SPEAKER 1: So far, we've gotten away with this abstract
little switch, which enabled us to build
all kinds of gates.
NOR gates and NAND gates and all kinds of fun stuff.
By the way, remember that once you can build these inverted
gates, you can always build non-inverted gates.
So for example, suppose you had a NAND gate, you could
turn that into an AND gate by
connecting to it to an inverter.
And you would end up with an AND gate.
So that would be simple enough, where you connected
the output off the NAND gate to the inverter and inverted
it, that would give you an AND gate.
So fundamentally, once we have this magical abstract switch,
we can build all kinds of gates, and life
becomes really nice.
Our challenge is, how do we get this physical device that
will behave like a switch.
OK.
So now, let's learn about this physical device.
And one such device-- and there's many possibilities.
But the one that is in common use and has been in common use
for almost 30 years--
I remember doing some designs using MOSFET devices, which is
what we'll talk about, in 1981 in the Tata Institute of
Fundamental Research in Bombay.
So they were doing designs with gates in the solid state
electronics group at TIFR in Bombay in India.
So these devices have been around for a long time.
And virtually all of our microprocessors and chips
today are built using these devices called MOSFETS.
So they've been in use for 30, 40 years and are still hugely,
hugely popular today.
So MOSFET device is what you will use to build this magical
switch of ours.
So MOSFET stands for Metal-Oxide Semiconductor
Field-Effect Transistor.
And we will look at what this device really,
really looks like.
And as I said earlier, today's microprocessors, like the ones
you might find inside your laptop, or the kind of
microprocessors you might find in your cell phones, might
contain close to a billion of these MOSFET devices.
In fact, in many cases, they could be on the order of 10's
of billions of these MOSFET devices, all acting like
switches and connected together to create these gates
that we've talked about.
And so, all these gates coupled together give rise to
all the logical functions and interesting things that we can
build, such as smartphones, or things like mice, and amazing
electronic devices like supercomputers, and
so on and so forth.
So what does a MOSFET look like?
Well, it is a three terminal lumped element, and it behaves
like a switch.
OK.
A switch has three elements.
Remember, we talked about the control port, the control
terminal, the input, and the output.
So MOSFET is a three terminal lumped element and behaves
like a switch.
OK?
So let's draw that out.
So the MOSFET looks like this.
The symbol for the MOSFET looks like this
So this is called D. It's called the drain.
The terminal below here is called the
source, or S for short.
And this terminal is called G for gate.
OK, this is similar to our switch, where we had this
little pattern here.
And it controls C, and input, and output.
So the MOSFET has terminals D, S, and G, much like a switch's
in, out, and C. And so, we won't go into details of why
this terminal is called a drain, gate, and source.
But you should feel free to and check out the textbook in
chapter 6.7 if you want to understand more details about
what transistors really look like on the inside.
So a transistor has a MOSFET device, which is a Metal-Oxide
Semiconductor Field-Effect Transistor.
They are often called a MOSFET for short, and sometimes
called a transistor for short.
It has three terminals, G, D, and S. G is
called the control terminal.
That's where, much like a switch, you apply high value
with respect to the source, and the
MOSFET behaves one way.
And then, you apply a low value with respect to the
source, it behaves a different rate.
And we'll look at that in more detail shortly.
The drain and source are like the input and
output for a switch.
And for the purposes of 6002x, the drain and source are
largely going to behave in a symmetric manner.
In general, the physics has different
behavior for the MOSFET.
But for our needs, let's just assume that they behave in a
largely symmetric manner for our needs.