Download UC Berkeley EE 105 Midterm: Microelectronic Devices & Circuits and more Exams Microeconomics 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 Spring 2008 MIDTERM EXAMINATION #2 Time allotted: 80 minutes NAME: _________________________ _________________________ _________________________ (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. Electron and Hole Mobilities in Silicon at 300K Page 1 PHYSICAL CONSTANTS Description Symbol Value Electronic charge q 1.6 10-19 C Boltzmann’s constant k 8.62 10-5 eV/K Thermal voltage at 300K VT = kT/q 0.026 V Note that VT ln(10) = 0.060 V at T=300K PROPERTIES OF SILICON AT 300K Description Symbol Value Band gap energy EG 1.12 eV Intrinsic carrier concentration ni 1010 cm-3 Dielectric permittivity Si 1.0 10-12 F/cm SCORE: 1 / 20 2 / 25 3 / 15 4 / 20 Total: / 80 Page 2 Problem 2 [25 points]: BJT Circuits and Frequency Response 2) Assume that VCC = 3 V, IREF = 100µA, IS = 10−17 A, VA = 50 V, and β = 100 for all transistors. AE1 = AE2 = 10AE3. RC = 1 kΩ, and RE = 1 kΩ. Assume Cμ = 10 fF, Cπ = 100 fF, and CCS = 20 fF. vIN vOUT Vcc = 3V IREF Q1 RE RC Vb Q2Q3 a) Identify the functions of Q1, Q2, and Q3. What is the function of this circuit? [3pts] b) Find the small-signal parameters of the main amplifier transistor ( 0, ,mr g rp ). [3pts] c) Find the expression and the value of the voltage gain. [4pts] Page 5 d) Show all parasitic capacitances of the BJTs in the circuit diagram above. Simplify the capacitances (e.g., combine all capacitances in parallel, remove capacitances that are shorted). Redraw the circuit diagram below with the simplified capacitances. [Hint: a constant DC voltage is AC ground]. [5pts] e) Find the input and output poles of this circuits. What is the dominant pole? Find the 3-dB bandwidth of this circuit. [5pts]. Page 6 f) Construct the Bode plot of the transistor. Clearly mark the scale of both axes. The Bode plot should show both the low-frequency voltage gain as well as 3-dB bandwidth of the amplifier. [5pts] Page 7 c) From a) and b), find the relative magnitudes of small-signal parameters: [3pts] i) , ,/m BJT m MOSg g ii) 0, 0,/BJT MOSr r iii) , 0,/BJT BJTr rp d) Derive the expressions of the output resistances for both cascade amplifiers shown above. You can drop small terms that are less than 10% of the dominant terms. Using the ratios you obtained in c), determine which cascode amplifier (Cascode-A or Cascode-B) has higher output resistance. [6pts] Page 10 e) Derive the expressions of the voltage gain for both cascade amplifiers shown above. You can drop small terms that are less than 10% of the dominant terms. Using the ratios you obtained in c), determine which cascode amplifier (Cascode-A or Cascode-B) has higher voltage gain. [6pts] Page 11
