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EE 461G Review Problems for the Final Exam Print your name. You must show your work to receive partial credit. You may bring a piece of paper with formula, a calculator, a ruler, a pencil, and an eraser. Problem 1 Draw the small-signal models for BJT and FET including both DC and AC components. Label components, current, and voltage. 1 Problem 2 Approximately draw transfer characteristics of circuits (a) and (b) separately and their output voltage in the space below. Point out which one is a rectifier and which one is a clipping circuit? (Vf=0.7V) R=2 k D1 + + vIN + vout D1 + vIN vout R=10 k – – – – (a) (b) Vout (V) Vout 2 VIN 1 vIN 1 2 3 4 5 6 -1 -2 Transfer characteristics for (a) Vout for (a) Vout (V) Vout 2 VIN 1 1 vIN 2 3 4 5 6 -1 -2 Transfer characteristics for (b) Vout for (b) 2 Problem 3 A bipolar junction transistor amplifier with a incremental signal gain o of 100 is shown below. (a) What type of the DC bias does this circuit have? (b) Find the DC voltage VB from the base B to the ground; (c) The ac signal voltage vb from the base B to the ground; (d) the output ac signal vout. VCC =9V RC =2k R1 =2k C VB+vb vs=2sint + iB Vout B R2 =1k iC - E iE RE =1k 3 Problem 4 An n-channel enhancement-mode MOSFET is connected to the circuit as shown below. The I-V characteristic of the transistor is also shown below. (VTR=1V) (a) Write the equation for the load line and draw the load line on the I-V curves to find the operating point A. What is the operating region? (b) If RL=0.4 k is connected to the output (or D and S), write the equation for the load line and draw the load line on the I-V curves to find the operating point B. What is the operating region? VDD =4V iD(mA) RD =0.4k D vs + – G V1=2.5V iD S 10 + 8 Vout 6 VGS=3V 2.5V - 4 2V 2 0 0 1 2 3 4 1.5V VDS(V) 4 Problem 5 An n-channel enhancement-mode MOSFET is connected to the circuit as shown below. (VTR=1V) The I-V curves are shown below. (a) Using the MOSFET model and the I-V curves below to calculate K approximately. (b) Using the results in Problem 4 (a) to find the transconductance gm. (c) Using the small-signal model to find output signal vout when vs= Sin(t) V. VDD =4V iD(mA) RD =0.4k D vs + – G V1=2.5V iD S 10 + 8 Vout 6 VGS=3V 2.5V - 4 2V 2 0 0 1 2 3 4 1.5V VDS(V) 5