There is an example in a text where it shows the small signal model of a circuit. Below on the left there is a transistor circuit and on the right its small signal equivalent:

enter image description here

I'm a bit confused whether I'm not mistaken about a point since in all editions they have the same example. Is the ground connection where I put red question mark wrong? It seems to me there shouldn't be ground there, is that correct?

  • \$\begingroup\$ Out of curiosity: what book is this? EDIT: never mind, it's Razavi's Fundamentals of Microelectronics. He also misnames Rc1 \$\endgroup\$ Jan 24, 2020 at 14:28

1 Answer 1


That is an error.

If you treat that node as ground, then there's no AC voltage across \$r_{\pi 2}\$, and so no AC output voltage.


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