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Unformatted text preview: (1 point) (1 point) (5 points) EE 20802 802 MIDTERM EXAM #2 Braun
CLOSED BOOK + 1 Cheat Sheet State any assumptions and show all work. Part 1 (5%Points) — ., Part 2 (16 Points) —
Print Your Name: BRH’Q lb ___,. Part 3 (Ill/Points) — Part4 (% oints) —
No unauthorized help given or received. Total (40 points) — Signature:
FOR THE ENTIRE EXAM, UNLESS OTHERWISE SPECIFIED, USE: The CVD model for all diodes —— including breakdown diodes  with Von = 0.7 V & Vz = 5.0 V.
For FETs, VTN =  VTP = 1.0 v, KN’ = 200 uA/Vz, KP’ = 50 uA/VZ, y = 0 v“, x = 0 VJ.
Show all work, state any assumptions, and test hypotheses. 1. Diode Circuits
For the circuit in part 1, please sketch the output voltage when the input voltage, vS is: OFF 3 i/ M +— . ,1 .‘y
m/ Egg/Wm" my? ”lg; 1;  V3 , sy Time [ms] K Le mom ALLC’I'JS us 711
'2 ﬂ/ﬂyf’ ﬁ/‘FOK/b/ /i‘ g (6 points) (2 points) (2 points) (2 points) (2 points) 2. MOS Transistor Operation The derivation of the MOS current vs. voltage characteristics discussed in class contains the following
equation: J =+ q,unE + qDﬂ
DRIFT “ﬁr;
DIFFUSION A) Deﬁne the following variables and indicate suitable units: J— The channel current density deﬁned as positive in the direction from source to drain has units of current
per unit area [A/cmz]. D — The electron or hole diffusivity (or diffusion coefﬁcient) with units of cmZ/s is the rate at which carriers
diffuse due to a gradient in concentration. y — The electron or hole mobility with units of cmZ/V s is the ratio of carrier velocity to electric ﬁeld.
B) Explain what the ﬁrst term on the rig ht hand side of the equation. represents. The ﬁrst term on the right hand side of the equation represents the electron drift current density. The drift
current density results from electron motion due to an applied electric ﬁeld. C) Explain what the second term on the right hand side of the equation represents. The second term on the right hand side of the equation represents the electron diffusion current density. The
diffusion current density results from electron motion due to a gradient in carrier concentration. D) F: plain which term (m the rioht hand ude nFthp pmmfinn malzps a mnrt: cinniannf («anL 1U11+1'm« n1 ._ E" “w“... .. V; n"! V‘lmwwAuAA “Amw w “AbAAALLVWL UU1 uuuvu u.) explain the current vs. voltage characteristics of a MOS FET operating in the linea mode of operation.
Explain why. Since the gradient of carrier concentration is almost zero, we can usually neglect the diffusion component
relative to the drift component. The drift current density term makes a more signiﬁcant contribution to
MOSFET current in both the linear and saturation modes of operation. E) When a BJ T operates in the FORWARD ACTIVE mode, (circle the appropriate word) the Base—Emitter junction is 9%
and the BaseCollector junction is 9%! OFF ' F) In the transport model of the B] T, equations 5.13 express the terminal currents of the NPNBJ T. Which
terminal current does the following expression represent? [circle the appropriate answer] ‘ Base Current, i3 1 l1 alt] Illlatel .1 Mew ,3 \VT, ﬂRL \VT,
WW}; 3. MOS Biasing (12 points) Please analyze the circuit shown to the right and determine the Q—point of the transistor. W/L = 5. w i e ~— WV”
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 Spring '08
 BRAUN

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