I tried to cascade two circuit consisting of BJT transistor : Common Emitter stage, Emitter follower.
I do abstraction like belows, which means you just need to know only each unit block one by one and when you cascading these blocks, then whole system does sort of cooperating all blocks's function (like LEGO blocks, it might also called 'decomposition' or something).

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As you know, each circuit has Input impedence, Output impedence, Voltage gain.

I want to know what relations each properties have when cascaded.

For example, I can guess that (Av_total) = (Av1) * (Av2).

But, what about Rin_total and Rout_total ? Are they related with Rin, Rout of each block, saying parallel connection of each Rin or something?

  • \$\begingroup\$ Please convert this to standard schematic symbols. Also, please define your actual questions with a question mark(?). What do you mean by 'properties'? They need to be defined as there are a books worth of properties per given function block. You need to narrow the scope of your questions, as what you have is too broad and ambiguous. \$\endgroup\$
    – user105652
    May 13, 2016 at 0:49
  • \$\begingroup\$ You want to abstract functions but then you also already assume a certain implementation. I suggest you look at a systematic design approach for amplifiers. This book: vssd.nl/hlf/e022.htm (and probably other books/articles from the same author: E.Nordholt) describes this method. It first describes how to design amplifiers using ideal blocks and then later fills in those blocks with CE, CB or CC stages. \$\endgroup\$ May 13, 2016 at 7:24

1 Answer 1


When you cascade the amplifiers, the net input impedance will the input impedance of the first stage and the net output impedance will be simply equal to the output impedance of the last stage. What needs to be taken care of are the central impedance or the impedance between any two stages. You need to make sure that the output impedance of one stage should be equal to the input impedance of the next stage. Mismatch of impedance can cause lot of power loss and your output signal may be weak.


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