So I'm trying to combine these two block, but is it correct to do this way ?

 

The block diagram doesn't make sense.

What do you mean the circuit with the X in it to be? Often it is a mixer or some kind, but that requires two signals to go into it. So what is the relationship between the signal coming out of that symbol to the signal going into it?

Also, you have to signals just coming together at the right side of the diagram. That implies two different blocks are driving that same line. You need a symbol there to combine them appropriately. Remember that a block diagram like this is nothing more than a graphical representation of a mathematical relation.

 

I already edited the picture, please check again

 

The signs in the mixer, normally one is used to seeing negative fdbk, so that
input would show a sign "-"

The second block pic seems to be a simplification of the first block ?


Regards, Dana.