ECE 250 Exam 1 ..

Winter 201~3

Section \

eM \~]

Scores: 1) ~CS 2) ~~ 3) dCS 4) \ oJ

Total to C/'

I pledge on my honor that I did not copy any of this exam, and that this work is entirely my own. Furthermore, I did not use PSpice during this exam.

Page 1 of7

Problem 1 (25 Points): Plot Vo(t) and Vinet) for the circuit below. Indicate numerical values for all breakpoints. Let Vin be a ±15 volt triangle wave.

Va

1k

1k

1k

. 0 . 2 _ o. 4 ~ 0 . 6.. 0.8 s 1 . 0s 1 . 2s ~ . 4s 1.65 1 . e s 2 . 05

o 0 T i..me

b) Sketch the transfer curve, VA versus Vin (8 Points).

r---~r-----t-----+~~-+----~~~~

- \ (1.­~~ :;/

Page 2 of7

Problem 2 (25 Points): Plot Vo(t) and Vinet) for the circuit below. Indicate numerical values for all breakpoints. Let Vin be a ±15 volt triangle wave. The Zener breakdown voltage is 4.3 V. Do not ignore the diode tum-on voltage of 0.7 V.

Rl

+-----'WIr------+----<lVO lk

Vin R2 lk

a) Sketch the wavefonns using the graph below: (17 Points) " , I ~_L~

--l- I .....-' -yo -",-t--r-i­ ..­ ~,-.. I-­

F~r--=-j--ll ~ -- ···I- I---=­·j-t-t---t- l-l·--l--·-I--+--1 -f----~- .=...... ~- ... t-­1 0 1 - I, ' ,­..

=~t-. /....7t-~ L~ " J ~~~I1_ ___ i=i-i-- ~ ==!=1__t-=II·-_~·~-_ .. -_·..+r-_+·_-=,-:=.-=!=t-l...-r­ ....­ ..... ...­ _ 1_ ..

I ···· --·7 -­ - --~~ '~..J . =H=J=.. --=~r-r: ':""ri- :

2.0s o 0

b) Sketch the transfer curve, Vo versus Vin (8 Points).

5\.upe -;::.-\ f--'----I---+--:---l--~-__+-~uS,t 0)')

~~Qe.- -=-- l IL

Page 3 of7

Problem 3 (25 Points): An n-type semiconductor has a drift current density of 55 Alcmz with an applied electric field of 18 V/cm at a temperature of 300 oK. The semiconductor is made of silicon. Determine the electron and hole concentration in the semiconductor. State any approximations that you make. (You should make at least one approximation.)

Useful Material Values: /lp = 480 cmz/(V-s), /In = 1350 cmz/(V-s) Eg = 1.1 eV B = 5.23xl015 #/(cm3.oK3/Z)

q = e = 1.602x 1 0. 19 coulombs K = 86xlO·6 eVfOK

Page 4 of7

ECE 250 Exam 1 Problem 3

Define some constants used in the equations

eV 1.602 1019

coul 1 volt Define an electron volt.

k 86.2 106

eV

K Boltzmann's Constant

q 1.602 1019

coul

Bsi 5.23 1015

1

cm3

K1.5

Egsi 1.1 eV μn 1350

cm2

volt sec

μp 480cm

2

volt sec E 18

volt

cm

J 55amp

cm2

First find the conductivity from J=E

σJ

E σ 3.056

1

Ω cm

Next, we know that the conductivity is related to the carrier contentrations by

=qn+qpp

where n and p are the carrier concentrations. Since n and p are unknown, we need to make an approximationSince the semiconductor is n-type, we know that n>>p so we will use the approximate equation of=qnWe can solve this equation for n

nσ

q μn

n 1.413 1016

cm3

Next, we know that np=ni2 so we need to find ni for silicon at T=300 oK

T 300 K

ni Bsi T1.5

e

Egsi

2 k T

ni 1.576 10

10 cm

3

Now we can solve for p

pni

2

n p 1.757 10

4 cm

3

Problem 4 (25 Points): In an attempt to make a research deadline for the development of an envirorunentally friendly electronic device, Professor Insignificant working at the University of Irrelevant (located in West Lafayette - in case you were wondering) devised the crcuit below to test the electrical properties of different insects

~Big Under Test (B.U.T) ] found in Indiana:

+

The I-V characteristic ofa ical "vacuum-tube" s ecies of bug is shown below:

9~--r---.---.---.----r--~--~---.

i ."....~_..~-...". '.... ....'... ..~~..t~ .~ . "* • • ~-. ~f.....,..,.... '''T-' ... ..... ,' •••~. ;..... ... .. --. - - ... . . . . . ..

, ' ! ' i I +- ".. t. . i . . . r

,. ! ! , :j i

-8 -2 6 B

Find numerical values of IB and V~ for this ,

Page 6 of7