Download - Electronics II Lab Manual 4
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EECE 322 Lab 4: MOSFET Amplifiers
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Laboratory oals
This project will show the biasing, gain, frequency response, and impedance properties ofthe MOSFET common source and common drain amplifiers.
!ea"i#g
Student Reference Manual for Electronic Instrumentation Laboratoriesby Stanley olf
and !ichard Smith, "opyright #$$%.
Oscilloscope &ser's (uide )"opies of this reference boo* are a+ailable in the lab, or at
the website
Tektronics 571 Curve Tracer Manual
-S#% Transistor /ata Sheet
!ead the pre0lab introduction below
E$%ipme#t #ee"e"
1ab noteboo*, pencil
Oscilloscope )2gilent or Te*tronics 3 oscilloscope probes )already attached to the oscilloscope
-4"5E6 7oo* test leads
Te*tronics 8# "ur+e Tracer 9-08%: 9roto0-oard or*station 9", with 9S;"E application
Parts #ee"e"
34%%% MOSFET
Lab safety &o#&er#s
Ma*e sure before you apply an input signal to a circuit, all connections are
correct, and no shorted wires e
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EECE 322 Lab 4: MOSFET Amplifiers
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1' Pre(Lab )#tro"%&tio#
Two of the most popular configurations of small0signal MOSFET amplifiers are thecommon source )"S and common drain )"/ configurations. These two circuits are
shown in
Figures =0# and =03 respecti+ely. The common source and common drain amplifiers, li*eall MOSFET amplifiers, ha+e the characteristic of high input impedance. The +alue of theinput impedance for both amplifiers is basically limited only by the biasing resistors !(#
and !(3. >alues of !(# and !(3 are usually chosen as high as possible to *eep the
input impedance high. 7igh input impedance is desirable to *eep the amplifier fromloading the signal source. One popular biasing scheme for the "S and "/ configurations
consists of the +oltage di+ider !(# and !(3. This +oltage di+ider supplies the MOSFET
gate with a constant /" +oltage. This is +ery similar to the -?T biasing arrangementdescribed in 9roject $. The main difference with the -?T biasing scheme is that ideally no
current flows from the +oltage di+ider into the MOSFET.
The "S and "/ MOSFET amplifiers can be compared to the "E and "" -?T amplifiersrespecti+ely. 1i*e the "E amplifier, the "S amplifier has a negati+e +oltage gain and anoutput impedance approT is aparameter of each particular MOSFET and is temperature sensiti+e. This parameter
sensiti+ity to temperature is one reason for establishing a stable /" bias. The 34%%%
MOSFET data sheet lists the minimum and maT as %.@ > and :.% >respecti+ely.
2' *esig#
/esign a common source amplifier as shown in Figure =0# with the following
specificationsA
#. use a 34%%% MOSFET and a 3% +olt /" supply
3. midband gain >O5>; B.%
:. low cutoff frequency F1 #%% 7C
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EECE 322 Lab 4: MOSFET Amplifiers
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=. >O symmetric swing :.% +olts pea* )B > p 0 p
8. load resistor !1 D 8 *
B. source resistance !; D 8% )this is in addition to the Te*troni< function generators
internal resistance
/esign a common drain amplifier as shown in Figure =03 with the following
specificationsA
#. use a 34%%% MOSFET and a 3% +olt /" supply
3. midband gain >O5>; %.8
:. low cutoff frequency F1 #%% 7C
=. >O symmetric swing 8.% +olts pea* )#% > p 0 p
8. load resistor !1 D 3%%
B. source resistance !; D 8% )this is in addition to the Te*troni< function generators
internal resistance
Figure = 0 #A "ommon Source MOSFET 2mplifier
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EECE 322 Lab 4: MOSFET Amplifiers
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Figure = 0 3A "ommon /rain MOSFET 2mplifier
Figure = 0 :A Small Signal FET Model
3' Lab Pro&e"%re
)steps # 3 may be omitted if done prior to this lab period and the same FET is used
4oteAThe MOSFET can be easily damaged by static electricity, so careful handling is
important
#. Find the +alue of the threshold +oltage >T and conducti+ity parameter G from the
digital cur+e tracer )remember the relation ;/ D GH>(S 0 >TI3 in the saturation region.
3. /etermine the +alue of rds from the digital cur+e tracer. The slope of the transistor
;/0>/S cur+es in the acti+e region is #5rds.
:. "onstruct the "S circuit shown in Figure =0#. !emember !; is installed in addition to
the internal 8% resistance of the function generator.
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EECE 322 Lab 4: MOSFET Amplifiers
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=. >erify that the specifications ha+e been met by measuring the J0point, midband
+oltage gain, and pea* symmetric output +oltage swing. 4ote any distortion in the output
signal.
8. 2djust the output signal to obtain the maerify that the input impedance specification has been met.
$. "onstruct the "/ circuit shown in Figure =03. !emember !; is installed in addition to
the internal 8% resistance of the function generator.
#%. !epeat steps =0@.
4' A#alysis
#. "ompare the gain, frequency response, input impedance, and output impedance of
the "S amplifier with the results from the "E amplifier. "ompare the "/
amplifier with the "" amplifier. "omment on the differences5similarities.