Procedure - Microelectronic Devices and Circuits - Solved Exam, Exams of Microelectronic Circuits

Download Procedure - Microelectronic Devices and Circuits - Solved Exam and more Exams Microelectronic Circuits in PDF only on Docsity! UNIVERSITY OF CALIFORNIA, BERKELEY College of Engineering Department of Electrical Engineering and Computer Sciences EE 105: Microelectronic Devices and Circuits Fall 2008 MIDTERM EXAMINATION #2 Time allotted: 80 minutes NAME: SoLtuTIons (print) Last First Signature STUDENT ID#: INSTRUCTIONS: 1. Use the values of physical constants provided below. 2. SHOW YOUR WORK. (Make your methods clear to the grader!) 3. Clearly mark (underline or box) your answers. 4. Specify the units on answers whenever appropriate. PHYSICAL CONSTANTS Description Symbol Value PROPERTIES OF SILICON AT 300K : Electronic charge @ 1.6x10? C Description Symbol Value : Boltzmann’s constant k 8.62x10° Band gap energy EG 1.12 eV. : eViK Intrinsic cartier concentration i 10" om? : Thermal voltage at 300K y= 0.026 V Dielectric permittivity &i 1.0x10? kTig Ffem Note that V7 In(10) = 6.060 V at 7=300K SCORE: 1 415 2 415 3 {20 4 /15 3 /15 Total: /80 Problem 1 [15 points]: Cascodes a) What is the advantage of using a BIT (Q;, as shown below on the left) rather than a resistor (Rp, as shown below on the right) to achieve a high value of output resistance (Rou)? [3 pts} Q provides & large desenerechon resistance (152) withowt sustaining a large voltage ofrop (Veer) oS compared with Re fav which he voltage Avop Ve™ Tey Re Can be large if Re is large. Thus, the use ofa BIT vather than a resistor previeles for larger neadroom for the output vo Haze. signed do swing. Vee Vee + 4 Vo2 Q2 Vera Re vp V, Vor a mt i R, Rout out b) Suppose a PNP cascode is to be used as a 0.1mA current source, as shown below, What should be the values of the bias voltages My and Py:? Assume that Js = 10°%A for each BJT, and that the @, collector junction is forward-biased by no more than 0.3V to ensure that Q, operates in active mode. Voc = 2.5V. Note that e°7"* = 10), [8 pts] Im order for Ee, 2 Tee = A) mA = rot A i y (te, Mpg | er each BIT s henld be Vy dn Ge) Neg] = 0.026£n bb ba 10" 2 \2% 0.060 = 0,72V Nun Veo Vee2 = en 73 | Circuit LL the Q, collector gunchon is forwarel- biaseol by D.3y, 0.1mA + Vy= Vpn 2 903M =) Vy = OBVELIGV 2 2.08V Void Vy - Veg, = 208 V~ Oe72N FL 26v | e) Suppose that a PNP cascode is to be used as a voltage amplifier, as shown below. Which transistor (Q, or Q2) should be used as the amplifying device? Explain briefly. [4 pts] Yi a a . “ Q, shoul be used as the amplify ing transistor. Vo2 Q2 TL fre Sa put voltaye signal is apphed +o the base ve 3 in is + as high alue te v of Q,, the voHage gain Is no igh, ove ‘out Ideal emitter cleqeneratian. Problem 4 [15 points}: MOSFETs a) Consider a long-channel MOSFET with the /-V characteristic as shown below. i) What is the threshold voltage (Vs) of this device? [2 pts] tp Ima] From the plot, Vosat 7 OSV. 24 Vy sat = Ves “Vin =? Vin = Vas~ Vpset =05V| 4 Lent Veg = LV ii) Indicate (by drawing a dashed curve on the plot) how the /-V fo en characteristic would change if Vgs- rm were to be decreased 1 i by a factor of 2. [3 pts] . sen 7 Nags Vey reduced ao | vy factor of 2 Vo cat deeveasts by 2X Lent & (Ves~ Vin) ctecreases by AX tt Vps [Volts] 2 ‘ A fs unchanged b) Indicate how the small-signal parameters of a long-channel MOSFET would change, if the gate-oxide thickness were to be decreased. Assume V’gs-/’7q remains the same, Give qualitative explanations for your answers. [6 pts] MOSFET Parameter will (check one) Parameter increase | decrease | not change | Brief Justification Capacitive coupling ef dre channel potenhial to fhe gate voHage is Transconductance, g, | V ineveased, 50 Veg will have ~ strenger, 6 . inftwewes on Dp The channel-length vod ulaten | effect is not offectedt by tox, Output resistance, r, Sf Ne, X does not change. Yat i+ +o Howevev, Tp tncreases if x ; increases (hoe The seemed reason AG aveve) anol Sa to ™ Kt, decreases. ¢) What is the channel length modulation effect? [2 pts] Inversion - lay ee channel decreasvag. e) Why does the drain current eventuaily saturate in a short-channel MOSFET, as the drain-to-source voltage (Vx) is increased? [2 pts] The lean cueren’ dn & short channel MOSFET sventually we locrty sadn ratts K A dug to thet ae cr, for cach MosFer Problem § [15 points]: MOSFET Amplifiers Assume ge Consider the MOSFET amplifier stage shown below. Assume that A # 0 for each of the long-channel MOSFETs. Yop a) What type of amplifier is this [2 pts[? Circle one of the following, and justify your answer: Common Emitter} Common Base Follower Cascode Noa y ot a Lnput signed is applied +o gate of My. Ma Row Oudpud signal is baleen Lom. drain of Ma. Fn ijt b) What is the purpose of transistor 4? [2 pts] ay Min Mag. Strves as & cuyerent Source. i soar c) What is the purpose of the capacitor C,? [2 pts] signal to the “sede af the amplifying transistor € M2), without Me chins the C, is useal lo couple the DC bras. d) Derive expressions for the low-frequency voltage gain (4,), input resistance (Rj,), and output resistance (Rw). [9 pts] 5 * . : A | . The resistance seen Jook’ag ite the drain ot My 15 approxi medtly 1 i Aves Yn" (5m il Yo) , ae a . 50 the -totad. vesistance seen forking lactto The ond put node. 1s Ve . . TY rl) 2 toa |] ren sine gem = Gena (since T= Fpn,) R, Hee. — FoR Rat Ri PRe