1. 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 µ

_{n}= 1350 cm^{2}/V-sec, µ_{p}= 450 cm^{2}/V-sec, and the
intrinsic carrier concentration, n

_{i}= 1.5x10^{10}cm^{-3}.**Ans :**hole concentration = 2.59 x 10

^{10}cm

^{-3}.

electron concentration = 0.866 x 10

^{10}cm

^{-3}.

2. In the common emitter amplifier shown in the figure below,
the

transistor has a forward current gain of 100, and a base-emitter

voltage of
V

_{BE}= 0.6 volts. Assume I_{CO}to be negligible.
Choose value of R

_{1}and R_{3}such that the transistor has a
collector of 1 mA and a collector to emitter
voltage of 2.5 volts.

Ans :

**R1 = 41 K**and**R3 = 2.2 K**
3. A typical CMOS interval has the transfer characteristics
(VTC)

(V

_{O}-V_{in}) as shown in the figure below. Evaluate the value of
the inverter threshold V

_{INV}, which is the value of the input
at which V

_{O}falls abruptly by ∆V_{o}= V_{Tn}+ V_{Tp}.
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