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Subject: enquiry on drain amplifier small signal model

Date: 08/15/03 at 12:36 PM
Posted by: Too
E-mail: toowang[AT55]yahoo.com (replace [AT55] with @ to reply)
Message Posted:

Hello Every Experts,

In my study of basic analog IC design, I have a few problems which I cant underrstand on drain amplifier. I need your help . Kindly see the page I have modified and uploaded in

http://www.geocities.com/toowang/drain_amp.gif

Ques 1:From figure 1 , it has been constructed the small signal model in figure2. But I do not know how shopuld we differentiate the current source symbol for the one in figure 3 and figure 4. Could you teach me when should I do the symbol in figure 3 and when is the right time to use in figure 4?

Ques 2: In figure 4, we see a pair of current source symbols of the same type, however the arrow is in the opposite ways. For gs1Vs1, it is said to be due to the body effec while for gm1vgs1, it is due to the current source for mosfet Q1. May I know how do we determine which direction is correct for both current source? How do we know the current source for Figure 4 is in the opposite way?

Ques3:If the arrows are in different direction for both current source in Figure4, then my question is when come to doing KCL, can I give both curent the same positive notation? Or one must in positive while the other must be negative due to the opposite direction in arrows?

I am still not familiar with such a small signal model and its basic. Kindly help to enlighthen me.
Thank you Experts in advance.
Please help .


regards and thanks
Too


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