Tuesday, March 25, 2014

GATE 1994 Electronic Devices (EDC) Video solutions

1. A small concentration of minority carriers is injected into a homogeneous semiconductor crystal at one point. An electric field of 10 V/cm is applied across the crystal and this moves the minority carriers a distance of 1 cm in 20 µsec. The mobility in cm2/volt-sec will be
a. 1000
b. 2000
c. 5000
d. 50000
Answer: C
Solution : https://www.youtube.com/watch?v=Pe9nM75oo1U

2. The threshold voltage of an n-channel MOSFET can be increased by
a. Increasing the channel dopant concentration
b. Reducing the channel dopant concentration
c. Reducing the gate oxide thickness
d. Reducing the channel length
Answer: A
Solution : https://www.youtube.com/watch?v=1C8CrsGguu0

3. The forward dynamic resistance of a junction diode varies ……………… as the forward current.
Answer: Inversely
Solution : https://www.youtube.com/watch?v=HfjrpzG7j8s

4. The transit time of the current carriers through the channel of an FET decides its ……………. characteristics.
Answer: Switching
Solution : https://www.youtube.com/watch?v=vQJjmHNsn3I

5. A p-type silicon sample has a higher conductivity compared to an n-type sample having the same dopant concentration. (TRUE / FALSE)
Answer: False
Solution : https://www.youtube.com/watch?v=WUKXrsePs-A

6. Channel current is reduced on application of a more positive voltage to the gate of a depletion mode n-channel MOSFET. (TRUE / FALSE)
Answer: False
Solution : https://www.youtube.com/watch?v=W34kWifl15o

7. Match the following :
Answer: a-2, b-3, c-1
Solution : https://www.youtube.com/watch?v=GWjW0DVZkSI

8. Show that the minimum conductivity of an extrinsic silicon sample occurs when it is slightly p-type. Calculate the electron and hole concentrations when the conductivity is minimum. Given that µn = 1350 cm2/volt-sec, µp = 450 cm2/volt-sec, and the intrinsic carrier concentration, ni = 1.5 X 1010 cm-3.
Answer: no = ni√µp∕µn and po = ni√µn∕µp
Solution : https://www.youtube.com/watch?v=_O5iozGDyEM

9. In the common emitter amplifier shown, the transistor has a forward current gain of 100, and a base to emitter voltage of 0.6 volts. Assume ICO to be negligible. Choose value for R1 and R3 such that the transistor has a collector current of 1 mA and a collector to emitter voltage of 2.5 volts.
Answer: 41 kΩ and 2.2 kΩ
Solution : https://www.youtube.com/watch?v=SjV5f5WC8GU

10. A typical CMOS inverter has the voltage transfer characteristic (VTC) curve as shown in the figure. Evaluate the value of the inverter threshold VINV, which is the value of the input at which Vo falls by ΔVo = VTn + VTp.
Answer: 2.5 volts
Solution : https://www.youtube.com/watch?v=7om91pj90XE

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