Set – 1 (15th February 2014 (Forenoon))
1.
When the optical power incident
on a photo diode is 10 µW and the
responsivity is 0.8 A/W, the photo current generated (in µA) is ____________.
Solution : https://www.youtube.com/watch?v=FdWts4kUgOI
2.
In the figure, assume that the
forward voltage drops to the PN diode D1 and Schottky diode D2
are 0.7 volts and 0.3 volts respectively. If ON denotes conducting state of the
diode and OFF denotes the non conducting state of the diode, then in the
circuit,
a.
Both are ON
b.
D1 is ON and D2
is OFF
c.
Both are OFF
d.
D1 is OFF and D2
is ON
Solution : https://www.youtube.com/watch?v=qteoesfhVco
3.
If the fixed positive charges
are present in the gate oxide of an N channel enhancement type MOSFET, it will
lead to
a.
a decrease in the threshold
voltage
b.
channel length modulation
c.
an increase in substrate
leakage current
d.
an increase in accumulation
capacitance
Solution : https://www.youtube.com/watch?v=em0VvbA7po4
4.
A good current buffer has
a.
Low input impedance and low
output impedance
b.
Low input impedance and high
output impedance
c.
high input impedance and low
output impedance
d.
high input impedance and high
output impedance
Solution : https://www.youtube.com/watch?v=vdYmByP9zYY
5.
A BJT is biased in forward active
mode. Assume VBE = 0.7 volts, KT/q = 25 mV and reverse saturation
current IS = 10-13 Amp. The Transconductance of the BJT
(in mA/volt) is…..
Solution : https://www.youtube.com/watch?v=nAh0aTdVp84
6.
The doping concentration on the
P side and N side of a silicon diode are 1x1016 cm-3 and
1x1017 cm-3 respectively. A forward bias of 0.3 volts is
applied to the diode. At T = 300oK, the intrinsic carrier
concentration of silicon, ni = 1.5 x 1010 cm-3
and KT/q = 26 mV. The electron concentration at the edge of the depletion
region on the P side is
a.
2.3 x 109 cm-3
b.
1 x 1016 cm-3
c.
1 x 1017 cm-3
d.
2.25 x 106 cm-3
Solution : https://www.youtube.com/watch?v=KJ1NDAVBw0U
7.
A depletion type N channel
MOSFET is biased in its linear region for use as a voltage controlled resistor.
Assume threshold voltage VTH = -0.5 volts, VGS = 2.0
volts, VDS = 5 volts, W/L = 100, Cox = 10-8
F/cm2 and µn = 800 cm2/volt-sec. The value of the voltage controlled
resistor (in Ω) is …..
Solution : https://www.youtube.com/watch?v=xzUDuBbZUXM
SET – 2 (15th February 2014 (Afternoon))
1.
A silicon bar is doped with
donor impurities ND = 2.25 x 1015 atoms/cm3.
Given the intrinsic carrier concentration of silicon at T = 300oK is
ni = 1.5 x 1010 cm-3. Assuming complete
impurity ionization, the equilibrium electron and hole concentrations are
a.
no = 1.5 x 1016
cm-3, p0 = 1.5 x 105 cm-3
b.
no = 1.5 x 1010
cm-3, p0 = 1.5 x 1015 cm-3
c.
no = 1.5 x 1015
cm-3, p0 = 1.5 x 1010 cm-3
d.
no = 1.5 x 1015
cm-3, p0 = 1.5 x 105 cm-3
Solution : https://www.youtube.com/watch?v=zvQFdUBhINg
2.
an increase in the base
recombination of a BJT will increase
a.
the common emitter DC current
gain, β
b.
the breakdown voltage BVCEO
c.
the unity gain cutoff
frequency, fτ
d.
the Transconductance gm
Solution : https://www.youtube.com/watch?v=mY6YLyFzlyc
3.
In CMOS technology, shallow P –
well or N – well regions can be formed using
a.
low pressure chemical vapor
deposition
b.
low energy sputtering
c.
low temperature dry oxidation
d.
low energy ion – implantation
Solution : https://www.youtube.com/watch?v=NA-HnsA124g
4.
Assume electron charge q = 1.6
x 10-19C, KT/q = 25 mV and electron mobility µn = 1000 cm2/volt-sec. If
the concentration gradient of electrons injected into a P type silicon sample
is 1 x 1021 per cm-3, the magnitude of electron diffusion
current density (in A/cm2) is ………….
Solution : https://www.youtube.com/watch?v=IBb_zfgQ1AY
5.
