Electronics Assignment 3 - Copy
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Electronics Assignment 3
Ans1(a): 3
Ans 1(b): 3
Ans 1(c): 3
Ans 1(d): 3
Ans 1(e): 1
Ans 1(f): 4
Ans 1(g): 1
Ans 1(h): 3
Ans 1(i): 1
Ans 1(j): 3
Ans 2(a) Conductor:A conductor is a material which has a very high conductivitybecause of the presence of large number of free electrons.
Insulator: An insulator is a material that offers a very low level of conductivity underpressure from an applied voltage source.Semiconductor:A semiconductor, therefore, is a material that has a conductivity levesome where between the e!tremes of an insulator and a conductor. "he figure shows
the conduction and valence band for insulator, semiconductor and metals.
"he energy band gap in insulators is #E$% &A$'E. "he energy bands (#E$&A) in metals.
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"he energy band gap is semiconductor is larger than metals."he semiconductors have *
valence electrons.
Ans+b-Common mitter Configuration
"he Emitter is a common terminal between input and output. ere, the input is applied atbase and output is ta/en at the collector.
0ig 12
"he Input and (utput characteristics ,0or Common mitter npn "ransistor-"he input characteristics are a plot of the input current I - versus the input voltage
#E- for a range of values of output voltage #CE- as shown in fig 11.
0ig 11
0or the commonemitter configuration the output characteristics are a plot of the output
current IC- versus output voltage #CE- for a range of values of input current I-. As
shown in fig 1+, for a fi!ed value of I, as we increase the #CE, the collector current
increases. "he $egion to the right of #CEsat- is called saturation region. In this region
both the Emitter ase and Collector ase 4unctions are 0orward iased."he Input and(utput characteristics ,0or Common mitter pnp "ransistor-"he input characteristics are same as that for npn transistor, but here #E is replaced by
#E and #CEis replaced by #EC.In output characteristics, the #CE is replaced by #EC
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0ig 1+ "he output Characteristics of npn "ransistor in CE Configuration.Ans+c- &oad &ines&oad line is a tool to find the e!act current and voltage.Consider the 0ig.13. "he current through the resistor is
If I56 2, #56 #S
If #562, I56 #S7$
"he line which is s/etched by 4oining these two
)oints are called 5C &oad &ine shown in 0ig 1*- 0ig. 13
0ig 1*. 5C load line8 point 8 point is also called the operating point. "his is point of intersection of 5C&oad line and the #I Characteristics of a 5iode
Ans+d- C9(S Inverter
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C9(S stands for complementary 9(S C9(S-,which is a combination of n channel
and p channel 9(S0E"s. 0ig above shows a C9(S inverter.
(peration of C9(S inverter"he C9(S inverter input voltage is either high #55- or low2#-.;hen the input
voltage is high, 81 is off and 8+ is on. In this case, the shorted 8+ pulls the output
voltage down to ground.
;hen the input voltage is low,81 is on and 8+ is off. uals #557+.At this point, both
9(S0E"S have e>ual resistances and the output voltage e>uals #557+
Ans+e-
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As shown in table 1 the first type has an input voltage and an output voltage. "he circuit
that uses this type of negative feedbac/ is called a #oltageControlled #oltage Source#C#S-. A #C#S is an ideal voltage amplifier because it has a stabili=ed voltage gain,
infinite input impedance, and =ero output impedance.
In the second type of negative feedbac/, an input current controls an output voltage. "he
circuit using this type of feedbac/ is called a CurrentControlled #oltage SourceIC#S-. "his circuit is also /nown as transresistance amplifier.
"he third type of negative feedbac/ has an input voltage controlling an output current
"he circuit using this type is called a #oltageControlled Current Source #CIS-sometimes called transconductance amplifier.
In the fourth type, an input current is amplified to get a larger output current. "he circuit
is called a CurrentControlled Current Source ICIS-. An ICIS is an ideal currentamplifier because it has a stability current gain, =ero input impedance, and infinite
output impedance.
0ig13 ,a-#oltageControlled #oltage Source ,b- CurrentControlled #oltage Source
0ig1*,a-#oltageControlled Current Source ,b- CurrentControlled Current Source#C#S is a voltage amplifier and ICIS is a current amplifier where as IC#S is a current to
voltage and #CIS is a voltage to current amplifier.
