SCEN103 11/19 Class
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Introduction to MOS Transistors and MOSFET Switches
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Review of Previous Class
Slide show on Integrated Circuit Yield
CMOS is the industry standard logic used in consumer digital electronics.
The CMOS NAND gate is the building
block of the digital revolution; our goal over the next week is to understand
the semiconductor origin of our digital world.
Today we will examine the 'MOS' of CMOS,
where MOS stands for metal-oxide-semiconductor.
As studied in previous classes,
the availability of n-type and p-type Silicon and compensation doping,
which permits one type to be turned into the other type by adding additional
dopants, is exploited to fabricate transistors.
In our previous class on binary counting,
we found a way to represent numbers using just two digits,
0 and 1. One simple representation of a binary system is the
electrical switch -- it is either on or off.
Transistor circuits can be constructed to operate as
miniature electrical switches, as we will see.
In addition, the state of a transistor switch may be controlled by the output
of another transistor switch.
Control of switches by other switches is the key
idea behind using semiconductors in the form of transistor switches
to carry out digital logic operations.
The ease with which transistor switches can be used to store information
in the form of binary numbers and their speed of execution in processing
logic operations are essential ingredients in digital electronics.
- Operation of MOSFET switch:
- Examination of circuit configuration
- Explanation of field effect in n-channel MOS transistor
- Key facts:
- "off" state resistance of MOSFET is 10^8 ohms; i.e. 100 megaohms!
- "on" state resistance of MOSFET is only 10^3 ohms as a result of induced
- Review of voltage divider
in preparation for analysis of switch
- Analysis of "OFF" and
"ON" states of switch
- n-channel MOSFET inverter
- Consider that the transistor had not been invented:
- Attempt to describe some personal events, at least one per group member,
that would have prevented
you from being here today (in class, alive) except that the transistor
was indeed invented and miniaturized so successfully.
- Next time, we will consider the "down side" of transistors in our society...
- Discuss group term project...
Results of this exercise in
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Last updated Nov. 14, 1996.
Copyright George Watson, Univ. of Delaware, 1996.