SPEAKER: At this point we're ready for a little demo.
I'm going to use my amplifier circuit and apply a DC offset
VI and apply a small signal input vi.
And I'm going to apply a bias voltage here, so this appears
as VI and the output has a bias V0.
So this is my point VI comma V0.
And as usual, this is my point vo equals vi minus VT.
And this is the point at which any point below that for VI
less than VT, the MOSFET goes into its cutoff region.
So I'm going to bias my MOSFET at VI and take very small
excursions of the input vi about the bias point.
And the corresponding output is given by the bias point V0
and the small signal output v0.
And I'm going to apply a triangular wave as before.
And I'm going to show you that the output in this case is
going to look, more or less, linear.
It is going to look triangular, and it's going to
be amplified by the amplification
factor of the amplifier.
And the reason this is going to be linear is that the small
signal vi is very small, and I have also boosted the input VI
by a sufficient value so that the MOSFET amplifier is in a
interesting region of its input-output curve.
So if I look at the input and the output as a function of
time, if this is vi.
So I'm going to have a triangular wave as the input.
And my v0 is going to be an amplified version of the same
signal like so.
So this would be small v0.
So this not only amplifies, but is also
more or less linear.
So we are now ready to take a look at a demo and check for
ourselves to see that the output is, indeed, linear when
I make vi very small.
So in this demo, I'm going to use the large VI initially,
and then make it smaller and show you that as it gets
smaller, the output gets to look more or less linear.