By William Arkush
PART III
Semiconductor
device technology
The who's who family mentioned
in Part I of this article [UPDATE , May
1, 1980] refers to the technologies of
the processes more than the applica-
tions of the device itself. The MOS
family has many derivatives within
the process but generally they are
used for creating logic functions . The
MOS structures act as a gating
mechanism which makes these de -
vices significant for digital system
processing . Computers being the
best example of this means in no way
that digital signal process is limited ,
for it is now deeply embedded in all
branches of the electronics , commer-
cial , and consumer industries .
MOS technology - metal oxide
semiconducter - is not generally suit-
ed for analog signal processing or
timing applications. However, the
manner in which the junctions of
the chips are doped will create the
variations in the type of the device.
This means the MOS technologies
-being C-D-N-P or VMOS and
MOSFETs (MOS field effect transis-
tors) allow the devices fabricated
from these processes to be used in
many applications . MOSFETs are
used in the front end of tuners and
radios while NMOS is used to fabricate
microprocessors (CPUs) and all sorts
of host hardware.
DMOS is used to make static RAM
memories and CMOS is used to
create non-volatile dynamic and
static memories .
Othern families of logic include the
bi-polar junctions where current is
directed through a semiconductor
material in the forward biasd mode
due to its low resistance in the
junction. When the junction sees a
high resistance , the current flow is
limited accordingly by the intrinsic
value of the junction .
This high resistance , low current
flow is known as reverse bias and is
the basis for the function and
performance of digital logic devices .
When a gate sees a 1-state as differ-
entiated from an 0-state , the device
reacts , depending on the elemrnt
type . In essence then , the transis-
tor/ transistor logic TTL and diode
/ transistor logic (DTL) are those bi-
polar junction structures which react
to biases and current flows and
thereby gate signals digitally as they
respond to the changing states at the
input.
Although there are basic gate
types , the computer industry has
created a demand so heavy on the
device manufacturers that the types
and functions are so numerous it
would be virtually impossible to list all
of them .
I mentioned earlier gates , counter,
drivers , buffers , registers , multiplex-
ers , demultiplexers, and others . That
is why all shops that are up to par
have data books on the device types
and a semiconductor reference man -
ual. An absolute necessity , the
technician's library has become an
as the bandpass of his oscilloscope .
"You can't tell the players without
the program. "
PROM and ROM memories are a
different story , however. The system
comes with the PROMs or ROMs and
no information on the software . This
means our only hope is that it works
and is reliable . There are very few
methods for testing PROMs a PROM
or ROM in the field, short of sub-
stituting the parts . It is a part with a
fixed program which we generally
have no access to , and there is
virtually no way to test a device
without burning a program or com-
paring its program with anm identical
copy.
If you want to test a memory part
in the field , in circuit , you need an
expensive system emulator or a
signature analyzer if the signatures
are available . A better way is to test
the semiconductor junctions of the
memory device or any other semi-
conductor device , in or out of circuit
with a reactance analyzer .
The Parametric Analyzer by
UWC , Inc. is an oscilloscope add-on
which allows you to determine the
condition of a device under test on a
non -powered circuit board . This
instrument removes the need to sub-
stitute parts or to shotgun a repair . It
removes the guesswork in trouble-
shooting integrated circuits , meories ,
and other semiconductor junctions
such as transistors and diodes .
Analog devices range from power
transistors ,
power
regulators ,
on -amp , comparators , linear ampli-
fiers , phase lock loops, timers ,
function generators , and oscillators,
to mention a few .
The same theory applies , referring
to biasing their junctions except that
in digital signal processing, you turn
on and off the device extremely
rapidly to accomodate the clock
which drives the system . But in ala-
log electronics , you have an ampli-
tude oriented system which must
track according to a variable input
applied to the device . Stereo ampli-
fiers and Servo amplifiers are
excellent examples of components
designed to accept a wide range of
inputs and produce a governed
output . The analog world , as the
digital electronic world , depend
entirely on the circuit die which drive
them .
All indicators still point us back to
the little chip of silicon which makes