Consider an abrupt PN junction
(at T = 300oK) shown in the figure. The depletion region width Xn
on the N side of the junction is 0.2 µm and the
permittivity of silicon (Ԑsi) is 1.044 x 10-12 F/cm. At the junction, the approximate
value of the peak electric field (in kV/cm) is………..
Solution : https://www.youtube.com/watch?v=6SGWS0QE-dQ
6.
When a silicon diode having a
doping concentration of NA = 9 x 1016 cm-3 on
P side and ND = 1 x 1016 cm-3 on N side is
reversed biased, the total depletion width is found to be 3 µm. Given that the permittivity of silicon is 1.04 x 10-12
F/cm, the depletion width on the P side and the maximum electric field in the
depletion region, respectively, are
a.
2.7 µm and 2.3 x 105 V/cm
b.
0.3 µm and 4.15 x 105 V/cm
c.
0.3 µm and 0.42 x 105 V/cm
d.
2.1 µm and 0.42 x 105 V/cm
Solution : https://www.youtube.com/watch?v=PRyI9roqNbA
7.
The diode in the circuit shown,
if Von = 0.7 volts but is ideal otherwise. If Vi = 5 sin(ωt) volts, the minimum and maximum values of Vo (in volts)
are, respectively,
a.
-5 and 2.7
b.
2.7 and 5
c.
-5 and 3.85
d.
1.3 and 5
Solution : https://www.youtube.com/watch?v=VNI1bsbW2i8
8.
For the N channel MOS
transistor shown in the figure, the threshold voltage VTH is 0.8
volts. Neglect channel length modulation effects. When the drain voltage VD
= 1.6 volts, the drain current ID was found to be 0.5 mA. If VD
is adjusted to be 2 volts by changing the values of R and VDD, the
new value of ID (in mA) is
a.
0.625
b.
0.75
c.
1.125
d.
1.5
Solution : https://www.youtube.com/watch?v=wsv90UUqYVY
9.
For the MOSFETs shown in the
figure, the threshold voltage |Vt| = 2 volts and K = 0.5µcox(W/L) = 0.1 mA/V2. The value of ID
(in mA) is …………
Solution : https://www.youtube.com/watch?v=abv9XXV0jks
SET – 3 (16th February 2014 (Forenoon))
1.
In MOSFET fabrication, the
channel length is defined during the process of
a.
Isolation oxide growth
b.
Channel stop implantation
c.
Poly-silicon gate patterning
d.
Lithography step leading to the
contact pads
Solution : https://www.youtube.com/watch?v=QPQ5hOdbGjE
2.
A thin P type silicon sample is
uniformly illuminated with light which generates excess carriers. The
recombination rate is directly proportional to
a.
The minority carrier mobility
b.
The minority carrier
recombination lifetime
c.
The majority carrier
concentration
d.
The excess minority carrier
concentration
Solution : https://www.youtube.com/watch?v=47L011RUiuM
3.
At T = 300oK, the
hole mobility of a semiconductor µp = 500 cm2/volt-sec and KT/q = 26 mV. The hole diffusion
constant Dp in cm2/sec is ………
Solution : https://www.youtube.com/watch?v=cfegvwvHk-A
4.
In the circuit shown, the PNP
transistor has |VBE| = 0.7 volts and β = 50. Assume that RB = 100 KΩ. For Vo to be 5 volts, the value of RC (in KΩ) is ……..
Solution : https://www.youtube.com/watch?v=ohf5m4r0gzs
5.
The donor and acceptor
impurities in an abrupt junction silicon diode are 1 x 1016 cm-3
and 5 x 1018 cm-3, respectively. Assume that the
intrinsic carrier concentration in silicon ni = 1.5 x 1010
cm-3 at 300oK, KT/q = 26 mV and the permittivity of
silicon Ԑsi =
1.04 x 10-12 F/cm. The built in potential and the depletion width of
the diode under thermal equilibrium conditions, respectively are
a.
0.7 volts and 1 x 10-4
cm
b.
0.86 volts and 1 x 10-4
cm
c.
0.7 volts and 3.3 x 10-5
cm
d.
0.86 volts and 3.3 x 10-5
cm
Solution : https://www.youtube.com/watch?v=W1tmcbDY0-4
6.
The slope of the ID
vs. VGS curve of an N channel MOSFET in linear region is 10-3
Ω-1 at
VDS = 0.1 volts. For the same device, neglecting channel length
modulation, the slope of the √ID
vs. VGS curve (in √A/V) under
saturation regime is approximately…………….
Solution : https://www.youtube.com/watch?v=rDjsCvkSUtk
7.
An ideal MOS capacitor has
boron doping concentration of 1015 cm-3 in the substrate.
