Small signal model

Question

I would want to derive the output impedance of the following current source stage. I tried to convert it in small signal, could you please tell me if I'm wrong and how I can derive it to have output impedance?

schematic

^{simulate this circuit – Schematic created using CircuitLab}

score 1 · Answer 1 · answered Jul 19 '23 at 18:43

Your small signal looks good to me. But I redrawn it to this form:

schematic

^{simulate this circuit – Schematic created using CircuitLab}

And the output resistance will be equal to \$R_{OUT} = \frac{V_X}{I_X}\$

Take a look at the example of how to do it:

I/O Resistance of common source MOSFET with source degeneration

And supper simplified version of \$R_{OUT}\$ equation will look like this

\$ \large R_{OUT} \approx r_{o1}+ r_{o1}\beta \approx r_{o1}\beta\$

thanks a lot it's more clear with your schematic – exolune Jul 20 '23 at 19:17 — exolune, Jul 20 '23 at 19:17

Small signal model

1 Answers1