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Department of Electrical Engineering and Computer SciencesUNIVERSITY OF CALIFORNIA, BERKELEY^ College of Engineering EE 105: Microelectronic Devices and Circuits MIDTERM EXAMINATION #2 Spring 2008 NAME: _________________________ _________________________^ Time allotted: 80 minutes _________________________ (print) STUDENT ID#: (^) Last (^) ____________________ First Signature INSTRUCTIONS: 1. 2. Use the values of physical constants provided below.SHOW YOUR WORK. (Make your methods clear to the grader!)
3. 4. Clearly mark (underline or box) your answers.Specify the units on answers whenever appropriate.
Electron and Hole Mobilities in Silicon at 300K
Description^ PHYSICAL CONSTANTS Symbol Value Electronic charge 1.6 10 q -19 (^) C Boltzmann’s constant 8.62 10 k -5 (^) eV/K Thermal voltage at 300K V 0.026 VT = kT / q Note that V T ln(10) = 0.060 V at T =300K
Description^ PROPERTIES OF SILICON AT 300K Symbol Value Band gap energy 1.12 eV E G Intrinsic carrier concentration 1010 n (^) cmi - Dielectric permittivity 1.0 10 Si-12 (^) F/cm
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d) What is the topology of “Amplifier-B” (i.e., common source, common base, etc)? [2pts]
e) Find the voltage gain, input and output resistance of Amplifier-B. Show both the expressions and the numerical values. You can make approximations in your expression as long as they are within 10% accuracy. [6pts]
Problem 2 [2 2) Assume that V AE1 = AE2 5 points]: BJT Circuits and Frequency Response = 10ACCE3 = 3 V, I. RC = 1 kΩ, and RREF = 100μA, IE = 1 kΩ. AssumeS = 10−17 (^) A, VA = 50 V, and β = 100 for all transistors. Cμ = 10 fF, Cπ = 100 fF, and CCS = 20 fF.
vIN
vOUT
Vcc = 3V IREF Q (^1) RE
RC Vb Q 3 Q (^2) a) Identify the functions of Q 1 , Q 2 , and Q 3. What is the function of this circuit? [3pts] b) Find the small-signal parameters of the main amplifier transistor ( rp^ ,^ g^ m , r 0 ). [3pts] c) Find the expression and the value of the voltage gain. [4pts]
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]
Problem 3 3) Below is the cross section of a PMOS transistor: [15 points]: MOS Devices
SubstrateGate(Body)
S G D
a) What is the doping type (n, n+, p, or p+, where “+” means high doping concentration) of [3pts] B i) ii) iii) Source:Drain:Substrate (body): b) Which carrier(s) are involved in current conduction? (i) electrons, (ii) holes), (iii) both electrons and holes. (choose one) [3pts] c) If the power supply voltage is 2V and ground is 0V, what bias voltage is usually connected to the body (substrate) of the transistor? Why? [3pts] d) Assume the threshold voltage of the PMOS is V gate voltages for which the PMOS is (i) cut-off, (ii) in between saturation and triode regions. [3pts] TH = -0.4V. If VS = 2V, VD = 0V, find the e) If a PMOS and an NMOS have exactly the same dimension (W, L, and oxide thickness), which transistor has higher g (^) m? Why? (Assume both are long-channel devices) [3pts]
c) From i) g (^) (^) m BJT a) , and / g b) m MOS ,, find the relative magnitudes of small-signal parameters: [3pts] ii) iii) rr 0, p^ , BJT BJT // rr 0,0, MOSBJT
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]
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]
