ac or dc

[jason]

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

 

[jason]

Dear Andrew Terry and Mike

It has been lucky to be able to see your posts with good explanation
Thanks a lot.
Terry you can refer to the same title under the group electronic
design, I think it is more comprehensive there


Hope everyone learns this

rgds and thanks
jason