"? How? You need to know what each block represents, that's why I am trying to understand and learn how to do this.

In this paper: Paper 2 you can see a similar situation but in there the author presents a "circuit schematic", figure 1, in an attempt to represent the "block diagram schematic", figure 2 and 4.

Now how does he went from one diagram to the other? For example, you can see there point A is the output of a differential pair, meaning that that block in the diagram 1 is a differential pair? Why is that for the second stage on the "circuit schematic diagram" he used a common source and not a differential stage again (figure 4)? And why on figure 2 he used another differential stage at the output? So there is two different circuits for the same "block diagram" (figure 1) possible? How come?

Best regards.
 
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