0
\$\begingroup\$

I have been trying to derive Av , Ai , Zi , Zo from a two port system model of a transistor. I know that the input voltage must be the voltage at the base to ground, and the output is from collector to ground. It seems that I have a confusion about which current I should consider the input and which current is the output.

In the following diagram the input current shows it is coming from an AC source. However, in the book it states that it is Ib. The output current is clearly shown that it's derived from Rc. Would it be safe to say that Ii comes from RB? enter image description here

When the transistor has a voltage divider network at the base would it change the input current? If so, to which component?

\$\endgroup\$
3
  • 1
    \$\begingroup\$ What you see in the diagram is an AC small signal equivalent circuit. Which shows the situation for the AC signal only. Thus, the AC signal source (not shown on the diagram) is the source of an input voltage and the input current. So Ib and the rest of the currents are just AC components. Do you get it? electronics.stackexchange.com/questions/518032/… \$\endgroup\$ Commented Apr 8, 2023 at 11:02
  • \$\begingroup\$ @G36 Okay it seems that I understand it further now. I know when AC signal is directly connected to the base Ii=Ib. However in the OP from the diagram, how would I find Ii to derive Ai? \$\endgroup\$ Commented Apr 8, 2023 at 13:51
  • 1
    \$\begingroup\$ No, the input current Iin is not equal to the base current Ib, because you forgot that Rb will also load the input signal source. Thus, Iin = Ib + I_Rb . And to find Iin you need to find Zin first. Take a look at this example electronics.stackexchange.com/questions/476659/… \$\endgroup\$ Commented Apr 8, 2023 at 19:56

0

Reset to default

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.