课程名称︰电子学一
课程性质︰必修
课程教师︰吕良鸿
开课学院：电机资讯学院
开课系所︰电机工程学系
考试日期（年月日）︰103/11/13
考试时限（分钟）：110分钟
试题 :
Microelectronic Circuit I (Midterm)
date: 2014/11/13 (Thur)
time: 15:30 ~ 17:20
ps. 试题可带回，可使用计算机
1. Fig. 1 shows the circuit model of a voltage amplifier loaded with a resistor
R_L and a capacitor C_L. The parameters are given as R_s = 40 kΩ,
R_i = 200 kΩ, A_vo = 150, and R_o = 2 kΩ.
(1) [7%] Find the minimum R_L allowed to maintain a voltage gain no less than
40 dB.
(2) [7%] Base on (1), what is the maximum C_L allowed to keep a 3-dB frequency
higher than 20 kHz?
(3) [9%] The input voltage form is given by 0.1xsin (10^4t) + 0.5xsin(10^5t)
[V]. With the minimum R_L and the maximum C_L, find the output voltage v_o.
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: R_1, R_2, R_3, and R_4 are different resistors.
(2) [12%] In Fig.3. Note: R_1 = R_2 = R_3 = R_4 = R_5 = R_6 = 10k
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 (E_G = 1.1
eV) is smaller than that of Germanium (E_G = 0.67 eV) 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
R_1 = 1 kΩ, R2 = 4kΩ, and the cut-off frequency f_t of the OP is 200 kHz
and slew rate is 0.5 V/μs. Please draw the output waveform v_o(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.
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, D_1 and D_2 are diodes with n = 1,
and C_1 and C_2 are large coupling capacitors. For very small input signals,
find the values of the ratio v_o/v_i for I = 0 μA, 100 μA, 500 μA, 900
μA, and 1 mA.
6. [4%] A shunt regulator utilizes a zener diode whose voltage is 5 V at a
current of 50 mA and whose incremental resistance is 5 Ω. 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 0.7-V drop for any current. What is the peak value of the
rectified voltage across 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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