Inpu
t
(utput Circuit Bin Bou
t
Converte
rs
$atio Symbol
# # #C#S 2 #out7#in Av
I # IC#S 2 2 i to v #out7Iin rm
# I #CIS v to i Iout7#in gm
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I I ICIS 2 Iout7Iin Ai
"able 10igure 13 a- shows the practical circuit of #C#S, the input impedance is not infinite but
it is very high. &i/ewise, the output impedance is not =ero, but it is very low. "he voltage
gain is symboli=ed by Av. 0igure 13 b- shows IC#S which has very low input and output
impedance. "he conversion factor of the IC#S is called transresistance rm-.
0igure 1* a- shows #CIS which has very high input and output resistance. "he
conversion factor #CIS is called transconductance gm-. 0igure 1* b- shows ICIS which
has very low input and very high output impedance. "he current gain is symboli=ed by Ai.
*.3 #C#S #oltage 'ain0igure 1? shows a
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Closed loop output impedance is given by
BoutC&- 6 $out7 1A#(&-
;here $out is the open loop output resistance.
"otal harmonic distortion is given by
"5C&
6 "5(&
7 1A#(&
-
;here "5(&is the open loop total harmonic distortion.
*.* "he IC#S Amplifier0igure 1@ shows a transresistance amplifier. It has an input current and an output
voltage. "he IC#S amplifier is an almost perfect currenttovoltage converter because it
has =ero input impedance and =ero output impedance.
0ig 1@ IC#S amplifier"he e!act e>uation of the output voltage is given by
(utput voltage is given by
#out6 iin$f-
"he circuit is a voltage converter by ta/ing different values $f we can very the output
voltage.
"he e!act e>uation of the output voltage is given by
Input and output impedances are given by
*.? "he #CIS Amplifier
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0ig 1 #CIS amplifier0igure 1 shows a transconductance amplifier. It is similar to a #C#S amplifier, e!cept
that $&is the load resistor as well as the feedbac/ resistor. "he active output is not the
voltage across voltage across $& $1F rather, it is the current through $&.
"he output current is given by
iout6 vin7 $1
iout6 vingm
"he e!act output current is given by
"he circuit is a voltagetocurrent converter . "he input and output impedances are given
by
*.@ "he ICIS Amplifier
0ig 1G ICIS amplifierAn ICIS circuit amplifies the input current. ecause of the heavy negative feedbac/, the
ICIS amplifier tends to act li/e a perfect current amplifier. It has very low input and very
high output impedance. "he closed loop current gain is given by
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"he input and output impedances are given by
Ans+f- 5#9: "he first digitalvoltmeter was invented and produced by Andrew Hayof
uantity to a digital number that
represents the >uantityJs amplitude. "he conversion involves >uanti=ationof the input, so
it introduces a small amount of error. "he inverse operation is performed by a digitalto
analog converter5AC-. Instead of doing a single conversion, an A5C often performs the
conversions KsamplesK the input- periodically. "he result is a se>uence of digital values
that have converted a continuoustime and continuousamplitude analog signalto a
discretetime and discreteamplitude digital signal. An A5C may also provide an isolated
measurement such as an electronicdevice that converts an input analog voltageorcurrentto a digital number proportional to the magnitude of the voltage or current.
