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1. A bar of Gallium Arsenide(GaAs) is doped with silicon in such a way that silicon atoms occupy Gallium and Arsenic sites in GaAs crystal. Which of the following statements is true?

a) Silicon acts as p-type dopants in Arsenic sites and n-type dopants in Gallium sites

b) Silicon acts as n-type dopants in Arsenic sites and p-type dopants in Gallium sites

c) Silicon acts as p-type dopants in both Arsenic and Gallium sites

d) Silicon acts as n-type dopants in both Arsenic and Gallium sites

Correct Ans : a

Background: amphoteric dopant -> element which can act either as a donor or an acceptor in a given semiconductor; e.g. Si is an amphoteric dopant of GaAs where it acts as a donor on a Ga site or as an acceptor on an As site.

2)

Hint : Apply Kirchoff’s law for the branch involving 10k, 5k and 3v source with vin =15v and for vin=-15v

3) A good transconductance amplifier should have

a) High input resistance and low output resistance

b) Low input resistance and high output resistance

c) High input and output resistance

d) Low input and output resistance

Correct Ans : c

4) Which one of the following is the general solution of this first order differential equation

$\frac {dy}{dx}$= $(x+y-1)^2$ where x and y are real.

a) y=1+x + $tan^-1 (x+c)$

b) y=1+x+tan(x+c)

c) y=1-x+$tan^-1 (x+c)$

d) y=1-x+tan(x+c)

where c is a constant

5)

Correct Ans : 43.3 to 45.3

6) Assuming that transistors M1 and M2 are identical  and have a threshold voltage of 1V, the state of transistors M1 and M2  are respectively

a) saturation, saturation

b) Linear, linear

c) saturation,linear

d) Linear, saturation