small-signal

Hi folks, Since I wanted to revise the basic configuration of BJT, I read this chapter from Purdue University based on the Book of Sedra (https://engineering.purdue.edu/wcchew/ece255s18/ece%20255%20s18%20latex%20pdf%20files/ece255Lecture_13_Feb27_BJT_Basic_Config.pdf) at page 13 where he wrote...

The other day I got the following exercise on one of my exams: For those who don't speak German, for transistor 1 lambda is 0, but not for the others. The backgate-effekt should be neglected alltogether. I drew the following small signal equivalent circuit (ignore the black texts for now)...