模拟电子技术基础考试卷(参考) AC

HUAZHONG UNIVERSITY OF SCIENCE AND TECHNOLOGY
Course：Electronic Circuit（B CLOSED BOOK）
CLASS： No. Full mark Score
1 20 2 10
NAME：
3 12 4 22 5 14 6 12
No.
7 10
Score
1). Consider the feedback circuit in Figure 5-1. ① Determine the feedback configuration and polarities, and you must label the instantaneous polarities in the figure. ② If |1+A |1，calculate the closed-loop voltage gain. Solution:
Rb1 33k C1 + vI +
Rc 3.3k T Re1 50 Re2 1k RL 3.3k + Ce 100uF
Figure 2
12V C2 + 20uF
+
20uF Rb2 10k
vO

A total of 8 pages，P.1
Score 2． （10 points） Consider the circuit shown in Figure 3. The bipolar transistor parameters are β=100,VBE(on)=0.7V ,VA=∞ for T1 and T2, the T3 and T4 are identical. (1) Determine the differential-mode voltage gain Avd2 (RL=∞). (2) Calculate the differential-mode input resistance Rid. (3) Calculate the output resistance Ro. Solution:
R2 R1 vI R3
+
A1
+ A2
R4 R5 RL
+
vO

Figure 5-1
2) The op-amp feedback circuit is shown in Figure 5-2. All capacitors act as short circuit to the sinusoidal signal.. ① Determine the feedback configuration and polarities, and you must label the instantaneous polarities in the figure. ② If |1+A |1，calculate the closed-loop gain. ③ Determine the effects of the feedback on the input resistor and the output resistor, and explain the output current or voltage tends to be stabilized. ④ Does the capacitor C2 effect the lower corner frequency or upper corner frequency? Solution:
R vi3 vi1 vi2 R R － A1 ＋ R vo1 － R ＋ A2 vo R R
Figure 4 (a)
(2)
v1 + A1 R2 R1 R2 v2 + A2 v O2 Figure 4 (b) R3 + A3 vO v O1 R3 R4
R4
A total ofpoints）
Final
100
1． （20 points） For the circuit in Figure 2, let β=125, VBE(on)=0.7V ,VA=∞, all the capacitors are assumed to act as short circuits at the signal frequency. (1) Calculate the Q-point (IB, IC, VCE). (2) Sketch the small-signal equivalent circuit. (3) Determine the small-signal voltage gain Av. (4) Determine the input resistance Ri and the output resistance Ro. (5) If capacitor Ce is open, determine the small-signal voltage gain Av. Solution: VCC
T1 T2 R4 V+ ＋ A － － R3 DZ2 － R2 VO RL R1 ＋
＋
Figure 8 Solution:
A total of 8 pages，P.8
– A + vI R1 R2 DZ R3 1k vO
Figure 7
A total of 8 pages，P.7
Score 7.（10 points） The voltage regulator is shown in Figure 8, the input voltage V+ = 25V，and R1=R2 =R3 =2k。The transistor parameters are = 100 and VBE(on) = 0.7V. The op-amp A has infinite open-loop gain Aod＝. The Zener voltage is VZ = 5V，and the Zener resistance is rz = 0. (1) There are two mistakes in the figure in all, find and correct them in the figure. (2) For IZ = 10mA，find the value of R4. (3) Determine the value range of the output voltage Vo.
＋VCC＝＋10V Rc1 8.1k Rb1 1k vi Rc2 8.1k T1 Re1 100 T3 T2 Re2 100 T4 R1 19.3k
vo2 Rb2 1k
－VEE＝－10V
Figure 3
A total of 8 pages，P.2
Score 3.（12 points） Assume the op-amps in Figure 4 are ideal. (1) For the Figure 4(a)，derive the expression of output voltage vO in term of vI1, vI2 and vI3. (2) For the Figure 4(b), Derive the expression for the output voltage vo= f （v1- v2） . Solution: (1)
A total of 8 pages，P.6
Score 6.（12 points） The saturated output voltages are VP = 12V for the Schmitt trigger in Figure 7, and VZ=5.3V for the Zener diode DZ, assume the op-amp A is ideal. (1) If R1 = R2 =10k, derive the expressions for the crossover voltages VTH and VTL, , and determine the switching point VS and the hysteresis width ? (2) Sketch the voltage transfer characteristics. Solution:
A total of 8 pages，P.5
R 20k C 0.01uF
Rt a b
+12V
+10V A + vo1 +3V R2 + R3 A2 DZ1 vo
vO1 6V 0 -6V Figure 6(b) t
R 20k
0.01uF C
c R1
d
-12V
-10V
DZ2
Figure 6(a) Solution:
A total of 8 pages，P.4
VCC Rb1 Rs T1 + vs I0 -VEE Figure 5-2 C1 Re2 Rf Re3 Rc2 T2 T3 RL Rc3 C2 + vO -
Score 5.（14 points） The wave-generating circuit is shown in Figure 6(a). The resistor Rt is thermal resistor，and VZ=5V for the Zener diodes DZ1 and DZ2( neglecting the forward voltage drop of the diode). Assume the operational amplifiers A1 and A2 are ideal. （1）Connect the point a、b、c、d , to make the circuit to oscillate; (2) The frequency of vo1； (3) To make the amplitude of vo1 stabilize， when the temperture increases, how to change the values of Rt？ (4) If A1 is 741(The gain-bandwidth product of 741 is BWG=1.4MHz)，determine the sine wave vo1 is stable or not? if not, what is the minimum value of the gain-bandwidth product of 741？ (5) Assume the waveform of vo1 is shown as Figure 6(b)，sketch the waveform of vo quantitatively；