R. B. Darling
EE-331 Laboratory Handbook
FET Driver, Load, and Switch Circuits
The objectives of this experiment are to observe the operating characteristics
of inverter circuits which use JFETs and MOSFETs as driver, load, and
switch devices, and to observe the effect of differing device parameters on the
resulting voltage transfer characteristics (VTCs).
The VTCs will be examined
both using an oscilloscope and a LabVIEW curve tracer.
Junction field-effect transistors (JFET's) involve only an internal pn-junction
and are thus relatively static insensitive and may be handled freely.
discrete MOSFETs involve a very thin gate oxide layer which may not have
any static protection diodes included as part of the device.
As a result, the
discrete MOSFETs can be very static sensitive and must be treated properly to
avoid having to buy replacements.
To avoid static discharge damage to the MOSFETs, keep their leads inserted
into the black conductive foam whenever possible.
Always touch a grounded
object, such as the frame of the lab bench, to discharge any built-up static
charges from your body before handling the MOSFET.
After this, carefully
remove the MOSFET from the black foam and insert it into either the curve
tracer or the solderless breadboard.
Pay particular attention to correctly
identifying the leads on the devices.
Improper connection of the device is
another means in which they can be destroyed.
Once the MOSFET is
correctly connected into its test circuit, it is reasonably well protected from
static, since there now exist resistors or power supply terminals which allow
current to flow from lead to lead.
As a basic rule, remember that static affects
only floating terminals on a device or circuit.
Simply connecting these
floating terminals to ground with a large value resistor, say 1 M
or so, is
often sufficient to provide a discharge path for any built-up charges.
This experiment will also use standard 4000-series unbuffered CMOS (metal
gate) integrated circuits.
These IC's have internal diodes to protect the
MOSFET gates, but even so, they can still be destroyed by careless handling
which may produce an electrostatic discharge (ESD) event.
Follow the same
precautions as for dealing with a discrete MOSFET.
To avoid static discharge damage to the IC's, keep the parts inserted into the
black conductive foam whenever it is not being used in a circuit.
Alternatively, the pins may be pushed into a small piece of aluminum foil, or
the part may be wrapped in the foil, if some conductive black foam is not
Always discharge any built up static charges from your body by
touching a grounded metal object, such as the frame of the lab bench, before