# Analog circuit design(amplifier with BJT) with abstraction(model)

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).

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?

• 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. – Sparky256 May 13 '16 at 0:49
• 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. – Bimpelrekkie May 13 '16 at 7:24