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# how to understan the content from a textbook?

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#### xuexucheng

##### Full Member level 2
how to understan the content from a textbook?
It's important to remember our constant theme when we design current mirrors, that is, if we can set both the gate-source and the drain-source voltages of a MOSFET, we set the drain current. Similarly if we can set the drain current and gate-source vlotage, then we set the drain-source voltage.

could any nice guy give some detail explanations.
Examples are very welcome.

It is from R. Jacob Baker's book
"CMOS: Circuit Design, Layout, and Simulation, Third Edition"

It means drain current depends on both Vgs and Vds for some certain transistor.

It means drain current depends on both Vgs and Vds for some certain transistor.
yes, right
however, this does not explain my question.

I think the meaning is clear.
I can't understand your confusion.

can any nice guy give other explanation?

If you look at the characteristic curves of a MOSFET they are usually shown as a graph of Vds against Id for different values of Vgs. If you fix any two of those three parameters then there is only on value for the third parameter that will exist i.e. it defines a single point on one curve.

The other way of looking at it is through equations. If you have an equation which defines the device characteristics and it has three variables, if you define two of the variables (i.e. give them a value) then the third variable can now only have one value.

Keith

xuexucheng

Points: 2