owever, some nonelectronic or only partially electronic devices, such as rotary
encoders, can also be considered A5Cs."he digital output may use different coding
schemes. "ypically the digital output will be a twoJs complementbinary number that is
http://en.wikipedia.org/wiki/Andrew_Kayhttp://en.wikipedia.org/wiki/Kayprohttp://en.wikipedia.org/wiki/Analog-to-digital_converterhttp://en.wikipedia.org/wiki/Integrating_ADChttp://en.wikipedia.org/wiki/Voltage_referencehttp://en.wikipedia.org/wiki/Weston_cellhttp://en.wikipedia.org/wiki/Quantization_(signal_processing)http://en.wikipedia.org/wiki/Digital-to-analog_converterhttp://en.wikipedia.org/wiki/Digital-to-analog_converterhttp://en.wikipedia.org/wiki/Sampling_(signal_processing)http://en.wikipedia.org/wiki/Analog_signalhttp://en.wikipedia.org/wiki/Digital_signalhttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Rotary_encoderhttp://en.wikipedia.org/wiki/Rotary_encoderhttp://en.wikipedia.org/wiki/Two's_complementhttp://en.wikipedia.org/wiki/Andrew_Kayhttp://en.wikipedia.org/wiki/Kayprohttp://en.wikipedia.org/wiki/Analog-to-digital_converterhttp://en.wikipedia.org/wiki/Integrating_ADChttp://en.wikipedia.org/wiki/Voltage_referencehttp://en.wikipedia.org/wiki/Weston_cellhttp://en.wikipedia.org/wiki/Quantization_(signal_processing)http://en.wikipedia.org/wiki/Digital-to-analog_converterhttp://en.wikipedia.org/wiki/Digital-to-analog_converterhttp://en.wikipedia.org/wiki/Sampling_(signal_processing)http://en.wikipedia.org/wiki/Analog_signalhttp://en.wikipedia.org/wiki/Digital_signalhttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Rotary_encoderhttp://en.wikipedia.org/wiki/Rotary_encoderhttp://en.wikipedia.org/wiki/Two's_complement -
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proportional to the input, but there are other possibilities
Section CAns 3,a- : "he Cho/e Input 0ilterCho/e Input 0ilter 0ig +- are used to filter the ouput of a $ectifier."he Cho/eor
inductor- has a primary charcterisitcs of opposing a change in current.ecause of this,a
cho/e Input filter ideally reduces the A.C current in the load resistor to =ero.
0or designing a cho/e input filter ,we have two re>uirements.
1. Cho/e Input filter should LCvalue much smaller than $&at the input fre>uency.;hen
this re>uirement is satisfied,we can ignore the load resistance $&.+. ;e should have L& much greater than LCat the input fre>uency.;hen this condition is
satisfied ,the ac output voltage approaches =ero.
0ig.+,a- Cho/e Input filter ,b- AC E>uivalent Circuit
0iltering the (utput of a $ectifier"he easiest way to understand the filtering operation is by using the superposition
theorem.
"he Superposition "heorem states that if we have two of more sources,we can analyse
the circuit for each source separately and then add the individual voltages to get the
total voltage0ig +G-.
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"he $ectifier output has two different components: a 5.C voltage the average value- and
an A.C voltagethe fluctuating part-.
;hen A.C voltage is concerned,the inductive reactance is =ero and capacitive reactance
is infinite."hus ,almost all the 5C component is passed on to the load resistor and almost
all the AC component is bloc/ed.
In this way, we get almost perfect 5C voltage."he only deviation is small AC load
voltages called $ipple.
0ig+G,a-$ectifier with Cho/e Input 0ilter ,b-$ectifer (utput has 5C and AC components
,c-5C E>uivalent Circuit ,d- 0ilter output is direct current with small ripple.
"he Capacitor Input 0ilter"he Cho/e Input 0ilter produces a 5C output voltage e>ual to the average value of the
rectified voltage."he capacitor input filter produces a 5C output voltage e>ual to the
pea/ value of the rectified voltage."his 0ilter is most widely used in power supplies.
Capacitor Input 0ilter with
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0or the capacitor input filter to be constant, we need to connect a load resistor across
the capacitor. As long as $&C time constant is much greater than the period, capacitor
remains almost fully charged and the voltage appro!imately #).
"he only deviation from perfect 5C voltage is small ripple. "he smaller the pea/ to pea/
value of this ripple, the more closely the output approaches a perfect 5C voltage.
etween the pea/s, the diode is off and the capacitor discharges through the load
resistor. Since the capacitor discharges only slightly between pea/s, the pea/ to pea/
ripple is small.
0ig.32 ,a- &oaded capacitor input filter ,b- (utput is direct current with small ripple,c-0ull wave output has less ripple.
Surge Current
0ig.31Surge $esistor limits surge current.;hen the power is turned on,the filter is uncharged.At the first instant,when the power is
applied,the capacitor loo/s li/e a short circuit."he initial charging current may be very
large.All that e!ists in the charging path to impede the current is the resistance of the
transformer winding and the bul/ resistance of the diodes.