When a gate voltage is applied, a depletion region of width 0.5 µm is formed with a surface (channel) potential of 0.2 volts. Given
that Ԑo =
8.854 x 10-14 F/cm and the relative permittivity’s of silicon and
silicon dioxide are 12 and 4 respectively. The peak electric field (in V/µm) in the oxide region is ……………..
Solution : https://www.youtube.com/watch?v=K4aRAJxegSI
8.
In the circuit shown, the
silicon BJT has β = 50. Assume VBE
= 0.7 volts and VCEsat = 0.2 volts. Which one of the following
statements is correct?
a.
For RC = 1 kΩ,
the BJT operates in the saturation region
b.
For RC = 3 kΩ,
the BJT operates in the saturation region
c.
For RC = 20 kΩ,
the BJT operates in the cutoff region
d.
For RC = 20 kΩ,
the BJT operates in the linear region
Solution : https://www.youtube.com/watch?v=zd_NFD2CN8E
9.
For the MOSFET M1
shown in the figure, assume W/L = 2, VDD = 2.0 volts, µncox = 100 µA/V2 and VTH = 0.5 volts. The transistor M1
switches from saturation region to
linear region when Vin (in volts) is …………..
Solution : https://www.youtube.com/watch?v=AWdemWJenw4
SET
- 4 (16th February 2014 (Afternoon))
1.
At T = 300oK, the
band gap and the intrinsic carrier concentration of GaAs are 1.42 eV and 106
cm-3 respectively. In order to generate electron hole pairs in GaAs,
which one of the wavelength (λc) ranges of incident radiation, is most suitable? (Given that
Plank’s constant = 6.62 x 10-34 J-sec, velocity of light is 3 x 1010
cm/s and charge of electron is 1.6 x 10-19C)
a.
0.42 µm < λc < 0.87 µm
b.
0.87 µm < λc < 1.42 µm
c.
1.42 µm < λc < 1.62 µm
d.
1.62 µm < λc < 6.62 µm
Solution : https://www.youtube.com/watch?v=NML_fLbqHxw
2.
In the figure, ln(ρi) is plotted as a function of 1/T,
where ρi is
the intrinsic resistivity of silicon, T is the temperature, and the plot is
almost linear. The slope of the line can be used to estimate
a.
Band gap energy of silicon
b.
Sum of electron and hole
mobility in silicon
c.
Reciprocal of the sum of
electron and hole mobility in silicon
d.
Intrinsic carrier concentration
of silicon
Solution : https://www.youtube.com/watch?v=nqt3J_lXwuU
3.
The cutoff wavelength (in µm) of light that can be used for intrinsic excitation of a
semiconductor material of band gap Eg = 1.1 eV is …………..
Solution : https://www.youtube.com/watch?v=bfF2NoqjjDU
4.
If the emitter resistance in a
common emitter voltage amplifier is not bypassed, it will
a.
Reduce both the voltage gain
and the input impedance
b.
Reduce the voltage gain and
increase the input impedance
c.
Increase the voltage gain and
reduce the input impedance
d.
Increase both the voltage gain
and the input impedance
Solution : https://www.youtube.com/watch?v=4YjclPDw5lM
5.
Consider a silicon sample doped
with ND = 1 x 1015 /cm3 donor atoms. Assume
that the intrinsic carrier concentration ni = 1.5 x 1010 cm-3. If the
sample is additionally doped with NA = 1 x 1018 cm-3
acceptor atoms, the approximate number of electrons /cm3 in the
sample, at T = 300oK, will be…………
Solution : https://www.youtube.com/watch?v=T4s49hCIrz0
6.
Consider two BJTs biased at the
same collector current with area A1 = 0.2 µm x 0.2 µm and A2 =
300 µm x 300 µm. assuming that all other device parameters are identical, KT/q =
26 mV, the intrinsic carrier concentration is 1 x 1010 cm-3,
and q = 1.6 x 10-19C, the difference between the base emitter
voltages (in mV) of the two BJTs (i.e. VBE1 – VBE2) is
…………….
Solution : https://www.youtube.com/watch?v=R-GogUWvN74
7.
An N type semiconductor having
uniform doping is biased as shown in the figure.
Solution : https://www.youtube.com/watch?v=XhOs_vAWETw
8.
A BJT in a common base
configuration is used to amplify a signal received by a 50Ω antenna. Assume KT/q = 25 mV, the value of collector bias current
(in mA) required to match the input impedance of the amplifier to the impedance
of the antenna is ………..
Solution : https://www.youtube.com/watch?v=HBjqJb91WbE
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