Hello All,

I have been studying electronics for some time but my understanding on ac and dc analysis is still not too clear.

I wish you all can put some time to explain a little about the following;

Say for a mosfet(or cmos inverter) which has a DC biasing and ac signal applied to it).

When we are using equation Id = 1/2.W/L.unCox.(Vgs-Vth)^2 ---------eq(1)

Actually we are calculating the Id in DC or ac? In most of the time, we are interested in Id(dc) or Id(ac)?

I see there is book that put Drain current = Id(dc) +id(ac)

So I just wondering if equation 1 will give us dc value or ac value?

Or the equation (1) is true for both ac and dc where we need to use it at a ac small signal circuit or dc small signal circuit?

Also for transfer function, we are interested to find the Vout/Vin at ac or dc value?

And also the input and output impedance, will there be difference for ac or dc analysis?

Anyone who has any document to explain about this, kindly share with me.

In books, it seems like when it use small signal circuit to analyse id, gmvgs and so on. All are written in small letter. Are they all ac value to be taken into consideration?

Kindly shed some lights on these topic. Please help

Thank you so much

rgds and thanks Jason