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About the problems after Chapter 2 of Razavi's book

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qiushidaren

qiushidaren

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When I was doing the problems given after Chapter 2, I got a problem, that is in front of all of the problems the author says that "Unless otherwise stated, in the following problems, use the device data shown in Table 2.1 and assume VDD=3V where necessary", in problem 2.1 I need the values of un and Cox or the product of un and Cox, but I can't find the values of these two parameters in Table 2.1 while in the solution manual it seems that the guy knows the values for the two parameters.
Then I just wanna know how you guys get them, or how can I get them in the book Design of Analog CMOS Integrated Circuits?
Thank you in advance!!!m(_ _)m
 

I haven't done the problems but atleast I can see U0 = channel mobility cm2/V/s and tox (gate oxide thickness) in the list. So, I think you should be able to find some formula to find Cox from these tox and the other values specified. I think the reason behind not giving a fixed value for Cox is that it varies with W of the mosfet, thus SPICE is supposed to calculate a new Cox for every new Mosfet that you put in.

You can also simulate a circuit in spice and get the effective value of U0*Cox from there.
 

zeeshanzia84 said:
I haven't done the problems but atleast I can see U0 = channel mobility cm2/V/s and tox (gate oxide thickness) in the list. So, I think you should be able to find some formula to find Cox from these tox and the other values specified. I think the reason behind not giving a fixed value for Cox is that it varies with W of the mosfet, thus SPICE is supposed to calculate a new Cox for every new Mosfet that you put in.

You can also simulate a circuit in spice and get the effective value of U0*Cox from there.
Click to expand...
You are right, my problem is that I can't find the value of Cox, but from the solution manual it looks like he knows the value of Cox, so I wanna know where I can find a typical value of Cox in this book.
You said that I should find some formula to find Cox I think it is a good idea, but I think maybe I can't find such a kind of formula to calculate the Cox, so maybe you can tell me how and where to find such a formula. Thank you!
 

Cox = εox/tox (this is Cox per unit length)

You can look up the permittivity of oxide (it's a constant). Then you can use equations in sec 2.4.2 to calculate the desired capacitances.
 

    qiushidaren

    qiushidaren

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Cox=6.9*50/90=3.833ff/um2
 

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