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Practice Final Exam
Dec. 10, 8:00-10:00am
Name:
(50 points total)
Problem 1: Consider the common source amplifier being used as an output stage in Fig. 1. The blocking capacitor CB is large enough to be considered a short at the signal frequency. For the transistor, Vtn = 1 V, μn = 5 × 10 −^2 m^2 /Vs, Cox = 2× 10 −^3 F/m^2 , and WL = 400. You may neglect channel length modulation effects. [14 points]
(a) Plot the voltages at nodes A and B in Fig. 1 on the axes in Fig. 2. You don’t have to draw the waveforms to scale. Hint: Use large signal equations for the bias levels and small signal equations for the signal waveforms. [6] (b) What class of operation is this output stage being operated in? [1] (c) What is the efficiency of this output stage? [3] (d) What is the average power dissipated in the transistor? [4]
Figure 1: Common source amplifier.
Problem 1 (cont’d)
Figure 2: Voltage waveforms.
Problem 2 (cont’d)
Problem 3: Consider the bistable circuit shown in Fig. 4, with power supplies of ±5 V. Assume the diode is ideal, turning on for VP N = 0.7 V. [12 points]
(a) Draw the voltage transfer characteristics in the space provided in Fig. 5, clearly indicating any hysteresis effects. [8] (b) What is the opamp output current for each of the stable states? [4]
Figure 4: Bistable multivibrator circuit.
Problem 4: Our friend Borat has presented us with the rectifier circuit shown in Fig. 6. Assume the diodes are ideal, turning on for VP N = 0 V. [12 points]
(a) Draw the output voltage for the specified input signal in the space provided in Fig. 7. [8] (b) Does this circuit function as a rectifier? [1] (c) What would the average output power of the circuit be if it were driving a 1 Ω load? [3]
Figure 6: Borat’s rectifier circuit.
Problem 4 (cont’d)
Figure 7: Output Voltage.