"he initial rush of current when the power is turned on is called the SM$'E CM$$E
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;e have to solve this e!ample using the same steps discussed in above e!ample.Ans
Ans *: A ipolar Nunction "ransistor N"- is a three terminal device whose operation is
dependent on the interaction of both ma4ority and minority carriers and hence it is called
bipolar device. "ransistor means transfer of resistor i.e, transfer of resistance from low
resistance input -to high resistance output- circuit.
Construction of a N"1. npn : "he n D p Dn transistor is formed by sandwiching a thin OpP type semiconductorbetween two OnP type semiconductors.0ig 1-ase comes between collector and emitter
region. ase is thin and lightly doped. 5oping level of Emitter is intermediate between
Emitter and ase .Emitter and collector are much wider than base and are heavily doped.
"he emitter is heavily doped than the collector.
0ig 1
0ig @Applying HC& ,we obtain IE 6 I IC
Alpha 5.CQdc-6 IC7IE , eta 5.C Rdc- 6 IC7I
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Ans ?: < channel enhancement Dtype 9(S0 ""he basic construction of the nchannel enhancementtype 9(S0E" is provided in 0ig.1
A slab of ptype material is formed from a silicon base and is referred to as the
substrate. As with the depletiontype 9(S0E", the substrate is sometimes internally
connected to the source terminal, while in other cases a fourth lead is made available for
e!ternal control of its potential level. "he source and drain terminals are connected
through metallic contacts to ndoped regions, but note in 0ig.1 the absence of a channel
between the two ndoped regions. "his is the primary difference between the
construction of depletiontype and enhancementtype 9(S0E"sthe absence of a
channel as a constructed component of the device. "he Si(+ layer is still present to
isolate the gate metallic platform from the region between the drain and source, but now
it is simply separated from a section of the ptype material. In summary, therefore, the
construction of an enhancementtype 9(S0E" is >uite similar to that of the depletion
type 9(S0E", e!cept for the absence of a channel between the drain and source
terminals.
0ig 1
asic (peration1. (peration with #'S62# and #5S6 positive.If #'S is set at 2 # and a voltage applied between the drain and source of the device of
0ig.1, the absence of an nchannel with its generous number of free carriers-will result
in a current of 2 Amperes.
+. (peration with #'S6 positive and #5S6 positive.In 0ig. + both #5S and #'Shave been set at some positive voltage greater than 2 #
establishing the drain and gate at a positive potential with respect to the source."he
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positive potential at the gate will pressure the holes since li/e charges repel- in the p
substrate along the edge of the Si(+ layer to leave the area and enter deeper regions
(f the psubstrate, as shown in the figure. "he result is a depletion region near the Si(+
insulating layer void of holes. owever, the electrons in the psubstrate the minority
carriers of the material- will be attracted to the positive gate and accumulate in the
region near the surface of the Si(+ layer. "he Si(+ layer and its insulating >ualities will
prevent the negative carriers from being absorbed at the gate terminal. As #'S increases
in magnitude, the concentration of electrons near the Si(+ surface increases until
eventually the induced ntype region can support a measurable flow between drain and
source.
"hreshold #oltage #" "he level of #'Sat which the channel begins to conduct is calledthe "hreshold #oltage, #". Since the channel is none!istent with #'S 6 2 # and
TenhancedU by the application of a positive gatetosource voltage, this type of 9(S0E"
is called an enhancementtype 9(S0E".
0ig +As #'Sis increased beyond the threshold level, the density of free carriers in theinduced
channel will increase, resulting in an increased level of drain current. owever,if we hold
#'Sconstant and increase the level of #5S, the following conditions results.
1. If #'S #5SV #", the n channel 9(S0E" will wor/ in &inear $egion, and the drain
current I5will increase linearly with increase in drain voltage #5S.
+. If #'S #5S6 #", the gate will become less and less positive with respect to drain. "hus,
the number of electrons near to the drain terminal also reduces and channel will be
become )I
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3. If #'S #5S V #",the n channel 9(S0E" will enter into SA"M$A"I(
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#CC
#1Inverting input
#+ uencies. Its reliability, stability, and ease of operation ma/e it suitable as a
general purpose laboratory instrument. "he heart of the C$( is a cathoderay tube shown
schematically in 0ig. 1.
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