# How do I treat a PMOS compared to an NMOS in small-signal analysis?

What exhaustive list can I use to determine the differences between NMOS and PMOS devices when doing small-signal analysis?

Equivalently, what are the fundamental differences between NMOS and PMOS devices, and how do related terms (i.e. treshold voltage, which is either positive in NMOS and negative in PMOS, or positive in both but with reversed polarity in PMOS, affecting many formulas) differ between them?

• I hope that the answer will clear up questions like this. – Andres Riofrio May 28 '12 at 22:25
• With equal respect. – Telaclavo May 28 '12 at 22:56

pMOS's $I_{SD}$ will be proportional to $V_{SG} - |V_T|$, where nMOS's $I_{DS}$ will be proportional to $V_{GS} - |V_T|$. Note that for the pMOS, you can flip SG and SD and still obtain the right values, as long as you use the absolute value of Vt.