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

Download Dogbone - Microelectronic Devices and Circuits - Solved Exam and more Exams Microelectronic Circuits in PDF only on Docsity! EELOS MrptTerRM 4b) SeLuTrens | Fall 2008 Problem 1 [15 points]; Semiconductor Basics Consider a Si sample of length 10 yun and cross-sectional area 11m’, uniformly doped with 10'° cm™ boron, maintained at 7 = 300K. 1 Volt is applied across its length, as shown below: t 41 Volt accept ¢ ado metallic’ }¢ ——————._ 10 pm naa contact contact a) Estimate the resistance of this sample. [6 pts] Naz 101? cm » Ng =e Since Na > Ny, dis tangle Bem*JVis andl Ba ® 1206 om® f Ves = 1 RL were b) Estimate the electron drift velocity, [5 pts] eo iv wet te oe 2 om 0 Re ¥On ~ Yo ¥ fom From plot en Page 1, py EEO GH Ve = Pn & = eo iw = 1.2. x10 * cm/s | c) Qualitatively (no calculations required), how would the resistivity of this sample change if it were to be additionally doped uniformly with 2x10" em? phosphorus? Explain briefly. [4 pts] t Agner odor Since N, > Ng } Pais sovmple now retype, with n=N, “Na 210 gd From The plot oh Pase i An® 4 OC on* vis, which is 2X greater than Pre hele vaobi Irby in the ance mpcrratect sample, Since the majordy- Carr ity om if anchangéd, ancl the ae Capri ée mobripeq Page 31s dovbled, the cesishyiky us halveet Cb eg, is veeluced by a factor of Problem 2 [15 points]: PN Junctions Consider a Si PN junction diode, maintained at 7 = 300K, with a structure and potential distribution as shown. — a) Calculate the built-in potential, /. [4 pts] Since Vy>O, the dlete 3: 4 Np = 1078 em O- v, +O V(x) [Volts] Ns x fuer] 0.2 0 0. Note that the wielt> af the ategietion reion is Ob Ams OKO Hem, ce) Calculate the areal junction (depletion) capacitance. [4 pts] &s; Ae oe Odes L Cha Weep 4% 107? cn Page 4 Problem 5 [20 points]: BJT Amplifier Consider the BIT amplifier stage shown below, operating at 7 = 300K with a bias current fc = 0.1mA. 0.72:0.026 12 slo". Assume dy = 1x18"°A, B= 100, Vy=0. Re = 10 kQ, Rp = 5 kQ, and Voc = 2.5V. Note that ¢ Vee DC biased ot a) What is the purpose of A, and R,? [2 pts] to establish dhe dC bias egy. b) What is the purpose of R_? |2 pts] . . : fp to reoluce the error sa Ee (hence am, ) resu thing wor 2 bn . ervovs iw The values of @, ane Ry. ¢) Is the BJT operating in the active mode? Justify your answer. [5 pts] | Yes ( Since Tesi", , Vag =O 7a eo Since Ep © Ep = OojmA, the vo Hase Ave pped sue Re IS (.tm ACE kD) = OSV SVE = Veet Vee 2 OEM + CFR Y 2 eZ Ve = Vee 7 Te Re F 25 ~ (Ol mA ID KR ps ZY IV ESV v : 3 . i . ; Since Ve > Ve 7 © Neetor sanchion is yews “prasad. d) Draw (in the box provided) the most simplified circuit that can be used for AC analysis to determine the small-signal voltage gain, A,. You can assume that C, and C, are large, so that their impedances are negligible at the small-signal frequency of interest. Label the various circuit elements. [6 pts] Shortne oot the capacitors arma Vee. Problem 5 (continued) €} Write expressions for the small-signal voltage gain (A,), input resistance (Rj,), output resistance (Ron). [5 pts] 1 = ~ Arm Re ( Frow Cirenat on part fd)) Vow Page 8