### GATE 1996 Video Solution on EDC (Electronic Devices and Circuits)

1. The n-channel MOSFET shown in figure is used as a voltage variable resistor. Determine the expression for the resistance and compute its value for Vi. Neglect body effect.
MOSFET Data :
Threshold voltage, VT = 1 volt
Channel Length Modulation parameter, λ = - 0.3 V-1
Transconductance parameter, KN(W/L) = 40 µA/V2

2. A JFET with VP = -4 volts and IDSS = 12 mA is used in the circuit shown. Assuming the device to be operating in saturation.
a. Determine ID, VDS and VGS.
b. Check to confirm that the device is indeed operating in saturation.

3. In bipolar junction transistor(BJT), at room temperature, if the emitter current is doubled, then the voltage across its base emitter junction
a. Doubles
b. Halves
c. Increases by about 20 mV
d. Decreases by about 20 mV

4. A Silicon N-channel MOSFET has a threshold voltage of 1 volts and oxide thickness of 400 Ao. [Ɛr (SiO2) = 3.9, Ɛo = 8.854 x 10-14 F/cm, q = 1.6 x 10-19]. The region under the gate is ion implanted for threshold voltage tailoring. The doping and type of the implant (assumed to be a sheet charge at the interface) required to shift the threshold voltage to -1 volt are…
a. 1.08 x 1012/cm2, p-type
b. 1.08 x 1012/cm2, n-type
c. 5.4 x 1011/cm2, p-type
d. 5.4 x 1011/cm2, n-type

Solution :

5. A Zener diode in the circuit shown has a knee current of 5 mA, and a maximum allowed power dissipation of 300 mW. What are the minimum and maximum load currents that can be drawn safely from the circuit, keeping the output voltage Vo constant at 6 volts ?

a. 0 mA, 180 mA
b. 5 mA, 110 mA
c. 10 mA, 55 mA
d. 60 mA, 180 mA

6. The p-type substrate in a conventional PN junction isolated integrated circuit should be connected to
a. Nowhere, i.e. left floating
b. A dc ground potential
c. The most positive potential available in the circuit
d. The most negative potential available in the circuit

7. If a transistor is operating with both of its junctions forward biased, but with the collector base forward bias greater than the emitter base forward bias, then it is operating in the
a. Forward active mode
b. Reverse active mode
c. Reverse saturation mode
d. Forward saturation mode

8. The common emitter short circuit current gain β of a transistor
a. Is a monotonically increasing function of the collector current IC
b. Is a monotonically decreasing function of IC
c. Increases with IC, for low IC, reaches maximum and then decreases with further increase in IC.
d. Is not a function of IC.

9. An N-channel silicon (EG = 1.1 eV) MOSFET was fabricated using N+ poly silicon gate and the threshold voltage was found to be 1 volt. Now if the gate is changed to P+ poly silicon, other things remaining the same, the new threshold voltage should be………..volts.
a. -0.1
b. 0
c. 1.0
d. 2.1