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Abstract This lab serves to distinguish the trans-
characteristic of a given transistor using DC analysis for a
specified configuration.
I ndex TermsMOSFET, NMOS, VDS, VGS, VDD, ID, RD
I. INTRODUCTION
HE type of transistor to be used in this experiment is the
MOSFET, or more specifically the metal-oxide-
semiconductor field-effect transistor, which is a three
terminal
device and whose use varies depending on the desired
application. In our case, we will simply investigate the
behavior of the transistor by defining its
trans-characteristic,
which will be accomplished by analyzing the circuit
configuration in the DC realm.
Our particular transistor will be utilized as an NMOS
transistor. By applying a positive voltage at the gate
terminal
and having the source terminal grounded, a channel is
induced
within the transistor which will allow for current to flow
from
drain to source when a positive voltage is applied at the
drain.
Several runs will be taken where certain voltages will be
applied at Vgg and Vdd to allow us to determine the trans-
characteristic of the transistor.
II. PROCEDURE
A. Building the configurationThe first thing placed in the
printed circuit board was the
transistor itself. Then the configuration involved two
resistors
connected in series. One having Vggapplied directly to it
while
the other was connected to a common ground. The values of
the resistors were in the order of magnitude of Mega Ohms.
The values chosen were 10M ohms. The purpose of having
extremely large values for the resistors is because they will
act
as a choke during AC applications. Essentially they will
guide
the current to the desired path.
The source terminal was connected to the common ground,
and the drain was connected to a resistor in the order of
magnitude of Kilo Ohms and measured in at 10K Ohms. This
resistor was connected directly to Vdd.
B. Measuring Vds ,Id and VgsThe lab required to measure
Vds,Id,and Vgs as Vgg and Vdd
varied. This would allow the plot of these values to display
the
trans-characteristic of the transistor. Idcould not be
measured
directly due to the hazards surrounding that type ofmeasurement
thus the voltage through the resistor had to be
measured instead which makes it possible to measure Idusing
Ohms Law.Finally, Vgswas measured just by measuring the
voltage from gate to source.
III. MATH
The Voltage drop between the drain and source of the
transistor is calculated by the voltage applied at the
Drain(VDD) and the drop across the resistor between them.
VDS = VDD - ID*RD
VGS is then calculated via the voltage input of VGG and the
ratio between the resistance values in the circuit.
VGS = VGG * RG2 / (RG1/RG2)
This formula is simply the voltage division of the two
resistors
in series.
RG1 =10.12 M(measured)
RG2 =9.81Mmeasured)
IV. FIGURES AND TABLES
In these tables Vggwill be the columns and Vddwill be the
rows.
Characterizing the MOSFET with DC Voltage
Joshua S. Flores
T
Voltagethrough Rd[V]
Vgg/Vdd 0 1 2 3 4 5
0 0 0 0 0 0 0
2 1.43 1.44 1.55 1.79 1.99 2
4 3.41 3.42 3.53 3.75 3.98 46 5.4 5.41 5.5 5.72 5.97 6
8 7.39 7.4 7.49 7.7 7.96 8
10 9.39 9.39 9.48 9.69 9.95 10
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VdsCalc.[V]
Vgg/Vdd 1 2 3 4 5
0 0 0 0 0 0 0
2 0.57 0.56 0.45 0.21 0.01 0
4 0.59 0.58 0.47 0.25 0.02 0
6 0.6 0.59 0.5 0.28 0.03 0
8 0.61 0.6 0.51 0.3 0.04 0
10 0.61 0.61 0.52 0.31 0.05 0
Vdsmeasured[V]
Vgg/Vdd 0 1 2 3 4 5
0 0 0 0 0 0 0
2 0.56 0.55 0.44 0.21 0.01 0.001
4 0.58 0.57 0.47 0.26 0.02 0.003
6 0.6 0.59 0.49 0.27 0.033 0.005
8 0.61 0.6 0.51 0.29 0.43 0.00610 0.61 0.6 0.52 0.31 0.53
0.008
Current of Id[mA]
Vgg/Vdd 0 1 2 3 4 5
0 0 0 0 0 0 0
2 0.0563 0.0553 0.0445 0.0208 0.00099 0
4 0.0583 0.0573 0.0464 0.0247 0.00198 0
6 0.0593 0.0583 0.0494 0.0277 0.00296 0
8 0.0603 0.0593 0.0504 0.0296 0.00395 0
10 0.0603 0.0603 0.0514 0.0306 0.00494 0
Vgs Measured[V]
Vgg Vgs
0 0
1 0.323
2 0.646
3 0.969
4 1.292
5 1.612
Vgs Calculated[V]
Vdd Vgs
0 0
1 0.488303
2 0.976605
31.464908
4 1.953211
5 2.441513
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V. CONCLUSION
The lab produced values that were negligibly different from
those measured during the lab when measuring Vds and Id.
However, due to some unknown reason during the
measurements, the values of Vgs were completely off when
comparing those values to the theoretical values. Even when
measuring the voltage drop between two different resistors
in
series, the same reading of 0.54V was always read which was
very bizarre to say the least. Although, when analyzing the
plot
it can be seen that our plotted values are in the same range
as
our calculated values. For instance, at plot line created for
5V
at Vgg, Vgsis approximately 2.27 V which is still 6 percent
off,
but better than the 34 percent using the measured values.
REFERENCES
[1] G. O. Young, Synthetic structure of industrial plastics
(Book style with
paper title and editor), inPlastics, 2nd ed. vol. 3, J. Peters,
Ed. New
York: McGraw-Hill, 1964, pp. 1564.
