课程名称︰电子学一 课程性质︰必修 课程教师︰吴肇欣 开课学院：电资学院 开课系所︰电机系 考试日期（年月日）︰2014/11/13 考试时限（分钟）：110 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : 1. Fig.1 shows the circuit model of a voltage amplifier loaded with a resistor RL and a capacitor CL. The parameters are given as RS = 40 kΩ, Ri = 200kΩ, AVo = 140, and Ro = 2kΩ. (1)[7%] Find the minimum RL allowed to maintain a voltage gain no less than 40dB. (2)[7%] Base on (1), what is the maximum CL allowed to keep a 3-dB frequency higher than 20 kHz? (3)[9%] The input voltage form is given by 0.1sin(10^4t) + 0.5sin(10^5t)[V]. With the minimum RL and the maximum CL, find the output voltage Vo. -----Fig.1 http://imgur.com/T23BVls 2. Differential amplifiers are one of the most important circuit block in analog circuits. For the following two kinds of differential amplifier please determine their differential gain, differential input resistance, and common-mode gain. Assume ideal operational amplifier. (1)[12%] In Fig.2. Note: R1, R2, R3, and R4 are different resistors. (2)[12%] In Fig.3. Note: R1 = R2 = R3 = R4 = R5 = R6 = 10k -----Fig.2 http://imgur.com/D92j5KV -----Fig.3 http://imgur.com/dkYSrRR 3.[10%] True or False. Correct the statements if they are wrong. Credits will be given only when you correct it right. (1) In thermal equilibrium, the intrinsic concentration of Silicon(EG = 1.1eV) is smaller than that of Germanium(EG = 0.67eV) at room temperature. (2) In thermal equilibrium, n-type silicon semiconductor is negatively-charged and p-type silicon semiconductor is positively-charged at room temperature. (3) In thermal equilibrium, the built-in voltage cannot be measured by a potential meter applied on the external terminals of the pn junction. (4) In thermal equilibrium, extrinsic silicon semiconductor shows larger electrical resistivity than intrinsic silicon semiconductor does at room temperature. (5) In thermal equilibrium, there is no current going on in the pn junction when the external terminals are left open-circuited. (6) The depletion region in the p-side will be larger than that in the n-side if the n-type doping is smaller than the p-type doping in the pn junction. (7) When the pn junction is forward-biased, the forward conducting current can be formed by holes drifting from p-side to n-side and electrons drifting from n-side to p-side, depending on the values of applied voltage and electrical field. (8) The charge-storage effects in the pn junction can be modeled by junction capacitance in reverse bias and diffusion capacitance in forward bias. (9) The excess concentration of minority carriers in the pn junction under forward bias will decay with distance linearly due to the recombination process with majority carriers. (10)The avalanche breakdown occurs when the majority carriers that cross the depletion region under the influence of the electric field gains sufficient kinetic energy to be able to break covalent bonds in atoms with which they collide. 4.[13%]Consider an OP connecting in Fig. 4. The input waveform is a continuous pulse with period of 100μs, as shown in Fig. 5. Assuming that R1 = 1kΩ, R2 = 4kΩ, and the cut-off frequency ft of the OP is 200kHz and slew rate is 0.5V/μs. Please draw the otput waveform Vo(t) with time. Label correctly the detailed information of the output waveform in your plot, i.e. voltage and time at every corner/turning point. -----Fig.4 http://imgur.com/RMI6EgX -----Fig.5 http://imgur.com/ytNhtrR 5.[10%]In the capacitor-coupled attenuator circuit shown in Fig.6, I is a dc current that varies from 0 mA to 1 mA, D1 and D2 are diodes with n=1, and C1 and C2 are large coupling capacitors. For very small input signals, find the values of the ratio Vo/Vi for I = 0μA, 100μA, 500μA, 900μA, and 1mA. -----Fig.6 http://imgur.com/o3zBy4e 6.[4%]A shunt regulator utilizes a zener diode whose voltage is 5V at a current of 50 mA and whose incremental resistance is 5Ω. The diode is fed from a supply of 15-V nominal voltage through a 150-Ω resistor. What is the output voltage at no load? [6%]Find the line regulation and load regulation. 7.[3%]A full-wave bridge rectifier circuit with a 1.5-kΩ load operates from a 100-V (rms) 60-Hz household supply through a 10-to-1 step-down transformer having a single secondary winding. It uses four diodes, each of which can be modeled to have a 0.7V drop for any current. What is the peak value of the rectified voltage accross the load? [4%]For what fraction of a cycle does each diode conduct? [3%]What is the average current through the load? --

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