J

#### jason

- Jan 1, 1970

- 0

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